Sign in Subscribe
Social services

NRC Requests Confirmation of Information for Exemption to Delete Diverse Auxiliary Feedwater Actuation System

Strategic Insights

— 2 min read

The United States Nuclear Regulatory Commission (NRC) has issued a request for confirmation of information regarding an exemption to delete the Diverse Auxiliary Feedwater Actuation System (DAFAS) for the Palo Verde Nuclear Generating Station, Units 1, 2, and 3. The exemption is based on the Risk-Informed Process for Evaluations (RIPE) and aims to reduce the risk from anticipated transients without scram (ATWS) events. The NRC staff has reviewed the application and accepted it on January 31, 2022, but requires additional information for complete evaluation.

Key Takeaways:

  • The NRC staff has issued a request for confirmation of information (RCI) to Arizona Public Service Company (APS) regarding the exemption to delete the DAFAS.
  • The exemption is based on the RIPE and aims to reduce the risk from ATWS events.
  • The NRC staff has accepted the application but requires additional information for complete evaluation.
  • The RCIs were transmitted on January 31, 2022, and APS has been requested to provide responses within 2 weeks.
  • The exemption does not alter the requirements for the Diverse Scram System (DSS) or Diverse Turbine Trip (DTT) at Palo Verde.
  • The NRC staff has noted that the Integrated Decisionmaking Panel (IDP) package provides insight into the beyond design basis case of a loss of normal feedwater flow accident, which occurs coincidently with a trip on supplementary protection system high-high pressurizer pressure, no auxiliary feedwater actuation signal (AFAS) -1, no AFAS-2, and no DAFAS.
  • The results of the IDP analysis show that in the worst-case scenario, approximately 10 minutes are available for the operators to manually actuate auxiliary feedwater before a lack of adequate inventory occurs in the steam generator.
  • The NRC staff has requested clarification on whether the "N" AFW Pump is Class 1E or Non-Class.
  • The RCIs also request verification that the described manual operator actions are formally credited in the exemption license basis as independent diverse means to actuate auxiliary feedwater upon RPS/AFAS failure.

Statistics:

  • The exemption is based on the RIPE process, which aims to reduce the risk from ATWS events.
  • The NRC staff has issued RCIs to APS, which must provide responses within 2 weeks.
  • The IDP analysis shows that approximately 10 minutes are available for operators to manually actuate auxiliary feedwater before a lack of adequate inventory occurs in the steam generator.
  • The RCIs also request clarification on the classification of the "N" AFW Pump.

Sources:

  • [1] United States Nuclear Regulatory Commission (NRC), "Requests for Confirmation of Information Regarding Exemption to Delete Diverse Auxiliary Feedwater Actuation System Using the Risk-Informed Process for Evaluations", February 10, 2022.
  • [2] Arizona Public Service Company (APS), "Exemption to Delete Diverse Auxiliary Feedwater Actuation System Using the Risk-Informed Process for Evaluations", January 14, 2022.
  • [3] United States Nuclear Regulatory Commission (NRC), "Acceptance of Exemption to Delete Diverse Auxiliary Feedwater Actuation System Using the Risk-Informed Process for Evaluations", January 31, 2022.

Read more