ML20082Q352

Forwards Responses to NRC Questions Re Util Request for Change to Tech Specs on RCS Flow,Discussed on 831202.Value of 1.8 for Sensitivity of DNBR to Power Appropriate

ML20082Q352
Person / Time
Site:	Mcguire
Issue date:	12/05/1983
From:	Tucker H DUKE POWER CO.
To:	Adensam E, Harold Denton Office of Nuclear Reactor Regulation
References
TAC-53214, TAC-53215, NUDOCS 8312120140
Download: ML20082Q352 (4)

Text

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DUKE POWER GOMPANY P.O. Box 33180 CHARLOTTE. N.C. 28242 HAL H.111CKER TEt.nenown vsca PaessusNT (704) 373-4531 N00LE.E PRODtMTsON December 5, 1983 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Ms. E. G. Adensam, Chief Licensing Branch No. 4 Re: McGuire Nuclear Station Docket No. 50-370

Dear Mr. Denton:

Attached are responses to NRC Staff questions concerning Duke Power Company's request for change to the McGuire Nuclear Station-Unit 2 Technical Specifica-tion on Reactor Coolant System flow. These were discussed with Staff reviewers on December 2, 1983.

Please advise if there are additional questions concerning this matter.

Very truly yours, g4 / 'x Hal B. Tucker.

GAC/php Attachment cc: Mr. W. T. Orders NRC Resident Inspector McGuire Nuclear Station Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303 plzl l:

8312120140 831205 PDR ADDCK 05000370 P PDR

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HRD/HBT/GAC December 5, 1983

'f l' McGuire Nuclear Station Response to Questions on Technical Specification Change on L . Reactor Coolant System Flow i

i

. 1. Attachment 2B of your letter of November 18, 1983 states that the plant-specific relationship for flow and DNBR based on thermal-hydraulic

. sensitivity studies for the worst case is aflow ,1  %

3DNBR 1.6%.

What:is the worst case that has been analyzed to determine this relation-

\ ship? .Is this 1.6 to 1 ratio of ADNBR vs AFlow the highest value for all

~

transients? Also provide a description of how the sensitivity studies

. are performed.

Response The conditions that resulted in the maximum DNBR sensitivity to flow were 120% power, 2400 psia, and a temperature necessary to yield the DNBR design limit (i.e., DNB core limits). .The typical cell sensitivity was used even though.the thimble cell was DNBR limited, since the typical cell is more '

sensitive to-flow. Statepoints representative of possible operating conditions (normal operation and accident) were analyzed using THINC IV. Conditions ranged from operating at core DNB limits to undergoing a loss of flow accident.

Each statepoint was analyzed 'at nominal flow (e.g. ,100% flow for core limit conditions, approximately 80% flow for loss of flow) and at 97.5% of nominal P ' flow.- The DNBR penalty-associated with each statepoint was calculated for

> both typical and thimble cells, and the largest penalty was determined. For a 2.5% reduction'in flow, the largest DNBR penalty was 4.0%. This results in a aflow ~

1- ~ % .

7 BDNBR 1.6%

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2. ' Attachment 2B-also states that " generally" the following relationships between core power, flow and DNBR are applicable:

DFlow 1%

BDNBR " 1% ~

! BPower ,1  %

BDNBR 1.8%.

l What'is the basis or justification for using the ADNBR vs APower ratio of 1.8 for this Technical Specification change? Is it the worst value, i.e..' the lowest value for all transient?

Response

l ..

~

The value of 1.8 used for the sensitivity of DNBR to power was derived from

, the work performed'in the area of rod bow penalty in 1976-1977. Information

dealing with the penalty and

generic margins is discussed in " Revised Interim

!  : Safety Evaluation Report on the Effects of Fuel Rod Bowing on Thermal Margin L

i _1_

~. _ _ _ . . .. . . _ . . . _ . - . _ _ , . _ . _ _ . . . , . . _ _ . _ _ _ _ . _ _ _ , _ _ _ _ , - _ _ ._.

HRD/HBT/CAC December 5, 1983 Calculations for Light Water Reactors'.', NRC report, February 16, 1977. The T/ H analyses performed to derive this value show that the conditions used are almost identical to those used to calculate the flow sensitivity as explained in Question 1. Previous DNBR sensitivity studies have shown that the DNBR sensitivity to power is very similar to the sensitivity to F A*

Therefore, a value of 1.8 is appropriate for power when considering the tradeoff between power and flow.

3. In the revised Bases for " Power Distribution Limits" of the McGuire Technical 5pecifications, a total of 9.1% credit is used, i.e., 5.9%

is used to partially offset fuel rod bowing penalty and 3.2% is used to trade off against measured flow being as much as 2% lower than thermal design flow plus uncertainties. Provide the sources of the 9.1% thermal margin, and explain how the credit is obtained. We will require that the Technical Specification Bases include the breakdown components of the 9.1% credit.

Response

The 9.1% thermal margin is due to conservatisms used in design analyses in comparison to conditions justified in the FSAR. The following is a summary of the conservatisms used in McGuire's cycle 1 analyses.

Design Limit DNBR of 1.30 vs. 1.28 Grid Spacing (Ks) of 0.046 vs. 0.059 Thermal Diffusion Coefficient of 0.038 vs. 0.059 DNBR Multiplier of 0.86 vs. 0.88 Pitch Reduction The margins associated with each of the above conservatisms was determined by using THINC IV to compare results with and without the conservatisms.

This work was performed to assess the amount of thermal msrgin available to offset rod bow penalties. From Duke Power's perspective, it would be preferable to have this information presented and explained in the FSAR rather than in the bases of the Technical Specifications. Operation of Unit 2 beyond Cycle 1 will not be based on the same conservatisms due to a change in the method of analysis. As a result, future comparisons to the above values would be inappropriate. However, Duke Power has no objectives to putting these values in the Technical Specification bases for the remainder of Cycle 1.

4. With regard to the Limiting Safety System Settings, it is stated that the current setpoint equation has been determined to be adequate if the f(AI) penalty on the Overtemperature AT equation is revised as shown.in the Note 1 of Table 2.2-1 of the proposed Technical Specification revisions.

What analysis have you done to determine its adequacy?

HRD/HBT/GAC.

December 5, 1983

' Response A reanalysis of the Overtemperature AT setpoint with a 2% reduction in Reactor Coolant System flow was performed using the methodology described in WCAP-8745, " Design Bases for the Thermal Overpower AT and Thermal Over-temperature AT Trip Function".

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