05000354/LER-2001-003
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DOCKET (2)
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor (BWR/4) Computer System (ID)
- Energy Industry Identification System {EIIS} codes and component function identifier codes appear as (SS/CCC)
IDENTIFICATION OF OCCURRENCE
Date determined to be reportable: October 2, 2001
CONDITIONS PRIOR TO OCCURRENCE
Mode 1 — 95% power. No structures, systems, or components were inoperable at the time,of Mac occurrence that contributed lo.The event. � .
DESCRIPTION OF OCCURRENCE .„.
On September 28, 2001 the Operating Experience Group received a fax from the Boiling Water Reactor Owners Group (BWROG). The fax contained a report titled, "Impact of Steam Carryover Fraction on Process Computer Heat Balance Calculations." This report noted that recent measurements of steam carryover fraction in BWR 4s, 5s, 6s, and ABWRs indicated that the fraction was significantly lower than 0.1%. The value of 0.1% is based on the specifications for the steam dryer and is used by the plant process computer as a constant term in the calculation of core thermal power.
On October 2, 2001, at 1620, a twenty-four hour notification was made to report potential operation outside of License Condition 2.0 (1), which authorizes PSEG Nuclear LLC to operate the facility at reactor core power levels not in excess of 3339 megawatts thermal (100 percent rated power). This event is being reported as a Special Report in accordance with the requirements of License Condition 2.F.
ANALYSIS OF OCCURRENCE
The impact of the use of an incorrect moisture carryover value in the plant process computer was that actual core thermal power may have been higher than the indicated thermal power.
The immediate recommendation was to limit shift average core thermal power to not exceed 99.9% of rated.
DOCKET (2) ANALYSIS OF OCCURRENCE (Cont'd) The GE report calculates a bias of 0.08% on core thermal power with use of 0.1% carryover fraction. At the time of occurrence, Hope Creek was operating at 95% of rated power. An administrative shift average power limit of 99.9 % was implemented. This was in effect until Tuesday, October 9, when Hope Creek began shutdown for RF10.
On October 2, 2001, at 1620, a twenty-four hour notification was made to report potential operation outside of License Condition 2.0 (1), which authorizes PSEG Nuclear LLC to operate the facility at reactor core power levels not in excess of 100 percent rated power. This event is being reported as a Special Report in accordance with the requirements of License Condition 2.F.
CAUSE OF OCCURRENCE
The apparent.paqse, ap described in the GE report, is that the design specification tor.the steam separatodsteani dryer moisture carryover of 0.1% was based on measurements for BWR/3s. This was assumed to be correct for all BWRs and was used as input to the 7,1ant process computer. Based on results from later model BWRs, carryover fractions on thc order of 0.003% are typical. This reduction has been attributed to design improvements.
PRIOR SIMILAR OCCURRENCES
Prior Hope Creek LERs were reviewed for similar potential overpower events. One event was identified that resulted in Operating in Excess of 100 Percent of Rated Core Thermal Power based on a nonconservative calculation assumption (see LER 95-039-00). This event was related to control rod drive (CRD) system flow. The previous corrective actions would not have prevented this event.
SAFETY CONSEQUENCES AND IMPLICATIONS
The magnitude of the impact (0.08% CTP) is such that nuclear instrumentation calibration would not be affected (APRMs must be within 2% of the heat balance power). There is also no impact on core operating limits since the power measurement uncertainties in the calculations that produce thermal limits are 2% (SLMCPR, for example). Therefore, this issue has no safety-significance. Reactor power was maintained within uncertainties used in the Hope Creek Accident and Transient Analysis.
A review of this condition determined that a Safety System Functional Failure (SSFF) has not occurred as defined in Nuclear Energy Institute (NEI) 99-02.
Based on the above this event did not present an undue risk to the health and safety of the public.
DOCKET (2) 4 OF Hope Creek Generating Station 05000354 2001 0 0 3 00 4
CORRECTIVE ACTIONS:
1. The carryover fraction input parameter used in plant process computer for core thermal power calculations was changed from 0.1% to 0.0% 2. Reactor Engineering has revised HC.RE-RA.ZZ-0001 to change carryover fraction used in manual heat balance.
3. A change notice has been posted to the Hope Creek Heat Balance Uncertainty,.
Calculation SC-BB-0525 to incorporate the change in carryover fraction from 0.1% to 0.0%. This is being tracked by the Corrective Action Program.
4. An actio: has been generated in the Corrective Action Program to review (E,TitAing calculations concerning Hope Creek Heat Balance and determine if revision necesst-o) based on this change to carryover fraction.
COMMITMENTS
The corrective actions cited in this Special Report do not constitute commitments.