ML20029B245

Application for Amend to License NPF-6,revising TS Section 3/4.1.1.3 to Reduce Min Flow Rate of Reactor Coolant Through RCS from 3,000 Gpm to 2,000 Gpm,Per Generic Ltr 88-17 Re Loss of DHR

ML20029B245
Person / Time
Site:	Arkansas Nuclear
Issue date:	02/25/1991
From:	Carns N ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20029B246	List: ML20029B245 ML20029B247
References
2CAN029101, 2CAN29101, GL-88-17, NUDOCS 9103060294
Download: ML20029B245 (7)

Text

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1e' bO1 leM-tit *6 Neil S.

• Buss" Carna vo Pinet DDeflM GAND February 25, 1991 2CAN029101 U. S. Nuclear Regulatory Commission Document Control Desk Mail Station F1-137-Washington, D. C. 20555

Subject:

- Arkarsi.s Nuclear One - Unit 2 Docket No. 50-368 License Nos. NPF-6 Minimum Flow for Boron Oilution Technical Specification Change Request Gentlemen:

Attached for your review and approval are prcposed changes revising section 3/4.1.1.3 of the ANO-2 Technical Specifications (TS) and the Bases for this specification. Entergy Operations has determined that a reduction in the minimum flow rate of reactor coolant through the reactor coolant system (RCS) from 3000 gpm to 2000 gpm will provide adequate-mixing to satisfy the. safety analysis. This proposed change will reduce the_ potential for vortexing as described'in Generic Letter 88-17, Loss of Decay Heat Removal. In our response to the Generic Letter we _ identified a -

change to the TS for Mode 6 RCS flow, however.we did _nct at that titw identify'this change. Additionally.we propose to change the applicable-pump for this specification'from low pressure safety injection pump to either low pressure safety injection'or containment spray pump for 2se_as a shutdown' cooling pump.

Inaccordancewith10CFR50.91(a)(1),andusingthecriteriain 10CFR50.92(c),-Entergy Operations has determined that the change involves no significant hazards consideration. - The basis for these determinations are included in the enclosed submittal. Although the circumstances of

'this' proposed amendment is not exigent or emergency, your prompt review and approval.is requested.

.We request-that _the effective date for this change.be 30 days after NRC issuance of the amendment to allow for procedure changes and distribution

-of_ this change. l Very truly-.yours,-

D Y -

W NSC/sgw-F Attachment--

1 9103060294 910225 '

PDR ADOCK 05000368 ' .

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U. S. NRC February 25, 1991 P ge 2 cc: Mr. Robert Martin V. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 nRC Senior Resident Inspector Arkansas Nuclear One - ANO-1 & 2 Number 1. Nuclear Plant Road j Russellville, AR 72801 Mr. Thomas W. Alexion NRR Project Manager, Region IV/ANO-1 U. St Nuclear Regulatory Commission NRR Mail Stop 13-D-18 One White Flint North 11555 Rockville Pike Rockville, Maryland 20852 Ms. Sheri Peterson NRR Project Manager, Region IV/ANO-2 U. S. Nuclear Regulatory Commission

,. NRR Mail Stop 13-D-18 One White Flint North 11555 Rockville Pike Rockville, Maryland 20852 Ms. Greta _Dieus, Director Division of Radiation Control and Emergency Mtnagement Arkansas Department of Health 4815 West Markham Street little Rock, AR 72201

$1 4

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• e STATE OF ARKANSAS )

) SS COUN1Y OF LOGAN )

A[FADAV_11 I, N. S. Carns, being duly sworn, subscribe to and say that I am Vice President, Operations ANO for Entergy; that I have full authority to execute this affadavit; that I have read the document numbered 2CAN029101 (minimum flew for boron dilution) and know tiie contents thereof; and that to the best of my knowledge, information and belief the f

statements in it are true,

_ 3 j./3 d&t_d_

N. . Carns SUBSCRIBED AND SWORN 10 before me, a Notary Public in and for the County and State above named, thisf]_f d ay of j k[t M S ,

1991.

11 - -. Jh 4ff8A }/O Notary Public My Commission Expires:

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{NCLO.SURJ PROPOSED TFCHNICAL SPECIFICATION AND RESPFCTIVE SAFETY ANALYSE $

IN Tile MATTER OF AMENDING License No, NPF-6 ENTERGY OPERATIONS, INC, ARKANSAS NUCLEAR ONE, UNIT 2 Docket No. 50-368

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PROPOSED CHANGE This change to the AND-2 Technical Specification 3/4.1.1.3 reduces the required minimum flow rate of reactor coolant through the reactor coolant system (RCS) from 2 3000 gpm to 2 2000 gpm. Additionally a change to the bases for this specification is included to change the flow rate from 3000 gpm to 2000 gpm and the number of cubic feet of reactor coolant circulated in 25 minutes from 9,975 to 6,650. Also being proposed is the change from

" low pressure safety injection pump" to " low pressure safety injection pump or containment spray pump as shutdown cooling pump".

. BACKGROUND AN0's 90-day response to Generir: Letter 88-17 described our plans for I addressing the six programmed enhancements reevhmended by the NRC concerning the loss of decay heat removal (DHR) issue, item 5 of the Generic Letter programmed enhancements recommended identification of l Technical Specifications that restrict or limit the safety benefit of the actions identified in the Generic Letter, and submittal of appropriate changes. Our response identified that the minimum Shutdown Cooling (SDC) loop flow rate of 3000 gpm, required to be periodically verified by TS surveillance 4.9.8.1, was not always appropriate, and stated that we anticipated proposing a change to that requirement. On December 15, 1989, ANO submitted a change to that requirement to reduce the minimum flow rate to 2000 gpm (2CAN128903). It was shown that this flow rate provide adequate mixing of the RCS to ensure a dilution accident would not occur.

On April 30, 1990, the Staff approved the change and issued Amendment

! . nun 6er 104 to the Facility Operating License, i Since that time, ANO has identified another condition, Mode 5 Operations, duriag which reactor coolant system flow rate can be reduced and the potential for loss of DHR further diminished.

Reduction of the required RCS flow rate specified in Techn cal Specification 3/4.1.1.3 to a value consistent with that of Specification l 4.9.8.) will allow reductions in boron concentration during reduced

-inventory operations without the need to increase RCS flow rate. During refueling, the RCS can be at higher boron concentrations than the Refueling Water Tank (RWT). When RCS levels are raised with the RWT as a makeup source, a small dilution within allowable limits of the required shutdown margin can occur. Other planned level changes may require some dilution. Requii bg the flow rate through-the RCS to be unnecessarily increased during these evolutions, in order to comply with Technical Specification 3/4.1.1.3, will increase the potential for vortexing. This is an unnecessary risk in that an RCS flow rate of 2000 gpm provides adequate mixing to preclude a dilution event.

The piping configuration for AND 2 allows use of either the low pressure safety injection pump or containment spray pump for decay heat removal.

The change to 4.1.1.3(b) is to reflect the option of using either shutdown cooling pump for decay heat removal.

s DISCUSSION Entergy Operations has determined that a reduction in the minimum reactor coolant system (RCS) flow from 3000 gpm to 2000 gpm is ppropriate and proposes to modify TS 3/4.1.1.3 and its basis accordingly. This change was determined to be acceptable by conservative evaluetions for the SDC pump long term minimum flow requirements, and the minimum flow requirements for RCS mixing as related to the ANO-2 Safety Analysis Report RCS Boion Dilution Accident Analysis (Section 15.1.4.2.2.2). Entergy Operations and the pump vendor evaluated the long term minimum flow rrcuuirements for the low pressure safety injection pump and containment spray pump and determined-that 2000 gpm was adequate to prevent abnormal pump wear.

Entergy Operations and Combustion Engineering evaluated +ne effect of a reduced RCS flow rito on the SAR Boron Dilution Accident Analysis and have determined that the reduction in flow rate does not impact the result of the analysis. This flow rate affccts the amount of mixing which occurs in the RCS during a postulated boron dilution event. Adequate RCS mixing is provided by any flow rate which is significantly larger than the dilution flow, which is analyzed to be 132 gpm from all three charging pumps.

Conservatively assuming no mixing due to turbulen:e or diffusion through the core, a reduced flow rate results in a larger step change in boron dilution with each loop transport cycle. However the average rate of decrease in boron concentration is unaffected by reactor coolant system loop flow. Therefore, the specific reactor coolant system flow is not an input parameter te this analysis, ihe 4000 gem reactor coolant system flow rate suggested in the ANC-2 SAR comes from a generic Combustion Engineering presentat.on on the boron dilution accident and is not directly related to ANO-2. TFa proposed 2000 gpm minimum flow will.

continue to provide adaquate RCS mixing and will mo -in the acceptance criteria for the prev a bomn dilution analysis.

The proposed reduced minimuni flow will also cuntinue to provide adequate flow for core cooling during shutdown conditions using either the low pressure safety injection pump or containmant spray pump, while providing the benefit of greater margin to SDC lint etexing and subsequent air entrain;aent during operation ac reduced 2ntory conditions, a principle concern of Generic Letter 88-17. ANO ormed a vortexing test during the 2R7 Refueling Outage to determine the level at which vortexing would occur at various flow rates. This test verified that the proposed 2000 gpm was aceptable with a minimum of ten inches above the bottom of the RCS hot leg. An RCS level of nineteen inches is the procedurally required minimum level for SDC operations.

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DElERMINATION OF SIGNIFICANT HAZARDS ,

An evaluation of the proposed change has been performed in accordance with 10CFR50.91(a)(1) regarding no significant narards consideration using the standards in 10CFR50.92(c). A discussion of those standards as they relate to this amendment request follows:

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4 Criterion 1 - Nes Not Involve a Significant Increase in thr Probability or Consequen m cf an Accident Previously Evaluated.

The RCS flow rate af fects the amount of reactor coolant circulating through the care during Mode 5 operations. This flaw cate determines the amount of mixing which occurs in the RCS during a postulated boron dilution event. The boron dilution event analysis are well understood, and adequate mixing is provided by any flow rate which is sigrificantly larger than the dilution flow, which is analyzed to be 132 gpm from all three charging pumps. In fact the specific RCS flow 1 s not an input parameter to these analyses. The proposed 2000 gpm minimum flow from either the low pressure safety in.jection pump or containment spray pump will continue to provide adequate RCS mixing and will maintain the acceptance criteria of the present enalyses. The 2000 opm minimem flow is adequate to prevent premature pump failure, Therefore this change does not involve an increase in the probability or con m uences cf an accident previously e"aluated.

! Criterion 2 - Does Not Create the Possibility uf a New or Different Kind of Accident i om any Previously Evaluated.

The reduced flow rate has been evaluated and found acceptabic for the SDC pump minimum continuous flow requirements, thereforo no possibility of -

different kind of accidant related to equipment failure is created. The reduced flow requirement from either shutdown cooling pump provides suf ficient flow for core cooling during Mode '. operations, therefore this change does not create the possibility of : new or different W d of accident from any previcusly evaluated.

Criterion 3 - Does Not Involve a Significant Reduction in the Margin of Safety. .i lne NRC evaluated varicus improvements in equipment and procedures relating to SDC oparation from a balanced risk perspective during preparation of Generic Letter 88-17. It was identified that during certain plant conditions, i.e. reduced inventory, the potential for vortexing in the SDC suction drop line was increased significantly at higher > RCS flow rates. This has been verified by AN0's own vortexing test during the 2R7 Refueling Outage. When the cooling requirements are met with either shutdown cooling pump, as in the proposed change, a reduction in the required flow rate has been determined to significantly improve the margin to safety with respect to potential loss of DHR events.

The Commission has provided guidance concerning the app ication of the o standards for determining whether a significant hazards consideration l exists in 51 F.R. 7750, dated March 6, 1986. The proposed amendment does not closely match the examples provided. The proposed change, however, reflects an improvement ident;fied during NRC and utility response to, and resolution of, a technical issue (Loss of Decay Hr.at Removal).

Based or +he above evaluation it is concluded that the proposed Technical Specification change does not constitute a sigrificant hazards concern.

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