ML20085M501

LER 75/022A:on 751223,restart of Primary Coolant Helium Circulator 1 Following Failure of Common Portion of Circulator Gas Buffer Sys Found to Be Jeopardized by Inability to Retract Circulator Static Seal

ML20085M501
Person / Time
Site:	Fort Saint Vrain
Issue date:	06/11/1976
From:	Hillyard H, Swart F PUBLIC SERVICE CO. OF COLORADO
To:	Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085M499	List: ML20085M501 ML20085M504
References
LER-75-022A, LER-75-22A, P-76129, NUDOCS 8311080609
Download: ML20085M501 (8)

Text

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\+k pubHe Service Company *F Cdonde j P. O. Box 361, Platteville, Colorado 80651 L

June 11, 1976 Fort St. Vrain Unit No. 1 P-

. Y e S h e-Mr. E. Morris Howard, Director // pg h, D yr'6 Nuclear Regulatory Commission Region IV 2 2

'23 N ANA2 h -

Office of Inspection and Enforcement Id G,7 >

Suite 1000 #

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,s Arlington, Texas 76012

,7 REF: Facility Opera Ibsnse No. DPR-34 Docket No. 50-267 i

Dear Mr. Howard:

Enclosed please find a copy of Unusual Event Report No. 50-267/75/22A, rinal, submitted per the requirements of the Technical Specifications.

Also, please find enclosed one copy of the Licensee Event Report for Unusual Event Report No. 50-267/75/22A.

Very truly yours, e

Frederic E. Svart Ex .

Superintendent, Nuclear Production Fort St. Vrain Nuclear Generating Station FES/alk cc: Mr. Roger S. Boyd soes .

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. REPORT DATE: June 11. 1976 ' UNUSUAL EVENT 75/22A Page 1 of 6 OCCURRENCE DATE: December 23, 1975 l

FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651

, , REPORT NO. 50-267/75/22A

, Final i

IDENTIFICATION OF OCCURRENCE:

It was discovered that the possibility of restarting one primary coolant helium circulator following a failure of a common portion of the circulator gas buffer system might be jeopardized by the inability to retract the circulator static. '

seal. This was identified as an unesual event per Fort St. Vrain Technical Specifications, Section 7.6, Non-routine Reports, Part C) 2).

i CONDITIONS PRIOR

'to OCCURRENCE: Steady State Power Routine Shutdown 4

Hot Shutdown Routine Load Chhnge Cold Shutdown X Other (specify)

Refueling Shutdown Not applicable.

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

Power RTR N/A MWeh ELECT N/A MWe  !

Secondary Coolant Pressure N/A psig Temperature N/A *F Flow N/A f/hr.

Primary Coolant Pressure N/A psig Temperature N/A 'F Core Inlet N/A 'F Core Outlet

Flow N/A #/hr.

This condition was postulated as a result of an anlysis of the circulator auxiliaries and plant conditions had no bearing on the analysis.

e.

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.O O UNUSUAL EVENT 75/22A Page 2 of 6 DESCRIPTION OF OCCURRENCE:

In reviewing the design adequacy of the primary coolant helium circulator's ,

auxiliary systems, it was discovered that an assumed failure (such as a line rupture) of a common portion of the buffer helium system, might seriously jeopardize the ability of the plant operator to restore forced circulation with at least one of the helium circulators within the 30 minutes analyzed and documented in the Final Safety Analysis Report.

APPARENT CAUSE -

OF OCCURRENCE: X Design Unusual Service Cond.

Includin,g Environment Manufacture Component Failure Installation /Const. Other (specify)

Operator Procedure A previously unrecognized problem with the auxiliary system under an extremely degraded system operating condition.

ANALYSIS OF OCCURRENCE:

As a result of the assumed failure of a common portion of the buffer helium system, it was postulated that both auxiliary loop surge tanks lose their pressurizing cover gas (helium), which lowers the bearing water system static pressure to atmospheric. The depressurization is expected to be fast enough to cause all four circulators to trip through automatic protective system action, and for their auxiliaries to be isolated. This included automatically setting all four circulator static shutdown seals. At this point, a condition of temporary loss of forced circulation would exist, with a critical need to immediately re-establish operation with at least one circulator.

However, the depressurized surge tanks presented an additional problem. With primary coolant pressure greater than 120 psig, the back pressure on the en-gaged static seal is sufficient to prevent its release and the subsequent re-turn to operation of the helium circulator. The conclusion was that some method of overcoming the primary coolant back pressure on the engaged static seal was needed.

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o o UNUSUAL EVENT 75/22A Page 3 of 6 4

CORRECTIVE ACTION:

1 The attached partial drawing (PI-21-7) indicate the changes required for circulator 1B. Test, RT-358C, was performed to verify that a circulator could be restarted in less than 30 minutes. Results of the test were that restart of the circulator under simulated loss of surge tank cover gas conditions required 22 minutes, less than the 30 minutes postulated'for the Final Safety Analysis Report temporary loss of forced coolant accident.

During the test, primary coolant moisture increased from 760 PPMV to 5,700 PPM in two hours, which was the result of approximately 24 gallons of water being injected into the primary coolant. The amount of water injected was attributed to high pressure separator flow of greater than 2 CPM. A sub-sequent test (T-31), performed with high pressure separator drain flow con-trolled at or below 2 GPM, injected 0.52 gallons of water in one hour.

l A bank of helium bottles with a minimue pressure of 1,500 psig and the re-quired controls were installed in each auxiliary loop. The gas inventory will provide a sufficient capacity to pressurize a circulator bearing car-tridge in each loop on an emergency, restart basis, to permit opening the static shutdown seal. The actuation of the emergency system will be accom-plished manually in the control room.

l The satisfactory testing and complete installation of the system modifica-tion on all circulators conclude this report. No further corrective action

is required or planned.

FAILURE DATA /SIMILAR REPORTED OCCURFuNCES:

None PROGRA)MATIC IMPACT:

None CODE IMPACT:

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UNUSUAL EVENT 75/22A .

Page 6 of 6 Submitted by: //

11'. V.11111y'9(d Jr.7 Technical S'ervices Supervisor Reviewed by: A/

H. Larry Brey \

Superintendent,\0perations {

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Approved by: .je .

F%deric E. Swart Superintendent, Nuclear Production e

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