ML17252A954

Letter Regarding Inspection of Bergen-Patterson Hydraulic Shock Suppressor at Dresden Nuclear Power Station Unit 3

ML17252A954
Person / Time
Site:	Dresden
Issue date:	08/16/1973
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
WPW Ltr. #592-73
Download: ML17252A954 (3)

Text

., . .. Regutatory

• Commonwe.Edison One First National Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 I\ s WPW Ltr.

A. Giambusso Deputy Director for Reactor Projects Director of Licensing u.s. Atomic Energy Commission Washington, D.C. 20545

• Dresden Nuclear Power Station R. R.-*fif --Morris, IL August 16, 1973

SUBJECT:

Inspection of Bergen-Patterson llydraulic Shock Suppressor at Dresden Nuclear Power Station, AEC Dkt 50-249

Reference:

Letter from Byron Lee, Jr. to Boyce H. Grier dated August 6, 1973, concerning Bergen-Patterson Shock Suppressors

Dear Mr. Giambusso:

• This letter is to report additional information concerning Bergen-Patterson "snubbers" subsequent to the referenced August 6 letter. on August 4, J973, two Bergen-Patterson hydraulic shock suppressors, size 2.5 inch bore inch stroke, (station identification nos. 23 and 25) were removed from the Unit #3.drywell for overhaul.

At the time of re* moval it was noticed that the 3 inch diameter pipe stub to which the two "snubbers" were affixed was broken at a circumferential weld. The broken weld was a saddle weld.benween the pipe stub and the cleanup line (figure 1). The failed weld was examined by the company's Operational Anajysis Department.

Tbe failure is believed to have.occurred due to fatigue. The crack initiation and propagation appears to be related to loss of fluid in the "snubbers".

the fillet weld left a crack initiation site between the stub tube face and the cleanup pipe surface. Since there was no dampening by the "snubbers" (the two "snubbers" were out of oil) vibrations in the system imposed cyclic loading on the weld which ultimately caused a fatigue failure of the weld. Repairs included replacing the pipe stub and strengthening the support by weld"ing the stub . to _the cleanup line with a full penetratiC>il weld. The failed weld was only a fillet weld. There are a total of ten (10) similar -welded snubber supports in the Unit #3 drywall. Eight (8) of the ten (10) including the one failed support were non-destructively utilizing dye penetrant.

The one failed support is unique to both Units 12 and 13 iniithat it has two "snubbers" attached to one support.

• - August 16, 1973 The High Pressure Coolant Injection (HPCI) line in both Unit 12 and 13 dry* wells has one support with three (3) attached snubbers. .These two supports were dye All examinations were performed on August 8 and 9. No indications of faulty welds were detected.

Based on this representative sample the station believes all supports to be in satisfactory condition.

During the next shutdown when the Bergen-Patterson "snubbers" are inspected, as stated in the referenced letter, the rep4'ired support for the Unit #3 cleanup line will again be examined.

The referenced letter of August 6 contains some information which must be updated. It states that two of the eleven other. snubbers on Unit #2 and one of the eleven other snubbers on Unit #3 were inoperable.

This information was based on the fact the snubber accumulators indicated no oil. This is the same criteria used f 0r determining inoperable snubbers in the drywell. Subsequent to the station's determination the manufacturer's representative came to the station and examined the snubbers.

He reported that they were operable, however, oil was needed in the accumulator.

Based on these facts it is now stated that all "other" snubbers were operable.

WPW:slb cc: File/AEC Corr.Cat I Sincerely,

w. P.* Worden * *superintendent Dresden Nuclear Power Station 6350

,, . c * .. * . FRIL.EQ .6350*