Application of RELAP/SCDAPSIM/MOD3.5 to a Representative BWR for Fukushima-Daiichi-like SBO transients

摘要

Immediately after the accident at Fukushima Daiichi, Innovative Systems Software, ISS, and other members of the international SCDAP Development and Training Program started an assessment of the possible core/vessel damage states of representative LWRs during Fukushima-Daiichi-like Station Blackout transients. The initial 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. These initial calculations have been documented in the open literature. Since that initial assessment, additional calculations have been performed using the original Laguna Verde model as well as models with expanded nodalization to (a) better represent the turbine driven cooling system and (b) add a detailed 2D/3D thermal hydraulic nodalization of the containment. The expanded models have been used to evaluate (a) the heatup and potential failure of the RCS piping, and (b) the influence of containment heat up on the rate of core uncovery and heatup. This paper will describe the expanded models and the response of the vessel, RCS piping (including the turbine driven cooling systems), and containment for a range of Fukushima-Daiichi-like transients using the new models and then discuss the influence of the extended nodalization and calculations relative to the initial assessment performed in 2011.