Specification of the Environment Loading Parameters during the Severe Accident dedicated to qualification of Severe Accident Mitigation Systems

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en

Severe accident mitigation measures are being implemented at Slovak nuclear power plants as a part of plant safety enhancement. The measures comprise also depressurization and injection systems, collaboration of which should effectively allow cooling and possibly also quenching of the core. Drawing quenching of the core in to the practise is one of the measures applied by Severe Accident Guidelines. It focuses onto analysis of applicability of the recent QUENCH programme results to core quenching in real core geometry. The specifics of the VVER440 design along with possible core states during the evolution of the core degradation should be also taken into account. From Severe Accident Guidelines point of view, core exit temperature is the only reliable entry parameter. Therefore the behaviour of the core and status (overheating) of the core has to be related with this temperature. Sufficiency of flow to quench the core geometry is evaluated for relevant scenarios of severe accidents, status of the core and temperature distribution within the core. Best estimate analyses to assess the status of the core were carried out using MELCOR 1.8.5 code. These analyses were focused on temperature distribution and predicted hydrogen production while core is being quenched. Core temperature distribution was visualized. The general goal of the analyses was to formulate requirements for core reflooding system taking into account both, the recommendations emerging from the performed experiments and real capabilities of the plant design. All the analyses were carried out using MELCOR 1.8.5RK (quench model implemented). The presentation will include: – Short overview of Slovak NPP VVER upgrades to cope with severe accident, with focus to measures coupled with quenching, – Possible states of the core in dependence on scenario and timing of operation/ action of mitigation systems, – Temperature behaviour in the core, reflooding requirements and design limitation, – Results of calculations carried out to verify cooperation between depressurization and injection systems in expected reflooding conditions.

Depressurization, Hydrogen production, Quenching, Cladding, Primary circuit, Reactor Pressure Vessel, Core

2013-09-26

American Nuclear Sociate

American Nuclear Society, LaGrange Park, IL (2013)

978-3-923704-77-4

Proceedings of the 17th International QUENCH workshop

1–11

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