Breakout Sessions

Session 1: Accident Progression Analysis

Moderator: Michael Corradini, committee member

Rapporteur: Arthur Motta, committee member

Questions:

1. How much fuel damage/core melting occurred in the reactors?

2. Did the core penetrate and react with the pressure vessels?

3. Did the core/pressure vessel material pierce the containment?

4. Is there evidence (e.g., vessel wall temperatures), other than from severe accident codes, that could indicate whether the lower head of the reactor vessel at any unit was penetrated and whether there was some amount of core-concrete interaction?

5. Is there any evidence of steam explosions and/or core material underneath the reactor?

6. Is there any evidence of recriticality?

7. Are there measurements of airborne concentrations of radionuclides (or accumulation of ground deposition) that would enable validation of core degradation timing and extent?

8. How were total release inventories of radionuclides estimated during the accident?

9. Is there any evidence of continued release of radionuclides by an airborne pathway from the plant site (such as the release of iodine vapor or radionuclide aerosol release) subsequent to the time at which core degradation was arrested at all three units?

10. Is there evidence of damage to any systems, structures, or components (beyond the damage to the electrical power lines and towers) of Units 1-6 due directly to the seismic events?

11. What is the current status of the cooling systems? To what extent were the reactor and their PV piping systems damaged during the earthquake?

12. What is the current status of electrical equipment and diesel generators?

13. How useful were the severe accident codes (e.g., MAAP, RELAP) for assessing core damage in real time?

14. How was the lack of information and uncertainty of parameters (e.g., IC, SRVs, RCIC, HPIC, RPV integrity) managed during the accident?

15. Were reactor simulators used to assess the condition of the reactors and/or potential operator responses?

16. What lessons have been learned in the operation of safety systems (RCIC, IC) during the accident? For example, was the IC properly used in Unit 1? If not, how would it be changed in the future?



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