ML20081A821
| ML20081A821 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 03/03/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17059A715 | List: |
| References | |
| NUDOCS 9503150328 | |
| Download: ML20081A821 (5) | |
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UNITED STATES 0
NUCLEAR REGULATORY COMMISSION I
WAEHINGTON, D.C. 2006H001
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e SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION j
RRATED'T0 AMENOMENT N0.153 TO FACILITY OPERATING LICENSE NO. DPR NIAGARA MOHAWK POWER CORPORATION l
l ilINE MILE POINT NUCLEAR STATION. UNIT NO. 1 DOCKET No. 50-220 i'
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1.0 INTRODUCTION
By letter dated July 21, 1994, as supplemented December 5, 1994, December 14, 1994, January 11, 1995, and February 1, 1995, Niagara Mohawk Power Corporation 4
(the licensee or NMPC) submitted a request for changes to the Nine Mile Point Nuclear Station Unit No.1 (NMP-1), Technical Specifications (TSs). - The requested. changes would add a tenth range'on the Intermediate Range Neutron-Flux Monitoring (IRM) system for_ plant shutdown and startup operations and
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would extend the calibration interval for the Source Range Neutron. Flux i
Monitoring (SRM) system and IRM system from prior to startup and shutdown to 30 months. TSs 2.1.2, " Fuel Cladding Integrity;" 3.1.7, " Fuel Rods;"
q 3.6.2/4.6.2, " Protective Instrumentation;" and the associated Bases would be-a modified. The December 5, 1994, December 14, 1994, January 11, 1995, and I
February 1,1995, letters provided clarifying information that did not change
' the initial proposed no 'significant hazards consideration determination.
In requests for additional information dated November 3,19H and November 9, 1994, the NRC staff asked the licensee questions related to overlap between the Average Power Range Neutron Flux Monitoring (APRM) and the IRM systems and analysis of design basis events. The NRC staff also asked-the licensee to submit observed instrument drift data to support the extension of calibration interval of the SRMs and IRMs to 30 months.
From these requests and further exchanges-on the telephone, the 5 taff
-1 determined that the licensee did not provide adequate drift data to enable the NRC staff to make a determination with confidence of the acceptability of the extension request and on February 1,1995, the licensee withdrew the portion of the amendnept associated with the extension of calibration interval for SRMS and IRMs.
Incorporation of IRM Range 10, as proposed in the amendment, would alleviate operational difficulty experienced while changing the mode switch between -
Startup and Run.
Present plant procedures require the mode switch change i
while using IRM Range 9.
The Range 9 upscale scram is at approximately 12%
power. Range 10 permits monitoring of neutron flux up to approximately 40%
power. However, normal Range 10 operation will generally involve increasing.
reactor power only within a few percent above 12% before switching to the APRM 95031503289h$20 yDR ADOCK O PDR
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system in the Run mode. Range 10 should increase the IRM/APRM overlap"to at I
least 1/2 decade and facilitate a smoother transition between Startup and Run.
With the addition of Range 10, the coincident IRM/APRM scram has been deleted.
The impact on plant safety of the deletion of the coincident scram is.
i contained in GENE 909-39-1093, "IRM/APRM Overlap Improvement for Nine Mile Point Nuclear Station, Unit One."
As operation in IRM Range 10 permits up to approximately 40% of rated power while in the Startup mode, a low pressure reactor isolation setpoint at 850 i
psig has been added for operation in Range 10 to avoid exceeding plant safety limits.
In addition, procedural limits on minimum core flow during Range 10 operation have been added to provide continued protection against the rod withdrawal event.
The NRC staff reviewed the use of IRM Range 10, the two new setpoints to be added and the deletion of the IRM/APRM coincident scram to ensure that the proposed changes do not reduce the present plant safety margin and also do not adversely affect the ability to mitigate design basis events (accidents and transients) and satisfy plant safety limits.
2.0 EVALUATION 2.1 Deletion of Coincident IRM/APRM Scram The amendment deletes the coincident APRM downscale/IRM upscale scram by deleting the APRM downscale scram setpoint. The impact of deletion of the APRM downscale trip has been evaluated in the licensee submittal and GENE.
909-39-1093, "IRM/APRM Overlap Improvement for Nine Mile Point Nuclear Station, Unit One." The coincident scram provides protection against noncontinuous neutron flux monitoring during transition between the APRM and the IRM systems.
If the switch to Startup to Run.is premature, and the APRM downscale setpoints have not cleared, the IRM scram remains active to provide backup scram protection.
Upon deletion of the APRM downscale scram, the remaining APRM downscale rod j
block should continue to offer protection against rod withdrawal errors and prevent power ascension while APRM monitors are downscale. The setpoint for APRM downscale rod block in TS Table 3.6.2g is revised to reflect the existing plant equipment setting, and the proposed allowable value is documented in.the Bases for TS 3.6.2.
The deletion of the downscale scram does not affect the 120% upscale reactor scram, which should continue to offer protection against design basis events previously analyzed. The TS Limiting Condition for Operationfor an inoperable /downscale APRM requires corrective action within' 4
one hour
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During startup, if the APRM monitors are not onscale for transfer from IRM Range 9, the IRM monitors can be transferred into Range 10.
In order to prevent violation of safety limits, entry into Range 10 is not permitted unless total core flow is greater than 20% and system pressure is greater than
i 850 psig..These limits are further discussed in the next section. Range 10 is designed to satisfy the continuous monitoring requirement previously provided by the coincident APRM/IRM trip by increasing the IRM/APRM overlap.
Addition of IRM Range 10 should provide at least a 1/t decade IRM/APRM overlap, allowing continuous monitoring of both systr as during transition.
In-consideration of the scram protection available during transition between Startup and Run mode and the overlap offered by Range 10, coupled with minimum i
pressure / flow requirements, the deletion of the coincident scram will not 4
impact plant safety or compromise safety limit margins.
2.2 Minimum Flow and Vessel Pressure Requirements Current TSs require recirculation flow to be greater than 20% before entering Run mode. The amendment also requires 20% flow in order to enter Range 10, Supportinginformation[lowbeforecontrolrodscanbewithdrawninRange10.
and also requires 30%
stipulates that above 205 power and less than 40%
power, 30% flow is required so that the Safety Limit Minimum Critical Power Ratio (SLMCPR) is not exceeded for rod withdrawal error transients. The control rod withdrawal error event is further discussed in the next section.
The amendment also adds a reactor low pressure isolation setpoint of 850 psig for entry into and operation in Range 10.
Presently, the 850 psig setpoint for minimum reactor pressure exists only in the Run mode. The setpoint has been added to satisfy the fuel cladding integrity safety -limit in TS' 2.1.1.b, which requires core power not to exceed 25% of rated thermal power when.
reactor pressure is less than or equal to 800 psia or core flow is less than.
10%.' Above 800 psia and 10% core flow, TS 2.1.1.a specifies a SLMCPR limit to offer protection against loss of cladding integrity.
2.3 Analysis of Design Basis Events j
The control rod drop event has been evaluated for operation with IRM Range 10.
NMP-1 uses a Rod Worth Minimizer (RWM) system which is designed to sequence rod withdrawals and should prevent fuel enthalpy from exceeding the 280 cal /g design limit for the rod drop event. TS 3.1.1.b.(3)(b) requires the RWM to be operable from 0 to 20% power. The control rod drop event is limiting for power levels below 10%; above 10%, Doppler and voiding reactivity feedbacks act to minimize the impact of the rod drop event. Analysis of this event conservatively assumes availability of only the 120% power APRM scram.
Therefore, the ability to successfully terminate the rod drop event will not be adversely impacted by the addition of Range 10.
The control rod withdrawal error event involves complete withdrawal of a control rod to the fully withdrawn position. Analysis of the event conservatively assumes credit only for the APRM scram at 120% of rated power.
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Occurrence of this event is bounding at low power levels, and results of' licensee analysis at low power levels satisfy the fuel cladding failure threshold limit of 170 cal /g. Above the RWM low power setpoint of 20%, the SLMCPR must be satisfied.
Licensee analysis states that for power levels less
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than 40%, operation with core flows greater than 30% should provide margin'to the SLMCPR. The licensee has provided requirements in the plant TS for 30%
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- flow while withdrawing rods while in Range 10.
If future reloads include-I changes.in the assumptions made for the control rod withdrawal event or i
changes in the core / fuel design, then the 30% flow requirement would also need i
further review and possible revision. The licensee considers t of operation above 20% power while in IRM Range 10 to be small.pe possibility Below 20%
power, the rod worth minimizer should be available to offer protection against rod withdrawal events. Evaluation of the rod withdrawal event, with.
consideration of IRM and APRM scram and rod withdrawal block setpoints and l
other existing operating / surveillance requirements, provides reasonable assurance that, for operation in Range 10 with core flow greater than 30% of rated, the.SLMCPR will not be violated for the control rod withdrawal event.
l Another possible source of positive reactivity insertion is a rapid cold water injection. Cold water injection transients include inadvertent high pressure coolant injection, loss of feedwater heater events and improper startup of an idle recirculation loop. These events were evaluated assuming inoperability of IRM scram setpoints so that reactor scram occurs at 120% power.
Results of the evaluation demonstrate margin to the licensing basis failure criterion of 170 cal /g. During low power operation, the cal /g is a more appropriate failure criterion that Minimum Critical Power Ratio (MCPR) due to the increased margin to MCPR limits which exists at low power levels.
NMPC has requested a change to the NMP-1 TSs. The amendment. incorporates a tenth range on the IRM system, adds setpoints on vessel pressure and core i
flow, and deletes the APRM downscale scram.
The NRC staff determined that IRM Range 10 would increase the IRM/APRM overlap and facilitate a smoother transition between Startup and Run.
Incorporation of Range 10 does not negatively impact the outcome of design basis events and transients.
Protective system setpoints for reactor vessel isolation and minimum core flow rates while operating with IRM Range 10 will offer added protection against.. exceeding plant TS safety limits. Deletion of the IRM/APRM coincident scram will not reduce plant safety margin. Therefore, the NRC staff has determined that the changes do not adversely affect continued safe operation of the plant, and are acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's ' regulations, the New York State official was notified of the proposed issuance of the amendment. The State official had no comments.
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. 4.0 ENVIR0fetENTAL CONSIDERATION l
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 surveillance requirements. The NRC staff has determined 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 cuculative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (59 FR 45028). 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.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, 3
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 Commissior.'s regulations, and (3) the issuance of the amendment will not be inimical to the commen defense and security or to the health and safety of the public.
6.0 REFERENCES
1.
Letter from B. Sylvia (NMPC) to USNRC, Withdrawal of Portion of Previously Submitted Amendment, dated February 1, 1995.
2.
GENE-909-39-1093, "IRM/APRM Overlap Improvement for Nine Pile Point Nuclear Station Unit One," p. 8, March 8, 1994.
i 3.
Nine Mile Point Unit 1 Technical Specifications, Table 4.6.2a.
4.
Letter from B. Sylvia (NMPC) to USNRC, Application for amendment to operating license, p. 10, July 21, 1994.
5.
Letter from 8. Sylvia (NMPC) to USNRC, Response to Request for Additional Information for Facility Operating License DPR-63, p. 3, December 5, 1994.
Principal Contributors:
G. Golub F. Gee Date: March 3, 1995 I