Nuclear Energy for New Europe 2009

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No: 309

Conference: Nuclear Energy for New Europe 2009

Title: The Price of Risk Reduction: Optimization of Test and Maintenance Integrating Risk and Cost

Theme: Probabilistic Safety Assessment

Author(s): Duško Kančev, Marko Čepin

Contact : Duško Kančev

E-mail: dusko.kancev@ijs.si

Address: Institut "Jožef Stefan" R4
1001 Ljubljana

Country: Slovenia

The primary purpose of surveillance testing and maintenance (T&M) is to assure the reliability of standby safety systems and components in nuclear power plants (NPPs). The optimal schedule of safety equipment outages due to testing and maintenance is one of the parameters of the plant safety. Early optimizations of single component test intervals were based on minimizing the risk, e.g. the time-average unavailability, without cost considerations. However, the appropriate development of T&M strategy depends not only on the T&M intervals but also on the resources (human and material) available to implement such strategies. Since these testing and maintenance activities are associated with substantial cost, they present an important domain, where risk reduction and costs can be balanced.
The objective of this paper focuses on assessing how the costs may affect the T&M optimization. The costs are expressed as a function of the selected risk measure. In that sense, analysis of the impact of different cost functions is performed. The time dependent function of the selected risk measure is obtained from probabilistic safety assessment (PSA), i.e. the fault tree (FT) analysis at the system level, extended with inclusion of time parameters. The testing strategy is also addressed. Sequential versus staggered testing comparison is stressed out. A properly selected engineered safety system is chosen as a case study.

No:	309
Conference:	Nuclear Energy for New Europe 2009
Title:	The Price of Risk Reduction: Optimization of Test and Maintenance Integrating Risk and Cost
Theme:	Probabilistic Safety Assessment
Author(s):	Duško Kančev, Marko Čepin
Contact :	Duško Kančev
E-mail:	dusko.kancev@ijs.si
Address:	Institut "Jožef Stefan" R4 1001 Ljubljana
Country:	Slovenia

The primary purpose of surveillance testing and maintenance (T&M) is to assure the reliability of standby safety systems and components in nuclear power plants (NPPs). The optimal schedule of safety equipment outages due to testing and maintenance is one of the parameters of the plant safety. Early optimizations of single component test intervals were based on minimizing the risk, e.g. the time-average unavailability, without cost considerations. However, the appropriate development of T&M strategy depends not only on the T&M intervals but also on the resources (human and material) available to implement such strategies. Since these testing and maintenance activities are associated with substantial cost, they present an important domain, where risk reduction and costs can be balanced. The objective of this paper focuses on assessing how the costs may affect the T&M optimization. The costs are expressed as a function of the selected risk measure. In that sense, analysis of the impact of different cost functions is performed. The time dependent function of the selected risk measure is obtained from probabilistic safety assessment (PSA), i.e. the fault tree (FT) analysis at the system level, extended with inclusion of time parameters. The testing strategy is also addressed. Sequential versus staggered testing comparison is stressed out. A properly selected engineered safety system is chosen as a case study.