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Allowing Risk
#1
Dave Lochbaum, Union of Concerned Scientists - Nuclear Leaks: The Back Story the NRC Doesn’t Want You to Know about Palo Verde http://www.allthingsnuclear.org/dlochbau...palo-verde

Excerpt:

"On December 23, 2016, and January 9, 2017, Differing Professional Opinions (DPOs) were initiated by member(s) of the NRC staff registering formal disagreement with NRC senior management’s plan to allow the 62-day EDG AOT for Palo Verde Unit 3. The initiator(s) checked a box on the DPO form to have the DPO case file be made publicly available (Fig. 1).

The DPO initiator(s) allege that the 62-day EDG AOT was approved by the NRC because the agency assumed that a loss of coolant accident simply would not happen. The DPO stated:

“The NRC and licensee ignored the loss of coolant accident (LOCA) consequence element. Longer outage times increase the vulnerability to a design basis accident involving a LOCA with the loss of offsite power (LOOP) event with a failure of Train A equipment.”

Palo Verde has two fully redundant sets of safety equipment, Trains A and B. The broken EDG provided electrical power (when unbroken) to Train B equipment. The 62-day EDG AOT was approved based on workers scurrying about to manually start combustible gas turbines and portable generators to provide electrical power that would otherwise be supplied by EDG 3B. The DPO stated:

“The Train B EDG auto starts and loads all safety equipment in 40 seconds. The manual actions take at least 20 minutes, if not significantly longer.”

Again, the rapid response is required to mitigate a loss of coolant accident that drains water from the reactor vessel. When water does not drain away, it takes time for the reactor core’s decay heat to warm up and boil away the reactor vessel’s water, justifying a slower response time.


The NRC staff considered a loss of coolant accident for the broken EDG at Cook but allegedly dismissed it at Palo Verde. Curious.

The DPO also disparaged the non-routine measures undertaken by the NRC to hide their deliberations from the public:
“The pre-submittal call occurred on a “non-recorded” [telephone] line. The NRC staff debated the merits of the call in a headquarters staff only discussion. Note that the Notice of Enforcement Discretion calls are done on recorded [telephone] lines.”
Pia
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