Nuclear? Mark Lynas - The green heretic persecuted for his nuclear conversion

"According to the Intergovernmental Panel on Climate Change, nuclear is just as low-carbon a power source as wind and solar: the world’s 439 operating nuclear reactors save the planet from 2 billion extra tonnes of carbon dioxide per year, which would have been emitted had coal been used instead.

And those dangers? They’re still there but we need to discuss them truthfully. Take Chernobyl. We all know it was a disaster: the Greenpeace website states a death toll of 60,000 already and predicts another 140,000 deaths in the future. But these statistics fly in the face of mainstream science: according to the World Health Organization and the United Nations Scientific Committee on the Effects of Atomic Radiation, 28 people died in the initial phase and several thousand more have suffered from nonfatal thyroid cancer because of the accident. The UN report concludes that “there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident” – so the real death toll from the world’s worst nuclear accident is tiny. On a deaths per gigawatt-year basis, nuclear is safer than coal and oil.

Curiosity whetted, I searched the scientific literature for evidence to support the other great green charge leveled at nuclear power: it kills its neighbors. I sifted through piles of rigorous epidemiological studies from all over the world, searching for proof that people who live near nuclear sites are more prone to cancer and leukemia. None of the reputable journals turned up a link.

These are just two examples of eco-myths: there are many more. If only we were allowed to discuss them without being flayed for heresy.

When I e-mailed a senior ecological scientist with my conclusions, he agreed, but only privately. “Do not cite me as promoting nuclear,” he begged. I am still shocked that people of his stature are too intimidated to speak out. The result of this fear is that the public is dangerously misinformed about nuclear power." ---
Mark Lynas - The green heretic persecuted for his nuclear conversion

Nuclear Issues: Waste Disposal Recycling Fuel Reserves Radiation Safety

If used nuclear fuel is repeatedly recycled - say, 10 - 15 recycle cycles - about 5% of its mass will eventually remain - almost nothing - and all of its uranium and plutonium will be gone. After about 300 years, that residue will be less radioactive than natural uranium ore.

Kids! Test drive all the different conventional nuclear reactors yourself - Official IAEA free downloads + others: http://www.iaea.org/NuclearPower/Education/Simulators/ http://www.ae4rv.com/games/nuke.htm Nuclear power plant simulators for PCs

Jobs!

Seriously, kids, in the United States alone, there are almost 50,000 nuke workers about to retire comfortably. The nuclear renaissance in the United States is just going to make things better for nuke workers. You don't have to spend your life working for chump change fixing computers at Best Buy. College or the Nuclear Navy is a great, but not essential way to start. Hundreds of training programs, many industry paid, are available if you are sharp enough. They have secure jobs with advancement making very good money, working in super-clean environments with folks and benefits that can't be beat. Things are opening up so fast I can't possibly provide up-to-date contacts. Just Goggle "Nuclear Jobs" any time you feel like it. You wouldn't believe what's available. Example: http://www.nukeworker.com/

http://www.entergy.com/Careers/

Waste Disposal, Fuel Recycling, Nuclear Fuel Reserves, Proliferation:

This is such a typical comment:

"Nuclear sounds great, but what happens when the price of uranium and plutonium goes up? Seriously, how much fuel is there and what’s the plan when it becomes scarce? How much energy is required to obtain more fuel? Where does the fuel come from and who does the work to extract it?"

Comment by Xx Xx - August 26, 2008 at 3:52 pm

Please bear in mind I am not a nuclear expert.

RESERVES:

The quick, glib answer is that since the Japanese have a way to extract uranium from sea water - 4 BILLION tons, originally from sand from granite mountains - (but at more than current street price) we will never be able to use up all that is available, much less start on the three times as plentiful thorium.

Uranium is about 40 times as abundant as silver and produces 3 million times as much heat as coal. http://en.wikipedia.org/wiki/Uranium#Occurrence

Few understand only the uranium-235 isotope is radioactive and amounts to only 0.7% of natural uranium. The remaining 99.3% is almost entirely non-radioactive uranium-238. After 70 years and high motivation, enriching the radioactive uranium-235 concentration to either 5% for conventional electricity reactor fuel or 90+% for weapons "pits" (cores) still remains a substantial technical challenge.

Thorium, about three times as plentiful as uranium can be made into fissile radioactive uranium-233 and is used as nuclear reactor fuel just like uranium-235 and plutonium-239. No way is mankind going to run low on this stuff for all time to come. We are being lied to by the anti-nukes and the fossil fuel folks.

The practical picture:

Only about 3% of the useable energy is consumed during a typical nuclear power plant run. Recovery through reprocessing will extend availability of easily mined uranium and thorium to many thousands of years. Uranium can be mined in situ using soda water as the recoverable solvent, thereby minimizing worker exposure and leaving only small well boreholes in the ground.

As with conventional fission nuclear fuel, only about 5% of a pebble's atomic energy is actually consumed during a power run, so pebbles will have to be crushed to powder like quarry rocks and recycled for their remaining energy as is done world-wide with conventional nuclear waste.

2007 World Uranium Production: Canada, 25%; Australia, 22%; Kazakhstan, 17%; Russia, 9%; Niger, 9%; Namibia, 7%; Uzbekistan, 6%; United States, 4%; Other, 9%. (Cameco estimate, totals may differ due to rounding.)

Uranium Enrichment: Today, at least a dozen countries are known to have facilities to enrich uranium. Eight have nuclear weapons: the U.S., the U.K., France, China, Russia, India, Israel, and Pakistan. South Africa used to have 6 nuclear weapons but gave all of them up - the only country in the world to have ever done so. The other countries capable of enrichment - Germany, Japan, Argentina, Brazil and the Netherlands - don’t have weapons. Africa (Niger and Namibia) and Canada have large natural deposits of uranium. South Africa and Canada are seeking to join the uranium enrichment club in order to produce more-profitable (5%) reactor-grade fuel. Saskatchewan alone produces a quarter of the world’s uranium. The intentions and capabilities of Iran, a nuclear client of Russia, are still in question.

RECYCLING:

Nuclear Fuel Reprocessing locations: France: COGEMA La Hague, 1,900 Tons/year, United Kingdom: B205 at Sellafield, 1,700 tons/year, United Kingdom: Thorp at Sellafield, 1,000 tons/year, Japan: Rokkasho, 900 tons/year, Russia: Mayak, 450 tons/year, India: Kalpakkam, 300 tons/year.

Reprocessing of spent (slightly used) fuel: Nuclear "waste" still has about 95% of its nuclear energy remaining at the time it becomes "too tired" to be useable in conventional reactors. Outside the United States, spent nuclear fuel is recycled at one of 6 reprocessing sites. Work was begun on a new reprocessing plant at the Savannah River site in the fall of 2005. In unreprocessed form, spent fuel often has both reactor and weapon value. If recycled about 10 times, reactor fuel is reduced to about 5% its original mass, is of no value for anything, and has no materials that will remain radioactive for more than a few hundred years. Pebbles would need to be crushed to dust - like pebbles - to be reprocessed. http://en.wikipedia.org/wiki/Nuclear_reprocessing

www.usnuclearenergy.org/PDF_Library/_GE_Hitachi%20_advanced_Recycling_Center_GNEP.pdf General Electric - Hitachi ARC Reactor. Spent Nuclear Fuel separation is accomplished using the dry Electrometallurgical process. A fast-neutron reactor electroplating extraction facility that burns used nuclear fuel to nothingness after extracting what is useable for both conventional slow-neutron and CANDU reactors.

"Today, in the US there are approximately 100 nuclear power reactors in operation. Assuming that they each produce 20 tons of Spent Nuclear Fuel a year for 60 years of operation, then the current fleet will produce 120,000 tons of SNF. 26 ARCs are capable of consuming the entire 120,000 tons of SNF. Additionally, they are capable of producing 50,000 MW of electricity (equal to 30 additional nuclear plants or 5 New York Cities) while avoiding the emission of 400,000,000 tons of coal's CO2 every year." --- GEH

"Of course, in all cases, my eventual solution is that the used fuel should be recycled. The actinides can become new fuel and the fission products can serve other uses that take advantage of their unique industrial properties. With concepts like the IFR, the LFTR (Liftr) and some ideas that are associated with TRISO based fuels, the energy value of used fuel alone is in the hundreds of billions of dollars." --- Rod Adams

WASTE DISPOSAL:

U.S. spent fuel storage: In the United States, spent fuel is currently stored at nuclear power plant sites. A Cold-War spent fuel idea was to store, rather than recycle, spent fuel in two underground facilities, one east (never built), and one west. The western facility is Yucca Mountain, Nevada. There is also an underground storage facility (Waste Isolation Pilot Plant - WIPP), near Carlsbad, New Mexico, run by the Department of Energy for the U.S. military.

Please bear in mind I am not a nuclear expert. But any person can have suspicions or opinions about anything. Acting on suspicions or opinions in the absence of all the facts is where we get into big trouble quick. The following is an interesting speculation.

This and the following several paragraphs are my possibly quite flawed understanding: In addition to slow and fast reactors, there is a third type, the "producer reactor" whose sole purpose is to produce weapons-grade plutonium. We built and used them at Hanford, Washington, to produce the plutonium used in the both the first test bomb at the Alamogordo Bombing and Gunnery Range, it was code-named "Trinity," and it's operational twin, the Nagasaki, Japan, bomb nicknamed "Fat Man." It didn't work as well as the first operational atomic bomb, it's uranium sibling the Hiroshima bomb nicknamed "Little Boy."

Plutonium-240

"Plutonium-240 (Pu-240) is an isotope of the metal plutonium formed when plutonium-239 captures a neutron. About 62% to 73% of the time when Pu-239 captures a neutron it undergoes fission; the rest of the time it forms Pu-240. The longer a nuclear fuel element remains in a nuclear reactor the greater the relative percentage of Pu-240 in the fuel becomes. For weapons use, the fuel needs to be as low in Pu-240 as possible, usually around 7% of the total plutonium, but this is achieved by reprocessing the fuel after just 90 days of use. Such rapid fuel cycles are highly impractical for civilian power reactors and are normally only carried out with dedicated weapons plutonium production reactors. Spent civilian power reactor fuel typically has under 70% Pu-239 and around 26% Pu-240, the rest being made up of other plutonium isotopes, making it extremely difficult but not impossible to use it for manufacturing nuclear weapons." (Emphasis added by author.)

²⁴⁰Pu has only about 1/3 as large a neutron absorption cross section as ²³⁹Pu, and nearly always becomes plutonium-241 rather than fissioning. In general, isotopes of odd mass number are both more likely to absorb a neutron, and more likely to fission on neutron absorption, than isotopes of even mass number. Thus, even mass isotopes tend to accumulate, especially in a thermal reactor.

Short-pass first-pass spent fuel from a power reactor (such as the Chernobyl RBMK ) resembles the product of producer reactors in that what plutonium it does contain is mostly plutonium-239 and is not very contaminated with plutonium-240, 242, etc., - elements that spell spontaneous fission - very bad news for bomb-builders. From what I know, MOX fuel that is making multiple passes through a reactor is considered very unsuitable for weapons since the pu-239 vs. pu-240 and pu-242 mix it contains presents a worse separation challenge than that of uranium-235 vs. u-238.

In the writer's opinion, storage, rather than complete destruction through power plant fission, of high-level radioactive materials that can be readily fashioned into nuclear weapons has ominous long-term implications - especially if certain fuel rods were covertly "short-cycled" during a reactor's routine power run. A simple WWII plutonium extraction process can then create, in effect, a nuclear bomb mine for some future Hitler out of what may be stored in Yucca Mountain.

In 1976, Charles Hollister, a geologist and senior scientist at the Woods Hole Oceanographic Institution, came up with a plan (The Sub-Sea Bed Solution) to inexpensively and quite irretrievably bury high-level nuclear materials in certain mid-ocean deep sea soft, sticky, mud deposits.

Instead, the United States opted for stockpiling these materials in a relatively easily retrievable manner at Yucca Mountain. We cannot know if covertly short-cycled rods are among what is being or has been stockpiled at our civilian nuclear power plants. We cannot know what other countries nuclear storage stockpiles contain.

This is why I support complete destruction of all radioactive energy metals everywhere through multiple reactor+recycle cycles for slow neutron systems and "single pass, total burn-down" for fast neutron systems. Best to be certain. If its been irradiated, keep splitting those energy metal atoms all the way down to nothingness.

PROLIFERATION:

"Burnup is one of the key factors determining the isotopic composition of spent nuclear fuel, the others being its initial composition and the neutron spectrum of the reactor. Very low fuel burnup is essential for the production of weapons-grade plutonium for nuclear weapons, in order to produce plutonium that is predominantly ²³⁹Pu with the smallest possible proportion of ²⁴⁰Pu and ²⁴²Pu." - Wikipedia, Burnup

"Pu-239 is produced artificially in nuclear reactors when a neutron is absorbed by U-238. Pu-240 has a high rate of spontaneous fission, which can cause a nuclear weapon to predetonate, and its concentration must be less than 7% for the plutonium to be weapons-grade. It is produced when Pu-239 absorbs a neutron. To avoid this the uranium fuel in a reactor must typically be replaced four to six times per year. This is necessary because the concentration of Pu-240 rises over time and its mass and chemical properties are too similar for it to be separated from Pu-239. With any reactor, plutonium is separated from the nuclear fuel, U-235 and U-238, chemically in a nuclear reprocessing plant."

"It is difficult to produce weapons-grade plutonium with a light water reactor because the reactor must be shut down frequently to replace the nuclear fuel rods, so weapons-grade plutonium is generally produced in small, specialized military reactors. However, a test of a nuclear weapon that used reactor-grade plutonium was successfully detonated, although the yield was relatively low." - http://en.wikipedia.org/wiki/Weapons-grade

The pebble bed reactor's pebble circulation system makes it easy to short-cycle uranium - an argument for only allowing only uranium-thorium MOX pebbles to be made. Another TRISO reactor in this family, the prismatic, has stationary fuel blocks instead of pebbles that are impossible to short-cycle. The 325 MWe General Atomics GT-MHR along with sibling Russian, Japanese, and others are examples of prismatics that thermally would be functionally identical to a circulating pebble bed reactor.

Coal2Nuclear ______________________________________________________________________ Top

Chapter Nine, Part Four:

Radiation:

Learn a little about radiation: http://en.wikipedia.org/wiki/Ionizing_radiation

(Below) Prof. Allison's radiation dose chart (milliSieverts on a log scale. [0.01 mSv = 1 mrem]). From the background radiation you are receiving now to what would be a fatal dose: http://en.wikipedia.org/wiki/Ionizing_radiation

Dr. Manuel Brown, a radiologist at Henry Ford Hospital in Detroit, has begun issuing doctor's notes to some of his traveling patients, explaining why they might trigger a U.S. Border nuclear radiation alarm. He says facilities in his region perform about 100 radiation procedures a day. While the amount of radiation used in less-serious procedures would trigger the alarms for only a day or two, more-serious therapy (like thyroid treatment) can set off alarms for weeks. People transporting tile, kitty litter, granite and bananas also set off the alarms. Out of 270 million vehicles searched and 1.5 million alarms, zero terrorists have been caught. Remember that on your road trip. --- MSN

"In the 18 years since I left my nuclear submarine, I have been trying to figure out how nuclear power got its bad rap and the best answer that I can find is that a large number of people worked VERY hard to spread as much Fear, Uncertainty and Doubt (FUD) about the technology as possible. From my experiences in other competitive industries and my deep research, I finally figured out that the energy business is the world’s largest single enterprise. I also figured out that people who sell coal, oil and gas are not all that concerned about the effects of their fuels, but they really like the money and power that those fuels can bring.

Every time a new nuclear power plant gets started up, it removes a market demand for about 1.8 BILLION cubic meters of natural gas worth about 150 million pounds. If it replaces a coal fired power plant, the number is about 4 million tons of coal - I do not have a market price available for that commodity, but I know that the number is pretty big.

Fossil fuel companies and the supporting industries and organizations (banks, railroads, unions, governments, shipping companies, pollution control equipment manufacturers, etc.) all have a vested interest in protecting their markets and making people afraid of nuclear power. They do not have to coordinate their efforts; opposing nuclear is natural for them. They do, however, often do a great job of hiding their real motives behind the actions of people hired to spread the FUD who call themselves “environmentalists. Feel free to disagree - but whatever you do, please think critically and follow the money.” --- Rod Adams

Coal2Nuclear ______________________________________________________________________ Top

Chapter Nine, Part Five:

Coal Power Plant Nuclear Emissions:

COAL POWER PLANTS: Burning coal spews out vast amounts of dust, sulfur dioxide, nitrogen oxides and carbon dioxide, creating air pollution and filling the atmosphere with greenhouse gases.

The Environmental Integrity Project report notes: “Nationwide, the power plants that provide electricity to run our homes, businesses, and factories also account for 40 percent of carbon dioxide, roughly two thirds of sulfur dioxide, 22 percent of nitrogen oxides, and roughly a third of all mercury emissions (in the U.S.) … Power plants are major contributors to global warming, emitting billions of tons of carbon dioxide (CO2) each year. In addition, power plants emit millions of tons of sulfur dioxide (SO2) and nitrogen oxides (NOx), pollutants that trigger asthma attacks and contribute to lung and heart disease, and cause smog and haze in cities and national parks. And, power plants emit dangerous toxins like mercury, a neurotoxin especially harmful to children and developing fetuses.” http://www.dirtykilowatts.org. http://carma.org/

There's also a lot of uranium in coal but no one seems concerned about that. One of the many impurities in coal is uranium. It's rare to hear anti-nuclear, anti-coal types point out the rather large amounts of uranium being emitted by coal burning power plants. Thousands of tons of uranium and thorium go through our coal power plant smokestacks every year. Nuclear power plants would be shut down immediately if they started throwing out coal's radiation. Uranium In Coal Mining for Uranium In Chinese Coal Ash Piles

It is not unreasonable to expect coal to be financing anti-nuclear political activities and publicity. Nuclear is a solid alternative to coal. Australia has no nuclear electricity and the coal organizations there are openly doing everything they can to block all attempts by Australians to "go green" by going nuclear on their next power plants. Australia has large reserves of easily mine-able uranium which they currently sell on the world markets with China being a major customer.

NUCLEAR POWER PLANTS: Some get all emotional about nuclear but gladly accept our highway system that kills over 40,000 people each year. There is a big disconnect with common sense here. There is no practical argument against nuclear. Everything has it's dangers. As with fire, electricity, and sanitation, public education programs are necessary to teach everyone what's important to know about nuclear energy's hazards.

Don't get me wrong, radiation can kill you. It's very likely the information you've have heard about radiation is incorrect. In the beginning, at the time of the atomic bomb, there were a lot of highly publicized "educated guesses" about what radiation would do to you. Here is what is known about radiation 60 years later: Academy of Medicine of France Radiation Hazard Position Paper http://www.radscihealth.org/rsh/

http://www.ans.org/pi/resources/dosechart/ If you are still concerned about how much radiation you are receiving from the environment around you, you can visit this web site, fill out a short questionnaire and get an idea of your exposure level.

What is not debatable is the fact that only nuclear reactors can permanently destroy the material that is left over once nuclear weapons are taken out of service as the result of arms control agreements. For the past ten years, just such a weapons material destruction program has been in place in what is known as the Megatons to Megawatts agreement between Russia and the United States.

You are afraid of nuclear energy for only one reason: You have been told to be afraid (usually by television news sensationalizing some nuclear-related event) and you believed whatever whoever told you. We can't allow fear to keep us from ending Global Warming.

This fear has real consequences. Heavily promoted by organizations like Greenpeace and The Sierra Club, who claim to care most about the environment, it may have actually brought about Global Warming: "Had the United States gone on with its nuclear power plant building program after Three Mile Island, it's likely there would be no climate change crisis today." - Dr. James Lovelock (World's top environmental advocate.) His Web Site & Papers

Nuclear reactors are almost as simple and natural as fire. They have occurred in nature long before man . Natural_nuclear_fission_reactor

What I think are a couple of unreasonable Nuclear Concerns: Proliferation: Nations that produce the most CO2 already have nuclear electricity programs and some have nuclear weapons. Waste: Recycling rather than accumulation of spent nuclear materials is common except for the United States, which abandoned its recycling program in 1980. The French have an excellent recycling program. Reprocessing adds about 10% to the retail cost of nuclear electricity.

Conventional reactor safety has proven itself over time. While Pebble Bed reactors are even safer, it is for their appropriate size and the fact that pebble heat resembles that of coal, gas, and oil that I am suggesting our fossil fuel power plants be converted to pebble bed reactors to speed the end of Global Warming. Because the physics that control the pebble's fission activity is inherit in the pebble's nature rather than controlled by external machinery, which is always subject to failure, Pebble Beds may be seen to fall between conventional pressurized nuclear power plants and a medical facility that uses nuclear or X-ray therapy equipment powerful enough to kill cancerous cells in humans. Nuclear fuel 101 How Pebbles Work

Chapter Nine, Part Six:

Safety:

The "official" PBMR is being made as a reactor to power a large helium gas (not steam) turbine. To do this, it is pressurized to 1,323 psi and 1,700°F. What I'm suggesting is an easier task for the reactor: Lower helium pressure and 400°F cooler. The Coal Yard Nuke version would be a low pressure reactor heating a gas-to-liquid heat exchanger not unlike your residential hot water heater. Since there is no liquid-to-gas phase-state change, there is no explosion hazard of the type steam can produce. A leak would just hiss out like a punctured tire with the helium being contained in the reactor's unoccupied silo. A circulating blower is used in this application to move the heated helium.

All conventional reactors have their radioactive cores under extremely high steam pressure - this is the reason the reactors have a huge steam explosion containment building over them. This is to keep radioactive reactor fuel from escaping into the environment in the event of a steam explosion inside the reactor.

LOCAs or "Loss Of Coolant Accident" are the major concern of the people running reactors. This could lead to the "Melt-Down" so highly publicized in the press. This was what happened at both Three Mile Island and Chernobyl. Three Mile Island's reactor was in a containment vessel so the event was contained. Chernobyl's wasn't, there was a fire, and the smoke carried radioactive fallout all over Northern Europe. Chernobyl killed about 50 people and the fallout is expected to produce several thousand thyroid cancers over the coming 50 years.

A reactor's radioactive water leak will always get a quick, frightening coverage by the press. They don't tell you they are spreading a meaningless message. The day-to-day hazard that conventional reactors pose is not exploding but rather, since the water used for cooling is in constant, direct contact with the hot radioactive fuel, mildly radioactive water isotopes like tritium are formed in the cooling water and could leak into the ground to become part of the groundwater, to be eventually picked up by wells supplying water to residential water systems. Tritium has a half-life of 12 years and pumped groundwater could be hundreds or even thousands of years old. 10 half-lives will make a radioactive material equivalent to dirt. Tritium's radiation cannot penetrate the skin but tritium is considered dangerous when high concentrations are ingested.

Since the world is constantly bathed in a significant amount of background radiation from both the natural uranium that is everywhere and radiation from space, it isn't surprising that there is a certain amount of natural tritium in all water.

Pebble bed reactors run dry. They do not use water as a coolant.

The process of splitting atoms causes a gas, xenon, to be produced. Xenon is harmless to humans (expensive, used as an anesthetic on fragile surgery patients) but is a neutron poison that will cause a reactor to stop running. Xenon caused Chernobyl to go out of control.

Pebble bed reactors need all the neutrons they can get just to keep running so a neutron poison like xenon or a strong neutron slowing down influence like water vapor are very bad news for a pebble bed reactor.

To keep xenon under control and out of the helium, pebble bed reactors' TRISO pebbles encapsulate their radioactive energy metals in three separate air tight layers of silicon carbon in tiny particles that are, in turn, sealed in a sphere about the size of a baseball. Four containment barriers have to be breached before uranium or it's fission product, xenon, can get into the helium. (see drawing, right)

Pebble bed reactors are cooled by the gas helium rather than water in a closed loop system whereby the helium gas then heats water. Like the air filter in your furnace, the circulating gas is constantly filtered to catch any microscopic particles in the helium.

At 1,300 psi pressure, the 1,700°F hot helium gas travels through tubes in the hot water heat exchanger to give up its heat before returning to the hot pebbles. The tubes are surrounded by liquid lead at room pressure to carry the heat away from the helium tubes and to the water tubes.

Notice that the 88 foot tall unpressurized reactor is underground and that the supercritical hot water is in the heat exchanger's steel pipes. The outside of the steel pipes touch the heat exchanger's pool of liquid lead which, in turn, touch the steel pipes which contain the helium gas which, in turn, touches the reactor's radioactive TRISO pebbles.

Helium gas cannot become radioactive and a gas filter, not unlike your furnace's air filter, is used to catch any microscopic fuel specks from broken pebbles. The pebble itself provides additional containment: The TRISO pebble has three different carbon layers of containment around each of it's microscopic specks of uranium and thorium so the helium gas is also at least triple isolated from the radioactive fuel specks.

While the helium is under pressure, it isn't changing from liquid to gas like steam does, so there is no state-change shockwave potential and thus no possibility of the reactor exploding from "helium steam" - a safety feature conventional reactors lack. See steam explosion hazard. If the reactor does spring a leak, the helium gas will always escape more slowly like a punctured tire. Since the reactor is in a sealed underground silo, it has the isolation equivalent, and does not need the volumetric equivalent, of the steam explosion containment vessel required for pressurized conventional reactors. This means we have FIVE layers of radioactive material containment in a Coal Yard Nuke system compared to two in a conventional Pressurized Water Reactor nuclear power plant or just one in some Boiling Water Reactor nuclear power plants.

Nuclear reactors run in a 'neutron-starved' state - just barely alive. Like conventional reactors, pebble bed reactors have neutron absorbing control rods (Reactivity Control System, Reserve Shutdown System - in reactor drawing) that can 'soak up' the available neutron supply to the point of starving it off. (Far Right: Notice the vertical control rod housings among the pebbles.) If, for any reason the rods won't work and the reactor begins to become hotter than it should, the pebbles themselves will shut the reactor off by consuming the neutrons like pac-man as Doppler broadening kicks in big-time - or as the Chinese say about their pebble beds, it goes to 'sleep' (Right).

Unlike conventional reactors, pebble beds can be 'fine-tuned' by 'diluting' the pebble mixture by adding pebble-sized spheres that are inert or adding pebble-sized spheres that, like the control rods, absorb neutrons. Reactor control and safety doesn't get any better than this. At the bottom of the reactor drawing, notice the "Core Unloading Device" or CUD. It constantly removes pebbles one at a time, measures them for strength, then the pebbles are either put back into the reactor or removed for recycling. This is how the diluting or absorbing spheres are added to, or removed from, the reactor. This also means that, unlike conventional reactors, the power plant doesn't have to be shut down for a month or two every two years to replace spent nuclear fuel. More running time, more electricity made, more money made.

Supercritical hot water was used in the twenties in the "Benson Boiler" as a way to reduce the catastrophic consequences of steam explosions in power plants. Like the Benson boiler, the Coal Yard Nuke system doesn't use a power plant's boiler with a steam drum containing a large amount of explosive steam, but supercritical hot water is still hot and under a heck of a lot of pressure, and, while not exploding like a boiler, it would flash into open steam which can be dangerous if you walk into it, so I would give it a 50% removal of a power plant hazard.

The really neat thing is that most of these safety and containment features are natural occurrences in a design that is much smaller, more thermally efficient, and costs far less than a conventional nuclear power plant.

So, in addition to five layers of radioactive fuel containment, we have a no-explosion heat source device, (the unpressurized PBMR reactor), driving a reduced explosion hazard device, (the supercritical hot water heat exchanger pair), driving a standard power plant steam turbine from a steam generator that has less than half the usual power plant's amount of water in the pressurized steam state. Compare this situation to a typical power plant's large boiler with a huge steam drum pressurized to 2,400 pounds per square inch with steam and water, located way up next to the ceiling, far away from most workers, so it will blow out the roof if it happens to explode (see item 17 in the Coal Yard Nuke power plant sketch).

I think this is as safe as a steam power plant can ever be made. Power plants converted to pebble bed reactors will be safer from explosions than when they were when running on coal.

Steam can explode with the force of dynamite. 1,500 people died in a single steam explosion near Memphis, Tennessee. Discussion about the danger of steam boilers and our boiler laws. http://www.memagazine.org/contents/current/features/harness/harness.html

End Of Chapter Nine

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