ML20113H771
| ML20113H771 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 07/28/1992 |
| From: | Simpkin T COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20113H773 | List: |
| References | |
| NUDOCS 9208050269 | |
| Download: ML20113H771 (13) | |
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July 28,1992 Dr. Thomas E. Murley, Director Office Of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 Attn; Document Control Desk
Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Application for Amendment to Facility 03erati,ig License NPF-37, NPF-66, NPF-72 and NPF-77 tHOJ1ocke1Nm00-45_4d5LA5LanL45Z
Dear Dr. Murley:
Pursuant to 10 CFR 50.90, Commonwealth Edison (CECO) pmposes to amend A3pendix A, Technical Specification of Facility Operatint,1cerr .s NPF-37, NPF-66. NPF-72 and NPF-77. The proposed amendment changes spuifications 3/4.1.1.2 and 3/4.3.1 and adds new specification 3/4.1.2.7 to refloct revisions to the current Boron Dilution Analyses.
A detailed description of the proposed chango is presented in Attachment A.
The revised Technical Specification pages are contained in Attachment B.
The proposed change has been reviewed and approved by both on-site and "
off-site review .n accordance with CECO procedures. CECO has reviewed this proposed amendment in accordance with 10 CFR 50.92(c) and has determined that no significant hazards consideration exists. This evaluation is documented in Attachment C. An Environmental Assessment has been completed and is contained in Attachment D.
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. Dr; Thomas E, Murley-- July 28,1992
- CECO is notifying the State of Illinois of our application for this amendment by
. transmitting _a copy _of this letter and its attachments to the designated State Official.
- To the best of my knowledge and belief the statements contained herein are L true and correct. In some respects, these statements are not based on my personal
- knowledge but upon information received from other Commonwealth Edison and
-contractor employees. Such information has been reviewed in accordance with Company practice and I believe it to be reliable.
Please direct any questions re0arding this matter to this office.
Sincerely,
^ .W.Ab Simpkin Nuclear Licensing Administrator cc: . R.MJ Pulsifer, Pro ct Manager - NRR J.B. Hickman, P ect Manager - NRR h S. Dupont, Resid nt Inspector - Braldwood W, Kropp, Resident inspector - Byron
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ATTACHMENIA DETAILEDJ2ESCRIPllON OE311EElOEOSED_CliANGES Doscription of the Current Operating Uconso (OL) Requirements:
The current boron dilution transient analysis assumes a SHUTDOWN MARGIN of
'1% Ak/ kin MODE 5. If the SHUTDOWN MARGIN drops below this value Technical Saecification 3.1.1.2 requires that boration be initiated immediately to restore it to 1%
Mk.
The Boron Dilution Protection System (BDPS) is designed to mitigate the consequences of accidents that result in a decrease in the reactor coolant boron concentration. These accidents may result from operator error or from a malfunction in the Chemical and Volume Control System (CVCS). In the event of a boron dilution transient, the nuclear instrumentation source range and the flux doubling detection system willidentify a neutron flux doubling. This information is sent to the solid state protection system which automatically initiates isolation valve movement to terminate the transient. This automatic action was assumed in the Byron /Braldwood accident analysis in MODES 3,4 and 5. However, the BDPS Flux Doubling signal may be blocked during reactor startup.
Current Technical Specifications do not directly require OPERABILITY of BDPS.
However, Technical Specification 4.3.1 Functional Unit 6 requires that the function of BDPS be verified as part of the channel calibration and analog channel operational test for the nuclear instrumentation source range (Table 4.3-1, Functional Unit 6). The
- requirements are as follows (from Table 4.3-1. Table Notations):
(9) ... Surveillance shall include verification of the Boron Dilution Alarm Setprint of less than or equal to an increase of twice the count rate within a 10-minute period.
(12) At least once aer 18 months during shutdown verify that on a simulated Boron Dilution Doualing test signal CVCS valves 112D and E open and 1128 and C close within 30 seconds.
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Bases for the Current OL Requirements:
The SliUTDOWN MARGIN requirements and BDPS OPERABILITY requirements -
ensure that the plant is protected from an inadvertent boron dilution when the plant is in
- HOT STANDBY, HOT. SHUTDOWN, and COLD SHUTDOWN. BDPS is designed to detect a dilution of the reactor coolant and automatically take corrective actions to t terminate the dilution and restore SHUTDOWN MARGIN before reactor criticality is reached. -
The Licensing Basis Acceptance Criteria is prescribed 10CFR50, Appendix A, -
- General Design Criteria (GDC):
GDC 10, as it relates to the Reactor Coolant System (RCS) beln designed with appropriate margin to assure that specified acceptable fuel desi limits are not exceeded during normal operations including anticipated operat nal occurrences.
GDC 15, as it relates to the RCS and its associated auxiliaries being designed with-appropriate margin to assure that the pressure boundary will not be breached during normal operations including anticipated operational occurrences.
GDC 26, as it relates to the reliable control of reactivity changes to assure that specified acceptable fuel design limits are not exceeded, including anticiaated operational occurrences. This is accomplished by assuring that appropr ate mrrgin for malfunctMns,'such as stuck rods, are accounted for.
Analysis was performed by Westinghouse which demonstrates that BDPS will successfully detect a boron dilution and prevent criticality provided that the plant meets o
The analysis inputs, assumptions, and(results conform to the requirem Standard Review Plan (SRP), NUREG-0800, Section 15.4.6, Revision 1. The results of the' analysis are summarized in the Byron /Braidwood Updated Final Safety Analysis
- Report (UFSAR), Chapter 15.4.6. -
The acceptance criteria of 10CFR50, Appendix A are met by demonstrating that BDPS can successfully mitigate a design basis dilution before RCS and residual heat removal system overpressure occurs and that departure from nucleate boiling does not
- occur. These conditions are prevented by demonstrating with analysis that criticality
.(and subsequent generation of nuclear heat)is not achieved.
Byron /Braidwood rel on the automatic actuation of BDPS to miti dilution accident in MOD S 3,4 and 5. BDPS is not required. in MODkate a b 6 because
- inadvertent dilution is precluded by administrative controls that isolate the RCS from unborated water sources (Surveillance Requirement 4.9.1.3).
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V The purpose o' SHUTDOWN MARGIN is to assure that (1) the reactor can be made subcritical from all operating conditions, (2) the reactivity transients associated with postulated accident conditions are controllable within acceptable limits, and (3) the reactor will be maintained sufficiently subcritical to preclude inadvertent criticality from a shutdown condition.
The SHUTDOWN MARGIN requirements vary throughout core life as a function of fuel depletion, RCS boron concentration, and RCS temperature. The most restrictive condition occurs at end of core life at no load operating temperature concurrent with a steam line break accident. In this analysis, a SHUTDOWN MARGIN of 1.3% Ak/kis required in MODES 3 and 4 to control the reactivity transient caused by rapid i cooldown. A reduced SHUTDOWN MARGIN of 1.0% Ak/k is allowed in MODE 5 since the limiting case of a steam !ine break is not credible below 200 *F.
Description of the Need for Amending the Technical Specirmations:
In March 1992, Westinghouse Electric Corporation notified Commonwealth Edison Company (CECO) of a Potential Issue involving nonconservative assumptions in the MODE 3,4 and 5 boron inverse-count-rate-ratio (ICRR) data. Recent informatE, from another utility indicated that the Westinghouse data is not bounding.
The Potential Issue also stated that the original analysis assumed no instrumentation uncertainties in the flux doubling setpoint (currently set at 2.0). The flux-doubling signal actuates the arotective function of BDPS to isolate the dilution ;
source and initiate reboration of t le RCS. After the uncertainties were factored into the analysis, it was not possible to obtain acceptable results under til plant conditions allowed by the current technical specifications and the current setooint. A substantial reduction in the setpoint would be required to recover the margin lost to the incorporation of the setpoint uncertainty into the analysis. A setpoint this low would result in frequent spurious actuations and is not considered a viable alternative.
Because of the instrument uncertainties, plus the non-conservatism in the ICRR data, BDPS is not capable of performing its design function under a'l conditions in MODES 3, 4,and5.
In addition to the deficiencies in the dilution analysis model, the assumed critical boron concentration no longer bounds current core design predictions. Since '991, an additional 100 parts per million (ppm) penalty has been applied to the predicted critical boron concentrations at 60 *F in order to account for uncertainties in control rad worths and the 50 ppm Hot Zero Power prediction uncertainty. Due to this penalty. the predicted critical boron concentration for Braidwood Unit 1 Cycle 4 was increased to 1119 ppm. The current licensing basis limit is 1050 ppm. The licensing amer.Jaent is required in order to obtain NRC concurrence with the results of the re analysis of the boron dilution transient prior to initial start-up of Braidwood Unit 1 Cycle 4. This concurrence is required by 10CFR50.59 because the results of the analysis determined that a change to Technical Specifications was required.
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Westinghouse and CECO have performed analyses to determine the conditions under which BDPS will aorform its intended safety f'uncilons. The analyses showed that in MODES 3,4 anc 5, BDPS was OPERABLE if the entire RCS inventory was available for mixing (i.e. at least one reactor coolant pump (RCP) running and allloop stop valves open), the SHUTDOWN MARGIN was greater than 1.3% Ak/k, and source range nuclear instrumentation counts were greater than or ec ual to 10 cps. However, the existing licensing basis analysis assumes that BDPS will function under all conditions in MODES 3,4, and 5. In order to assure that the analysis remains bounding, administrative controls were put in place to assure that if the above conditions could not be met, BDPS would be declared inoperable and dilution flow paths would be isolated.
In the future, additional analysis and/or plant modifications may enable BDPS to function under all conditions as assumed in the initial safety analysis. However, until that time, the analysis has been revised to reflect the current functionality of BDPS. In order to preserve the assumptions of this now analysis, CECO requests the attached license amendment request.
Description of the Proposed Amendment:
- The proposed amendment modifies the LCO for Specification 3.1.1.2. The new specification increases the required shutdown margin requirement in MODE 5 from 1.0% to 1.3% Ak/k.
The proposed amendment modifies the ACTION for Specification 3.1.1.2. The new Action i': divided into two parts as follows:
- a. With the SHUTDOWN MARGIN less than 1.3% Ak/k, declare both Baron
- Dilution Protection System subsystems inoperable and apply Specification 3.1.2.7.b.
- b. With the SHUTDOWN MARGIN less than 1% Ak/k, immediately initiate and continue boration at greater than or equal to 30 gpm of a solution containing greater than or equel to 7000 ppm boron or equivalent until the SHUTDOWN MARGIN is restored to greater than or equal to 1% Ak/h.
This revised ACTION 3rovides the additional contingency to protect the analysis assumption that the S iUTDOWN MARGIN will be above 1.3% AWh at the initiation of a boron dilution transient. Closure of the boron dilution flow paths aer Specification 3.1.2.7.b precludes inadvertent dilution by the Reactor Coolant Makeup System (RCMS). The SHUTDOWN MARGIN of 1% Ak/k remains adequate to mitigate all other reactivity transients The proposed amendment creates a separate LCO for BDPS (3.1.2.7). Two independent subsystems are required to be OPERABLE in MODES 3,4, and 5. Each l subsystem of BDPS is capable of isolating all dilution flowpaths. The title of this LCO is added to page IV of the Index.
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v The proposed ACTION 3.1.2.7.a allows 72 haurs to restore BDPS if one channelis inoperab's. The ACTION then requires isolation of the dilution flow paths within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> if the LCO cannot be met. The ACTION also requires verification of isolation of the flow paths once every 31 days thereafter. This allowed outage time is comparable to other similar Engineered Safety Feature equipment, if both trains of BDPS are inoperable. ACTION 3.1.2.7.b requires that the dilution flow 3aths be isc:ated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and ver3iad at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter.
ACT ON 3.1.2.7.b also requires verification of the SHUTDOWN MARGIN. Both ACTIONS allow the dilution valves to be opened under administrative control in order to support plant evolutions.
The creation of a separate BDPS Specification allows the indhidual accident analysis ansumptions to be verified as part of the surveillance requirements.
Surveillance 4.1.2.7.a verifles 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 cpe, all RCS loop stop valves are open and that at least one RCP is operating. These surveillances assure that sufficient RCS mixing volume is available and that incirument uncertainties are tr'nimized. Surveillance 4.1.2.7.b provides additional assurance of the analysis assumptions by verifying that the valves in the dilution flow paths are in their correct position at least once per 31 days.
Surveillance 4.1.2.7.c verifies the flux doubling setpoint. This surveillern.e replaces the portion of Notation 9 on Table 4.3-1 that is being deleted. This change does not alter the original requirement, but merely relocates the requirement to the new LCO.
Similarly, Surveillance 4.1.2,7.d replaces Notation 12 of Table 4.31 which is being deleted. No changes to the content of this surveillance are requested, The footnote " on Table 3.0-1, Functional Unit 6, is deleted and moved to the new Specification 3.1.2.7. This footnow permits the BDPS Flux Doubling signals to be
. blocked during reactor startup. No change was made to this requirement.
The Bases for S 3ecification 3/4.1,1.2 were modified to state that the 1% Ak/k SHUTDOWN MARG N is adequate as long as the dilution flowpaths are isolated. A sentence is added to include the new requirement of a 1.3% Ak/k SHUTDOWN MARGIN to support OPERABILITY of BDPS. The last paragraph of this section was deleted as it no longer accurately describes the function of BDPS.
The Bases of Specification 3/4.1.2 were modified to include a description of the analysis that supports the OPERABILITY of BDPS. This addition provides the Bases for the new Specification 3.1.2.7.
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w Basis for tho Proposed Amendment:
Analysis was performed by Westinghouse which demonstrates that BDPS will successfully detect a boron dilution and prevent criticality provided that the plant meets the LCOs as defined in the proposed amendment.
The acceptance criteria of 10CFR50, Appendix A are met by demonstrating that BDPS can successfully mitigate a design basis dilution before RCS and residual heat removal system overpressure occurs and that departure from nucleate boiling does not occui. These conditions are prevented by demonstrcting with analysis that criticality (and subsequent generatien of nuclear heat) is not achleved.
The results of the analysis are attached. The key time intervals predicted by the analysis are defined as follows:
Ilme iLomlaglanlag_otDilulioD_to_Qrit!cality: This is the number of minutes from the time the dilution begins to the tirae the reactor would reach the critical boron concentration (assuming no mitigating actions).
Time.fron1EluddultiplicatioIL6elpDiGLlo3titi.cality: This is the number of minutes between the time the flux has multiplied by the setpoint from the initial count rate to the time the reactor reaches the critical boren concentration.
Ilma_fam.Eluddultiplicationlatp.oinLiojindsLEutga; This is the number of minutes between the time the flux has multiplied by the setoolnt from the initial count rate to the time that 2000 ppm boric acid is injecting Into the reactor. It conservatively includes the max mum credible time delays atsociated with the flux multiplication circuitry, protection system delays, and valve stroke time. It also includes the pellod of time required to purge the charging pump suction and discharge lines from the suction valve swapover point to the cold leg charging nozzle.
In the analysis, two cases were performed to demonstrate that BDPS can successfully mitigate criticality in HOT STANDBY, HOT SHUTDOWN, and COLD SHUTDOWN. In both cases, the perioa of time from the flux multiplication setpoint to end of purge is predicted to be less than the period of time from flux multiplication setpoint to criticality. This means that the acceptance criteria has been met.
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The SRP requires that the parameters and assumptions used in the anal,lical model should be suitably conservative. For HOT STANDBY, HOT SHUTOOWN, and COLD SHUTDOWN the SRP prescribes the following assumptions:
- 1. The boron dilution is assumed to occur at the maximum possiblo rate.
- 2. The core burnup and corresponding boron concentration are selected to yield the most limiting combination of moderator temperature coefficient, Doppler coefficient, axlal power profile, and radial power distribution. This will usually be the beginning of life (BOL) condition.
- 3. All fuel assemblies are installed in the core.
- 4. For each event analyzed, a conservative high reactivity addition rate is assumed taking into account the effect of increasing boron worth with dilution.
- 5. Conservative scram characteristics are assumed, i.e., maximum time delay with the most reactive rod held out of the core.
The analysis performed by Westinghouse meets each one of these criteria. The analysis assumptions and parameters are described below:
- 1. lOBB_Curres: The ICRR is a measure of the change in Source Range Nuclear Instrumentation count rate for a particular change in core reactivity conditions. This curve is used to predict how the Source Range detector will respond to the reactivity change resulting from a boron dilution. The analysis was aerformed using ICRRs measured at Braidwood Unit 1 Cycle 3 during its initial approach to enticality. The secondary source was located in core location G-2 rather than the normallocation, H 3. This curve represents the most limiting source to detector geometry for Byron /Braidwood. This ICRR curve is a revision to the curve assumed in the current licensing basis. The curve was revised to disaosition the non-conservative assumptions reported by Westinghouse regarcing the boron dilution analysis performed in 1991.
- 2. Satpoint: The actuation setpoint is the value of the ratio of the flux at the time of alarm to the flux ten minutes prior. The actuation setpoint used in the analysis is higher than the value calibrated into 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. The estimated uncertainty can only be assured for source range nuclear instrumentation count rates greater than or equal to 10 cps.
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- ? - g This setpoint is a revision to the setpoint assumed in the current licensing .
basis. The actual setpoint in the plant is unchanged. The setpoint assumption in the analysis was revised to disposition the non-conservative assumptions reported by Westinghouse regarding the boron dilution analysis performed in 1991,
- 3. - BeacioLCoolanLSySiendolume: The assumed RCS volume is 9700 cubic feet. The full RCS volume includes only the coolant in the ves'sel, the loops, the pressurizer, and the steam generator tubes. It does not credit any volume in the vessel head, the charging system, or the RHR system. This volume is available whenever all Loop Stop Valves are open and at least one RCP is in service. One reactor coolant pump can provide sufficient driving force to ensure _ adequate mixing of all four reactor coolant loops.
' The assumed volume for HOT STANDBY, HOT SHUTDOWN, and COLD SHUTDOWN is the same volume assumed for Full Power operation in the current licensing basis. However, for HOT STANDBY, HOT SHUTDOWN, and COLD SHUTDOWN the volume is a revision to the volumes assumed in the current licensing basis. The revision was required to analytically gain margi_n lost to the affects of the increased critical boron concentration, the new setpoint uncertainty assumption, and the change in ICRR curve characteristics.
- 4. DilutionEowtates: In all MODES, the analysis assumes that the RCMS can provide an inadvertent dilution flow up to 205 gallons per minute (gpm). This value has been calculated based on actual measurements from plant data with additional conservatism applied to account for abnormal plant conditions.
(: - 5. CdticalB_oIDD_Goncenkallon: 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 verified to be less than these values during the reload safety analysis process. The design value includes a conservative 100 ppm penalty to account for the uncertainties of control rod
!- worths and the _50 ppm Hot Zero Power prediction uncertainty.
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The most limiting time in life for the transient occurs early in core life when a significant fraction of the fixed burnable absorbers have been depleted. After this point in core life, the critical boron concentration decreases until the end of the cycle where it typically equals 200 ppm.
This COLD SHUTDOWN critical boron concentration is a revision to the concentration assumed in the current licensing basis. The concentration was revised to disposition the original non-conservative assumptions regarding uncertainties in control rod worths at 60 *F and the 50 ppm Hot Zero Power prediction uncertainty.
- 6. SHUID.QWNJMBGJN: The analysis assumes that the transient begins at the minimum technical specification SHUTDOWN MARGIN. The boron concentration provided to the operator includes a conservative 100 ppm penalty to account for the allowed 1% Ak/k reactivity imbalance in Technical Speciflcation Surveillance 4.1.1.1.2. The "most reactive rod withdrawn" assumption provides an additional 80 ppm conservative bias.
The COLD SHUTDOWN SHUTDOWN MARGIN is a revision to the value assumed in the current licensing basis. The revision was required to gain margin lost to the affects of the increased critical boron concentration, the new setpoint uncertainty assumption, and the change in ICRR curve characteristics.
- 7. DitletentialEpan Worth: The maximum differential boron wor'h assumed by the analysis is 12.5 pcm/ ppm below 200 *F or 12.0 pcm/ ppm above 200 F.
The design differential boron worths are verified to be less than :hese values during the reload safety analysis process. (1000 pcm is equal to 1% Ak/k).
- 8. BCSlemperatur.e: Temperature is f actored into the analysis by varying the RCS density, critical boron concentration, and differential boron worth. The analysis is conservative because for each temperature range, the lowest density occurs at the high end of the range and the highest differential boron worth and critical boron concentration occur at the lower end. The analysis assumes lowest density, the highest differential boron worth, and the highest critical boron concentration simultaneously for each condition.
The amended technical specifications require that the dilution flowpaths be administratively controlled when the plant conditions do not meet the initial conditions of the transient analysis. Administrative control of dilution flowpaths are sufficient to preclude an inadvertent dilution.
The SHUTDOWN MARGIN requirement for COLD SHUTDOWN was revised to 1.3% Ak/k in order to ensure acceptable results for the boron dilution transient.
Administrative control of dilution flowpaths are sufficient to preclude an inadvertent dilution, and all other transient evaluations are acceptable if the SHUTDOWN MARGIN is greater than or equs.1 to 1.0% Ak/k. The current COLD SHUTDOWN requirements for borated water sources are sufficient to ensure that the 1.0% Ak/k SHUTDOWN MARGIN can be maintained, so no additional requirements on borated water sources are required.
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-- y Boron Dilution Analysis Results I Case i I _
1 I 2 I I Case I MODE 5 I HODE 3 I I Description RCP I RCP I I I in I in I I I Serrice. I _ Service I I Differential I I I I Boron I 12.5 I 12.0 I I Worth I I I ip_cnLppm) i I I E
I RCS i T I I Temp I 200 I 557 I I ('F) I I I I RCS I I I I Volume i 9700 I 9700 Y Z lLL11 I I I I Dilution I I I I Flow I 205 I 205 I I [gpm) I I I I- Shut I I I I Down I 1.3 I 1.3 I I Margin I I I I (1Wjt/ k ) .I I I I Critical I I I I Boron I 1300 I 1190 I
! I Conc I I I I (ppm) I I j i I Initial I I I I I Boron I 1404 I 1298.3 I I Concentration I I I I (ppp) I I I I Time from.Beginning of I -I I I Dilution to Criticality I 23.75 I 27.15 I I (miRRtesi I I I I Time From Flux I I I I Multiplication Setpoint I 3.49 I 3.68 I I to C-iticality I I I I (minutes 1- I I_ I I Time From Flux I I I I Multiplication Setpoint I 2.65 I 2.93 I I to End of Purge I I I I I I I (mi.nRtRE_)
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Schedular Requiromonts:
- CECO requests that this license amendment request be approved no later than September 5,1992 which correspords to the first day of the Braidwood Unit 1 Cycle 3 Refuel Outage, ZNLD/2038/13 l