ML20149H078
| ML20149H078 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 10/31/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20149H076 | List: |
| References | |
| NUDOCS 9411100019 | |
| Download: ML20149H078 (4) | |
Text
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UNITED STATES j
B NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D.C. 20555 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 96 TO FACILITY OPERATING LICENSE N0. DPR-80 AND AMENDMENT NO. 95 TO FACILITY OPERATING LICENSE N0. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT. UNITS l'AND 2 DOCKET NOS. 50-275 AND 50-323
1.0 INTRODUCTION
By letter of February 16, 1994, Pacific Gas and Electric Company (or the licensee) submitted a request for changes to the Technical Specifications (TS) for Diablo Canyon Power Plant, Units 1 and 2 (DCPP). The proposed amendments would revise TS 4.2.2, " Heat Flux Hot Channel Factor - Fo(z)," and 6.9.1.8,
" Core Operating Limits Report," as follows:
(1)
The 2-percent Fo(z) penalty listed in TS 4.2.2.2.e.1) would be deleted and the statement revised to indicate the use of an appropriate factor to be specified in the Core Operating Limits Report (COLR).
(2)
TS 6.9.1.8.b.1. would be changed to reference Revision 1 of WCAP 10216-P-A, " Relaxation of Constant Axial Offset Control Fo(z)
Surveillance Technical Specification," dated February 1994.
2.0 EVALUATION F (z) is the maximum local heat flux on the surface of a fuel rod at core o
elevation z, divided by the average fuel rod heat flux.
The Fo(z) limits specified in TS 3.2.2 preclude core power distributions that violate the following fuel design criteria at DCPP:
(a) during a large-break loss-of-coolant accident (LOCA), the peak cladding temperature must not exceed 2200*F; (b) during a loss-of-forced-reactor-coolant-flow accident, there must be at least 95 percent probability at the 95 percent confidence level that the hot fuel rod in the core does not experience a departure from nucleate boiling (DNB);
(c) during an ejected rod accident, the fission energy input to the fuel must not exceed 280 cal /gm; and i
9411100019 941031 PDR ADOCK 05000275 P
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(d) the control rods must be capable of shutting down the reactor with a minimum required shutdown margin with the highest worth control rod stuck fully withdrawn.
Limits on Fo(z) ensure that the value of the initial total peaking factor assumed in the accident analyses remains valid.
A full-core flux map is taken under equilibrium conditions to determine a meat,ured Fo(z).
This Fo(z) is then increased to account for manufacturing tolerances and measurement uncertainties. The resulting equilibrium-measured M
F{z)includinguncertaintiesiscalledFo (z). During normal operation, o
Fo (z) is shown to be within its limits by performing surveillances.
Fo(z) surveillance must be performed when power has been increased by 20 percent of M
rated thermal power over the thermal power when Fo (z) was last determined, or at least every 31 effective full-power days (EFPDs), whichever occurs first.
M To verify operation below the TS F (z) limit, Fo (z) is shown to be less than o
or equal to a more restrictive limit, which is the surveillance Fo(z) limit.
The surveillance Fo(z) linit is the Fo(z) limit divided by the W(z) transient function. W(z) is a cycle-dependent function that accounts for power distribution transients encountered during normal operation. At DCPP, cycle-specific W(z) is specified in the COLR, based on the Westinghouse Reload Safety Evaluation.
M To account for the increases in Fo (z) that may occur between surveillances, l
DCPPTS4.2.2.2.ereguiresthatwhentheFo(z)surveillanceisperformed,the M
resulting maximum Fo (z)/K(z) value be compared to the maximum Fo (z)/K(z) determined from the previous flux map, where K(z) is the normalized F (z) as o
M a function of core height.
If the maximum Fo (z)/K(z) has irareased since the previous determination of F (z), then TS 4.2.2.2.e allows two options:
o M
(1) either the current Fo (z) must be increased by an additional 2 percent to account for further increases in F (z) before the next surveillance, or o
(2) the surveillance must be performed every 7 EFPDs.
M If it is then determined that fo (z), with the 2 percent penalty applied, exceeds the surveillance Fo(z) limit, continued operation is acceptable provided operational restraints are applied.
Either the uhl flux difference (AFD) limits of DCPP TS 3.2.1 are to be reduced 1 percent for each P?rcent that Fo(z) exceeds its limit, or the requirements of DCPP TS 3.2.2 rmt be met, which include reducing thermal power at least 1 percent for each I percent F (z) axceeds the limit and reducing the power range nuclear flux-o high, trip setpoints.
Tae licensee adopted the F (z) surveillance recommendation in WCAP-10216-P-A, o
" Relaxation of Constant Axial Offset Control F Surveillance Technical o
Specification," dated June 1983, in the fourth operating cycla of DCPP.
WCAP-i 10216-P-A includes the assumption that the F (z) margin will decrease by no o
l
more than 2 percent between month?y flux maps. This assumption was based on previous (pre-1983) core designs that predate low-low leakage loading patterns, high amounts of burnable poisons (such as integral fuel burnable absorbers), and 18-month fuel cycles.
A decrease in the F (z) margin of greater than 2 percent between monthly flux a
maps results in a nonconservative penalty being used to evaluate the Fo(z) margin for surveillances performed in accordance with TS 4.2.2.2.e.
Therefore, Fa(z) could exceed the Fa(z) limit between monthly flux maps without implementation of the operational restraints of TS 3.2.1 or 3.2.2.
DCPP operating experience has shown that Fo"(z) increases in the beginning of the fuel cycle, with a subsequent peak at a burnup of approximately 3000-megawattdayspergetrictonuranium(MWD /MTU),andthenexhibitsa general decrease in Fo (z) throughout the remainder of the cycle.
The licensee submi+ted DCPP Licensee Event Report (LER) 1-93-004-00 on October 19, 1993, regarding the use of a nonconservative penalty for the Fo(z) surveillance.
Revision I to WCAP-10216-P-A was approved by the NRC on November 26, 1993. As an enhancement to the TS surveillance methodology, Revision 1 to WCAP-10216 accounts for Fa(z) margin decreases of greater than 2 percent between monthly flux maps. DCPP has experienced decreases in Fo(z) margin of more than 2 percent between monthly flux maps in the early portions of Unit 1 Cycle 6 and Unit 2 Cycles 4 and 5.
For those DCPP core designs which are predicted to have margin decreases of greater than 2 percent in F (z) over certain burnup a
ranges, a larger penalty to Fo(z) will be provided by Westinghouse on a cycle-specific basis. Otherwise, a minimum F (z) penalty of 2 percent will a
be used.
The licensee has implemented administrative controls to apply a more conservative F (z) penalty than the current TS. These administrative a
controls will ensure that the F (z) penalty adequately bounds predicted o
margin decreases between surveillances.
The proposed changes would require an F (z) penalty of at least 2 percent, o
which is currently listed in TS 4.2.2.2.e.1), to be included in the COLR.
For a core design which predicts margin decreases larger than 2 percent, a larger penalty would be included in the COLR on a cycle-specific basis.
Thus, the proposed changes conservatively ensure that the F (z) penalty adequately a
bounds margin decreases of greater than 2 percent between surveillances.
Revisions to the COLR will be evaluated in accordance with 10 CFR 50.59. COLR 1
revisions will assure conformance to 10 CFR 50.36.
The NRC will be notified of all revisions to the C0LR in accordance with TS 6.9.1.8.
All COLR I
revisions will be based on NRC-app.7ved methodologies.
Revisions to the F (z) penalty will be based on the Westhghouse methodology, previously a
reviewed and approved by the NRC, in WCAP-10216-P-A, Revision 1.
Calculating i
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this cycle-specific parameter in accordance with an approved NRC methodology ensures that the parameters are consistent with the applicable safety analysis addressed in the DCPP final safety analysis report (FSAR) update.
Therefore, the staff finds the proposed changes acceptable.
3.0 STATE CONSULTATION
i In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendments.
The State official i
had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
j These amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve 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 proposed finding that the amendments involve no significant hazards considera-tion, and there has been no public comment on such finding (59 FR 17603).
Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in i
connection with the issuance of the amendments.
5.0 CONCLUSION
i The Commission has concluded, based on the considerations discussed above, I
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:
S. Peterson i
)
Date:
October 31, 1994
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