Evaluation of the Impact That PARs Have on the Hydrogen Risk in the Reactor Containment: Methodology and Application to PSA Level 2

Abstract

This paper presents a methodology and its application to a Level 2 Probabilistic Safety Assessment (PSA-2), to evaluate the impact of the Passive Autocatalytic Recombiners (PARs) on the hydrogen risk in the reactor containment in case of a severe accident. Among the whole set of accidental scenarios calculated in the framework of the PSA-2, nine have been selected as representative in terms of the in-vessel hydrogen production rate and in-vessel total produced hydrogen mass. Five complementary scenarios have been added as representative of the core reflooding situations. For this set of selected scenarios the evolution of the conditions in the containment (i.e., pressure, temperature, and composition) during the in-vessel phase of the accident has been evaluated by means of a lumped parameter approach. The use of spray systems in the containment has also been considered as well as the presence of recombiners. Moreover, the ignition by recombiners of the flammable atmosphere has been considered.

Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident in the APR1400 Containment Using a Multi-Dimensional Hydrogen Analysis System

“…Figure 8 shows the initial conditions of the gas concentrations, temperature, pressure, and turbulence for the COM3D calculation after transferring from the GASFLOW results. According to the distributions of the mixture gas of the hydrogen and air, the flame acceleration may sufficiently occur along the mixture gas vertical column with approximately 0.5 m diameter and 57 m length [16]. When the grid model was transferred from the GASFLOW to the COM3D, its cell length was decreased to approximately 50 cm from 100 cm to accurately resolve the pressure wave propagation generated from the combusted region, model the important structures to the hydrogen flame acceleration in the containment, and complete the calculation of the hydrogen flame acceleration in the proper time [10,11].…”

Development of a Hydrogen Management Concept for the Canadian Supercritical Water-Cooled Reactor

“…For a CANDU-6 reactor, a H 2 release rate of up to 0.15 kg·s −1 is the highest value reported [16] for a loss of coolant accident coincident with a loss of emergency core cooling (LOECC). For a 900-1000 MWe pressurized-water reactor, the predicted H 2 production rate is 0.1-0.2 kg·s −1 [8,17]. Finally, for a boiling-water reactor (BWR), 1-2 kg·s −1 has been suggested [9].…”

“…Without a hydrogen management strategy, the hydrogen concentration within containment can reach flammable concentrations (above 4.0 vol%) within minutes of the hydrogen release to containment. From the Shapiro diagram (Figure 1), it is evident that hydrogen detonation can occur at hydrogen concentrations above 18 vol% and flame acceleration could occur at hydrogen concentrations of approximately 11 vol% [17]. Unmitigated, 11 vol% hydrogen would also be reached within minutes of the hydrogen release to containment assuming a generation rate of 0.3-1.1 kg·s…”

Progress of IRSN R&D on ITER Safety Assessment

“…In this case, the risk of formation of an explosive gas-dust cloud, its evolution along time and its consequences should be evaluated more precisely. As the explosive phenomena are complex and an accidental explosion could generate high pressure loads beyond the VV pressure design, IRSN decided to assess the gas and dust explosion risk inside the VV and the neighbouring tanks (VVPSS, DT) by adapting to ITER conditions (high temperature and low pressure) an existing methodology developed initially for hydrogen risk in PWR containment in case of severe accident [4]. This methodology is based on CFD codes to predict gas dispersion and to evaluate pressure and temperature loads generated by gas combustion.…”