ML20235F979
| ML20235F979 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 07/01/1987 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| Shared Package | |
| ML20235F982 | List: |
| References | |
| NUDOCS 8707140059 | |
| Download: ML20235F979 (4) | |
Text
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Duxn Pownn COMPANY P.O. DOX 33180 CIIAHLOTTE N.O. 28242 IIAL H. TUCKEH TELEPHONE m ecuensur,y (704) 373-4531 NE& LEAR PRODUO110N i
July 1, 1987 l
U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washingtan, D. C. 20555
Subject:
Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 Technical Specification Amendment Reactor Coolant System (RCS) Flow Rate
Dear Sir:
Per telephone conversations between Duke Power personnel and members of the NRC Staff, attached is further clarification of our Technical Specification amendment request which was transmitted by letters dated July 31, 1985 and November 8, 1985.
This request deals with allowing unit operation above 50% power with RCS flow between 90% and 100% of the total required flow.
The attachment also contains a proposed ACTION statement to be included in the affected Technical Specification. This proposed ACTION statement would add an additional restriction to the Specification which is an additional limitation not presently included in the Specifications. Therefore, this change is cimilar in nature to example (ii) contained in the Federal Register Notice (FR 14870, Volume 48, no. 67), and thus does not involve a significant hazard consideration.
If you required any further information please advise.
Very truly yours, dA'72P Hal B. Tucker RWO/85/sbn Oh Attachment l
8707140059 870701 PDR ADOCK 05000413 p
U. S. Nuclsar Pssguletory Commission July 1, 1987 Page Two xc:
Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. P. K. Van Doorn NRC Resident Inspector Catawba Nuclear Station Mr. Heyward Shealy, Chief Bureau of Radiological Health South Carolina Department of Health &
Environmental Control 2600 Bull Street Columbia, South Carolina 29201 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 American Nuclear Insurers c/o Dottie Herman, ANI Library The Exchange, Suite 245 270 Farmington Avenue Farmington, CT 06032 M&M Nuclear Consultants 1221 Avenue of the Americas New York, New York 10020 l
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Technical Specification 3.2.3 requires the Reactor Coolant System (RCS) total flow rate to be greater than 396100 gpm or thermal power must be reduced to less than 50% Rated Thermal Power (RTP) and the Power Range Neutron Flux - High Trip Setpoint must be reset to less than 55% RTP. The flow is determined by precision heat balance measurements at Jeast once per 18 months and the elbow meter flow constants are changed such that the indicated flows and precision heat balance calculated flows are equal. The elbow meters are used for continuous flow indications with verification that the total flow is greater than 396100 gpm required by Technical Specification 4.2.3.3 at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The proposed Technical Specification revision allows operation at flows slightly lower than 396100 gpm if thermal power is reduced by 2% RTP for each 1% RCS flow is less than 396100 gpm.
The impetus for the proposed revision was that the measured flow for Catawba Unit I has been approximately 398000 gpm which provides only 0.5%
flow margin. Given the expected measurement variations due to instrumentation and process effects, potential exists for a flow measurement below 396100 gpm.
The limitation of power to less than 50% RTP is an unnecessarily sever penalty for minor flow discrepancies.
Such power restrictions due to RCS flows slightly less than Technical Specification limits were experienced at the McGuire Nuclear Station and led to the development of the graduated power / flow specification. As FSAR analyses have been redone for a variety of reasons for Catawba (MTC limit justification, core reloads, etc.), the RCS flow assumption has been redueed and a future Technical Specification revision request will propose reducing the 396100 gpm flow to 387600 gpm.
The proposed graduated power / flow specification (2% RTP per 1% flow) remains desirable due to the potential for a required major power reduction in response to a minor change in the measured RCS flow.
The low flow reactor trip is set at approximately 90% of the Technical Specification required 396100 gpm and thus prevents operation with significant flow reductions.
The justification for the 2%
RTP power reduction per 1% RCS flow deficiency was originally based upon the sensitivities of DNBR to power and flow determined by several independent sources using different assumptions and computer codes. The plant response to a FSAR Chapter 15 transient initiated from the reduced flow / reduced power operating regions would continue to satisfy the applicable acceptance criteria based upon margins available in the Chapter 15 analyses, protection system setpoint calculations, and thermal-hydraulic analyses including the use of a minimum allowable DNBR greater than that justified by the Improved Thermal Design Procedure.
Duke has confirmed that adequate margins exist in the related analyses to justify the proposed Technical Specification changes.
The limiting events in regard to the proposed operating regions are the reactivity insertion transients which increase reactor power. The RCCA group withdrawal analyses provide the most limiting cases with the reactor trip signal assumed to be due to either the Overtemperature Delta-T or the Power Range Neutron Flux-High Trip Setpoint trip functions.
The review determined that the low flow penalties for the RCCA group withdrawals initiated from the proposed operating regions would require dedication of most of the available DNBR margin and thus Duke has decided to use protection system setpoint reductions and more restrictive limits on core power distributions to compensate for the potential RCS flow deficiency.
The attached revision to the proposed Technical Specification includes an action statement requiring a reduction in the Power Range Neutron Flux-High Trip Setpoint to below the nominal setpoint by the same amount (%RTP) as the power reduction required by Figure 3.2-3 (2% RTP per 1% RCS flow). By maintaining the 2% RTP per
1% RCS flow tradeoff at the trip conditions as well as the steady-state conditions, the high flux setpoint reduction ensures the DNBR margin existing in the FSAR analyses is maintained for those events assumed to utilize the Power Range Neutron Flux-High Trip Setpoint trip function.
For those FSAR Chapter 15 events which assume Overtemperature Delta-T protection, the review concluded that an administrative control on a term within the setpoint equation and the restriction of core power distributions are adequate to ensure margins in the analyses are maintained. The term Delta-T in the setpoint equation is defined as the indicated Delta-T at rated thermal power.
The ratio of the measured Delta-T to Delta-T. is thus equivalent to %RTP and is compared to the Overtemperature Delta-T setpoint. By maintaining Delta-T. at or below the equivalent Delta-T at 100% RTP and 396100 gpm, any flow deficiency will result in an increase in the actual Delta-T and an overestimation of power level.
The overestimation of power is equivalent to a trip setpoint reduction of approximately 1% RTP per 1% flow deficiency. The limitations placed on F Delta-h for reduced RCS i
flow conditions prevent the usual allowance for increasing F Delta-h at reduced power levels. Reductions in power levels combined with a RCS flow deficiency and increased radial peaking do not maintain DNER margin and thus the F Delta-h restrictions in Figure 3.2-3 are required.
In summary, the review of the FSAR Chapter 15 analyses resulted in the RCCA group withdrawals being identified as the limiting events in regard to the proposed reduced flow / reduced power operating regions.
For those cases assumed to trip due to the Power Range Neutrou Flux-High Trip Setting trip function, reduction of the i
Setpoint by 2% RTP power 1% RCS flow deficiency ensures DNBR margin is maintained.
I The definition of Delta-T. as the equivalent Delta-T at 100% RTP and the greater of I
the measured RCS flow or 396100 gpm results in an effective Overtemperature Delta-T setpoint reduction and maintains DNBR margins for those cases reliant upon the Delta-T trip. The additional restrictions on F Delta-h ensure that the margins gained by the power and setpoint reductions are not reduced by the normally allowable increases in radial peaking at reduced power levels.
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