ML19257A788

Updates Util 791101 Ltr Re Qualified Life of Resistance Temp Detectors.Forwards Westinghouse re-evaluation & Calculations Justifying Rtds.Util Radiation Exposures More Conservative than Values Used by Westinghouse

ML19257A788
Person / Time
Site:	North Anna
Issue date:	01/04/1980
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, Parr O Office of Nuclear Reactor Regulation
References
855A-01879, 855A-1879, NUDOCS 8001080448
Download: ML19257A788 (4)

Text

o PCO VIRGINI A ELECTRIC AND POWER COMP ANY, RICHMOND, VIRGINI A 23261 January 4, 1980 Mr. Harold R. Denton, Director Serial No. 855A/101879 Office of Nuclear Reactor Regulation PSE&C/JMD:adw:me Attn: Mr. O. D. Parr, Chief Light Water Reactors Branch No. 3. Docket No. 50-339 Division of Project Management U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Denton:

In item 1 of our letter, Serial No. 855 dated November 1,1979, we indicated further information would be provided concerning qualified life of resistance tem-perature detectors (RTDS).

Attachment 1 is a copy of Westinghouse's re-evaluation and calculations justify-ing the RTDS for North Anna Unit 2.

We have calculated the radiation exposures specifically for North Anna Unit 2, using item B of your letter for guidance, and they are more conservative than those Westinghouse. These calculations show a post-LOCA 100 da integrated values used dose of 2x10 pRads for RTD external connection environment, leaving 8x10y Rads to cover in-service effects. The in-service dose rate for narrow range RTDs in the by-pass loop is 62 R. per hr. and for the wide range RTDs in the main coolant loops is 745 R. per hr., considering 1% failed fuel. Therefore the time required for the in-ternal parts of the RTD's to attain the remaining qualified dose is we'l in excess of the 14 years derived by Westinghouse.

The post-accident exposure basis recommended in part C(2) of your letter is excessively conservative and the more realistic approach is a release of the fission products to the containment. With this assumption, th 100 day post-LOCA internal pipingdosetotheWideRangeRTDswouldapproach2x10 grads.

Using the realistic approach of part C(1) in your letter, the demonstrated life for the narrow range RTD's is greater than 40 years and for the Wide Range RTD's is 14 years.

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WINIA ELECMC AND POWER COMPANY TO Mr. Harold R. Denton, Director '""'"

2 We feel this completes the response to your October 16, 1979, letter. Iffur-thsr information is necessary, please advise. ,

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Sen or Vice President Powe Station Engineerf and Construction Attachment 6

1706 061 l

Serial No. 855A/101879 Docket No. 50-339 ATTACHMENT 1 (NorthAnnaUnit2)

Radiation Dose Calculations for RTD's The object of the following calculations is to estimate the plant specific in-service life that, when taken in conjunction with assuming the RTD's operate {or 100 days in a post-LOCA environment, yields a total dose equal to 1 x 10 Rads as employed by Westinghouse for the testing reported in WCAP-9157.

External Environment WCAP-8587, Figure 6-4, indicates a containment atmosphere dose of 1 x 108 Rads for 100 days post-LOCA. This value is based on a TID calculation for a 4100 MW reactor and a containment volume of 1.1 x 10b ft. 3 The Westinghouse calculated dose can be approximately scaled for your plant application by the formulae:

D = 1.0 x 108 P 1.1 x 106 Rads ITOU v Inserting a value of 2900 MW (P) and 2.4 x 106 (V) as appl plant yields a post-LOCA 100 day integrated dose of 3.2 x 10jcable Radstoforyour the RTD external connection. Since the narrow range RTD is only required for a short time after the event this calculation only applies to the wide ranga measurement. The external dose for the narrow range is on the order of 106 Rads and is insignificant compared to the test condition.

The remaining dose available to cover in-service effects is the difference between the total dose employed in the Westinghouse test reported in WCAP-9157 (i e., 1 x 108 Rads) and th above calculated post-LOCA dose (i.e., 3.2 x 107 Rads), which is 6.8 x 10 Rads. The dose rate during normal operation appropriate to the extr oal connection is taken as 165 R/hr (Table 6-2, WCAP-8587). Thus, assuming an 80 percent load factor, the time required to attain this remaining dose is:

Wide Range 6.8 x 107 = 59 years 165x24x365x0.8 Narrow Range 1.0 x 108 = 86 years 165x24x365x0.8 The Westinghouse calculated dose post-LOCA employed for this calculation is conservative with respect to those recommended by the Staff in Appendix D of NUREG-0588. -

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. Internal Environment WCAP-8587, Figure 6-8, indicates a RCS internal pipe dose of 1.8 x 107 Rads for 100 days post-LOCA. Without considering any reduction in this value by scaling for your plant, the remaining dose available to cover in-service radiation effects on the RTD is 8.2 x 107 Rads. The dose rate during normal operation for wide range RTD's installed directly in the reactor coolant system is conservatively taken as 820 R/hr as defined for the RCL pipe center in Table 6-2, WCAP-8587. For the bypass line, narrow range RTD's, the dose rate is conservatively taken as 165 R/hr as defined for the RCL outside surface. Thus, assuming an 80 percent load factor the time required for the internal part of the RTD to attain the remaining dose is:

Narrow Range 1.0 x 108 = 86 years 165x24x365x0.8 Wide Range 8.2 x 107 = 14.3 years 820x24x365x0.8 The assumptions used in developing Westinghouse internal post-LOCA radiation dose for the wide range RTD's are more realistic than those recommended by the NRC in paragraph C(2) of their letter. It is overly conservative to assume that all of the fission products are contained within the RCS after a LOCA as the NRC recommended. If the overly conservative assumptions recommended by the NRC were used the internal post-LOCA dose would exceed 1 x 108 Rads to which the RTD's were tested.

Sunmary Using Westinghouse dose estimates from WCAP-8587 scaled for your plant, the shortest demonstrated life for the wide range RTD is 14.3 years and greater than 40 years for the narrow range RTD.

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