1/4: A little light reading for your weekend: @NRCgov has released the first installment of its mammoth, decade-long "Level 3" Probabilistic Risk Assessment study. nrc.gov/docs/ML2206/ML…. It is seeking public comment by June 21. nrc.gov/reading-rm/doc… 2/4: The bottom line: the risk of a large, #Fukushima-like radiological release from the two-unit "reference" plant due to "internal" accidents and internal floods only is about 1 in 11,000 to 1 in 29,000 per critical-year, depending on whether FLEX measures are credited.

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…

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.