ML20209D710

Forwards Response to 860826 Request Re Static O-Ring Differential Pressure Switches Installed in Plant to Allow NRC Safety Analysis Review Prior to Startup.Addl Response to IE Bulletin 86-002 Provided Separately

ML20209D710
Person / Time
Site:	LaSalle
Issue date:	08/29/1986
From:	Allen C COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20209D714	List: ML20209D710 ML20209D729
References
2053K, IEB-86-002, IEB-86-2, NUDOCS 8609090413
Download: ML20209D710 (11)

Text

[m') One Commonwealth First National EdisonPlaza. Chicago, Illinois

, ( -. 7

't / Addreas Reply to: Post Omco Box 767 V Chicago. Illinos 60690 0767 August 29, 1986 Mr. Harold R. Denton U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, DC. 20555

Subject:

LaSalle County Station Unit 1 Information Regarding "SOR" Differential Pressure Switches NRC Docket No. 50-373

Dear Mr. Denton:

In a telecon with your staff on August 26, 1986, Commonwealth Edison was asked to supply additional information concerning the SOR

'itfferential pressure switches installed in LaSalle County Station Unit 1 to allow the staff to perform a safety analysis review for Unit I startup. We also were asked to describe the actions which have been taken to ensure these switches operate reliably and continue to operate within technical specification limits. This information is provided in the enclosure to this letter.

In addition, your staff requested a supplemental response to IEB 86-02 updating the information provided in our inititi response dated July 25, 1986. This response will be provided under separate cover to Region III in addition to the enclosure to this letter.

Plaase direct any additional questions you may have regarding this matter to this u?fice.

Very truly yours, 0Oscas C. M. Allen Nuclear Licensing Administrator 1m i

Enclosure cc: R. Bernero - NRR Dr. A. Bournia - NRR G. Wright - RIII Resident Inspector - LSCS 2053K h0DI 8609090413 860829 PDR ADOCK 05000373 llI G PDR

EXECUTIVE SUNIARY

, A. PURPOSE The purpose of this summary is to provide information concerning the SOR, l Inc., differential pressure switches installed in LaSalle County Station Unit 1 and to describe the actions that have been taken to ensure these switches operate reliably and operate within technical specification limits.

B. BACKGROUND SOR series 102 and 103 differential pressure switches were installed in LaSalle County Station Unit I during the first two quarters of 1986 as part of environmental qualification modifications. A total of 58 switches are installed in Unit 1. These switches are used to actuate various safety system functions including the reactor protection system, emergency core cooling system, and primary containment isolation system. The attached Table 1 lists the system application and function for cach SOR switch.

On June 1, 1986, LaSalle 2 experienced a feedwater transient that resulted in low water level in the reactor vessel (see Figure 1 for illustration of

~

water levels). One of four low-level trip channels actuated, resulting in a half scram. The operator recovered level and power operation was continued. However, subsequent reviews raised concerns that the level apparently had gone below the scram setpoint and the reactor scram system did not actuate. This event is described in more detail in reference 1.

After recalibrating the reactor protection system low level (level 3) switches, switch performance was tested by lowering the water level in the reactor (level drop test) and reading levels indicated on level transmitters when each of the four level 3 switches tripped. At 950 psig reactor pressure, the switches tripped at levels between 3.9 inches and 10.8 inches. At 0 psig reactor pressure, the switches tripped at levels between 10.7 inches and 13.5 inches. These measurements are relative to instrument zero, which is 161.5 inches above the top of active fuel. The Technical Specifications established the allowable trip point for level 3 at 11 inches above instrument zero. <

Testing of other SOR Model 102 and 103 differential pressure switches on Unit 2 used to actuate the emergency core cooling system, primary containment isolation system, and other engineered safety feature systems 7 revealed that these switches displayed the same type of behavior as the switches used for reactor protection system level 3.

3 i

DOCUMENT ID 41141/1265W

C. SPECIAL TESTS AND SBTPOINT REVISIONS The initial investigation to determine the source of the variability in SOR differential pressure switches setpoint concluded that additional special testing was required to quantify the setpoint variability. These

, setpoint characterization tests measured the shift in setpoint due to the l differences in static pressure between calibration and operation, the effects of cycling the switch during calibration, and the random repeatability of the switch setpoint. These tests were performed on a special test rig that allowed simultaneous testing at operating static pressure and the specified differential pressure setpoint. This Unit 2 testing program was described in detail in reference 2.

During the Unit 2 testing program, enough was learned about the behavior

, of the switches to develop a more refined calibration methodology that minimizes the offset from the last calibration "as-left" setting to the ,

next first-actuation trip. This methodology requires that each time the switch is cycled to obtain trip and reset values, the applied calibration differential pressure should first be reduced to zero (for switches with increasing trip points) or 100% of adjustable range (for switches with decreasing trip points). This form of cycling is more representative of actual process operation, and results in the highest expected trip values for the switch at any given setting. This method of calibration was used in the Unit 1 test program to put each switch into a known starting condition prior to the characterization testing on the special test rig.

The Unit 1 test program consisted of performing a static pressure cycling test (to determine repeatability) on all installed switches, and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> static pressure " soak" test performed on all switches, except for five of the eight ECCS minimum flow switches. (The five switches were not " soak" tested because the setpoint chosen for the function served by those switches was very conservative with respect to the measured static shift found on the three identical switches that were tested for this function.) The results of the tests for setpoint shift with static pressure and setpoint repeatability measured in the Unit I test program are presented in Table 2. The effects of cycling were confirmed and have resulted in revised calibration procedures.

Information justifying the validity of 24-hour test results was submitted l to the NRC by references 3 and 4.

l l

l t

DOCUMENT ID 41141/1265W l

C. SPECTAL TESTS AND SETPOINT REVISIONS (Continued)

On the basis of the setpoint characterization tests described in the preceeding paragraphs, setpoints of the LaSalle County Station Unit 1 SOR differential pressure switches have been revised to provide additional margin for static pressure snift and repeatability. The revised

setpoints and margins are listed in attached Table 3. These revisions will increase the margin between the existing Technical Specification allowable limit and the calibration setpoint, therefore Technical Specification changes are not necessary at this time. Note that for LaSalle Unit 1, 100% of the Reactor Level, Main Steam Line Break, and RHR/RCIC line break switches were tested and static offset and repeatability values were determined. This allows a less conservative setting of the switches than the Unit 2 bounding margins (which were used in Table 3) allowed. The availability of complete test data shows that in some cases that the worst-case measured static pressure offset was much smaller than the bounding value. The values shown in the table reflect the Unit 2 values, however these may be changed in the future to take advantage of the more complete test data.

D. CONCLUSIONS The setpoint variability of the SOR differential pressure switches installed in LaSalle County Station Unit I has been fully characterized and will be incorporated into new setpoints. In addition to the margins and bases for switch actuation included in the revised setpoints shown in attached Table 3, corrective actions listed in attached Table 4 will be completed. These actions ensure the SOR differential pressure switches will perform within Technical Specification limits with high rel:tability.

E. REFERENCES i Reference 1 - Letter to J.G. Keppler from C. Reed, dated July 1, 1986.

Reference 2 - Letter to H.R. Denton from C.M. Allen, dated August 8, 1986.

Reference 3 - Letter to H.R. Denton from M.S. Turbak, dated July 21, 1986.

8 Reference 4 - Letter to H.R. Denton from M.S. Turbak, dated July 23, 1986.

Reference 5 (Attached) - Letter to J. G. Keppler from I. M. Johnson containing revised response to I.E. Bulletin 86-02, dated August 29, 1986.

DOCUMENT ID 41141/1265W

TABLE 1 LASALLE COUNTY UNIT 1 LIST OF INSTALLED SOR DP SWITCHES Taq Number Service Range Setpoint Model Number B21-N024A,B,C,D Rx. Level 3 7"-100" W.C. 63.78" W.C. 103-B212 B21-NO31A,B,C,D Rx. Level 2 20-200" W.C. 143.3" W.C. 103-B203 B21-N037AB,BB Rx. Level 2 20-200" W.C. 145.5" W.C. 103-B203 CB,DB Rx. Level 2 20-200" W.C. 145.5" W.C. 103-B203 B21-NO37AA,BA Rx. Level 1 40-300" W.C. 200" W.C. 103-BB205 CA,DA Rx. Level 1 40-300" W.C. 200" W.C. 103-BB205 E22-N006 HPCS Min. Flow 5-35" W.C. 18.1" W.C. 103-BB202 E21-N004 LPCS Min. Flow 5-35" W.C. 11.01" W.C. 103-B202 E12-N010AA RHR LPCI "A" Flow 5-35" W.C. 6.2" W.C. 103-B202 AB Alarm 5-35" W.C. 13.3" W.C. 103-B202 BA RHR LPCI "B" Flow 5-35" W.C. 6.2" W.C. 103-B202 BB Alarm 5-35" W.C. 13.3" W.C. 103-B202 CA RHR LPCI "C" Flow 5-35" W.C. 6.2" W.C. 103-B202 CB Alarm 5-35" W.C. 13.3" W.C. 103-B202 B21-NO38A,B Rx. Level 3 7-100" W.C. 63.14" W.C. 103-B212 B21-N026AB,BB Rx. Level 2 20-200 W.C. 143.3" W.C. 103-BB203 CB,DB Rx. Level 2 20-200 W.C. 143.3" W.C. 103-BB203 E31-N008A,B,C,D Main Steam Line Break 100-500 psid 111 psid 102-B305 4

E31-N009A,B,C,D Main Steam Line Break 100-500 psid 111 psid 102-B305 E31-N010A,B,C,D Main Steam Line Break 100-500 psid 111 psid 102-B305 E31-N011A,B,C,D Main Steam Line Break 100-500 psid 111 psid 102-B305 l E31-N012AA,BA RHR Shutdown Cooling 20-200" W.C. 170" W.C. 103-B203 E31-N012AB,BB RHR Shutdown Cooling 20-200" W.C. 170" W.C. 103-B203 i

i E31-N007AA,AB RCIC Steam Hi Flow 20-200" W.C. 117" U.C. 103-B203 E31-N007BA,BB RCIC Steam Hi Flow 20-200" W.C. 87" W.C. 103-B203 l

E31-N013AA,BA RCIC Steam Hi Flow 20-200" W.C. 170" W.C. 103-B203 E31-N013AB,BB RCggg{ggm 20-200" W.C. 170" W.C. 103-B203 DOCUMENT ID 41141/1265W

TABLE 2 ,-

SUMARY OF SETPOINT CHARACTERIZATION TESTS RESULTS FOR UNIT 1 l24-HourStaticl 24-Hour Static l Repeatabilityl l lPressureTest l Pressure Shift l Test Sanple l l Switch Application l Sanele Size l Results l Size i Repeatability Results l l l l l 1 l l l l 1 l l l l l

-Reactor Vessel level 3 l 100% l0.9"-5.4"W.C.(1)l 100% l Less Than 2% l (6 switches) (6 switches)

-Feactor Vessel Level 2 100% l-0.9"-+5.0" W.C. 100%

l (12 switches)l l(12 switches)l Less Than 2% l

-Reactor Vessel Level 1 l 100% l2.9"-6.0"W.C. l 100% l l l (4 switches) l l(4 switches)l Less Than 2% l

-RHR/RCICSteamlineBreak)l l l l l

)l l l 1 -l

-RHRShutdownCoolingLine)l 100% l-6.9"-+6.3"W.C. l 100% l 0.3% to 3.3% (2) l

)l (12 switches)l l(12 switches)l l

-RCIC Steam Line Break )l l l l l l l l l 1 1 I l l l

-RHRLPCI-A,B,CMin. Flow)l l l l l

)l l l l l

-LPCS Min. Flow )l 37.5% l-2.08-+3.61"W.C.l 100% l 0.5% to 11% (2) l

)l (3 switches) l l(8 switches)l l

-1PCS Min. Flow )l l l l l

I l 1 I .

l j -Main Steam Line HI Flow l 100% l-1.3-7.7PSID l 100% l 0.1% to 0.7% l i l (16 switches)l l(16 switches)l l i

Notes: (1) Switches exceeding 3.0" W.C. were replaced with switches 3.0" W.C. or less.

(2) Safety action switches with repeatability exceeding 2% of adjustable range will be replaced with switches with 2% or less.

TABLE 3

.l LASALLE COUNTY UNIT 1 ,

SETPOINT CHARACTERIZATION TESTING CONCLUSIONS Switch Application l Margin from LCO l l Proposed l 1 (4)l Existing Tech l l Existing l New (6) l Static Shift l Repeatability l Spec. Drift l Total l L.C.O. lSetpoint l 1 l 1 I I

-Reactor Vessel Level 3 l 4.2" RWL l 2.6" RWL l 1.5" RWL I 8.4" RWL i11.0"RWL l19.4"RWL ,

I l l 1 l l

-Reactor Vessel Level 2 l 11.2" RWL l 5.0" RWL l 7.0" RWL I23.2"RWL l-57.0"RWLI-33.8"RWL l l l 1 l 1 '

-Reactor Vessel Level 1 l 11.2" RWL l 7.3" RWL l 7.0" RWL I25.5"RWL l-136.0"RWLi-110.5"RWL

l l l l l l

-RHR/RCIC Steamline Break l 8.0" W.C. l 3.6" W.C. l 5.0" W.C. l16.6"W.C. l128"W.C.l111.4"W.C. j l l I l 1 I l

-RHR Shutdown Cooling Line l 8.0" W.C. l 3.6" W.C. I 6.0" W.C. l17.6"W.C. l186"W.C.l168.4"W.C.  !

l I I l 1 l

-RCIC Steam Line Break l 7.2% rated flowl 3.0% rated flow l 5.0% rated flow l 15.2% rated l295% rated l280% rated ,

l l 1 l flow l flow lficw l I I I I I

-RHR LPCI-A,B,C Min. Flow l 237 gpm l 73 gpm I 450 gpm l 1427 gpml l550gpm l1977gpm i I I I I I

-LPCS Min. Flow l 233 gpm I 71 gpm l 110 gpm l 1079 gpm2 l640gpm l1719gpm i I I I l 1

-HPCS Min. Flow l 151 gpm l 50 gpm l 100 gpm l640gpm3 I900gpm i1540gpm i I I I l 1

-Main Steam Line HI Flow l 8.0 psid (5) l 5.4 psid (5) l 5.0 psid l18.4psid(5)l116psid l97.6psid(5) l I I I I l NOTES: Includes Additional Margin of 1) 666 gpm for LPCI 2) 664 gpm for LPCs and 3) 339 gpm for HPCS

4) For applications other than main steam line high flow, repeatability for each switch tested was less than 2%

of range; therefore 2% was used for repeatability. For mainsteam line high flow switches, repeatability of the most variable switch in service was used. Repeatability was calculated for each switch to bound 95% of the population with a 95% confidence level.

5) It is planned to inprove these values in the future by replacement of the waist perfonning switches with switches that have better repeatability and static offset perfonnance.

6) Since 100% of the switches were tested on Unit 1, the static offset and repeatabilities are known for every switch. This allows a knowledgeable setting of the switch which is not dependent on a bounding margin established for Unit 2 switches. The values shown in this column represent initial Unit I setpoints based on Unit 2 setpoints. They may be changed in the future to take advantage of the more complete test data.

! DOCUMENT ID 4114i/1265W

TABLE 4 LaSalle County Unit 1 CORRECTIVE ACTIONS

1. Final LaSalle County Station Unit 1 This Executive SOR Investigation Report Summary dated 8/29/86

2. Unit 1 Plow testing to verify ECCS prior to startup minimum flow switch setpoints

3. A reactor vessel level drop test will be Prior to startup performed at 0.0 psig in order to verify following system operability. The results of the current outage, and 950 psig level drop testing on Unit 2 at shutdown for the was successful in proving that operability second refueling of the scram function may be relied upon by outage.

adjusting the switch setpoints to take into account the results found in the SOR set-point characterization program. Additional thermal cycles, pressure tests and other challenges to the Unit 1 safety system equipment are not techr>1cally justified.

4. Complete calibration procedure revisions Week of 8-25-86

a. New setpoints including: static pressure shift, repeatability margin and drift margin.

b. New calibration methods including: The "as-fcund" setpoint will be the first actuation and during calibration the switch will be cycled from the appropriato 0% or 100% of differential pressure span to the setpoint.

c. "As-found" setpoint acceptance limits will be included into the procedures, and actions will'be defined for each limit. The limits and actions will be the following:

(1) Action Limit (a) Except Main Steam Line High Flow, 1 3% of adjustable range from new calibration setpoint.

(b) For main steam line high flow this limit was 1.5X repeatability of the most variable switch in service.

Repeatability was calculated for each switch to bound 95% of the population with a 95% confidence level.

DOCUMENT ID 41141/1265W

TABLE 4 (cont.)

LaSalle County Unit 1

4. Complete calibration procedure revisions (cont.)

c. "As-found" setpoint acceptance limits (cont.)

(1) Action Limit (continued)

(c) If this limit is exceeded, the next surveillance will be performed at the same interval as the last successful surveillance within this limit.

(d) If this limit is exceeded during the second consecutive surveillance, the switch will be scheduled for replacement within 14 days.

(2) Rejection Limit (a) i (2% of adjustable range + tech.

spec. margin for drift)

(b) For main steam line high flow switches this limit is (repeatability + tech.

spec. drift) for the most variable switch in service. Repeatability was calculated for each switch to 95% of the population with a 95%

confidence level.

(c) If this limit is exceeded the switch will be rejected, and appropriate actions will be taken in accordance with the LaSalle County Technical Specification.

5. Complete recalibration of switches with revised setpoints and revised procedures. Prior to startup from current outage.

6. Implement Increased Surveillance After startup from current outage.

a. Level 3 switches (6 switches) - Based on the successful two-week calibration performed on the Unit 2 Level 3 switches, in which all six switches were found to be within 1 0.6" W.C. of their initial settings, the surveillance cycle will be initially supplemented with more frequent inspections, as follows: Two of the four SCRAM switches (one in each channel) will be surveilled after one month. The other two SCRAM switches will be surveilled after the second month. The two ADS

$![$hSke#kYfbm$$t$ t D*eSNenEon

> satisfactoryresultsfrom$hese surveillances, the switches will then be surveilled on a quarterly basis.

DOCLEENT ID 41141/1265W

TABLE 4 (cont.) l l

LaSalle County Unit 1

b. Main Steam Line Break Switches (16 switches) - At least four of the main steam line (MSL) switches will be calibrated 4 weeks after startup. Of the remaining 12 switches, at least four of the MSL switches will be calibrated 8 weeks after startup. Of the remaining eight switches, at least four of the MSL j switches will be calibrated 12 weeks after startup. The maximum interval for each individual switch will be limited to a quarterly frequency.

c. Remaining switches (36 switches) - A sample (grouped by model numbers) representative of the remaining switches (approximately 1/3) will be calibrated 4 weeks after startup. Of the remaining switches, approximately 1/3 will be calibrated 2 months after startup. The remaining switches will be calibrated 3 months after startup. The maximum interval for each individual switch will be limited to a quarterly frequency. The representative samples will be chosen, where possible, to include a sampling of various switch model numbers.

7. Complete evaluation of alternative level sensing instruments to replace SOR l-1-87

a. Review requirements

b. Review vendor environmental qualification data.

c. Review vendor performance test data.

d. Recommend technically acceptable alternatives.

e. Complete preliminary conceptual design and obtain reviews and approval. General description i

of key features affecting design installation, operation and maintenance, and project plan.

E. Initiate detailed conceptual design.

8. Establish acceptance limits for new SOR Completed switches. The Purchase Order with SOR will be revised to require tests similar to setpoint characterization tests including i a 24-hour test and to require switches perform within the static shift and repeatability Itmits.

1 DOCUMENT ID 41141/1265W

Reactor Water Levels Figure 1-1 1

800 -

750 -

745 - Vessel llange Level 8 55.5 inches above instrument zero RCIC turbine tnp HPCS enjection valve close 700 -

Reactor feed pump trip Main turbine trip g 40.5 inches above instrument zero I648- Main steam line High-levet alarm 36.0 inches above instrument zero Normal reactor level 600 -

31 .5 inches above instrument zero 583(8) / 587.

f Low-levet alarm C

568(7) ,$$9(4) NcircWam Nw Wack peessne Bottom of steam 550  : Level 3 12.5 inches.above instrument zero dryer skirt

- 540(3)

Reactor scram 527.5- Instrument zero - PCIS groups 6 and 7

/ Feedwater 500 -

493.25 ADS low-level confirmation Recirculation pumps transfer to slow speed

-479.25 - Core spray 477.5(2) -

Level 2 50.0 inches below instrument zero 450 - PCIS groups 1. 2. 3 4 and 5 H PCS initiation HPCS diesel generator starts

- 416 RCIC initiation 400 - Recirculation pumps'inp l -

397.5(1)  : Level 1 129.0 inches below instrument zero 377.5 Division 1 and 2 diesel generators start 350 = 366 ,

LPCS initiation LPCI initiation

__ ___ ADS initiation 300 - L Level 0 211.5 inches below instrument zero Two-thirds core height Active tuel 250 -

ir

- 216 200 -

( j -181 - Recire. discharge %

A nozzle Recire. suction 172.5 nozzle 150 -

100 -

50 Vessel zero 0-695s.-17 Scale in inches above vessel zero.

07 39' I-10

.