This issue was identified in an AEOD memorandum[1] 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."
[1] Memorandum for H. Denton from C. Michelson, "Lessons Learned from the Crystal River Transient of February 26, 1980Correcting Atmospheric Dump Valve Opening upon Loss of Integrated Control System Power," May 23, 1980. [8009150079]
Page Last Reviewed/Updated 07/10/2025