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Pebble Nuclear Reactor: A Safer and Cheaper Alternative to Conventional Nuclear Power

September 22, 2010

Pebble Bed Reactor Technology (PBMR)
This article discussed the Pebble Bed Modular Reactor (PBMR) is a new type of meltdown-proof high temperature helium gas-cooled nuclear reactor, which builds and advances on world-wide nuclear technology. A reactor small enough to be assembled from mass-produced parts and cheap enough for customers without billion-dollar bank accounts.

The PBMR reactor promises to be a better way to harness the atom. The PBMR is a new type of meltdown-proof high temperature helium gas-cooled nuclear reactor. A reactor small enough to be assembled from mass-produced parts and cheap enough for customers without billion-dollar bank accounts. A reactor small enough to be assembled from mass-produced parts and cheap enough for customers without billion-dollar bank accounts. A reactor whose safety is a matter of physics, not operator skill or reinforced concrete. And, for a bona fide fairy-tale ending, the pot of gold at the end of the rainbow is labeled hydrogen.

PBMR is a new type of high temperature helium gas-cooled nuclear reactor, which builds and advances on world-wide nuclear operators’ experience of older reactor designs. The most remarkable feature of these reactors is that they use attributes inherent in and natural to the processes of nuclear energy generation to enhance safety features.

PBMR’s are designed to produce 110 MW each which means that 30,000 average homes could be sustained by one such reactor. More than one PBMR can be located in a facility thus creating energy parks. It is possible for a PBMR energy park to be made up of a maximum of 10 modules which share a common control center. This system allows sequential construction of modules to match users’ growth requirements; as the area grows, so more modules can be added to meet the industrial and domestic needs for electricity in an area

A single PBMR reactor would consist typically of a single main building, covering an area of 0.3 acres (165 x 85 ft). The height of the building would be 140 ft, some of it below ground level, depending on the bed rock formations as the building would sit on bed-rock. The part of the building that would be visible above ground is equivalent to a six story building. There would be a unit control room, a high voltage switch yard, and a cooling tower for inland facilities and a sea pump-house for coastal facilities.

These relatively small power stations would be versatile and flexible. They could be erected anywhere there is a steady and ready supply of water. They could be used as base-load stations or load-following stations, and could be adjusted to the size required by the communities they serve.

Concerning safety, the PBMR is walk-away safe. Its safety is a result of the design, the materials used and the physics processes rather than engineered safety systems as in traditional nuclear type reactors.

The peak temperature that can be reached in the reactor core is far below any sustained temperature that will damage the fuel. The reason for this is that the ceramic materials in the fuel such as graphite and silicon carbide – are tougher than diamonds.

Even if a reaction in the core cannot be stopped by small absorbent graphite spheres or cooled by the helium, the reactor will cool down naturally on its own in a very short time. This is because the increase in temperature makes the chain reaction less efficient and it therefore ceases to generate power. The size of the core is such that it has a high surface area to volume ratio. This means that the heat it loses through its surface (via the same process that allows a standing cup of tea to cool down) is more than the heat generated by the decay fission products in the core. Hence the reactor can never (due to its thermal inertia) reach the temperature at which a meltdown would occur. The plant can never be hot enough for long enough to cause damage to the fuel.

In terms of radiation leakage, the helium itself, which is used to cool the reaction, is chemically and radioactively inert: it cannot combine with other chemicals, it is non-combustible, and non-radioactive.

Because oxygen cannot penetrate the helium, oxygen in the air cannot get into the high temperature core to corrode the graphite used in the reaction or to start a fire. If, through some accident, the helium gas duct (inlet and outlet lines) is ruptured, it would take some nine hours for natural air to circulate through the core. Even if this could happen, it would only lead to less than 10-6 (one millionth) of the radioactivity in the core being released per day. That means that the amount of activity released in 24 hours under this very severe (and recoverable) situation would be some 10,000 times less than that requiring any off-site emergency actions. To avoid such a total failure of the main gas ducting it is designed to leak before it breaks, so that the depressurization will be gradual and cannot lead to such a rupture.

The helium pressure inside the closed cycle gas turbine is higher than the air pressure outside it, so nothing can get inside the nuclear circuit to contaminate it.

In closing, it is unclear why Pebble Bed Modular Reactor technology is not widely known or discussed in the U.S. Bill Gates has given a good deal of money for research in a new type of reactor that addresses many of the concerns/objections about nuclear power. It would be advantageous to see a more diverse mix of energy solutions in the future including nuclear, renewables, as well as responsible use of more traditional sources (fossil). It would be really nice to see oil’s near monopoly in the transport sector broken up for lots of reasons besides the environment.

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19 Comments leave one →
  1. September 22, 2010 10:23 AM

    Are these being used anywhere?

  2. Rainier permalink
    September 22, 2010 10:24 AM

    Barry,

    1. Just 6 days ago the South African government closed down the PBMR project almost completely. Westinghouse Nuclear left the PBMR project in May this year.

    2. There are many arguments against the PBMR, particularly based on bas experience with the 2 PBRs operated in Germany: It is an undisputable fact that the German PBR AVR ist most heavily contaminated nuclear facility worldwide and thus cannot be dismanteled for the next 60 to 70 years. Because the contamination is also in the soil, the whole reactor vessel was filled with concrete and will be transported in 2012 by airlifters to an intermediate storage (in order to clean the soil under the reactor from Strontium).

    3. PBMR supporters were very successfull with their advertisements, but not so much in technical areas.

  3. September 22, 2010 12:34 PM

    The “pot of gold” is going to explode! The idea of unatended hydrogen plants powered by unatended nuclear reactors is insane! Thousand degree hydrogwen will exlode if there is a crack in a pipe in the reactor and hydrogen is known for its abilitiy to cause pipes and other metal parts to crack. The metal naturally absorbs hydrogen and cracks are almost guranteed. Cracks or other breeches in the containment system will cause a huge explosion when the hot hydrogen comes into contact with air. It will spread a cloud of nuclear fuel and it will also poison the underground water table. There seems to be no end to the power of greed. They are pressing their luck.

  4. September 22, 2010 5:15 PM

    What stops the nuclear reaction when it overheats?

  5. September 23, 2010 6:50 AM

    Comment posted in LinkedIn on this discussion.

    LinkedIn Groups
    • Group: Linked:Energy (Energy industry expertise)
    • Discussion: Pebble Nuclear Reactor: A Safer and Cheaper Alternative to Conventional Nuclear Power

    It is far from new 1 has been in operation over 15 years in Texas and there are quite a few in China. Pebble bed reactors are great they can be scaled and are able to consume the spent fuel of our 2nd generation reactors. Pretty simple grind up the spent fuel and encapsulate the grains in graphite. Allow the fuel to react at full temperature. The resulting waste is hot for centuries instead of millennia.
    Posted by Laura Bailey

  6. September 23, 2010 6:50 AM

    Comment posted in LinkedIn on this discussion.

    LinkedIn Groups
    • Group: Power Gen
    • Discussion: Pebble Nuclear Reactor: A Safer and Cheaper Alternative to Conventional Nuclear Power

    PBMR does not exist, the first plant was never built and the south-african government has announced after decades of research to stop funding it. As far as U.S. nuclear involvement, Westinghouse had some interest but faded away as they pulled out of the consortium.
    Posted by Karim Berrada

  7. September 23, 2010 5:14 PM

    Is anyone using Pebble Bed Reactor Technology?
    China’s Second Pebble Bed Reactor Steam Plant; World’s Third Commercial HTGR
    Go to: http://tinyurl.com/barry-stevens55

  8. September 24, 2010 8:54 PM

    first post

  9. Linux permalink
    September 27, 2010 12:17 AM

    Being somewhat conservative minded it’s sounds odd that I should say it’s time for some real change. It is time to pick up where we left off so many years ago with this form of energy. We have been subservient children to these out of control oil prices for to long. It’s long overdue to allow this technology to succeed unmolested this time.

  10. September 27, 2010 9:39 AM

    The had a big accident in Japan a few years ago. A technican was filling a bucket with fuel pellets for insertion into a pebble bed reactor. He put too many pellets into the bucket causing a subcritical reaction. He deliberately violated the instructions he was given a thousand times and radioactive smoke began pouring out, filling up the room. If he had put a few more pellets in, the reaction would have progressed to a full scale critical reaction resulting in an atomic explosion
    like Hiroshima.

  11. September 30, 2010 1:59 PM

    Comment posted in LinkedIn on this discussion.

    LinkedIn Groups
    • Group: Linked:Energy (Energy industry expertise)
    • Discussion: Pebble Nuclear Reactor: A Safer and Cheaper Alternative to Conventional Nuclear Power

    Good comment on the Pebble Bed Reactor. Bill Gates has given a good deal of money for research in a new type of reactor that addresses many of the concerns/objections about nuclear power. I would like to see a more diverse mix of energy solutions in the future including nuclear, renewables, as well as responsible use of more traditional sources (fossil). It would be really nice to see oil’s near monopoly in the transport sector broken up for lots of reasons besides the environment.
    Posted by Scott Ullman

  12. Nuke permalink
    October 2, 2010 6:38 AM

    Inventor: Your analysis is completely wrong. First of all, the reactor when shutdown is always subcritical. Secondly, once critical, it would absolutely not cause an explosion as the geometry of a power reactor is completely different than that of a bomb. Lastly, power is stable when critical.

  13. October 2, 2010 2:33 PM

    The first atomic reactor almost went critical. Its in a book called “we almost lost Detroit”
    about the manhattan project most dangerous secret- that the experiments almost destroyed Detroit with a nuclear explosion. The nuclear accident in japan is well documented.

    That’s a lot of bull nuke. A reactor that has gone critical is undergoing an explosion.

  14. October 3, 2010 11:12 AM

    You bull act is really dangerous. If you were the technican there you would have caused a nuclear explosion and exposed yourself and eveybody else to radioactive smoke.

  15. October 3, 2010 11:18 AM

    Hey Barry what do you say? I know your a PhD and nuclear scientist. What’s the definition of a critical reaction? How do nuclear reactors operate? They don’t operate at critical mass, they’d explode. You know what a controlled reaction is.

  16. November 1, 2010 7:30 PM

    I stand corrected. I found this in a wikipedia article; “Critical mass”

    “When a nuclear chain reaction in a mass of fissile material is self-sustaining, the mass is said to be in a critical state in which there is no increase or decrease in power, temperature or neutron population.

    A numerical measure of a critical mass is dependent on the neutron multiplication factor, k.”

    where f is the average number of neutrons released per fission event and l is the average number of neutrons lost, either by leaving the system or being captured in a non-fission event. When k = 1, the mass is critical.

    A subcritical mass is a mass of fissile material that does not have the ability to sustain a fission reaction. A population of neutrons introduced to a subcritical assembly will exponentially decrease. In this case, k 1.

  17. November 1, 2010 7:36 PM

    “Even if a reaction in the core cannot be stopped by small absorbent graphite spheres or cooled by the helium, the reactor will cool down naturally on its own in a very short time. This is because the increase in temperature makes the chain reaction less efficient and it therefore ceases to generate power.”

    What design feature makes the reaction less efficient as the temperature rises?

  18. November 1, 2010 7:59 PM

    A 15 MWe demonstration reactor, Arbeitsgemeinschaft Versuchsreaktor (AVR translates to experimental reactor consortium), was built at the Jülich Research Centre in Jülich, West Germany. The goal was to gain operational experience with a high-temperature gas-cooled reactor. The unit’s first criticality was on August 26, 1966. The facility ran successfully for 21 years, and was decommissioned on December 1, 1988, in the wake of the Chernobyl disaster and operational problems. During removal of the fuel elements until 1998 it became obvious that the graphitic bottom reflector under the pebble bed core was broken during operation. Some hundred fuel elements remained stuck in the crack. During this examination it became also obvious that the AVR is the most heavily beta-contaminated (Strontium) nuclear installation worldwide and that this contamination is present in the worst form, as dust. [21] In 1978 the AVR suffered from a water/steam ingress accident of 30 metric tons, which led to contamination of soil and groundwater by strontium and by tritium. The leak in the steam generator, leading to this accident, was probably caused by too high core temperatures.

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