ML19312C445
| ML19312C445 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/31/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19312C442 | List: |
| References | |
| NUDOCS 7912130972 | |
| Download: ML19312C445 (4) | |
Text
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UNITED STATES 1
NUCLEAR REGULATORY COmlSSION f
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CASHINGTON, C. C. 20005
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 49 TO LICENSE NO. OPR-38 AMENDMENT N0. 49 TO LICENSE NO. DPR-47 AMENDMENT N0. 46 TO LICENSE NO. DPR-55 DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS I, 2 AND 3 DOCKET NOS. 50-269, 50-270 AND 50-287 Introducticn By letter dated October 26, 1977, Duke Power Company (the licensee) requested chalLqes.to the Technical Specifications appended to the Oconee Unit 1 operating license.
These changes provide for oper1ttion with a flux tilt greater than 3.41%.
For operation with a flux.* tit in excess of 3.41% but below 6.03%, operation would not exceed 75%
rated power.
Operation with a flux tilt greater than 6.03% is not authorized.
Evaluation
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During the Cycle 4 physics startup test program at Oconee 1, a quadrant flux tilt, defined as (100_((Quadrant Power / Average Power of. All Quadrants)-1)), was discovered to be greater than current Technical Specifications limits.
This condition is allowed during physics teating.
This anomaly was first observed as low ejected rod wc rth measurements at ilot zero power, critical boron conditions.
Since all other parameters were within acceptance criteria and the ejected rod worth measurements were more conservative than predicted, continued physics testing to evaluate icw ejected rod worth was initiated.
The next physics tests were conducted at 15% power. The incore instrument power distribution measurement showed quadrant flux tilts of +10% and -12%.
The pat Uve tilt qu.hirant contains the rod of maximum ejected rod worth as would be expected.
In order to obtain a more accurate power distribution measurement, additional physic's t'ests were performed at 40% of full
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power. The results of the power distribution measurements confinned i
the presence of the tilt and showed that the magnitude decreased with I
power level.
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. physics test power, was performed. The results of the peger distribution measurements confirmed the presence of the tilt and showed that the magnitude decreased with power level.
The licensee and fuel manufacturer (bebcock and Wilcox) have performed numerous analyses, tests and administrative reviews to identify the cause of the quadrant flux tilt.
They have considered the following potential causes:
1.
Uncoupled control rod assembly (CRA) 2.
Broken CRA fingers in controlled assembly 3.
Broken CRA fingers in non-controlled assembly 4
Misloaded fuel assembly 5.
Flow blockage 6.
Abnormal enrichment 7.
Cycle 3 operational anomolies 8.
New axial power shaping rod (APSR) 9.
Patching of CRA may be incorrect
- 10. Shuffling of unborated poison ~ ass ~embly~
- 11. Cycle 1 assemblies
- 12. Cycle 3 misloading Testing has been performed to detect uncoupled control rods and/or missing control rod pois a pins.
The integrity of the control rods has been verified by the absense of silver in the reactor coolant.
Reviews of manufacturing and design records have been conducted with no evidence of misloading. These previously enunerated items have been extensively evaluated and currently none have been identified as th2 cause.
The licensee has proposed to continue physics testing at the next planned test sequence for 75% of full power. The licensee shall perform a three dimensional, power distribution measurefiieits a~ t equilibrium xenon condi tions.
This power distribution measurement will be used to observe the effect of increased power on the tilt. The licensee has also proposed a change to the Oconee 1 Technical Specifications to provide additional safety margin for thi_s power level. The change would allow operation with flux tilt greater than 3.41% under the following conditions:
(1) restrict power operaticn to 75%, (2) reduce the overpower trip set point to 84%, (3) limit the quadrant tilt to 6.03% and (4) establish new rod position limits.
The high power, reactor trip is provided to prevent damage to the fuel cladding from riactivity excursions too rapid to be detected by pressure and temperature measurements.
During normal plant operation with all reactor coolar.t pumps operatirq reactor trip is initiated when reactor power level raaches 105.5% of rated power. The safety analysis for these 1
" rapid reactivity excursions is perfonned conservatively with consideration of calibration and instrument errors. Thereforeuthe reduction _qf this trip function to 84% of full power with flux tilt in excess of 3.41%
will provide substantial additional safety margin.
The quadrant power tilt limit is to prevent peaking increase in the linear heat generation rate (LHGR).
The analyses which established the current quadrant tilt limit was based on a 3.4% tilt which results in a 5.1% power peaking increase.
The proposed 6.03% tilt would produce a maximum power peaking increase of 9%. The power restriction to 75% power or below ensures that the proposed specification on tilt maintains a substantial margin (25%
power reduction as compared to =4% power peaking increase) for LH6R limits.
The licensee has stated that the observed tilt is not a localized effect, i.e., within a region.
Because of this non-localized characteristic of the tilt and the potential power peaking increase, the proposed quadrant tilt limit is acceptable.
The rod position limits are based on the most limiting of the following criteria:
Emergency core cooling system (ECCS) power peaking, shutdown margin, and potential ejected rod worth. The proposed rod position limits are more conservative than those currently in the Oconee Unit 1 Technical Specifications.
The licensee has stated that based on maintaining the current power imbalance Specification 3.5.2.6 with the 75% power restriction and the proposed rod position limits, the maximum cladding temperature in the event of a LOCA will not exceed the Final Acceptance Cri te ri a. These proposed rod position limits also ensure the shutdcwn margin and ejected rod worth criteria are met. The measured and predicted hot zero power values of rod worths were compared and the most restrictive value was used to determine the proposed rod insertion limits. Based on these considerations the proposed rod position limit is acceptable.
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We consider operation at 75% power or below acceptable provided tilt does not exceed 6.03% and maximum power peaking increases does not exceed 9%.
Nevertheless, we believe that the investigation of the quadrant tilt observed should be continued and resolved promptly.
Consequently, we have required that within 25 EFPD the licensee provide a report and analysis of the quadrant flux tilt observed and projections for the next 25 EFPD. Operation above 75% is not autnorized if flux tilt is above 3.41% unless an amendment request is submitted accompanied by detailed evaluation and justification.
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Based on our evaluation, operation in the proposed manner does not reduce the safety margins of the current Technical Specification limits.
Operation with a higher flux tilt has been compensated with (1) a restriction to operate at a lower power level, (2) a restriction to the overpower setpoint by, lowering the setpoint and (3) a more restrictive control rod position specification. These restrictions will assure that neither the probability nor consequences of any transients and accidents considered in the FSAR are not increased and that the safety margins are not reduced.
Thus we conclude that these changes do not involve a significant hazards consideration.
Environmental Consideration We have determined that these amendments do not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that these amendments involve an action which is insignificant from the standpoint o' environmental impact and pursuant to 10 CFR 551.5(d)(4) that an enviroi mental impact statement, negative declaration, or environmental impact appraisal need not be prepared in connection with the issuance of these amendments.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendments do not involve a significant increase in the probability or consequences of accidents previously considered and do not involve a significant decrease in a safety margin, the amendments do not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Date: October 31, 1977 i
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s UNITED STATES NUCLEAR REGULATORY COMMISSION DOCKET NOS. 50-269, 50-270 AND 50-287 DUKE POWER COMPANY NOTICE OF ISSUANCE OF AMENDENTS TO FACILITY OPERATING LICENSES The U. S. Nuclear Regulatory Comission (the Comission) nas issued Amendment Nos. 49, 49 and 46 to Facility Operating Licenses Nos. DPR-38, DPR-47 and DPR-55, respectively, issued to Duke Power Company which revised Technical Specifications for operation of the Oconee Nuclear Station Unit Nos.1, 2 and 3, located in Oconee County, South Carolina. The amendments are effective as of their date of issuance.
These amendments revise the Technical Specifications to allow operation of Oconee Unit 1, Cycle 4 with a quadrant flux tilt in excess of 3.41%, provided power is restricted to 75% rated pcwer for operation with flux tilt in excess of 3.41% and provided that flux tilt does not exceed 6.03%.
The application for these amendments complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Comission's rules and regulations. The Comission has made appropriate findings as required by the Act and the Comission's rules and regulations l
in 10 CFR Chapter I, which are set forth in the license amendments.
Prior public notice of these amendments was not required since the amendments do not involve a significant ha::ards consideration.
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. The Commission has determined that the issuance of these amendments will not result in any significant environmental. impact and that pursuant to 10 CFR 551.5(d)(4) an environmental impact statement, negative declaration, or environmental impact appraisal need not be prepared in connection with issuance of these amendments.
For further details with respect to this action, see (1) the application for amendments dated June 6,1977,(2) Amendment Nos. 49,
49 and 46 to Licenses Nos. OPR-38, OPR-47 and DPR-55, respectively, and (3) the Commission's related Safety Evaluation.
All of these items are available for public inspection at the Commission's Public Document Room, 1717 H Street, N. W., Washington, D. C.
20555 and at the.0conee County Library, 201 South Spring, Walhalla, South Carolina 29691.
A copy of items (2) and (3) may be obtained upon request addressed to the U. S.
Nuclear Regulatory Commission, Washington, D. C.
20555, Attention:
Director, Division of Operating Reactors.
Dated at Bethesda, Maryland, this 31st day of October 1977.
FOR THE NU EAR REGULATORY COMMISSION A
r A Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors O
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