05000483/LER-2003-004, For Callaway Plant Unit 1 Regarding Boron Dilution Mitigation System Blocked in Mode 3 Which Not Consistent with FSAR Accident Analysis

For Callaway Plant Unit 1 Regarding Boron Dilution Mitigation System Blocked in Mode 3 Which Not Consistent with FSAR Accident Analysis

ML031681324
Person / Time
Site:	Callaway
Issue date:	06/09/2003
From:	Witt W AmerenUE
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC04862 LER 03-004-00
Download: ML031681324 (6)

LER-2003-004, For Callaway Plant Unit 1 Regarding Boron Dilution Mitigation System Blocked in Mode 3 Which Not Consistent with FSAR Accident Analysis

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4832003004R00 - NRC Website

text

PO Box 620 Fulton, MO 65251 June 9, 2003 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC04862 Ladies and Gentlemen:

UE DOCKET NUMBER 50-483 Callaway PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2003-004-00 Boron Dilution Mitigation System blocked in Mode 3.

The enclosed licensee event report is submitted in accordance with 10CFR50.73(a)(2)(ii)(B) and 10CFR50.73(a)(2)(v)(D), to report events where the Boron Dilution Mitigation System was blocked while in Mode 3. This action is inconsistent with Final Safety Analysis Report accident analysis.

Very trly yours, Warren A. Witt Manager, Callaway Plant WAW/ewh Enclosure a subsidiary of Ameran Corporation AmerenUE Callaway Plant

SE,Z

ULNRC-04862 June 9, 2003 Page 2 cc:

Mr. Thomas P. Gwynn Acting Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 Senior Resident ispector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 7E1 Washington, DC 20555-2738 Manager, Electric Department Missouri Public Service Commission PO Box 360 Jefferson City, MO 65102 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339

Abstract

On 4/11/03, while at 100 percent power, it was discovered that a note contained in Technical Specification (T/S) 3.3.9 for the Boron Dilution Mitigation System (BDMS), had been inappropriately applied during past reactor startups. This had been interpreted to allow blocking BDMS while withdrawing Shutdown (S/D) Bank rods in Mode 3. This action is not allowed in Mode 3 per Final Safety Analysis Report (FSAR) accident analysis Section 15.4.6.2 where BDMS is credited for automatically terminating a dilution event while in Mode 3.

Wording of T/S 3.3.9 and T/S 3.3.9 Bases did not provide clear guidance as to what constitutes "reactor startup". The Bases indicate BDMS could be blocked prior to withdrawing "rods" for startup. These words do not delineate between control banks and shutdown banks. Based on this unclear guidance, procedure OTG-ZZ-00IA was incorrectly revised allowing the blocking of BDMS prior to withdrawing shutdown banks. The discovery of the unclear T/S wording was the result of requested procedure enhancements to clarify when it was allowable to block BDMS.

A review of reactor startups within the last 3 years indicated that BDMS was inappropriately blocked on three separate startups.

The first occurred on I 1/24/02, the second on 12/17/02, and the third on 4t2103. Plant procedures governing reactor startup were revised to remove statements allowing blocking BDMS while withdrawing S/D Bank rods in Mode 3.

NRC FORM 36 (1-ZID)

I (if more space is required, use addftional copies of SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES On 4/11/03, while at 100 percent power, it was discovered that a note contained in Technical Specification (T/S) 3.3.9 for the Boron Dilution Mitigation System (BDMS), had been inappropriately applied during past reactor startups. This note states: "The boron dilution flux multiplication signal may be blocked in Modes 2 (below P-6 (Intermediate Range Neutron Flux) interlock) and 3 during reactor startup." This had been interpreted to allow blocking BDMS while withdrawing the Shutdown Banks in Mode 3. This action is not allowed in Mode 3 per Final Safety Analysis Report (FSAR) accident analysis.

The Callaway Mode 3 Accident Of Record (AOR) is discussed in FSAR Section 15.4.6.2. The acceptance criterion for a Mode 3 boron dilution event is that there is sufficient time available for automatic mitigation prior to the complete loss of shutdown margin. The BDMS generates a neutron flux-multiplication alarm that indicates an inadvertent boron dilution is in progress. The BDMS also initiates signals to automatically open valves BN-LCV-1 12D/E (Centrifugal Charging Pump Suction from Refueling Water Storage Tank) to initiate boration and then to close valves BG-LCV-I 12B/C (Volume Control Tank outlet isolation valve) to terminate the dilution. Re-boration occurs within 3.14 minutes after reaching the flux-multiplication condition. This occurs prior to the loss of shutdown margin at 6.22 minutes after reaching the flux-multiplication condition, had the condition gone unmitigated.

Since the Callaway Mode 3 Boron Dilution Event AOR has insufficient time available to credit operator actions to terminate this event prior to the loss of shutdown margin, the BDMS must be credited to mitigate the consequences of an inadvertent dilution in Mode 3. Therefore, the T/S 3.3.9 note which allows blocking the boron dilution flux multiplication signal in Mode 3 only applies to blocking BDMS just prior to withdrawing Control Bank rods. BDMS cannot be blocked while withdrawing Shutdown (S/D) Bank rods without blocking all potential dilution sources within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> specified by T/S 3.3.9. Withdrawing shutdown banks with BDMS blocked is not consistent with FSAR Section 15.4.6.2 Mode 3 analysis.

This problem was discovered while researching a revision for plant operating procedure OTG-ZZ-000 IA, SHUTDOWN BANK WITHDRAWAL.

While researching the requested procedure revision, it was identified that T/S 3.3.9 and T/S 3.3.9 Bases were not explicit in providing guidance for implementing the FSAR Accident Analysis for a boron dilution event. Safety Analysis engineers reviewed the wording and concluded that BDMS could not be blocked while withdrawing Shutdown Bank rods in Mode 3.

(ff moe space is required, use additional copies of NRC Form 3664) (17)

A historical review of reactor startups within the last 3 years indicated that BDMS was inappropriately blocked while withdrawing S/D Bank rods in Mode 3, on three separate startups. The first occurred on 1 l/24/02, the second on 12/17/03, and the third on 4/2/03.

An inmediate corrective action was to issue OTG-ZZ-OOOIA revision 6. This revision removed a step which stated that BDMS could be blocked.

E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR This problem was discovered while researching a revision for plant operating procedure OTG-ZZOOOlA, SHUTDOWN BANK WITHDRAWAL.

II.

EVENT DRIVEN INFORMATION A. SAFETY SYSTEMS THAT RESPONDED Not applicable at the time of discovery on 4/11/03.

B. DURATION OF SAFETY SYSTEM INOPERABILITY

Not applicable.

C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.

The source range or intermediate range reactor trip functions are available in Modes 2 and 3. Licensed operators are trained to immediately enter Emergency Operating Procedures (EOP) following any indication of a reactor trip.

"Subcriticality" is one of the critical safety functions continuously monitored throughout the EOPs to ensure reactor power does not exceed 5 percent. These procedures require the licensed operators to immediately borate the reactor coolant system if neutron flux is not decreasing. These procedural controls would ensure that there is no resulting fuel damage or radiological release from the plant. Therefore, this concem had low safety significance with minimal impact on the health and safety of the public.

Ill.

CAUSE OF THE EVENT

Wording of T/S 3.3.9 and T/S 3.3.9 Bases did not provide clear guidance as to what constitutes "reactor startup". The Bases indicate BDMS could be blocked prior to withdrawing "rods" for startup. These words do not delineate between control banks and shutdown banks. Based on this unclear guidance, procedure OTG-ZZ-OOOlA was incorrectly revised allowing the blocking of BDMS prior to withdrawing shutdown banks.

IV.

CORRECTIVE ACTIONS

T/S 3.3.9 Bases wil be revised to clearly specify that BDMS can be blocked prior to withdrawing control rods for reactor startup.

An immediate corrective action was to issue OTG-ZZ-OOOlA revision 6. This revision removed a step, which stated that BDMS could be blocked, plus added steps to monitor source range counts and halt S/D Bank withdrawal if approaching a BDMS setpoint.

(If more space Is required, use addtional copies of NRC Form 366A) (17)

V.

PREVIOUS SIMILAR EVENTS

This event is documented in Corrective Action Request (CAR) 200302704. A 3-year historical review of the CAR system identified no other related events beyond the three events reported in this LER A review of Callaway LERs from 2000 to present confirmed that there were no past LERs involving BDMS.

ADDITIONAL INFORMATION

The system and component codes listed below are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 respectively.

System:

Component:

Not applicable.

Not applicable.VI.