ML20086S094

RO S2-77-01, Missing Steam Generator Tube Plug-Hot Leg,Generator B,Row 1,Column 42

ML20086S094
Person / Time
Site:	Surry
Issue date:	09/30/1977
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20086S067	List: 05000280/LER-1977-012, RO S1-77-01 Re Failures of Hydraulic Shock Supports (Snubbers).Extent of Failures Reported in LER 77-12.All Snubbers Operable on 771207 Startup ML20086S064 ML20086S094 ML20086S116
References
RO-S2-77-01, RO-S2-77-1, NUDOCS 8403010361
Download: ML20086S094 (3)

Text

_ . . - . . ._

~

. . . O '

O -

SR-S2-77-01 MISSING STEAM GENERATOR TUBE PLUG-HOT LEG, GENERATOR B, R0W 1, COLUMN 42.

SURRY POWER STATION UNIT 2 DOCKET NO. 50-281 LICENSE. NO. DPR-37 SEPT. 1977 1

i VIRGINIA ELECTRIC AND POWER COMPANY

~

8403010361 780105 PDR ADOCK 05000280PDR S ,

l

O

. O INTRODUCTION' During the Surry Unit 2 Outage of July 11, 1977'an explosive plug was discovered to be missing from Row 1 Column 42 in the hot leg of Steam Generator B. It is the intent of this report to discuss the plug lost and possible stopping places.

DISCUSSION The location, Row 1 Column 42, in the inlet (T H) side 'of 2B Steam Generator was plugged on October 20, 1976 as a preventive measure. Plugging was verified by second visual check. On July 11, 1977, a visual inspection determined that no plug was inserted at Row 1 Column 42. Two possibilities present themselves to explain the. fate of this plug.

First, in March, 1977 a plug was found in the channel head of Unit 2 Steam Generator B, inlet. By the identification number, Westinghouse concluded that the plug came from one of six tubes (R36/C76, R42/C61, R42/C63, R43/C60, C43/C62, R43/C63) and recommended that all six of those tubes be checked for plugs. However, Vepco Non-Destructive Testing and Quality Assurance efforts verified that the six tubes in question were in fact still plugged. .

Westinghouse had further stated that a visual examination of the plug showed it had been only partially expanded and a total detonation was not achieved upon installation. Since Rl/C42 was not a leaking

• tube, it is not unlikely that a plug missing from that location would not be noticed during a subsequent hydrostatic test. It is possible that the plug found in the channel head in March, 1977 came from Row 1, Column 42.

Second, during the same inspection that found the Rl/C42 plug missing, a plug was found loosely inserted into R29/Cll, a location not in the plugging program and not intended to be plugged. The R29/Cll plug was sent to the.

Westinghouse Nuclear Service Division Waltz Mill Facility for examination. A h

DISCUSSION (CONTINUED) dimensional check was performed showing no change from fabrication dimension indicating that the plug had not been " fired". Microscopic examination of the plug by Westinghouse determined that the plug came from heat number NX7853, but the identification number was not legible and positive identifi-cation of when or where the, plug was installed was impossible. It is possi-ble that the R29/C11 plug was inserted into that location by mistake and was never exploded. However, the supposition can be made that the Rl/C42 plug may have dropped out and reinserted itself, under flow conditions, into the R29/C11 position.

On the possibility that back flow may have carried the plug into the reactor at some time when RCP "B" was idle, a thorough examination of the reactor vessel above and below the core was carried out by CCTV. No loose material was found by this inspection.

CONCLUSIONS Two explanations concerning the missing R1/C42 plug have been presented, the first being more credible, but more importantly it must be concluded that no plugs are loose in the loop or unaccounted for. Tubes R1/C42, R29/C11 and those tubes around R29/Cll were all plugged on July 21, 1977. With the recent achievement of a new, more reliable method of photographic verification of plugging maps, speculative explanations of missing plugs should not be necessary.

l 4

.-- - - - . , , - , y - r ,