05000361/LER-2001-001
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 3612001001R00 - NRC Website | |
U.S. NUCLEAR REGULATORY COMMISSION 2001 00 DOCKET (2) LER NUMBER (6 - 001 - FACLJTY NAME(1) Reactor Vendor:
Mode:
Power:
Temperature:
Pressure:
Combustion Engineering Mode 1 — Power Operation 99.8 percent 540 degrees F 2250 psia Combustion Engineering Mode 5 — Cold Shutdown N/A 141 degrees F 349 psia
Background:
San Onofre Units 2 and 3 each have two emergency diesel generators (EDGs) {EK}, four total. Each EDG is equipped with two automatic voltage regulator (AVR) {RG} circuits. If one AVR becomes inoperable, plant operators are able to manually switch to the other AVR to restore EDG operability.
Because the AVR selector switch momentarily interrupts power to the generator field, AVR swapping can be performed only when the EDG is not powering loads.
There are four basic features that an AVR must be capable of performing.
- Maintain voltage under no load (minimum field current).
- Maintain voltage under full diesel generator load (corresponding field current).
- Operate in parallel with offsite power source.
- Respond dynamically under transient conditions.
Technical Specification (TS) 3.8.1, AC Sources - Operating, requires, in part, two EDGs to be operable in Modes 1 through 4, and each EDG capable of supplying one train of the onsite Class 1E AC Electrical Power Distribution System. Various TS surveillance requirements (SRs) confirm different aspects of EDG operability as shown in Table 1 (see Additional Information section).
Description of the event:
During the 6-month and 24-month EDG surveillance testing, only the AVR {RG} aligned to the EDG at that time undergoes surveillance testing, SCE's practice has been to alternate EDG AVR lineups for the monthly surveillance tests. In 1999, SCE evaluated whether this practice complies with the requirements of the TS because an EDG is often aligned to an AVR that has not undergone the most recent 6-month or 24-month surveillance testing. SCE concluded that the AVR was a sub-component of the EDG and determined an AVR, which had previously passed a 24 month surveillance test and was tested bimonthly, was considered capable of performing its intended function.
In February 2001, after observing a recently performed EDG surveillance test, an NRC resident inspector questioned the adequacy of the EDG surveillance testing. The issue at the time was whether the AVR is an integral part of the EDG, which therefore requires each AVR to have the same level of testing as the EDG to comply with the TS. On February 22, 2001 (discovery date), SCE recognized that at times in the past, one or more of the four EDGs have been aligned to an AVR that was not included in all of the TS SR testing for its associated EDG (AR 010201358). Consequently, even though this discrepancy is considered administrative in nature and surveillance testing in itself does not impact the operability of an EDG, SCE is reporting this condition in accordance with 10 CFR 50.73(a)(2)(i)(B) as this occurrence does not consist solely of a case of a late surveillance.
U.S. NUCLEAR REGULATORY COMMISSION LER NUMBER (6) FACILITY NANE(1) DOCKET (2) 05000-361 — 001 — I � 00 2001
Cause of the Event:
The cause was an inappropriate assumption that the AVR could be adequately tested as a sub- component to demonstrate its operability in support of the EDG. When the applicable surveillance procedure was developed, SCE did not incorporate the most conservative application of these TS SRs.
Corrective Actions:
On February 22, 2001, TS compliance was achieved by selecting an AVR that had been tested or by completing the required surveillance testing.
On February 27, 2001, operator training was provided on the revised methodology for performing EDG surveillance testing.
On April 6, 2001, SCE submitted a TS amendment application to clarify the applicable EDG surveillance requirements for ensuring AVR operability.
Safety Significance:
Because the AVRs were found operable when tested, SCE concludes this occurrence has no safety significance. SCE also evaluated this issue using NRC Manual Chapter 0610* (dated 10/6/00) for Significance Determination Process (SDP) entry (Attachment 0609.02). SCE concludes the issue would be categorized as a minor violation with no color assigned.
Additional Information:
In the last two years, SCE submitted one report involving an EDG and an AVR. LER 3-1999-006 reported that plant operators caused an EDG to be inoperable for longer than allowed by the TS when they inadvertently aligned an EDG to an inoperable AVR (an AVR that had been tagged out as inoperable), a cause not present in this case.
U.S. NUCLEAR REGULATORY COMMISSION — 001 -- I � 00 2001 Table 1 Emergency Diesel Generator Technical Specifications Applicable to Automatic Voltage Regulators Technical Specification Surveillance Requirement (Paraphrased) Frequency AVR Functions verified Operable SR 3.8.1.2 Start testing (w/prelube); Maintain voltage and frequency within limits. Monthly (1) SR 3.8.1.3 Synchronized and loaded run for >= 60 minutes. Monthly (2) (3) SR 3.8.1.7 Fast-start testing (w/o prelube); Verify voltage and frequency are maintained within limits. Semi annual (1) SR 3.8.1.9 Largest load rejection test; Verify voltage and frequency are maintained within limits. 24 months (1) (4) SR 3.8.1.10 Full load reject; Verify voltage and frequency are maintained within limits. 24 months (1) (2) (3) (4) SR 3.8.1.11 Verify a Loss of Voltage Signal causes EDG Start and that EDG loads within 10 seconds; Verify voltage and frequency are maintained within limits.
24 months (1) SR 3.8.1.12 Verify a Safety Injection Actuation Signal (SIAS) causes EDG Start and that EDG attains minimum voltage and frequency within 9.4 seconds; Verify voltage and frequency are maintained within limits.
24 months (1) SR 3.8.1.14 Verify EDG runs for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (at >= full load) while paralleled to the grid. 24 months (2) (3) SR 3.8.1.15 EDG Restart test after a 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or longer run at full load; Verify voltage and frequency are maintained within limits.
24 months (1) SR 3.8.1.16 On simulated restoration of offsite power, Verify EDG can be synchronized with offsite source while loaded and transfers loads to offsite source; Verify voltage and frequency are maintained within limits.
24 months (3) SR 3.8.1.17 With EDG operating in parallel with offsite power, verify a simulated or actual SIAS overrides EDG test mode, returns EDG to ready-to-load mode, maintains voltage and frequency within limits, and automatically re- energizes emergency loads from offsite power.
24 months (1) (3) SR 3.8.1.19 On a simulated restoration of offsite power in conjunction with an actual or simulated ESF signal, verify (a) emergency busses de-energize, (b) loads are shed from emergency busses, (c) EDG auto-starts from standby and (1) energizes permanent loads within 10 seconds, (2) auto sequences emergency loads, (3) maintains voltage within limits, (4) maintains frequency within limits, and (5) powers loads for >= 5 minutes.
24 months (1) (4) SR 3.8.1.20 Simultaneous start of both EDGs; Verify both maintain voltage and frequency within limits. 10 years (1) AVR Functions:
1. Maintain voltage under no load (minimum field current).
2. Maintain voltage under full diesel generator load (corresponding field current).
3. Operate in parallel with offsite power source.
4. Respond dynamically under transient conditions.