B17474, Forwards Response to NRC 980916 RAI Re Licensee Proposed TS Amend Changing Reactor Protection & ESFs Trip Setpoints, Submitted 980721.No Regulatory Commitments Are Contained in Ltr

Forwards Response to NRC 980916 RAI Re Licensee Proposed TS Amend Changing Reactor Protection & ESFs Trip Setpoints, Submitted 980721.No Regulatory Commitments Are Contained in Ltr

ML20154G510
Person / Time
Site:	Millstone
Issue date:	10/06/1998
From:	Bowling M NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B17474, NUDOCS 9810130203
Download: ML20154G510 (6)

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7 N e sst R pe Ferry Rd. (Route 156), Wcterford, CT 06385 l

Nucl:ar Entrgy Min. tone Nuclear Power Station Northeast Nuclear Energy Company P.O. Box 128

, . Waterford, CT 06385-0128 (860) 447 1791 Fax (860) 444 4277 The Northeast Utihties System OCT 6 1998 Docket No. 50-336 B17474 Re: 10CFR50.90 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Nuclear Power Station, Unit No. 2 Response to a Request for Additional information Regarding Technical Specification Amendment Request Reactor Protection and Enaineered Safety Features Trio Setooints (TAC NO. MA2340)

In a letter ' dated July 21,1998,m Northeast Nuclear Energy Company (NNECO)

- requested a change to the Millstone Unit No. 2 Technical Specifications which involved changes to the Reactor Protection and Engineered Safety Features Trip Setpoints. In -

response to this letter, the NRC has requested, in a letter dated September 16,1998,* l additional information to aid in the review of the proposed License Amendment Request. The purpose of this letter is to transmit the requested additional information,

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which is contained in Attachment 1.

There are no regulatory commitments contained within this letter, q

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W- M. 'L. Bowling, Jr. letter to U.S. Nuclear Regulatory Commission, " Millstone Nuclear I Power Station, Unit No. 2, Proposed Revision to Technical Specifications, Reactor i Protection and Engineered Safety Features Trip Setpoints," dated July 21,1998.

• D. G. Mcdonald, Jr. letter to Northeast Nuclear Energy Company, " Request for Additional Information_ Regarding Technical Specification Amendment Request -

Millstone Nuclear Power Station, Unit No. 2 (TAC NO. MA2340)," dated September 16, 1998.

9810130203 981006 PDR

.P ADOCK 050003363 P pop wy

I U.S. Nucl;rr R:gulatory Commission B17474/Page 2 i

If you should have any questions on the above, please contact Mr. Ravi Joshi at (860) 440-2080.

! Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY

/ 1 M. L. Bowling, Jr. /

Recovery Officar - Technical Services l Attachments (1) l cc: H. J. Miller, Region I Administrator D. G. Mcdonald, Jr., NRC Senior Project Manager, Millstcr.3 Unit No. 2 S. Dembek, NRC Project Manager, Millstone Unit No.1 D. P. Beaulieu, Senior Resident inspector, Millstone Unit No. 2 W. M. Dean, Director, Millstone Project Directorate W. D. Lanning, Director, Millstone inspections l J. P. Durr, Chief, Inspections Branch, Millstone Inspections E. V. Imbro, Director, Millstone ICAVP inspections l Director Bureau of Air Management Monitoring and Radiation Division Department of Environmental Protection 79 Elm Street Hartford, CT 06106-5127 l

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Docket No. 50-336 B17474 i

f Attachment 1 Millstone Nuclear Power Station, Unit No. 2 Response to a Request for Additional Information Concerning a Proposed Revision to Technical Specifications Reactor Protection and Engineered Sefety Features Trip Setpoints i..

October 1998 i

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. U. S. Nucircr Regul tory Commission B17474/ Attachment 1/Page 1 l

l Response to a Request for Additional information Concerning a Proposed Revision to Technical Specifications Reactor Protection and Enaineered Safety Features Trio Setoolnts i

Question 1: The NRC staff has not reviewed or approved ISA RP67.04, Part II,1994 l Standard. The approved standard, which provides guidance for setpoint (SP) calculations for instrumentation in safety-related systems, is ISA i 67-04, 1982, which has been endorsed by the staff in Regulatory l Guide 1.105, Revision 2.

Please confirm the following, since the SP methodology used by Northeast Nuclear Energy Company (NNECO) is based on ISA RP67.04, Part II,1994 Standard, which has not yet been approved by the NRC:

L a) That the methodology used by NNECO treats all elements of the l instrument loop unceriainties the same way as is prescribed by the 1982 version of the ISA standard.

. Responc x Mi!! stone is not committed to either RG 1.105, Rev 2 or ISA 67.04,1982.

The methodology previously used by Millstone Unit No. 2 was consistent with the Combustion Engineering approach as detailed in Combustion Engineering calculations 4467-lCE-3607, " Maine Yankee Instrument Error I Analysis," dated July 29,1974, and 18767-ICE-3622 Rev. 01, "Nusco  ;

l RPS Error Calculation," dated May 15,1975. The present Millstone Unit

! No. 2 methodology envelops (is more conservative than) this historical Combustion Engineering methodology.

I While ISA RP67.04, Part il,1994 is used for auidance in the Millstone i Unit No. 2 methodology, the treatment of elements of instrument loop l uncertainty in the Millstone methodology is consistent with the treatment required by RG 1.105, Rev. 2, and ISA 67.04, 1982. The Millstone methodology merely provides additional guidelines to the preparers of uncertainty and setpoint calculatiuns beyond that found in RG 1.105, Rev. 2 and ISA 67.04,1982. As described in the responses to 1b) and ic) below, the calculation of the trip setpoint and allowable value are based on allowances which take into account the test methods of the monthly and refueling surveillance procedures. The methodology requires appropriate treatment of those elements of uncertainty which are

and which are not observed during each type of surveillance test and i ensures that mitigating actions are initiated prior to each variable

!' encroaching on its respective analytical limit.

In summary, while Millstone Unit No. 2 is not committed to RG 1.105 or ISA 67.04,1982, the Millstone Unit No. 2 methodology is consistent with t

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'. U. S. Nuclaar Regulatory Commission B17474/ Attachment 1/Page 2 these documents and envelops (is more conservative than) the historical Combustion Engineering methodology.

b) That the selected nominal SP will always initiate the required l mitigating action (s) prior to the monitored variable encroaching its

! analytical limit when considering all elements of instrument ,

l uncertaintiec and the response time of the actuated l equipment / system. Please provide a description of the allowable value (AV) and its development with respect to the analytical limit and trip SP.

l Response: The methodology ensures that the selected nominal setpoints will initiate l

mitigating actions (s) (i.e., reactor trip or engineered safety feature actuation) prior to the monitored variable encroaching on its analytical limit by appropriately considering all elements of instrument uncertainty u and response time of the actuated equipment. Response time of the

! actuated equipment is considered in the development of the analytical limit. For each trip or actuation credited in the safety analysis (for  !

l operation in the presence of normal or harsh environment), the corresponding analytical limit has been shown to have acceptable consequences. The analytical limit is used by the methodology to l develop both the trip setpoint and the allowable value. ,

The allowable value differs from the analytical limit by an allowance that includes all elements of instrurnent uncertainty that are not observed during the monthly functional test. These typically include process measurement effects, sensor effects and environmental effects including '

any biases conservatively applied. The allowable value differs from the trip setpoint by an allowance that includes elements of the instrument uncertainty that are observed during the monthly test. These typically include calibration uncertainties for the tested equipment and drift for the monthly surveillance interval. Taken together, the two allowances ensure that the difference between the analytical limit and trip setpoint includes all elements of instrument uncertainty.

c) That the calculation of the AV is consistent with the channel functional test and calibration surveillance requirements in that the uncertainty terms included in the AV calculation are representative i of the associated component uncertainties under test. (Reference l IEEE-338) i Response: The setpoint methodology requires the preparers of setpoint calculations  !

to determine the scope of each channel tested in the monthly and l refueling surveillance procedures. The allowances used to calculate the trip setpoint and allowable value are then based on the surveillance l

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I U. S. Nuctur Regu!atory Commission l B17474/ Attachment 1/Page 3 1

procedures. The setpoint methodology also includes the calculation of

' as-found and as-left acceptance criteria for the monthly and refueling l surveillance procedures. The acceptance criteria in the surveillance procedures must be at least as restrictive as the values determined in the

, setpoint calculations. Engineering review of surveillance procedures ensures the correct implementation of the trip setpoint, allowable value and acceptance criteria. .

Question 2: The current surveillance frequency at Millstone Nuclear Power Station, Unit No. 2, is 18 months. However, as noted in the submittal, the revised SP calculations are based on 24 months drift, which is conservative with regard to SP determination. Please confirra that the surveillance-test-acceptance criteria for the 18-month surveillarice test is compatible to the drift-values used in SP calculations. Please note that the staffs review of the referred submittal is limited to revised SP/AV calculations only and does not include areas relating to extending surveillance frequency from 18 months to 24 months including drift extension methodology.

Response: Drift analyses were performed to estimate the 30 month drift (24 months plus 25%) values used in the uncertainty calculations. Historical surveillance test and calibration data were collected for the applicable instrumentation and entered into databases. Selected items of

" time-tagged" data from the verified databases were then copied into spreadsheets for analysis. Linear regression analyses of the data were pe' formed to determine if the drift values were time dependent. The data were tested for normality, and estimates of bounding values of drift were determined using the method for normal distributions, or a distribution free method, as appropriate. Scatter plots and histograms were prepared  !

to assist in visualization of the data. The regression analyses confirmed that most drifts did not increase with time. Based on the historical data and the results of the analyses, there should be no difference between i

the drift for the 30-month interval and the drift for the surveillance period (18 months plus 25%) for these variables. In the few cases where drift

was time dependent, a conservative multiplier was used to determine l bounding drift for 30 months. The 30-month bounding values for time l dependent drift are conservative for the current surveillance period l (18 months plus 25%). As long as the as-found values are within the acceptance criteria, the assumptions of the setpoint calculations are valid.

Therefore, the surveillance testing is compatible with the drift values.

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