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Fukushima Update 03/27/11

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Enough things have happened at the plant that I thought it time for an update.

The good news is that power has been restored to Units 1,2 and 3. Work on 4 is still underway. Since 4 was defueled at the time of the shake, there is no particular rush to get that one powered up.

Note that though the power has been restored to the plant, all is not complete. Many of the vital pumps and MCC (motor control centers – the switches that control the motors) are located in or near the basements of the reactor and turbine buildings. These have been wet with seawater and so will have to be cleaned before the high voltage power is applied. Some have already been cleaned according to one report that I read.

Where All that Water Went

As you know they’ve been pumping thousands of gallons of seawater into the plants for several days now. I’ve been wondering where all that water was going. From the IAEA updates from the last couple of days the destinations have become apparent. They’ve been filling up the basements of the turbine and reactor buildings and discharging some to sea. The latter has resulted in detectable but harmless amount of I-131 and Cs-137 in the seawater off the coast of the plant. The ocean currents rapidly disperse and dilute this already-harmless amount so there is no concern there.

Unfortunately it now appears that little if any of that water was reaching the reactors cores, particularly 1 and 2 and is probably leaking out of the spent fuel pits as rapidly as it is being pumped in. The indication of this is the relatively high release rates of I-131 and Cs-137. This means that fuel is un-cladded and uncovered with water. Had water been present the I and Cs would combine to make the cesium iodide that I talked about earlier. That would remain in solution and would not be released to the air.

The same IAEA updates report that the normal feedwater path to 1, 2 and 3 have been re-established and that fresh water is being pumped in instead of seawater. This should result in water flowing into the reactors as it would under normal conditions. There has been no indication that they have the reactor water level indicator instrumentation functioning again so the effectiveness of this is unknown.

There is some fear that the reactor vessel and maybe the floor of the primary containment have been breached. This could be a melt-through or it could be the result in the case of the containment of falling equipment. Given the volume of I and CS release I suspect a melt-through.

The Iodine and Cesium Releases

The relatively high release of Cs and I is troubling. That means that a very large amount of fuel has been damaged and is still not covered with water. The suspected source is primarily the #4 spent fuel pit. Though no reports have said so I speculate that there is a crack in the stainless steel liner (remember that the concrete shell fell away during the shake as reported earlier) that is letting the water run out as fast as it’s being pumped in.

This will likely remain problematic, as the area around the spent fuel pit is much too hot to attempt any repairs or even any manned inspections. They’ve reportedly taken high resolution aerial photos of the spent fuel pit but for whatever reason the utility has not released them.

If the pit is damaged as I speculate then they’ll probably have to resort to a Chernobyl-like solution such as filling the pit with concrete to seal in the fuel.

The iodine will decay away fairly rapidly since it has an 8 day half-life. In a month or so it will be gone. That leaves Cs-137 as the long term problem child. With a 30 year half life it will be around for quite a while.

Fortunately the majority of the release has been carried out to sea. The concentrations measured on the ground are low and are of no health concern. The IAEA status report linked to above contains some actual numbers for a change. Unfortunately they’re reported in the hideous SI units, in this case Becquerel. To convert the readings to the more familiar curies, divide by 3.7E10.

The highest daily deposition rate for I-131 in Tokyo is reported as 220 Bq per sq meters. Converted to Curies, that works out to 5.9 nanoCuries per square meter – a trivial amount that mostly shows how sensitive the detection equipment is. Even that amount will decrease as the I decays with its 8 day half life.

“Radiation” Detected in the US

Of course it has been. The trade winds blow this direction and we have detection equipment capable of detecting individual atoms of radioactive material. Note that it is radioactive material that has been detected and not radiation. Any time you see the word radiation used think “light”. Would the word “light” make sense in the sentence? Radioactive materials give of radiation just like luminous substances give off light.

The amount of radioactive material detected is so minuscule that it pushes the limit of detection of even the most sensitive detectors. This is almost lost in the sea of radiation from naturally occurring radioactive materials in the environment.

If radiation were water then we’d be aquatic animals swimming around in it. The stuff coming from Japan would be a few rain drops.

Just one example. On this page about half way down is a photo of a container of Morton’s salt substitute which consists of potassium chloride. Interesting thing is that a certain amount of natural potassium is the radioactive isotope K-40. For the second photo I poured the contents of that container of salt substitute into a zip-lock bag and laid it on a survey meter pancake probe. You an see the activity indicated on the meter. If you use a salt substitute or eat veggies high in potassium then you’re loading your body with K-40. Your own body exposes itself to order of magnitude more radiation than the stuff coming over from Japan.

What Next?

With power on and fresh water available, cooling the reactors should not be a problem. If the unit 2 reactor is breached then they will simply fill the entire primary containment with water to a level sufficient to cover the fuel. If the primary containment is also breached, then they’ll fill the reactor building.

The major issue is stopping the release of I and Cs, the primary source probably being the #4 spent fuel pit. I have no way of knowing what the utility engineers’ thinking is but based on what I know I’d be looking at a concrete fill, followed by a permanent roof over the the pool to keep rain out of the pool.

The reactors will have to radiologically cool for several years before people can enter the reactor containment structure to see what happened. Unlike TMI and other brands of PWR reactors, the GE BWR reactor sends it control rods in through the bottom. At TMI we could remove a control rod drive from the lid of the reactor and send in a camera to look around. Can’t do that here.

Options include boring a hole in the reactor lid to insert a camera or simply waiting awhile longer and then removing the lid normally as if for refueling.

Units 1 through 3 are destroyed and will never run again. Unit 4, lacking a spent fuel pit also will probably never run again. The other units’ futures are unknown. Certainly there will be years of inspections to assess the earthquake damage. If the plants are deemed safe then there will be more time expended to upgrade the earthquake and tsunami standards. And most likely to move the diesel generators to high ground.

Remember that this is all speculation by someone thousands of miles away. Informed speculation to be sure but still speculation. So if I get it wrong, well, stuff happens. In any event it’s going to be an interesting several years.

John

Posted by neonjohn on March 27th, 2011 under Energy, Nuclear



One Response to “Fukushima Update 03/27/11”

  1. Jeff Klopotic Says:

    Let’s wait until we get more on where he Iodine and Cesium are coming from. Those materials are gaseous in nature and could very well have come from a ruptured pipe or instrument line off the vessel.

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