ML20076E052
| ML20076E052 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/06/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20076E048 | List: |
| References | |
| NUDOCS 9108150041 | |
| Download: ML20076E052 (4) | |
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.E SAFETY EVALUATION BY THE OFFICE UF NUCLEAR REACTOR REGULATION RELATED TO AME,NDMENT NO.122 TO FACILITY OPERATING LICENSE NO. NPF-6 ENTERGY OPERATIONS INC.,
ARKANSAS NUCLEAR ONE, UNIT NO. 2 DOCKET NO. 50-368 INTRODUCTION By letter dated January 29, 1991 as revised July 29, 1991, Entergy Operatior,s, Inc. (the licensee) requested an amendment to the Technical Specifications (TS) appended to Facility Operating License No. NPT-6 for Atkansas Nuclear One, Unit Nn. 2 (ANO-2).
Thu proposed amendment would revise TS 3.2.1 and 3.2.4 for ANO-2.
The change increases the time limit that the Core Operating Limit Supervisory System (COLSS) may be out of service before the action requirements based on the more restrictive Core Protection Calculator (CPC) limits apply.
The proposed amendment also adds a distinction between the action requirements for exceeding a COLSS calculated power operating limit and a CPC calculated operating limit (when COLSS is out of service).
Finally, the proposed change modifies the minimum power required by action requirements to be consistent with the present TS applicability.
The July 29, 1991, letter provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
EVALUATION Presently, if COLSS is out of service, TS 3.2.1, Linear Heat Rate (LHR), and TS 3.2.4, Departure from Nucleate Boiling Ratio (DNBR) Margin, require that LHR and DNBR must be maintained with#a a more restrictive set of limits based on the CPCs.
With these limits not,eing maintained, corrective action must be initiated within 15 minutes to restnre LHR and DNBR to within the applicable set of limits (depending on whether or not COLSS is operable) within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or the plant must be in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
With COLSS out of service, the proposed changes will replace the current 15 minute time limit for initiating corrective action with a requirement to restore the DNBR and LHR limits within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
If the DNBR and LHR limits are not restored within the proposed 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, the proposed change would require reactor power to be reduced to less than or equal to 20% of rated thermal power within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
The intent of TS 3.2.1 and 3.2.4 is to maintain the reactor within the range of initial conditions that was assumed in the licensee's safety analysis.
Maintaining the LHR within the specified range ensures that in the event of a 9100150041 910006 PDR ADOCK 05000368 P
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.g.
loss of coolant accident (LOCA), the fuel cladding temperature will not exceed the 2200*F limit imposed by 10 CFR 50.46.
Maintaining the DNBR within the specified range will ensure that no postulated accident will result in con-sequences more severe than those described in Chapter 15 of the licensee's Final Safety Analysis Report.
Since COLSS does not provide any trip functions, continued power operation when COLSS is out of service is permissible provided an alternate means of monitoring the approach to the specified limits is available.
The TS allows the CPC to be utilized to maintain the appropriate parameters within limits.
However, the CPCs cannot perform the required LHR and DNBR calculations as accurately as COLSS.
As a result, tne TS limits based on the CPC's monitoring capability are more restrictive than the TS limits based on the COLSS monitoring capabilities.
Due to the more restrictive CPC limits when COLSS is out of service, the current LCOs cannot be satisfied without a reduction in the core power level.
The percentage of power reduction depends upon the cycle specific core design and the specific conditions that exist when COLSS indication is lost, however, a power reduction of appr)ximately 15% per hour is neccessary if COLSS is out of service.
The magnitude of the required power reduction increases near the end of the fuel cycle due to changes in the axial core power distribution.
Since the end of cycle core power distribution may necessitate core power reductions of up to 25 to 30%, the current COLSS out of service limits may force power reductions at a rate approaching 30% per hour.
Power reductions of this magitude performed in I hour or less subject the plant to large transients and increase the probability that an avoidable challenge to the Reactor Protection System (RPS) would occur.
In addition, maneuvers such as this are difficult to perform near the end of the fuel cycle due to the reduced capability of rapidly deborating the Reactor Coolant System to offset the buildup of Xenon.
These considerations contribute to the potential for increased RPS actuations and subsequent challenges to safety systems.
However, the proposed change would increase the allowed out of service and power reduction times to bring them in
.line with current core design restraints without decreasing existing safety protections.
Increasing to two hours the time to restore LHR and DNBR to within limits would reduce the number and rate of power reductions.
While decreasing the potential for RPS actuations, the proposed change would not significantly increase the probability of exceeding the core power oper3 ting limits based on LHR and DNBR.
While COLSS is out of service, detection of changes in LHR and DNBR is made easier by maintaining steady-state conditions and by increasing the monitoring frequency of the CPC calculatea values of LHR and DNBR.
If. the CPC LHR and DNBR limits cannot be restored within the proposed 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, the proposed change will require a further power reduction to "less than or equal to 20% of Rated Thermal Power" within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
The LHR and DNBR LCOs currently require the reactor to be brought to at least Hot Standby conditions if the LHR and DNBR limits cannot be restored.
This change maintains consistency with the current TS Applicability Statement which requires limits on LHR and DNBR only when the thermal power exceeds 20%.
. The primary consideration in extending the COL 55 out of service time limit is the remote possibility of a slow, undetectable transient that degrades the LHR and/or DNBR slowly over the 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> period and is then followed by an anticipated operational occurrence or an accident, Upon approval of the proposed change the licensee will increase the monitoring frequency of the CPC-calculated values of LHR and DNBR.
Currently, immediately following the loss of COLSS and every 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> thereafter, the licensee records (among other things) the CPC calculated values of LHR and DNBR.
Following approval of the proposed change, the licensee will increase the monitoring frequency for LHR and DNBR f rom once every 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to once every 15 minutes.
Moreover, the licensee is currently working to define a maximum allowable change in the CPC-calculated LHR or DNBR such that further degradation will require the operators to take immediate action to reduce reactor power and comply with the appropriate COL 55 out of service Technical Specification limits.
Imrlementation of this change will provide additional assurance that potential reductions in core thermal margin will be quickly detected and, should it prove necessary, result in a decrease in reactor power and subsequent compliance with the existing COLS$ out of service lechnical Specification limits. Operation in the proposed manner is an acceptable balance between CPC determination and extending the period before power changes are required.
The level of safety is maintained.
The proposed changes do not alter the current power operating limits nor do they involve any changes to COLSS or CPC software.
The licensee will make no physical change to plant systems, structures or components nor will the proposed changes af fect the ability of any of the safety-related equipment required to j
mitigate accidents.
Therefore, for the reasons stated above, the staff concludes that the proposed changes to Technical Specifications 3.2.1 and 3.2.4 are acceptable.
STATE CONSULTATION in accordance with the Commission's regulations, the Arkansas State official was notified of the proposed issuance of the amendment.
The State official had no comments.
ENVIRONMENTAL CONSIDERATION The amendment changes 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 in surveillance requirements.
The NRC staff has dotermined that the amendment involves 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 pro-posed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (56 FR 9378).
Accordingly, the amendment meets 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 amendment.
4 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, 1
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 Date: August 6, 1991 e