ML20114F807
| ML20114F807 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 10/05/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114F801 | List: |
| References | |
| NUDOCS 9210130317 | |
| Download: ML20114F807 (6) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D C. 20%$
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SAFflY EVALVATION BY THE OFFlCE OF Nt)1 LEAR REACTOR REGULATION EELATED TO AMEfRMJNT NO. 51 TO FACILITY OPERATIM LICENSE NO. NPF-37, b_MI@ MENT NO. 51 TO FACILITY OPERATING LICENSE NO. NPF-66, j
AMENDMENT NO. 40 TO FACILITY OPERATING LICENSt NO. NPF-72, eND AMENDMENT NO. 40 TO FACILITY OPERATING LICENSE NO. NPF-77 COMMONWEALTH EDISON COMPAfiY BYRON STATION. VrilT NOS. 1 AND 2 BRAIDWOOD STATION UNIT NOS. 1 AND 2 QOCKET N05. STN 50-454. SIN 50-455. STN 50-456 AND STN 50 457
1.0 INTRODUCTION
By letter dated July 28, 1992, Commonwealth Edison Company (CECO,-the licensee) requested amendments to the Technical Specifications for the Byron and Braidwood Stations.
The proposed changes would modify the existing specifications related to shutdown margin requirements and create a new specification for the Boron Dilution Protection System (BDPS).
The changes were necessitatad by deficiencies identified in the dilution analysis model and to account for uncertainties in control rod worths and the 50 parts per million (ppm) Hot Zero Power prediction uncertainty.
2.0 EVALVATION The BDPS is intended to mitigate the consequences of accidents which result in a decrease in the reactor coolant system boron concentration.
Such an accident may result from operator error or from a malfunction in the Chemical Volume Control System (CVCS).
In the event of a boron dilction transient, the nuclear instrumentation source range in conjunction with the flux doubling detection system will detect a doubling of the neutron flux.
This information is sent to the solid state protection system which automatically initiates isolation valve movement to terminate the transient. An alarm is also sounded to alert plant operators that flux doubling has been detected and isolation valve trovement should have !. tarted.
Analyses were performed by Westinghouse to demonstrate that the BDPS would detect a boron dilution and prevent criticality provided that the plant meets the Limiting Conditions for Operation (LCOs) as defined in the Technical Specifications.
The results of the analyses are summarized in Section 15.4.6 of the Byron /Braidwood Updated Final Safety Analysis Report (UFSAR).
This system was provided to address staff concerns for an inadvertent dilution transient and was accepted in the 9210130317 921005 PDR ADOCK 05000454 P
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. Byron Safety Evaluation Report issued in February 1982 and the Braidwood Safety Evaluation Report issued in Novemoer 1983.
Subsequently, the licensee identified deficiencies in assumptions used in the dilution analysis model.
Information from Westinghouse and another utility indicated that there may be nonc nservative assumptions in the boron inverse-count-rate-retto (ICRR) data for Modes 3, 4, and 5.
In addition, the original analysis assumed no instrumentation uncertainties in the flux doubling i
setpoint (currently set at 2).
When the uncertainties were factored into the analysis, acceptable results were not obtained for all plant conditions allowed by the current technical specifications.
A retpoint reduction sufficient to allow for the uncertainties was determined to potentially result in frequent spurious actuations and was rejected by the licensee.
Therefore, the licensee has proposed an amendment to the technical spccifications to spectfy more restrictive LC0e necessary to maintain BDP5 operability.
In addition to the deficiencies in the dilution analysis model, the assumed critical boron concentration no longer bounds current core design-predictions.
An additional 100 ppm penalty has been applied to the predicted critical boron concentrations at 60*f in order to account for uncertainties in control rod worths and the 50 ppm Hot Zero Power p 9 diction uncertainty.
Therefore, the predicted critical boron concentration for Braidwood, tinit 1, Cycle 4 was increased to 1119 ppm.
This is an increase from the current licensing basis limit of 1050 ppm.
The licensee performed analyses to determine the conditions under which BDPS would perform its intended function.
The analysis showed that in Modes 3, 4, and 5, the BDPS was operable if the entire Reactor Coolant System (RCS) inventory was available for mixing (i.e., at least one reactor coolant pump (RCP) was running and all loop stop valves were open), the Shutdown Margin was greater that 1.3% AK/K, and source range nuclear instrumentation counts were greater than or equal to 10 counts per second (cps).
Since the current LCOs did not bound these conditions, administrative controls were put in place to assure that the above conditions would be met and BDPS would remain operable and the subject license amendment was proposed to establish appropriate LCOs.
an_ly3 s Evaluation 2.1 a
i The methodology used for the analysis justifying the proposed changes is the same analysis code (ABORT) previously used for Byron and Braidwood and that was approved in the Comanche Peak Safety Evaluation Report.
The key assumptions, as provided in the Standard Review Plan, are addressed as folluws.
The boron dilution is assumed to occur at the maximum possible rate.
For all modes the analysis assumes that the_ Reactor Coolant Makeup System can provide a dilution flow of 205 gallons per minute (gpm).
This value is based on measured plant data with additional conservatism added.
The maximum critical boron concentration assumed by the analysis is 1300 ppm at 60'F, or 1190 ppm at 200*F.
The design critical boron concentrations are
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3-verified to be less than these assumed values during the reload safety analysis process.
The desian value includes a 100 ppm penalty to account for the uncertainties of control rod worths and the 50 ppm Hot Zero Power prediction uncertainty.
The reanalysis was performed only for Modes 3 (Hot Standby), 4 (Hot Shutdown),
and 5 (Cold Shutdown). The BDPS is not assumed to be operable for Modes 1 (Power Operation), 2 (Startup), or 6 (Refueling).
Since the BDPS is not relied upon for Mode 6, the only Mode in which fuel would be removed, the analysis for Modes 3, 4, and 5 assumed that all fuel assemblies are installed in the core.
The assumed RCS volume includes the coolant in the vessel, the loops, the pressurizer, and the steam generator tubes.
It does not credit any volume in the vessel head, the charging system, or the Residual Heat Removal (RHR) system.
This volume is a conservative value of what would be available based on the revised assumptions of all loop stop valves open and at least one RCP running.
This volume is an increase to the volume used for Modes 3, 4, and 5 in the original licensing analysis but is appropriate for the revised conditions of BDPS operability.
The maximum differential boran worth assumed in the analysis is 12.5 pcm/ ppm below 200*F or 12.0 pcm/ ppm above 200*f (1000 pcm is equal to 1% M/K).
The design differential boron worths are then verified to be less than then values during the reload safety analysis process.
The analysis also assumes that the transient begins at the minimum technical specification shutdown margin.
However, the boron concentration provided to the operator includer a conservative 100 ppm penalty to account for the allowed 1% M/K reactivity imbalance verified in Technical Specification Surveillance 4.1.1.1.2, and an additional 80 ppm conservative bias for the "most reactive rod. withdrawn" assumption.
A revised correlation for the change in Source Range Nuclear instrumentation count rate resulting from a particular change in core reactivity was used for this analysis.
This correlation is used to predict how the Source Range detector will respond to the rea:tivity change resulting from a boron dilution. The new correlation was determined from measurements taken during the initial approach to criticality for Braidwood, Unit 1, Cycle 3 and was revised to resolve some non-conservative assumptions identified in earlier boron dilution analyses.
The BDPS actuation setpoint (the ratio of the current flux to the flux ten minutes prior) used in the analysis is higher than the value calibrated into the BDPS.
This conservative assumption accounts for the estimated uncertainty associated with the fixed errors within the circuitry and random errors due to calibration test and measurement equipment and channel drift. However, the estimated uncertainty can only be assured for source range nuclear instrumentation count rate greater than or equal to 10 cps.
Therefore, corresponding operability requirements have been proposed as part of this amendment.
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. 1 The staf f review, of the analysis results vrovidad by the licensee in support 3
of the proposed technical specification chang 9s, indicates that the methodology used was previously approved by the staff and is acceptable and the assumptions used are sufficiently conscrvative and, therefore, also r.ccept able.
The results of the analysis aemonstrated, for both cases analyzed, that the period of time from the flux multiplication setpoint being reached to the purge being terminated by the BDPS is predicted to be less than the period of time from flux multiplication setpoint to criticality.
Therefore, the analysis demonstrated that RCS and RHR system overpressure does net occur and that departure from nucleate boiling does not occur. The staff considers the analysis and results ;cteptable.
7 2.2 Technical _ Specification Evaluati.ca
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The first proposed change would modify the LCO for SpecificaH<, 3.1.1.2.
The new specification increases the required shutdown requirem'-
Mode 5 from 1.0X to 1.0% AK/K.
This reflects the revised operability i '
ations at incorporated into the revised analysis and is acceptable.
The licensee also proposed to modify the ACTION in Specification 3.1.1.2.
The current requirement for a shutdown margin less than 1% AK/K is retained, with an additional proposed action for a shutdown margin less than 1.3% AK/K.
The new ACTION would require that the BDPS be declared inoperable and refers to the BDPS specificatio.
That specification would require closurt. of the boron dilution flow paths and preclude inadvertent dilution by the Reactor Coolant Makeup System (RCMS This ACTION would assure that appropriate shutdown margin is maintained to support BDPS operability and is acceptable.
The propcsed amendment would also create a separate Technical Specification for BDPa (Section 3.1.2,7).
The proposed LC0 would require two independent BDPS subsystems to be operable in Modes 3, 4, and 5.
The proposed LC0 represents the design bas's operability requirement for the BDPS and is acceptable, w first of two proposed ACTION reciuirements for the new section would allow 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore BLiS if one channel is inoperable and then require isolation of the dilution flow paths within I hour if the LCO cannot be met.
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The ACTION would also require verification of isolation of the flow paths on< e every 31 days thereafter.
The second ACTION requirement would r Males that w
the dilution flow paths be isolated stithin I hour if both trains of BDPS are inoperable, and that the isolation be vcrified once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter.
Ir addition, the second proposed ACTION would require verification of the shutdcwn margin.
Both ACTIONS would allow the dilution valves to be opened under administrative control. The allowed outage times of the proposed ACTION requirements are comparable to similar engineered safety feature equipment and is, therefore, acceptable.
The first proposed surveillance requirement for the new section would reautre verification every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> that the source range detector is indicating greater than or equal to 10 cps, all RCS loop stop valves are open, and that
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, at least one RCP is operating.
The second surveillance wuld require verificattun that the valves in the dilution flow i aths are in their correct position at least once per 31 days. The third surveillance would require verification once every 92 days that the BDPS setpoint is less than or equal to an increase of twice the count vate within
'0-minute period.
The final proposed surveillance would rt. quire that a :.mii' 'd BDPS flux daubling test signal be generated at least every 13 mantie a (nat appropriate valve movement occur in less %an c equal to 9.. onds. These surveillances provide assurance that the c.alysis assumptions are met to maintain BDPS operability and are acceptable.
The la;,t two surveillances exist currently in the Technical Specifications and would be deleted from their other locations to be incorporated into the BDPS section, in addition, footnote ** on Table 3.3-1, functional Unit 6, which permits the BOPS Thx Doubling signals to be blocked during reactor startup, is proposeo to be moved to the new specification. This is acceptable, finally, the Bases for Specificat.on 3/4.1.1.2 is modified to sddress the new requirement of a 1.3% M/K shutdown margin to support operability of BDPS and the Bases of Specification 3/4.1.2 is modified to include a description of the analysis that supp rts the operability of BDPS 2.3 Summary As a result of the idei,tified defic'.encies in previous assumntions the licensee conducted a reanalysis with some specified changes in initiating conditions for an assumed boron dilution transient. The reanalysis was conducted for hot standby, hot shutdown, and cold shutdown conditions. These events were evaluated by the licensee using a model that was eviously found acceptable by tne staff.
These analyses indicated that the dilution transients were terminated by the BDPS without operator ac' 'n before the shutdown margin was eliminated and, therefore, no feel dan.
occurred.
Based on our review of the analyses and the proposed supporting changes to the technisal speci 9 cations the staff considers the proposed amendment acceptable.
3.0 STATE CONSULTAT QU In accordance with the Commission's regulations, the Illinois State official was no?ifit-of the proposed issuance of the amendmentc. The State official had no comments.
4.0 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 iequirements. - 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
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, proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (57 FR 40208). 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.
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 wi'th the Commission's regulations, and (3) the issuance of the amendments will r.ot be inimical to the common defense and security or to the health and cafety of the public.
Principal Contributor:
John B. Hickman, NRR Date: October 5, 1992
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