Nuclear Crisis in Japan

Japan was dealt a double blow with the enormous earthquake causing secondary problems with their nuclear power plants. To clarify and explain some of the problems that the Japanese are occurring with the plants, here’s a brief explanation of the design and what could be going wrong.

The design of failing nuclear power plants in Japan are known as a Boiling Water Reactor or BWR. As the picture below shows, the reactor vessel serves as the boiler for the nuclear steam supply system. The steam is generated in the reactor vessel by the controlled fission of enriched uranium fuel which passes directly to the turbo-generator to generate electricity. The water then goes into a another vessel where it is cooled further before returning to the reactor vessel in a closed loop.

As you can see, the pump must be kept active for the cooling to continue, a critical component in the design. To assure that the pumps keep going, several redundant systems are built in. If the electricity fails, backup diesel generators are standing by to supply electricity. If the diesel generators fail, batteries are available to supply a short amount of pump run time. But the batteries are not meant for any extended period of pump operation, just for short power outages.

If anything can be learned about relying on technology for safety, Mother Nature has a way of dealing out situations that haven’t been planned for. The record magnitude earthquake, measuring 9.0 on the scale, has knocked out the power grids for an extended amount of time.

In addition, diesel generators were knocked out because of tsunami waters flooding the switching circuitry that was installed to switch over from main power to the diesel generators. The backup to the backup generators, the batteries, only give about 8 hours of operation, but the AC grid never was able to come back online because of it’s damage. So now the cooling pumps cannot operate.

The reactor core fission process can be shut down in a matter of seconds but it will remain superheated for a very long time. Without that pump cooling loop that is used to carry away the heat, the reactor core is so hot that it will actually begin to melt it’s surrounding structure. Another side effect is that the metal that clads the fuel rods, zirconium, reacts with the extreme heat producing hydrogen, a very explosive gas.

But the reactor designers have even planned for that scenario because a containment structure is built around the entire reactor structure itself. A protective shield that encapsulates the process. That’s the good news.

The bad news is that the Fukushima Daiichi reactors are a GE Mark I reactor containment vessel design.

Our own Nuclear Regulatory Commission did an analysis of the potential failure of the Mark I under accident conditions. They concluded in a 1985 report that Mark I failure within the first few hours following core melt would appear rather likely.

In 1986, Harold Denton, then the NRC’s top safety official, told an industry trade group that the “Mark I containment, especially being smaller with lower design pressure, in spite of the suppression pool, if you look at the WASH 1400 safety study, you’ll find something like a 90% probability of that containment failing.

To address this design concern, it was deemed necessary to have the capability to vent any high pressure buildup. As a result,  a vent system was designed as another safety precaution. Called the “direct torus vent system” it was designed into all Mark I reactors.

Designed to be used as a last ditch operation to save the containment from rupturing, it’s operated from the control room of the plant. Although it’s a venting of radioactive high pressure steam, it’s considered a better option than allowing the containment vessel to rupture by explosion. But the venting releases high levels of radiation, particularly Cesium-137 and Iodine-121.

To complicate things even more, Unit 3 of the group of nuclear reactors was using something called MOX for fuel. This is the normal reactor fuel, Uranium-235, mixed with plutonium for the purpose of disposing of bomb grade weapons material. This gives the additional hazard of venting not only radioactive Cesium-137 and Iodine-121 but plutonium and other actinides, which are far more hazardous.

Courtesy of Union of Concerned Scientists/GE BWR Systems

Japan is facing an unimaginable crisis from a multitude of fronts. The world needs to give any and all support that is asked for, not just for the earthquake victims but to avoid a catastrophe on a world wide scale.

Of the 104 nuclear plant operating in the United States, 23 of them are of the GE Mark I design.

GE Mark 1 designs currently in the United States

 

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About Krell

I used to have superpowers… but a therapist took them away.
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10 Responses to Nuclear Crisis in Japan

  1. Stimpson says:

    Useful information. There’s a piece at The Daily Beast telling us why it’s “no Chernobyl.” That seems to be true, but then there have been two explosions so far and a third appears to be on the way.

    • Krell says:

      I don’t think that there is even the remote chance of a Chernobyl type event now because of the difference of what Chernobyl was, RMBK type, and this type of reactor. The RBMK type had a serious design flaw in that the water could act as a neutron moderator, actually causing a higher fisson rate. Not only was the design of Chernobyl very crude, sorta like the pile that Fermi had, but they had disabled what little safety systems they had to do a test.

      But there is the possibility of large amounts of radiation being released in Japan. They have already detected radiation 100 miles away on a Navy fleet.

  2. scaredstiff says:

    Krell, you should have been a teacher. You break things down so that even I can understand them. I do have a question about the salt water being used. It obliviously is going right back into the sea. I know they have no choice, but it can’t be good for the environment. Also I have to wonder why they don’t have desensitization facilities right there ae salt water heat up faster then fresh. Also is this in anyway like the China syndrome? When they say melt down…what are we talking about. Thanks Man.

    • Krell says:

      Tim, I’m not sure about what the effects of the seawater will have. Do you know if they have retention ponds instead of letting if go back into the sea? Or are they basically opening up the cooling of the core to the sea, letting if flow in and flow out freely? If the seawater is used to cool the core and the cooling loop is breached, that seawater is going to be very radioactive. I’m going to look further into seeing if it would react with the salt to produce radioactive Sodium. Get back with you on that one.

      The meltdown term is from the reactor core being so hot that it melts down into whatever is below it. The term “China Syndrome” is sort of a spin off of that melting process in which the core is described as being so hot that it melts it’s way clear to China. Obviously an exaggeration.

  3. Morgalla says:

    They have already begun venting the radioactive steam. It is somewhat of a relief to see there are no Mark 1 reactors on the faultlines in the US.

    I’m still waiting for confirmation on a disturbing piece of news: that nuclear engineers have found a safer fuel – Barium- could be used, but the defense department doesn’t want to do this because it would mean no DU for their weapons…!

    • Krell says:

      The AEC and the defense industry has known about other fuels and designs that could be used for reactors. In particular, Thorium, which is so safe that it could be operated without a containment vessel at all.

      The Molten Salt reactors, IMHO, have always been the true alternative to what is being used. But you are absolutely right, the supply of plutonium was the driving reason for what we have now.

  4. Gwendolyn H. Barry says:

    Thank you David for the explanation.
    Any US politician that suggests nuclear energy is a clean, safe resource should be taken out and horsewhipped at high noon in the village square. IF this is just the beginning of revelation about those nuclear reactors, ………. fuck. My first and last concern is the Earth Mother… with the Gulf gone dead and decaying the people who live on, spewing into the rest of the Atlantic and the Pacific now dealing with radiation….
    Can anyone just say this is THE FRIGGING WAKE UP CALL!!! ??

    • Krell says:

      Germany had a lot of nuclear reactors that were scheduled to be decommissioned in 2011 but they granted them a 10 year extension. I bet they are looking closely at that decision and wouldn’t be surprised that it suddenly gets reversed.

      The problem with the United States is that the old AEC and now the Dept. of Energy never had the mission of nuclear safety. Their task was always nuclear promotion at any cost. Some of the stuff that the old AEC did was downright criminal in suppressing anything bad said about nuclear energy.

      Plus it’s a lot like the MMS where it’s a revolving door of industry insiders and DOE officials.

  5. I’m also worried about where all the seawater is going. If it’s all going right back into the environment. . .
    It doesn’t look like any possibility of a doomsday melt down senario since cooling has been going on for three days now.
    Good post Krell!

    The general public sure isn’t gtting any comprehensive information from the media.
    I am so sick of seeing Anderson Cooper standing around look grave with his hands on his hips as if he has some clue about the anguish of desperate people or has some power to do anything while he spins dramatic tales. . .

  6. oso says:

    Krell,
    Thank you for breaking this down. You made it clear and understandable. And scary.

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