ML19347C806

AO 50-219/74/1:on 740104,low Pressure Main Steam Line Pressure Switch Trip Setpoint of 850 Psig Determined Incorrect & in Violation of Tech Specs.Caused by Design, Procedure & Unusual Svc Condition

ML19347C806
Person / Time
Site:	Oyster Creek
Issue date:	01/14/1974
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:
References
AO-50-219-74-1, NUDOCS 8103040718
Download: ML19347C806 (4)

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y OYSTER CREEK NUCLEAR GENERATING STATION FORKED RIVER, NEW JERSEY 08731 Abnormal Occurrence Report No. 50-219/74/1 Report Date:

January 14, 1974 Occurrence Date:

January 4,1974 i

1 j Identification of Occurrence:

' Violation of the Technical Specifications, paragraph 2.3.7,- low pressure main steam line pressure switch (RE23C) was found to trip at a pressure less than 850 psig. . Additionally, in the investigation and i review of this_ event by the PORC, it was determined that an instrument sensing line head correction of 9 to 10 psig was not accounted for in the original switch trip set point of 850 psig, thus resulting in a condition whereby all the RE23 sensors have been set in violation of i

this specification since initial startup. This event is considered to

! be an abnormal occurrence as defined in the Technical Specifications, paragraph 1.15A and G.

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 - Core, 1830 MWt J Elec. , 642 MWe (g)

( Flow - Recirc., 60.2 x 106 #/hr.

! Feed., 6.77 x 106 # /hr.

Stack Gas - 24,000 pCi/sec.

I Description of Occurrence:

1 On Friday, January 4,1974, at 1105, .while performing routine surveillance i testing on the four main steam line low pressure switches, it was discovered that RE23C tripped at 841 psig. This was 9 psig below its set point of 850 psig. As part of the review process for this occurrence, it was dis-covered that the 850 psig set pressure did not take into account the instru-ment sensing line head correction. To account for this factor, the switch settings should have been as follows:

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Abnormal Occurrence Report No. 50-219/74/1 Page 2 RE23Al- 859 psig RE23B - 860 psig RE23C - 859 psig RE23D - 860 psig As found switch settings were:

RE23A . 850 psig RE23B - 851 psig -

RE23C - 841 psig RE23D - 851 psig

. Apparent Cause of Occurrence:

Design, procedure and unusual service condition are factors contributing to the cause of this event.

Sensor drift is a recognized problem and work is in progress to formulate a final solution. An investigative program has been initiated by the manufacturer, but as yet, a formal report of the results has not been issued.

4 The failure to properly account for the instrument sensing line head pressure has been attributed to an apparent improper application of the

Technical Specification requirements.

Analysis of Occurrence:

l As indicated in the bases of the Technical Specification, "The low pressure

j. isolation of the main steam lines at 850 psig was provided to give protection

against fast reactor depressurization and the resultant rapid cooldown i 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 L limit."

The adverse consequences of reactor isolation occurring at reactor pressures approximately 9-10 psi below the specified minimum value of 850 psig is

limited to those effects attendant to a greater than normal reactor cooldown 4

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 MWt with less than 10% recirculation flow. Therefore, the consequences of a 9-10 psi Iower than normal reactor isolation and scram set point has no threatening effect whatsoever on the fuel cladding integrity.

The effects .of a too rapid cooldown due to the lower isolation set pressure are inconsequential cince there is only about l'F difference between the saturation temperature for 850 psig and 840 psig.

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Abnormal Occurrence Report No. 50-219/74/1 Page 3 The adverse safety effect of RE23C actuating at 841 psig is in the loss of system redundancy. The other three sensors, RE23A, B, and D, would have limited the adverse consequences to those previously discussed.

Corrective Action:

The pressure switch RE23C, upon discovery of the condition, was recalibrated and checked to actuate at 852 psig.

The following actions are planned to prevent repetition of this event:

1. Evaluate " hydraulic noise" data collected and conduct further -

testing to determine whether, as an interim measure, the operating

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set point can be incrcased above the 850 psig plus head correction value, and still provide some reasonable operating margin to avoid spurious trips. (Letter to Mr. A. Giambusso from Mr. D. A. Ross ,

dated December 24, 1973.) It should be noted that the sensors have not been recalibrated to take into consideration the head correction factor as of this' time. In making this decision, consideration was given to the test data already collected and the very minimal adverse safety significance of a 9-10 psi lower than required set pressure.

2. To insure the avoidance of spurious trips, pursue an investigation into the basis for the steam line low pressure setting of 850 psig and develop a Technical Specification change to lower the set point if results of transient analyses indica;e this possibility.

3. Evaluate vendor recommendations as socn as they are available to pcssibly reduce or eliminate the sensor set point drift problem.

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

Failure Data:

Manufacturer data pertinent to these switches are as follows:

Meletron Corporation (subsidiary of Barksu" ale)

Los Angeles, California Pressure Actuated Switch Model 372 Catalog #372-6SS49A-293 Range 20-1400 psig Proof psi 1750 G i

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ADDENDUM TO ABNORMAL OCCURRENCE REPORT NO. 50-219/74/1 On Thursday, January 10, 1974, prior to recalibrating the low pressure main steam line sensors to take the head correction factor into account, a surveillance check was again performed on these sensors. In addition, set point repeatability of the sensors was also checked by observing two consecutive trip points on the test. The following results were obtained:

Final "As Left" Test #1 Test #2 Test #3 Set Point RE23A 832 840 --- 860 RE23B 845 840 --- 860

~RE23C 855 875 875 .

860 RE23D 845 845 --- 860 Upon reviewing the results of this surveillance check on Friday, January 11, 1974, it was decided to perform the check again for repeatability. The "as found" set points of this calibration check yielded th( following results:

Before Calibration Test #1 Test #2 After Calibration RE23A 862 862 860 RE23B 860 860 860 RE23C 860 860 860 RE23D 850 851 860

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