ML20059C420
| ML20059C420 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/26/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059C415 | List: |
| References | |
| NUDOCS 9311010149 | |
| Download: ML20059C420 (5) | |
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UNITED STATES f))N, j NUCLEAR REGULATORY COMMISSION j
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c WASHINGTON. D.C. 20555-0001
'%; v*... f' ENCLOSURE 3 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.171 TO FACILITY OPERATING LICENSE NO. DPR-77 AND AMENDMENT NO.161 TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SE0VOYAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
By application dated June 21, 1993, the Tennessee Valley Authority (TVA or the licensee) proposed amendments to the Technical Specifications (TS) for Sequoyah Nuclear Plant (SQN) Units 1 and 2.
The requested changes would revise the method of determining the most negative moderator temperature coefficient (MIC) for end of cycle (E0C) and the associated 300 ppm surveillance requirement (SR) limits specified in the Core Operating Limits Report (COLR).
The purpose of the 300 ppm SR is to ensure that the most negative MTC at E0C remains within the bounds of the SQN Units 1 and 2 safety analyses, in particular for those transients and accidents that assume a constant value of the moderator density coefficient (MDC) of 0.43 delta-K per gm/cc.
The SQN SR involves an MTC mea:urement at any thermal power within 7 effective full power days (EFPD) after reaching an equilibrium primary coolant boron concentration of 300 ppm.
After appropriate corrections are made, the measured value is compared to the 300 ppm SR limit value specified in the COLR j
at the all-rods-out (ARO) rated thermal power (RTP) condition.
In the event i
that the measured HTC is more negative than the 300 ppm SR limit, the MTC must i
be remeasured and compared with the E0C MTC limiting condition of operation
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(LCO) value at least once per 14 EFPD during the remainder of the operating cycle.
The 300 ppm SR and E0C LCO values for the most negative MTC are conservative (less negative) when compared to the value of the MTC used in the safety analyses.
SQN also proposed to revise the current method for determining the 300-ppm surveillance and the E0L MTC limits specified in the COLR.
i The rev sed method for determining the COLR MTC limits will result in a change to the IS Bases Section B 3/4.1.1.3.
This revised method and the COLR MTC limi; changes do notaffectthemaximum(MDC]F.value of 0.43 delta k/gm/cc, wht:.n corresponds to an MTC value of -52.68 pcm/
These changes apply to the current and future reload cycles for SQN Units 1 and 2, and are supported by a NRC approved Westinghouse Methodology evaluation (WCAP 13631). This evaluation applies only to SQN and is similar to that approved for use at other nuclear power plants.
9311010149 931026, PDH ADOCK 0S00 7
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1 A proposed change to TS 6.9.1.14.a would add a reference to WCAP 13631 as one of the documents that contain the analytical methods used to determine the core operating limits, The staff's review of these proposed changes follows.
2.
EVALUATION 2.1 Methodoloav 2.1.1 Amendment to End of Cycle Moderator Temoerature Coefficient The current method used to determine the most negative MTC is described in Bases Section B 3/4.1.1.3 of the TS for SQN Units 1 and 2, This method is based on incrementally correcting the conservative MDC used in the safety analyses to obtain the most negative MTC value or, equivalently, the most positive MDC at the nominal hot full power (HFP) core conditions.
The corrections involve subtracting the incremental change in the MDC, which is associated with the ccre condition of all control rods inserted (ARI), to an ARO core condition.
The HTC is then equal to the product of multiplying the MDC by the rate of change of the moderator density with the temperature at rated thernal power (RTP) conditions.
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The TS Bases provide a method of determining the most negative MTC LC0 value that results in an ARO MTC value that is significantly less negative than the MTC used in the safety analysis and that may be less negative than the best estimate EOC ARO MTC for extended burnup reload cores.
This could result in TS 3.1.1.3 specifying that the plant be placed in a hot shutdown condition even though it *ould retain a substantial margin to the safety analysis MDC.
The problem with the current method is caused oy adjusting the MDC from an HFP ARI condition to an HFP ARO condition in defining the most negative MTC. The TS on control rod positions does not allow the HFP ARI condition for allowable power operation in which the shutdown banks are completely withdrawn from the core and the control banks meet the rod insertion limits (RIls).
The licensee provided an alternative method for adjusting the safety analysis MDC to obtain a most negative MTC.
The "most negative feasible" (MNF) method seeks to determine the conditions for which a core will exhibit the most negative value that is consistent with operation allowed by the TS.
The licensee uses the MNF method to determine E0C MTC sensitivities to those design and operational parameters that directly affect the MTC in such a way that the sensitivity to one parameter depends on the assumed values for the other parameters.
The licensee stated that this MNF MTC approach has a number of advantages over the previous method for determining the most negative MTC LCO value.
The MNF MTC would be sufficiently negative that repeated MTC measurements from a concentration of 300 ppm of boron in the core to E0C would not be required.
The MNF MTC method does not change the moderator feedback assumption or the value of the MDC in the safety analysis.
The MNF MTC method is a conservative and reasonable basis to assume for an MTC value of a reload core and is consistent with plant operation defined by other TS.
Finally, the MNF MTC method retains the SR on MTC at the 300 ppm core condition to verify that the core is operating within the bounds of the safety analysis.
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i The licensee stated that the SR MTC value would be obtained in the same manner as currently described in the Westinghouse Standard Technical Specification (STS) Bases.
The SR MTC value is obtained from the EOC ARO MTC value by making corrections for burnup and boron at a core condition of 300 ppm of boron.
The staff review of the assumptions and basis for the MNF MTC method described in this safety evaluation concluded that they are acceptable because they will result in conservative (more negative) MTC SR and EOC values during allowed operation of SQN Units 1 and 2 at nominal conditions and because the MTC j
measurement at 300 ppm of boron core condition will ensure, using the SR value of MTC, that the safety analysis MDC will not be exceeded.
After evaluating the proposed changes to the TS, the staff has determined that-the proposed change to the TS Bases method of determining the EOC MTC and 300 ppm SR limit values specified in the COLR is acceptable for the following
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reasons:
i (1)
The most negative feasible MTC method considered the important factors affecting the MTC and the limits on the these factors.
(2)
Westinghouse used approved methods and computer codes in the analysis.
(3)
Measuring the MTC at or near 300 ppm of boron will ensure that the MTC at E0C HFP ARO conditions will be less negative than the safety analysis.
(4)
The licensee will analyze future reloads for SQN Units 1 and 2 to confirm the most negative MIC TS at E0C and SR on MTC at a core condition of 300 ppm of baron.
(5)
The licensee will analyze future reloads for SQN Units 1 and 2 to confirm that the safety analysis value of the MDC applies.
(6)
Upon receipt of this amendment, the licensee will revise the current COLR as appropriate and submit the revised COLR to the staff as required by TS 6.9.1.14.c.
The licensee also proposes to change to TS 6.9.1.14.a by adding a reference to i
the Westinghouse document (WCAP 13631) that describes the analytical methods used to implement the revised methodology.
This change is in accordance with Generic Letter 88-16, " Removal of Cycle-Specific Parameter Limits from Technical Specifications," and will assure that future reloads will meet all applicable limits and acceptance criteria of the safety analysis, that the cycle-specific parameter limits will continue to be determined in accordance with NRC-approved methodology, and that operation will be limited / consistent with 10 CFR 50.36(c).
Accordingly, the staff finds the changes acceptable.
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3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments. The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change 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 amendment also changes recordkeeping or reporting 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 consideration, and there has been no public comment on such finding (58 FR 41515). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9) and 10 CFR 51.22(c)(10).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of.the amendments.
5.0 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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
A. Attard Dated:
October 26, 1993 l
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AMENDMENT NO. 171 FOR SEQUOYAH UNIT NO.1 - DOCKET NO. 50-327 and j
AMENDMENT N0. 161 FOR SEQUOYAH UNIT NO. 2 - DOCKET NO. 50-328 DATED: October 26, 1993 4
i DISTRIBUTION:
Docket Files.
NRC & Local"PDRs SQN Reading File S. Varga 14-E-4 i
F. Hebdon i
B. Clayton D. LaBarge E. Merschoff RIl P. Kellogg RII R. Crlenjak Ril OGC 15-B-18 D. Hagan MNBB-3206 G. Hill Pl-37 (2 per docket)
C. Grimes ll-E-22 R. Jones 1
A. Attard ACRS(10)
OPA 2-G-5 0C/LFDCB MNBB-9112 cc:
Plant Service List
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