ML20078Q529

Application for Amends to Licenses NPF-37,NPF-66,NPF-72 & NPF-77 Re Positive Moderator Temp Coefficient

ML20078Q529
Person / Time
Site:	Byron, Braidwood
Issue date:	02/15/1995
From:	Saccomando D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20078Q530	List: ML20078Q529 ML20078Q539
References
NUDOCS 9502210299
Download: ML20078Q529 (10)

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'w.l February 15, 1995 Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C 20555 Attention: Document Control Desk

Subject:

Supplement to Application for Amendment to Facility Operating Licenses:

Byron Station Units 1 and 2 NPF-37/66: NRC Docket Nos. 50-454/455 Braidwood Station Units 1 and 2 NPF-72/77: NRC Docket Nos. 50-456/457

" Positive Moderator Temperature Coefficient"

References:

1. J. Bauer letter to W. Russell dated March 23, 1994, transmitting Technical Specification amendment request regarding the Positive Moderator Temperature Coefficient and Reduced Thermal Flow

2. J. Bauer letter to W. Russell dated July 26, 1994, transmitting a Supplement to the March l 23,1994 Technical Specification Amendment i Request

3. D. Saccomando letter to NRC dated August 16, 1994, transmitting response to NRC RAI

4. G. Dick letter to D. Farrar dated October 21, l 1994, transmitting Safety Evaluation l pertaining to the Reduced Thermal Design Flow I

5. D. Saccomando letter to NRC dated December 21, 1994, transmitting Additional Information Regarding the Positive Moderator Temperature l Coefficient Proposed Technical Specification Amendment Reference 1 transmitted Commonwealth Edison Company's (Comed) request to amend the Technical Specifications for Braidwood and Byron Stations addressing positive moderator temperature coefficient (PMTC) and reduced thermal design flow. This amendment request was subsequently supplemented in Reference 2.

Reference 3 transmitted Comed response to the Requcat for Additional Information regarding the effects a positive MTC would have on the results of the Anticipated Transient Without Scram (ATWC) analysis. Comed subsequently received approval for e n u uyov:w c,a u 0

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NRC Document Control February 15, 1995 '

i the reduced thermal design portion from the Nuclear Regulatory Commission (NRC) and was issued the Referenced Safety Evaluation.

Several conference calls were held between the NRC and Comed  !

concerning the PMTC portion of the amendment. During those calls Comed agreed to provide the Staff with a document that describes which sections of the previously submitted material are applicable to Comed's application of the Unfavorable Exposure Time methodology, which was transmitted in Reference 5. As a result of these various correspondence and teleconferences, Comed .

is submitting the attached package which proposes that the MTC t value be maintained within the limits specified in an operating limits cycle specific report with a maximum upper limit specified in the Technical Specifications. Comed proposes to expand the Operating Limits Report (OLR) to include cycle specific MTC i value.

Attached you will find the following package which supersedes the previous correspondence: '

Attachment A: Description and Safety Analysis of Proposed Changes Attachment B: Marked Up Technical Specification Pages Attachment C: Evaluation of Significant Hazards Considerations Attachment D: Environmental Assessment Attachment E: D. Saccomando letter to the NRC dated December 21, 1994, transmitting an attachment that documents applicable sections of WCAP-119992/11993 and Comed application of the UET methodology addressed in

" Additional Information Regarding Application for Amendment to Facility Operating Licenses-Reactivity Controls Systems" Attachment F: Example of the Operating Limits Report Comed requests approval of the proposed amendment during April 1995. Approval by this date is necessary because a six month lead time is require to procure any necessary burnable poisons to suppress the core in the event the amendment request is denied.

Comed plans to utilize this amendment request during Braidwood Unit 1 Cycle 6 core loading, which is scheduled for October 1995.

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l Comed also requests that the Staff permit a thirty day implementation period for the proposed amendment to allow for the updating of the Byron and Braidwood OLRs. This implementation period is necessary to allow Comed's Nuclear Fuel Services group time to revise, approve, and issue each units' cycle specific OLR and submit these reports to the NRC. An example of the updated OLR is provided in Attachment F. i Comed appreciates the Staff's expeditious review of this supplement. If your have any questions concerning this  ;

correspondence, please contact this office.

Sincerely, I m. /m)

.f Denile accomando I Nuclear Licensing Administrator i i

Attachments cc: R. Assa, Braidwood Project Manager-NRR .

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G. Dick, Byron Project Manager-NRR J. Martin, Regional Administrator-RIII S. DuPont, Senior Resident Inspector-Braidwood ,

H. Peterson, Senior Resident Inspector-Byron  ;

Office of Nuclear Safety-IDNS  !

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y 3 ATTACHMENT A DESCRIPTION AND SAFETY ANALYSIS OF PROPOSED CHANGES TO APPENDIX A TECHNICAL SPECIFICATIONS OF FACILITY OPERATING LICENSES NPF-37, NPF-66, NPF-72, and NPF-77 Commonwealth Edison Company (Comed) requests a supplemental change to the Technical Specification amendment for the Positive Moderator Temperature Coefficient (PMTC). The proposed Technical Specification changes are in response to additional requests for informaticn and clarification on the implementation of a positive moderator temperature coefficieni value for Byron and Braidwood.

The change removes the values of the cycle-specific core operating limits for Moderator Temperature Coefficient (MTC) from the Technical Specifications (TS) and i references these values in an Operating Limits Report (OLR). Although the values for  !

MTC are being relocated to the OLR, the Limiting Condition for Operation (LCO) will continue to require compliance with these limits. I

1. Description of the Proposed Change:

In a letter dated March 23,1994, from J.A. Bauer to W.T. Russell, Commonwealth Edison Company (Comed) requested a Technical Specification Amendment allowing '

use of a Positive Moderator Temperature Coefficient (PMTC) and Reduced Thermal Design Flow (RTDF). This Amendment was later supplemented in a letter dated July 26,1994, from J.A. Bauer to W.T. Russell to provide additional cycle specific ,

implementation footnotes for clarification. Another letter responding to an additional request for information, dated August 16,1994, transmitted additional information to the NRC regarding the effects a positive MTC would have on the results of the Anticipated Transient Without Scram (ATWS) analysis. Comed subsequently received approval of the proposed Technical Specification Amendment on October 21,1994, in a letter from G.F. Dick to D.L. Farrar. However, the approval specifically excluded the proposed PMTC Technical Specification change.

Based on subsequent meetings, discussions, and correspondence with the NRC, Comed is resubmitting the Technical Specification Amendment allowing use of a PMTC. The proposed changes are consistent with Standard Technical Specifications for Westinghouse Plants (NUREG-1431). That is, the Amendment request proposes  ;

that the MTC value be maintained within the limits specified in an operating limits j cycle specific report with a maximum upper limit specified in the Technical Specifications. Therefore, Comed proposes to expand the OLR to include a cycle k : nla \ tsyr twd \ tat c a up 4 w - __- ,-- __ _m _ -_

a specific MTC value. Currently, the OLR contains a cycle specific limit for the radial I peaking factor, Fxy. Determination of a cycle specific MTC value will include an evaluation of Anticipated Transient Without Scram (ATWS) risk on a deterministic basis, since the ATWS rule was based in part on a given MTC value.  ;

2. Description of Current Requirements:

1) Moderator Temoerature Coefficient l

Technical Specification 3.1.1.3, Moderator Temperature Coefficient, requires the ,

moderator temperature coefficient (MTC) to be less positive than 0 ak/k/ F  :

for the all rods withdrawn, hot zero thermal power condition or less negative than -4.1 ,

X 10" Ak/k/ F for the all rods withdrawn, end of cycle life, rated thermal power condition.

The current surveillance requirements 4.1.1.3, measures MTC at the Beginning of Life (BOL), and the End of Life (EOL) and verifies acceptability of the limiting MTC values.

Also, the EOL MTC is measured at any THERMAL POWER and compared to -3.2 x 4

10 Ak/k/ F limit when the RCS boron concentration is at 300 ppm to verify the MTC is within the predicted limits. The surveillance requirements for measurement of the MTC at the beginning and near the end of the fuel cycle are adequate to confirm that the MTC can be maintained within its limits. The BOL MTC measurement combined with the predicted MTC throughout core life, is used to impose administrative limits on rod withdrawal.

2) Ooerating Limits Reoort (OLR)

The Operating Limits Report is the unit-specific document that provides operating limits for the current operating reload cycle. These cycle-specific operating limits are determined for each reload cycle in accordance with Specification 6.9.1.9. Plant operations within these limits are addressed in the individual specifications.

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3. Bases for the Current requirements:

1) Moderator Temoerature Coefficient j The limits on MTC are provided to ensure that the value of this coefficient remains within the limiting condition assumed in the Updated Final Safety Analysis Report (UFSAR) accident and transient analysis.

The MTC values of this specification are applicable to a specific set of plant conditions; accordingly, verification of MTC values at conditions other than those explicitly stated will require extrapolation in order to permit an accurate comparison, k:nla\byrbwd\pmtesup u

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2) Ooerating Limits Reoort (OLR)

The Operating Limits Report, specification 6.9.1.9, establishes and documents ,

operating limits before each reload cycle or any remaining part of a reload cycle.

Specification 6.9.1.9 provides a listing of the analytical methods used to determine the operating limits. These analytical methods were reviewed and approved by the NRC as Topical Reports. The reload safety evaluation methodology is included in the listing .

of analytical methods. The operating limits are determined so that all applicable limits (fuel thermal-mechanical limits, core thermal-hydraulic limits, ECCS limits, nuclear limits such as shutdown margin, and transient and accident analysis limits) of the safety analysis are met. The Operating Limits Report, including any mid-cycle revisions or supplements thereto, is provided upon issuance, for each reload cycle, to the NRC Document Control Desk with copies to the Regional Administrator and Resident inspector.

4. Description of the Need for Amending the Technical Specifications:

Operation of the plant with a slightly positive MTC satisfies all design criteria and results in significant benefits. The primary benefits of a positive MTC are:

1) the reduced burnable poison rods required to control peaking during the early portion of each cycle,

2) reduced burnable poison handling requirements,

3) fewer problems associated with storage and disposal of spent burnable poisons,

4) a reduced probability of enforcing administrative control rod withdrawal limits at low power which improves operational flexibility,

5) increased fuel discharge burnups, and

6) significant fuel cost savings.

5. Description of the Prooosed Amendment:

1) Maderator TemoeratyIe Coefficient The proposed surveillance requirements and the associated Bases will change the Moderator Temperature Coefficient limits to those specified in the OLR. The change to 3.1.1.3 shall read as follows:

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9 "The moderator temperature coefficient (MTC) shall be within the limits specified in the Operating Limits Report (OLR). The maximum upper limit shall be less than or equal to that shown in Figure 3.1-0.

APPLICABILITY: Beginning of Life (BOL) limit - MODES 1 and 2" only#

End of Life (EOL) limit - MODES 1,2, and 3 only#."

in addition to the above changes, the ACTION requirement stated in section a. shall read "With the MTC more positive than the BOL limit specified in the OLR, operations ,

in MODES 1 and 2 may proceed provided:". This will delete reference to Specification 3.1.1.3a. In action a.1., the specified MTC value of 0 ak/k/*F will be replaced with "the MTC is to be less positive than the BOL limit specified in the OLR".

I For action b, the requested change sirnJarly deletes reference to Specification 1 3.1.1.3b, and replaces it with the EOL IFnit specified in the OLR.

Surveillance Requirement (SR) 4.1.1.3.a references a BOL limit specified in the OLR and deletes reference to specification 3.1.1.3 a. The measured BOL MTC shall be maintained within the limits specified in the OLR and compared to the predicted MTC throughout core life to establish any administrative rod withdrawal limits.

Surveillance Requirement (SR) 4.1.1.3.b also deletes reference to any specific value for MTC. The SR will compare the MTC value measured within 7 effective full power days (EFPD) after reaching an equilibrium boron concentration of 300 ppm (all rods withdrawn, RATED THERMAL POWER condition) with the 300 ppm surveillance limit specified in the OLR. If this comparison indicates the measumd value of MTC to be more negative than the 300 ppm surveillance limit, it shall be compared to the EOL MTC limit specified in the OLR and remeasured at least once per 14 EFPD during the remainder of the fuel cycle.

A new figure, Figure 3.1-0 " Moderator Temperature Coefficient vs. Power Level",

identifies the acceptable operating range for MTC based on a maximum upper limit.

However, the cycle specific operat;ng limits will be specified in the OLR.

A discussion of the limitations on MTC with respect to ATWS risk will also be added to the associated Bases for MTC. The Unfavorable Exposure Time (UET) methodology will be used for evaluating ATWS risk on a deterministic basis. A UET value will be calculated every cycle. UET is defined as the amount of time during the operating cycle for which the reactivity feedback is not sufficient to prevent Reactor Coolant I System (RCS) pressure from exceeding 3200 psig for a given plant configuration. The l

ATWS risk is considered acceptable for a UET of less than 5% of cycle length. This j UET value will be calculated every cycle and appropriately consider the effects of I l changes in MTC, including any variations that are more adverse than those originally l modeled in the analyses supporting the basis for the final ATWS rule.

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References to the limiting EOL MTC value (-4.1 x 10~' ak/k/ F) and the MTC value

(-3.2 x 10'd ak/k/ F) at an equilibrium boron concentration of 300 ppm will be deleted from the associated Bases. The measured MTC value at a boron cnncentration of 300 ppm represents a conservative value and is obtained by making corrections to the limiting EOL MTC value. The BOL MTC limit identified in the bases will be changed from always be less positive than 0 Ak/k/ F to always remain within the llmits specified in the OLR.

2) Doerating 1.imits Reoort (OLR)

Specification 6.9.1.9 provides a listing of the analytical methods used to determine the operating limits. Comed proposes to revise the listing of analytical methods by adding a reference to the letter documenting the UET methodology which will be used by Comed to establish an acceptable MTC value with respect to ATWS risk. This information was transmitted to the NRC in a letter dated December 21,1994, from D.

Saccomando to the Office of Nuclear Reactor Regulation, see Attachment E. The information contained in the letter is based on the methodology described in Westinghouse WCAP 11992, "ATWS Rule Administration Process" and WCAP 11993,

" Assessment of Compliance with ATWS Rule Basis for Westinghouse PWHs". These WCAPs were provided as Attachments in the Comed response to the Request for Additional Information dated August 16,1994.

A format change to the listing of analytical methods is included for clarity.

6. Bases of the Proposed Amendment:

The basis for the MTC limit is to ensure that the value of the coefficient remains within the limits assumed in the UFSAR accident and transient analyses. In keeping with this basis, Westinghouse and Comed's Nuclear Fuel Services group performed the necessary accident and transient analyses with the new MTC values to ensure that the results remain within all design and safety criteria. The Westinghouse analysis provides the basis for the proposed MTC Technical Specification change. This analysis, entitled " Byron and Braidwood Units 1 and 2 Increased SGTP/ Reduced TDF/PMTC Analysis Engineering and Licensing Report" was provided in Attachment 5 of the original submittal dated March 23,1994.

A power level dependent MTC was chosen to minimize the effects of the Technical Specification change on postulated accidents at higher power levels. Moreover, as the l power level is raised, the average coolant temperature becomes higher as allowed by i the programmed average temperature controller, tending to make the MTC more I negative. Also, the boron concentration can be reduced as xenon builds into the core.

Thus, there is less need to allow a positive MTC as full power is approached. As fuel burnup is (4chieved, boron is further reduced and the MTC will eventually become m.mmmme 8

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i negative over the entire operating power range.

Ir3 addition ;o a positive reactivity feedback with increasing core average temperature as a result of a positive MTC, there is a negative reactivity feedback with increasing fuel temperature as a result of the fuel temperature coefficient which is always negative. The fuel average temperature increase over the operating power range is significantly greater than the core average temperature increase. Thus, the cumulative reactivity feedback as core power approaches 100% is always negative.

Determination of a cycle specific MTC value willinclude an evaluation of ATWS risk on a deterministic basis. The UET methodology will be used for evaluating ATWS >

risk. A UET value will be calculated for each cycle. The ATWS risk is considered acceptable for a UET of less than 5% of cycle length. This UET value will be updated for each core reload and appropriately considers the effects of changes in MTC, including any variations that are more adverse than those originally modeled in the analyses supporting the basis for the final ATWS rule.

7. Impact of the Proposed Change:

The accidents which are sensitive to MTC were analyzed as part of the overall program to justify a positive MTC, a reduction in reactor coolant system thermal design flow rate and an increase in steam generator tube plugging levels. All Departure from Nucleate Boiling Ratio (DNBR) design limits wre determined such that there was a 95 percent probability at a 95 percent confidence level that DNB would not occur on the t most limiting fuel rod for any Condition I or Condition ll event. The present Technical .

Specification limit for Nuclear Enthalpy Rise Hot Channel Factor, F Nsg, of less than ,

1.65 ensures that the DNB design basis stated above would be met, thus fuel integrity l will not be challenged. The analyses results demonstrated that implementation of the overall program will result in a small increase in offsite doses; however, the total doses remain a small fraction of the 10CFR100 limits. As such, the accident analysis [

acceptance criteria continue to be satisfied.

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8. Schedule Requirements:  ;

i Comed requests approval of the proposed amendment prior to loading the Braidwood  !

Unit 1 Cycle 6 core scheduled for early October 1995, with reasonable assurance regarding approval of the Amendment provided by the NRC, six months before the start of the Braidwood Unit 1 outage. This would allow adequate lead time for Comed to procure any necessary burnable poisons to suppress the core in the event the l Amendment is not approved. This assurance date also coincides with the determination of the final loading pattern for the Braidwood core. Confirmation of the amendments' approval would be required before the start of the Unit 1 outage. The k.nlail"3 bwM prtrs v 9 9

I reload safety evaluation process begins wellin advance of a given refueling outage.

Typically, design of a core begins approximately 10-12 months before the applicable refueling outage begins. Though several factors could influence the final MTC value, the preliminary load pattern for Braidwood Unit 1 Cycle 6 currently indicates a slightly negative MTC. The final load pattern for MTC value may differ slightly from the preliminary load pattern MTC value due to uncertainties in the current cycle end of life burnup at the time of design. This could result in a slightly positive MTC value and would require rod withdrawal limits be establishe! and maintained. ^.pproval of the proposed amendment within the time frame requested would provide some flexibility and may eliminate the need for the restrictive operational limits.

A thirty (30) day implementation period is requested by Comed after the NRC issues the proposed PMTC amendment to allow updating of the Byron and Braidwood OLRs.

This will give Comed's Nuclear Fuel Services group time to revise, approve, and issue each units' cycle specific OLR and submit these reports to the NRC. An example of the updated OLR is provided in Attachment F.

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