ML20249B427

Application for Amends to Licenses NPF-10 & NPF-15,reducing Minimum Primary RCS Cold Leg Temp from 544 F to 535 F Between 70% & 100% Rated Thermal Power Levels & Eliminating Max RCS Flow Rate Limit

ML20249B427
Person / Time
Site:	San Onofre
Issue date:	06/19/1998
From:	Nunn D SOUTHERN CALIFORNIA EDISON CO.
To:
Shared Package
ML20249B424	List: ML20249B423 ML20249B427 ML20249B429
References
NUDOCS 9806230086
Download: ML20249B427 (10)

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! UNITED STATES OF AMERICA NUCLEAR REGULATORY COMISSION Application of SOUTHERN CALIFORNIA )

EDIS0N COMPANY, H R. for a Class 103) Docket No. 50-361 License to Acquire, Possess, and Use )

a Utilization Facility as Part of ) Amendment Application Unit No. 2 of the San Onofre Nuclear ) No. 179.

Generating Station )

SOUTHERN CALIFORNIA EDIS0N COMPANY, H R . pursuant to 10 CFR 50.90, hereby submit Amendment Application No. 179. This ainendment application consists of Proposed Change No. PCN-491 to Facility Operating License NPF-10. PCN-491 is a request to revise the Unit 2 Technical Specification (TS) 3.4.1, "RCS DNB (Pressure, Temperature, and Flow) Limits." The proposed change includes:

1) A reduction in the minimum primary Reactor Coolant System (RCS) cold leg temperature (T,,u) from 544 F to 535 F between the 70% and 100% rated thermal power levels.

2) A conversion of the specified RCS minimum flow rate from a " Mass" (i.e., lbm/hr) to a " Volumetric" (gpm) flow basis.

3) Elimination of the maximum RCS flow rate limit.

9906230086 980619 PDR ADOCK 05000361 P PDR _

Subscribed on this /9 day of - , 1998.

O Respectfully submitted, SOUTHERN CALIFORNIA EDISON COMPANY i

By "

DwightE.% unn ~

Vice President State of California County of San Diego On 6-/'l-9E before me, tete M/dut/ f. personally 1

appeared DRHN E JunrL , perskallyknowntome(orprovedtome on the basis of satisfactory evidence) to be the person (s) whose name(s) is/aresubscribedtothewithininstrumentandacknowledgedtomethat he/she/theyexecutedthesameinhis/her/theirauthorizedcapacity(ies),and that by his/her/their signature (s) on the instrument the person (s), or the entity upon behalf of which the person (s) acted, executed the instrument.

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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMISSION Application of SOUTHERN CALIFORNIA )

EDISON COMPANY, El R. for a Class 103) Docket No. 50-362 License to Acquire, Possess, and Use )

i a Utilization Facility as Part of ) Amendment Application Unit No. 3 of the San Onofre Nuclear ) No. 165.

Generating Station )

SOUTHERN CALIFORNIA EDIS0N COMPANY, El E. pursuant to 10 CFR 50.90, hereby submit Amendment Application No. 165. This amendment application consists of Proposed Change No. (PCN)-491 to Facility Operating License NPF-15. PCN-491 is a request to revise the Unit 3 Technical Specification (TS) 3.4.1, "RCS DBN (Pressure, Temperature, and Flow) Limits." The proposed change includes:

1) A reduction in the minimum primary Reactor Coolant System (RCS) cold leg temperature (T,,u) from 544 F to 535 F between the 70% and 100% rated thermal power levels.

2) A conversion of the specified RCS minimum flow rate from a " Mass" (i.e., Ibm /hr) to a " Volumetric" (gpm) flow basis.

3) Elimination of the maximum RCS flow rate limit.

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Subscribed on this I9 day of e6 , 1998.

U Respectfully submitted, SOUTHERN CALIFORNIA EDIS0N COMPANY

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By: .$ -- _

Dwight E. Nun Vice President State of California County of San Otego On /o - / 9- 79 before me, ACLMCAAM bMYpersonally appeared 8g4 41 E ft - ,perbnallyknowntome(orprovedtome on the basis of satisfactory evidence) to be the person (s) whose name(s) is/aresubscribedtothewithininstrumentandacknowledgedtomethat he/she/theyexecutedthesameinhis/her/theirauthorizedcapacity(ies),and thatbyhis/her/theirsignature(s)ontheinstrumenttheperson(s),orthe entity upon behalf of which the person (s) acted, executed the instrument.

WITNESS my hand and official seal.

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DESCRIPTION OF TECHNICAL SPECIFICATION CHANGE PCN-491 SAN ONOFRE Units 2 and 3 Change No. PCN-491 will revise Technical Specification 3.4.1, "RCS DNB (Pressure, Temperature, and Flow) Limits."

Existing Technical Specifications:

Unit 2: See Attachment A Unit 3: See Attachment B Proposed Technical Specifications:

Unit 2: See Attachment C (redline and strikeout)

Unit 3: See Attachment D (redline and strikeout)

Proposed Technical Specifications:

Unit 2: See Attachment E Unit 3: See Attachment F Proposed Technical Specification Bases:

Unit 2: SeeAttachmentG(ForInformationOnly/ Unit 3issameasUnit2)

UFSAR Chapter 15 Assessment:

Units 2 and 3: See Attachment H Proposed UFSAR Pages:

. Units 2 and 3: See Attachment I (For Information Only)

Description of Change:

The proposed change to Technical Specification 3.4.1 consists of:

1) A reduction in the minimum primary Reactor Coolant System (RCS) cold leg temperature (Tg,) from 544*F to 535 F between the 70% and 100%

rated thermal power levels.

2) A conversion of the specified RCS minimum flow rate from a " Mass" (i.e., lbm/hr) to a " Volumetric" (gpm) flow basis.

3) Elimination of the maximum RCS flow rate limit.

Background:

Technical Specification (TS) 3.4.1 addresses Mode 1 requirements for maintaining RCS pressure, temperature, and flow rate within limits assumed in the plant safety analyses. The safety ar.alyses in the Updated Final Safety Analysis Report (UFSAR) (Chapters 6 and 15) of anticipated operational occurrences and design basis accidents assume initial conditions within the normal steady state operating envelope defined by the TSs as a whole. The limits placed on Departure from Nucleate Boiling (DNB) related parameters (i.e., parameters having a primary influence on DNB) ensure that these parameters will not be less conservative than those assumed in the safety analyses and will, thereby, provide assurance that the minimum Departure from Nucleate Boiling Ratio (DNBR) will meet the required criteria for each of the transients analyzed.

Southern California Edison (SCE) is proposing these changes for the following reasons:  !

i Reduction in RCS Minimum Temperature The San Onofre Nuclear Generating Station (SONGS) steam generators have seen the onset of corrosion-induced tube cracking similar to that experienced by other Combustion Engineering designed steam generators (all with Alloy-600 tubing).  !

SCE has retained outside expert consultants for several years who have helped to '

project future degradation based on industry experience and specific inspection findings at SONGS. The result of these ongoing analyses is a forecast of new cracking at rates which will increase geometrically with time and which eventually would have unacceptable safety (and economic) considerations. These forecasts also predict that over the next several years, greater than 90% of future degradation (requiring repair or plugging) will be caused by thermally l activated corrosion mechanisms. Temperature reduction reduces: '

• The occurrence of corrosion-induced tube cracking, and

• The rate of growth of these cracks.

Based on the foregoing and the best advice of industry experts, SCE has concluded that reducing operating temperatures below the minimum currently l permitted by LC0 3.4.1 is important to reduce the rate of forecast degradation to a manageable condition and to maximize the remaining safety and operating margins. SONGS is engineering a planned reduction of operating temperatures l which is expected to significantly reduce the rate of corrosive attack and which requires approval of PCN 491. This reduction is planned for implementation at the Cycle 10 refueling outage since it is the earliest opportunity to make major j modifications to the turbine plant to operate at lower steam pressure. Timely l approval of PCN 491 is necessary to successfully complete this project and '

! reduce degradation of margins associated with steam generator tube corrosion.

RCS Flow Rate Unit Conversion Reactor Coolant System (RCS) Total mass flow rate is a function of temperature, pressure, and volumetric flow. A change to the engineering units for RCS flow from lbm/hr to gpm is being requested to distinguish the independent variable of volumetric flow from the temperature and pressure parameters specified in the LC0. This change is consistent with the primary safety analysis variable.

Elimination of Maximum RCS Flos Rate Elimination of the maximum RCS Total Flow Rate is being proposed because 1) it is not a limiting DNBR criterion, 2) the safety margin to departure from nucleate boiling increases as the flow rate increases, and 3) actual reactor coolant pump (RCP) flow output is physically limited to values well below the approximately 120% of RCS design basis. Consequently, a shiftly surveillance has no meaningful DNBR significance.

For accident analyses that can be adversely be affected by elevated flow rates, a flow rate which is conservatively large compared to baseline measured flow is used.

Discussion:

The primary parameters which influence DNB.are RCS pressure, temperature, and flow rate. Attachment H provides summary results of engineering assessments that have been performed which support the proposed technical specification changes. These assessments consist primarily of the evaluated changes in the thermal hydraulic response to postulated transient and accident events given in Chapters 6 and 15 of the UFSAR in consideration of the expanded range of allowable operating temperatures at full power.

The T coi, LC0 limits are applicable to plant operation in Mode 1 (i.e., Power Operation, K ,, 20.99, and Rated Thermal Power >5% Rated Thermal Power (RTP)).

With respect to RCS Two, at Power Levels <70% RTP, the LC0 limits remain unchanged. The proposed TS change expands the allowable range for Two at power j levels >70% of RTP commensurate with the intended future operation at temperatures less than the current minimum allowable Two. Likewise, the conversion of. the minimum RCS Flow Rate to a volumetric flow basis necessitated j a review of the safety analyses for consistency with values used therein. l Therefore, under these conditions affected safety analyses have been assessed to assure continued compliance with regulatory requirements.

The requirements of LC0 3.4.1 represent the initial conditions for DNB limited transients analyzed in the safety analyses presented in Chapter 15 of the UFSAR.

The safety analyses have shown that Moderate Frequency Events initiated from the limits of this LC0 will meet the criterion of DNBR > 1.31. This is the

. acceptance limit for the RCS DNB parameters. Changes to the facility that could impact these parameters must be assessed for their impact on the DNB criterion.

The transients analyzed include Excess Load, Loss of Coolant Flow, Dropped Control Element Assembly (CEA), and CEA Withdrawal events. A key assumption for ,

the analysis of these events is that the core is operated within the limits of  ;

LC0 3.1.7, " Regulating CEA Insertion Limits"; LC0 3.1.8, "Part length CEA Insertion Limits"; LC0 3.2.3, " AZIMUTHAL POWER TILT (T,)"; and LC0 3.2.5, " AXIAL l POWER SHAPE INDEX (ASI)". The current safety analyses are performed for each fuel cycle over the following range of initial values (including uncertainty):

RCS pressure 2000 - 2300 560"F (for s 70% RTP_and > 30%and RTPpsia, Tg,) (for 520 - 560*F 542s-30%

560 RTP) F (forand power reactor > 70% RTP),

vessel inlet coolant flow rate > 95% of design volumetric flow. For fuel

cycles subsequent to this TS change, safety analyses will be performed using the

! same parameters except that for power levels > 70% of RTP a Two of 533 - 560 F will replace the 542 - 560*F previously used.

Similarly, an assessment of the Loss-of-Coolant Accident (LOCA) analyses presented, in part, in both UFSAR Chapters 6 and 15, have shown that transients initiated from the limits of the proposed TS change continue to meet the

.. acceptance criteria of 10 CFR 50.46.

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By performing new safety analyses or confirming the bounding nature of the existing analyses for the proposed TS changes, it is demonstrated that the acceptance criteria for'LOCAs are satisfied and that plant responses to transients meet the limiting DNBR criterion.

The LC0 limits for minimum and maximum RCS pressure remain consistent with operation within the nominal operating envelope and continue to be bounded by

-those used as initial pressures in the safety analyses. Likewise, the LC0 limits for minimum RCS total flow rate remain consistent with operation within the nominal operating envelope and continue to be bounded by those used as initial flow rates in the safety analyses. The specified flow rate has, however, been-converted from a " Mass" (i.e.,148x10 6 lbm/hr) to a " Volumetric" (396,000 gpm) flow basis. This change represents a straight flow " unit" conversion at original design operating conditions and does not represent any change to the actual magnitude of flow.

The LC0 for maximum RCS Total Flow Rate does not have a relevant basis in TS 3.4.1. This TS is applicable to Mode 1 operation and assurance of protection of the DNBR_ criterion. Rather, specification of a maximum RCS Total Flow Rate

was originally intended to afford protection against core uplift which is actually a Mode 3 operation concern.. Further, core uplift has been evaluated at flow rates of approximately 120% of the RCS design basis minimum total flow rate. The actual physical limitations of pump design in concert with the overall RCS flow' resistance limits RCP output to flow rates well below 120% of the RCS design basis minimum total flow rate in MODE 1. For accident analyses that can be adversely affected by elevated flow rates, a flow rate which is conservatively large compared to baseline measured flow is used.

Attachment I is.being provided for information only. This attachment contains the proposed revision to The Loss of Condenser Vacuum, and The Loss of Condenser Vacuum with a Concurrent Single Failure of an Active Component descriptions contained in Sections 15.2.1.3 and 15.2.2.3 of the UFSAR. Changes to Section 15.10 of the UFSAR will also be revised prior to implementation of the T,,,,

reduction amendment.

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No Significant Hazards Considerations:

The Commission has provided standards for determining whether a significant hazards consideration exists as stated in 10 CFR 50.92. A proposed amendment to an operating license for facility involves no significant hazards consideration if operation of the facility in accordance with a proposed amendment would not:

( (1) involve a significant increase in the probability or consequences of an l accident previously evaluated; or (2) create the possibility of a new or l different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety. A discussion of these standards as they relate to this amendment request follows:

1) Involve a significant increase in the probability or consequences of an accident previously evaluated.

i No.

The proposed change to Technical Specification (TS) 3.4.1 does not adversely impact structure, system, or component design or operation in a manner which would result in a change in the frequency of occurrence of accident initiation. Nor are the affected parameters themselves accident initiators. As such, the proposed TS change will not significantly increase the probability of accidents previously evaluated. Likewise, the proposed TS change does not significantly increase the consequences of an accident previously evaluated. The safety analysis assessments (Attachment H) confirm that the existing Analyses of Record (AORs) for San Onofre Units 2 and 3' remain valid or have been re-analyzed to demonstrate continued compliance with applicable Acceptance Criteria.

The change in Reactor Coolant System (RCS) " Mass" flow to " Volumetric" flow is a change in measuring units to be consistent with the measure used in '

the performance of the safety analysis. Therefore, there is no impact on any evaluated accidents.

The elimination of the upper RCS flow limit has no effect on Departure from Nucleate Boiling which is a concern at lower flows, and the maximum flow that is physically possible is less than the current upper limit.

Therefore,.this amendment request does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2) Create the possibility of a new or different kind of accident from any accident previously evaluated.

No.

T coi, is an input parameter used in event analysis, it is not an event initiator. No new or different accidents have been identified which could  !

result from operating at the proposed Tc io. The safety analysis assessments performed confirm that the existing safety system settings for San Onofre Units 2 and 3 remain valid, thereby assuring continued conformance to the Acceptance Criteria for all events.

A change in RCS flow measuring units can not initiate an accident, nor can the elimination of an upper RCS flow limit which can not be attained.

l Therefore, this amendment does not create the possibility of a new or different kind of accident from any accident previously evaluated.

3) Involve a significant reduction in a margin of safety.

No.

Updated Final Safety Analysis Report (UFSAR) safety analyses have been assessed and remain valid or have been re-analyzed to demonstrate continued compliance with applicable Acceptance Criteria for operation at the reduced-T,g o . All other safety limits and safety system settings remain unchanged.

l A change in measuring units for RCS flow does not reduce the margin of safety.

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Elimination of an RCS flow limit that can not physically be reached does not reduce the margin of safety. The shiftly surveillance requirement for maximum flow has no practical basis or safety benefit. Additionally, the margin to departure from nuclear boiling increases as the flow rate increases.

Therefore, this amendment does not involve a significant reduction in a margin of safety.

Based on the responses to these three criterion, SCE has concluded that the proposed amendment involves no significant hazards consideration.

Environmental Consideration:

SCE has determined that the proposed amendment involves no changes in the amount or type of effluent that may be released offsite, and results in no increase in individual or cumulative occupational radiation exposure. As described above, the proposed TS amendment involves no significant hazards consideration and, as such, racets the eligibility criteria for categorical exclusion set forth in 10 CFR51.22(c)(9).

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