Problems at Reactor Number 4

Monday, April 25, 2011

Problems at Reactor Number 4









NHK reports:





The operator of the troubled Fukushima Daiichi nuclear power plant is carefully monitoring the situation at the Number 4 spent fuel pool, where the water temperature is rising despite increased injections of cooling water.



Tokyo Electric Power Company, or TEPCO, says it will inject 210 tons of water into the pool on Monday, after finding on Sunday evening that the temperature in the pool had risen to 81 degrees Celsius.



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On Friday, TEPCO found that the pool's temperature had reached 91 degrees, so it began injecting 2 to 3 times the amount of water.



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The Number 4 spent fuel pool stores 1,535 fuel rods, the most at the nuclear complex.





(Bear in mind that the amount of radioactive fuel at Fukushima dwarfs Chernobyl.)



As I noted on April 2nd:





Nuclear engineer Arnie Gundersen notes that the spent fuel rods in reactor number 4 have no water, and the rods are exposed:











In addition, the official Japanese atomic energy website shows 4,250 sieverts/hour of radiation inside the containment vessel at reactor 4 ("S/C" stands for suppression chamber).



These are very high levels of radiation. As I noted on April 10:





Radiation levels were apparently about 300 sieverts per hour ... right after Chernobyl exploded.



To be clear, the Chernobyl figure is radiation released into the environment, while the reactor 4 figure is radiation within the containment vessel. I have seen no evidence to date that reactor 4 is leaking.





In contrast, the radiation inside the cores of the other reactors are much lower:



•Reactor 1: 0

•Reactor 2: 26.3



•Reactor 3: 11.1



•Reactor 5: 0



•Reactor 6: 0

Indeed, the Japanese nuclear agency prominently displays the radiation data for all of the reactors except number 4 on it's main page. Number 4 is conspicuously absent, and you have to type in the url for the correct web page to find it.



The building housing reactor 4 doesn't seem to be quite as badly damaged as those housing other reactors:







The fact that there is no radiation being measured in the drywell of reactor 4 (noted by "D/W" in the nuclear agency's tables) - while there is in several of the other reactors - might imply that the containment vessel has maintained its stability.



At this point, I don't have enough information to determine why the radiation levels inside reactor 4 are so high and what it means.