7 Jan (NucNet): Analysis of passive safety systems in nuclear reactors has identified a number of intrinsic difficulties that need further research, France’s Institute for Radiological Protection and Nuclear Safety (IRSN) has said.
In a report published today IRSN says the intrinsic difficulties particularly concern the assessment of performance and reliability of such systems.
The report says further research is needed to properly assess the performance and reliability of passive safety systems to be implemented in new reactor designs.
The report says assessing the performance of passive safety systems requires a very good understanding of the physical phenomena underlying their operation, as well as the necessary simulation capabilities for such phenomena.
It says assessing reliability calls for specific development approaches in order to properly evaluate the reliability of passive safety systems, with particular emphasis on assessing the failure probabilities of thermal-hydraulic mechanisms used by these systems.
IRSN said certain reactor designs proposed by nuclear power plant designers make more extensive use of passive safety systems to bring the reactor to a safe shutdown state and maintain this state for a long period of time – 72 hours for Westinghouse AP1000 reactors – without human intervention and with limited reliance on support functions.
IRSN said that since the accident at Fukushima-Daiichi in March 2011 there has been a growing interest in passive safety systems, particularly to mitigate accident conditions involving long-term loss of electrical power or heat sink.
The report published today outlines the main characteristics of passive safety systems and the main difficulties associated with assessing the performance and reliability of such systems, as well as priority research areas to be developed in order to overcome these difficulties.
Initial considerations have already been identified as part of IRSN’s scientific strategy, with the emphasis on understanding physical phenomena influencing the operation of passive safety systems, simulation capabilities for such phenomena, and the testing for validation of simulation software.
IRSN said it is pursuing research into passive safety systems within the framework of joint actions with foreign organisations so as to ensure “fruitful exchanges and benefit” from available knowledge.
In particular, IRSN coordinates a working group devoted to discussing new safety approaches applicable to these systems on the behalf of Western European Nuclear Regulators Association (Wenra) reactor harmonisation working group.
IRSN also participates in the Nusmor project to be proposed as part of the Horizon 2020 EU framework programme for knowledge development on passive safety system performance, and coordinates a working group with French industry stakeholders to identify priority research areas.