ML20215C687

Confirmatory Vessel Water Level Drop Tests (Lst 86-183)

ML20215C687
Person / Time
Site:	LaSalle
Issue date:	12/02/1986
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20215C684	List: ML20215C681 ML20215C687
References
NUDOCS 8612150334
Download: ML20215C687 (5)

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ATTACHIENT A , ,

- / i; LASALLE COUNTY STATION UNIT 2 '

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CONFIRMATORY VESSEL WATER LEVEL Df0F TESTS ,

(LST 86-183) '

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• Introduction >

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 : I, Three Level Drop tests were run on LaSalle Unit :2 prior to' sta'r,tup.

The O psig Test was run on July 31, 1986 in accordance w?.ch the preapproved' test plan LST-86-174, and the 950 psig and 500 psig tests were run on August 10, 1986 in accordance with the pre-approved' test plan LST-86-183. A ~

copy of the test plans and the observed results are filed with the tesc / <

report at the station. A formal 10 CFR 50.59' review dated July 19,. 1986' concluded that the elevated pressure tests could be performed WP.hir the '

I existing limits of the Technical Specification. i e .~.t The scope of the testing covers four level 3 differential ress no switches used as water level sensors in the reactor protection syste1 (RPS)~

and two Level 3 ADS permissive logic switches. .A scran actiontis J '

accomplished when the decreasing vessel level 2d tains the setpo'.nt of the /

scram switches per a 1:2:2 logic arrangement. The two level 3 differentisl' pressure switches are used to establish permissivd logic actions in the -

Automatic Depressurization System (ADS), one in each of the two ADS' groupings.  ;

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Purpose *

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The purpose of these tests was to demonstrats OPERABILITY of the level 3 scram and ADS low level sensors to confirm SOR swithh (trip) action at or near the desired instrument setpoints when the vessel sater level reaches the switches' desired setpoint. j t

Test Description The 0.0 psig test was conducted by placing.each switch into its calibrated condition using the new setpoint (+19.4" RWL), and then ,

controlling reactor water level via blowdown flow to the condenser thrope,h Reactor Water Cleanup System.

For the pressurized tests, the' reactor was operated in a critical condition at or near zero power with the vessel pressurized'io 950 + 50;pnig for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to obtaining the daya. "All rods in" was used to '

indicate that the scram function occurred.

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r Both the wide range and narrow range vessel water level recorders were operating during the level drop test. The Startree transient data system was also utilized for data gathering.

Water level for the pressurized zero-power condition was controlled by control rod drive leakage flow (approx. 20 gpm).

The water level was decreased until all four level 3 RPS channels tripped and until both ADS permissive switches actuated. The level was then increased to record the reset points of all the switches.

The reactor pressure was then allowed to decrease to 500 1 50 psig for the second data run. Because the decay heat of the core was low, the pressure decay rate following scram was very rapid even with the MSIV's closed and steam leakage (MSL drains, RWCU, etc.) closed off. The reactor attained 500 psig within 17 minutes of the initial scram of this test.

With the reactor pressure at 500 1 50 psig, the startree transient data system was indexed and placed in SCAN position to record data. CRD leakage flow was utilized to control vessel level at a slowly decreasing rate so that closure of each differential pressure switch could be recorded. After the 500 psig trip actuations occurred, the level was then increased above the trip points to record the reset values for each switch.

The reactor was maintained in its suberitical condition until the data were evaluated and approval to startup was received.

Results Test LST-86-174 (0.0 psig Level Drop Test) was performed satisfac- ,

torily. The switches had been set to trip at +19.4" RWL, and when the reactor water level was lowered, the six switches ranged in trip actuation from +19.0" RWL to +20.7" RWL.

Test LST 86-183 was performed satisfactorily at two pressures, 950 psig and 505 psig. At each pressure water level was lowered at approximately 7 inches per minute until each of the Level 3 switches tripped.

In both of the pressurized level drop sequences, each water Level 3 switch actuated prior to the tech spec nominal trip setpoint of +12.5 inches Reactor Water Level. Tables 1 and 2 indicate the trip points observed during the tests. Data are in vessel inches of the operator's narrow range scale.

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i The data for 950 psig reactor pressure displayed a static pressure offset as anticipated. The magnitude of this offset was close to the offset valte observed during the extensive setpoint characterization testing at LaSalle. Switch 2B21-NO38A, which tripped at 14.5" was noted to have larger than predicted static offset. This value was still within the acceptable range, however.

Testing at 500 psig reactor pressure began about 17 minutes after completion of the 950 psig test ended. The observed setpoints differed in the conservative direction from those at the 950 psig conditions. This was apparently due to:

1. Reduction in applied static pressures between 950 and 505 psig causes the trip actuation to have a lesser magnitude of static pressure offset. The SOR setpoint characterization program established a total static shift bound from ambient pressure (0 psig) to service pressure (1000 psig). This was measured at 4.2 in RWL. The specific fraction of this bounding value action between 0 and 500 psig had not been measured previously nor accounted for in establishing a predicted value for the 500 psig point.

2. The "first-to-second" cycle shift which was represented in the short time interval between the 950 psig the 500 psig sequences caused the setpoints to move further in the conservative direction. This effect had been observed in prior testing which showed that the second actuation of the GOR dp switch within a short time period (about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) occurs at a more conservative setpoint than the first actuation.

These combined effects had not been pre-analyzed in an estimate of the expected values for the 500 psig test condition because it was observed that the 1st to 2nd cycle shift is always in the conservative direction, and that only the 1st actuation is relevant. The RPS circuit functions on the first actuation and the ADS circuit is enabled by the level 3 closure, but controlled by the Level 1 switch setpoint. Subsequent actuations (second cycles and beyond) do not affect the operation or function of any equipment.

Conclusions The following conclusions can be drawn from the preceding test information:

1. Actuation of Level 3 switches was demonstrated to occur at or above the Tech. Spec NTSP of +12.5" RWL for instruments at all reactor vessel pressures.

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2. The SOR differential pressure switches behave as expected for first cycle actuations and more conservatively for subsequent actuations.

3. The setpoint stability for level 3 indication was conservatively demonstrated under current Tech Spec constraints.

Summary The confirmatory vessel water level drop tests for level 3 differential pressure switches produced results that are consistent with the SOR setpoint characterization tests being run at LaSalle.

The predicted and actual mean trip points at the service pressure of 950 psig tracked closely. At 505 psig, the observed trip actuations showed that when pressure proration of the 1000 psig measured static offset was included and an adjustment was made for the difference between first and second actuations of the switch, the switch will behave in an even more conservative manner.

This confirmation by test means that measured static offset, instrument repeatability, calibration accuracy, etc. can be used to characterize the performance of the SOR differential pressure switches.

Further, this level drop test confirms that the requisite safety actions will occur within the approved Technical Specification limiting values.

2466K

TABLE 1 Summary of Test Results from LST-86-174 conducted 7/31/86 "0.0 PSIG LEVEL DROP TEST" Switch Tag # "As-Left" 0.0 Psig Calibration Level Drop Test "W.C./"RWL Switch Actuation 2B21-N024A 58.9 / 19.4 19.5" RWL 2B21-N024B 58.9 / 19.4 19.0" RWL 2B21-N024C 58.9 / 19.4 19.2" RWL 2B21-N024D 59.0 / 19.3 20.7" RWL 2B21-NO38A 58.9 / 19.4 20.0" RWL 2B21-N038B 58.9 / 19.4 19.7" RWL TABLE 2 Summary of Test Results from LST-86-183, conducted 8/10/86 Swtich Tag # Predicted

• Trip 950 Psig 500 Psig Actuation at Level Drop Test Level Drop Test 1000 Psig Switch Actuation Switch Actuation 2B21-N024A 17.3" RWL 16.5" RWL 21.7" RWL 2B21-N024B 16.0" RWL 15.3" RWL 19.0" RWL 2B21-N024C 16.6" RWL 17.3" RWL 25.5" RWL 2B21-N024D 17.9" RWL 16.7" RWL 24.0" RWL 2B21-NO38A 18.5" RWL 14.5" RWL 21.9" RWL 2B21-NO38B 16.6" RWL 14.8" RWL 20.6" RWL

• Predicted Value was determined by subtracting the as-measured static pressure offset (from the setpoint characterization program) from the "as-left" calibration setting.

2466K