05000336/LER-2002-001, Two Reactor Coolant System Pressure Boundary Leakage Events on 02/19/2002 and 02/22/202
| ML021210508 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/16/2002 |
| From: | Schwarz C Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| B18624 LER-02-001-00 | |
| Download: ML021210508 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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 |
| 3362002001R00 - NRC Website | |
text
411'N" a r, '&
6 I 0 J1 Dominion-Dominion Nuclear Connecticut, Inc.
Millstone Power Station Rope Ferry Road Waterford, CT 06385 APR I 6 2002 Docket No. 50-336 B18624 RE: 10 CFR 50.73(a)(2)(i)(B)
U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Nuclear Power Station, Unit No. 2 Licensee Event Report 2002-001-00 Two Reactor Coolant System Pressure Boundary Leakage Events This letter forwards Licensee Event Report (LER) 2002-001-00, which documents two conditions that were discovered at Millstone Nuclear Power Station, Unit No. 2, on February 19, 2002, and February 22, 2002. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B).
There are no regulatory commitments contained within this letter.
Should you have any questions regarding this submittal, Mr. David W. Dodson at (860) 447-1791, extension 2346.
please contact Very truly yours, DOMINION NUCLEAR CONNECTICUT, INC.
Nula Statirz, Operntoa Nuclear Station Operaunls and Maintenance Attachment (1):
LER 2002-001-00 cc:
H. J. Miller, Region I Administrator R. B. Ennis, NRC Senior Project Manager, Millstone Unit No. 2 NRC Senior Resident Inspector, Millstone Unit No. 2
,I-x
Docket No. 50-336 B1 8624 Attachment I Millstone Nuclear Power Station, Unit No. 2 LER 2002-001-00
NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004 700 C O
, the NRC may not conduct or sponsor, (See reverse for required number of digits/characters for each block) and a person is not required to respond to, the information collection.
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Millstone Nuclear Power Station - Unit 2 05000336 1 OF 5
TITLE (4)
Two Reactor Coolant System Pressure Boundary Leakage Events EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED (8)
MO DAY YEAR YEAR SEQUENTIAL REV MO DAY YEAR FACILITY NAME
] DOCKET NUMBER NUMBER NO. 1 1
05000 02 19 2002 2002 -
001 00 04 16 2002 FACILITY NAME DOCKETNUMBER 02 22 2002 1
05000 OPERATING 4,5 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) (11)
MODE (9) 20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(ix)(A)
POWER 000 20.2201 (d) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(x)
LEVEL (10) 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)
__OTHER j
20.2203(a)(2)(iii) 50-46(a)(3)(ii) 50.73(a)(2)(v)(C)
Specify in Abstract below or 20.2203(a)(2)(iv) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) in (If more space is required, use additional copies of NRC Forn 366A) (17)
The actual safety significance of the cracking found in these heater sleeves is low. The cracks from PWSCC are very tight and the leakage rate was well below the allowable rate of 1 gpm for unidentified leakage. The situation at Millstone Unit No. 2 is similar to the cracking found at all other CE designed Nuclear Steam Supply Systems.
The potential worst case situation of a circumferential crack that could result in the complete loss of the penetration would be well below the limiting hole size, less than 3 inch, for a Small Break Loss of Coolant Accident, and is therefore bounded by the current analysis basis.
- 4.
Corrective Action
The leaking heater sleeves have been repaired by the use of Mechanical Nozzle Seal Assembly (MNSA) clamps.
The use of the clamps was approved by the Nuclear Regulatory Commission's (NRC) Safety Evaluation Report (SER), "Safety Evaluation of Relief Request RR-89-35, Temporary Installation of Mechanical Nozzle Seal Assemblies on Pressurizer Heater Nozzles, Millstone Nuclear Power Station, Unit No. 2," dated March 22, 2002 (TAC No. MB4039).
5. Previous Occurrences
The PWSCC of the Alloy 600 heater sleeves at Millstone Unit No. 2 is similar to the PWSCC that has been found in the Control Element/Rod Drive Mechanisms (CEDM/CRDMs) at various plants (including Millstone Unit No. 2) within the past year and a half. The materials of construction and the design with partial penetration J-groove welds for the pressurizer heater sleeves are the same as for the CEDM/CRDM and Incore Instrumentation (ICI) nozzles. Millstone Unit No. 2 has recently completed an inspection of 100% of the Reactor Vessel Head Penetrations (RVHPs), 69 CEDMs, 8 ICIs and the vent line, via Ultra Sonic to comply with NRC Bulletin 2001-01.
Three penetrations with shallow cracking on the outer diameter of three CEDMs below the J-groove weld were repaired.
Second Event:
1. Event Description
On February 22, 2002, with the plant in Mode 6 (Refueling) at zero percent Rated Thermal Power, helium leak tests were performed on the "A" and "C" Reactor Coolant Pump (RCP) [AB,P] seal coolers [AB,HX] and thermal barrier heat exchangers in an effort to identify the source(s) of the leakage from the Reactor Coolant System (RCS) [AB] into the Reactor Building Closed Cooling Water (RBCCW) [CC] system. This testing confirmed leakage on the "C" RCP. The RCP seal cooler is part of the RCS pressure boundary.
The RCP (Byron Jackson pump) is sealed from the atmosphere by mechanical seals mounted in a removable cartridge consisting of four seals in series. The reactor coolant entering the seal cavity is forced by the auxiliary impeller through an integral heat exchanger (seal cooler) cooled by RBCCW. By maintaining approximately 1 GPM of reactor coolant through the cartridge, the seals are kept at a temperature of approximately 80 to 90 degrees F during normal operation.
Millstone Unit No. 2 began to experience elevated levels of radionuclide activity in RBCCW on October 25, 1999.
The RBCCW samples showed the presence of xenon and iodine consistent with reactor coolant isotopes. After much trouble shooting, initial indications revealed the primary sample cooler as the suspected leak source. After repair of the primary sample cooler indications of the leak disappeared. On November 3, 2000, the leak reappeared and sampling of other systems verified the contamination was limited to the RBCCW system.
(If more space is required, use additional copies of (if more space is required, use additional copies of NRC Form 366A) (17)
4. Corrective Action
The leaking "C" RCP cover and rotating element (which contains the RCP seal cooler) was replaced with a rebuilt spare. The rebuilt spare had been tested prior to the outage and was shown to have no leakage through the thermal barrier heat exchanger. Subsequent to Millstone Unit No. 2's return to power operation, there has been no detectable evidence of reactor coolant ingress to the RBCCW system. The system is continuously monitored for radioactivity via an in-line detector, and water samples are analyzed weekly for long term trending of radioactive contamination in accordance with IE Bulletin 80-10.
5. Previous Occurrences
There have been no similar events of RCP seal cooler leaks at Millstone Unit No. 2.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].