Symbiosis of static and dynamic probabilistic approaches to support the design process and evaluate the safety of a SFR

• ASTRID, the Advanced Sodium Technological Reactor for Industrial Demonstration, is a GEN IV technological demonstrator to be commissioned near the end of the 2020 decade. The aim is to demonstrate the progress made in the field of Sodium Fast Reactor technology on an industrial scale, by qualifying innovative options, especially those pertaining to safety and operability. An original combined methodology for probabilistic safety assessment (PSA) is being developed by the CEA and its partners, AREVA NP and EDF at the conceptual design stage of ASTRID. It consists at first, of a static level 1 PSA based on the conventional fault trees (FT)/event trees (ET) approach, taking into account a time period of a week without repair of component malfunctions. Its goal is to provide probabilistic insights in the assessment of design choices and to suppress the weaknesses of the design in terms of safety considerations. A reference configuration of the safety systems is evaluated in order to identify dominant accident sequences. Sensitivity studies are then performed on various design alternatives to define the optimal safety systems configurations that will minimize core damage frequency. It takes into account recent design evolutions for decay heat removal (DHR) systems and support systems, and re-evaluates the preliminary results from ASTRID PSA modeling. The conventional FT/ET approach initially developed for PWRs (Wash 1400) appears to be unsuitable for Sodium Fast Reactors (SFR) PSA because: This approach is binary and static, The probabilistic study for SFR cannot be limited to short periods of time - when repair is not possible - because several months are necessary for the thermal leakage to be equivalent to decay heat, SFR technology cannot rely simply on DHR complementary systems, The modeling by FT/ET is not designed for long periods of time, Repair, on along and middle term basis, of failed components is not considered. Therefore, dynamic PSA approaches have been investigated to extend the conventional PSA to longer periods of time by taking into account the specific characteristics of a sodium reactor such as its great thermal inertia - which allows the operator to make interventions - and the fact that sodium circuits present risks of irreversible and temperature-sensitive failures. What these approaches have in common is the possibility of taking into account the repair of failed components. Simplified thermal-hydraulic calculations were performed to characterize the reactor at any given moment in the accident scenario. The benefits of dynamic approaches on short periods of time will be quantitatively evaluated in 2015.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Inbäddad systemteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Embedded Systems (hsv//eng)

Nyckelord

Accidents

Conceptual design

Design

Fast reactors

Forestry

Pressurized water reactors

Repair

Safety engineering

Security systems

Sodium

Complementary systems

Conceptual design stages

Core damage frequency

Probabilistic approaches

Probabilistic safety assessment

Systems Configuration

Temperature sensitive

Thermal-hydraulic calculations

Accident prevention

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