ML20205S215

Safety Evaluation Supporting Util 860110 Proposal to Remove Four Peak Recording Accelerographs Mounted on Reactor Piping

ML20205S215
Person / Time
Site:	Grand Gulf
Issue date:	05/27/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20205S206	List: ML20205S202 ML20205S215
References
TAC-60467, TAC-61931, NUDOCS 8606120091
Download: ML20205S215 (3)

Text

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Enclosure 4

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO DELETION OF PEAK RECORDING ACCELEROGRAPHS MISSISSIPPI POWER AND LIGHT COMPANY GRAND GULF NUCLEAR STATION UNIT NO. 1 DOCKET NO. 50-416

1. 0 INTRODUCTION In accordance with the guidance provided in Regulatory Guide 1.12, Revision 1, a total of three triaxial peak recording accelerographs (PRAs) should be provided at one location on each of the following:

i (1) A selected location on the reactor equipment; 4

(2) A selected location on the reactor piping; I

(3) A selected location on Seismic Category I equipment or piping outside of the containment structure.

In Grand Gulf Nuclear Station (GGNS), Unit 1, four out of 11 PRAs pro-vided are installed on the reactor piping, namely, one each on reactor recirculation piping, main steam piping, the low pressure core spray line, and the high pressure core spray line. As reported by the licensee in its letter AECM-84/0252, dated May 4, 1984, these four instruments were found non-functional in July, 1983, during surveillance.

The licensee's commitments to review this matter were documented in its letter AECM-84/0307, dated May 31, 1984. This included a commitment to implement appropriate design changes prior to restart following the first refueling outage, as well as a commitment to submit a proposed i

Technical Specification change on a schedule consistent with the implementation of these modifications. The NRC staff review of this issue was subsequently documented in Supplement No. 6 to the SER (Section l 16.3.1). It was concluded that no change to the Technical Specification l would be required because the instruments were not used to actuate engineered safety features and post seismic damage could be evaluated, j if necessary, using conservative antlyses based on the measurements of t

other seismic instruments which were operable.

l In its follow-up letter AECM-86/0006, dated January 10, 1986, the licensee described its proposed deletion of the above four PRAs, in fulfillment of the commitments made in letter AECM-84/0307. The staff's up-to-date evaluation of this issue is provided in the following.

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2. 0 EVALUATION There are currently 11 PRAs provided in the GGNS-1 design. One is located on a reactor vessel support, four on reactor piping systems as stated previously, one on the containment dome, one on the control building foundation, one in the control room, one on the standby diesel generator, one on the auxiliary building foundation, and one in standby service water pump house B.

While seven of the PRAs functioned satisfactorily, the four units mounted on the reactor piping were subject to repeated failures. All four were found non-functional in July, 1983, during surveillance. Two of these were again found non-functional during surveillance in January,1985.

The probable cause of malfunction of the PRAs which are mounted on the reactor piping is believed to be the following. A PRA is a passive device capable of recording peak acceleration during a transient event.

The reactor piping is subjected to various transients during startup and normal plant operation. During these transients, the peak acceleration recorded by instruments mounted on the piping can be very high, and can exceed the range of the PRAs (0.01 to 2g) so as to render them inoperable.

The licensee, therefore, in its letter of January 10, 1986, proposed to remove the PRAs mounted on the reactor piping. The licensee's justification for such a proposed action is as follows.

(1) The vendor (Kinematrics) has confirmed that a passive device (PRA) is not suitable for installation on a system which is subjected to frequent transients.

(2) The peak acceleration response due to a seismic event can not be separated from the response due to the system transients. In many cases the predicted peak seismic response is less than that due to the system transients.

(3) A meaningful and conclusive evaluation of the piping response due to a seismic event cannot be performed by relying on a peak l acceleration value at a single location on the piping system.

(4) Currently there are five Triaxial Time History Accelerographs (SMAs) installed in the plant. One SMA is installed on the containment foundation, one on the drywell wall, one in the standby service water pump house, and one on the standby gas treatment system filter drain.

The fifth SMA is installed on the free field. These recorders will provide reliable acceleration time history, which can be converted to seismic response spectra. These can easily be compared with the respective GGNS design seismic spectra for post-seismic damage evaluation. -

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(5) A sixth SMA will be installed on a reactor piping support for the high pressure core spray system by restart from the first refueling outage [0perating License Condition 2.C.(7)]. This SMA will provide an acceleration time history at the support location, which can better serve to confirm the post-seismic evaluation for this plant component than the PRA which is currently located on the corresponding piping system.

(6) The are seven PRAs mounted at various locations inside and outside the containment which will provide reliable and meaningful information for post-seismic damage evaluation.

3.0 CONCLUSION

The staff has reviewed the above licensee's justification and concluded that the four PRAs which are mounted on the reactor piping do not serve any meaningful purpose for post-seismic damage evaluation and, therefore, can be deleted. The staff also concludes that with the sixth SMA which will be installed and the already available devices in GGNS-1, there are sufficient seismic instruments which will provide required information for post-seismic damage evaluation. Therefore, we conclude that the intent of Regulatory Guide 1.12, Revision 1, and Standard Review Plan Section 3.7.4 (NUREG-0800) has been met.

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