05000400/LER-2010-003
| Harris Nuclear Plant - | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4002010003R00 - NRC Website | |
EVENT DESCRIPTION
The Refueling Water Storage Tank (RWST) is seismically-qualified, safety-related and within the scope of plant Technical Specifications (TS). Plant design includes the capability of using the Fuel Pool Purification System for cleanup of the RWST. The Fuel Pool Purification System is a non-safety, non-seismic system and is separated from the RWST by a normally closed, safety-related, manually-operated boundary valve 1CT-23.
On March 3, 2006, procedure OP-116.01, Fuel Pool Purification System, was revised to permit purification of the RWST in plant operating Modes 1-4 without declaring the RWST inoperable and entering the TS Limiting Condition for Operation (LCO) action statement. The alignment for purification of the RWST opens manual valve 1CT-23, RWST to the Spent Fuel Pool (SFP) Pump suction valve, which un-isolates safety and seismic piping from non-safety piping. The 10CFR50.59 evaluation supporting the procedure revision credited a manual action to shut 1CT-23 to maintain operability of the system.
The evaluation concluded that a license amendment was not required to implement the procedure change.
In 2010, the NRC Resident Inspector at Harris Nuclear Plant (HNP) questioned this practice. HNP placed a caution tag on valve 1CT-23 to prevent operation of the valve until the question was resolved. A discussion was held between the plant staff and the NRC Nuclear Reactor Regulation staff. During that discussion, plant staff realized that HNP should have obtained prior approval from the NRC to perform this activity without entering the TS LCO action statement. The condition was entered into the corrective action program and the procedure was revised to prevent the activity without entering the action statement.
TS LCO 3.1.2.6 Action (b) requires "with the RWST inoperable, restore the tank to Operable status within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or be in at least hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />." Since the RWST was not declared inoperable, TS LCO actions were not entered. This resulted in a condition prohibited by TSs. Purification of the RWST while online in Modes 1-4 from August 16, 2007, through August 16, 2010, occurred for approximately 91 hours0.00105 days <br />0.0253 hours <br />1.50463e-4 weeks <br />3.46255e-5 months <br /> in 2008, 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> in 2009, and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in 2010.
SAFETY CONSEQUENCES
Sensitivity calculations show that with the RWST considered out of service during the cleanup period (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) the increase in core damage frequency due to a seismic event is 1.50E-8/yr. The result is considered very low risk.
CAUSE OF EVENT
A 10CFR50.59 evaluation failed to identify that opening valve 1CT-23, RWST to SFP pump suction valve, when purifying the RWST online would require declaring the RWST inoperable regardless of what controls could be put into place to close the valve. Ambiguous procedural guidance resulted in a misinterpretation of requirements when performing the 10CFR50.59 evaluation for procedure OP-116.01.
CAUSE OF EVENT (continued) NEI 96-07 Revision 1 states: Although this criterion allows minimal increases, licensees must still meet applicable regulatory requirements and other acceptance criteria to which they are committed (such as contained in regulatory guides and nationally recognized industry consensus standards, e.g., the ASME B&PV Code and IEEE standards). Further, departures from the design, fabrication, construction, testing and performance standards as outlined in the General Design Criteria (Appendix A to 10 CFR 50) are not compatible with a "no more than minimal increase" standard.
Because the RWST is required to be seismically-qualified, opening 1CT-23 to connect the Fuel Pool Purification System (non-seismic) to the RWST resulted in a deviation from GDC 2. The change should have been considered "more than a minimal increase" which requires prior NRC approval to perform the activity.
CORRECTIVE ACTIONS
Immediate Corrective Actions
Revised procedure OP-116.1, Fuel Pool Purification System, to remove the capability to purify the RWST in Modes 1-4.
Actions to Prevent Recurrence Clarify procedural guidance regarding the impact of proposed activities on the design and licensing bases.
PREVIOUS SIMILAR EVENTS
On August 1, 1996, HNP personnel identified, via a review of industry operating experience, a "condition outside the design basis". This condition was that the RWST had been connected to non-seismically qualified piping (non-seismic piping under consideration was the purification system piping and piping leading to the hydrostatic test pump). HNP reported this event to the NRC in Licensee Event Report (LER) 96-13. The cause of this LER was determined to be a failure to reconcile operating procedure lineups with the plant design basis during original procedure development. Corrective actions from that LER included placing administrative controls on ICT-23 by locally verifying ICT-23 shut as an immediate action and ensuring procedure requirements do not permit opening without declaring the LCO. In 2006, HNP staff concluded that subsequent changes to the industry 50.59 process under NEI 96-07 provided additional flexibility such that prior NRC approval for the activity was no longer needed. This error resulted in not entering the Technical Specification Limiting Condition for Operation action statemtent during the purification activity, which is a condition not allowed by Technical Specifications and requires this Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(i)(B).