ML20045J069
| ML20045J069 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/16/1993 |
| From: | Denton R BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20045J070 | List: |
| References | |
| NUDOCS 9307230016 | |
| Download: ML20045J069 (9) | |
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, BALTIMORE
, GAS AND ELECTRIC ,
1650 CALVERT CUFFS PARKWAY . LUSBY, MARYLAND 20657-4702 ROBERT E. DENTON VCE PRE $tDENT NUCLEAR ENERGY (4to) MO-4455 July 16,1993 U. S. Nuclear Regulatory Commission Washington,DC 20555 ATTENTION: Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318 Request for License Amendment; Reduction of Incore Instrument Reauirements i REFERENCEE. (a) Ixtter from Mr. R. E. Denton (BG&E) to Document Control Desk '
(NRC), dated March 9, 1993, Request for Exigent License Amendment; Reduction ofIncore Instrument Requirements (b) Ixtter from Mr. D. G. Mcdonald (NRC) to R. E. Denton (BG&E),
dated April 2,1993, Issuance of Exigent Amendment for Calvert Cliffs Nuclear Power Plant, Unit No.1 (c) CENPD-153-P, Rev.1-P-A, Evaluation of Uncertainty in the Nuclear Power Peaking Measured by the Self Powered, Fixed In-Core Detector System, dated May 1980.
Pursuant to 10 CFR 50.90, the Baltimore Gas and Electric Company (BG&E) hereby requests an Amendment to Operating License No. DPR-69 by the incorporation of the changes described below into the Technical Specifications for Calvert Cliffs Unit No. 2.
DESCRIPTION Calvert Cliffs Unit 2 Cycle 10 has experienced a number of InCore Instrumentation (ICI) detector failures. A small number of additional detector failures could render the system incapable of meeting the Technical Specification requirements. This proposed change will allow a reduction in the number of required ICI detectors for the remainder of Unit 2 Cycle 10, yet still provides the ability to adequately monitor the Technical Specification power distribution limits.
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HACKGROUND j De ICI system at Calvert Cliffs consists of 45 neutron detector strings positioned in the center of selected fuel assemblics as shown in Attachment (1). The detector strings are inserted from the top- :
of the fuel assembly and electrical connection of the detectors is~made on the reactor vessel head.
Each detector string contains 4 rhodium neutron detector segments located at 20,40,60, and 80% of [
core height. The neutron flux indicated by the detector segments is processed by a full-core power '
distribution system (CECOR 3.3) to determine the peak linear heat rate, peak pin power, radial peaking factors, and azimuthal power tilt for comparison to the Technical Specification limits.. He l detector strings typically operate for two cycles and are then replaced. ;
J During the Calvert Cliffs Unit 2 Cycle 10 refueling outage, which ended on June 13,1993, new ,
detectors were to be installed in 27 of the 45 locations. Because of the ICI detector failures during ,
the startup of Unit 1 Cycle 11 (Reference a), we closely examined the receipt and installation process I for the Unit 2 ICI strings. However, four st;ings could not be installed due to mechanical binding.
While it is not unusual to be unable to insert one or, occasionally, two detector strings into their guide paths, we have never operated with more than two detector strings uninstalled. We made "
several attempts to determine the problem including boroscope examinations and modifying a guide ~ ,
tube. These efforts were unsuccessful and the strings in CECOR locations 1,7,17 and 39 could not -
be installed. Insertion attempts stopped on April 22. We are currently working _ with '
ABB/ Combustion Engineering (ABB/CE) to prevent recurrence and expect that new insertion tools will be developed before the next refueling cutage.
On April 26, we requested an analysis from ABB/CE to support a license amendment to reduce the incore detector requirements. His request was a contingency as four failed strings is not sufficient justification to pursue a license amendment. De analysis was received on June 8.
4 During startup testing on June 13, 1993, three additional failed strings were discovered '(CECOR l ids 2.0,27 and 15). These strings had completed one cycle of use. -Three additional detector t segments were also inoperable. These detector segments were in newly-installed strings.
Additional detector segment failures led to the failure of string 25 (a new string) on June 14, string 42 (second cycle of use) on June 27, and 3 detector segments failed on July 6 and 7, in already inoperable second cycle strings. Currently,9 strings and 39 detectors segments are inoperable. .
I Specification 3.3.3.2.b requires that 75% of the detector segments be operable for recalibrating the' Excore Neutron Flux Detector System. We could not meet this requirement if an additional seven detector segments fail.
Specification 3.3.3.2.a requires that for monitoring azimuthal power tilt, there be at least 2 quadrant -t symmetric incore detector segment groups at each of the 4 detector elevations in the outer 184 fuel assemblics. A quadrant symmetrjc incore detector segment group consists of a minimum of three operable detector segments in 90 symmetric fuel assemblies. Furthermore, there must be sufficient operable detector segments in these detector groups to compute at least two azimuthal power tilt. ;
values at each of the four axial elevations. We could not meet the quadrant symmetric tilt requirement in Specification 3.3.3.2.a if there were an additional four selected failures in the second or third axial position (40 or 60% of core height). :
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July 16,1993 Page 3 I There are currently nine inoperable detector strings (e.g., locations). This includes the four strings which were not installed. Specification 3.3.3.2 states that for a detector string to be considered operable, three of the four detector segments in that string must be operable. Currently three additional strings have one failed detector segment each, and an additional segment failure in any of these three strings would result in failure of the entire string. Specification 3.3.3.2.c requires that at least 75% of the detector strings be operable for the purpose of monitoring Unrodded Planar Radial Peaking Factor, the Unrodded Integrated Radial Peaking Factor, and the linear heat rate.
Therefore,34 detector strings must remain operable to meet this requirement. The failure of three additional detector strings would render the incore detector system incapable of meeting this requirement.
- In summary, three Technical Specification limits are threatened by additional failures. Any seven additional detector segment failures would exceed Specification 3.3.3.2.b on the percentage of operable segments. Four selected detector segment failures would exceed Specification 3.3.3.2.a on the distribution of symmetric groups for measuring azimuthal power tilt. As few as three additional segment failures could exceed the Specification 3.3.3.2.c limit on the number of operable strings.
Based on the pattern of failures, it is most likely that Specification 3.3.3.2.c will be the first to be ;
challenged if there are additional failures.
Should the number of operable detector strings drop below 75%, the monitoring of Total Planar ,
Radial Peaking Factor (Suncillance 4.2.2.1.2), Total Integrated Radial Peaking Factor :
(Surveillance 4.2.3.2) and linear heat rate (Surveillarce 4.2.1.4) would be affected. The radial peaking factors must be measured every 31 days or the plant must be in Hot Standby in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> .
(Actions 3.2.2.1.b and 3.2.3.a). Linear heat rate must be continuously monitored (Surveillance 4.2.1.2) using either the excore or incore detectors (Surveillance 4.2.1.4). If the excore detectors are being used, as would be required if less than 75% of the strings are operable, i Suncillance 4.2.1.3.c requires the determination of the factor "N." Specification 3.2.2.2 and Surveillance 4.2.2.2.2.b require that the fa; tor "N" be verified within its limit every three days of accumulated Mode 1 operation or be in Hot Standby within six hours. Verification that the factor >
"N" is within its limit requires the measurement of Total Planar Radial Peaking Factor, which cannot -
be accomplished without 75% of the detector strings operable. Therefore, upon the failure of greater than 75% of the detector strings, the plant must be in Hot Standby within three days, six hours.
t Baltimore Gas and Electric Company is still examining the cause of the detector failures. It does not appear that the cause is the same as the Unit 1 failures (Reference a). The Unit I failures occurred in the newly-inserted detectors and the majority of the new detectors failed shortly after startup. The ,
detector failures experienced on Unit 2 are not associated with any particular manufacturing batch and two-thirds of the failed detector strings have experienced at least one full cycle of operation. It is unlikely that the failures were cause by mishandling during the outage as the operations involving ICIs were very carefully monitored as part of the corrective actions following the Unit 1 failures.
ABB/ Combustion Engineering has previously analyzed similar situations. Explicit analyses of current and projected detector failure patterns were performed for Fort Calhoun Unit 1 Cycle 6; St. Lucie Unit 1 Cycle 4; and Calvert Cliffs Unit 1 Cycle 8. In each case, the licensees requested and were granted Technical Specifications changes which allowed operation with a reduced complement of .
incore detectors. The Calvert Cliffs Unit 1 Cycle 11 request (Reference a) was based upon those analyses and was approved (Reference b) 'Ihe changes proposed for Calvert Cliffs Unit 2 Cycle 10 are identical to the Unit 1 Cycle 11 request.
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.. Document Control Desk July 16,1993 Page 4 REOUESTED CIIANGE Revise Technical Specifications as shown in Attachment (2). Specifically:
Specifications 3.2.2.1. 3.23 ud 4.2.1.4.b.1 - A footnote applicable for only Unit 2 Cycle 10 is added. a The footnote requires that when the percentage of operable incore detector locations (e.g., strings) falls below 75%, the measured values be increased by 1% prior to being compared to the Technical Specificationslimits. :
Surveillances 4.2.1.4.a. 4.2.2.1.2.b. and 4.23.2.b - A footnote applicable for only Unit 2 Cycle 10 is added. The footnote requires that when the percentage of operable incore detector locations (e.g., strings) falls below 75%, the full core power distribution mapping frequency be increased to at least once per 15 days of accumulated operation in Mode 1. ;
Snecification 333.2.a - A footnote which supersedes the current requirement for only Calvert Cliffs Unit 2 Cycle 10 was added. The current requirement for two quadrant symmetric incore detector-segment groups at each axial location is changed to a total of eight quadrant symmetric incore detector segment groups. The current requirement for at least two azimuthal power tilt values at each detector segment axial elevation is changed to at least one azimuthal power tilt value at each detector segment axial elevation and at least two azimuthal power tilt values at three detector segment axial elevations.
Specifications 333.2.b.1 and 333.2.c.1 - Footnotes were added which supersede the current requirement for only Calvert Cliffs Unit 2 Cycle 10. The minimum number of operable detector segments and strings is reduced from 75% to 60%. ,
SAFETY ANALYSIS The monitoring of incore neutron flux is accomplished by the incore detectors which provide the detailed power distributions necessary for Technical Specification smveillance of power peaks and for trending of core data. Oroups of incore detector strings are used to detect anomalous power distributions. This is important, as persistent anomalous power distributions can degrade core ,
thermal hydraulic performance.
The current Technical Specification 333.2.a requires at least eight azimuthal power tilt estimates with a minimum of two estimates of each of the four detector segment axial elevations. - The proposed revision still requires at least eight azimuthal power tilt estimates, but requires only one estimate at each elevation and two estimates at three of the four elevations. These changes preserve the statistical validity of the tilt estimates and ensure adequate core coverage since the requirement -
that there be at least one operable segment in each quadrant at each elevation is maintained. This degree of coverage is sufficient because azimuthal tilts at one elevation are seen at adjacent levels. -
Detector data is also used to calculate power peaking factors which are used to verify compliance with fuel performance limits. As the number of inoperable detector segments increases, the uncertainties in the CECOR power distribution calculation increase. The determination of the CECOR uncertainties is described in Reference (c). Explicit analyses have been performed in the past for several reactor cycles to evaluate the effect of unexpected detector failures on the CECOR uncertainties using the known and extrapolated failure patterns. These previous analyses are k
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l described in Attachment (3). In those cases, the extrapolated failure patterns had up to 75% of the detector segments failed. The cases are similar to and bound the extrapolated failure patterns of up to 40% failed detector segments in Calvert Cliffs Unit 2 Cycle 10.
For Calvert Cliffs Unit 2 Cycle 10, the requested change would reduce the operability requirement from 75% to 60% of the detector segments and strings. It is expected that the increase in CECOR uncertainties with 40% of the detector segments and strings failed will be below those determined in previous analyses and the resulting uncertainties still remain less than those in the topical report.
However, as a conservative measure in the absence of explicit evaluation of Cycle 11 uncertainties, if the percentage of operable detector strings falls below 75%, then the linear heat raie, total planar radial peaking factor (F T) and total integrated radial peaking factor (F rT) calculated by CECOR will be increased by 1% fefore they are compared to the values given in the Technical Specifications.
As discussed in Attachment (3), this will more than offset any increase in the uncertainties due to increased detector string failures. In this way, the comparison of the augmented measured values to q the setpoint values in the Technical Specifications will be valid, and the setpoint analyses will remain valid. This will be checked with the periodic surveillance maps to show continued compliance.
If the number of operable incore detector strings falls below the current limit of 75%, BG&E will take the power distribution surveillance maps on a frequency once-per-15-days of accumulated Mode 1 operation, which is twice as often as the Technical Specifications now require.
I)ETERMINATION OF SIGNIFICANT IIAZARI)S The proposed change has been evaluated against the standards in 10 CFR 50.92 and has been determined to not involve a significant hazards consideration, in that operation of the facility in accordance with the proposed amendments:
- 1. Would not invoh?e a significant increase in the probability or consequences of an accident previously evaluated.
The proposed change would relax the requirements for the number and distribution of operable incore detectors. The safety function of the incore detectors is to verify that the core power distribution is consistent with the assumptions used in the safety analyses.
Sufficient measurements will be required to adequately verify compliance with power distribution Technical Specification limits. Penalties will be applied to the values measured by the incore detectors prior to comparison with the Technical Specifications limits when the number of operable detector strings falls below the current requirement. This will ensure that all current Technical Specification and fuel design limits are protected and the core power distribution assumptions in all analyses remain valid. Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Would not create the possibility of a new or difference type of accident from any accident previously evaluated.
The proposed change does not represent a change in the configuration or operation of the plant. The current Technical Specifications limits measured by the incore detector system will still be met. Therefore, the proposed change does not create the possibility of a new or different type of accident from any accident previously evaluated.
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- 3. Would not involve a significant reduction in a margin ofsafety.
'Ihe proposed changes will continue to protect the current power distribution Technical Specifications limits. When the number of operable incore detector strings falls below the current Technical Specification requirement, a penalty will be added to the measured values before they are compared with the Technical Specification limits. This penalty has been shown by prior analysis to be greater than the increased uncertainty. This penalty ensures that the Technical Specifications limits monitored using the incore detectors will continue to be protected. Therefore, the proposed change does not involve a significant reduction in a margin of safety.
ENVIRONMENTAL ASSESSMENT The proposed amendment changes requirements with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes an inspection or surveillance requirement. We have determined that the proposed amendment involves no significant hazards consideration, and that operation with the proposed amendment would result in no significant change in the types or significant increases in the amounts of any effluents that may be released offsite, and in no significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR Part 51.22(c)(9). Pursuant to 10 CFR SL 2(b) no environmental impact statement or er vironmental assessment is needed in connection with the approval of the proposed amendment.
SCIIEDULE We request that this change be processed as quickly as possible. It is impossible to predict when, or if, additional detector failures will occur. However, should additional detector failures threaten continued operation of Unit 2, BG&E will submit a request that this amendment be processed as an exigent amendment under the provisions of 10 CFR 50.91(a)(6).
SAFETY COMMFITEE REVIEW These proposed changes to the Technical Specifications and our determination of significant hazards have been reviewed by our Plant Operations and Safety Review Committee and Offsite Safety Review Committee. They have concluded that implementation of these changes will not result in an undue risk to the health and safety of the public.
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. Document Control Desk 1 July 16,1993 Page 7 Should you have any questions regarding this matter, we will be pleased to discuss them with you.
D truly yours, (r M STATE OF MARYLAND :
- TO WIT :
COUNTY OF CALVERT :
IState hereby certifyinthat of Maryland and foron theCh/[1993, baybefore me the subscriber, a Notary Public of the of Jubi,/verf Ccunh,/
, personally appeared ,
Robert E. Denton, being duly sworn, and states that he is Vide President of the Baltimore Gas and Electric Company, a corporation of the State of Maryland; that he provides the foregoing response for the purposes therein set forth; that the statements made are true and correct to the best of his knowledge,information, and belief; and that he was authorized to provide the response on behalf of said Corporation.
WITNESS my Hand and Notarial Seal: YMNotary [IPublic '
i My Commission Expires: 4cav2a - 8, /9 9[
Dde RED /BDM/bdm/ dim Attachments: (1) Incore Instrumentation System Detector Locations (2) Unit 2 Technical Specification Revised Pages (3) Description of Previous Analyses cc: D. A. Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. H. Walter, PSC
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