ML20128F210

Submits Addl Response to Generic Ltr 84-11, Insp of BWR Stainless Steel Piping. Proposed 20% Sampling Will Provide Most Comprehensive & Technologically Sound Assessment of IGSCC

ML20128F210
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	07/02/1985
From:	Frisch R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
References
GL-84-11, IEB-83-02, IEB-83-2, NUDOCS 8507080169
Download: ML20128F210 (4)

Text

4 Consumers Power Company General offices: 1945 West &arnall Road, Jackson, MI 49201 e (517) 788-0550 July 2, 1985 Director, Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT -

RESPONSE TO GENERIC LETTER 84 ADDITIONAL CLARIFYING INFORMATION Consumers Power Company submitted the results of augmented inservice inspection required by IE Bulletin 83-02, Stress Corrosion Cracking in Large-Diameter Stainless Steel Recirculation System Piping at BWR Plants, by letter dated August 11, 1983. Our response to Generic Letter 84-11, Inspection of BWR Stainless Steel Piping was submitted by our letter dated May 25, 1984. Recent telephone conversations between respective members of our staffs has determined that the NRC staff needs additional information to resolve the inspection issues. The following information is provided to clarify our position.

Per our August 11, 1983 submittal, fifty-nine (59) welds were considered to be susceptible to Intergranular Stress Corrosion Cracking (IGSCC) of which eleven (11) were selected to be examined to fulfill the requirements of IE Bulletin 83-02. Discussion with NRC staff at that time indicated the intent of the bulletin was to examine 20% of the large diameter welds of BWR Main Recirculation Systems. Generic Letter 84-11 also requires a 20% sampling of susceptible welds in the Main Recirculation System and the Residual Heat Removal System. In addition to the examination scope of IEB 83-02, Generic Letter 84-11 includes piping four (4) inches and larger in diameter and requires a 20% sampling from each pipe size. Minimum examination requirements are further placed on this 20% inspection criteria.

Table 1 of our August 11, 1983 submittal identified susceptible welds of the .

Main Recirculation System for consideration under Bulletin 83-02. This table identified fifty-nine (59) welds on piping fourteen (14) inches and larger in diameter, of which the four (4) twenty (20) inch diameter welds have limited access of approximately one-third (1/3) the circumference on the pipe to safe-end welds and slightly more than this on the safe-end to nozzle welds. A thorough review of this table and associated documents has reduced the number of susceptible welds by thirteen (13). This reduction is due to two reasons:

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Director, Nuclear Reactor Regulation 2 Big Rock Point Plant GL 84 Additional Information July 2, 1985

1) an apparent error in the number of welds on the risers (14 inch diameter) due to one set of welds being counted twice and, 2) the shop made welds on the risers being built to specification (s) requiring a solution heat treatment (ASTM A-358).

Item 1 above results in a reduction of six (6) welds because reactor vessel nozzle to safe end welds were apparently counted twice. The second item above results in a reduction of seven (7) welds due to the solution heat treatment.

This correction now indicates forty-six (46) welds instead of fifty-nine (59) welds as being susceptible to IGSCC.

In addition, since our August 11, 1983 submittal our IGSCC inspection program has expanded to include the following additional welds. Big Rock Point has a shutdown cooling system which provides residual heat removal for the reactor core. This system contains ten (10) stainless steel welds of six (6) inch diameter which must be included. The balance of welds on this system are of carbon steel material.

Three Main Recirculation System lines four (4) inches or greater in diameter must be added to the total number of susceptible welds. Two of the lines are five (5) inch diameter and the third line is a four (4) inch line. As a result twenty (20) five (5) inch diameter welds and eleven (11) four (4) inch diameter welds must be added to the susceptible weld selection table. The total number of susceptible welds now totals eighty-seven (87).

Table 1 provides a breakdown of susceptible weld information. Although our May 25, 1984 submittal indicates forty-two (42) additional welds were to be included due to the additional requirement of four (4) inch and greater lines, a subsequent review has established that only forty-one (41) additional welds need to be included.

Since Generic Letter 84-11 requires both 20% inspection of IGSCC susceptible welds previously inspected as well as 20% of the welds not previously inspected, strict compliance to the minimum requirements of Generic Letter 84-11 for Big Rock Point would constitute a 35% sampling. This percentage is due to Big Rock Point being small in size and consequently having a generally corresponding smaller number of welds. The newer generation of BWRs can most likely institute a 20% sampling without minimum requirements being imposed.

It is the position of Consumers Power Company that a sampling of 20% of IGSCC susceptible welds, some of which have been examined under Bulletin 83-02 and some of small diameter piping (4", 5", and 6" diameter), will constitute a sufficient cross section of piping sizes and inservice conditions. Of the examinations proposed, none of the four (4) twenty (20) inch diameter welds were selected. This is due to the confidence level being higher for inspection of a complete weldment (360*) rather than a partial weld. In addition, the time and exposure associated with a partial examination is not conducive to ALARA principles.

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f Director, Nuclear Reactor Regulation 3 Big Rock Point Plant GL 84 Additional Information July 2, 1985 The proposed 20% sampling (18 welds) in Table 1 will require approximately thirty-five (35) hours in a field of 2 rem / hour and fif ty-five (55) hours in a field of 0.5 rem / hour. Consequently, the estimated exposure for these inspections is 97 man-rem.

Notwithstanding the exposure burden, this 20% sampling, the largest and mont diverse to date, will provide the most comprehensive and technologically sound assessment of IGSCC at Big Rock Point, i

Ra R r Senior L censing Analyst CC Administrator, Region III, USNRC NRC Resident Inspectors - Big Rock Point Plant OC0685-0235-NLO4

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TABLE 1 - ICSCC SUSCEPTIBLE WELDS Accessible, Number not Not Not Susceptible Number of Number Number not Previously Previously Previously Previously Proposed Pipe Number Welds Selected Previously Inspected & Inspected Inspected Inspected for Size of Welds Accessible for IEB 83-02 Inspected Accessible (20% or 2) (20% or 4) (20% or 4) GL 84-11 24" 2 2 2 0 0 2 0 0 2 20" 4 1/3 of Each II) 0 4 0 1/3 ea III 4 0 1/3 ea II) 0 4 0 1/3 eaII) 4 0 1/3 eaII) O(2) 17" 10 10 4 6 6 2 4 4 3 14" 30 12 5 25 7 2 5 4 4 6" 10 4 0 10 4 0 4 4 3 5" 20 20 0 20 20 0 4 4 3 4" 11 11 0 11 11 0 4 4 3 Total 87 63 11 76 52 6 25 24 18 Percent 54% 32% 46% 20%

(6 of 11) (25 of 76) (24 of 52) (18 of 87)

NOTES:

(1) These welds have limited access of approximately 1/3 the N circumference on the pipe to safe-end and slightly more than this on the safe-end to nozzle. 335% [

(31 of 87)

(2) No welds selected due to the confidence level being higher for inspection of a complete weldment (360*) rather than a partial weld.

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