05000305/LER-2006-005

LER-2006-005,

Docket Number
Event date:	05-30-2006
Report date:	06-06-2007
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
3052006005R01 - NRC Website

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Kewaunee Power Station 05000305 YEAR

Event Description:

On 5/30/2006, with Kewaunee Power Station at 100 percent power, train B of the service water (SW) system was determined to be inoperable due to service water pump [P] B1 inoperability. SW pump bearing lube water is normally supplied from a well water source, (plant equipment water (PEW)), with a backup safety-related supply from the discharge of the SW pumps. At 09:34, when PEW was isolated for maintenance, the backup safety-related bearing lube water regulator for SW pump B1 did not provide any lube water pressure or flow.

Bearing lube water was immediately reestablished from PEW, and SW pump B1 and train B were declared inoperable. Maintenance was performed, SW pump B1 was returned to service, and both the pump and train B were declared operable at 15:31 on 5/30/2006.

The regulator was last determined to be operable during rotating equipment checks at 21:07 on 4/16/2006.

Thus, the inoperability is assumed to have existed since that time. During that 43.5 days of inoperability, the plant was at power twice (once for 10 days and once for 8 days). Also during that time, various Train A engineered safety features equipment was concurrently inoperable.

The SW system consists of two trains with two pumps per train. The SW system is designed to provide redundant cooling water supplies to the containment fan coil units [FCU], emergency diesel generators [DG], air compressors [CMP], component cooling heat exchangers [HX], safety injection pump stuffing boxes and coolers [CLR], and control room air conditioners [ACU]. The SW system also provides a backup supply source to auxiliary feedwater and other safety related systems.

PEW is supplied through filter media (cartridge filters) [FLT] and a single pressure regulator [RG] set at 28 psig to all four SW pumps downstream of their individual backup safety-related pressure regulators. The backup safety-related supplies are from the discharge of each SW pump through filter media (CUNO filters) and a separate pressure regulator set at 10 psig to the pump bearings. When the PEW source is lost, the backup safety-related supply automatically provides bearing lube water.

The SW pump technical manual states that positive bearing lube water flow must be maintained at all times when the pump is operating. The vendor has stated that any flow is sufficient to meet this requirement.

Procedurally, if bearing lube water flow is 0.0 gpm or lube water pressure is 0.0 psig, the affected SW pump is stopped and declared inoperable.

Analysis has determined that the direct cause of the safety-related bearing lube water flow disruption for SW pump B1 was the service water backup lube water supply pressure regulator stem sticking in the stem guide bushing as a result of contaminants in the PEW adhering to the stem. Inspection of the PEW system found the filter tanks and internal components severely corroded allowing water and contaminants to bypass the cartridge filters. This condition developed because the original PEW cartridge filter retaining cup material was not suitable for the application. The affected materials were effectively exposed to highly oxygenated water in a stagnant environment, a condition very conducive to corrosion of the carbon steel retaining cups.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Kewaunee Power Station 05000305 YEAR

Event Analysis:

This is being reported in accordance with 10 CFR 50.73(a)(2)(v)(B) & (D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat & mitigate the consequences of an accident", and 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications.

Technical Specification (TS) 3.3.e.1.A.1 states:

The reactor shall not be made critical unless the following conditions are satisfied, except for LOW POWER PHYSICS TESTS and except as provided by TS 3.3.e.2.

A.� TWO service water trains are OPERABLE with each train consisting of:

1. TWO service water pumps Technical Specification 3.3.e.2 states:

During power operation or recovery from an inadvertent trip, ONE service water train may be inoperable for a period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If OPERABILITY is not restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, then within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> action shall be initiated to:

- Achieve 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 />.

- Achieve HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

- Achieve and maintain Reactor Coolant System Tavg less than 350 degrees F by use of alternate heat removal methods within an additional 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

On a semi-monthly frequency, PEW was procedurally isolated to each SW pump for a short period of time, and the backup safety-related source verified to assume the supply. Prior to this event, the last time this was performed for SW pump B1 was at 21:07 on 4/16/06 (43.5 days prior). The interim semi-monthly checks were not performed due to an unexpected plant shutdown and restart. Since the backup lube water regulator for SW pump B1 is last known to have functioned properly on 4/16/06, the pump and train were inoperable from that time until operability was restored on 5/30/06.

During the 43.5 day period of SW Train B inoperability, the plant was critical twice: first from the initial inoperability at 21:07 on 4/16/06 until 20:36 on 4/26/06 (239.5 hrs), and again from 21:26 on 5/22/06 until operability was restored at 09:34 on 5/30/06 (180.1 hrs). Both of these periods of criticality exceeded the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation of TS 3.3.e.2. The plant restart on 5/22/06 with an inoperable SW train violated TS 3.3.e.1.A.1.

Since components supported by an inoperable SW train are also inoperable, power operation and the restart were performed in violation of various additional Technical Specifications.

Also during the 43.5 day period, various Train A engineered safety features equipment was concurrently inoperable which, (since components supported by an inoperable SW train are also inoperable), violated the individual equipment Technical Specifications.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Kewaunee Power Station 05000305 YEAR � SEQUENTIAL I REVISION Technical Specification 3.0.c states:

When a LIMITING CONDITION FOR OPERATION is not met, and a plant shutdown is required except as provided in the associated ACTION requirements, within one hour action shall be initiated to place the unit in a MODE in which the Specification does not apply by placing it, as applicable, in:

1. 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 />, 2. At least HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and 3. At least COLD SHUTDOWN within the subsequent 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

Each of the above listed failures to meet LCOs should have resulted in entry into TS 3.0.c. These entries did not occur.

With one SW train inoperable, procedural requirements exist to apply the TS LCO for service water system and 1) Test the other diesel generator daily to ensure operability every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and 2) Verify engineered safety features associated with the other diesel generator are operable. These actions were not taken.

Safety Significance:

The total Incremental Core Damage Probability (ICDP) is 4.8E-7, which is categorized in the NRC Significance Determination Process as a very low risk.

Cause:

The filter retaining cup material design was not suitable for the application and maintenance of the PEW filters was inadequate. The affected materials were effectively exposed to highly oxygenated water in a stagnant environment, a condition very conducive to corrosion of the carbon steel retaining cups. This design issue in conjunction with inadequate maintenance practices led to the regulator stem sticking in the stem guide bushing as a result of iron particles.

Corrective Actions:

The following corrective actions were taken to address the PEW cartridge filter vessel design issue:

• New PEW cartridge filter vessels have been installed. These vessels have internals with stainless steel bottom retaining cup and filter holders, and incorporate 5 micron or smaller filters.

• A preventative maintenance task was created for changing the PEW filters.

Additionally, before the PEW to service water supply is returned to service, the supply piping from the PEW system will be replaced. This will effectively eliminate any sediment remaining in the lines.

Similar Events:

None.