Modelling of HTR Confinement Behaviour during Accidents Involving Breach of the Helium Pressure Boundary

Abstract

Development of HTRs requires the performance of a thorough safety study, which

includes accident analyses. Confinement building performance is a key element of the

system since the behaviour of aerosol and attached fission products within the building

is of an utmost relevance in terms of the potential source term to the environment. This

paper explores the available simulation capabilities (ASTEC and CONTAIN codes) and

illustrates the performance of a postulated HTR vented confinement under prototypical

accident conditions by a scoping study based on two accident sequences characterized

by Helium Pressure Boundary breaches, a small and a large break. The results obtained

indicate that both codes predict very similar thermal-hydraulic responses of the

confinement both in magnitude and timing. As for the aerosol behaviour, both codes

predict that most of the inventory coming into the confinement is eventually depleted on

the walls and only about 1% of the aerosol dust is released to the environment. The

cross-comparison of codes states that largest differences are in the inter-compartmental

flows and the in-compartment gas composition.