ML20085M504
| ML20085M504 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 01/22/1976 |
| 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: |
| References | |
| LER-75-022, LER-75-22, NUDOCS 8311080611 | |
| Download: ML20085M504 (5) | |
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f 1 1 P.O. Eo:: 351, Plattcville, Colorado 60651 January 22, 1976 Fort Uni * . S N. 4 % m% h t. %, (m\ 19 Mr. E. l' orris 1:oward, Director - w I!uclear Ecgulatory Co::tission Region IV
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<'f Offico of Inspection and Enforcenent #/ ittiObe' Suite 1000 -
Arlinr, ton, Tc::as 76012 1 FIF: Facility Operating License No. DPR-34 Dochet :!o. 50-257
Dear tir. Howard:
Enclosed please find a cooy of Unusu11 Event Report 17o. 50-267/75/22,
?reliminarf, au>citted per t':c requiret ents of the Teclutical Specif1-cstions. Also nicase find encioned one copy of tho' Licenseo Event report for Unusu.11 ': vent Report !*o. 50-267/75/22.
Very truly yours, Frederic'E. Start Superintendent, Nucicar Production Fort St. Vrain Euclear. Generating Station FES/dme cc: Mr. Poger S. Boyd 1/4
REPORT DATE: o January 22, 1976 o. UNUSUAL EVENT 75/22 Page 1 of 3 OCCURRENCE DATE: December 23, 1975 t TORT ST. VRAIN NUCI FAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/75/22 Preliminary IDENTIFICATION OF . OCCURRENCE: It has been 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 circu-lator static seal. This has been identified as an unusual event per Fort St. Vrian Technical Specifications, Section 7.6, Non-routine Reports,'Part,C) 2).
.s CONDITIONS PRINV ' 'q'i TO OCCURRENCE:
IY ~ Steady State Power Routine Shutdown 3 Hot Whutdown Routine Load Change Cold Shutdown X Other (specify) Refueling Shutdown Not applicable. Routine Startup
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The major plant parameters at the time of the event were as follows: Power RTR N/A Nth ELECT N/A We - 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-I Flow N/A f/hr.
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EK O . O l UNUSUAL EVENr 75/22 Page 2 of 3 l DESCRIPTION OF i OCCURRENCE: In reviewing the design adequacy of the primary coolant helium circulator's auxiliary systems, it has been discovered that an assumed failure (such as a line rupture) of a common portion of the buf fer helium system, might seriou' sly 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 FSAR. APPARENT CAUSE t OF OCCURRENCE: X Design Unusual Service Cond. Including Environ. 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 is postulated that both auxiliary loop surge tanks loose 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 includes automatically setting all four circulator static shutdown seals. At this point, a condition of temporary loss of forced circulation exists, with a critical need to immediately reestablish operation with at least one circulator. However, the depressurized surge tanks create an addition problem. -With pri-mary coolant pressure greater than 120 psig, the back pressure on the. engaged static seal is sufficient to prevent its release and the s'ubsequent return to operation of the helium circulator.- The conclusion is that some method of overecs'.ng the primary coolant back pressure on the engaged static seal is-needed.- . . CORRECTIVE . ACTION: ' A bank of helium bottles with a minimum pressure of l'500 psig and' the required ' controls will be installed in each auxiliary loop. The gas inventory will pro-
- vide a sufficient capacity to pressurize a circulator bearing cartridge-in each loop on an emergency, restart basis, and open the static shutdown seal. The-actuation of the emergency system will be~ accomplished manually in the control
-room. -
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&W USUAL EVENT 75/22 e ,
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( Page 3 of.3
, CORRECTIVE ACTION (continued):
Following completion of the installation, a test will be conducted under l simulated accident conditions, which demonstrates the ability of the system ! to provide the emergency restart.
' FAILURE DATA /SIMILAR REPORTED OCCURRENCES:
None PROGRAMMATIC IMPACT: None CODE IMPACT: None Submitted by. -- -r - H. W. Hilly /rd, Jr. i Technical Services.Su ervisor Reviewed by: 'vL'v } H. Larry Br'y p Superintendent, Operatibns l Approved by: JA s M wp Fjederic E. Swart - superintendent, Nuclear Production r e e a
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