ML20085M614

RO 50-267/75/19:on 750926,spare Control & Orifice Assembly Modified by Addition of New Seals to Reduce Helium Bypass Flow.Caused by Seal Ring Larger in Outside Diameter than Inside Diameter at Refueling Penetration

ML20085M614
Person / Time
Site:	Fort Saint Vrain
Issue date:	10/17/1975
From:	Hillyard H, Mathie F, Swart F PUBLIC SERVICE CO. OF COLORADO
To:	Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085M616	List: ML20085M614 ML20085M618
References
RO-50-267-75-19, NUDOCS 8311090058
Download: ML20085M614 (6)

Text

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F. O. Box 361, Platteville, Colorado 80651 lo.

October 17, 1975

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I Hr. E. Morris Howard, Director Nuclear Regulatory Commission Region IV Office of Inspection and Enforcement Suite 1000 Arlington, Texas 76012 REF: Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Howard:

Enclosed ple'ase find a copy of Unusual Event Report No. 50-267/75/19, Final, submitted per the requirements of the Technical Specifications.

Very truly yours, h ederic E. Swart Superintendent, Nuclear Production Fort St. Vrain Nuclest Generating Station .

FES/alk cc: Mr. Roger S. Boyd

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O O REPORT DATE: October 17, 1975 UNUSUAL EVENT 75/19 l

OCCURRENCE DATE: September 26, 1975 i

i FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 .

PLATTEVILLE, COLORADO .80651 REPORT No.- 50-267/75/19

- Final ITENTIFICATION OF OCCURRENCE: ,

A spare control and orifice assembly had been modified by addition of new seals to reduce helium bypass flow. When an attempt was made to install the assembly in the core, the assembly was hindered in the refueling penetration, preventing installation.

CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown Hot Shutdown Routine Load Change

X Cold Shutdown Other (specify) 1 Refueling Shutdown Routine Startup The major plant parameters at the time of the event were as follows

Power RTR 0 MWth ELECT 0 MWe Secondary Coolant Pressure

• psig Temperature * 'F Fl'ow

• f/hr.

Pri'ary m Coolant Pressure .5 psig Temperature * *F Core Inlet

- * 'F Core Outlet Flow 1 circulator at 4,000 rpm

• These parameters have.no bearing on this . incident.

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UNUSUAL EVENT 75/19 Page 2 of 5 DESCRIPTION OF .

OCCURRENCE:

Control and orifice assembly serial #28 had been modified in accordance with FCN #2774. .

Af ter modification was complete, an attempt was made to install this assembly in region 21' replacing the assembly originally there which had been removed for the same modification.

Assembly #28 was one of seven spare assemblics which had not been installed in the core at the time the modification was approved. It was decided to modify the spare assemblics first and then use them as replacements for assemblies removed from the core for modification.

The original assembly had been removed from region 21 and placed in an equipment storage well using the auxiliary transfer cask. Assembly #28 was removed from an equipment storage well with the auxiliary transfer cask and moved to region 21 for installation. While the assembly was being lowered into the penetration it wa's observed that the indicated weight of the assembly was decreasing before the assembly had reached the vertical position at which this indicated weight decrease was to be expected. Installation of the assembly was stopped and the {

assembly raised back up into the auxiliary transfer cask. j APPARENT CAUSE OF OCCURRENCE: Design Unusual Service Cond.

Including Environ. ,

X Manufacture Component Failure J

• Installation /Const. Other (specify) l 1

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Operator Procedure When the control and orifice assembly was placed in a work stand for inspec-tion it was found that the new seal ring (10 on drawing SLR D1201-700, attached) showed signs of rubbing over almost its entire- periphery. This indicated that the ring had been fully compressed,during installation of the assembly and had been the cause of the observed weight decrease when the seal ring began to bind in the refueling penetration. The apparent cause of the occurrence is therefore a seal ring slightly larger in outside diameter than the inside diameter of the refueling penetration. .

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UNUSUAL EVENT 75/19 Page 4 of 5 ANALYSIS OF OCCURRENCE:

A dimensional check of the seal ring was made and the outside diameter of the ring was found to be 17.980 inches. A check of dimensions at the seal ring area where the penetration ne'cks down and ~ joins the cavity liner re- ~

vealed that the penetration is slightly eliptical with a maximum diameter of The diameter of 18.070 inches and athe minimum diameter clevation where of the 17.968 sealinches.

ring was binding is believed the penetration at to be of the same order. .

17.960 +.005, .000. The source The specified design size of the seal ring is of the increase in size over the design value was traced to a nitriding treatment.

A total of 5 seal rings have been identified as having been nitrided with the original procedure, which resulted in these rings being slightly oversized. Of thesc 5 rings,the ring which was on assembly #28 and two otuers which were on assemblics outside the core at the time of this occurrence have been modified to bring them back within design tolerance.

The remaining 2 rings are part of modified assemblics which had been success-fully installed in the core before the problem occurred.

'0ORRECTIVE ACTION:

The seal ring on assembly #28 which caused the binding was removed and replaced with a.new ring. The outside diameter of the new ring was 17.968* inches.

The assembly was reinstalled in region 21 with no indication of binding ob-served during installation.

' Die nitriding treatment has been modified to maintain seal ring size within tolerance. A ch,eck will be made of seal ring size prior to inscallation on ,

each assembly. ~

• This dimension was taken af ter application of a dry lube . film which is an.

acceptabic addition to design tolerance for ring size. [;

Y FAILURE / DATA /SIMILAR REPORTED OCCURRENCES:

None ,

i PROGRAMMATIC IMPACT:

None .

CODE IMPACT: .

None s

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UNUSUAL EVENT 75/19 Page 5 of 5 Submitted B,: 9[ ,

Harvey W. llilly;nrd, Jr. /

Technical Services Supervisor Reviewed By: 9 ~7 A ---^-

Frank M. Mathic Superintendent, Maintenance

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Approved By: l e ,(/0 r ,c,r /

frederic E. Swart Superintendent, Nuclear Production 9

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