ML20086K160
| ML20086K160 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 11/29/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20086K152 | List: |
| References | |
| NUDOCS 9112120244 | |
| Download: ML20086K160 (9) | |
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$AFETY EVALVATION BY THE OFFICE OF NUCtEAR REAC10R REGUt ATION REL ATED TO AMENOMENT NO.161 TO FACILITY OPERATING LICENSE NO. DPR-46 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. 50-?98
1.0 INTRODUCTION
By letter dated July 29,1991 (Ref.1), the Nebraska Public Power District (the licensee) submitted a proposal to change the Technical Specifications (TS) of the Cooper Nuclear Station (CNS). Additional information provided by the licensee by letter dated October 3, 1991 (Ref. 2) was a clarification of previously provided information and did not change the action noticed or affect
'the initial proposed no significant hazards considerations determination.
The changes are required to provide for implementation of an extended operating region of the
-monitor (APRM) power / flow map and implementation of the average power range
, rod block monitor (RBM), Technical Specification (ARTS)
Improvement Program. The ARTS improvements are intended to increase the plant operating efficiency, update the compliance with the thermal margin requirements im instrumentation, prove the accuracy and response of the pertinent and to improve the man / machine interface.
ThelicenseehasprovidedExtendedLoadLineLimit(ELLL)andARTSImprovement analyses in General Electric Topical Report NEDC-31892P (Ref. 3) which is provided as Attachment 2 to Reference 1.
The ELLL analysis is provided as a basis for normal reactor operation in the region of the poaer/ flow map above the rated rod line. Operation in the extended region is achieved by char.ging the slope of the flow bias scram trip algorithm and revising the APRM rod block line. The ARTS im requirements, (2) provements involve (1) elimination of APRM trip setdown power and flow dependent limits on Maximum Average Planar LinearHeatGenerationRate(MAPLHGr)andMinimumCriticalPowerRatio(MCPR),
(3) changes from flow to power reteienced setpoints for the RBM, (4) an eltered rod withdrawal error at power analysis, and (S) changes in normalization procedure and new trip logic in the RBM providing definition of a limiting rod pattern for RBM bypass decisions, in support of the request the licensee has submitted (1) a description and evaluationofthechanges,(2)theproposednewTS,)(3)anidentificationof changes to the Core Operating Limits Report and (4 a General Electric Company (Ref. 3) ysis of the consequences of operation in an extended operating dom (GE) anal to justify the proposed changes for CNS. The licensee's submittal included proposed Table changes to the CNS TS relating to APRM reactor protec-tion system instrumentation requirements and control rod withdrawal block instrumentation.
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. 2.0 EVALUATION 2.1 Elimination of Flow-Biased APRM Scram and Rod Block Trip Setpoint Setdown Reovirement
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In the current CNS Technical Specifications the flow-blased APRM scram and rod block trip setpoints are reduced (set down) when the core Total Peaking Factor (TPF) is greater than the design TPF. This requirement is associated with a now obsolete Hench-Levy Minimum Critical Heat Flux P.atio criterion. GE has since developed the General Electric Thermal Analysis Basis (GETAB/GEXL) critical power correlation, which allows e,n acceptable alternative to the setdown requirement. The GE amlysis (Ref. 3) enclosed with the CNS submittal includes results from analyses marte to determine a set of power and flow dependent operating limits (MCPR and MAPLHGR) that would be needed to satisfy the pertinent licensing criteria if APRM setdown was eliminated. The new limits should (1) prevent violation of the MCPR safety limit, (2) keep the fuel thermal-mechanical performance within the design and licensing basis, and (3) keer Peak cladding temperature and maxim;m cladding oxidation within allowable l'imits. The results of the analyses with approved analytical methods are stated below.
In order to restore safety margins which might be reduced een the APRM setdown is removed, the limiting transients were reanalyzed assuming the absence of this feature. The analyses assumed operation within the proposed extended power / flow domair with flows up to 100 percent of rated flow.
Analyses or the transient
.ints were made as a function of initial power and flow and the results used
'etermine multipliers to be applied to full power-full flow values of f
' and MAPLHGR. The power dependence was most sensitive at full flow and eedwater controller failure was the transient showing the largest sensitivity. This event was then used to construct a curve of MCPP multiplier K and MAPLMGR multiplier, MAPFAC as a function of core Cycle-specIfiE, curves will be placed in the CoEe, Operating Limits power.
Flow dependenca of MCPR and MAPLHGR was determined from analyses of flow runout events in which the core flow is raicped upward to the maximum value permitted by the setting of the recirculation pump scoo; The flow multipliers MCPR(F) and MAPFAC, are thus a function of tie initial flow and the maximum flow and afamilyofcurvesisdrawn_. The multipliers are chosen so that a flow runout to the maximum flow wil? not result in a violation of MCPR or linear heat generation rate (LH3R) safety limits. The MAPFAC, curves are combined with-the results of loss of coolant accident (LOCA) analysis described in the following Section 2.2 and the combined family of curves is used in the COLR.
In connection with this amt:ndment request, the new flow depender,t MCPR factors will replace the previously used MCPR tultiplier, K, which will no longer be utilized.
f The above discussion applies to the power range from 30 to 100 percent of full power. Below 30 percent of full power the turbine stop and control valve scrams are bypassed and the analyses do not apply.
Below 25 percent of full
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e-power no MCPR and MAPLHGR limits are defined.
In the interval between 25 and 30 percent of full power, flow dependent effects are taken into account by having two power dependent curves - one for flows greater than 50 percent of rated and one for lower flows. Analyses are then performed to obtain limiting MCPR and MAPLHGR values in these domains.
The development of the adjustment factors dest.ribed above used the ARTS imprc<ement program which, in part, supports both the implementat).n of s
updated operating limits and the elimination of the APRM trip setdown require;-
ments. The transient analysis resalts discussed in the following Safety Evaluation (SE) Section 2.2 are a part of the ARTS program. The ARTS concept has been used over the past few years successfully and with staff approval by a number of utilities having boiling water reactors (BWRs).
Its use in the present amendment request is acceptable to the staff. We also conclude that deletion e' the APRM setdown requirement is acceptable when it is replaced by the power and flow dependent operating limits described above.
2.2 AlicemalOperationalTransient All core-wide anticipated operational occurrences (A00) of the Cooper licensing
-basis were considered fo.' the ELLL. The transients re-evaluated were generator load reduction without turbine bypass (LRNCP), feedwater controller failure manimum demand (FWCF), and inadve-tent high pressure coolant injection (HPC1) events. The potentially limiting LRNSP and FW:F events were re-evaluated at the power / flow conditions correspondin power /87% flow) and rated conditions (g to the ELLL bounding point (100%
100% power /100% flow). The HPCI event was analyzed at both points with an additional 2% power uncertainty allowance as prescribed by the use of the approved GEMINI methodology. These are presented for each fuel type presently loaded in the CNS core and are compared with the values for standard operating conditions. All transient analyses were done with approved methodology (Ref. 4).
GE has also examined other events and affected system components related to the requested extension. These include overpressure protection, thermal-hydraulic stability, LOCA events, and pressure differentials on reactor internal *,. The results show that_ design limits will not be exceeded. The containment LOCA response was analyzed and the results show ro significant i.'. st of the ELLL.
For thermal-hydraulic stability, Cooper Station is opero,.1g. nder the " Interim Reconinendations for Stability Actions" of the NRC )ulletin No. 88-07, Supple-ment 1.
These operations are applicable to-the CN3 operations with ELLL/ ARTS, as is the case for other operating reactors with similar systems.
An evaluation of the-standard LOCA methodology (Ref. 5) has established that.
when the ARTS improvement program is considered, the full power MAPLHGR _ limits should be multiplied by a f actor of 0.86 at or below 65% core flow to ensure compliance with 10 CFR 50.46 PCT limits.
This factor will be incorporated in the new MAPFAC curves for CNS. The staff review of these varicas GE p
examinatiens has concluded that suitable analyses were performed and the results are comparable to other reviews and are acceptable for CNS.
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2.3 Modification of Flow-Biased APRM Scram and Rod Block Trip Equations The ELLL proposal changes the APRM flux scram lines on the power / flow map and permits operation up to the new APRM flux scram line (0.58W + P ?,) and up to the intersection with the 100 percent power line occurring at a s low of 87 percent. This is a standard change for ELLL previously approved at cther facilities and is acceptable. The flow-biased rod block trip equation is changed to 0.58W + 50% with a maximum value of 108%.
2.4 Modification of RBM Trip Setpoints and.RBM Svstem Operability Requirements The RBM system is used to prevent withdrawal of a control rod under conditions which could lead to violation of the fuel integrity safety criteria. A modified RBM system configuration is described in Reference 3 and will be implemented during the upcoming refueling outage for CNS. The process of defining RBM operating requirements entails replacing the present deterministic bounding cycle specific analysis with a statistical analysis that forms the basis for the modified system. This modification is made in coordination with the ARTS program and allows the selection of the RBM setpoint such that the RWE analysis results are bounded by the limiting transient analysis (Section 2.2).
The fe~llowing sumaari:es the RBM changes which have been considered in past revie,s and the current Cooper proposal.
(1) The RBM is used to block rod motion to prevent exceeding MCPR limits during control rod withdrawal at power.
For ARTS there is an optimization in the assignment of LPRMs to RBM channels. This change provides better and more uniform sensitivity to rod motion.
(2) ARTS has a more direct trip logic including a calibration to a fixed reference upon selection of a control rod for movement rather than calibration to the APRM, and an upscale trip level which is a step function of core power rather than a flow biased trip. Upon selecting a control rod for movement, each of two RBM channels automatically computes the average of all assigned local power range monitor channels. The average signal is then processed to produce a signal calibrated to a fixed reference signal. The signal is subsequently compared to an auto-matically selected preset rod block alann/ trip level which is aependent upon the current reactor power level. The trip level is selected based on the magnitude of a reference APRM.
If the local neutron flux level increases to the upscale trip setpoint, further control rod motion is blocked, thus limiting the increase in local power. Thus, the ARTS modification to the RBM trip logic replaces the-standard RBM flow biased trip feature with power biased trips.
(3) The changes to the system require a reevaluation of the rod withdrawal event and new analyses to provide setpoints for the system. The previous deterministic analysis is replaced with a statistical analysis using a large number of calculations of various operating states and giving
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. -3 results valid for all CNS cores using GE fuel through type BP8x8R.
Currently approved methods were used ta the calculations. The calcula-tions give, as a function of RBM trip setting, values of an initial MCPR which assure that 95 percent of withdrawal crrors do not violate the MCPR safety liott (1.07) with a 95 percent confidence level. This was used to select setpoints for the RBM, chosen with respect to the other ARTS APRM limits so that the withdrawal event is not limiting.
For a rated MCPR limit the setpoints-(as used for analyses) are divided into three intervals with a constant setpoint in each interval.
For CNS at a rated MCPR limit of 1.20, the setpoints for power intervals of 30-65, 65-85 and 85-100 percent power are 117,111.2, and 107.4 percent of the referenc,e signal respectively. Values for other MCPR limits (1.25, 1.30, 1.35) are also provided in Reference 2.
The setpoints are designated as low Trip Setpoint (LTSP), Intennediate Trip Setpoint (ITSP) and High Trip Setpoint (HTSP)~ and are applicable to the three designated power intervals (that is, the LTSP is applied-at 30% power up to 65% power, the ITSP is applied at 65% power up to 85%, and the HTSP is applied at and above 85% power.
These values are in the proposed TS for CNS and are acceptable based on the use of approved methodology.
-(4)- Calculations were done to examine the sensitivity of the results for core periphery rods (with fewer LPRM strings) and for LPRM failures (up to a 30 percent failure rate). The results indicate that the setpoints are suitable.
(5)-- An analysis of the effects of filters and time delays in the system was made. Results were presented foi system setup with and without a RBM filter. Hebraska Public Power District (NPPD), by Reference 2, has proposed-to use RBM setpoints for CNS. based on the use of system filters.
Use of filters will: require a reduction of setpoints and values for adjustments required, if used, are given in Reference 3.
A value for time delay setting in-the system was not used since supporting analyses for CNS have not been made.
Values for power-referenced RBM upscale trip level settings based on lowest rated MCPR limits and adjusted for the use of-filters are in the proposed TS for CNS.
(6) The data base. described above has been used to determine operating limit E'
MCPRs such that no rod withdrawal error could-. lead to exceeding. safety limits. Two MCPR limits are defined, for below 90' percent power and for equal to or above 90 percent power, which are 1.70 and 1.40 respectively.
When the operating MCPR is below tMsc values the plant is on a limiting control rod pattern and the RBM system must be operable. When above these-values bypass is allowed.
We.have reviewed these changes and analyses for the RBM and have concluded, as was the case in previous ARTS reviews, that the instrumentation changes, analyses, methods used, criteria and setpoints are acceptable,
O
.e t 0 2.5 Technical Specification Changes for ELLL and ARTS The proposed changes to the CNS Technical Specifications are identified in the licensee's submittal. The changes include (1) deletion of the current setdown requirement, (2) new power and flow dependent MCPR and MAPLHGR limits, and (3) new RBM limits and operability requirements. There would normally be a number of TS changes to parameters required to implement these changes.
However, most of the significant changes are proposed to be made to the existing CNS COLR rather than directly to the TS. The RBM limits, which are not considered cycle-specific by the licensee, are proposed for the CNS TS.
The changes to the MCPR and MAPLHGR limits, i.e., the new multipliers and limits which are, or may be, cycle specific, are proposed to be in the COLR, which is designed for such parameters and has been approved for CNS (Reference 6). The standard MCPR and MAPLHGR values already appear in the COLR. Directions for applying the multiplying factors and new limit curves are also provided in the COLR along with the corresponding limits. NEDC-31892 which describes the changes and methodology, becomes a reference in the COLR and the TS bases.
There are also the following direct changes to the TS supporting the ELLL-ARTS changes.
(1) TS 2.1.A.I.a "APRM Flux Scram Trip Setting (Run Mode)".
The flow-biased APRM flux scram trip setting is changed to a new setting to allow operation in the ELLL power-flow operating region. This is changed for both two loop and single loop operation. This change is necessary for ELLL operation and is simila" to previously approved ELLL setpoints for other plants. Administrative changes for clarification and consistency are also proposed. The last two paragraphs in the Bases for TS 2.1.A.1.a concerning the APRM setdown requirements will be deleted since they are no longer applicable when the setdown requirement is removed. These changes are acceptable.
(2) TS 2.1.A.I.d "APRM Roa Block Trip Setting". The APRM rod block trip setting is changed to a new setting for operation in ELLL. This is changed for both two loop and single loop operation. A Bases section discussing the setdown requirement for the rod block setting while operating when the MFLPD is greater than the fraction of rated power (FRP) will be deleted since it is no longer applicable.
These changes are acceptable.
-(3) TS 4.1.B and TS 4.1.C would be deleted. These specifications provide surveillance requirements for the APRM scram and rod block trip settings when operating with a MFLPD greater than the FRP. - The proposed deletion is acceptable since the settings would no longer be applicable.
The first and third paragraphs of Bases Section 4.1.B discussing the surveillance requirements will also be deleted.
(4) Table 3.1.1
" Reactor Protection System Instrumentation Requirements".
The flow-biased APRM flux scram trip setting discussed in Item (1) above
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o will be changed in Table 3.1.1, and Note 20 will be deleted. The 120%
APRM Fixed High Flux trip level setting will be listed separately from the flow biased trip setting.
These changes are consistent with the LCO changes and are acceptable.
(5) Table 3.2.C, " Control Rod Withdrawal Block Instrumentation", has the APRM and RBH rod block trip setpoints changed similarly to that for the APRM scrams in TS 2.1.A.a discussed above. The rod block changes are acceptable, as they were for the scram changes. A current reference to Note 14 is deleted since it was only applicable when a setdown requirement was imposed. The elimination of the setdown requirement will make the current Note 14 no longer applicable.
In its place, a new Note 14 is written to discuss the use of a set of power referenced RBM upscale trip settings designated as LTSP, ITSP, and HTSP discussed earlier in this staff evaluation. The setpoints themselves are identified in TS Table 3.2.0 as a function of lowest rated MCPR limit. The RBM Downscale trip setting would also be changed from the current value of greater than or equal to 2.5% of rated power to a new value of greater than or equal to 91/125. This change is made to provide a value which is relative to a RBM initialization reference of 100/125 of full scale. This is consistent with other trip level setting usage in Table 3.2.C.
This results in a control rod withdrawal block when abnormally low RBM signals are detected.
The setpoints were derived using acceptable ARTS methodology (Ref. 3).
A new Note 15 is added to define RBM operability requirements which states: "The RBM is only required when core thermal power is greater than or equal to 30% of rated power and a limiting control rod pattern (defined in Specification 3.3.B.5) exists. Requirements for operating with a limiting control rod pattern are specified in Specification 3.3.B.5.b."
For clarification, a Note 16 is added to Table 3.2.C which states "RBH trip level settings are relative to the initialization reference signal of 100/125 of full scale which takes place upon control rod selection." This change is administrative and is acceptable.
Table 4.2.C, " Surveillance Requirements for the Rod Withdrawal Block Instrumentation", will be updated to identify a chan RBM Upscale function from "RBM Upscale (Flow Biased)ge in the name for the
" to "RBM Upscale (Power Biased)." This is a change resulting from the ARTS system hardware modifications and is acceptable.
Additional changes to notes for Table 3.2.C are proposed as follows:
(a)
In Note 1, the second sentence is revised to read "The SRM and IRM rod blocks need not be operable in the RUN mode, and the APRM (flow biased) rod blocks need not be operable in the STARTUP mode." These l
-changes are acceptable, based on the new definition of RBM operability in proposed Note 15.
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o (b)
In Note 2, the third sentence concerning the definition for the equation variable N is deleted. This is acceptable since H is no longer used in the RBM upscale trip setting calculation.
(c) In Note 3, the definition of the minimum number of RBM instrument channels is deleted and will be moved to the new Note 15. This is acceptable.
(6) TS 3/4.3.B.5, "U$ eration with a limiting Control Rod Pattern (for Rod Withdrawal Error, RWE)" would be changed to reflect the changes to the RBM, rod withdrawal error analysis, and limiting rod pattern definition.
The surveillance requirement would be changed to indicate that surveil-lance would only be required when only one of the two RBM channels is operable. These are consistent with the ARTS program and are acceptable.
(7) TS 3.11.A, " Average Planar Limiting Heat Generation Rate (APLHGR)", would be revised to specify that the APLHGR for each fuel type as a function of average planar exposure shall not exceed the limiting value specified in the COLR for two recirculation loop operation. TS 3.11.A would also specify (nat "If at any time during steady state operat'on it ie. deter-mined by normal surveillance that the limiting value for APLHGR is being exceeded action will be initiated within 15 minutes to restore operation within the prescribed limits.
If the APLHGR is not returned to within the prescribed limits ^* thin two (2) hours, reduce reactor power to less than or equal to 25% os rated power within the next four (4) hours."
for single loop operation, a sentence is added to state:
"For one recir-culation loop operation the MCPR limits are 0.01 higher than the comparable two-loop values."
The Bases Section 3.11.A would be revised to discuss the bases for the flow and power dependent correc'. ion factors. These changes are based on approved methodology and are acceptable.
(8) TS 3.11.C. " Minimum Critical Power Ratio (MCPR)", would be revised to eliminate the requirement to place the reactor in a cold shutdown condi-tion when the steady state MCPR is not returned to lower than the limiting value specified in the COLR.
Instead, reactor power will be reduced so that MCPR limits are no longer required. This change is a consequence of the application of the ARTS approach and is acceptable. The LCO for TS 3.11.C would include a specification similar to TS 3.11. A above for-exceeding the limiting value of MCPR and for single loop operation.
_(9) Surveillance Requirement 4.11.C will be revised to state:
"MCPR shall be determined daily during reactor power operation at greater than 25% rated thermal power and following any change in power level or distribution that could cause operation on the operating limit MCPR." This is a result of the change from a limiting control rod pattern and is acceptable.
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(10) The Bases for the prcposed revised TSs have been changed to reflect the relevant ARTS changes and TS changes 1 described above. These Bases changes reasonably reflect the TS ~ changes and are acceptable. Many of the explicit limits are presented in the COLR as well as in NEDC-31892P (now referenced in the CNS TS and COLR). These provide an acceptable complete description of the ARTS program and limits for CNS.
3.0 STATE CONSULTATION
In accordance with the Comission's regulations, the Nebraska State official was notified of the proposed issuance of the amendment. The State official had no comment.
4.0 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 NHC 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 cumulative-occupational radiation exposure. -The Comission has previously issued a pro-posed finding-that the amendment involves no significant hazards consideration and there has been no public coment on such finding (56 FR 43810).
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Section 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, i
(1) there is reasonable assurance that the hea hh and safety of the
-that:
-public will not be endangered by operation in the-proposed manner, (2) such activities-will be conducted in compliance with the Comission's regulations, and (3) the issuance of the amendment will not be inimical to the comon defense and security or to the health and safety of the public.
Principal Contributor:
M. McCoy i
Date: November 29, 1991 i;
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