ML20085L612

RO 50-267/75/05B:on 750323,helium Circulators 1A & 1B Tripped & Buffer Differential Pressure Indication of Helium Circulators 1C & 1D Dropped.Caused by Increased Pressure in Surge Tanks Due to Water Inflow.Procedures Revised

ML20085L612
Person / Time
Site:	Fort Saint Vrain
Issue date:	09/30/1976
From:	Swart F PUBLIC SERVICE CO. OF COLORADO
To:	Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085L618	List: ML20085L612 ML20085L619 ML20085L622
References
P-76222, RO-50-267-75-05, RO-50-267-75-5, NUDOCS 8311020123
Download: ML20085L612 (5)

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Ep Unit No. 1 P-76222 .

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i G Mr. 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 Final Supplement, please find a copy of Unusual Event Report No.

50-267/75/05B ,

fications. submitted per the requiraments of the Technical Speci-Also please find enclosed one copy of the Licensee Event Report for Unusual Event Report No. 50-267/75/05B.

Very truly yours,

./ .2 n  %%%0 Frederic E. Swart l Superintendent, Nuclear Production l Fort St. Vrain Nuclear Generating Station .

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. O O REPORT DATE: September 30, 1976 UNUSUAL EVENT 75/05B Page 1 of 4 OCCURRENCE DATE: March 23, 1975 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P.O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/75/05B Supplement Final .

IDENTIFICATION OF OCCURRENCE:

A situation occurred while testing the helium circulator backup bearing water

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system which resulted in helium circulators 1A and 1B automatically tripping off and the buffer differential pressure indication of helium circulators 1C and ID to drop, resulting in operator action to set the brake and seal.

This is identified as an Unusual Event, per Technical Specification definition AC 7.6c, paragraph 3.

00NDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown Hot Shutdown Routine Load Change X _ Cold Shutdown Other (specify)

Refueling Shutdown Routine Startup The major plant parameters at the time of the event were as follows:

I Power RTR 0 Wth ELECT 0 We Secondary Coolant Pressure N/A psig Tempera ture N/A 'F Flow N/A #/hr.

Primary Coolant Pressure 85 psig Temperature s200 *F Core Inlet N200 *F Core Outlet Flow Helium circulator self- #/hr.

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i DESCRIPTION OF i

OCCURRENCE:

The emergency feedwater. header had been isolated via V-21453 in order to repair the pressure control for valve PV-21105. Upon completion of this repair, pressurization of the emergency feedwater header was initiated by slowly opening the isolation valve V,-21453. The following events then occurred:  :

1. Helium circulators lA and 1B tripped on negative buffer-mid- ,

buffer differential pressure.  !

2. HV-2366-1 and HV-2366-2 changed the supply of makeup buffer gas to the helium circulators from the purified helium header to the helium storage system. At a PCRV pressure of 85 psig helium -

density is barely sufficient to place the purified helium com-pressors in service. Loss o' f a major helium user such as circu-lator 1A and 1B buffer, caused the purified helium compressor to trip and the automatic controls to switch to the high pressure helium storage system.

3. The bearing water surge tank pressure in both loops increased to 140 psi, causing the buffer return flows to drop to 0 on the remaining circulators. Circulator 1C buffer differential pressure decreased to 10" negative but did not trip. Circulator ID buffer differential pressure dropped but did not go negative. The operator set the brake and seal on both of these circulators be-cause the return flow was so low. The Rix recovery compressors were then set up to vent to atmosphere in order to get the bearing water surge tank pressure down. When surge rank pressure equalled ,

reactor vessel pressure,1C and ID helium circulators were 1 restarted.

APPARENT CAUSE OP OCCURRENCE: X Design Unusual Service Cond.

Including Environment

_iManufacture Component Failure Installation /Const. Other-(specify)

Operator Procedure The increased pressure in the surge tanks due to the water inflow displaced helium from these tanks, thereby . increasing the buffer helium recirculation suction pressure. This reduced the buffer return flow from the helium circu-lators causing them to trip on buffer-mid-buffer.

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UNUSUAL EVENT 75/05B Page 3 of 4 ANALYSIS OF OCCURRENCE:

i' It appears that PV-21105 failed to control as did PDV-2191 and PDV-2192. With  !

these valves not operating while V-21453 was being opened, there was no con-  !

trol of the backup bearing water flow. The large amount of flow into the bearing water surge tanks caused a displacement of the helium from the surge tanks (due to a level increase). This helium flowed backward through the equalization line to the suction of the buffer helium recirculators, which caused reverse flow of the buffer return from the helium circulators. . The ,

reverse flow of buffer return caused a buffer-mid-buffer differential suffici-ently negative to initiate the automatic circulator trips. l l

Ihe level increase would not have occurred under normal operating conditions l because with the normal bearing water pumps tripped and bearing water supplied i from the backup bearing water system, a feed forward signal from the control  !

system would have opened the surge tank drain valves. Under these conditions,  !

the possibility of high rate of change in the surge tank level and the reversal of return flow from the circulators, is eliminated. I I

l CORRECTIVE ACTION: .

A test of the backup bearing water system was completed. This test, RT-356, was i performed to verify that backup bearing water will function correctly and re-lated transients are repeatable. This test was performed at (1) pressures simulating the most adverse requirements for backup bearing water, and (2) at the pressure which also causes the most adverse helium buffer-mid-buffer inter-actions.

This test of (1) was performed five (5) times by simultaneously transferring all

, four circulators to backup bearing water. The results of the test show that on the most severe transient there was a margin of 25 psid between the transient and the circulator trip point. All other' test results show a larger.

margin.

The test of (2) was performed and the results show that the most severe' differ-ential pressure transient on the buffer-mid-buffer decreased but remained positive. The trip point is -9" water differential pressure. The results of test RT-356 verify the operability of the backup bearing water system and con-ciudes this report.

Rev. A procedure to establish backup bearing water without tripping operating B circulators, has been added to the appropriate System Operating Procedure.

No further corrective action is planned or' required.

PAILURE DATA /

SIMILAR REPORTED OCCURRENCES:

Unusual Occurrence No. 50-267/75/02 reports a. failure of PV-21105-1 in the backup.

bearing water system which occurred on April 10,- 1975.

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UNUSUAL EVENT 75/05B Page 4 of 4 PROGRAMMATIC IMPACT:  ;

None CODE IMPACT:

. i None Submitted by: . . f  ; .

H.W. Hillyard,/Jr. / '

Technical Services Supervisor Reviewed by:

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H. Larry Brey \ \

Superintendent, Operations .

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Fr eric E. Swart

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atT 0 Mr. E. Morris lloward, 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. Iloward :

Enclosed please find a copy of Unusual Event Report No. 50- 267/ 75 /07A, Final Supplement, submitted per the requirements of the Technical Speci-fications.

Also please find enclosed one copy of the Licensee Event Report for Unusual Event Report No. 50-267/75/07A.

Very truly yours, .

&E-Frederic E. Swart Superintendent, Nuclear Production FES/alk cc: Mr. Roger S.-Boyd

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• August 9, 1976 UNUSUAL EVENT 75/07A REPORT DATE:

, , Page 1 of 3 OCCURRENCE DATE: April 28, 1975 FORT ST. VRAIN NUCLEAR CENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/ 75/07A FINAL SUPPLEMENT IDENTIFICATION OF JD_CCURRENCE :

Temporary cables from the auxiliary c1ccerical equipment cabinets to the temporary instrumentation and test equipment were not segregated from the permanent cables accocding to specification 1-N-2. Color coding on the temporary cables was not consistent with the scheme used in the permanent ins tallation.

CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown.

Hot Shutdown Routine Load Change -

4 Cold Shutdown Other (specify)

Refueling Shutdown X' Routine Startup The major plant parameters at the time of the event were an follows:

Power RTR - 116 . 4 7 HWth /

2 ELECT 0.0 HRe Secondary Coolant Pressure 1,216 psig -j

. .Temperatnre 30 6 'F Flow 1. 209 ~ x 100 #/hr.

. Primary ~ Coolant Pressure 411- ps ig' -

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• F Corei Inlet

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'F Co'reJoutlet.

350 I

Flow -0.31 x 108 f/hr.1

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. , UNUSUAL EVENT 75/07A Page 2 of 3 l DESCRIPTION OF l OCCURRENCE.

l Inspection revealed that some of the temporary cables to the temporary in-strumentation and test equipment in the auxiliary electrical equipment room were not segregated from the permanent cables above the auxiliary electri-cal equipment cabinets, either by physical separation or by fire resistant zipper tubing according to Specification 1-N-2.

APPARENT CAUSE OF OCCURRENCE: Design Unusual Servica Cond.

Including Environment Manufacture Component Failure X Installation /Const. Other (specify)

Operator Procedure ANALYSIS OF OCCURRENCE:

Adequate separation and segregation should exist between the temporary -

and permanent cables ~, according to Specification 1-N-2. l CORRECTIVE ACTION:

Cencral Atomic Work Authorization No. 99F1849 has been issued to correct  !

color coding on 'the temporary cables and to zipper tube cables that do not meet segregation criteria according to Specification 1-N-2. The work ,

will be inspected af ter the work authorization h. s been completed. **

An extensive modification to correct violations of separation and segre -

gation has been completed. This was followed by an audit to verify that A separation and segregation criteria were met. .The results of this work are documented in Public. Service Company letter P-76105,. dated May 11, 19 76, from R. F. Walker to R. P. Denise. .!

l No further corrective action is anticipated or required.

PROGRAMMATIC IMPACT:

13 Months-CODE IMPACT: .

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.. O .O UNUSUAL ~ EVENT 75/07A

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Submitted by: ~ , .

H. W. Hillyagd, Jr. d' '

Technical Services Supervisor i

Reviewed by: Nk d 6 4 1 [r M. blcBride /

Resident Engineer Approved by: _ A.e uu W M F)Eederic E. Swart .

Superintendent, Nuclear Production 4

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