Information Notice 1979-29, Loss of Nonsafety-Related Reactor Coolant System Instrumentation During Operation

Loss of Nonsafety-Related Reactor Coolant System Instrumentation During Operation

ML031180187
Person / Time
Issue date:	11/16/1979
From:	NRC/IE
To:
References
IN-79-029, NUDOCS 7910250508
Download: ML031180187 (3)

SSINS No.: 6300

Accession No.:

791025049'T

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D. C. 20555 November 16, 1979 IE Information Notice No. 79-29 LOSS OF NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION DURING

OPERATION

This notice contains information regarding a loss of reactor coolant system

instrumentation as a consequence of a failure of a static transfer switch to

transfer to an alternate supply.

At 3:15 p.m. on November 10 with Unit 3 of the Oconee Station at 100 percent

power, the main condensate pumps tripped, apparently as a result of a technician

performing maintenance on the hotwell level control system. This led to

reduced feedwater flow to the steam generators, which resulted in a high

reactor coolant system (RCS) pressure reactor trip and simultaneous turbine

trip at 3:16:57 p.m. At 3:17:15 p.m., the inverter power supply, nonsafety- related, feeding all power to the integrated control system (ICS) tripped and

failed to automatically transfer its loads from the DC power source to the

regulated AC power source. The inverter had tripped due to blown fuses, resulting in loss of RCS indicators and recorders in the control room, except

one wide range RCS pressure recorder.

This condition existed for approximately three minutes, until an operator

could reach the equipment room and switch the inverter manually to the regulated

AC source. As a result of the power failure to the ICS, all valves controlled

by the system assumed their respective fail positions. This resulted in a

cool down of the RCS to 1635 psi and 530 degrees F. The ooerator, expecting

this condition, started all makeup pumps and ooened the associated high

pressure injection valves to the RCS which limited the rate of RCS pressure

reduction and associated reduction in pressurizer level. At 3:20:42 p.m.,

power was restored to the ICS and RCS conditions were restored.

Although RCS cooldown limits were exceeded, the pressurizer and steam

generators did not go dry, and at least 79 degrees F subcoolinq was maintained

during this event. No engineered safety features actuation setpoints were

reached, and, except for the components discussed above, no component malfunc- tions occurred.

The licensee has installed a redundant electromechanical transfer switch

between the loads and the regulated supply. This switch will actuate and

power the loads from the regulated supply should the original static switch

fail to transfer.

Longer term resolution of the need or desirability to seoarate these instruments

onto diverse electrical supplies or to provide redundant instrumentation

display channels for operator use from essential power supplies are also under

IE Information Notice No. 79-29 November 16, 1979 consideration. It is anticipated that further MRC evaluations will result in

issuance of an IE Circular, Bulletin, or NRR Generic letter in the near future

which will recommend or request specific applicant or licensee actions.

This Information Notice is provided to inform licensees of a possibly

significant matter. It is expected that reciDients will disseminate the

information to all operational personnel working at their licensed facilities.

If you have questions regarding this matter, please contact the Director of

the appropriate NRC Regional Office.

No written response to this Information Notice is required.

IE Information Notice No. 79-29 Enclosure

November 16, 1979

RECENTLY ISSUED

IE INFORMATION NOTICES

Information Subject nate Issued To

Notice No. Issued

79-28 Overloading of Structural 11/16/79 All power reactor facilities

Elements Due to Pipe Support with an OL or CP

Loads

79-27 Steam Generator Tube 11/16/79 All power reactor facilities

Ruptures At Two PVIR holding OLs and CPs

Facilities79-12A Attempted Damage To New 11/9/79 All Fuel Facilities, Fuel Assemblies research reactors, and

power reactors with an

OL or CP

79-26 Breach of Containment 11/5/79 All power reactor facilities

Integrity holding OLs and CPs

79-25 Reactor Trips At Turkey 10/1/79 All power facilities with

Point Units 3 And 4 an OL or a CP

79-24 Overpressurization Of 10/1/79 All Dower reactor facilities

Containment Of A PWIR Plant with a CP

After A Main Steam Line

Break

79-23 Emergency Diesel Generator 9/26/79 All power reactor

Lube Oil Coolers facilities holding OLs

and CPs

79-22 Qualification of Control 9/14/79 All power reactor

Systems facilities with

operating licenses

and construction permits.

79-21 Transoortation and Commercial 9/7/79 All power and research

Burial of Radioactive Material reactors with OL's

79-20 NRC Enforcement Policy 9/7/79 All Holders of Reactor

(Rev. 1) NRC Licensed Individuals OLs and CPs and Production

Licensees with Licensed

Operators