Title 10 of the CFR, Part 50.65(a)(4) requires, in part, that before performing maintenance activities the licensee shall assess and manage the increase in risk that may result from the proposed maintenance activities. Wolf Creek Procedure APF
22B-001, Safety Function Status and Assessment Sumary, revision 3, requires that two or more
steam generators have greater than 66 percent wide-range water level to be credited for core
decay heat removal risk during Mode 5. Otherwise, the assessment escalates risk due to the absence of one method core
decay heat removal. Procedure APF
22B-001 is required to be performed daily. Contrary to the above, on February 6, 2012, the licensee failed to assess risk by identifying entry into a Yellow shutdown risk assessment for core
decay heat removal due to three of four
steam generators being drained to less than 66 percent wide range level. Specifically, while performing the daily shutdown risk assessment, operators failed to identify that planned work to drain and refill the
steam generators for cold wet layup chemistry control was to occur on several
steam generators simultaneously. Concurrently, the
reactor coolant system power operated relief valves were unavailable for feed and bleed, another method of decay removal. Operators recognized the elevated risk after
8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> with three
steam generators being drained below 66 percent water level. This finding is more than minor because it is associated with the equipment performance attribute of the
Mitigating Systems Cornerstone and adversely affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to
initiating events to prevent undesirable consequences (i.e., core damage). Specifically, operators failed to identify that they had crossed a shutdown risk management threshold, from Green to Yellow. A Region IV senior reactor analyst verified that the finding was of very low safety significance (Green) and the delta-CDF was less than
1E-6. The licensee has entered this issue into their corrective action program as condition report 48775.
