A simple method for estimating the structure temperatures and the cesium revaporization inside the reactor pressure vessel - II: Feasibility study for the Fukushima Daiichi Nuclear Power Plant

The present article is the second part of a two-part article, examining the feasibility of the method proposed in the preceding part. In this method, the ratio of the core uncovered from water x(u), the ratio of the core flooded by water x(f), the ratio of the core slumped into the pedestal area of the drywell x(s), and the ratio of the injected water leaking before reaching the core x(wl) are the four important uncertain parameters. The base case study shows that water injection via the core spray line is more effective to cool the uncovered core and to reduce the amount of cesium hydroxide (CsOH) released from the drywell. The sensitivity study is conducted by introducing the dimensionless decay heat N-qd, which combines the effects of x(f), x(s), and x(wl) on the steam generation rate associated with the forced convection cooling in the reactor pressure vessel (RPV). The results show that the temperatures of the uncovered core and the other structures increase with N-qd. Consequently, the release rate of CsOH also increases with N-qd. The relationships of the measurable RPV wall temperature with the temperatures of the uncovered core and the structures as well as the release characteristics of CsOH are also examined.