I noticed there was a lot of interest in #Pennsylvania in my tweet about the inoperable high-pressure coolant injection (HPCI) system at the Limerick-1 #nuclear reactor. The HPCI is needed to provide emergency makeup water if a small-break loss-of-coolant accident occurs.
The Limerick plant was previously allowed to operate for 14 days without a functioning HPCI. Last year @NRCgov approved a "risk-informed" license amendment allowing outages of HPCI or other emergency systems of up to 30 days. For more details, please see nrc.gov/docs/ML2003/ML…
The basic logic is that the likelihood of such an accident occurring is so small that the increased risk to the public of the outage extension is also small. Plant owners must demonstrate this using detailed risk calculations.
In general, this could make sense. However, such risk assessments involve many uncertainties and some guesswork. The concern is that these analyses may underestimate the risk of operating nuclear plants with emergency safety systems out of service.
I don't believe there is cause for panic. But I do believe that members of the public near these plants, who may have a different appetite for risk than the plant owners, should have more of a say in such decisions.
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To put to rest the erroneous claim that a reactivity excursion and sodium boiling can't occur in a fast reactor, please see the following results for a transient with EM pump failure from the @NRCgov preapplication safety review for the PRISM reactor, the model for the Natrium.
1. Positive sodium density reactivity increase versus negative reactivity from core expansion.