05000263/LER-2004-001, Regarding Both Control Room Ventilation Trains Inoperable Due to Failure of Seal on the In-Service Ventilation Train Compressor

Regarding Both Control Room Ventilation Trains Inoperable Due to Failure of Seal on the In-Service Ventilation Train Compressor

ML042640529
Person / Time
Site:	Monticello
Issue date:	09/20/2004
From:	Thomas J. Palmisano Nuclear Management Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-04-054 LER 04-001-00
Download: ML042640529 (5)

LER-2004-001, Regarding Both Control Room Ventilation Trains Inoperable Due to Failure of Seal on the In-Service Ventilation Train Compressor

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(B)
2632004001R00 - NRC Website

text

Monticello Nuclear Generating Plant Operated by Nuclear Management Company, LLC September 20, 2004 L-MT-04-054 10 CFR Part 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Monticello Nuclear Generating Plant Docket No. 50-263 License No. DPR-22 LER 2004-001, Both Control Room Ventilation Trains Inoperable due to Failure of Seal on the In-Service Ventilation Train Compressor A Licensee Event Report for this occurrence is attached.

This letter makes no new commitments or changes any existing commitments.

Contact Ron Baumer at (763) 295-1357 if you require further information.

Thomas J. Palmisano Site Vice President, Monticello Nuclear Generating Plant Nuclear Management Company, LLC Enclosure cc:

Administrator, Region III, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC 2807 West County Road 75

• Monticello, Minnesota 55362-9637 Telephone: 763-295-5151

• Fax: 763-295-1454

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (6-2004)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB NO. 3150-0104 EXPIRES 6-30-2007

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME (1)

DOCKET NUMBER (2)

PAGE (3)

Monticello Nuclear Generating Plant 05000263 1 of 4 TITLE (4)

Both Control Room Ventilation Trains Inoperable due to Failure of Seal on the In-Service Ventilation Train Compressor EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MO DAY YEAR YEAR SEQUENTIAL NUMBER REV NO MO DAY YEAR FACILITY NAME DOCKET NUMBER 05000 07 21 2004 2004

- 001

- 00 09 20 2004 FACILITY NAME DOCKET NUMBER 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) (11)

MODE (9)

N 20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(ix)(A)

POWER 20.2201(d) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LEVEL (10) 100 20.2203(a)(1) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 73.71(a)(4) 20.2203(a)(2)(i) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(5) 20.2203(a)(2)(ii) 50.36(c)(2) 50.73(a)(2)(v)(B) 20.2203(a)(2)(iii) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 20.2203(a)(2)(iv) 50.73(a)(2)(i)(A)

X 50.73(a)(2)(v)(D) 20.2203(a)(2)(v) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(C) 50.73(a)(2)(viii)(A) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(B)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Area Code)

Ron Baumer 763-295-1357 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX B

VI SEAL C147 Yes SUPPLEMENTAL REPORT EXPECTED (14)

MONTH DAY YEAR YES (If yes, complete EXPECTED SUBMISSION DATE).

X NO EXPECTED SUBMISSION DATE (15)

ABSTRACT On July 21, 2004 while the B train of Control Room Ventilation was out-of-service for maintenance, the A train tripped due to a compressor seal failure. This rendered both trains of Control Room Ventilation inoperable. The B train of Control Room Ventilation was restored to service within an hour. The A Train compressor seal was replaced on July 23, 2004 restoring both trains to operable status. The cause of the A Train seal failure was that the seal face cracked when the compressor started.

In accordance with 10 CFR 50.72 (b)(3)(v)(D), Event or Condition that could have Prevented Fulfillment of a Safety Function, an 8-hour event notification was made to the USNRC due to the loss of both trains of CRV, which are required to mitigate the consequences of an accident.

OTHER Specify in Abstract below or in NRC Form 366A NRC FORM 366 (7-2001) U.S. NUCLEAR REGULATORY COMMISSION (1-2001)

LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL NUMBER REVISION NUMBER Monticello Nuclear Generating Plant 05000263 2004 001 00 2 of 4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)

Description

While operating at 100% power, at 4:02 am on July 21, 2004 the A Control Room Ventilation (CRV) system1 (V-EAC-14A) was placed in service, so that B CRV System (V-EAC-14B) could be removed from service for planned maintenance. At 4:20 am V-EAC-14B was removed from service. At 5:12 am the V-EAC-14A ventilation system compressor2 tripped. Operations personnel investigated the cause of the trip and noted an oil mist spraying out of the V-EAC-14A compressor mechanical seal3 area. Operations placed V-EAC-14B back in service at 5:45 am. The compressor seal on V-EAC-14A was replaced and V-EAC-14A was restored to an operable status at 9:55 am on July 23, 2004.

All Technical Specification requirements were met during this event.

The seal that failed was a Carrier4 Model 5F40-276.

Event Analysis

The CRV System provides air conditioning and heating as required to maintain a suitable environment in the main control room. During a high radiation event, the CRV System continues to operate. The Monticello Technical Specifications contain operability requirements for the CRV system.

In accordance with 10 CFR 50.72 (b)(3)(v)(D), Event or Condition that could have Prevented Fulfillment of a Safety Function, an 8-hour event notification was made to the USNRC, due to the loss of both trains of CRV, which are required to mitigate the consequences of an accident. Per 10 CFR 50.73 (a)(2)(v)(D), a Licensee Event report is required for this event.

The event is classified as a safety system functional failure.

Safety Significance

The safety significance of the seal failure on V-EAC-14A was low. This was attributed to V-EAC-14B being available to be placed in service within one hour following the V-EAC-14A compressor seal failure. A review of Control Room Logs for July 21, concluded that while there was a slight temperature increase in the control room no temperature limits were exceeded.

A probabilistic risk analysis evaluated the risk associated with a compressor seal failure on one division of the CRV while the redundant train was removed from service. The assessment was conservatively performed by assuming the complete unavailability of both CRV trains rather than the actual case in which the operating train had only lost air conditioning capability. Control room habitability is potentially challenged during either a radiological event, or a toxic chemical event upon the loss of CRV function.

It is highly unlikely that control room habitability would be challenged by radiological conditions unless a significant core damage event and subsequent radioactive release from containment had already 1 EIIS System Code - VI 2 EIIS Component Code - CMP 3 EIIS Component Code - SEAL 4 Manufacturer Code - C147 U.S. NUCLEAR REGULATORY COMMISSION (1-2001)

LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL NUMBER REVISION NUMBER Monticello Nuclear Generating Plant 05000263 2004 001 00 3 of 4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17) occurred. This risk is then limited to values less than baseline Core Damage Frequency (CDF). The risk associated with accidental release of toxic chemicals was assessed as part of the Individual Plant Examination of External Events (IPEEE), and found to be small. Taking into account that the duration of CRV train unavailability was short, the risk imposed by having both trains of CRV inoperable for less than one hour is negligible.

Cause

The apparent cause of the seal failure on V-EAC-14A was infant mortality due to excessive manufacturing tolerances with the carbon insert in the seal. This is based on the seal failing the second time that V-EAC-14A was placed in service following seal replacement in conjunction with an alteration on the week of July 5, 2004. Prior to the seal replacement, there had been no seal performance issues.

Inspection of the failed seal concluded that the carbon insert, which serves as the rotating sealing surface, was relatively loose in its carrier. This condition, in conjunction with the axial and rotational forces imparted by the motor during compressor startup, apparently resulted in the carbon insert being cracked as a result of rotation within the carrier and the associated shock due to that rotation.

Discussions with the Machinist who performed the replacement of the seal on V-EAC-14A as a result of this failure indicate that the carbon insert in the replacement seal was significantly tighter in its carrier than the failed seal when the two were compared side by side. Discussions with the Machinist who last replaced the seal on V-EAC-14B in February 2004 indicate that the carbon insert on that seal was secure in its carrier during assembly. Inspections of remaining spare seals in warehouse stock determined that the carbon inserts vary in the degree of looseness within the carrier.

The V-EAC-14A compressor has operated satisfactorily since the seal replacement on July 23, 2004.

Review of operating logs shows that this train has been placed in and out of service five times since the replacement as a result of routine equipment rotation. The performance of the compressor since the seal replacement provides a reasonable degree of assurance that the compressor will continue to perform its function.

The V-EAC-14B compressor has operated satisfactorily since seal replacement in February 2004.

This train has been in and out of service numerous times as a result of routine equipment rotation. The trains are normally rotated on a weekly basis and the performance of the compressor since seal replacement provides a reasonable degree of assurance that it will continue to perform its function.

Corrective Action

1. Station personnel installed a new Carrier 5F40-276 type seal.

2. Station Engineering is investigating obtaining a different seal design for the CRV compressors.

3. Maintenance Planning personnel will capture the lessons learned from this event in the Equipment notebooks for both the CRV and Off-gas chilled water compressors. U.S. NUCLEAR REGULATORY COMMISSION (1-2001)

LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL NUMBER REVISION NUMBER Monticello Nuclear Generating Plant 05000263 2004 001 00 4 of 4 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)

4. Engineering and Maintenance will evaluate and disposition the spare replacement seals and spare compressors with regards to this event. An administrative hold has been placed on the spare seals and spare compressors pending the evaluation.

This failure has been captured in the station corrective action program for final resolution.

Failed Component Identification Carrier Model 5F40-276 compressor seal.

Previous Similar Event The extent of condition review found that the redundant compressor, V-EAC-14B, has the same seal design as V-EAC-14A compressor. The maintenance history for the V-EAC-14A and V-EAC-14B compressors over the past ten years shows that there have been a total of four additional seal performance issues. Three of the issues were small leaks that resulted in planned seal replacements.

The remaining one was on V-EAC-14B which was due to an over compression of the seal assembly.

The Off-gas storage system chilled water compressors utilize the same seal design. There have been no significant issues with the seals on the Off-gas chilled water compressors.

A search of the previous ten years of station Licensee Event Reports (LERs) did not find any previous LERs similar to the event in LER 2004-001.