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.