Research on passive cooling system with isolation condenser. (1) Evaluation of the operating condition in Fukushima Daiichi unit 1

In the Fukushima Daiichi Nuclear Power Plant unit 1, isolation condenser (IC) should play an important role in core cooling during station blackout. To evaluate cooling capability of the IC, two phase flow analyses with the TRAC code and experiments for high pressure conditions were conducted. The analyses for the actual BWR indicated that decay heat could be removed if the IC worked properly at 18:18. However, our results showed that core uncovery occurred at 17:30, which will lead to hydrogen production from the heated core. Further efforts should be made to properly consider the effect of hydrogen accumulation for degradation of core cooling. The experiments simulating IC operation indicated that the natural convection occurred and decay heat could be removed by the IC at high pressure conditions. (author)