A simple method for estimating the structure temperatures and the cesium revaporization inside the reactor pressure vessel - I: Basic concepts and model descriptions for the Fukushima Daiichi Nuclear Power Plant

This paper presents a simple approach for estimating the structure temperatures including the uncovered reactor core inside the reactor pressure vessel (RPV) and the release rates of fission products deposited in the RPV to the reactor building (R/B) at a certain time after the occurrence of a severe accident at a nuclear power plant (NPP). First, basic concepts are presented and then, a simplified steady-state heat balance model is proposed for estimating the temperatures of the uncovered reactor core and the upper structure in the RPV as well as the temperature of the RPV wall. In addition, models for estimating the revaporization rate of cesium hydroxide (CsOH) in the RPV and the leak rate of CsOH to the R/B via the drywell are also presented. The proposed approach is anticipated to be applicable to the damaged Units 1-3 of the Fukushima Daiichi NPP.