Integration of Passive System Reliability in PSA Studies

Conference · Sat Jul 01 04:00:00 EDT 2006

OSTI ID:20995684

Burgazzi, Luciano ^[1]; Marques, Michel ^[2]

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1. ENEA, Italian National Agency for New Technologies, Energy and the Environment (Italy)
2. Commissariat a l'Energie Atomique - CEA (France)

The treatment of passive safety systems within the probabilistic safety assessment models is a difficult and challenging task. The main concern arises from the nature of the passive systems whose predominant operating principles are based on physical phenomena rather than on active components. The present study provides a consistent approach for the integration of passive safety systems into fault tree and event tree based Probabilistic Safety Assessment (PSA) model of accident sequences, in the fashion of and in combination with a front line system or a human action. With reference to the thermal-hydraulic passive systems (e.g. natural circulation systems), in addition to the component failures (i.e. mechanical and electrical faults), the impairment of the physical principle upon which the system relies, deserves special consideration. This makes the relative assessment process different as regards the system model commonly adopted in the fault tree approach (i.e. exponential failure model). For the thermal-hydraulic passive system, since the failure process is driven mainly by the occurrence of the phenomenological failure modes, each pertinent basic event will be characterized by defined critical parameters (e.g. non-condensable fraction) that are expected to drive the failure mechanisms. An application of this approach is presented, with reference to a system designed for decay heat removal of advanced Light Water Reactors, relying on natural circulation and provided with a heat exchanger immersed in a cooling pool, acting as heat sink, and connected to the pressure vessel via steam and condensate lines. (authors)

• Research Organization: The ASME Foundation, Inc., Three Park Avenue, New York, NY 10016-5990 (United States)
• OSTI ID: 20995684
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
ACCIDENTS
AFTER-HEAT REMOVAL
ELECTRICAL FAULTS
FAILURES
FAULT TREE ANALYSIS
HEAT EXCHANGERS
HEAT SINKS
NATURAL CONVECTION
PRESSURE VESSELS
PROBABILISTIC ESTIMATION
RELIABILITY
RISK ASSESSMENT
SAFETY
THERMAL HYDRAULICS
WATER COOLED REACTORS
WATER MODERATED REACTORS