05000388/LER-2001-004

LER-2001-004,

Docket Number
Event date:	03-20-2001
Report date:	05-18-2001
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
3882001004R00 - NRC Website

EVENT DESCRIPTION

On March 20, 2001, at 0803 hours0.00929 days <br />0.223 hours <br />0.00133 weeks <br />3.055415e-4 months <br />, with Unit 2 in Condition 5 (Refueling) at 0 percent power, both of the in-series Control Rod Drive System (CRD) (EIIS Code: AA) Seismic Island Check Valves (non 10CFR50, Appendix J, Option B valves) failed their leakage acceptance criteria. The Minimum Pathway leak rate was 858 ml/hr as compared to the acceptance criteria of 508 ml/hr. The valves were disassembled and inspected. The valve internals (body and disc) and the seating surfaces had a light coating of oxide on them.

CAUSE OF EVENT

The cause of the failure was oxide buildup on the valve internals and seating surfaces. This buildup resulted in the valve disc not seating properly.

REPORTABILITY/SAFETY SIGNIFICANCE

The CRD Seismic Island in each unit is designed to provide a 30-day water seal in the CRD supply line post-LOCA. The CRD Seismic Island eliminates a potential water bypass pathway from the CRD insert/withdrawal lines to the CRD supply line. The CRD supply line originates outside secondary containment and the CRD insert/withdrawal lines enter primary containment. In addition, the Seismic Island prevents the CRD purge supply lines to the reactor recirculation pumps from becoming an air bypass leakage pathway. During the performance of the leak rate testing in Unit 2, both CRD Seismic Island Lift Check Valves had leakage past the valve seat that exceeded the acceptance criteria of 508 ml/hr. The Minimum Pathway leak rate was 858 ml/hr. This constituted a condition that involves a degradation of secondary containment bypass leakage for Unit 2. This event was determined to be reportable in accordance with 10CFR50.73(a)(2)(ii)(A). If a Design Basis Accident-Loss of Coolant (DBA- LOCA) with fuel failure had occurred in Unit 2, the CRD Seismic Island would not have been able to provide the 30-day water seal. This would have resulted in an increase in offsite dose. However, the increase in dose would not have exceeded either 10CFR100 or 10CFR50, Appendix A, GDC 19 dose limits. Therefore, there were no safety consequences or compromise to the public health or safety as a result of not having the 30-day water seal.

These check valves had been scheduled for replacement during this Unit 2 refueling outage due to problems seen in the Unit 1 CRD Seismic Island Check Valves. The Unit 1 CRD Seismic Island Check Valves were replaced with in-line check valves during the refueling outage in the spring of 2000.

In accordance with the guidelines provided in NUREG-1022, Revision 2, Section 5.1.1, the required submission date for this report was determined to be May 21, 2001.

CORRECTIVE ACTION

The carbon steel CRD Seismic Island Lift Check valves in Unit 2 have been replaced with stainless steel in-line check valves which will reduce corrosion.

ADDITIONAL INFORMATION

Past Similar Events: � LER 98-007-00, Docket No. 387/License No. NPF-14 Failed Component: � Check Valves: 246027 and 246028 Manufacturer: � Anchor Darling