Simulation of the Lower Head Boiling Water Reactor Vessel in a Severe Accident

Abstract

The objective of this paper is the simulation and analysis of the BoilingWater Reactor (BWR) lower head during a severe accident. The COUPLE computer code was used in this work to model the heatup of the reactor core material that slumps in the lower head of the reactor pressure vessel. The prediction of the lower head failure is an important issue in the severe accidents field, due to the accident progression and the radiological consequences that are completely different with or without the failure of the Reactor Pressure Vessel (RPV). The release of molten material to the primary containment and the possibility of steam explosion may produce the failure of the primary containment with high radiological consequences. Then, it is important to have a detailed model in order to predict the behavior of the reactor vessel lower head in a severe accident. In this paper, a hypothetical simulation of a Loss of Coolant Accident (LOCA) with simultaneous loss of off-site power and without injection of cooling water is presented with the proposal to evaluate the temperature distribution and heatup of the lower part of the RPV. The SCDAPSIM/RELAP5 3.2 code was used to build the BWR model and conduct the numerical simulation.

Modelling of Severe Accident and In-Vessel Melt Retention Possibilities in BWR Type Reactor

“…Similar model and investigations are presented in [19]. However, in this article, it was reported that for the longterm simulation the problems of the heat transfer in the lower head occurred and calculations of the RELAP/SCDAPSIM code crashed.…”

“…For our calculations the model was improved. In [19] presented problems were avoided by adjusting the time step ratio between the thermal-hydraulic calculations and 2D finite-element solver for the heat transfer in the lower head and setting it to be equal to 1.…”

Comparative study of the hydrogen generation during short term station blackout (STSBO) in a BWR

“…Immediately after the accident at Fukushima Daiichi several authors presented an assessment of the possible core/vessel damage states of the Fukushima Daiichi Units 1-3 station blackout, LOCA, among other scenarios using RELAP5/SCDAPSIM (Allison et al, 2012;Nuñez-Carrera et al, 2012;Trivedi et al, 2014). Allison et al (2012) presented an assessment of the possible core/vessel damage states of the Fukushima Daiichi Units 1-3 station blackout scenarios; the main conclusion is that the responses to the accident once the accident is underway can make a significant difference in the consequences of the accident.…”