ML20003C391

AO 50-219/74/22:on 740315,low Pressure Main Steam Line Pressure Switch RE23D Tripped at Pressure Less than Min Required Value of 860 Psig.Caused by Switch Repeatability & Design.Basis for Steam Line Low Pressure Setting Studied

ML20003C391
Person / Time
Site:	Oyster Creek
Issue date:	03/22/1974
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:
References
AO-50-219-74-22, NUDOCS 8103030317
Download: ML20003C391 (3)

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OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 l l

Abnormal Occurrence l Report No. 50-219/74/22 Report Date March 22, 1974 Occurrence Date March 15,1974 Identification of Occurrence Violation of the Technical Specifications, paragraph 2.3.7, low pressure main steam line pressure switch RE23D was found to trip at a pressure less than the minimum required value of 860 psig. This event is considered to be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15A.

Conditions Prior to Occurrence The plant was operating at steady-state power.

The major plant parameters at the time of the event were as follows:

Power: Reactor,1902 MWt Electric, 661 MWe Flow: Recirculation,15.3 x 104 gpm Feedwater, 7.10 x 106 lb/hr Reactor Pressure: 1020 psig Stack Gas: 40,600 pCi/sec Description of Occurrence On Friday, March 15,1974, at 1550, while perfonning a routine surveillance test on the four main steam line low pressure switches, it was discovered that RE23D tripped at 850 psig. This value is below the minimum required trip point of 860 psig which is derived by adding to the Technical Specification limit of 850 psig a 10 psig head correction factor.

The "as found" and "as left" switch settings were:

"As Found" Settings "As Left" Settings RE23A 865 psig 861 psig RE23B 864 psig 864 psig RE23C 865 psig 865 psig RE23D 850 psig 860 psig 7/03o303/7 . . .

o i Abnormal Occurrence No. 50-219/74/22 Page 2 Pressure switch RE23D was immediately recalibrated and rechecked to actuate at 860 psig.

Apparent Cause of Occurrence Design is considered to be a major factor contributing to this event. Switch repeatability is a recognized problem and work is in progress to formulate a final solution.

Analysis of Occurrence As indicated in the bases of the Technical Specifications, "The low pressure isolation of the Main Steam Lines at 850 psig was provided to giv; protection against fast reactor depressurization and the resultant rapid ccol-down of the vessel. Advantage was taken of the scram feature which occurs when the main steam isolation valves are closed to provide for reactor shutdown so that high power operation at low reactor pressure does not occur, thus providing protection for the fuel cladding integrity safety limit."

The adverse consequences of reactor isolation occurring at reactor pressure approximately 10 psig below the specified minimum value of 860 psig is limited to those effects attendant to a greater than normal reactor cool-down rate. The fuel cladding integrity safety limit only comes into effect for power operation at reactor pressures less than 600 psig or for power operation greater than 354 mkt with less than 10% recirculation flow. Therefore, the consequences of a 10 psig lower than normal reactor isolation and scram set point has no threatening effect whatsoever on the fuel cladding integrity.

The effects of a too rapid cool-down due to the lower isolation pressure are inconsequential since there is less .han 2 F difference between the saturatiot temperature for 860 psig and 850 psig.

Corrective Action Continuing corrective actions being taken at this time are as follows:

1. Investigation is being conducted into the basis for the steam line l low pressure setting of 850 psig. Development of a Technical

! Specification change to lower the set point will follow if results of l transient analyses indicate this possibility.

2. Recommendations to possibly reduce or eliminate the sensor set point

[ dhange problem have been received. It was reported that General Electric L tests on a pulsating line to simulate plant conditions show that pre-cycled Barksdale switches show improvement but that the switches still do not meet 1% repeatability. General Electric, therefore, recommended an Ashcroft switch as it is more accurate. The Ashcroft catalog number is 61 S 6080 BN20-06L-1028.

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Abnormal Occurrence No. 50-219/74/22 Page 3 As a result, one switch of each type (pre-cycled Barksdale and Ashcroft) has been purchased for test and evaluation at Oyster Creek. An Ashcroft switch is currently on hand and undergoing evaluation.

Failure Data Manufacturer data pertinent to these switches are as follows:

Meletron Corporation (Subsidiary of Barksdale)

Los Angeles, Califomia Pressure Actuated Switch Model 372 Catalog No. 372-6SS49A-293 Range 20-1400 psig Proof Psi 1750 G Previous Abnormal Occurrence Reports involving these switches are:

1. Letter to Mr. A. Giambusso from Mr. D. A. Ross dated December 24, 1973.

2. Abnormal Occurrence Report No. 50-219/74/1

3. Abnormal Occurrence Report No. 50-219/74/9

4. Abnormal Occurrence Report No. 50-219/74/10

5. Abnormal Occurrence Report No. 50-219/74/12

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