ML20127P036

Forwards Request for Temporary Waiver of Compliance from TS 3.3.2.G.1 Re Low Temp Overpressure Protection PORV Setpoints to Permit Util to Implement Conservative PORV Setpoints Consistent W/Results of Recent Evaluation

ML20127P036
Person / Time
Site:	Zion File:ZionSolutions icon.png
Issue date:	01/28/1993
From:	Stimac S COMMONWEALTH EDISON CO.
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
NUDOCS 9302010170
Download: ML20127P036 (9)

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- C:mm:nw:alth Edison

- : 1400 opus Place Downers Grove, Illinois 60515 January 28.1993 I

Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission ,

Washington, DC 20555 l Attn: Document Control Desk

Subject:

Zion Station Unit 2  :

Request for NRR Waiver of Compliance to Facility Operating License No. DPR 48 Appondix A, Technical Specification 3.3.2.G.1.a i Low Temperature Overpressure Protection i NBC__ Docket No. 50-304 i l

Dear Dr. Murley:

l The purpose of this letter is to request a NRR Temporary Walver of -

Compliance (TWO from the Low Temperature Overpeessure Protection Power Operated Re ef Valve (PORV) setpoint requirement of Technical ecif! cat Sp(LTOP) 3.3.2.G.1.a as it applies to Zion Unit 2 during the startup from the current refuel outage (Z1R12). The proposed TWOC would allow Commonwealth Edison Company (CECO) to implement conservative PORV setpoints consistent with the results of a recent -

engineering evaluation of PORV operability durin LTOP operation. A detailed description of the TWOC and its basis is include in Enclosure 1.

This request for NRR TWOC and its basis were discussed during a teleconference between CECO and NRC (NRR and Region lil) personnel on January 28,1993. At this time, CECO and NRC agreed to the general content of the enclosed material. Supporting technicalinformation requested by the staff during the teleconference is included with Enclosure 2.

To avoid delay in the startup and return to service of Zion Unit 2 from the current refuel outage, CECO requests that NRC approve this TWOC by close of normal business on January 28,1993. CECO requests that the TWOC be effective from the date and time of approval until February 22,1993 at 11:59 PM. This will ensure that -

Zion Unit 2 has extted the mode of a pilcability for the subject specification prior to expiration of this TWOC. Additional ustification for this duration is included in Enclosure 1.

The follcwing information is provided in Enclosure 1 in support of this request for TWOC.

Discussion of the requirements for which the TWOC is requested; Discussion of the circumstances leading to the request; Description of compensatory actions; Evaluation of safety significance and potential consequences; Discussion which justifies the duration of the request; Basis for concluding that the request does not involve a significant hazards consideration;

Basis for concluding that the request does not involve irreversible environmentai consequences.

930201017o 93o120 (11000' SDR ADOCK05oog4 ZNLD/2484/1 \

Dr. Murley _Jcnuary 28,1993

- This request for NRR TWOC has been reviewed and approved by CECO senior manegement as well as on site review in accordance with Company procedures.

CECO will submit a request for technical specification amendment for NRC -

review which will resolve this issue by February 22,1993. This amendment request will propose relocation of the PORV setpoint to an owner controlled document consistent with the guidance of the Westinghouse improved Standard Technical Specifications, NUREG-1431, Revision 0.

Please direct any questions you may have to this office.

Very truly Yours, l .-

n~' Stephen F. Stimaca Nuclear Licensing Administrator

Enclosures:

1. Request for NRR TWOC

2. Supporting Technical !nformation cc: A. Bert Davis, Reg:onal Administrator - Rill C.Y. Shiraki. Project Manager - NRR J.D. Smith, Senior Resident inspector - Zion Office of Nuclear Facility Safety - IDNS ZNLD/2484/2

4 ENCLOSURE 1 l REQUEST FOR NRR TEMPORARY WAIVER OF COMPLIANCE LTOP SETPOINT' i

1. REQUIREMENTS FOR WHICH THB TEMPORAkY WAIVER OF COMPLIANCE IS REQUESTED  !

l The Low Temperature Overpressure Protection.(LTOP) System providus low temperature overpressure protection for the Reactor Coolant System (RCS) such that the integrity of the RCS Pressure Boundary is not compromised by violating the pressure and teoperature limitations specified to assure the fracture toughness requirements of 10CFR50 Appendix Gj are not exceeded. The Pressurizer Power Operated Relief valve (s)(PORV) (a) are utilized in event mitigation at Zion Station. The PORVs at Zion Station respond to fixed pressure setpoints. Th's low pressure setpoint of concern is derived from analysea which assume several liniting conditions (le; RCS temperature, PORV stfroke time, system response characteristics, etc.)

The pressure sensors providing input to the LTOP system sense RCS pressure from tape located on the Loop "C" RCS Hot Leg (core outlet) and from the suction piping tolthe Residual Heat Removal Suction piping which taps of f the "A" Hot Leg piping. The critical veld used in the LTOP System analysisiis located in the vessel boltline region (RCS Downcomer - Cold Leg pressura). Due to the location of the pressure censing tapsi rolative to the critical weld, a pressure correction factor must be applied-to-the LTOP setpoints whenever Reactor Coolant Pumps (RCPs) or Residual Heat Romoval (RHR) Pumps are in operation. Based on operational data at Zion and typical f our loop Westinghouse PWR values, these correction factors range from 5 to 50 polg depending on operational combination. As described in section 2, the need to apply these correction factors was only recently identified. As such, the current LTOP setpoints do not account for these correction factors.

Commonwealth Edison is requesting;a NRR Temporary Waiver of Compliance for Zion- Unit 2 Technical Specifications 3.3.2 G.1.a.

. which specifies a fixed LTOP setpoint,of 435 psig,. The proposed change replacet the fixed value with i a 5 435 psig limitation, thereby allowing the LTOP setpoints to be. set at values lower than and more conservative than currently allowed. This will allow the LTOP setpoints to be adjusted-in such a manner as to account for the additional correction factors requi' red when RCPs or RHR pumps are running, t

2. CIRCUESTANCES LEADING TO THE REQUEST On January 13, 1993, Zion Station was notified by the Connonwealth Edison Nuclear Engineering Department that the LTOP analysis f or Zion Station did not account for the correction factors necscsary when RCPs or EHR pumps are in operation, t

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ENCLOSURE 1 ;

REQUEST FOR NRR TEMPORARY WAIVER OF COMPLIANCE LTOP SETPOINT!

On January 15, 1993, a preliminary operability assessment was completed which concluded that the pump correction factors could not be accommodated within the current Technical Specification setpoint of 435 psig without imposing significant restrictionc on-RCP operation. '

options were reviewed to increase RCS temperature to a temperature sufficient to allow for th'e operation or one or two RCPs during RCS venting and heatup operations with the current 43$

psig setpoint. On January 26, 1993, after reviewing the means available to raise and maintain RCS temperature,-it was concluded that RHR pump heat and Reactor decay heat were inadequate. At this time it was concluded that relief from the existing Technical Specification setpoint would be necessary to allow heat up of Unit 2 utilizing the RCPs from the current refueling outage (Z2R12).

3. DESCRIPTION OF COMPENSATORY ACTION'S Correction factors appropriate for the. number of pumps in operation and the RCS pressuro tap location have been used in the determination of more conservative LTOP setpoints, assuring compliance with the f racture toughness!' requirements specified by10C overpressure event. The LTOP System will be set consistent with these new values (Enclosure 2) not to esceed the current specified 435 psig. Since this action ensures the LTOP systems safety function is' preserved, no further compensatory actions are required.

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i EVALUATION OF SAFETY SIGNIFICANCE AND I POTENTIAL CONSEQUENCES:

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' Cold overpressure protection at Zi'on Station is accomplished i

through restricting mass inventory makeup capability at reduced temperatures, and restricting the startup of the first RCP when-L secondary side temperature is greater than or equal.to 50'F above l- RCS temperature. In addition to the above restrictions one of the following mitigative measuros is required;

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1) Maintaining tne RCS in a depressuri' ed z cont'ition with one PORV and its associated isolation valve open, or

2) Maintaining 3CS pressure less than 100 psig and pressurizer' level less than 25%, or

3) Maintaining two PORVs operable with setpointo of 435 psig.

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' ENCLOSURE 1

• REQUEST FOR NRR TZXPORARY WAIVER CP COMPLIANCE LTOP SETPOINT '

Revising the PORV setpoints to S $3d psig has no inpact on either option 1 or 2 above. Revising the "0RV setpoints to 5-435 puig will allow for the incorporation ofl c < vection f actors in the determination of a more conservative setc sint (option 3) . These conservative setpoints have been determined consistent with standard Westinghouse methodology. In addition, the revised-setpoints incorporate correction factors necessary due to pressure sensor location. The new LTOP setpoints account for known unCortainties and correction f actors in 'such a manner as to assure compliance with the fracture toughness ? requirements specified by 10CFR50AppendixGintheeventofanpnalyzed overpressure event.

low temperature The requested TWOC adopts the a'pproach utilized in the Westinghouse Standardized Technical Specifications, NUREG-0452, Revision 4. This approach allows the flexibility to set the LTOP setpoints to any value which is less than or equal to the value that was ' assumed in the LTOP analyses. ' This approach recognizes the safety function is to provide relief capability at a pressure which does not exceed the analytical basis for the LTOP System. It is not necessary to require a minimum LTOP setpoint in order to ensure LTOP operability. ,The revised setpoints which have been developed (or any setpoint which wouldlbe implemented) have been (or will be) evaluated to ensure that any. reduction in the setpoint is consistent with system operating parameters (i.e. will not result in spurious PORV actuation, will!not have adverse impact on RCp seal operation, etc). ,

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A DISCUSSION WHICH JUSTIFIES THE DURATION OF THE REQUEST l

This TWOC is reques*.ed to remain lin effect for Unit 2 f rom issuance until 11:59 pm on Februarr 22, 1993. This-duration is based on the following con.;ideratio;ns;;

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1) Current schedule projections for reaching Mode 3 of February 11, 1993 (which ents the Mode of ' Applicability for the LTOP System),

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2) Heatup to normal operating pressure and temperature, and the performance of RCS walkdowns (Febru ny 12, 1993), and

3) An addition 41 10 days to account for a Unit cooldown, repairs, and subsequent return to Mode 3 in the event of any significant problems enccuntered during the Unit startup.

This duration is considered accepthbla cased on the saf ety Significance and Potential Consequences provided in section 4 above.

• ENCLOSURE 1 REQUEST FOR NRR TEXPORARY WAIVER OF COMPLIANCE LTOP 9ETPOINT l

6. BASIS FoR CONCLUDING THAT THE REQUEST DOES NOT INVOLVE A '

SIGNIFICANT HAEARDS CONSIDERATION ,

commonwealth Edison ha evaluated this proposed temporary waiver and has determined th t involves no significant hazards considerations. According t' . ICPR 50.92 (c) , a proposed change to an operating license involves to significant hazards considerations if operation of the f acility in accordance with the proposed change would not:

1) involve a significant increa'ae in the probability or consequences of an accident previously evaluated; or

2) Create the possibility of a new or dif f erent kind of accident from any accident previously evaluated; or

1) Involveacignificantreductipninamarginofsafety.

The proposed change does not involve a significant increase in the probability or consequencea oflan accident previously evaluated. With respect to an increase in the probability of previous , = valuated accidents, the incorporation of additional correctier ractors into the setpoint calculations has no impact on any event procursor, therefore probability will remain unchanged.

With regard to the consequences of accidents previously evaluated, the incorporation of additional correction f actors into the setpoint calculations will provide additional assurance that the LTOP Systen will actuate to assure compliance with the fracture toughness requirements of 10CFR50 Appendix G in the event of an analyzed low temperature overpressure event. As such, the consequences of previously evaluated accidents, with respect to offsite dose considerations, would not,be significantly impacted.

The proposed change does not creathe the possibility of a neV or different kind of accident from any:previously analyzed. The proposed change does not result in plant operations or configurations that could create a new or dif f erent type of accident. Any LTOP setpoint changes implemented have or will be evaluated to ensure they do not result;in any component or system being placed in an unanalyzed configuration. As such, the proposed change does not create the possibility-of a new or different kind of accident from any previously analyzed.

The proposed change does not involve a significant reduction-in a margin of safety. The incorporation of addi.tional correction factors into the LTOP setpoint calculation is being performed to provide assurance that the LTOp system will function at a setpoint consistent with assuring that the fracture toughness requirements of 10CFR50 Appendix G are maint+1ned in the event of an analyzed

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ENCLOSUAE.1 !

REQUEST FOR NRR-TEMPORARY WAIVER OF COMPLIANCE I. TOP SRTPOINT

~ low temperature overpressure event.

As doasnotinvolveasignificantreduction!such,-theproposedchange- 'in a margin of : safety..

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BASIS FOR CONCLUDING TEAT THE REQUEST DOES NOT INVOLVE IRREVERSIBLE ENVIRONMENTAL CONSEQUENCES This proposed temporary valver doe ls not involve k change.in' tun installation or use of the facilities or couponents located ,

within the restricted areas as defined in 10CFR20._ i _ Commonwealth Edison has determined that this proposed. temporary waiver-does not:

involve a significant increase in the ; amount, or a significant change in the types, of any effluent that may be released _off-site,.

and that there cumulative is no sianificant-increase occupational fadiation exposure. inAccordingly, individua1 Lor-thir proposed temporary waiver meets the eligibility criteria"for" categorical exclusion set'forth in 10cFR Section 51.22 (c) (9) .'

Pursuant to 10CFR51~.22 , no environmental impact statement ~or environmental assessme(b)' nt need be prepared in connection with granting of this proposed temporary valver.

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d ENCLOBURE 2 \

LTOP Satpoint Changest Setpoint for Pcv 455: l402 psig H, Setpoint for PCV 456 l407 psig Minimum RC8 Temperaturet 871F for two RCPs I (solid Plant) and one'RH pump nula Based on the available information, operating two RCPs induces an error of approximately 35 psig (ref. Douth Texao Utilitien LER 92-019-00) on the pressure sensors of af fected loops (running loops) .

This error alone reduces the LTOP setpoint for each PORV to 400 psig, assuming the RCP for each loop (A= and c) is running.

The most recent Westinghouse LTOP setpoint analysis for Zion assumed PORV stroke times of 5.1 seconds. Zion ISI records )

indicate that the slowest PORV stroke time is 3.2 seconds. Figure l 1 of Westinghouse document CWE-92-245 'shows that if PORV stroke  !

times are maintained less than or equal!to 3.4 seconds, there is a j 7 psig setpoint benefit to be gained (this is valid up to 14 EFPY) .

This results in a setpoint of 407 psig. I j

Recent discussion with Zion station personnel has also revealed that the operation of one or both trains of RHR has an effect of lowering the indicated pressure sensed by PT-403 by approximately- i 5 psig for one RH pump in operation and 20 psig for two RH pumps in operation. Both trains of RHR connect to the A RCS loop (for each unit). The wide range pressure transmitter PT-403 senr.es pressure via connection to the RHR suction piping connection to the A RCS loop for each unit. This means that for operation of one PH pump, the 407 psig setpoint for PCV-455 (the PORV controlled.by input from PT-403) should be reduced to 402-psig. The result is _ an assumed net crror correction of 33 psig!for PT-403 and 28 psig for PT-405. This is based on the assumption that the A and C RCPs are running with one RH pump in operation. The expected pressure error introduced into the values indicated by PT-4 03 and PT-405 by running any other combination of two! RCPs with one RH pump in operation is slightly smaller than that assumed for the combinati.on of the A and C RCPs with one RH pump injoperation. This addresses the expected RCP and RH pump combinations for heatup prior to establishment of a bubble in the Pressuriser.

I The limitation of a minimum RCS temperature of 87'? for operation of two RCPs is based on the PORV setpoint plus the PoRV assumed overshoot pressure during assumed transient (stroke time 3.4 seconds) plus 35 psig (assumed error for 2 RcPs) plus 5 psig (for PORV 4 JS being aff ected by the operation of one RH pump) not exceeding the applicable steady-state pressure-temperature curve (consistent with the standard Westinghouse methodology).

A minimum temperature requirement for the start of one RCP (while one RH pump is in operation) is not considered necessary. Linear

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RNCLOSURE2f LTOP Setpoint Changes setpoint for Pcv 455:'402'psig.

setpoint for-lPCV 456 407 psig Minimum RCS Temperature 87?F for-two RCPs-(solid Plant) and onelRH purp extrapolation of-the steady-state-pressure-temperature curva to lower temperatures indicates that the 402 peig and 4 07 peig-setpoints are valid for one RCP operating with one RH pump at_-

temperatures as low as _35

• F. It is- not expected that RCS temperature will be reduced to this value, i

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