Chernobyl Nuclear Accident Congressional Hearings Transcript

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QUESTION 10. (Continued) - 8 -
radioactivity release magnitudes similar to those in WASH-1400 PWR
3 or BWR 3 release categories. These release categories contain
many accident scenarios, including small break loss of coolant
with failure of the containment sprays, interfacing systems loss
of coolant (i.e'. , accidents involving overpressurization of low
pressure piping that is outside of the containment but is
connected to the high pressure primary cooling piping such that
the loss of coolant occurs outside of the containment rather than
the design basis loss of coolant inside containment), anticipated
transients without scram, station blackout, and loss of coolant
accidents with failure of emergency core cooling injection.
The specific release category that results from these scenarios is
dependent on core meltdown phenomena and containment response
thereto. While much progress has been made in understanding these
since WASH-1400 was published in 1975, there remain very
substantial uncertainties in evaluating them. For example, during
a core meltdown, theoretical source term calculations include
models for plating out of significant quantities of fission
products within the primary system. However, the models do not
evaluate or poorly evaluate the effects of the heating of the
primary system by the plated-out fission products to determine
whether this phenomenon alters the sequence of events and the
release category. Steam explosions and their effects on
containment and resuspension of fission products are still in
dispute. These are just two examples of the mary uncertainties