Internal/External Risk Experience in Level 1 PSA (SF G.S.-1.10)

The CSN GS-1.10, in Safety Factor 7 (SF7), identifies internal and external hazards that may affect the safety of Nuclear Power Plants. The Guide require, for the PSR, to analyse deviations and strengths over them.

Independent of these analyses, the PSA analyse plant experience if any of the events covered by the model (initiator events, special events, failures or unavailabilities) have been caused by those hazards to quantify their contribution into the Core Damage Frequency (CDF).

Example shown below:

To know how important these events are in the PSA, the Fussel-Vesely (FV) measure is used, which gives to the CDF the contribution of an event.

Significant events: 3 initiating events (SBO, 380/400kV LOOP and Loss of vacuum in the condenser) and 1 special event (220kV LOOP during the sequence).

Once the main PSA events have been identified, their hazard type is studied. And the process is repeated.

Assuming an CDF of 8,00E-06/year, the part due to these hazards is as following:

Grouping by hazards:

In total 7.79E-07/y (10%CDF), enough significant to develop preventive or improvement actions:

  • Rivers, reservoirs, sea Monitoring
  • Protection against storm/overvoltage
  • Operational practices
  • Coordination with official bodies

This exercise allows focusing hazards, improvement actions and strengths of the plant.


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