ML20214X180

Safety Evaluation Supporting Modified Design Basis Documented in Amend 61

ML20214X180
Person / Time
Site:	Comanche Peak
Issue date:	06/08/1987
From:	NRC
To:
Shared Package
ML20214X144	List: ML20214X141 ML20214X180
References
NUDOCS 8706160364
Download: ML20214X180 (4)

Text

.

i ENCLOSURE COMANCHE PEAK STEAM ELECTRIC STATION , UNITS 1 AND 2 DOCKET NOS. 50-445 AND 50-446 SAFETY EVALUATION FOR IMPLEMENTATION OF REVISED GDC-4 Backaround In a letter dated August 29,1984 (Ref.1) the staff granted the applicant, Texas Utilities Electric Company (formerly Texas Utilities Generating Company),

a partial exemption from General Desian Criterion 4 (GDC-4)of 10 CFR 50, Ap-pendix A for Unit 1 of the Comanche Peak Steam Electric Station (CPSES). The partial exemption eliminated the requirement to install jet impingement shields at eiaht locations in the pipina loop of the reactor coolant system (RCS) for Unit 1. Based on its evaluation of the analyses for CPSES, contained in the Westinghouse Report WCAP-10527 (Ref. 2), the staff determined that the applicant had presented an acceptable technical justification for not installina protective devices to mitigate the dynamic effects associated with a postulated pipe break in the RCS pipina of CPSES Unit 1. In orantino the exemption, the staff had determined that the advance fracture mechanics techniques used by the ap-plicant provided assurance that leakace from a flaw in the primary system piping would be detected before such a flaw reaches a size that could lead to unstable crack growth. For this reason, further protection provided by jet impingement shields aaainst the dynamic effect of jet impingement resultina from the dis-charae from a double-ended cuillotine break in the primary pipina was found to be unnecessary. Although the analysis contained in the Westinahouse Report (Ref. 2) encompassed relief from the need to install pipe break protective devices (i.e., pipe whip restraints, reactor cavity non-crushable insulation, and jet impinaement shields) in Units 1 and 2, the applicant's request for exemption pertained solely to the installation of jet impingement shields as-sociated with eight pipe break locations per loop in CPSES Unit 1. The partial exemption was incorporated into Amendment 8 of the Comanche Peak Steam Electric Station Unit 1 Construction Permit (CPPR-126), by letter dated October 26, 1984 (Ref. 3).

1 I

8706160364 870600 PDR ADOCK 05000445 PDR P

i Evaluation In letters dated. March 12, 1985 (Ref. 4), and July 15,1985 (Ref. 5), the ap-plicant requested a partial exemption to GCD-4 for CPSES Unit 2. The Westing-house Report (Ref. 2) provided the bases for obviating the requirement for protection of structures, systems, and components from all dynamic effects associated with the eight RCS pipe breaks per loop in Units 1 and 2. Further-more, the applicant stated that granting the exemption would not affect the ECCS design bases, the containment and compartment design bases, the equipment qualification bases, the ESF systems response, and the design of RCS heavy com-ponent supports.

The Commission approved the final rule on this matter which stated that ap-plicants for operating licenses seeking to modify aesign features to take advantage of the rule are required to reflect the revised design in an amend-ment of the FSAR. On April 11, 1986 the final rule was published in the Federal Register (Ref. 6). By letter dated June 20,1986(Ref.7)thestaff informed the applicant of the final rule regarding the relief sought by the applicant for Unit 2. By letter dated November 10, 1986 (Ref. 8), the '

applicant transmitted advance copies of FSAR revisions which incorporated design changes related to the implementation of GDC-4 as modified by the April 11, 1986 final rule. The FSAR revisions were subsequently incorporated into the CPSES FSAR by Amendment 61 (Ref. 9) in a letter dated December 19, 1986 (Ref. 10).

Amendment 61 to the CPSES FSAR reflects a modified design basis for CPSES Units 1 and 2. The dynamic effects associated with eight postulated primary loop breaks per loop have been removed from the design basis of CPSES Units 1 and 2. However, the dynamic effects associated with the postulated rupture of the primary coolant loop branch line nozzles are still considered in the design basis. Accordingly, the jet impingement shields will not be installed in either Unit 1 or Unit 2. The applicant is currently evaluating the optimum

time to remove the primary coolant whip restraints and reactor covity non-crushable insulation from Units 1 and 2. Their removal will be documenteo in a future FSAR dmendment. It should be noted that dithough the mein RCS loop breaks are not part of the modified design basis, they are still included in the load ond stress evaluation for the RCS heavy component supports. Any future changes to the CPSES Unit 1 or Unit 2 RCS heavy component supports based upon the modified design basis will require prior staff dpprovdl.

Conclusion The technical justification for the exemption previously granted by the staff (Ref. 1), provided the basis for eliminating from the design basis the dynamic effects ossociated with the postulated primary coolant loop pipe breaks. These dynamic effects include pipe whip and jet impingement. Since technical justifi-cation had been reviewed and approved previously by the staff in granting the August 28, 1984 exemption for Unit 1, the staff considers the justification dssociated with that exemption to be adequate in demonstrating compliance with the revised GDC-4 as well. Therefore, the modified design basis documented in Amendment 61 of the CPSES FSAR is acceptable for Units 1 and 2. Furthermore, the staff concludes that for CPSES, the jet impingement shields, reactor cavity non-crushable insulation, and pipe whip restraints associated with primary coolant loop pipe breaks are unnecessary for compliance with the revised GDC-4.

Principal Contributor: D. Terao, OSP

' References

1) Letter for B. J. Youngblood (NRC) to M. D. Spence (TUGCO), dated Auoust 28, 1984.

2) Westinghouse Report WCAP-10527, " Technical Bases for Eliminatino Large Loop Pipe Rupture as the Structural Design Basis for Comanche Peak, Units 1 and 2 " April 1984, Westinghouse Class 2 proprietary.

3) Letter from B. J. Youngblood, (NRC) to M. D. Spence (TUGCO), dated October 26, 1984.

4) Letter from M. D. Spence (TUGC0) to H. R. Denton (NRC), dated March 12, 1985 (TXX-4426).

5) Letter from W. G. Counsil (TUGCO) to V. S. Noonan (NRC), dated July 15, 1985 (TXX-4692).

6) 51 Federal Register 12502, April 11, 1986.

7) Letter from V. S. Noonan (NRC), to W. G. Counsil (TUGCO), dated June 20, 1986.

8) Letter from W. G. Counsil to V. S. Noonan (NRC), dated November 10, 1986 (TXX-6086).

9) Letter from W. G. Counsil (TUGC0), to H. R. Denton (NRC), dated December 19, 1986 (TXX-6161).

10) Letter from W. G. Counsil (TUGC0), to V. S. Noonan (NRC), dated December 19, 1986 (TXX-6162).

4

. . - - - - . - , _ . . . - , - . , - e r__ _ ,, --- . - , , -- e-