RELAP5/SCDAPSIM/MOD3.4 Analysis of the Influence of Water Addition on the Behavior of a BWR during a Fukushima-like Severe Accident

Abstract

Immediately after the accident at Fukushima Daiichi, Innovative Systems Software (ISS), and other members of the international SCDAP Development and Training Program (SDTP) started an assessment of the possible core/vessel damage states of the Fukushima Daiichi Units 1-3. The assessment included a brief review of relevant severe accident experiments and a series of detailed calculations using RELAP/SCDAPSIM. The calculations used a detailed RELAP/SCDAPSIM model of the Laguna Verde BWR vessel and related reactor cooling systems. The Laguna Verde models were provided by the Comision Nacional de Seguridad Nuclear y Salvaguardias, the Mexican Nuclear Regulatory Authority. The initial assessment was originally presented to the International Atomic Energy Agency on March 21, 2011 to support their emergency response team and later to the SDTP Japanese members to support their Fukushima Daiichi specific analysis and model development.

Since the initial calculations were performed and documented in the open literature, a series of related calculations have been performed by ISS and SDTP members. This paper documents the first in a series of assessment calculations performed by the lead author at the Indian Institute of Technology, Kanpur. Specifically, these calculations have looked at the influence of water addition using thermal hydraulic conditions representative of the reactor core isolation cooling (RCIC) system where the water injection is impacted by time and reactor vessel pressure. Although these calculations were extended to the point of likely vessel failure or stable core cooling, this paper focuses on water addition during the initial heating and melting of the core where water addition may be the most effective in limiting the extent of fuel melting. The paper also presents the results of a base case, a station blackout transient without water addition, for comparison purposes. The base case calculations were carried out to 10 hours after reactor scram to a point beyond the point of likely vessel failure.