10 CFR 50, Appendix B, Criterion V, requires in part that activities affecting quality shall be accomplished by documented instructions of a type appropriate to the circumstances. Contrary to this, on August 4, 2009, the licensee failed to accomplish documented work instructions contained in ECR50585 to install floor drain orifices to act as SPBs to protect SR components from the effect of a
HELB. NRC
IMC 0609.04 and NRC
IMC 0609 Appendix A screening determined that the finding represented a loss of the short term heat removal safety function within the
Mitigating Systems Cornerstone and required a detailed risk evaluation. A bounding analysis was performed by a regional
SRA using the
VC Summer
SPAR model. The finding was modelled as a Steam Line Break Outside Containment (SLBOC) initiating event assessment. A forty five day bounding exposure was utilized. No recovery was assumed. Equipment impacts from potential
HELBs were determined using the results from Gothic Analyses performed to assess the temperature, pressure and relative humidity increases in mild environment spaces in the Intermediate Building due to the various
HELB boundary breaches associated with the finding. For non-Loss of Offsite Power (
LOOP) conditions,
HELB impacts in mild areas were minimal. For
LOOP conditions, the
HELB was assumed to impact the chilled water system such that one train of safety related equipment was assumed failed as a bounding impact. The dominant sequence was a SLBOC initiator with a failure to isolate the break and a failure of high pressure injection impacted by loss of chilled water leading to loss of core heat removal. The risk evaluation determined that the finding represented a risk increase of < 1.0E-6/year, a GREEN finding of very low safety significance. The licensee has documented this problem in their
CAP as CR-16-04716.
