05000255/LER-2008-002, Breaker Cubicle Switch Failure Results in High Pressure Safety Injection Pump Inoperability

Breaker Cubicle Switch Failure Results in High Pressure Safety Injection Pump Inoperability

ML081480505
Person / Time
Site:	Palisades
Issue date:	05/27/2008
From:	Schwarz C Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 08-002-00
Download: ML081480505 (6)

LER-2008-002, Breaker Cubicle Switch Failure Results in High Pressure Safety Injection Pump Inoperability

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
2552008002R00 - NRC Website

text

Entergy Nuclear Operations, lnc.

Palisades Nuclear Plant 27780 Blue Star Memorial Highway Covert, MI 49043 Tel269 764 2000 May 27,2008 10 CFR 50.73(a)(2)(i)(B)

I 0 CFR 50.73(a)(2)(v)

U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Palisades Nuclear Plant Docket 50-255 License No. DPR-20 Licensee Event Report 08-002, Breaker Cubicle Switch Failure Results in High Pressure Safety lniection Pump Inoperability

Dear Sir or Madam:

Licensee Event Report (LER)08-002 is enclosed. The LER describes a breaker cubicle switch failure resulting in high pressure safety injection pump, P-66A, inoperability. The occurrence is reportable in accordance with 10 CFR 50,73(a)(Z)(i)(B) as a condition prohibited by the Technical Specifications, and 10 CFR 50.73(a)(Z)(v) as a condition that could have prevented fulfillment of a safety function.

Summarv of Commitments This letter contains no new commitments and no revision to existing commitments.

Z Site Vice President Palisades Nuclear Plant Enclosure CC Administrator, Region Ill, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USNRC

ENCLOSURE 1 LER 08-002, Breaker Cubicle Switch Failure Results in High Pressure Safety Injection Pump Inoperability 4 Pages Follow

Eshmred burden per response to comply wrth tiGs mandatwy infwmallon cdlect~on request 80 h r s Reporld lewrls learned are ~ncorporated lnto the licenwng process and fed back :o LICENSEE EVENT REPORT (LER) 20.2203(a)(2)(iii) 50.36(~)(2)

On March 26, 2008, with the plant in Mode 1 at 100% power, during planned maintenance on high pressure safety injection (HPSI) pump P-66A, operators experienced difficulty in removing the P-66A 2400VAC breaker 152-207 from its cubicle. A mechanism-operated cell (MOC) switch operator (bayonet) located inside the breaker cubicle was found with two broken connections.

The condition of the MOC switch bayonet would have prevented operating a contact that provides a permissive to open H PSI subcooling control valve CV-3071, there by rendering P-66A inoperable. It was concluded that the MOC switch bayonet failed when breaker 152-207 operated on January 3,2008. The MOC switch bayonet was replaced on March 26,2008.

The cause was determined to be that the MOC switch bayonet design is marginal for the force applied by the stored energy vacuum breaker 1 52-207. The contributing cause is a failure to validate that the MOC switch used during manufacturer testing matched the switches installed at The opposite train MOC switch bayonet was inspected and no damage was found. Subsequently NRC FORM 366 (S-ZW7)

EVENT DESCRIPTION

On March 26, 2008, with the plant in Mode 1 at 100% power, during planned maintenance on higt pressure safety injection (HPSI) pump P-66A [P; BQ], operators experienced difficulty in rernovin~

the P-66A breaker 152-207 152; EB] from its cubicle. A mechanism-operated cell (MOC) switch operator (bayonet) 133; EB] located inside the breaker cubicle, was found with two broken brazed or welded connections. The condition of the MOC switch bayonet would not have prevented proper operation of breaker 152-207. However, it would have prevented operating a contact that provided a permissive to open HPSl subcooling control valve CV-3071 [V; BQ] during a recirculation actuation signal (RAS). Opening CV-3071 on a RAS provides P-66A with adequate net positive suction head. Failure of the contact's ability to change states, which disabled automatic opening of CV-3071, rendered P-66A inoperable.

P-66A 2400VAC breaker 152-207 was operated on January 3,2008, during performance of a Technical Specification (TS) surveillance procedure. P-66A was successfully started and stopped twice. It was concluded that during the last breaker open operation on January 3, 2008, the MOC switch bayonet failed. This rendered P-66A inoperable for approximately 83 days, from 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br /> on January 3,2008, to 2058 hours0.0238 days <br />0.572 hours <br />0.0034 weeks <br />7.83069e-4 months <br /> on March 26,2008, when P-66A was returned to an operable condition following completion of maintenance.

TS Limiting Condition for Operation (LCO) 3.5.2 requires two emergency core cooling system (ECCS) trains to be operable. An inoperable P-66A results in one inoperable train of ECCS. It was not recognized that P-66A was inoperable until March 26, 2008. Therefore, the 72-hour completion time of TS 3.5.2 required action B.l for restoring ECCS trains to operable status and the subsequent completion times for TS 3.5.2 required actions C.l and C.2 were not met. This condition is reportable in accordance with 10 CFR 50m73(a)(2)(i)(B) as a condition prohibited by TS.

During the period of time P-66A was inoperable, the opposite train HPSl pump P-668 was inoperable on four occasions for maintenance and testing, for a total of about five and a half hours. On these four occasions both trains of ECCS were inoperable. TS 3.5.2 required action D.l requires immediate entry into LC0 3.0.3 when less than 100% of the required ECCS flow available. The completion time was not met on the four occasions that two ECCS trains were inoperable. This represents a condition prohibited by TS. This condition is also reportable in accordance with 10 CFR 50m73(a)(2)(v)(A),

(B), and (D) as a condition that could have prevented fulfillment of a safety function. This condition represents a safety system function failure.

CAUSE OF THE EVENT

The MOC switch operator (bayonet) in the breaker 152-207 cubicle is original plant equipment LICENSEE EVENT REPORT (LER) supplied with the Allis Chalmers type "Dl' switchgear [SWGR]. The MOC switch is an auxiliary contact switch assembly mounted in the switchgear breaker cubicle. A fork shaped lever on the circuit breaker engages the MOC switch bayonet and rotates the switch when the breaker opens and closes. The same type of MOC switch is installed in all Palisades 2400VAC (busses 1 C, 1 D, and 1 E) and 41 6OVAC (busses 1 A, 1 B, 1 F, and 1 G) Allis Chalmers switchgear, except one breaker cubicle that does not contain a MOC switch. 2400VAC busses 1 C and 1 D supply engineered safeguards loads. Prior to 2003, the majority of breakers in busses 1 C and 1 D were solenoid operated. Between 1999 and 2004, breakers in buses 1 C and 1 D were replaced with stored energy vacuum breakers. Breaker 152-207 was replaced in February 2004 with a stored energy vacuum breaker. The closing times for the solenoid operated breakers were four-to-five times longer than the newer stored energy vacuum breakers. The stored energy breakers impart higher forces onto the bayonet. The higher forces led to the failure. A possible cause or contributing cause may be a deficiency in the braze or weld connections that failed.

The present switchgear manufacturer, Siemens, indicated that the MOC switch bayonet was redesigned in the 1980s to strengthen the bayonet. Siemens conducted endurance tests when the vacuum breaker model was designed. The endurance tests were done with the stronger MOC switch bayonet and not with the MOC switch bayonet that is in use at Palisades. The Palisades staff was unaware of the 1980s design change for strengthening the bayonet, and it was not identified during the purchasing of the stored energy breakers. Therefore, this is a contributing cause for the failure.

CORRECTIVE ACTIONS

The failed MOC switch bayonet was replaced.

The extent of condition (EOC) was addressed by inspection of the opposite train breaker's MOC switch bayonet. No damage was found on the opposite train bayonet. The MOC switch bayonets for safety busses 1 C and 1 D were subsequently inspected. One other breaker, 152-206 for low pressure safety injection pump P-67A, was found with one switch bayonet having a similar braze or weld broken, however, the switch performed no safety function. The breaker remained Entergy Nuclear Operations, Inc. plans to install higher strength MOC switch bayonets in busses 1 C and 1 D breaker cubicles and in other stored energy breaker cubicles by June 2009.

Interim corrective action to address the EOC includes monitoring the same type of MOC switch bayonets until they are replaced. Visual inspections will be done following breaker operation for the 2400VAC and 41 6OVAC switchgear equipped with the faster operating stored energy LICENSEE EVENT REPORT (LER)

ALISADES NUCLEAR PLANT

SAFETY SIGNIFICANCE

This event is considered to be of very low safety significance. In this condition, the failure disabled automatic opening of HPSI subcooling control valve CV-3071 and rendered P-66A inoperable. While automatic opening was defeated, the ability to manually open the valve from the control room was not impacted and the valve was available to perform its intended function.

Emergency Operating Procedure (EOP) Supplement 42, Pre and Post RAS [recirculation actuation signal] Actions, requires that P-66A be stopped if found operating with CV-3071 closed.

Subsequently, the EOP supplement allows manual starting of P-66A and manual alignment of CV-3071 if an additional HPSI pump is desired. Therefore, the condition did not result in the inability of P-66A to perform its required function.

The risk evaluation considered the periods when P-66B was inoperable while P-66A was in the discovered condition. The risk increase due to this combination is insignificant when compared to the risk increase due to the unavailability of P-66B alone.