ML20195H358
| ML20195H358 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/14/1988 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| Shared Package | |
| ML20195H364 | List: |
| References | |
| 87-621, NUDOCS 8801190278 | |
| Download: ML20195H358 (15) | |
Text
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10 CFR 50.90 VIHUINIA ELucTHIC AND l'OWHH COMPANY HicnwoNo,V NOINIA 20061
- w. I.. sr===r January 14, 1988 Vice Passepant Ncessam oranAtsome United States Nuclear Regulatory Commission Serial No.87-621 Attention: Document Control Desk E&C/JRH/cdk Washington, DC 20555 Docket No.
50-338 License No.
NPF-4 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT NO. 1 PROPOSED TECHNICAL SPECIFICATIONS CHANGE RELAXED POWER DISTRIBUTION CONTROL Pursuant to 10 CFR 50.90, the Virginia Electric and Power Company requests amendments, in the form of changes to the Technical Specffications, to Operating License No. NPF-4 for North Anna Power Station Unit No. 1.
These amendments support the implementation of Virginia Power's Relaxed Power Distribution Control (RPDC) Methodology, as described in topical report VEP-NE-1-A of the same name, for North Anna Unit 1.
The me'.hodology provides a wider range of allowable axial power asym:setry by performing analyses of the pertinent key safety parameters on a reload basis. RPDC has already been licensed for North Anna Unit 2,
and the proposed changes to the Unit 1
Technical Specifications are identical to those which were approved for Unit 2.
The Core Surveillance Report required by proposed Technical Specification 6.9.1.7 is also attached.
In order to benefit from RPDC during the latter part of cycle operation when it is needed most, we request approval of these changes by June 15, 1988.
This request has been reviewed by the Station Nuclear Safety and Operating Comit tee and the Safety Evaluation and Control staff.
It has been determined that this request does not involve any unreviewed safety questions as defined in 10 CFR 50.59 or a significant hazards consideration as defined in 10 CFR 50.92.
The basis for the determination that no ef.gnificant hazard consideration is involved is presented in Attachment 1 in accordanca with 10 CFR 50.91(a).
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We have evaluated this request in accordance with the criteria in 10 CFR 170.12. A voucher check in the amount of $150.00 is enclosed as an application fee.
Very truly yours, "m
M W. L. Stewart Attachments 1.
Safety Evaluation 2.
Proposed Technical Specification Changes Unit 1 3.
Core Surveillance Report 4.
Application Fee cc: U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W.
Suite 2900 Atlanta, GA 30323 Mr. J. L. Caldwell NRC Senior Resident Inspector North Anna Power Station Mr. Charles Price Department of Health 109 Governor Street Richmond, Virginia 23219 i
COMMONWEALTH OF VIRGINIA )
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CITY OF RICHMOND
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The foregoing document was acknowledged before me, in and for the City and Commonwealth aforesaid, today by W. L. Stewart who is Vica President - Nuclear Operations, of Virginia Electric and Power Company. He is duly authorized to execute and file the aforegoing document in behalf of that Company, and the statements in the document are true to the best of his knowledge and belief.
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130-JRH-2330B-1 9
r SAFETY EVALUATION PROPOSED TECHNICAL SPECIFICATION CHANGES - NORTH ANNA UNIT 1 INTRODUCTION The heat flux hot channel factor (FQ) operating limit specified in the North Anna Technical Specifications is established by LOCA/ECCS analyses performed in accordance with 10 CFR 50 Appendix K.
These analyses show that if the FQ limit is not exceeded, the predicted LOCA peak clad temperature will not OReed the 2200'F limit specified in the Final ECCS Acceptance Criteria. The Technical Specifications also establish the required method for verification that the actual peaking factor realized during operation will not exceed the axially dependent peaking factor (FQ(Z)) limit.
This verification is currently performed by combining the axially dependent radial peaking factor, Fxy(Z), which is determined by periodic surveillance with the core flux monitoring system, with an analytically determined axial peaking factor (PZ(Z), Refs.
1-2).
The determination of PZ(Z) involves evaluating various plant operating maneuvers such as load following.
The analysis currently assumes the Constant Axial Offset Control (CAOC) operating strategy discussed in Reference 1.
During CA0C operation, the measured core axial flux difference (AFO) is maintained within a fixed band (+ or - 5%) of a target value.
The target AFD is established by equilibrium operating conditions.
130-JRH-2330B-2
The proposed changes will replace the CA0C AFD limits with a set of limits established by the Relaxed Power Distribution Control (RPDC) methodology discussed in Reference 2.
These changes have been approved previously (Ref. 3) for North Anna 2.
The important feature of the RPDC strategy is that, instead of analytically verifying the peaking factor (FQ) margin for a fixed AFD limit band, the AFD band is varied until the available FQ margin, which increases as power decreases, is utilized.
Because a wider range of axial shapes can be realized under RPDC normal operation, additional analyses must be performed to verify that the overtemperature delta-T (0 TDT) and averpower delta-T (0PDT) trips continue to provide adequate DND and local overpower (high kw/ft) protection over the entire range of anticipated Condition II events.
In addition, the shapes are evaluated as potential preconditions for the Complete loss of Flow accident, to ensure that no DNB violations would occur during the bounding, non-0 TDT-protected accident. The methodology for performing this verification is discussed in further detail in Reference 2.
Additionally, the current requirement for monitoring the axially dependent radial peaking factor, Fxy(Z), is being replaced by a requirement to monitor the total peaking factor FQ(Z). This is accomplished by taking a full core flux map under equilibrium conditions and increasing the measured value by appropriate factors to account for manufacturing tolercnces and measurement uncertainties.
Finally, since FQ(Z) is measured under equilibrium conditions, a nonequilibrium factor, N(Z),
is applied.
N(Z) accounts for the maximum potential increase in local peaking which could occur during transient, nonequilibrium operation.
In accounting for transient effects, N(Z) thus has a function which is similar to PZ(Z) in the current approach.
The difference is that where P(Z) is a nonequilibrium axial peaking factor N(Z) envelopes the 130-JRH-2330B-3
d' potential equilibrium-to-nonequilibrium FQ increase and accounts for both axial and radial xenon and power redistribution effects.
ITEM BY ITEM DISCUSSION 0F CHANGES 1.
Replacement of CAOC Axial Flux Difference (AFD) Limits with RPDC Limits (Sections 3.2.1,4.2.1,B3/4.2.1and3.10.2)
All references to the indicated AFD target and operating band have been deleted, replacing them with AFD limits consistent with the RPDC methodology of Reference 2.
These limits will be provided on a cycle specific basis in the Core Surveillance Report.
In the Action Statement associated with the Limiting Condition for Operation (LC0), the requirement to restore the indicated AFD to within the limits within 15 minutes has been retained.
If this requirement is not met, power must be reduced to less than 50% of rated within 30 minutes. As discussed in Reference 2, maintaining the AFD within the prescribed limits will ensure that:
- 1) the maximum expected FQ(Z) will not exceed the limit specified in Section 3.2.2; 2)the axial power distribution in the core will not fall outside the range of preconditions used to ensure that the overtemperature delta-T and overpower delta-T functions provide adequate core protection; and
- 3) the UFSAR analysis of the complete loss of Flow event remains limiting. The lower limit of 50% power on imposing AFD limits is consistent with the current i
Technical Specifications.
Reference to the Special Test Exception of Section 3.10.2 has been removed from Section 3.2.1.
Thus the specified axial flux difference limits will apply during the performance of physics tests.
130-JRH-2330B-4
t 1
a 2.
Deletion of the Requirement to Place the Reactor in at least Hot Standby' to Reduce the Overpower Delta-T Trip Setpoint (Section 3.2.2, Action a)
The requirement to place the unit in Hot Standby in order to reduce the Overpower delta-T trip setpoint has been deleted since the reduction can be performed, one channel at a time, while at power.
3.
Removal of all References to the Axial Power Distribution Monitoring System (APDMS) (Section 3.2.2, Action a.2, Sections 3.2.6, B 3/4.2.6, 6.9.1.7)
Under the existing Specifications, use of APDMS is required at or above power levels for which the product of the analytically predicted FQ (from the load follow analysis discussed previously) and power exceeds the current LOCA limit.
Under the RPDC philosophy, the operating limits on axial offset are established to ensure that the FQ LOCA limit is not exceeded.
Thus the cycle-to-cycle variations in analytically predicted maximum FQ (and therefore APDMS turn-on power level) which occur under the existing specifications will be eliminated.
Rather, the delta-I (Axial Flux Difference) envelope is now the important analysis output variable that is subject to cycle-by-cycle analytic verification.
The revised Specifications provide a method for compensating for any FQ violations that could potentially occur under nonequilibrium conditions by narrowing the delta-1 limits. APDMS is a redundant measure and therefore not required for operation with RPDC/FQ surveillance.
130-JRH-2330B-5
4.
Replacement of Fxy Surveillance Requirement with FQ Surveillance (Sections 4.2.2, B3/4.2, B3/4.2.3, 6.9.1.7) i The existing specifications require periodic verification that FQ(Z) remains below its limit by monitoring the radial peaking factor Fxy(Z) and comparing to a cycle-specific limit.
This limit is established such that the maximum product of the Fxy(Z) limit and the analytically predicted nonequilibrium axial peaking factor PZ(Z) remains below the FQ(Z) limit (Ref. 1). The revised specifications require a direct measurement of FQ at least once per 31 effective full power days.
The measured FQ is then increased by the nonequilibrium factor N(Z) to account for power distribution transients during normal operation.
Development of the cycle-specific N(Z) factor negates the requirement to generate the axial peaking factor (PZ(Z)) for each reload cycle.
Since FQ is measured directly, the requirement for cycle-dependent Fxy surveillance is no longer necessary.
5.
ModificationoftheCoreSurveillanceReport(Section6.9.1,7) i As discussed previously, FQ surveillance requires the use of the N(Z) function as a cycle specific multiplier on FQ(measured) in order to incorporate nonequilibrium effects. The Core Surveillance Report provides this function to the commission on a cycle-by-cycle basis, replacing the current requirement to provide the Fxy limit, the surveillance power level and the FQ flyspeck.
The Core Surveillance Report also contains the cycle specific Axial Flux Difference limits for Technical Specification 3.2.1.
130-JRH-23308-6
SAFETY EVALUATION RESULTS Virginia Power has performed a detailed review of the impact of operation with Relaxed Power Distribution Control /fQ Surveillance on the various accident scenarios discussed in Chapter 15 of the North Anna UFSAR.
Specifically, the impact of the wider axial flux difference on key safety parameters which could influence accident analysis results has been assessed. Among those parameters considered are: trip reactivity, both total value and reactivity as a function of rod insertion; shutdown margin; reactivity insertion rates due to rod withdrawal from subcritical and at power; and rod worths and/or peaking factors for ejected, dropped or misaligned control rods.
This review has demonstrated that, apart from the RPDC limit generation procedures discussed in detail in Reference 2, no changes will be required to other core reload safety analysis methods to incorporate the effect of the widened delta-I band resulting from the RPDC methodology.
The current analysis i
methods used by Virginia Power (Ref. 4) already employ a conservative method i
for incorporating the effects of skewed axial power distributions.
These methods, including the interaction with RPDC, are described in Reference 4 which has been approved by the NRC (Ref. 5). As is currently the practice, the accident analyses will continue to be evaluated on a reload basis for RPDC i
operation to ensure that the key input parameters remain bounding. Should an i
accident analysis be determined to be impacted by a specific reload design, 2
that accident will be evaluated or reanalyzed, as appropriate.
i l
l 130-JRH-23308-7
b APPLICATION TO UNIT 1. CYCLE 7 The North Anna Unit 1 Cycle 7 (NIC7) reload core design has been evaluated for i
operation under the proposed RPDC Technical Specifications in accordance with the methodology presented in Reference 2.
The analysis included examination of the LOCA and complete Loss of Flow Accident (LOFA) preconditions, the peak linear power (kw/ft), the overtemperature delta-T f(delta-I) function and the fuel rod design criteria.
The appropriate Core Surveillance Report and AFD limits were also generated. These analyses assumed implementation after 3000 MWD /MTU burnup; the analyses for subsequent cycles will support RPDC operation throughout the entire cycle.
The analysis results yielded two conclusions:
- 1) none of the normal operation conditions allowed by RPDC were found to violate the key safety criteria, and 2) all of the Condition II events examined in the FSAR were shown to yield acceptable results when initiated from any of these normal operation conditions.
The RPDC bands were thus found to be an l
acceptable operating space.
10 CFR 50.59 SAFETY REVIEW Based on a detailed safety evaluation, Virginia Power has concluded that implementation of the proposed Relaxed Power Distribution Control /FQ Surveillance Technical Specifications will not introduce an unreviewed safety question as defined in 10 CFR 50.59.
Specifically:
130-JRH-23308-E
1.
Since the proposed changes involve only a relaxation of the limits in axial power distribution skewing, neither the probability of occurrence nor the consequences of any accident or malfunction of equipment important to safety previously evaluated in the safety analysis report is increased by these proposed changes.
Furthermore, the RPDC analysis procedures and continued application of current reload design and safety analysis methodology will ensure that the UFSAR accident analyses remain bounding.
2.
The proposed changes do not involve any alterations to the physical plant which introduce any new or unique operational modes or accident precursors.
Thus the possibility for an accident or malfunction of a different type than any evaluated prt.viously in the safety analysis report is not being created by these proposed changes.
3.
While a relaxation of the axial offset operating limits is realized, the margin of safety as defined in the basis for any technical specification is not reduced by these proposed changes; the margins of safety are preserved by the imposition of a frequent FQ surveillance requirement and by effectively reducing the limit on measured equilibrium FQ by a conservative nonequilibrium factor, N(Z).
130-JRH-2330B-9
i 10 CFR 50.92 SIGNIFICANT HAZARDS CONSIDERATION REVIEW Based on a detailed safety evaluation, Virginia Power has concluded that implementation of the proposed Relaxed Power Distribution Control /FQ Surveillance Technical Specifications will not result in a significant hazards consideration as defined in 10 CFR 50.92.
Specifically:
1.
The changes do not involve a significant increase in the probability or
~
consequences of an accident previously evaluated.
The proposed changes involve only a relaxation of the limits in axial power distribution skewing which has been previously reviewed and approved by the NRC staff for application to North Anna Unit 2.
Furthermore, the approved RPDC analysis procedures and continued application of current reload design and safety analysis methodology will ensure that the UFSAR accident analyses remain bounding.
2.
The proposed changes do not involve any alterations to the physical plant which introduce any new or unique operational modes or accident precursors.
[
Thus the possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report is not being created by these proposed changes.
f I
J 130-JRH-23308-10
t 3.
There is no significant reduction ia the margin of safety.
While a relaxation of the axial offset operating limits is realized, the margin of safety as defined in the basis for any technical specification is not reduced by these proposed changes; the margins of safety are preserved by the imposition of a frequent FQ surveillance requirement, by effectively reducing the limit on measured equilibrium FQ' by a conservative nonequilibrium factor, N(Z), and by reload verifications of the DNB, linear power and clad integrity criteria.
130-JRH-23308-11
h REFERENCES 1.
- Morita, T.,
et al.:-
"Topical Report - Power Distribution Control Load Following Procedures," WCAP-8385, Westinghouse Electric Corporation, (Septe-N r 1974).
2.
- Basehore, K.,
et al.:
"Relaxed Power Distribution Control Methodology and Associated FQ Surveillance Technical Specifications," VEP-NE-1-A, Virginia ElectricandPowerCompany,(March 1986).
3.
Letter from L.
B.
Engle (NRC) to W. L. Stewart (Vepco), approval of the Relaxed Power Distribution Control Methodology for North Anna Unit 2, dated April 14,1986.
4.
"Reload Nuclear Design Methodology," VEP-FRD-42 Revision I-A, (September, 1986).
5.
Letter from C. E. Rossi (NRC) to W. L.
Stewart (Vepco),
"Acceptance for Referencing of Licensing Topical Report VEP-FRD-42 Revision 1
' Reload Nuclear Design Methodology,'" dated July 29, 1986.
b l
i i
i 130-JRH-23308-12