THAI experimental research on hydrogen risk and source term related safety systems

Abstract

In the defense-in-depth concept employed for the safety of nuclear installations, maintaining integrity of containment as the last barrier is of high importance to limit the release of radioactivity to the environment in case of a severe accident. The active and passive safety systems implemented in containments of light water reactors (LWRs) are designed to limit the consequences of such accidents. Assessing the performance and reliability of such systems under accident conditions is critical to the safety of nuclear installations.

In the aftermath of the Fukushima accident, there has been focus on re-examining the existing safety systems to demonstrate their capabilities for a broader range of boundary conditions comprising both the early as well as the late phases of an accident. In addition to the performance testing of safety systems, their interaction with containment atmosphere needs detailed investigations to evaluate the effects of operation of safety systems on H₂ risk and fission product (FP) behavior in containment, which may ultimately have an impact on the source term to the environment.

In this context, an extensive containment safety related experimental research has been conducted in a thermal-hydraulics, hydrogen, aerosols, and iodine test facility (THAI, 60 m³, single vessel)/(THAI⁺, 80 m³, two interconnected vessels). Related to the subject of this paper, experimental investigations covered performance testing of various safety and mitigation systems, i.e., containment spray, passive autocatalytic recombiner (PAR), pressure suppression pool (water pools), and effects of their operation on H₂ risk and in-containment FP behavior. The experimental results have provided a better phenomenological understanding and database for validation and further improvement of a safety analysis tool based on computation fluid dynamic (CFD) and lumped parameter (LP) modeling approach. This paper summarizes the main insights obtained from the aforesaid THAI experimental research covering safety systems installed in containments of LWRs. The relevance of experimental outcomes for reactor safety purpose is also discussed.

Graphical abstract

Keywords

severe accident / containment / safety / mitigation / H₂ risk / source term

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Acknowledgment

THAI experimental research program is funded by the German Federal Ministry for Economic Affairs and Energy, on the basis of a decision of the German Bundestag. The sponsorship by the countries of the OECD/NEA THAI, THAI-2, THAI-3 and the ongoing THEMIS projects is gratefully acknowledged.

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