ML20076M367
| ML20076M367 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/27/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20076M357 | List: |
| References | |
| NUDOCS 9411070224 | |
| Download: ML20076M367 (7) | |
Text
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UNITED STATES
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~t WASHINGTON, D.C. 20066-4001 k.....
SAFETY EVALUATION By THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.113TO FACILITY OPERATING LICENSE NO. NPF-10 AND AMENDMENT NO.102 TO FACILITY OPERATING LICENSE NO. NPF-15 SOUTHERN CALIFORNIA EDISON COMPANY SAN DIEGO GAS AND ELECTRIC COMPANY THE CITY OF RIVERSIDE. CALIFORNIA THE CITY OF ANAHEIM. CALIFORNIA SAN ONOFRE NUCLEAR GENERATING STATION. UNITS 2 AND 3 DOCKET NOS. 50-361 AND 50-362
1.0 INTRODUCTION
By letter dated December 31, 1992, Southern California Edison Company, et al.
(SCE or the licensee) submitted a request for changes to the Technical Specifications (TS) for San Onofre Nuclear Generating Station (SONGS), Unit Nos. 2 and 3.
The proposed changes would revise TS 3.2.1, " LINEAR HEAT RATE,"
and TS 3.2.4, "0NBR MARGIN," and the corresponding Bases. These changes (1) add a distinction between the action requirements when the core operating limit supervisory system (COLSS) is in service and the action requirements when the COLSS is out of service (005), (2) increase the ACTION time from 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> when the COLSS is 00S, (3) add a new surveillance requirement (SR) to require monitoring the departure from nucleate boiling ratio (DNBR) and/or the linear heat rate (LHR) every 15 minutes, when the COLSS is 005 and the corresponding parameter is not being maintained as required, and (4) change the power reduction requirements from " HOT STANDBY" to "less than or equal to 20 percent of Rated Thermal Power" when the DNBR margin and/or the LHR limiting condition for operation (LCO) cannot be met within the allowed ACTION time.
These amendments also include an editorial change to TS 3.2.4.d and revisions
-to the Bases of the above TS to reflect the changes, and changes to TS 3/4.5.2 to correct errors made in an earlier TS amendment change.
2.0 BACKGROUND
The COLSS is designed to assist the plant operators in implementing TS requirements for monitoring various LCOs.
Specifically, the COLSS uses inputs from various plant sensors (core inlet temperature, in-core detector signals, reactor coolant pump speeds and differential pressures, reactor coolant system 9411070224 941027 gDR ADOCK 05000361 PDR
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l pressure, etc.) to calculate a core power that corresponds to the LC0 on DNBR margin. This power level is the DNBR power operating limit (POL).
Concurrently, as a function of the in-core power distribution, COLSS performs a similar calculation to determine the LHR POL. These two POLS, in conjunction with the licensed core power level, are the highest power level at which the core can safely operate. Maintaining the actual core power below these COLSS calculated POLS ensures that no anticipated operational occurrence (A00) will violate specified acceptable fuel design limits and that no postulated accident will have consequences more severe than those analyzed in Chapter 15 of the Updated Final Safety Analysis Report (UFSAR).
Since COLSS operation is not required for plant safety (i.e., the COLSS does not initiate any direct safety-related function during A00s or accidents), it is permissible to continue power operation when the COLSS is 00S provided an alternate means of monitoring the specified parameters can be substituted.
Under such circumstances, the TS allow the core protection calculators (CPCs) to be used to maintain the parameters within their specified limits. However, because the CPCs cannot perform the required LHR and DNBR calculations as accurately as COLSS, the TS limits based on the CPC's monitoring capability are more restrictive than those based on the COLSS's monitoring capabilities.
When the COLSS becomes unavailable, DNBR TS limits cannot usually be satisfied without a reduction in core power because the DNBR, as determined using CPCs, usually exceeds the COLSS 005 TS limits at full power. Therefore, if the COLSS becomes inoperable for more than 15 minutes, full-power operation cannot be maintained in accordance with the TS.
The amount of power reduction depends on the cycle-specific core design and the existing core conditions when the COLSS becomes inoperable.
The existing DNBR and LHR TS ACTION time limits originated from estimated time requirements for returning the COLSS to service and anticipated power reduction requirements.
These time limits were established before initial plant operation and without the benefit of practical experience.
Currently, reinitializing the plant monitoring system (PMS) computer or transferring from the PMS to the COLSS backup computer system (CBCS) requires approximately 15 minutes. Therefore, a potential situation exists in which a power reduction would be required when the COLSS is lost, because inadequate time is provided by the TS for appropriate corrective action.
In general, a 15-percent power reduction is required when COLSS is lost to restore CPC DNBR margin to within TS limits. According to the TS, this power reduction must be completed within I hour following a loss of the COLSS.
However, during the last third of the operating cycle, when boron concentration is low, large power reduction rates are difficult to control and could result in a reactor trip.
In addition, this power maneuver is required at a time when the most accurate means of monitoring reactor conditions is not available. Consequent'y, the existing TS may reduce plant reliability by unnecessarily increasing the potential of reactor protection system (RPS) actuation.
. In the proposed changes, the licensee will revise operating instructions (01s) to require a new DNBR margin. These changes will also require that LHR SRs be performed when the COLSS is 00S and TS 3.2.1 or TS 3.2.4 LCOs are not met.
The DNBR margin and the LHR will be monitored using an operable CPC channel every 15 minutes. Monitoring will begin within the first 15 minutes of when the COLSS becomes inoperable.
If an adverse trend is observed, operator action would be required to restore these parameterA conservatively with iespect to the initial values.
If LHR or DNBR canntt be restored within the COLSS 00S 4-hour action time, a power r' eduction to less than or equal to 20-percent rated thermal power will be required within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Increasing the amount of time available for restoring LHR and DNBR when the COLSS is not available will potentially reduce the number and rate of power reductions, thereby decreasing the probability of actuating the RPS. This proposed change accordingly increases TS 3.2.1 and TS 3.2.4 action times for restoring LHR and DNBR margin when the COLSS is 00S so as to provide a reasonable opportunity for appropriate corrective actions.
The existing safety margins and the proposed changes will not significantly increase the probability of exceeding the initial conditions assumed in the safety analysis.
3.0 EVALUATION The licensee proposes to change TS 3.2.1 and TS 3.2.4 to (1) separately address the cases when the COLSS is in service and 00S, (2) initiate a new surveiltance, within 15 minutes after COLSS is 00S, to monitor DNBR margin and/or LHR every 15 minutes, (3) increase the ACTION time from I hour to 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> when the COLSS is 00S and either the LHR or DNBR margin is not being maintained within limits as indicated by any 0PERABLE CPC channel, and (4) add SRs to verify, every 15 minutes, that no adverse trend in either LHR or DNBR margin exists when the COLSS is 00S and the limits are not maintained. The intent of these changes is to provide reasonable time for appropriate corrective action when the COLSS becomes inoperable while maintaining the safety of the plant.
The proposed changes do not affect the actions and time requirements when the COLSS is in service.
However, when the COLSS is 00S, the action time is increased by 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (from I hour to 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />).
The primary consideration in extending the COLSS 00S time limit is the remote possibility of a slow, undetectable transient that degrades the DNBR margin or LHR within the new time limit and that is followed by an anticipated operational occurrence or accident.
Plant parameters monitored by the COLSS which could affect DNBR margin and LHR include reactor coolant system (RCS) flow rate as determined from reactor coolant pump shaft speed, axial power distribution, cold leg temperature, reactor core power, RCS pressure, and azimuthal tilt. Of these parameters, CPCs directly incorporate measured values for reactor core power, RCS flow rate as determined from reactor coolant pump shaft speed, RCS pressure, and cold leg temperature into the calculations of DNBR and LHR.
Therefore degradation of conditions with respect to these parameters is expected to be evident in the equivalent CPC margins.
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, Additionally, the licensee has stated that the operating history of San Onofre Units 2 and 3 has shown that the reactor core is stable with respect to azimuthal power tilt within any 4-hour time period. The only credible events affecting azimuthal tilt at San Onofre are an inadvertent drop or misalignment 1
of a control element assembly (CEA). Though these events are remote for any 4-hour period and are beyond the basis of LC0 monitoring, a CEA calculator indicating light and alarm (requiring corrective action) will alert the operators if these events occur. Therefore, any degradation of azimuthal tilt during the 4-hour time limit will be quickly and positively identified.
Because of the core design of San Onofre Units 2 and 3, axial xenon oscillations, particularly near the end of a fuel cycle, are normal.
Therefore, axial core power fluctuations and axial power shape are strictly controlled.
By controlling these parameters, SONGS ensures efficient fuel burnup, maintains the axial power shape within the limits assumed in the safety analysis, and maintains the axial shape index (ASI) within 0.05 ASI units of the equilibrium shaoe index (ESI). A full xenon oscillation typically takes 26 hours3.009259e-4 days <br />0.00722 hours <br />4.298942e-5 weeks <br />9.893e-6 months <br />. Therefore, with the proposed requirements of monitoring the CPC calculated LHR and DNBR every 15 minutes, any significant change in ASI will be promptly identified.
Because of CPC uncertainties, the TS LCOs for DNBR margin and LHR are more restrictive when operating with the COLSS 00S.
Therefore, with the COLSS 00S, the existing DNBR margin limits can only be satisfied by either reducing power or returning the COLSS to service.
By itself, the loss of the COLSS or its return to service does not mean that the actual core power should immediately be changed. Therefore, during normal operation within the COLSS POLS, if there are no indications that the actual DNBR margin or LHR have degraded, the required overpower margin discussed in Chapter 15 of the UFSAR will continue to be maintained. Also, when either TS 3.2.1 or TS 3.2.4 is not satisfied, compensatory actions will provide additional assurance that the actual DNBR margin and LHR do not exceed the safety limits in the UFSAR. The proposed SRs will ensure that DNBR margin and LHR are monitored every 15 minuten and that appropriate action is taken if an adverse trend is noted when COLSS is out of service and the LHR or DNBR TS LCOs are not met. Additionally, core power distribution during all phases of normal operation and A00s will remain bounded by the initial conditions assumed in Chapter 15 of the UFSAR. The COLSS-calculated POLS and the CPC-based LHR and DNBR operating limits will remain unchanged.
The staff finds the proposed changes to TS 3.2.1 and TS 3.2.4 acceptable for the following reasons:
(1)
As explained in the above discussion, the plant operators will continue to adequately maintain the actual core power below the allowed limits with the proposed changes.
(2)
The proposed changes do not involve any modifications to the COLSS or CPC software.
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. (3)
The proposeri changes are consistent with the improved Standard Technical Specifications for Combustion Engineering plants (NUREG-1432).
The licensee also requests that power reduction requirements be changed from
" HOT STANDBY" to "less than or equal to 20% of RATED THERMAL POWER" when the DNBR margin and/or LHR LCOs cannot be met within the allowed ACTION time.
This change is considered administrative because these TS currently apply only at rated thermal power greater than 20 percent. This change provides consistency between the action and applicability statements and allows in-core and ex-core neutron detectors to provide meaningful data for COLSS trouble shooting and operability determination without decreasing safety margin.
Therefore, the staff finds this change acceptable. This change is also consistent with the STS.
Additionally, in TS 3.2.4.d, the licensee proposes to change from "neither CEACs is" to "neither CEAC is" and to change the Bases for TS 3.2.1 and TS 3.2.4 to document the principal elements of the changes. The change to TS 3.2.4.d is administrative in nature. The changes to the Bases were reviewed and found to be consistent with the above discussed changes. Therefore, the staff finds these changes acceptable.
Also included in the enclosed amendments are changes to TS 3/4.5.2, "ECCS Subsystems - T Greater than or Equal to 350*F."
During the last update of y
this TS section (Amendment 98 for Unit 2 and Amendment 87 for Unit 3), some of the pumps values in the TS amendments transmitted by NRC letter dated September 5, 1991, were incorrect.
The enclosed changes to TS 3.5.2 correct these typographical errors by reinstating the pump values that were in the TS before the September 5, 1991, letter. The specific editorial changes are as follows:
Unit 2 In TS 4.5.2.g.1, the developed head for pumps P017, P018, and P019 were changed to 2142 feet, 2101 feet, and 2103 feet, respectively.
In TS 4.5.2.g.2, the low-pressure safety injection pump developed head at miniflow was changed to 406.1 feet.
In TS 4.5.2.h.1.a, the sum of the injection flow rates for pumps P018 and P019 were changed to 667 gpm and 672 pgm, respectively.
In TS 4.5.2.h.1.b, the total pump flow rates for pumps P017, P018, and P019 were changed to 900 gpm, 913 gpm, and 918 gpm, respectively.
Unit 3 i
In TS 4.5.2.h.l.a the sum of the injection lines flow rate for pump P017 was changed to 647 gpm.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendment.
The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The 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 (58 FR 12269).
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 connection with the issuance of the amendments.
6.0 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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
H. Shuaibi Date:
October 27, 1994 i-
FW EL i
Messrs. Ray and Guiles October 27, 1994 A copy of our related Safety Evaluation is also enclosed. The notice of issuance will be included in the Commission's next regular biweekly Federal Reaister notice.
Sincerely, Original signed by:
Mel B. Fields, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation
Enclosures:
1.
Amendment No.113 to NPF-10 2.
Amendment No.102 to NPF-15 3.
Safety Evaluation cc w/ enclosures:
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