ML19309A342

AO 74-06:on 741007,operator Tripped Reactor Following Loss of Condenser Vacuum & Shutting of Turbine Bypass Valves. Main Steam Valve Lifted.Cause Not Stated.Operator Manually Initiated HPI to Regain Pressure Level

ML19309A342
Person / Time
Site:	Rancho Seco
Issue date:	10/08/1974
From:	Reinaldo Rodriguez SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:
Shared Package
ML19309A338	List: ML19309A337 ML19309A342
References
NUDOCS 8003270798
Download: ML19309A342 (1)

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.RJR 74-389 October 8, 1974

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Mr. R. H. Enge en

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U. S. Atomic Energy Commission 1990 No. California Boulevard Wa'Inut Creek Plaza, Suite 202 Walnut Creek, California 94596 Re: ABC Docket No. 50-312

. Rancho Seco Nuclear Generating Station, Unit No. 1 Abnormal Occurrence No. 74-6

Dear Mr. Engelken:

This letter is to report Abnormal Occurrence No. 74-6.

At approximately 1110 on October 7, 1974, while operating at 15% reactor power, the Operator tripped the reactor following a loss of condenser vacuum and the shutting of the turbine bypass valves.

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ensuing transient a main steam relief valve lif ted and continued to blow down for approximately five minutes. This heat load on t!e reactor coolant system. caused a rapid cooldown condition ev'sulting in a decreasing pressurizer level. The Operator manually initiated hiQ pressure injection to regain pressurizer lev'e1. The high pressure injection initiation also started the auxilia.. feedwater pumps which contributed additionally to the cooldown.

Upon regaining pressurizer IcVel control high pressure injection and auxfliary feedwater flow vero secured at approximately 1130. The minimum reactor coolant water tempessture reached approximately 408* at this time.

However, this temperature change was affected by injecting cool water via the high pressure injection system. At 1200 the reactor coolant system temperature had returned to approximately 470*.

Therefore, over an approximate one hour period, the actual system temperature had changed by about 110*.

The Technical Specifications call for a-100* per hour cooldown rate maximum, neer

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