05000315/LER-2010-001

LER-2010-001, 1AB EDG Fuel Oil Transfer Pumps Inoperable

Donald C. Cook Nuclear Plant
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)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3152010001R00 - NRC Website

Conditions Prior to Event Unit 1 was in Mode 3. The initial event was ascending from Mode 3 to Mode 2 on April 9, 2010 at 0233, with 1 AB Emergency Diesel Generator (EDG) [EK] inoperable without meeting the provisions of Limiting Condition for Operation (LCO) 3.0.4.

Unit 2 was in Mode 1 at 100 percent reactor power.

Description of Event

Synopsis:

On April 23, 2010, at 2211 hours0.0256 days <br />0.614 hours <br />0.00366 weeks <br />8.412855e-4 months <br />, during a scheduled surveillance of Unit 1 AB Emergency Diesel Generator (EDG), the breaker for AB EDG Fuel Oil Transfer Pump No. 1 tripped when the pump 'attempted to start. AB EDG Fuel Oil Transfer Pump No. 2 had been previously removed from service for maintenance. Unit 1 AB EDG had been declared inoperable on April 23, 2010, at 2047 hours0.0237 days <br />0.569 hours <br />0.00338 weeks <br />7.788835e-4 months <br /> to perform the surveillance, and remained inoperable due to no available fuel oil transfer pump.

Investigation into the cause of the Fuel Oil Transfer Pump No. 1 breaker tripping identified that the power supply cable [CBL4] for AB EDG Fuel Oil Transfer Pump No. 1 had been mistakenly cut during a maintenance activity that was intended to cut and replace the power supply cable for Fuel Oil Transfer Pump No. 2, which had been out of service under clearance since March 7, 2010, to replace its degraded cable.

The power supply cable for AB EDG Fuel Oil Transfer Pump No. 1 was cut on April 8, 2010, sometime �

• between the hours of 1343 and 1707, the time-frame that the maintenance individual was signed onto the AB EDG Fuel Oil Transfer Pump No. 2 clearance.

Result:

From the time Unit 1 AB EDG Fuel Oil Transfer Pump No. 1 power cable was cut on April 8, 2010, to approximately 15 days later when the surveillance commenced on April 23, 2010, U1 AB EDG had been inoperable; however, the inoperability had not yet been recognized. Once the previous inoperability due to the cut power cable was recognized on April 25, 2010, AB EDG Fuel Oil Transfer Pump No. 1 cable repairs were made and U1 AB EDG was restored to operable status at 1643 hours0.019 days <br />0.456 hours <br />0.00272 weeks <br />6.251615e-4 months <br /> on April 29, 2010.

During the time of unrecognized inoperability, several equipment configurations and plant manipulations were conducted that were prohibited by Technical Specifications:

Unit 1 AB EDG (Train B) was inoperable for approximately 15 days, from April 8, 2010 to April 23, 2010, a time greater than the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by Technical Specifications (14 days are allowed when taking credit for the Supplemental Diesel Generators):

Unit 1 ascended from Mode 3 to Mode 2, and then from Mode 2 to Mode 1, both on April 9, 2010. This is contrary to LCO 3.0.4 for Mode change.

There were two periods of time that U1 CD EDG (Train A) was inoperable at the same time U1 AB EDG (Train B) was inoperable: 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> 36 minutes on April 14, 2010, and 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> 59 minutes on April 15, 2010. Both of these periods were greater than the 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> allowed by Technical Specifications.

Emergency Power (EP) was inoperable for 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br /> 7 minutes on April 20, 2010. This is longer than the 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> allowed by Technical Specifications.

Unit 1 Train B Reserve Feed [EA] was inoperable on April 21, 2010, for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 16 minutes. This is longer than the 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> allowed by Technical Specifications.

These conditions are being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), Operation or Condition Prohibited by Technical Specifications:

The two periods of time when Unit 1 EDGs were simultaneously inoperable are reportable in accordance with 10 CFR 50.73(a)(2)(v)(D), Event or Condition that Could Have Prevented Fulfillment of a Safety Function.

Cause of Event

An In-Depth Apparent Cause Evaluation analysis determined that the Apparent Cause of cutting the wrong power supply cable was that verification actions performed by electricians failed to verify the correct cable to be cut.

Contributing causes were: Incorrect labels, a difficult to read label, incorrect drawing, and using an instrument to check for voltage when no voltage should be expected.

These causes and associated corrective actions are complete and accurate pending final approval of the cause evaluation. If any significant differences are identified upon final approval, an LER supplement will be submitted.

Analysis of Event

In this event, the Unit 1 AB EDG, a Unit 1 AC electrical power source, was disabled from design basis capability

• due to maintenance activity inadvertently disabling both fuel oil transfer pumps for this single engine. With no functioning fuel oil transfer pumps, the Unit 1 AB EDG fuel oil day tank [DC] [TK], holding enough fuel oil sufficient for only a short period of full load operation, was the only source of fuel oil available to the AB EDG. For most of the duration (from 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on April 8 to 2238 hours0.0259 days <br />0.622 hours <br />0.0037 weeks <br />8.51559e-4 months <br /> on April 23, 2010) the engine was not operable, it was capable of automatic starting and operation at full load for a short period, after which time it would have exhausted its day tank fuel oil supply. After it was recognized that no long term source of fuel was available for the engine, at 2238 hours0.0259 days <br />0.622 hours <br />0.0037 weeks <br />8.51559e-4 months <br /> on April 23, 2010, the engine was secured until a fuel oil transfer pump was again available at 1320 on April 29, 2010. During the Unit 1 AB EDG inoperability period Unit 1 was initially in Mode 3 for approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, Mode 2 for approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, and for the remainder of the period the.unit was in Mode 1, following a refueling outage.

During the period that the Unit 1 AB EDG was not operable, other electrical sources were also not available. The specific instances are, surveillance testing carried out on the remaining EDGs on both units resulting in the tested EDG to also be unavailable while clearing cylinders prior to starting the engine. However, these were limited time periods on the order of 40 minutes or less, and the engines are readily recoverable by closing petcocks [VTV] and resetting the associated engine lock-out relay [RLY] on the control room panel near the engine controls, all of which can be accomplished in several minutes by the crew running the surveillance. There was a planned outage on Emergency Power (EP), the qualified alternate offsite source, rendering both the 69kV supply to EP, and the Supplemental. Diesel Generators (SDGs) [DG] supply to EP, unavailable. In this case, EP was unavailable for approximately 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />, and the SDGs were unavailable for approximately an additional 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> beyond the.initial 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br />. On a different occasion, cable degradation on Unit 2 resulted in differential protection features [87] to interrupt power to the Unit 1 and 2 Train B Reserve Auxiliary Transformers (RATs) [XFMR], the preferred qualified offsite circuit to Train B. The Unit 1 Train B RAT was restored to available status in less than 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, after NRC'FORM 366A (9-2007) switching isolated the Unit 2 Train B RAT for repair. At no time were both the Train B preferred and alternate qualified offsite power sources unavailable.

Unit 1 Train A Engineered Safety Features (ESF) equipment was operable the entire period the Unit 1 AB EDG was inoperable except for approximately 9 minutes on April 15, 2010, during a stroke test on the Unit 1 East Residual Heat Removal (RHR) train heat exchanger RHR outlet valve [BP] [FCV]. During the Unit 1 AB EDG inoperability period, two sources of offsite AC power and the SDGs were available for Train A ESF equipment in addition to the Train A, Unit 1 CD EDG, except during the EP and SDG planned outage that took place on April 20, 2010.

During the Unit 1 AB EDG inoperability, no challenges occurred to the offsite power grid from either weather or load that affected the availability of power to the Donald C. Cook Nuclear Plant (CNP) switchyards or operation of the CNP units.

While not meeting design basis criteria, this event did not pose a significant risk in that:

1 — An AC source was available to the Unit 1 Train B equipment at all times while the Unit 1 AB EDG was unavailable. For most of the time period, except when the RAT, or EP and the SDGs, were unavailable, more than one AC power source was available for Train B use (i.e., RAT, EP, and SDG).

2 — No challenges to unit operation or grid condition occurred while the Unit 1 AB EDG was unavailable.

3 — With exception of a short period of time (9 minutes), both Train A and B ESF equipment were available while the Unit 1 AB EDG was unavailable.

4 — A Probabilistic Risk Assessment evaluation of risk metrics based on this event indicate that they are within the limits defining low risk (i.e., ICCDP

Corrective Actions

Completed:

A clearance was placed on the AB EDG Fuel Oil Transfer Pump No. 1 power supply; the Motor Control Center breaker and power cable were replaced.. The new cable allowed AB EDG Fuel Oil Transfer Pump No. 1 and U1 AB EDG to be restored to operable status at 1643 on April 29, 2010. A new cable for AB EDG Fuel Oil Transfer Pump No. 2 was also installed, and the difficult-to-read cable, labels have been replaced.

Planned:

The incorrect drawings will be revised to accurately show pull boxes [PBX] for cables 1-8505R-1 and 1-8506R-1, the Unit 1 AB EDG Fuel Oil Transfer Pump power supply cables.

Electrical Maintenance will design and implement techniques (e.g. use a circuit / signal tracer, hand-over-hand walk down, etc.) to positively identify cables in the field before cutting or pulling them during planned replacement activities.

Previous Similar Events

Licensee Event Reports (LERs) for both units for the past three years were reviewed for similar events.

There are no LERs related to the simultaneous inoperability of two power sources.