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AO 50-267/74-21B:on 741121,high Pressure in Gas Waste Vacuum Tank Lifted Relief Valve Allowing Release of 700 Scf Uncontaminated Gas.Caused by Operator Error.Inlet Valve Seats Will Be Replaced W/Soft Seats
	ML20086B115
Person / Time
Site:	Fort Saint Vrain
Issue date:	09/26/1975
From:	Brey H, Hillyard H, Swart F; PUBLIC SERVICE CO. OF COLORADO
To:	;
Shared Package
ML20086B083	List: ML20086B079; ML20086B100; ML20086B107; ML20086B115; ML20086B123; ML20086B129;
References
	NUDOCS 8311170059
	Download: ML20086B115 (4)
	v • d • e

l O O~

REPORT DATE: J 2tspber 26. 1975 ABNORMAL OCCURRENCE 74/21B Page 1 of 4 OCCURRENCE DATE: November 21, 1974 M)RT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 ,

REPORT NO. 50-267/74 /21B Final IDENTIFICATION OF OCCURRENCE:

November 21, 1974, *gh pressure in the gas waste vacuum tank ruptured u d u. u uuo u tted a relief valve allowing an unauthorized release

'of approximately 700 SCF of uncontaminated gas to the reactor building ventilation system. This is identified as an abnormal occurrence per Technical Specifications 2.1 (c).

CONDITIONS PRIOR Steady State Power Routine Shutdown

~

TO OCCURRENCE:

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:

Power, RTR N/A WLh ELECT N/A We Secondary Coolant Pressure N/A psig .

Temperaturc N/A *F Flow N/A *F Primary Coolant Pressure O psig 8311170059 760903 Temperature 135 .F Core Inlet PDR ADOCK 05000267 S pon 135

F Core Outlet

~

Flow 'O

/hr.

9

O O' ABNORMAL OCCURRENCE 74/21B

- Page 2 of 4 DESCRIPTION OF .

OCCURRENCE:

While venting down the helium purification regeneration systea, to the gas waste vacuum tank, at the conclusion of the regeneration of "A" low temperature adsorber, high pressure on "A" gas waste surge tank uas alarmed.

The reactor operator immediately switched to the "B" tank but the inlet valve (HV-6336) to "B" surge tank had been handjacked shut, effectively shutting off the discharge flow path' of both gas waste compressors and lif ting the relief valves on the discharge of the compressors. The resulting abrupt pressure increase in the vat;uum tank. caused the rupture. disc and safety valve to be blown, releasing = 700 SCF of gas to the ventilation system exhaust. The ventilation exhaust is monitored and these instruments showed no detectable change in count rate. Subsequent lab analysis of the "A" surge tank contents contained that no detectabic activity was present in the gas.

APPARENT CAUSE OF OCCURRENCE: X Design Unusual Service Cond.

Including Environ.

Manufacture Component Yailure Installation /Const. Other (specify)

X Operator X Procedure ANALYSIS OF OCCURRENCE:

Design: The isolation valves at the inlet to each gas waste surge tank have leaked in the past and a practice has been established to set the handjack on a valve during a release from the tank to prevent inleakage and release of unanalyzed gas. The handjack was set but not' released af ter the tank was empty.

Operator: A hold tag should have been placed on the handswit<;h to alert the ,

operator that the handjack on IIV-6336 was ' set closed.

Procedtire: The valvc list does not specifically list a check of handjack re-moval or a test of valve operation.

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ABN0letAL OCCURRENCE 74/21B Page 3 of 4 t

CORRECTIVE -

ACTION:

Des g : A change Notice (#101) has been issued to replace the seats in the inlet valves to the gas waste surge tanks with soft seats. A good seal in these valves will make the use of the handjack unnecessary.

Change Notice #91 issued to change the wiring so either llV 4335 or llV-6336 will always be open has been cancelled. Field Change Notice #2655 has been issued by Concral Atomic Company to interlock flow from the regeneration l l

' system with vacuum tank pressure to prevent overpressurization of the vacuun tank. Referring to the attached drawing, PV-2352 will close whenever the vacuum tank pressure reaches 13 psia as sensed by PSit-6315. This will pre-vent large additionn to the gas vaste system inventory f rom the regeneration system at a time when the vacuum tank is not being properly evacuated.

Operator: Operators have been issued a memo to place a "Il0LD" tag on the tank selector switch when a handjack is set on either valve.

Procedure: The System Operating Procedure valve list has been modified to ,

, call for handjack removal af ter the discharge is complete and includes a test of valve operation. This step will be removed af ter the sof t seat

< valves at the tank inlet are installed and proven to be leak free.

FAILURE DATA /SIMILAR REPORTED OCCURRENCES:

1 i

Nonc CODE IMPACT:

Nonc ,

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9 Submitted by:

Harvey W.11& lyard,j_r J.

_J

> Technical Services Supervisor Reviewed by: L _

w C4

11. Larry B cy Superintendent, Operations Approved by: f 2/ hp onM/

F cderic E. Swart.

uperintendent, Nuclear Production 9

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