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  (Source: www.popsci.com)
The containment vessel of reactor No. 3 at the Fukushima Daiichi nuclear power plant may be ruptured after three workers within the plant stepped into water that contained "10,000 times the amount" of radiation that is normal for that area

While there has been some speculation surrounding the accuracy of CNN's reports on radiation in Japan as of late, the cable/web news giant has now released a new report stating that there may be a rupture in the containment vessel in reactor No. 3 at the Fukushima Daiichi nuclear power plant, and that it may be the cause of surrounding water that contains 10,000 times the amount of radiation normally found in the area.

The 9.0-magnitude earthquake that struck Japan on March 11 has led to tsunamis, blackouts, radiation issues such as contaminated food, and a death toll that has passed the 10,000 mark and is expected to exceed 18,000

Now, CNN.com has reported that the containment vessel of reactor No. 3 at the Fukushima Daiichi nuclear power plant may be ruptured after three workers within the plant stepped into water that contained 10,000 times the amount of radiation that is normal for that area. The job of the containment vessel is to keep radioactive material from entering the atmosphere, and according to Hidehiko Nishiyama from the Japan nuclear and industrial safety agency, "contaminated water likely seeped through the containment vessel protecting from the reactor's core."

The three workers, which were laying cables in the basement of the No. 3 reactor, were escorted to Japan's National Institute of Radiological Sciences after stepping in the radioactive water. According to Japan's Health Ministry, a person living in an industrialized country is exposed to 3 millisieverts of radiation annually. For those working directly with the nuclear plant during the current situation, the maximum level of exposure is 100 to 250 millisieverts per year. The three men who stepped in the radioactive water was a 30-year-old with an exposure level of 180.7 millisieverts, a 20-year-old with 179.37 millisieverts and a third man with no age specified that was exposed to 173 millisieverts of radiation. All three men spent 40 to 50 minutes in the 15-centimeter deep water. 

While water in this area is normally boiled and has low levels of radiation, Nishiyama is concerned for the 536 other people working at the plant Friday when the incident occurred, and would like to improve radiation management measures. 

Nishiyama would also like to improve radiation management measures at reactor's 1 and 2, which have been manageable as of late but are still experiencing difficulties. For instance, reactor No. 1 has had issues with increased pressure, and reactor No. 2 needs to switch the water for its spent fuel pool from saltwater to freshwater in order to prevent further corrosion from the salt. 

Reactors 4, 5 and 6 are being watched as well, but do not pose as much of a threat since they underwent scheduled outages during the earthquake. 




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RE: The Secret of Reactor 3
By phlogiston on 3/28/2011 9:34:57 AM , Rating: 2
I hadn't heard about this, but a little web research found a good description of MOX fuel and its likely impact on the situation at Fukushima Daiichi Unit 3 at:

http://www.ans.org/misc/ANS-Technical-Brief-MOX-Fu...

Some of the key points:

At the time of the earthquake, Fukushima Daiichi Unit 3 was operating with 32 mixed oxide (MOX) fuel assemblies and 516 low enriched uranium (LEU) fuel assemblies in its reactor core. This equates to less than 6% of the fuel in the Unit 3 core being MOX fuel. There were no other MOX fuel assemblies (new, in operation or used) at the Fukushima Daiichi plant at the time of the accident.

It is important to note that while LEU fuel begins its useful life with no plutonium, as it is used in a light water reactor it builds up plutonium as a result of the nuclear reactions in the core. By the end of its useful life an LEU fuel assembly contains about 1% plutonium and actually generates more power by fission of plutonium than from uranium. All reactor cores contain plutonium; those cores loaded with some MOX fuel contain more.

Mixed oxide (MOX) fuel is comprised of a blend of uranium oxide and plutonium oxide. MOX fuel is predominantly uranium, with average concentrations of plutonium that range from 3-10%. The presence of plutonium produces modest changes in some physical characteristics of the fuel material such as thermal conductivity. However, MOX fuel and low-enriched uranium (LEU) fuel are fundamentally similar. Moreover, the physical dimensions and structural material of a MOX fuel assembly are essentially identical to that of a LEU fuel assembly. To the naked eye, a MOX fuel assembly and a LEU fuel assembly are identical.

Unit 3 was loaded with only 32 MOX fuel assemblies during refueling operations in the fall of 2010. There are a total of 548 fuel assemblies in the Unit 3 reactor core, so this represents less than 6% of the total fuel in the core. The MOX fuel had been operating in Unit 3 for less than five months; fuel assemblies are typically used for a total of 3-4 years in reactor cores before being replaced by new fuel and discharged to used fuel pools. Therefore, the MOX fuel would have built up relatively few radioactive fission products and actinides at the time of the earthquake and subsequent damage to the reactor core. With these facts in mind – the low percentage of MOX fuel in the core and the short operation time for the MOX fuel – it is evident that the presence of MOX fuel at Fukushima Daiichi Unit 3 has had no significant impact on the offsite releases of radioactivity following the earthquake and tsunami.


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