Nuclear Energy for New Europe 2009

(This is a HTML version of the abstract for information only. It can differ from the original, submitted by the author(s). Special characters, formulas and figures are not properly reproduced here. Please, contact the author(s) or refer to the printed Book of Abstracts for the correct version.)

No: 306

Conference: Nuclear Energy for New Europe 2009

Title: Proposal for a suitable strategy of exceedance frequency computation. Implementation on SCAIS simulation-based safety code cluster

Theme: Probabilistic Safety Assessment

Author(s): Jose M. Izquierdo, Javier Hortal, Miguel Sanchez, Enrique Meléndez, César Queral, Antonio Expósito, Gabriel Rodríguez, Israel Canamón, Jesus Gil, Horacio Fernandes, Santiago Murcia

Contact : Miguel Sanchez

E-mail: msp@csn.es

Address: Consejo de Seguridad Nuclear
28040 – Madrid

Country: Spain

The process of Safety Margin Assessment, as proposed in the SMAP framework [1], is based on the identification of the Risk Space and the extensive application of uncertainty analysis methods with the objective of obtaining an estimation of the Exceedance Frequencies of specified safety limits. The Risk Space can be understood as an extension of the design scenarios aimed at including every possible malfunction susceptible to challenge any safety limit of interest. The additional malfunctions are included in the event trees associated to each safety limit.
CSN, with the help of UPM and Indizen, is developing the SCAIS (Simulation Code System for Integrated Safety Assessment) simulation-based computational framework implementing the CSN integrated PSA approach for independent assessment of safety studies. Current efforts are being directed to extend its current capabilities (automatic event tree delineation, coupling simulation of plant dynamics and operator actions, coupling of different simulation codes depending on phenomenology requirements) with suitable modules that obtain a realistic estimation of exceedance frequency as the figure of merit of safety margin, that merges both deterministic and probabilistic information corresponding to the safety case being assessed.
This paper surveys the work performed. It will elaborate on the following points:
a) TSD (Theory of Stimulated Dynamics, [2]) as theoretical framework that guides the computational approach.
b) Main concepts: Dynamic Events and Dynamic Sequences, Damage Domain of a Sequence.
c) Uncertainty analysis in the context of exceedance frequency calculation.
d) Proposal of a suitable strategy for calculation of exceedance frequencies.
e) Specification of the designed computational modules (Risk Assessment and Path Analysis modules).
f) On the use of current PSA fault tree models to feed the computational approach.
Results of the application of the tool to the assessment of a power up-rate in a PWR plant, currently being performed within the NEA/OCDE SM2A project, will be reported to illustrate the method.

[1] SMAP Task Group (2007). Safety Margins Action Plan. Final Report. Technical Report NEA/CSNI/R(2007)9, Nuclear Energy Agency. Committee on the Safety of Nuclear Installations, http://www.nea.fr/html/nsd/docs/2007/csni-r2007-9.pdf.
[2] J. M. Izquierdo, I. Canamón, "TSD, a SCAIS suitable variant of the SDTPD", Proc. ESREL 2008, Valencia, Spain.

No:	306
Conference:	Nuclear Energy for New Europe 2009
Title:	Proposal for a suitable strategy of exceedance frequency computation. Implementation on SCAIS simulation-based safety code cluster
Theme:	Probabilistic Safety Assessment
Author(s):	Jose M. Izquierdo, Javier Hortal, Miguel Sanchez, Enrique Meléndez, César Queral, Antonio Expósito, Gabriel Rodríguez, Israel Canamón, Jesus Gil, Horacio Fernandes, Santiago Murcia
Contact :	Miguel Sanchez
E-mail:	msp@csn.es
Address:	Consejo de Seguridad Nuclear 28040 – Madrid
Country:	Spain

The process of Safety Margin Assessment, as proposed in the SMAP framework [1], is based on the identification of the Risk Space and the extensive application of uncertainty analysis methods with the objective of obtaining an estimation of the Exceedance Frequencies of specified safety limits. The Risk Space can be understood as an extension of the design scenarios aimed at including every possible malfunction susceptible to challenge any safety limit of interest. The additional malfunctions are included in the event trees associated to each safety limit. CSN, with the help of UPM and Indizen, is developing the SCAIS (Simulation Code System for Integrated Safety Assessment) simulation-based computational framework implementing the CSN integrated PSA approach for independent assessment of safety studies. Current efforts are being directed to extend its current capabilities (automatic event tree delineation, coupling simulation of plant dynamics and operator actions, coupling of different simulation codes depending on phenomenology requirements) with suitable modules that obtain a realistic estimation of exceedance frequency as the figure of merit of safety margin, that merges both deterministic and probabilistic information corresponding to the safety case being assessed. This paper surveys the work performed. It will elaborate on the following points: a) TSD (Theory of Stimulated Dynamics, [2]) as theoretical framework that guides the computational approach. b) Main concepts: Dynamic Events and Dynamic Sequences, Damage Domain of a Sequence. c) Uncertainty analysis in the context of exceedance frequency calculation. d) Proposal of a suitable strategy for calculation of exceedance frequencies. e) Specification of the designed computational modules (Risk Assessment and Path Analysis modules). f) On the use of current PSA fault tree models to feed the computational approach. Results of the application of the tool to the assessment of a power up-rate in a PWR plant, currently being performed within the NEA/OCDE SM2A project, will be reported to illustrate the method. [1] SMAP Task Group (2007). Safety Margins Action Plan. Final Report. Technical Report NEA/CSNI/R(2007)9, Nuclear Energy Agency. Committee on the Safety of Nuclear Installations, http://www.nea.fr/html/nsd/docs/2007/csni-r2007-9.pdf. [2] J. M. Izquierdo, I. Canamón, "TSD, a SCAIS suitable variant of the SDTPD", Proc. ESREL 2008, Valencia, Spain.