05000456/LER-2010-005, Incorrect Methodology Used in Calculations in 1999 Resulted in Non-Conservative Control Room Outside Air Intake Monitor Alarm Setpoints

Incorrect Methodology Used in Calculations in 1999 Resulted in Non-Conservative Control Room Outside Air Intake Monitor Alarm Setpoints

ML110120148
Person / Time
Site:	Braidwood
Issue date:	01/11/2011
From:	Shahkarami A Exelon Nuclear, Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BW110001 LER 10-005-00
Download: ML110120148 (4)

LER-2010-005, Incorrect Methodology Used in Calculations in 1999 Resulted in Non-Conservative Control Room Outside Air Intake Monitor Alarm Setpoints

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4562010005R00 - NRC Website

text

10 CFR 50.73 January 11, 2011 BW110001 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Subject: Licensee Event Report 2010-005 Incorrect Methodology Used in Calculations in 1999 Resulted in Non-Conservative Control Room Outside Air Intake Monitor Alarm Setpoints The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, "Licensee event report system," paragraph (a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications. On November 12, 2010, an error was identified in the methodology used in a historic calculation (1999) of the setpoints for the control room outside air intake noble gas channels, making the setpoints non-conservative. 10 CFR 50.73(a) requires an LER to be submitted within 60 days following discovery of the event. Therefore, this report is being submitted by January 11, 2011.

There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Ronald Gaston, Regulatory Assurance Manager, at (815) 417-2800.

Respectfully, Amir Shahkarami Site Vice President Braidwood Station

Enclosure:

LER 2010-005-00 cc: NRR Project Manager - Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety US NRC Regional Administrator, Region III US NRC Senior Resident Inspector (Braidwood Station)

Illinois Emergency Management Agency - Braidwood Rep

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.

13. PAGE Braidwood Station, Unit 1 05000456 1 of 3

4. TITLE Incorrect Methodology Used in Calculations in 1999 Resulted in Non-Conservative Control Room Outside Air Intake Monitor Alarm Setpoints

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

MONTH DAY YEAR Braidwood Station Unit 2 05000457 FACILITY NAME DOCKET NUMBER 11 12 2010 2010. 005.

00 01 11 2011 N/A N/A

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) o 20.2201(d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4) o 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) o 50.36(c)(1 )(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)

10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1 )(ii)(A) o 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71(a)(4) 099 o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(B) o 73.71(a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi)

I:8J 50.73(a)(2)(i)(B) o 50.73(a)(2)(v)(D)

Specify in Abstract below or in D.

Safety Consequences

2010 005 00 There were no safety consequences impacting plant or public safety as a result of this event.

There are two trains of VC. Detectors OPR31 Band OPR32B are interlocked with the A train, and detectors OPR33B and OPR34B are interlocked with the B train. On a high radiation signal for the detectors of the respective train, the train-specific ventilation systems realign to the Emergency mode to support control room habitability.

The applicable design basis accidents are main steam line break, reactor coolant pump shaft seizure, rod cluster control assembly ejection, steam generator tube rupture, loss of coolant accident, and postulated fuel handling accident. For control room habitability analysis, activity released during the initial 30 minutes of the accident is assumed not filtered to compensate for time to manually realign the VC system to the Emergency mode of operation.

The TS required monitor is the noble gas detector in the control room outside air intakes. The High alarm was set at 2.9 mrem/hr verses required 2.0 mrem/hr (noble gas exposure) for the automatic ventilation swap to Emergency mode. This yields a net 0.9 mrem/hr above the expected dose rate. Since the accident analysis calculations assume manual swap of ventilation within 30 minutes, the excess dose rate for the alarm would only affect the control room for a maximum of 30 minutes. This yields 0.9 mrem/hr x 0.5 hr = 0.45 mrem (noble gas exposure).

The radiation exposure consequence to control room personnel from the 45% higher trip alarm is approximately an additional 0.5 mrem for noble gas exposure.

Since the design basis accidents do not credit automatic actuation of the VC system into the Emergency mode from a high radiation signal, this event did not result in a safety system functional failure.

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Corrective Actions

The corrective actions include:

An extent of condition review was performed and verified that required TS radiation monitor setpoints are set in compliance with TS requirements.

The setpoint calculations were revised and the setpoints for OPR31 B, OPR32B, OPR33B and OPR34B were reset to the correct values.

Review the applicable radiation monitor procedures that perform setpoint calculations for the process radiation monitors, and revise them to address details on the method used for setpoint calculations, and include instructions for the basis of the review criteria.

F.

Previous Occurrences

There have been no previous, similar Licensee Event Reports identified at the Braidwood Station.

p.

Component Failure Data

Manufacturer N/ANomenclature N/A Model N/A Mfg. Part Number N/A