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Probabilistic Safety Assessment (PSA)

PSA Level 1 - Core damage frequency assessment:

• Complete, detailed and structured event tree and fault tree model

• Full set of initiators (LOCA, Transients, External and Area Events, Common Cause Initiators (CCIs))

• Full set of operating states (Power operation, start-up, outage and shutdown)

PSA Level 2 - Release frequency assessment. A level 2 analysis builds on a level 1 analysis and is extended with:

• Containment analysis
• Phenomena investigation and assessment
• Level 1 to level 2 interface
• Plant damage states, containment event trees and release categories
• Release calculations

External Events: Fire and Flooding - Core damage frequency assessment:

• Screening analysis assuming that equipment exposed to fire/flooding has failed with the probability of 1.0
• Detailed analysis taking into account component possibility to survive, hazard detection and mitigation
• Full dependency information used as input

LPSA, Living PSA – models and applications:

Living PSA (LPSA) models allow instantaneous risk calculations based on the actual plant status and configuration. RELCON has the methods and procedures for the whole LPSA model development process. We also have the tools and procedures for efficient creation of LPSA models.

The LPSA model can be used in a number of LPSA applications:

• Risk Follow-up - calculation of the actual risk at each moment when looking back (all known component states are taken into account). Risk follow-up is used to identify situations that have had a large impact on the risk and to provide guidance on safety improvement measures.
   
• Risk Monitoring - calculation of the risk in real time, on-line. The risk monitor application (RiskSpectrum RiskWatcher) support operators, maintenance and planning staff.
   
• Surveillance Test Interval Optimisation - the instantaneous risk model is used to optimise surveillance test intervals with regard to:
• Maximum safety level with a given number of tests
• Minimum number of tests for a given safety level
   
• Allowed Outage Times - the LPSA model is used to optimise AOT's. The risk for remaining at power operation is assessed and compared to the risk of shutting down.
   
• Preventive Maintenance - the preventive maintenance analysis is carried out in order to find:
• Which measures, e.g. tests, are most effective for keeping a high safety level during preventive maintenance.
• Which actions should not be carried out during the preventive maintenance, e.g. shifting of pumps. 

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