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Astronuc
Staff Emeritus
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2023 Award
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The fuel in the core is in the form of oxide, usually UO2, or (U,Pu)O2 in MOX, and the fission products produced during the course of operation. An oxide will not combust. In contact with high temperature water, the UO2 and MOX can oxidize to higher order oxides, M3O8, M4O9, or MO3, where M = U,Pu, or a hydrated oxide, or hydroxide, which is soluble.DevilsAvocado said:Yes, thanks very much Astro for explaining these things.
Just one question: I read more about MOX, and there’s only small amount (7%) plutonium in the fuel. The 'risk' with plutonium is that it’s a radioactive poison that can spontaneously ignite when exposed to moist air. All uranium isotopes are only weakly radioactive. To me this means – if all the fuel in the three reactors is 'old'; then there is no bigger 'security difference'. It the fuel is 'new'; there could be some difference in possible 'risks'...
Correct?
At beginning of cycle, a reactor core contains fresh fuel (no irradiation), one-cycle fuel, two-cycle fuel, and perhaps three-cycle fuel. At end of cycle, we refer to once-burned (one-cycle), twice-burned, thrice-burned, or whatever, depending on the number of cycles used.
We measure utilization of fuel in terms of burnup, e.g., GWd/tU, or GWd/tHM (HM = heavy metal = U or Pu), which is just energy per unit mass. For consumption of 1% of the initial U (U235+U238), the equivalent burnup is about 9.7 GWd/tU.
The question is however, how much of the fuel cladding reacted with the steam, or how much of the fuel failed, and we will not know for months until they open the core, which they can't do with fission gases or fission products in the coolant.
The damaged/destroyed equipment, e.g., upper containment structure, overhead crane, fuel handling equipment will have to be replaced. They will likely have to construct some special containment to replace that which has been destroyed. That will take a lot of time.
And because of the radiation field, any inspection of the damage cores will be done remotely.