United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9903110156


LICENSEE EVENT REPORT (LER)


PAGE: 1 OF 6
FACILITY NAME: Beaver Valley Power Station Unit 1
DOCKET NUMBER: 05000334
TITLE: Non-Conservative Concurrent Iodine Spike Radiological Dose Calculation Methodology
EVENT DATE: 01/21/99 LER #: 99-002-00 REPORT DATE: 03/03/99
OTHER FACILITIES INVOLVED: Beaver Valley Power Station
Unit No. 2 DOCKET NO: 05000412
OPERATING MODE: 1 POWER LEVEL: 100%
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION: 50.73(a)(2)(ii)
OTHER: 10CFR21
LICENSEE CONTACT FOR THIS LER:
NAME: R. D. Hart, Senior Licensing
Supervisor TELEPHONE: (412) 393-5284
 
COMPONENT FAILURE DESCRIPTION:
CAUSE: SYSTEM: COMPONENT: MANUFACTURER:
 
REPORTABLE EPIX:
SUPPLEMENTAL REPORT EXPECTED: NO


ABSTRACT:

A review of Beaver Valley Power Station (BVPS) design basis accident (DBA) dose calculations is being conducted as an extent of condition evaluation pursuant to BVPS Unit 2 LER 97-008 to verify that parameters and assumptions are appropriate and are applied in a conservative manner. Four input parameters associated with the methodology for calculating dose during DBAs with concurrent iodine spikes were identified as producing non-conservative calculated values. It was concluded on February 9, 1999 that the four identified non-conservative input parameters could have resulted in tile calculated control room dose for the Main Steam Line Break DBA and Small Line Break DBA at BVPS Unit 1 exceeding the 10CFR Part 50 Appendix A, Criterion 19 limit interpreted as 3 )O REM thyroid in the Standard Review Plan. Since BVPS no longer has reasonable assurance that acceptance criteria for control room personnel dose limits per Criterion 19 would have been met during past operation at BVPS Unit 1, use of the identified dose calculation non-conservative input parameters are reportable pursuant to 10CFR 50.73(a)(2)(ii)(B) as a condition Outside the design basis of the plant. Similarly the identified dose calculation non-conservative input are reportable pursuant to 10CFR21(c)(3)(ii) as a failure to comply that could create a substantial safety parameters hazard were it to remain uncorrected in accordance with 10CFR21(a)(1).

Administrative controls have been implemented at both BVPS Units to control plant operation, thereby ensuring that station operation remains within licensed limits until dose calculations can be formally revised.

END OF ABSTRACT


TEXT PAGE 2 OF 6

PLANT AND SYSTEM IDENTIFICATION

Westinghouse-Pressurized Water Reactor System

CONDITIONS PRIOR TO OCCURRENCE

Unit 1: Mode 1 at 100 % power
Unit 2: Mode 1 at 100 % power

There were no structures, components, or systems that were inoperable that contributed to the event.

DESCRIPTION OF EVENT

As an extent of condition corrective action for Beaver Valley Power Station (BVPS) Unit No. 2 LER 97-008, a review of BVPS design basis accident (DBA) dose calculations is being performed to verify that parameters and assumptions are appropriate and are applied in a conservative manner. This review has spanned many months due to the extremely detailed review being conducted and is still continuing. Several changes have been determined to be warranted based on the extensive review conducted to date. The impact of four nonconservative radiological dose input parameters have been ascertained and based on preliminary calculations, potentially could have led to notable dose increases. The four non-conservative input parameters are associated with the methodology for calculating dose during DBAs with concurrent iodine spikes.

The initial radiation dose calculations for BVPS Units 1 & 2 were performed by Stone & Webster Corporation with input supplied by the Westinghouse Electric Corporation during the initial licensing of each Unit. Following Standard Review Plan criteria assuming a concurrent iodine spike, offsite and control room dose is calculated for a Main Steam Line Break, a Small Line Break (outside containment) and for a Steam Generator Tube Rupture, which is included in each Unit's UFSAR. The initial analysis used for a concurrent iodine spike significantly underestimated the potential spike magnitude and resulting calculated radiation dose. It has been determined that calculation input parameters need to maximize the removal of Reactor Coolant System (RCS) activity during steady state plant operation preceding a postulated DBA to also maximize the resultant calculated concurrent iodine spike dose because this maximizes the allowable pre-existing reactor core leakage rate within Technical Specification limits. Four input parameters were identified which previously underestimated tile overall DBA dose: (1) letdown flow rate needs to be the maximum operational value, (2) letdown demineralizer removal efficiency needs to be the maximum nominal value, (3) RCS leakage needs to be credited as a RCS activity removal mechanism, and (4) RCS volume needs to be a consistently applied value which serves to bound the potential maximum dose. [Note: the RCS volume parameter itself has competing influences within the overall dose model.]


TEXT PAGE 3 OF 6

DESCRIPTION OF EVENT (Continued)

Following the initial identification of the potential issues on January 21, 1999 in Condition Report 990132, additional information was being researched and preliminary calculations were being developed to determine the reportability of the potential issues. It was concluded on February 9, 1999 that the four identified nonconservative input parameters could have resulted in the calculated control room dose for the Main Steam Line Break DBA and Small Line Break DBA at BVPS Unit 1 exceeding the Standard Review Plan interpreted limit of 30 REM thyroid per 10CFR50 Appendix A, Criterion 19. The calculated offsite dose for these same DBAs would also have increased above the Standard Review Plan criteria of a small fraction of 10CFR100. However, the dose would not have exceeded the 10CFR100 limit.

It was also concluded that these same changes would not have exceeded 10CFR100 limits for BVPS Unit 2, though the increase would have exceeded the Standard Review Plan criteria of a small fraction of 10CFR100. These changes also would not have exceeded the 10CFR50 Appendix A, General Design Criterion 19 criteria for BVPS Unit 2.

Since BVPS no longer has reasonable assurance that acceptance criteria for control room personnel dose limits per Criterion 19 would have been met during past operation at BVPS Unit 1, the identified dose calculation non-conservative input parameters is reportable pursuant to 10CFR 50.72(b)(1)(ii)(B) as a condition outside tile design basis of the plant. This issue was reported to the NRC Operations Center on February 9, 1999 at 18:45.

A Basis for Continued Operation (BCO) and plant administrative controls were implemented at both BVPS Units to address one dose calculation issue initially identified in the summer of 1998. A revision to these BCOs have been approved by tile BVPS Nuclear Safety Review Board and are being implemented to specifically address the four collective non-conservative input parameters. However, no additional controls were warranted for BVPS Unit 1 operation to continue during the time frame needed to revise the BVPS Unit 1 BCO because the current Technical Specification limit of 0.35 micro Ci/gm DE-131 and current conditional BCO limit of 0.17 micro Ci/gm DE-131 are adequate. The limit for post-Main Steam Line Break (MSLB) Steam generator tube leak rate was administratively reduced as a conservative measure to ensure that the current Alternate Repair Criteria (ARC) criteria remain valid and bounding. the projected BVPS Unit 1 End of Cycle limit for steam generator post-MSLB steam generator leak rate remains less than the revised lower ARC limit.

Additional BVPS Unit 2 operations controls were implemented on February 9, 1999 to limit Reactor Coolant System activity to below 0.35 micro Ci/gm as a conservative measure until the BCO could be revised for BVPS Unit 2.


TEXT PAGE 4 OF 6

DESCRIPTION OF EVENT (Continued)

For similar reasons described above, this issue was determined to also be reportable pursuant to 10CFR Part 21 on February 18, 1999. This was reported to the NRC Operations Center on February 19, 1999 at 11:22. Although the calculated dose would potentially only have exceeded 10CFR50 Appendix A Criterion 19 at Unit 1, this 10CFR Part 21 issue applies to the previous input parameters used in calculating concurrent iodine spikes at both BVPS Units 1 and 2. Westinghouse Electric Corporation used these input parameters to produce concurrent iodine spike release rates for use in UFSAR accident analyses. These analyses were conducted to support a BVPS Unit 1 licensing submittal in 1982 and the initial licensing of BVPS Unit 2 at this same time period.

Duquesne Light Company issued Operating Experience Report 9686 through INPO notifying the industry of the Beaver Valley Power Station DBA radiological dose calculation conclusions for concurrent iodine spikes described above on February 22, 1999.

The review of BVPS dose calculations to verify that parameters and assumptions are appropriate and are applied in a conservative manner is continuing as previously addressed in BVPS Unit 2 LER 97-008. BVPS Unit 1 and Unit 2 have implemented administrative controls on plant operations which offset the identified nonconservative dose input parameters described above to ensure that calculated public dose do not exceed a small fraction of 10CFR100 and the calculated control room dose do not exceed 10CFR50 Appendix A, Criterion 19 limits for DBAs which address a concurrent iodine spike.

CAUSE OF THE EVENT

Non-conservative input parameters were used by Westinghouse Electric to calculate the concurrent iodine spike release rate for the BVPS Units. No documentation could be identified that indicated Westinghouse had previously recognized the non-conservatism of these input parameters. No specific reason has been identified why this performance error was made by Westinghouse.

CORRECTIVE ACTIONS

1. An Operations administrative control was implemented on February 9, 1999 to limit BVPS Unit 2 Reactor Coolant System activity to below 0.35 micro Ci/gm as a conservative measure until a more detailed Basis for Continued Operation could be implemented.

2. Radiological Engineering Administrative Procedure 1.103, "Control of Engineering Calculations" has been revised to include an instruction to submit parameters to the Nuclear Engineering Department and/or the System Performance Engineering Department for review and concurrence prior to their use in design basis calculations.


TEXT PAGE 5 OF 6

CORRECTIVE ACTIONS (Continued)

3. A revised Basis for Continued Operation (BCO) has been implemented for BVPS Unit 1 addressing the information/controls needed for the identified non-conservative radiological dose calculation input parameters to ensure that continued operation of the plant would remain within both 10CFR100 and 10CFR50 Appendix A GDC 19 radiation ose criteria.

4. A revised Basis for Continued Operation (BCO) has been approved by the BVPS Nuclear Safety Review Board and is being implemented for BVPS Unit 2 addressing the information/controls needed for the identified non-conservative radiological dose calculation input parameters to ensure that continued operation of the plant would remain within both 10CFR100 and 10CFR50 Appendix A GDC 19 radiation dose criteria. This BCO will be complete either a) before BVPS Unit 2 enters Mode 3 from its scheduled refueling outage or b) by March 31, 1999, whichever occurs first.

5. The review of design basis accident radiological consequence calculations for BVPS Unit 1 and Unit 2, as previously committed in BVPS Unit 2 LER 97-008, is continuing. This review will verify that parameters and assumptions are appropriate and are applied in a conservative manner. This review and any calculations revisions which are needed as a result of this review will be completed by August 30, 1999. [Note tile commitment date from BVPS Unit 2 LER 97-008 for this action to be completed was previously revised to be August 30, 1999 via a Duquesne Light Company Letter (L-98-211) dated November 18, 1998.]

6. BVPS will perform a surveillance of Westinghouse design basis calculations conducted for BVPS. The plan for conducting the surveillance will be developed by May 28, 1999.

REPORTABILITY

It was concluded on February 9, 1999 that the four newly identified non-conservative dose calculation input parameters could have resulted in the calculated control room dose for the Main Steam Line Break DBA and Small Line Break DBA at BVPS Unit 1 exceeding the 10CFR Part 50 Appendix A, Criterion 19 limit interpreted by the Standard Review Plan as 30 REM thyroid. Since BVPS no longer has reasonable assurance that acceptance criteria for control room personnel dose limits per Criterion 19 would have been met during past operation at BVPS Unit 1, the identified dose calculation non-conservative input parameters are reportable pursuant to 10CFR 50.73(a)(2)(ii)(B) as a condition outside the design basis of the plant.

The radiological calculation methods used to calculate design basis accident dose is a Basic Component as defined by 10CFR Part 21. Similarly, since BVPS no longer has reasonable assurance that acceptance criteria for control room personnel dose limits per Criterion 19 would have been met during past operation at BVPS Unit 1, tile identified dose calculation non-conservative input parameters are reportable pursuant to 10 CFR


TEXT PAGE 6 OF 6

REPORTABILITY (Continued)

Part 21 (c)(3)(ii) as a failure to comply that could create a substantial safety hazard were it to remain uncorrected in accordance with 10CFR21(a)(1).

SAFETY IMPLICATIONS

The methodology used to calculate design basis accident concurrent iodine spike dose is based on the plant assumed to be operating at the extreme limit of allowable conditions. The analyses assume that the station is operating at the Technical Specification limit for RCS specific activity (0.35 micro Ci/gm DE I-131 for BVPS Unit 1 and 1.0 micro Ci/gm DE I-131 for BVPS Unit 2). Tile level of RCS specific activity has a very strong influence in the calculated concurrent iodine spike dose. Typically the BVPS units operate at a specific activity much less than the Technical Specification limits. Historically, the steady state RCS specific activity at either BVPS Unit resides in the E**-4 -E**-5 micro Ci/gm DE I-131 range during power operation and have risen to the E**-2 -E**-3 micro Ci/gm DE I-131 ranges when fuel leakage was present. However this range is well below the Technical Specification limit which would consequently result in much smaller concurrent iodine spike dose if a design basis accident were postulated to occur.

The DBA concurrent iodine spike analysis follows the NRC Standard Review Plan criteria (15.1.15, App. A, III.4.b) which requires that the iodine release rate from the fuel rods to the primary coolant be increased to a value 500 times greater than the pre-event steady state fuel release rate as a result of the event occurring. This 500 factor increase is believed to be a very conservative assumption for what may occur to the fuel release rate during a design basis accident.

The methodology also assumes that the RCS leakage is occurring at the Technical Specification limits. Historically the BVPS units operate at an RCS leakage much less than the Technical Specification limits. Thus, although there were insufficient assurances that post-accident dose to the control room operators would have remained within General Design Criterion 19 limits during bounding operating conditions, neither BVPS Unit has operated at the extreme limit of the analytical operating condition boundaries for all of the parameters used in the concurrent iodine spike dose calculations. This would have resulted in lower concurrent iodine spike doses than those calculated in the analyses.

PREVIOUS SIMILAR EVENTS

A review of LERs issued for the previous two years did not reveal any BVPS Unit 1 or Unit 2 LERs involving inadequate radiological dose calculation methodology, other than BVPS Unit 2 LER 97-008 which originated the corrective action that led to identifying the issues described within this LER.


ATTACHMENT TO 9903110156 PAGE 1 OF 2

Duquesne Light
Nuclear Group
P.O. Box 4
Shippingport, PA 15077-0004
Telephone (412) 393-6000

March 3, 1999

L-99-035
Beaver Valley Power Station, Unit No. 1
Docket No. 50-334 License No. DPR-66
LER 99-002-00

United States Nuclear Regulatory Commission
Document Control Desk
Washington, DC 20555

In accordance with Appendix A, Beaver Valley Technical Specifications, the following Licensee Event Report is submitted:

LER 99-002-00, 10 CFR 50.73(a)(2)(i), "Non-Conservative Concurrent Iodine Spike Radiological Dose Calculation Methodology."
K. L. Ostrowski
Division Vice President
Nuclear Operations and
Plant Manager

Attachment
NP
The Nuclear Professionals


ATTACHMENT TO 9903110156 PAGE 2 OF 2

LER 99-002-00
L-99-035
Page 2

cc: Mr. H. J. Miller, Regional Administrator
United States Nuclear Regulatory Commission
Region 1
475 Allendale Road
King of Prussia, PA 19406
Mr. D. S. Collins
BVPS Project Manager
United States Nuclear Regulatory Commission
Washington, DC 20555
Mr. David M. Kern
BVPS Senior Resident Inspector
United States Nuclear Regulatory Commission
Mr. J. A. Hultz
Ohio Edison Company
76 S. Main Street
Akron, OH 44308
INPO Records Center
700 Galleria Parkway
Atlanta, GA 30339-5957
Mr. Michael P. Murphy
Bureau of Radiation Protection
Department of Environmental Protection
RCSOB-13th Floor
P.O. Box 8469
Harrisburg, PA 17105-8469
Manager, Nuclear Licensing and Operations Support
Virginia Electric & Power Company
5000 Dominion Blvd.
Innsbrook Tech. Center
Glen Allen, VA 23060

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