PNO-IV-88-025, on 880404,following Manual Reactor Scram, Unplanned Release of Noble Gas Occurred When Relief Valve Opened to Relieve Pressure in Vent Line Between the Core Support Floor & Waste Gas Sys

PNO-IV-88-025:on 880404,following Manual Reactor Scram, Unplanned Release of Noble Gas Occurred When Relief Valve Opened to Relieve Pressure in Vent Line Between the Core Support Floor & Waste Gas Sys

ML20151B783
Person / Time
Site:	Fort Saint Vrain
Issue date:	04/05/1988
From:	Westerman T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
PNO-IV-88-025, PNO-IV-88-25, NUDOCS 8804110265
Download: ML20151B783 (1)

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. April 5, 1988 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PN0-IV-88-25 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The infonnation is as initially received without verification or evaluation, and is basically all that is known by the Region IV staff on this date.

FACILITY: Public Service Company of Colorado Licensee Emergency Classification:

Fort St. Vrain X Notification of Unusual Event Platteville, C0 Alert DN: 50-267 Site Area Emergency General Emergency Not Applicable

SUBJECT:

UNPLANNED RELEASE At 2:21 p.m. (MDT) on April 4,1988, Fort St. Vrain was manually scrammed from 72% power by the control room operators as a result of electrical power and voltage fluctuations on the main distribution grid for Colorado and othe western states. All systems functioned as required and all control rods were inserted. A normal plant cooldown was initiated.

Following the reactor scram, an unplanned release of noble gas occurred at 3:15 p.m. (MDT) for approximately 20 minutes and again from 5:10 p.m to 9:00 p.m. (MDT). The release occurred when a relief valve that functioned properly opened to relieve pressure in a vent line between the core support floor and the waste gas system. A minor leakage path exists between the primary system (Helium) and the fore support floor. The total release was a fraction of M of the Technical Specifications and was estimated to be 420 millicuries of noble gas and occurred via the plant vent system (a monitored path).

The licensee declared an unusual event at 5:10 p.m. (MDT) and terminated the e3ent at 9:00 p.m. (MDT) when the release was also terminated. The NRC resident inspectors were on site at the time of the event.

The utility has made a press release as a result of the declaration of an unusual event and the grid instability that occurred in Colorado and western states. Several fossil plants were also tripped off the grid in this portion of the country.

Fort St. Vrain is a high temperature helium gas cooled reactor.

The state of Colorado was informed by the licensee.

Region IV received notification of this occurrence by the Headquarters Duty Officer at 6:50 p.m. (CDT). Region IV has informed E00/NRR/PA.

This information has been confirmed with a licensee representative.

CONTACT: T. F. Westeman (FTS: 728-8145)

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