Most existing SAM (Severe Accident Management) approaches do not cover shutdown states. However, PSA results are consistently showing the importance of potential severe accidents occurring from shutdown conditions. There is therefore a trend towards extending coverage of SAM to cover these states.

For the transition from EOP to SAMG (SAM Guide), most existing (“at-power”) approaches use a criterion based on core exit temperature. Core exit thermocouples are not available in many shutdown plant states and so a pre-requisite of extending SAM coverage to shutdown is the development of an alternative transition criterion/parameter.

In addition, while some existing SAM approaches have identified alternative criteria to core exit temperature (in order to provide some level of redundancy), many have not. For these cases, it may be of interest to review and identify potential alternative transition symptoms, even for the “at-power” only SAM approaches.

It is therefore proposed to perform a benchmarking exercise for “alternative” EOP-SAMG transition criteria, and including:

• Comparison of different alternatives, including benefits and disadvantages.
• Recommended symptoms.
• Analytical requirements to develop setpoints. 
• Technical and analytical basis.

Proposed Approach

It is proposed to perform the work in the following steps:

• This will be done using a questionnaire which will be prepared by Areva NP and distributed to all members
  for completion.
• Areva NP will prepare a benchmarking report which compares members approaches, includes any other
  approaches (i.e. used by non-members), and summarizes their technical bases. Any recommendations
  for improvement will also be provided.

This approach is the same as that suggested for the at-power entry condition benchmark proposal (see FRA OG 2210). However, in both cases, the benchmark report will not be limited to information gathered from members in the questionnaire. This is of particular importance for this proposal, since most existing SAM approaches do not consider shutdown,

Benefits/Reasons

For members whose SAM approach currently does not cover shutdown, the work will provide recommended symptoms and the technical basis for the recommendation. Similarly, for members who would prefer to have diverse means of entering their current SAM guidance, alternatives will be identified and discussed and recommendations formulated. For members whose SAM already covers shutdown states, the benchmarking will provide a comparison with alternate means and therefore help to justify the selected approach.