Hydrogen Distribution Analysis for PHWR Containment and Inter-Code Comparison

摘要

Generation and accumulation of hydrogen in containment atmosphere during certain postulated accident conditions could pose a potential threat to the integrity of the containment as the hydrogen can form flammable or even explosive mixture with air in the containment. The aim of this modeling and calculations is to observe the effect of condensation and forced convection on the concentration of hydrogen in various compartments of the containment and to see the hydrogen distribution in compartments. The objective is also for inter code comparison of CTHC with PACSR. The governing accident sequence considered for modeling is dual failure involving a loss of coolant accident simultaneous with unavailability of emergency core cooling. In case of rupture of reactor inlet header with loss of emergency core cooling, hydrogen is generated due to metal water reaction and expected to be released in fuelling machine vault and mix uniformly with air and steam in vault. The containment hydrogen distribution analysis has been carried to verify the results submitted by Utility. The results obtained using thermal hydraulic code are compared with Utility results obtained with PACSR. The analysis performed was divided into two parts. Part-1 is analysed as per the existing design and Part-2 was analysed with a proposed fan for forced mixing and effective distribution of hydrogen. The magnitudes for hydrogen mass and concentration (volume percent) predicted by containment thermal hydraulics code are lower and steam concentrations predicted by containment thermal hydraulics code are higher compared to PACSR code predictions. However, the predictions by PACSR are on conservative side regarding flammability mixtures. The forced circulation between break compartment and pump room is simulated using a fan with a capacity of 13600 m~(3)/h. The hydrogen concentrations follow the similar trends and again the peak hydrogen concentration predicted by PACSR is about 11.5percent in the break compartment compared to about 10percent by containment thermal hydraulics code with the proposed fan. The steam concentrations are differing quite significantly in both the analysis.