Resolution of Generic Safety Issues: Issue 33: Correcting Atmospheric Dump Valve Opening upon Loss of Integrated Control System Power ( NUREG-0933, Main Report with Supplements 1–34 )
This issue was identified in an AEOD memorandum106 to NRR in May 1980. The concern is related to a feature on some B&W reactors in which the failure of the Non-Nuclear Instrumentation and Integrated Control System (NNI/ICS) power supply results in automatic opening of the steam generator atmospheric dump valve to the fifty percent open position. Therefore, on the loss of NNI/ICS power, an overcooling transient could ensue.
This issue is covered in Task Item 2 of USI A-47, "Safety Implications of Control Systems."