Sunday, December 25, 2011

Today Is Christmas!

Christmas is probably the most important holiday in the calendar of most European nations as well as in the United States. Many countries in Asia have also started celebrating Christmas in some fashion as many cultures have holidays and cultural traditions surrounding the winter solstice, which is December 21st. After all, who could say no to receiving gifts from friends and family or pass up cookies, candy, or Christmas dinner?

I hope that everybody gets what they asked for this year and I do hope that they remember that "family" should also include their pets if they have any, so please make sure that they are having a good time on Christmas as well. Please remember not to drink too much alcohol, and make sure that you have somebody that can drive you home safely if you have overindulged.

Finally, I found an interesting documentary on the history of Christmas. It may surprise people to know that Christmas in the United States is a relatively recent invention because the Puritan colonists that settled in New England thought that Christmas was a sacrilegious holiday because of the frequency of drunken and gluttonous revelers and imposed fines on anybody who was caught celebrating.

This is the first of a five part series on YouTube but I found it very interesting to watch.

Monday, October 31, 2011

Today is Halloween!

Aside from a few religious fundamentalists and malcontents, Halloween is typically a fun occasion in which people dress up in fun costumes and go to parties. Children frequently go trick-or-treating by going from house to house to collect candy from strangers. While Halloween itself is a melange of mythologies from various cultures, it is one of most popular non-governmental holidays during the year in the American calendar.

Sadly, more and more people are trying to restrict or outright ban children from trick-or-treating; citing fears of children running into pedophiles and degenerates, gorging themselves on too much candy, teenagers causing trouble, or objections on religious grounds by framing Halloween has having irreligious connotations. I fear that this aspect of Halloween may soon be doomed simply because of how paranoid and over-protective people are becoming about their children. Although my childhood was far from ideal, I fondly remember the time I spent making my Halloween costumes and getting whole trash bags full of candy when I finally decided to retire for the evening. As with all holidays, the true meaning behind celebrating them is to have a good time, and I feel that the joys of Halloween should not be allowed to languish.

As you can see, my blog seems to have been engulfed by some sort of strange biomass that is slowly infiltrating the premises. Some people are terrorized by vampires, werewolves, and ghosts, but those people are lucky by comparison as sitting in a room with the walls covered in pink, squishy, meat is quite disturbing. I have changed the music selection on the radio in celebration for Halloween while I figure out how to reclaim my infested facility and the robots that have also fallen to this disgusting mass of tissue.

Friday, July 22, 2011

Fantastic Friday: How About Some Music?

I have been having trouble with my blog radio as it will only play one song on the playlist now. I do not know what the problem is, but I might have to overhaul it if it continues. So, I will give you some music of a different nature this Friday.

For those of you who are unaware, there was a series of albums produced by Josh Homme of Kyuss and Queens of the Stone Age fame known as the Desert Sessions. The Dessert Sessions was a project of Josh Homme and various other artists who would go out in the middle of the Nevada desert, hook their equipment up to a generator and start playing to see what would happen. All five albums are entirely improvised and feature material from names such as Chris Goss and Mark Lanegan. The result is an interesting mixture of material ranging from psychedelic, drug-induced guitar haze, to acoustic folk and blues. However, it all evokes the feeling of traveling across a massive, sun-baked desert alone and stoned out of your mind; while your flesh broils in the blistering heat or is scoured by blowing sand storms.

All five compilations are well worth getting but some of them are sadly out of print. My favorite collections of the series are 1&2 but my favorite single song is probably "Making A Cross" from volume 7&8. It is perfect music for listening to while driving as well as a lazy afternoon on the porch with a beer or for a late-night shot.

Friday, July 15, 2011

Fantastic Friday: What A Week!

For today's Fantastic Friday I give you a YouTube series called Epic Meal Time. Epic Meal Time features a group of young Canadian men who get together to make some of the most outrageous and fatty meals in existence. Each episode features a dish with unholy amounts of meat and cheese and they make a point of using bacon in every recipe. The end result is a sort of meat-nirvana that only the most dedicated eaters can ever hope to attain. The main host pretends to be constantly drunk and angry, and the sound of a bird cawing plays whenever he swears. They have a whole bunch of episodes and they come out with a new one every Tuesday. This week's episode features the "Epic Stockyard Burger", a bacon, cheese, bone marrow, and beef monstrosity that is stacked and then deep fried. I pity vegetarians, as they miss out on bliss such as this.

Thursday, July 14, 2011

Nuclear Technology Basics: Part 8 Liquid Metal Cooled Reactors

Introduction

Part 1

Part 2

Part 3

Part 4


Part 5

Part 6

Part 7

Liquid metal-cooled reactors are both moderated and cooled by a liquid metal solution. These reactors are typically very compact and could also potentially be used for naval propulsion. While there are a few currently existing liquid metal-cooled reactors that are being used for electricity generation, most examples are prototypes that have been built around the world as experimental reactors.

1. Sodium-Cooled Fast Reactors (SFRs)



Sodium-cooled fast reactors use a sodium-potassium alloy that remains liquid at room temperature. While the compound reacts violently on contact with air or water, its effects on steel are minimal. This makes NaK a possible coolant and moderator choice for a fast neutron reactor such as this one. Using water as a neutron moderator would effectively reduce the speed of the neutrons to those of thermal neutrons unless it was under massive amounts of pressure, while the NaK coolant and moderator does not need to be pressurized.

Fast reactors have advantages over reactors of other types as they achieve a high fuel "burn-up" ratio and greatly reduce the long-lived actinides that are present in the spent fuel when compared to other reactor types. This has made SFRs an attractive energy option for many countries around the world. Unfortunately, the Integral Fast Reactor project (IFR) was cancelled in the US because during the Clinton administration because of political reasons despite only being thee years away from completion. As of yet, a standard SFR design has not emerged from one of the many prototypes that have been built.

The NaK compound is pumped through the bottom of the reactor where it is heated up by the core. Hot coolant in the primary coolant loop is pushed into the heat exchanger, which is used to heat up coolant within the secondary coolant loop and the heated secondary coolant is used to turn a turbine connected to the generator. After leaving the turbine, the coolant flows into a condenser connected to a heat sink to help absorb some of the excess heat energy. The cold secondary coolant is pumped into the top of the heat exchanger while the primary coolant enters to bottom of the reactor again, completing the cycle. The control rods are inserted into the top of the reactor vessel.

Moderator Type: Liquid metal

Technology: Generation IV

Existing Examples: Three, but many more are being planned and built.

Advantages

-This reactor design has a high fuel burn-up ratio.

-NaK does not corrode steel.

-The reactor design is very compact yet has a high power output for its size.

-Liquid metal-cooled reactors are not pressurized leading to simpler piping systems.

-The liquid metal coolant cannot turn to steam unlike water during a meltdown, making a steam explosion impossible.

-Some variants of this design can be used as breeder reactors.

Disadvantages:

-The high temperature of the reactor could also pose design challenges.

-Sodium reacts violently with water and air.

Variants: BN-350, BN-600, Clinch River, Dounreay Prototype, Fermi 1, Experimental Breeder Reactor 1, Experimental Breeder Reactor 2, Fast Breeder Test Reactor, Integral Fast Reactor, Jōyō, Monju, Phénix, Prototype Fast Breeder, S1G, S2G, SNR-300, Sodium Reactor Experiment, Superphénix, Rapsodie

2. Lead-Cooled Fast Reactors (LFRs)



Fast reactors can also be used with a lead-bismuth coolant and moderator. Lead has a low degree of neutron absorption and does an excellent job of reflecting neutrons. In addition, lead is a very effective radiation shield and its extremely high boiling point makes lead-bismuth eutectic (LBE) an effective coolant even at higher temperatures. While LBE is somewhat corrosive to steel unlike NaK, it is unlikely that this poses a major problem as this issue can be overcome with proper engineering.

The design of the lead-cooled fast reactor is is slightly different from that of the sodium-cooled fast reactor. the LBE coolant on the outside of the coolant module flows downward where it is drawn into a pair of chambers in the center. The core of the reactor is contained with in a block in the center as well which heats the coolant as it is pushed upwards towards the top of the coolant module. This design has a pair of heat exchangers that are inserted into the top of the coolant module with the control rods in the center. Primary coolant transfers its heat energy to the coolant in the secondary coolant loop through heat exchangers where it is sent to a pair of turbines. After circulating through a secondary heat-exchange system to cool the LBE down, the returning secondary coolant is pumped through the top of the reactor to be drawn into the reactor core to complete the circuit.

Moderator Type: Liquid metal

Technology: Generation IV

Existing Examples: None that have been completed, but several LFRs are in the construction phase around the world.

Advantages

-This reactor design has a high fuel burn-up ratio.

-The entire reactor core can be removed and replaced during refueling procedures.

-The reactor design is very compact yet has a high power output for its size.

-Liquid metal-cooled reactors are not pressurized leading to simpler piping systems.

-The liquid metal coolant cannot turn to steam unlike water during a meltdown, making a steam explosion impossible.

-Some variants of this design can be used as breeder reactors.

Disadvantages:

-Lead-bismuth eutectic is slightly corrosive to steel.

-The lead-bismuth eutectic coolant can cause problems if it is allowed to solidify within the coolant circuits.

-The high temperature of the reactor could also pose design challenges.

Variants: OK-550, BM-40A, SVBR-100, Hyperion Power Module, MYRRHA

Friday, July 8, 2011

Fantastic Friday: For the Love of Quake!

I am not much of a gamer. The games that I do like and play are mostly older games for classic platforms such as the SNES and the Sega Genesis. As such, my knowledge of recent games is somewhat lacking, because I find most current computer games to be rather lacking in originality or fun. This is because many PC games are little more than an exercise to show off the graphical capabilities of the game rather than the gameplay itself. This is particularly problematic with the first-person shooter genre of games as they all seem to be imitators of each other, complete with boring enemies and rife with cliches.

I despise the Halo series as I find the main character to be little more than your average mindless military grunt like you see in almost every first-person shooter. Bioshock had some interesting ideas, but far too many of them got cut out in the final two games of the series, as a quick glance at the concept art books will show you. The Half-Life series is a refreshing change from the usual first-person shooter pablum as its protagonist, Gordan Freeman, is a theoretical physics researcher rather than the usual big and stupid marine. However, one of my favorite older games of all time remains the first Quake game.

It was originally for the PC but it has come out on numerous platforms. Unlike its later sequels, the enemies of the first Quake game were a strange mixture of horror-inspired monsters and formerly human soldiers that had apparently been captured and augmented by the enemy to make them mindlessly obedient in carrying out orders to kill you on sight. The antagonists of Quake all had very distinct characteristics in terms of how they attacked you and what their strengths and weaknesses were. All of the enemies were very well thought out and implemented and the environments that you fought them in were extremely varied. The game had a rather sparse plot, as you were supposedly a lone soldier left behind in a base after everybody else had been killed, as an enemy that was codenamed "Quake" had come through a sort of interdimensional device that your base was working on before the attack.

The game had four "episodes" of levels that were somehow related to each other. You could choose which episode you wanted to play in after selecting which entrance of difficulty you wanted to enter at the beginning of the game. You did not have to play the episodes in a specific order, but the episodes increased in difficulty so it is usually advisable to start with the first episode as it was the easiest one.

The first level of each episode was unique as it featured some sort of futuristic military base. However, the "base" levels had the same dismal and oppressive feeling that characterized the rest of the Quake levels. The walls were dingy and scratched, and were often covered in blood stains. Pools of grimy water and poisonous sludge were not uncommon and while the "base" levels lacked the horrifying textures of some of the later levels, they did imply that the current inhabitants were nearly mindless and that they were not the original builders as the current denizens seemed to lack the intelligence or autonomy to repair or maintain these crumbling structures.



The enemies that you fought in the "base" levels consisted of shambling human soldiers called "grunts", along with rabid rottweiler dogs, and the slightly more dangerous "enforcers" which were like grunts that have been upgraded. Grunts were humans that had cybernetic implants put into their brains by Quake that gave them feelings of bliss whenever they killed somebody. Grunts are not much of a challenge to defeat as two shots with the shotgun weapon that you start the game with was more than enough to put them down permanently and their reactions and movements were slow. Grunts were only challenging in large groups as they were quite accurate with their guns and could overwhelm you if taking on too many at once. When defeated, you could pick up a grunt's backpack which contained a few shells of shotgun ammunition. Rottweilers were even less of a threat than a grunt because all they could do is run towards you and attack you with a lunging bite. They had even less defense than a grunt and two blasts would quickly make them drop. The enforcers, which were the resident "tough guys" of the base levels were tougher than grunts as they wore full combat armor and were faster and had more defense than a grunt as it took four shotgun blasts to defeat them. In addition, they had some sort of energy weapon that fired blobs of light that cause quite a bit of damage to your character if he was hit. Unlike the grunts which could only snarl or growl, the enforcer apparently retained some degree of intelligence as it could utter simple phrases like "HALT!", "STOP!" or "FREEZE!" when it spotted you. When killed, an enforcer dropped a backpack containing "cells" which was ammunition for the "thunderbolt" weapon which you got later in the game.

After completing the "base" level at the beginning of each episode, you entered the world of your antagonist, which was some sort of dimension filled with rotting castles or malign dungeons. While the grunts, rottweilers and enforcers were absent in these levels, you had scrags, knights, death knights, fiends, zombies, rotfishes, ogres, spawn, vores, and shamblers.

Scrags are floating enemies that look like a cross between an armless man and a snake. They spit some sort of poisonous blob of fluid at you with a high degree of accuracy and damage if it hit you. Knights were twisted humanoid creatures wearing rusty armor and wielding battered and blood-covered swords that they used to great effect if they ever managed to get close enough to attack you with them if you did not fill them full of buckshot or nails first. Ogres were brutish humanoids that carried small grenade launchers and held chainsaws in the other arm. They were one of the most common enemies in the game and their grenades could be a real hassle at times. Continuing on with the rather easy enemies, the rotfish were undead piranha-like creatures that would chomp on you in the water and could easily be defeated by a single shotgun blast. Zombies were undead corpses that attached you by throwing pieces of their own flesh at you, and while they could be easily knocked down by any weapon, they would quickly rise up again and start attacking you unless you blew them to pieces using your explosive weapons.

Later on, you would encounter the more dangerous, mid-level enemies such as the death knight, spawn, fiend, and vore. Death knights are larger, tougher, and faster versions of the regular knight and could quickly kill you with a few swipes of their massive swords or their magical ranged projectiles. Spawn are bouncing blobs of slime that would harm you on contact and had a nasty habit of inflicting even more damage when killed as they tended to explode in your face when defeated. The fiend was a highly aggressive, eyeless, and clever beast that reacted by quickly charging at you and lunging across great distances to tear you open with its hook-like forelegs and would quickly rip you apart with them at close range as they did a lot of damage. Vores are bizarre, tripedal creatures that send explosive projectiles that homed in on your presence when they spotted you and a vore could take a lot of hits before killing it.



The undisputed "king" of the Quake monsters is the shambler. Shamblers are hulking, foul-tempered beasts that could send a powerful burst of lightning to reduce you to a pile of ashes, or rend your body to bloody chunks with their massive claws at close-range. Their heads lack visible eyes; and large, jagged, and frightening teeth jutted out of their mouths. They could soak up a lot of damage before falling, and they were especially resistant to your grenade launcher and rocket launcher which were normally very powerful weapons in the game. A shambler stops at nothing to defeat its enemies, even if it means crushing any allied monsters in its way. The shambler is never something that you want to see or take lightly.



Although Quake is a "mess" from a concept standpoint, there has never been anything like it before or since. The mish-mash of varied monsters and environments just seems to somehow work within the atmosphere of the game and Quake revels in its morbid, chaotic, and violent glory. While violence in video games often comes off as being over-the-top to the point of being cartoonish or laughable, the muted palette of Quake along with the otherworldly level architecture make the grisly world of Quake a truly chilling experience.

While the following sequels of the Quake franchise featured a race called the Strogg, they were little more than boring rip-offs of the Borg from Star Trek. Quake deserves a true sequel, but making one that captures the essence of the original game would be very difficult as Quake has an intensity that is not easily replicated by many modern games. This is an example of a game that transcends genres.

Sunday, July 3, 2011

Nuclear Technology Basics: Part 7 Graphite Moderated Reactors

Introduction

Part 1

Part 2

Part 3

Part 4


Part 5

Part 6

Many reactor designs use graphite as a moderator. Graphite is not as effective of a moderator as heavy water, but it is cheaper and it also has a low degree of neutron capture like heavy water. This makes it possible to use un-enriched or natural uranium as fuel. Graphite is somewhat susceptible to corrosion and annealing because the moderator blocks are often located in the hottest part of the reactor. Graphite also has a tendency to expand with prolonged neutron exposure. However, modern reactor designs have mitigated these issues so graphite remains a viable choice for a neutron moderator. The earliest energy reactor designs were graphite moderated, but some generation IV designs also use graphite as a neutron moderator.

1. Gas-Cooled Graphite Moderated Reactors (GCRs)



These reactors use graphite as a neutron moderator, but use pressurized carbon dioxide gas to cool the reactor. The primary example of this reactor type is the now obsolete MAGNOX design, so named for the "magnox" alloy of magnesium and aluminum which was used in the cladding of the reactor's core. The MAGNOX reactor grew out the nuclear weapons production program in Britain, but it also served a dual role for energy production.

The reactor itself consists of a pressure vessel similar to the BWR, with the fuel rods inserted in the top of the pressure vessel like in the LWR. The fuel rods of the reactor are surrounded by blocks of graphite, serving as the neutron moderator. These are situated inside the pressure vessel where carbon dioxide gas is heated by the fuel rods and flows upward and out of the hot gas duct connected near the top of the pressure vessel. The gas is pushed through a heat exchanger where water circulating within a closed loop is heated by the hot carbon dioxide and the resulting steam is used to turn a turbine. As the gas cools, it exits via the cool gas duct at the bottom of the heat exchanger and is sent back to the pressure vessel where it is heated again to complete the cycle.

A more advanced type of GCR was developed from the MAGNOX reactor, which is known as the advanced gas-cooled reactor or AGR. The AGR is similar to the design of the MAGNOX except that the heat exchanger of the AGR is contained within the reactor vessel itself instead of being outside of it like in the MAGNOX reactor. The AGR requires its fuel to be enriched unlike the MAGNOX design because the cladding of the AGR is made out of steel which has a tendency to capture neutrons. The original design of the AGR used beryllium cladding but this proved to be too costly, as beryllium is a very difficult material to process because of its high melting point and its affinity for oxygen at very high temperatures.

The AGR was built to overcome some of the MAGNOX reactor's shortcomings as the AGR was specifically built for energy production rather than the dual production of military grade plutonium. It was seen as a potential challenger to LWR designs, as the AGR was designed to allow refueling while the reactor was still in operation like in the MAGNOX reactor, but the fuel rod removal equipment was shown to be very prone to failure. In addition the design of the AGR was overly complex which added to the costs of construction and operation. In short, GCR reactors have a history of being fraught with technical difficulties and it is unlikely that any more of these types of reactors will be built.

Moderator Type: Graphite

Technology: Generation I-II

Existing Examples: Eighteen GCRs continue to operate in the UK, both of the MAGNOX and AGR designs.

Advantages

-Using a gas as a coolant allowed for higher operating temperatures and thermal efficiency.

-Some designs can use naturally occurring uranium without requiring further enrichment.

-It is more efficient in its fuel utilization than light-water moderated designs.

-It can be refueled without having to shut down the reactor.

-The resulting spent fuel can be stored in a more compact manner because it generates less heat when coming out of the reactor as it is less reactive.

Disadvantages:

-The fuel rod removal systems of these reactors was prone to technical problems.

-The design of the reactors was overly complex it often led to malfunctions.

-These reactors were more costly to build and operate than some reactor types.

-The first reactors of this type were not optimized for power production.

Variants: MAGNOX, AGR

2. High Power Channel-Type Reactors
(RBMKs)




This was a Russian design, and it was the reactor responsible for the infamous Chernobyl incident. This was both because of inherent flaws in this reactor's design as well as the fact that the staff on duty during the Chernobyl incident had attempted to run an unauthorized experiment with the reactor during its operation. With that being said, this reactor type is now considered to be obsolete.

The Reaktor Bolshoy Moshchnosti Kanalniy (RBMK) means "high power channel-type reactor" in Russian. It was similar to the MAGNOX design except it was water-cooled instead of gas-cooled and it heated water directly into steam within a pair of steam separators located inside the reactor pit which was used to turn dual turbines for energy. Because of the graphite moderator, the RBMK can run on unenriched uranium and the fuel rods can also be changed while the reactor is still in operation.

Part of the problem with this reactor design is the fact that it had a very high void coefficient. As the reactor is water-cooled, increases in temperature and pressure can cause the coolant to boil away and turn into steam, and the intensity of nuclear fission rises as the heat increases as the graphite moderator enables fission to continue. The control rods in the Chernobyl reactor were also controlled manually rather than automatically during an emergency. The Chernobyl accident resulted in a loss of coolant flow, which caused massive amounts of heat to build up in the core of the reactor triggering a positive feedback loop. The overheated core immediately vaporized the coolant within the reactor causing a huge steam explosion, similar to that of an overheated boiler within a steam engine.

The resulting steam explosion scattered radioactive particles from the core for hundreds of miles. The graphite surrounding the control rods was ignited by the heat of the reactor core and the roof of the reactor contained bitumen which also started burning. The official death toll released by the Soviet government was a total of thirty one deaths, and most of these were reactor workers and rescue personnel but many more people were thought to be sickened by the release of radioactive particles. To this day, an exclusion zone surrounding the reactor has been declared off-limits to humans but wildlife appears to be thriving there and the degree of ambient radioactivity has dropped considerably since the incident. If the Chernobyl reactor had a containment dome over it like all modern reactor designs do today, the effects of the meltdown on the workers and nearby populace would have been negligible. However, while the Chernobyl disaster and the resulting casualties was indeed a tragedy that could have been prevented with the proper engineering precautions, it was by no means the most severe industrial accident in the modern world. When compared to the Bhopal incident in India or the Banqio dam collapse in China or the yearly death toll resulting from a fossil fuel-based infrastructure dwarfs that of Chernobyl several times over.

Ever since the Chernobyl incident, the few remaining RBMK reactors still in operation have had their safety systems updated to prevent something like this from ever happening again. As it is, RBMKs only exist in Russia. Because this design of reactor is considered to be obsolete, it is unlikely that any new RBMKs will be built in the future.


Moderator Type: Graphite

Technology: Generation I-II

Existing Examples: Eleven in Russia, one in Lithuania.

Advantages

-It can use naturally occurring uranium without requiring further enrichment.

-The reactor generated a lot of electricity with its dual-turbine design

-It can be refueled without having to shut down the reactor.

Disadvantages:

-This design has a very high void coefficient.

-The control rods were under manual instead of automatic control

-The safety features of this reactor design are obsolete

-The Chernobyl disaster has effectively ended interest in the RBMK design.

Variants: None, other than RBMKs with modified safety features.

3. High Temperature Gas-Cooled Reactors
(HTGRs)



Improvements on GCRs has led to interest in developing gas-cooled reactors with a higher operating temperature that would allow for a greater degree of thermal efficiency and a higher degree of fuel utilization than the previous GCR designs. In addition, these reactors are also of a simpler design and use gas turbine systems for power generation leading to a more compact turbine assembly. Unlike previous GCR reactors, HTGRs use helium rather than carbon dioxide as a coolant because of the fact that it is inert even at higher temperatures leading to less corrosion on the piping systems of the circulating coolant.

Early experimental HTGR designs such as the Fort Saint Vrain Generating Station in the US, and the THTR-300 in Germany experienced technical problems or financial difficulties. However, the pebble bed reactor (PBR) shows great promise. The PBR is revolutionary in that its fuel is contained within spherical pellets of graphite that are piled within a chamber inside the reactor vessel. The pyrolytic graphite shells surrounding the fuel cores serves as a neutron moderator while the helium gas that circulates through the spaces between the pebbles serves as a coolant, avoiding the complex piping systems needed for designs that utilize fuel rods. These fuel pellets are circulated through the reactor every thirty seconds or so to be inspected for damage, allowing worn pellets to be removed and new ones to be put into circulation without shutting down the reactor for refueling. In addition, the reactor can hypothetically use graphite shelled pellets of thorium or fuel made from decommissioned nuclear warheads. Finally, the PBR pellets lack the fuel density to allow a meltdown to happen making a meltdown of the reactor physically impossible.

Of course, the PBR carries its own disadvantages, mainly that the PBR design utilizes a once-through fuel cycle and the graphite-sealed fuel pellets are very difficult to recycle in addition to increasing the volume of spent fuel to be disposed of by up to fifty percent. While there is certainly no shortage of fissile material that can be used in a PBR, once-through fuel cycles that make it difficult to engage in nuclear reprocessing are inherently wasteful.

Even though the PBR was originally a German design, political pressure within Germany's government has effectively stalled any and all research for nuclear power generation for the foreseeable future. There was interest in the PBR in South Africa, but political hurdles surrounding the construction of the Koeburg reactor has scared away investors and the reactor project was mothballed in 2010 by the South African government. The only active PBR project that remains is in China where the HTR-10 prototype at Tsinghua University is scheduled to be commissioned in 2013.

Moderator Type: Graphite

Technology: Generation III

Existing Examples: None currently in operation.

Advantages

-The fuel pellet design makes meltdowns physically impossible.

-The reactor core is cooled by helium gas which is chemically inert at high temperatures.

-The coolant system of the PBR is cooled passively and its simple design eliminates the extensive piping of active cooling systems.

-It can be refueled without having to shut down the reactor.

-Alternative fissile fuels can hypothetically be made into pellets to be used by this reactor design.

Disadvantages:

-The PBR uses a once-through fuel cycle.

-The pellet design of the reactor makes the reprocessing of spent pellets very difficult.

-The graphite shells of the spent pellets increases the total volume of material to be disposed of by up to fifty percent.

Variants: Dragon, TTR-300, Peach Bottom Unit 1, Fort St. Vrain 1, PBR, PBMR

4. The Very High Temperature Reactor (VHTR)

The VHTR (Very High Temperature Reactor) is a generation IV design that could be said to be an extension of HGTR reactor designs. It is also cooled with helium gas and uses graphite as a moderator. The core of pebble bed VHTRs would be similar to the PBR while prismatic block VHTRs would have its fuel shaped into fuel rods that are inserted in holes drilled into the hexagonal graphite blocks surrounded by control rods. The helium gas would be heated by circulating around the control rods to be carried to a heat exchanger to heat up water to spin a turbine.

True to its name, the VHTR concept operates at temperatures reaching 1000°C. This would make it very useful for providing process heat to carry out many industrial applications such as cheap hydrogen production and hydrocarbon reactions. The reactor would be extremely safe in addition to having a very high degree of thermal efficiency because of its high operating temperature. While this reactor design would have a once-through fuel cycle, the VHTR has a much higher fuel utilization ratio and the resulting spent fuel would have a much shorter half life than fuel from traditional LWRs. Prototype VHTRs are under development in China and the US has expressed interest in the VHTR for its Generation IV program.


Moderator Type: Graphite

Technology: Generation IV

Existing Examples: None currently in operation.

Advantages

-The fuel pellet design of the pebble bed variant makes meltdowns physically impossible.

-The reactor is an extremely safe design.

-The reactor core is cooled by helium gas which is chemically inert at high temperatures.

-The coolant system of this reactor is very simple.

-It can be refueled without having to shut down the reactor.

-Alternative fissile fuels can hypothetically be made into pellets to be used by this reactor design.

-The very high temperatures lend themselves to higher thermal efficiencies.

-The reactor would serve a dual purpose as a source of process heat for thermochemical production.

Disadvantages:

-It uses a once-through fuel cycle.

-The pellet design of the PBR variant VHTR makes the reprocessing of spent pellets very difficult.

-The graphite shells of the spent pellets of the PBR variant of the VHTR increases the total volume of material to be disposed of by up to fifty percent.

Variations: PBR VHTR, Prismatic Block VHTR

Friday, July 1, 2011

Fantastic Friday: Best Macaroni and Cheese Ever!

I thought that I would share one of my favorite recipes of all time. This is a version of baked macaroni and cheese that is made with bechamel sauce. Although the reputation of macaroni and cheese has suffered immensely with those abominations in a box such as Kraft, you will no longer allow such culinary mockeries in your kitchen again. This is a simple and fast recipe that even the most inept cook will find success.



Included here is the sauce that you will need for the recipe.

As a bonus, I am including a rare recipe that I saved from a newspaper article many years ago. It is for "onion marmalade" which is a savory spread that goes well with roasted meats or cold cut and cheese sandwiches. It is made from onions that have been carmelized over low heat for a long period of time, making them mellow and sweet instead of their characteristic pungent flavor when raw.



Enjoy, everybody!

Thursday, June 30, 2011

Nuclear Technology Basics: Part 6 Heavy Water Reactors

Introduction

Part 1

Part 2

Part 3

Part 4


Part 5

Heavy water reactors use water, or deuterium oxide as a moderator. Deuterium oxide has a lower neutron absorption ratio than regular water, allowing the use un-enriched, natural uranium as fuel. Although most heavy water reactors are cooled with heavy water, the Swiss Lucens reactor was gas-cooled.

1. The Pressurized Heavy Water Reactor (PHWR)



Most examples of the PHWR are of the CANDU (CANada Deuterium-Uranium) design which originated in Canada. The PHWR is a radically different design from the light water reactor family because the fuel bundles of the reactor are contained within their own pressurized tubes rather than the reactor containing one large pressure as is seen in the BWR. This is because Canada lacked the large steel forging presses required to manufacture large pressure vessels and found it easier to make a series of smaller tubes, one for each fuel rod bundle. Surrounding pressure the tubes is the reactor core, and the control rods are inserted at a perpendicular angle. Each tube contains pressurized heavy water which flows around the fuel bundles within, serving as a moderator during the primary coolant loop. Heated primary coolant flows into a heat-exchanger within the steam generator where it causes the temperature of the surrounding fluid in the secondary coolant loop to heat up and turn into steam which turns the turbine. After the steam has condensed into water again, the secondary coolant is pumped into the bottom of the steam generator to repeat the cycle. The returning primary coolant from the heat exchanger is pumped into the pressure tubes to be heated up again by the fuel bundles.

Moderator Type: Heavy Water

Technology: Generation II

Existing Examples: Twenty-nine in several countries.

Advantages

-It can use naturally occurring uranium without requiring further enrichment.

-It is more efficient in its fuel utilization than light-water moderated designs.

-It can be refueled without having to shut down the reactor.

-The resulting spent fuel can be stored in a more compact manner because it generates less heat when coming out of the reactor as it is less reactive.

Disadvantages

-Heavy water is relatively expensive, even though this cost is partially offset by the reduced cost of fuel processing.

-Because the fuel for PWHR reactors is not enriched, fuel is used up at a faster rate.

-It generates higher volumes of spent fuel because of the greater frequency of refueling.

Variants: Advanced CANDU, CANDU 6


2. Heavy Water Gas Cooled Reactors (HWGCRs)

These reactor designs used heavy water as a moderator but used carbon dioxide as a coolant. Although there were experimental reactors of this type, such as the KS 150 and Lucens reactor, both of these experimental reactors proved to be fraught with problems. Since then, there have been no existing reactors of this type.

Friday, June 24, 2011

Fantastic Friday: Wrangling With Woo

Magical thinking and other forms of anti-scientific nonsense are as pervasive in the developed world as ever and they show no signs of abating. In recent decades, these attitudes have become established in everything ranging from the prevalence of "organic" foods in grocery stores, the popularity of alternative "medicine", anti-vaccination movements, and errant fears over genetically engineered foods to name a few. The anti-nuclear hysteria that has re-arisen in the aftermath of Fukushima Daiichi is just the tip of the iceberg.

Although on the surface, most woo appears harmless, it can have very disastrous consequences for some people. This is because it can distort the process of scientific research, or cause the results of a legitimate study to be highly politicized by people who are not familiar with the field in question, or who are willfully trying to distort and mislead in order to fit an ideological agenda. In political terms; the "left" has become immersed in a strange mixture of naturalistic fallacies and neoluddism while the "right" (In the US at least) has been taken over by religious fundamentalism which makes a point of promoting young earth creationism and other Christian mythology. Unfortunately the war against science has gone mainstream as is under continual attack from political movements on all sides of the aisle. These are just a few areas where politics have trumped science

-Fears of radio frequency radiation have been around for years, despite there being no evidence for any of these concerns being justified. However, the World Health Organization recently issued a report saying that radiation from cellular telephones may cause cancer.



Now this will lend an air of undeserved credibility to RF-phobes without any studies pinpointing a definite link between cellular telephone exposure and what constitutes an unsafe dose, and other necessary details. Hypothetically, something may cause a condition, but until there is solid evidence that it does, the empirical assumption is that such a claim is invalid.

There is a five-part lecture on this topic given by Professor Christopher Davis who has a background in electrical and computer engineering. It is well worth listening to the whole thing. This is the first video, the other four parts can be found by following the links underneath it.



Part 2

Part 3

Part 4

Part 5


-Anti-vaccination activists such as Jenny McCarthy and Viera Sheibner and the rest of their ilk have been whipping parents up into a frenzy over vaccines, citing fears over mercury, and formaldehyde; or for fears that they might be responsible over conditions such as childhood cancer and autism, when the only report that they are using as the basis for these claims has been the infamous Wakefield study which has since been retracted by the General Medical Council as being fraudulent and Andrew Wakefield was stripped of his medical license last year.

However, the damage has been done as the anti-vaccine movement continues to distort information and spread misinformation to suit its needs, out of some misguided idea that they are doing it in the name of public health. Many of these diseases such as diphtheria, polio, and whooping cough were deadly for children before the vaccines against them were available, and while other illnesses like measles and mumps were mostly benign, they could cause permanent sensory impairment in some cases. Because of vaccines, these diseases are no longer a common occurrence. Unfortunately, this has lead society to forget the havoc these pathogens could cause, especially in newborn infants.



This child's brush with death and permanent deafness could have been prevented if her mother had given her the MMR vaccine like her physician recommended. Her daughter is now paying the price. Even as we speak there is an outbreak of measles that is happening in the US that has in no doubt been helped along by public fears against vaccination. There is no reason why anybody should suffer from these preventable illnesses in the 21st century yet they are making a comeback. The anti-vaccination movement is responsible for the deaths or permanent disability of people around the world because whenever vaccination rates go down, herd immunity also goes down, making it more likely that diseases can find carriers. Nobody is going to be championing the resurgence of polio if and when it returns at this rate, and I doubt that pressure ventilation systems would become a fashion statement.

-Alternative medicine is a catch-all phrase for medical treatment using folk remedies, traditional practices, or supernaturally-based therapy rather than modern medical science. Alternative medicine has not been shown to be supported by scientific evidence, and the only benefit that anybody seems to derive from it is the placebo effect. While the placebo effect can be beneficial, it often means that people who suffer from serious medical conditions often put off real medical treatment which can cause their illnesses to worsen.

The motivation for this movement is somewhat understandable, as many people in the US cannot afford access to medical treatment as medical insurance companies here are notorious for their dysfunctional practices. The US medical system is in need of a serious overhaul. But this is from an administrative and financial standpoint as modern medicine has been proven to work and therefore the issues behind the broken American medical system ARE mostly administrative and financial. The issue is one of access rather than the effectivity of modern medical treatment.

Because many people lack access to basic medical care, they turn to whatever options are open to them. Although homeopathy, ear candling, and faith healing and the like have not been proven to be effective, an entire industry has sprung up to cater to the alternative medicine movement and play on people's feelings, even though alternative medicine accomplishes nothing other than fooling people into paying for things that do not work rather than seeing a real medical professional.



Unfortunately, the alternative medicine movement is growing, and it is showing no signs of stopping. The NHS in the UK has even started allocating funding for treatment to visit alternative medicine practitioners, yet none of these treatments have ever been shown to work. Quackery exists in many forms and now it seems that many people are supporting it and encouraging it. Speaking of "quackery", there is an in-depth discussion on the subject by pathologist, Dr. Ed Uthman. It is in four parts. I recommend watching it in its entirety.



Part 2

Part 3

Part 4

-It has become fashionable to deride foods produced on "factory farms" in favor of "organic foods". Promoters of organic foods claim that they are safer to eat, contain more nutrients, are better for the environment, or have benefits that are not found in foods produced by conventional farming techniques. Organic foods have become a huge industry in the past twenty-years as it is marketed brilliantly by its producers. As growers of organic foods cannot compete in cost or quantity of foods grown using conventional means, they justify the higher prices of their products based on their own moral or environmental superiority.



This is largely false, because "organic" foods are often worse for the environment. Organic produce uses more land to grow while generating lower yields, ultimately leading more land to be converted into farmland. Chemical fertilizers are not allowed, so growers of organic foods must resort to using animal manure. Bacterial contamination from manure has led to outbreaks of food poisoning across the world because it is difficult to wash off pathogens using water alone. While organic food growers claim that they do not use pesticides, this is not true as "natural" pesticides such as rotenone and nicotine are permitted under the "organic" label. Although the judicial application of pesticides is a necessary evil when growing any food on a large scale, "organic" pesticides have not been specially formulated in a laboratory to meet certain standards and are often just as dangerous if not worse than their manmade counterparts.

In regards to other labels such as "free range", chickens in an outdoor environment are often subject to many parasites that cause the birds suffering such as gapeworm in addition to preventing them from reaching a desirable weight as a result of increased parasite loads. Predation is also an issue from prowling animals, and this raises the question on whether or not "free range" actually brings any sort of tangible benefit to the animals at all.

The third attack on conventional foods comes from people who are wary of genetically engineered plants and animals in our food supply. Humans have been "genetically" engineering their produce and livestock for thousands of years. By all accounts, there is nothing "natural" about modern day corn or the Holstein cow as they have both been bred by humans to produce higher yields of a desirable product in a shorter period of time than their wild ancestors. Their very existence depends on humans to raise and care for them. With genetic engineering, it will enable humanity to select for desirable traits in a shorter period of time using less money rather than running selective breeding experiments over several years. Eating further "genetically modified" food would be no more or less dangerous than eating food that has been modified for humans since its domestication by humanity. While I do not excuse the business practices of Mosanto, that is a legal and political issue and it has nothing to do with the application and implementation of genetic engineering technology.

Some clarification on "organic" foods.



-Religious fundamentalism has been fighting back against the encroachment of science upon its perceived domains in the modern world. Politicians of both the left and right pay homage to imaginary beings to increase their chances of getting elected, while science in public school curriculums is being subverted by groups trying to sneak in creationism under the guise of intelligent design or claim that Noah's ark was indisputable fact. Faith-based initiatives continue to receive funding from the US federal government despite there being a codified separation of church and state within the law of my country and it is considered politically acceptable for presidents to publicly claim that they were told to launch military campaigns against foreign nations by their god. Both men and women continue to have their genitals butchered for religious reasons worldwide, and suicide bombers have blown themselves up and the surrounding area under the illusion that doing so will allow them to enter some sort of erotopian afterlife.



There continues to be no evidence that there is a god or any other sort of supernatural entities, yet people waste so much time and cause themselves so much suffering in trying to appease something that really is not there. Abuses are allowed in the name of religion that would be shouted down if perpetuated by any other sort of institution. The effects of religious beliefs foisted on children by their parents can have lasting psychological damage, and religious schools can often impair or inhibit children from receiving a proper education.

While one cannot be absolutely certain of everything, the things that we do know about the nature of the universe and the beings that are in it has shown that the existence of gods is highly unlikely, and even if they did exist they would be unnecessary as the universe seems to be self-maintaining. Why do we allow religion to control people's minds and direct their thoughts when it has proven to be a very destructive phenomenon? Although it would not be acceptable for atheists to bully and harass theists for their religion, there is certainly no place for religion in guiding the decisions of our political leaders as their actions would have consequences for us all.

Fantastic Friday: Book Review, Z Is For Zombie




The popularity of the zombie mythos has contributed to many books and movies as of late. One need only glance at recent video games such as the Left 4 Dead series or the movies 28 Weeks Later, Zombieland, and Shaun of the Dead to get a sense as to how much of an extent popular culture is obsessed with zombies. Although people have yet to write a romance story aimed towards teenage girls involving zombies ala the Twilight series it does not look like the human fascination with animated, rotting corpses is going to die down anytime soon. Zombies are still rising from the graves in our heads and continue to shamble onward through the corridors of our minds.

I admit I do have somewhat of an interest in the zombie genre myself, particularly when it knows not to take itself too seriously. I came upon Z Is For Zombie by Adam-Troy Castro by accident when browsing various fiction books published by HarperCollins. I was not sure what to expect, so I decided to read it on a whim.

I was not disappointed. The book cleverly gives each of the twenty-six letters of the English alphabet its own page on a subject dealing with zombies; such as "A is for Apocalypse", "B is for Buried", etc. written in a very tongue-in-cheek manner. In addition, a delightfully morbid illustration accompanies the subject for each page. The artists certainly did not skip on the gruesome details here. The illustrations are all in greyscale but the color of blood or viscera is rendered in various shades of pink and red in contrast to the monochromatic images. It was an interesting choice for effect as it made the scenes of carnage stand out more.

This was a fun little book, but I do have some rather small criticisms. The book was sweet but short as it only spanned sixty-four pages and a person could probably finish it in five minutes or less. I am also not sure what category to put this book in. Although I am sure that I lot of us remembered how much we delighted in hearing about violence and gore when we were children, overly concerned parents might snatch such a book as this out of their little hands. Also, since the book is so short, older individuals might not want to read it and simply dismiss it out of hand as being a "children's book" without wanting to read it. Such is a pity, for I think most people would find Z Is For Zombie worth spending a few minutes with.

In conclusion, Z is For Zombie makes an excellent book for a Halloween party or a rainy afternoon. I highly recommend it for anybody with an interest in the subject of zombies or survival horror. This is a nice little gem that is too unique to miss.

Thursday, June 23, 2011

New Blog Feature

For a long time, I have been thinking about having a "Friday Fun Day" on my blog like many other bloggers do. This is because I am not an entirely serious person as some of you can probably guess from my music player widget in the sidebar as well as the fun I had in designing the layout of my blog. Starting tomorrow, I am going to experiment with having a day dedicated to "miscellany" as I would like to post my reviews of recent books that I have read for NetGalley in addition to posting material on the topic of atheism/rational skepticism. Although it may seem like I am trying to crowd everything into Friday, there are other things that I want to blog about as well occasionally, yet I do not think that it is worth creating several blogs to do this with. N^4 is and will remain my only blog for the foreseeable future simply because I fear that another blog would become neglected in trying to balance the demands of different blogs at different times.

So, starting tomorrow, my blog will have its first post in a feature I will call "Fantastic Friday". Fantastic Friday will be like a variety show where I will post anything ranging from cooking recipes, book reviews, playthroughs of computer games, to thoughts on philosophy and atheism. Just remember to follow the safety procedures at all times when visiting, lest casual Friday go too far. The last thing I need is a big mess for all of the maintenance robots that run my blog to clean up in addition to lawsuits from angry parents and relatives.

Saturday, June 11, 2011

Nuclear Technology Basics: Part 5 Light Water Reactors

Introduction

Part 1

Part 2

Part 3

Part 4


Light water reactors are the most common type of nuclear reactor that has been built in the world so far. These reactors use regular water as a neutron moderator in addition to a coolant. Although there are different sub-types of light water reactors, they are all similar in their design and operation.

1. The Pressurized Water Reactor (PWR)



This design was covered in detail in my last post regarding nuclear energy. It uses a heat exchanger consisting of heated water in the primary coolant loop flowing through a pipe that is surrounded by cool water in the secondary coolant loop. This takes place in the steam generator where the heated water in the primary coolant pipe produces steam from the feedwater that is pumped in from the secondary coolant loop. The steam is then used to drive the turbine and produce electricity.

Moderator Type: Normal water

Technology: Generation II

Existing examples: Ubiquitous around the world.

Advantages:

-It is a very familiar Generation II design that has been around since the mid-20th century.

-The majority of reactors used for electricity generation are of this design.

-It is also very safe as the fuel rods are held upwards using electromagnets. If the electricity is disabled, the fuel rods will automatically drop into the reactor vessel and cause the reactor to shut down.

Disadvantages:

-It must use fuel rods that have had their uranium-235 content enriched up to four percent, necessitating increased costs for fuel production.

-Ninety percent of the available uranium-235 within the spent fuel pellets remains un-fissioned, which means that the spent fuel pellets must either be reprocessed into usable fuel or disposed of.

-The reactor must be shut down to engage in refueling.

-Some of the actinides that remain in the spent fuel such as cesium-137 and strontium-90 are a cause for concern and have half-lives that are measured in decades. Although many of the remaining radioisotopes in spent fuel from light water reactors are only weakly radioactive, they have half-lives measuring thousands of years.

-Although there are no hurdles to reprocessing spent fuel from a technical and industrial standpoint, sociopolitical hysteria has effectively blocked any and all discussion of such a practice and has also prevented the construction of a centralized location where the spent fuel can be moved for long-term storage.

-A combination of politics and perceived investment risks has effectively prevented the construction of any new nuclear electricity generation facilities for decades in many countries.

Variants: European Pressurized Reactor (EPR), Advanced Passive 1000 (AP1000)

2. The Boiling Water Reactor (BWR)



The BWR is similar to the PWR in that it uses ordinary water as a coolant and neutron moderator. However, unlike the PWR it lacks a pressurizer and steam generator as water is heated into steam within the reactor vessel itself. This is the second most utilized reactor design in the world.

Moderator type: Normal water

Technology: Generation II

Existing Examples: Ubiquitous, as with the PWR.

Advantages:

-The design is one that nuclear engineering projects are very familiar with.

-It is of a simpler design than the PWR.

-Because of the nature of the BWR there are options for passive and active safety systems that are not available with the PWR.

-Like the PWR it is a very safe design.

Disadvantages:

-Because of the nature of coolant circulation within the upper half of the reactor chamber, the reactor still requires active coolant flow to remove residual heat even after the reactor has shut down.

-The control rods are inserted in the bottom of the reactor chamber rather than the top which requires an active hydraulic system rather than a passive fail safe using electromagnets like in the LWR.

-The reactor must be shut down to be refueled.

-A large portion of the uranium-235 in the fuel rods remains un-fissioned like with the PWR.

-The nature and quantity of the spent fuel produced by BWRs is the same as with PWRs and the same sociopolitical hurdles stand in the way of closing the fuel cycle or building a centralized location for spent fuel in some countries.

Variants: Advanced Boiling Water Reactor (ABWR), Simplified Boiling Water Reactor (SBWR), Economic Simplified Boiling Water Reactor (ESBWR)

3. Supercritical Water Reactor (SCWR)



This is a theoretical design that would utilize water as a coolant and neutron moderator. The water is heated and pressurized past the critical point in which liquid water and gaseous steam become virtually indistinguishable. Because of the higher operating temperature, it would be able to reach a higher degree of thermal efficiency than either the BWR or the PWR. Supercritical water is a less efficient moderator than water in its liquid state but it is also a better conductor of heat. Because of this, less moderating fluid might be needed. This might lead to the operation of a SCWR as a fast neutron reactor. The control rods would likely be inserted into the top of the reactor chamber like in the PWR. The design is being researched by several dozen countries across the world.

Moderator Type: Normal water in a supercritical state.

Technology: Generation IV

Existing Examples: None, as the reactor is still theoretical

Advantages:

-The greater thermal efficiency would allow the reactor to utilize the Brayton cycle

-The higher efficiency of the reactor would allow for a smaller reactor and smaller components

-The design of the SCWR is simpler making it cheaper to build and maintain.

-Fast breeder SCWR designs would be able to "burn up" more of the actinides produced during fission, leading to less actinides in the spent fuel and the spent material produced would have a half-life of an average of three hundred years.

-Breeder variant SCWRs would be quite flexible in the fuel they would be able to use as feedstock ranging from spent fuel from other reactors to thorium, to decommissioned nuclear warheads.

Disadvantages:

-Supercritical water presents unique challenges from a metallurgical and chemical standpoint when designing the ductwork for the circulating coolant and moderator.

-Activating a SCWR requires more complex operations than a BWR or PWR.

-Designing the reactor core to avoid a positive void coefficient would require a fairly high degree of complexity which would raise the cost of construction.

Variants: Fast Spectrum Supercritical Water Reactor (FSSCWR), Supercritical Heavy Water Reactor (SCHWR)

Conclusion

Light water reactors are the most common reactor types in the world today. This is because they have proven to be both reliable and relatively simple to operate, and have become to be regarded as "traditional" within the nuclear industry. However, they are by no means the final word in nuclear fission technology. The SCWR does show some promise, but there are other reactor designs that would be even more impressive in their application for electricity generation and for breeding more fuel.

That concludes my post on the light water reactor family. Next time, we will look at heavy water reactors. If you have any questions or comments, feel free to ask me as I welcome your interest.

Sunday, April 24, 2011

Easter Sunday

Easter is a holiday that is important to Christians because they believe that it is the day that Jesus Christ rose to heaven after being crucified by the Romans. However, as with most religious holidays different religions have been stealing each other's events and repackaging them for their own. In the case of Easter, it started off as a celebration of the vernal equinox as this signified the end of winter and the beginning of spring. It was not until the first Council of Nicaea in 325 C.E. that Easter became a floating Christian holiday.

I am am an atheist, but I still enjoy the trappings of Easter because of the fact that I like chocolate and Easter candy. I really like the different chocolate eggs that are made by the British chocolate company, Cadbury. The peanut butter-filled eggs are my favorite, but the cream-filled eggs are good as well. I bought some of those for myself today in addition to a chocolate rabbit. I also colored hard-boiled eggs on Friday simply because it is fun to do. For dinner, I made a roast leg of lamb and had an enjoyable evening. Although I do not believe in or follow the religious mythologies behind Easter, I think that the holiday is more about the renewal and the awakening of plants and animals during the spring after the monotony of winter.

The grass is finally starting to turn green where I live and leaf buds are appearing on the trees. Early spring is a rather depressing time of year because everything is drab and dirty after the snow melts and things do not begin to brighten up where I live until late March. Spring in most of the midwest is a rather short affair, and Illinois is no exception because the transition between winter and summer weather is rather abrupt here. The summer is my favorite time of year because that is when the weather is most conducive to swimming and other activities in addition to the fact that is usually when the local gardens and trees are in full bloom and the fragrance of their flowers hangs on the humid air.

I hope that today was an enjoyable day for my readers and I hope that their local weather is pleasant. At the moment, I am boiling a whole pot of lamb and beef bones that had been in my freezer for awhile as I am making stock for future use. I will see if I can get part 5 of my Nuclear Technology Basics series tomorrow as I want to start talking about different types of light water reactors.

Wednesday, April 13, 2011

Nuclear Technology Basics: Part 4 Reactor Components

Introduction

Part 1


Part 2

Part 3

The process of nuclear fission can be carried out by several different fissile isotopes, depending on the design of the nuclear reactor. Most reactors that have been built in America for energy generation are what are called light water reactors or simply "LWRs" as an abbreviation. Light water reactors are thermally-based reactors that use regular water for both coolant and as a neutron moderator as opposed to heavy water which has a high ratio of deuterium which is an isotope of hydrogen that has a greater atomic mass than normal hydrogen.

In future posts I will go over the different types of light water reactors, but in this case I will use the layout of a typical pressurized water reactor or "PWR". PWRs constitute the most common type of nuclear reactor in the world, including the US. Although many different types of reactor designs exist, the PWR remains the most common design because of both politics and technical familiarity with engineers in the nuclear field.

While I normally frown on Wikipedia as a source of accurate technical information, I did find a nice animated diagram of a PWR reactor layout there.



So, here are the basic components of our nuclear reactor:

1. The Reactor Vessel
The reactor vessel is the component within a nuclear reactor that contains the reactor core and where coolant circulates to prevent the core from overheating. Some designs lack a reactor vessel but the BWR and the PWR types of light water reactors both have this component in their similar designs. The basic layout is that of a cylindrical tube made out of a steel alloy containing manganese and molybdenum because of its durability, while the interior of the reactor itself lined with a layer of stainless steel to prevent corrosion from rust since it comes into contact with the coolant fluid, which is water in LWR designs. The top of the reactor vessel is designed to be removable to facilitate the replacement and insertion of fuel assemblies. Coolant is pumped in through the inlet nozzles where it flows around the fuel assembly; removing heat in the process. The heated coolant is then pumped out of the reactor vessel and into the steam generator.

2. The Pressurizer



The coolant circulation system and the steam that is produced within the steam generator is under constant pressure. Maintaining the degree of pressure within the coolant circulation system and the steam generator is an important task and this is carried out by the pressurizer. An increase in the temperature of the circulating coolant causes the density of the fluid to drop, and the volume of the liquid to expand in volume. This pushes the fluid into the pressurizer, causing the steam within the top of the component to become compressed, and pressure levels to increase. A drop in the temperature of the coolant increases the density of the water, causing it to contract. Fluid drops out of the pressurizer, reducing the degree of steam compression within the top of the pressurizer. Should the pressure increase too much or decrease below safe levels, the pressurizer will bring fluid pressure levels back to a safe equilibrium by either spraying cold water through the top of the pressurizer which would cause the compressed steam to cool down and turn back into water. Lower than normal pressure levels will cause the pressurizer to activate a series of electric heaters embedded within the walls of the component to raise the ambient temperature of the water within the pressurizer. Should pressure levels continue to fall, safety systems will cause the reactor to shut down automatically.

3. The Control Rods


The control rods regulate the speed and ratio of fission within a nuclear reactor. Each control rod is composed out of materials that can capture and absorb neutrons without undergoing fission themselves, such as indium, cadmium, and boron to name a few. When nuclear fission occurs within the nuclear fuel rods, control rods serve to prevent some of the neutrons from striking fissile atoms within the fuel assembly which slows down the nuclear reaction. The speed of fission can be increased by lifting the control rods further out of the reactor vessel, leaving more neutrons available to initiate fission. Lowering the control rods into the reactor vessel can decrease the rate of fission as they absorb more the neutrons that were being emitted by the fuel rods. In the event of an emergency, the control rods will be pushed into the reactor vessel at their maximum depth in order to slow down the rate of fission as much as possible.

4. The Neutron Moderator


A neutron moderator is a material that serves to slow down the speed of fast neutrons so that they will cause a fission reaction when they strike the nucleus of a fissionable atom. As reactor designs are grouped by their moderator type, light water reactors use ordinary water as their neutron moderator but moderators can be made out of many substances. In water moderated reactors, a bluish glow can be seen around the control rods as charged particles are moving faster than the speed of light within the medium. Since the electric field of the particles is unable to keep up with them as they travel, photons are produced in an optical equivalent of a "sonic boom", producing light towards the blue wavelengths of the color spectrum.

5. The Containment Structure



All nuclear reactors in the world are now constructed with a containment building over the reactor vessel to protect the reactor from damage and to physically prevent the release of radiation in the event of a core meltdown. The containment building is a solid concrete or steel shell that is several feet thick that is extremely durable and tests have shown their ability to withstand earthquakes or impacts with aircraft with minimal damage. The containment building is what prevented the release of any significant degree of radiation during the Three Mile Island incident in 1979 and what prevented the damaged reactors at Fukushima Daiichi in Japan from irradiating the populace after being subjected to a massive earthquake. If the infamous Chernobyl reactor had been built with a containment building over the reactor vessel, the effects of the meltdown on the surrounding area would have been negligible.

6. The Steam Generator



The PWR light water reactor design has a steam generator, the BWR design does not. Hot coolant flows from the reactor vessel into pipes that are surrounded by secondary coolant within the steam generator. The pipes containing the hot coolant cause the fluid surrounding them to heat up and begin to boil and generate steam. Heat energy is transferred from the hot pipes into the secondary coolant causing the primary coolant to cool down as it is pumped back into the reactor vessel. The steam generated by the boiling secondary coolant rises and is forced through a moisture separator into the turbine chamber.

7. The Reactor Turbine



Within the reactor turbine, steam is pushed through the center of the turbine which then turns the blades of the turbine assembly as it expands outward. Most turbine designs have a moisture separator after the first high-pressure turbine which separates the condensed water from the steam and forces the steam through a series of low pressure turbines. This is how pressurized steam is converted into mechanical energy.

8. The Generator



The generator coverts mechanical energy into electricity. A rod runs from the generator to the turbine that spins along with the motion of the turbine. Within the generator, the rod is wrapped with a piece of wire that is surrounded by magnets. Electrical current is generated within wires surrounding the magnets on the side of the generator shaft as it spins, which is then sent out of the nuclear power plant.

9. The Condenser



Steam passes into the condenser chamber after passing through the turbine where cool water circulated from a water box causes the steam to condense into water. The water is then circulated within the secondary coolant loop to the steam generator. Then it is used to generate steam from the heated pipes of the primary coolant loop.

This was just a brief summary on the major components of a "typical" nuclear reactor such as a pressurized water reactor, or PWR. On my next entry, I will be taking a look at how reactor designs differ, starting with the different types of light water reactors. The PWR is by no means the final word in nuclear reactor technology.