The Framatome Owners Group (FROG) recently completed a specific technical program focused on the issue of reactor trips initiated during the performance of periodic tests.

The overall objective was to answer the following two questions:
• Is there any periodic test responsible for most reactor trips common to most
  participating FROG Members?
• If so, how can this test procedure be improved?

Analyses of operating experience feedback demonstrated that incidents occurring during periodic tests and leading to reactor trips contributed less than 15% of the total number of reactor trips, and they had a minimum impact on the plant unavailability factor. These results were confirmed by a specific study performed on US plants.

The exchanges between Members revealed that no single periodic test could be identified as being a common source of incidents at all FROG Member NPPs. They also showed that the most contributing systems were the reactor protection system (RPR) and the main steam system (VVP), and demonstrated that most incidents involved human errors.

This technical program was then redirected to focus on the analysis of human errors that have occurred during performance of periodic tests, whatever the consequences for the NPP unit were (reactor trip or not).

Detailed analyses of operating events highlighted that fact that most of the human errors were occurring during test performance on the RPR system and were due to personnel errors rather than inadequacy of the test procedures.

The outcome of these analyses was the issuance of several recommendations, either system-specific and more general. Their overall objective is to facilitate personnel activities in such areas as enhancement of communications between plant shifts, reinforcement of training, and assistance for test scheduling.