ML20044C604
| ML20044C604 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/02/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20044C603 | List: |
| References | |
| NUDOCS 9304080309 | |
| Download: ML20044C604 (6) | |
Text
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WASHINGTON. D C. 20S55-0001
%.....f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.180 TO FACILITY OPERATING LICENSE NO. DPR-53 BALTIMORE GAS AND ELECTRIC COMPANY CALVERT CLIFFS NUCLEAR POWER PLANT. UNIT NO. 1 DOCKET NO. 50-317 1
1.0 INTRODUCTION
By letter dated March 9,1993, Baltimore Gas and Electric Company (the i
licensee) submitted a request for changes to the Calvert Cliffs Nuclear Power Plant, Unit No.1, Technical Specifications (TSs). The requested changes.
would change the number of required in-core detectors necessary for continued operation for the remainder of Operating Cycle 11'only. The proposed changes are necessary because the plant has experienced an unexpectedly large number of failures, thus far, in Operating Cycle 11 and further failures could result in the shutdown of the unit.
The In-Core Instrumentation system at Calvert Cliffs consists of 45 neutron detector strings positioned in the center of selected fuel assemblies.
Each detector string consists of 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) to determine the peak linear heat rate, peak pin power, radial peaking factors, and azimuthal power tilt for comparison to the TS limits.
Presently 32 of the 180 detector segments (17.8%) are inoperable. Three TS limits are threatened by additional failures. Any 14 additional detector segment failures would exceed the TS 3.3.3.2.b limit on the percentage of l
operable segments. Two selected detector segments failures would exceed the TS 3.3.3.2.a limit on the distribution of symmetric groups for measuring azimuthal power tilt. Three additional segment failures could exceed the TS 3.3.3.2.c limit on the number of operable strings.
Based on the pattern of
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failures, TS 3.3.3.2.c would most likely be the first to be challenged by additional failures.
2.0 EVALUATION Essentially all PWR TSs contain a requirement for operability of 75% of the incore detector locations for mapping of the core power distribution. On a number of occasions, for various reasons,' failures of detector strings in operating PWRs have approached or exceeded 25%, and relaxation of the 75%
requirement has been permitted for the duration of the affected operating cycle.
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In-core detector data is 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. Asea Brown Boveri-Combustion Engineering (ABB-CE) has previously analyzed similar situations including Fort Calhoun Unit 1, Cycle 6, St. Lucie Unit 1, Cycle 4, and Calvert Cliffs Unit 1, Cycle 8.
These analyses showed the increase in the CECOR uncertainties for extreme instrument failure rates of 60 to 75% was in the range of 0.5 to 1%.
The analyzed cases are similar to and bound the extrapolated failure patterns of up to 40% failed detector segments in Calvert Cliffs Unit 1, Operating 1
Cycle 11. As a conservative measure in the absence of explicit evaluation of Operating Cycle 11 uncertainties, if the percentage of operable detector strings falls below 75%, the linear heat rate, total planar radial peaking factor and total integrated radial peaking factor calculated by CECOR will be increased by 1% before they are compared to the values given in the TSs.
Another safety concern relating to degradation of incore mapping ability,is i
the ability to detect anomalous conditions in the core. The current TSs 3.3.3.2.a requires at least eight azimuthal power tilt estimates with a minimum of two estimates of each of the four detector segment axial r
elevations. The proposed revision still requires at least eight azimuthal power tilt estimates, but requires only one estimate at each elevation and two l
estimates at three of the four elevations.
These changes preserve the statistical validity of the tilt estimates and ensure adequate core coverage l
since the requirement that there be at least one operable segment in each quadrant at each elevation is maintained.
This is sufficient because i
azimuthal tilts at one elevation are seen at adjacent levels.
In addition the proposed changes will require that the full core power distribution mapping frequency be increased to at least once per 15 days of accumulated operation in MODE I from the present requirement of once per 31 days of accumulated MODE 1 operation, if the number of operable strings falls below 75%.
The specific TS changes proposed are:
TSs 3.2.2.1, 3.2.3 and 4.2.1.4.b.1 - A footnote requires that when the percentage of OPERABLE incore detector locations fall below 75%, the measured values be increased by 1% prior to being compared to the technical I
specification limits.
Surveillance requirements 4.2.1.4.a, 4.2.2.1.2.b, and 4.2.3.2.b - A footnote requires that when the percentage of OPEPABLE incore detector locations 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.
TS 3.3.3.2.a - A footnote changes the requirement from two quadrant symmetric incore detector segment _ groups at each axial location 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
i b :
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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.
t TSs 3.3.3.2.b.1 and 3.3.3.2.c.1
- A footnote is added to change the minimum number of operable detector segments and strings to be 60%.
Based on the staff evaluation in Section 2.0 above, the staff concludes that the proposed Technical Specification changes are acceptable. These changes are for the remainder of Operating Cycle 11 only.
3.0 STATEMENT OF EXIGENT CIRCUMSTANCES The licensee states that exigent circumstances pursuant to 10 CFR 50.91 exist with respect to the need for consideration of the proposed amendment. The need for this change could not have been foreseen in that 19 of the 45 incore detector strings were replaced during the previous outage and one was removed and not replaced due to mechanical problems.
Prior to reaching 100% power following the refueling outage, 20 detectors had failed.
There have been eight additional detector failures since reaching 100% power. All 28 of these detector failures were in the group of new detector strings installed during the outage. Adding the 4 detectors which were not replaced, 32 of the 180 available detectors (17.8%) are inoperable.
The TSs require that 75% of the detector strings be operable and specific groups be operable for azimuthal power tilt monitoring.
During a phone call on March 26, 1993, the licensee stated that it completed a study and Root Cause Analysis in December of 1992 that justified 60% operable incore detector locations, but was unable to identify the cause of the detector failures nor account for the unexpected large number of failures of l
the newly installed detectors. The licensee assumed that the failure rate i
would decrease and proceeded to initiate a normal TS amendment request because no additional failures had occurred for a 2 month period.
However, 3 l
additional detector failures occurred with the last one being on March 1, 1993. At that point, the licensee determined that the TS limits could be i
exceeded earlier than expected and that exigent circumstances existed.
The licensee further notes that it is impossible to predict when, or if, additional incore detector failures will occur. The time between failures has varied from as much as 62 days to as little as 10 days. As noted in Section 1.0, Introduction, additional failures or combination of failures could result in the shutdown of the unit.
Based on the above, the NRC staff has determined that the licensee has used best efforts to make a timely application and that exigent circumstance are present which warrant processing the requested amendment pursuant to 10 CFR 50.91(a)(6).
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
The Commission has provided standards for determining whether.a_significant l
hazards consideration exists (10 CFR 50.92(c)). A proposed amendment to an l
l l
1 1
, r operating license for a facility involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:
(1) involve a significant increase in the probability or consequences of and accident previously evaluation; or (2) create the possibility of a new or different kind of accident from an accident previously evaluated; or (3) involved a significant reduction in a margin of safety.
The following evaluation, by the licensee and with which we agree, demonstrates that the proposed amendment does not involve a significant 7
hazards consideration.
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 involve a significant increase in the probability or f
consequences of an accident previously evaluated.
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The proposed change would relax 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 i
consistent with the assumptions used in the safety analyses.
Sufficient measurements will be required to adequately verify compliance with power distribution Technical Specification limits.
i P:.nalties 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 l
probability or consequences of an accident previously evaluated.
t 2.
Would not create the possibility of a new difference type of accident from any accident previously evaluated.
i' 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.
3.
Would not involve a significant reduction in a margin of safety.
The proposed changes will continue to protect the current power distribution Technical Specification limits. When the number of operable incore detector strings fall balow the current Technical Specification requirement, a penalty will be added to the measured values before they are compared with the Technical Specification l
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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.
Based on the foregoing, the Commission has concluded that the standards of 10 CFR 50.92 are satisfied.
Therefore, the Commission has made a final determination that the proposed amendment does not involve a significant hazards consideration.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Maryland State official was notified of the proposed issuance of the amendment. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20, and changes surveillance requirements. The NRC staff has determined l
that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a t
proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (58 FR 14594). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.?2(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
M. Chatterton Date: April 2, 1993 L
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April 2,1993 Docket No. 50-317 Mr. Robert E. Denton Vice President - Nuclear Energy Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, Maryland 20657-4702 1
Dear Mr. Denton:
SUBJECT:
ISSUANCE OF EXIGENT AMENDMENT FOR CALVERT CLIFFS NUCLEAR POWER PLANT, UNIT NO. 1 (TAC NO. M85939)
The Commission has issued the enclosed Amendment No.180to Facility Operating License No. DPR-53 for the Calvert Cliffs Nuclear Power Plant, Unit No.1.
This amendment consists of changes to the Technical Specifications (TS) in response to your application transmitted by letter dated March 9,1993.
The amendment revises Technical Specifications 3/4.2, " Power Distribution Limits," and 3/4.3, " Instrumentation," to relax the requirements for the number and distribution of operable incore detectors for the remainder of Operating Cycle 11. The changes also apply penalties to the values measured by the incore detectors prior to their comparison with TS limits to assure that the TS limits monitored by the incore detectors will continue to be valid.
A copy of the related Safety Evaluat.on is enclosed. A Notice of Issuance will be included in the Commission's next regular biweekly Federal Reaister notice.
Sincerely, Original Signed By:
Daniel G. Mcdonald, Senior Project Manager Project Directorate I-l Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation
Enclosures:
1.
Amendment No.180to DPR-53 2.
Safety Evaluation cc w/ enclosures:
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