05000271/LER-2002-001, For Vermont Yankee Nuclear Power Station, Regarding Core Thermal Power Exceeded Due to a Non-Conservative Moisture Carryover Assumption
| ML023030440 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 10/24/2002 |
| From: | Bronson K Entergy Nuclear Northeast |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BVY 02-85 LER 02-001-00 | |
| Download: ML023030440 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 2712002001R00 - NRC Website | |
text
'OEntergy Entergy Nuclear Northeast Entergy Nuclear Operations, Inc Vermont Yankee 322 Governor Hunt Rd PO Box 157 Vernon, VT 05354 Tel 802-257-771 1 October 24, 2002 BVY 02-85 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)
Reportable Occurrence No. LER 2002-001, Rev. 0.
As defined by 10CFR50.73, we are reporting the attached Reportable Occurrence LER 2002-001, Rev. 0.
Sincerely, ENTERGY NUCLEAR OPERATIONS, INC.
VERMONT YANKEE Kevin H. Bronson General Manager cc:
USNRC Region I Administrator USNRC Resident Inspector - VYNPS USNRC Project Manager - VYNPS Vermont Department of Public Service a--
Abstract
On 10/03/01, as a result of information received from General Electric Nuclear Energy (GENE) in September of 2001, it was determined that Vermont Yankee (VY) had potentially been operating slightly above its licensed Maximum Power Level as set forth in License Condition g.3.A. A moisture carryover fraction of 0.1% had been used from previous guidance by GENE. On 10/03/01 this value was changed to 0.0% in VY's calorimetric calculation model, pending the determination of an actual average moisture carryover content value. On 09/05/02, it was determined that the average moisture carryover fraction was approximately 0.029%; therefore core power may have been exceeded by approximately 1 Megawatt-thermal (MWth), which correlates to 0.06% of the Maximum Power Level. Use of the non-conservative moisture carryover fraction of 0.1% does not represent a safety issue. The change in core thermal power is an order of magnitude less than the precision of the MCPR safety limit evaluation process and is enveloped by the allowed uncertainties in the evaluation process and computer core thermal power estimate. The cause of this event is the failure to empirically determine the value of the percentage of moisture carry-over present once the plant became operational, and subsequent use of a design assumption in determining Core Heat Balance.
NRC FORM 366 (7-2001)
NRC FOtRM 366A U.S. NUCLEAR REGULATORY COMMISII (7-2001)
LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET (2)
LER NUMBER 56)
PAGE (3)
SEQUENTIAL REVISION VERMONT YANKEE NUCLEAR YEAR NUMBER NUMBER POWER STATION (VY) 05000271 2002 --
001 00 2 OF 3
NARRATIVE
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Fonn 366A) (17)
CAUSE
The root cause of this event is the failure to empirically determine the value of the percentage of moisture carry-over present when the plant became operational, and the subsequent use of a design assumption in determining Core Heat Balance.
CORRECTIVE ACTIONS
- 1. The constant used in the calculation of the Core Thermal Power was adjusted to be 0.0% moisture carryover.
This partially corrects the root cause. Complete.
- 2. The average value of moisture carryover from the reactor was empirically determined to be 0.029%. This action, in conjunction with corrective action number one, corrects the root cause. Complete.
ASSESSMENT OF SAFETY CONSEQUENCES
As stated in GE SIL No. 639, use of the moisture content of 0.1%, while non-conservative in determining core thermal power if actual moisture content is lower, does not represent a safety issue. This change in core thermal power is an order of magnitude less than the uncertainty in the MCPR safety limit evaluation and has no significant effect on safety analyses. This condition did not have the potential to cause fuel thermal limits to be exceeded. Therefore, there was no increased risk with respect to the health and safety of the public.
ADDITIONAL INFORMATION
Two events have been identified during the past five years in which core thermal power limits have been exceeded. The corrective actions prescribed in these LERs would not have prevented the overpower conditon described in this event since the moisture carry-over fraction was an assumed input provided by GE.
LER Event Report Date Event Title 2001-004-00 97-017-00 08/21/01 10/19/01 Exceeded Core Thermal Power Limit Due to Feedwater Nozzle Fouling An Equipment Malfunction Remaining Undetected by the Operating Crew Results in Plant Operation in Excess of Rated Thermal Power.
NRC FORM 366 (7-2001)