ML18081A450

Responds to IE Bulletin 79-21, Temp Effects on Level Measurements. Info Re Steam Generator Narrow Range Water Level,Pressurizer Water Level & Table of Leg Heatup Compensation Included

ML18081A450
Person / Time
Site:	Salem
Issue date:	10/05/1979
From:	Schneider F Public Service Enterprise Group
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 7911010019
Download: ML18081A450 (13)

Text

Frederick W. Schneider Vice President Pub I ic Service Electric and Gas Company 80 Park Place Newark, N.J. 07101 201 /430-7373 Production Mr. Boyce H. Grier, Director U.S. Nuclear Regulatory Commission Off ice of Inspection and Enforcement Region 1 October 5, 1979

---~6--3-l-P-a-E-k---Ave.~n~u~e~~-----:;-----.--~~~

King of Prussia, Pennsylvania 19406:-----------------------

Dear Mr. Grier:

NRC IE BULLETIN NO. 79-21 NO. 1 & 2 UNITS SALEM GENERATING STATION Pursuant to the subject bulletin, we hereby submit the attached response.

Although the bulletin addresses our operating plant~

Salem Unit No. 1, the setpoint and operating procedure revisions described in this response are also applicable to Unit No. 2 and will be implemented prior to its startup.

If you have any further questions on this matter, we will be pleased to discuss them with you.

Sincerely, Attachment CC:

Director, Office of Inspection

& Enforcement USNRC Washington, D.C. 20555

SALEM NUCLEAR GENERATING STATION NOS. 1 AND 2 UNITS NRC BULLETIN 79-21 RESPONSE TEMPERATURE EFFECTS ON LEVEL MEASUREMENTS

1.

Steam generator levels and the pressurizer lev.els are utilized for pro-tection system actuation and post accident monitoring tu*nctions. These are the only level measurements within the containment performing safety functions.

-~----Steam Generator Narrow Range Water Level Three instruments are provided for each steam generator.

An *open column reference leg is utilized in determining this measurement.

The following functions are performed:

A.

Initiation of turbine trip, feedwater isolation, and feedwater pump trip on high-high steam generator water level.

B.

Initiation of reactor trip on low steam generator water level in co-incidence with steam flow-feedwater flow mismatch.

C.

Initiation of reactor trip on low-low steam generator water level.

D.

Initiation of auxiliary feedwater system on low-low steam generator water level.

E.

Post accident monitoring for operator action.

Pressurizer Water Level Three instruments are provided for the pressurizer. A sealed reference leg is utilized in detennining this measurement.

The following functions are performed:

A.

Initiation of reactor trip on high pressurizer water level.

B.

Post accident monitoring for operator action.

2.

The effects of reference leg heatup, varying fluid pressure and potential flashing in the reference leg have been evaluated for steam generator level and pressurizer level measurements.

Calculations were made to determine the potential fostrument indication errors. The calculations were based on the instrument calibration data and design characteristics of the Salem plant. The results of our evaluation are presented in the attached Tables A through D.

Correction factors are provided for reference leg heatup and varying fluid pressure only. Reference leg boiling could occur following the depressurization of the steam generator which was affected by the high energy line break.

The remaining steam

.-------tlQner rs should not experience reference leg boiling in the steam generator level measuremen.

!Tes-e-'i-~s wil 1 provide suita.ble indi ca ti on for operator action/post accident monitoring.

3.

A review of setpoints and protection system actuation indicates that only the low-low setpoint of the steam generator level measurement results in a problem because of ambient temperature effects on the reference legs.

A review of the safety analyses for accident conditions indicates that the only high energy line rupture within the containment, for which the steam generator water level provides the primary trip function, is a feedwater line rupture.

For such a case, the low-low water level trip must be actuated at a setpoint level which is above the steam generator tubes. Thus, the trip setpoints must be at or above the value that would be indicated by the instruments when the actual level is just above the steam generator tubes. Because large steam generator pressure changes are not expected before the trip, only the reference leg heatup effects need be considered, and not the effects of system pressure changes.

Correction factors are required for the level setpoints to compensate for the reference 1 eg heatup effects.

The backup trip function for the feedwater line rupture is provided by the high containment pressure signal. In addition, this signal will initiate operation of the motor driven auxiliary feedwater pumps.

Therefore, re-visions to the level setpoints are only required to compensate for ref-erence leg heatup to the temperature at which the containment high pressure signal is received. A conservative upper bound for reference leg tempera-ture would be at the peak containment temperature reached following a

.t

• feedwater line break before the containment high pressure bi-stables are tripped.

Steam line break results provide an upper bound for a feedwater line break due to the design characteristics of the system at Salem.

Based on the results of the steam line break analysis for Salem presented in the response to FSAR Question 5.82, the containment high pressure set-point would be reached prior to a containment temperature of 240°F.

Assuming that the reference leg is at a~ ambient temperature of 240°F (a conservative assumption), the indication error bias is 5.7% of span.

The indication error bias is constant over the entire span for a partic-ular reference leg temperature.

The existing steam generator low-low level setpoint is 5%, and will require a revision to assure that the protection system actuation is initiated in a time frame consistent with the safety analysis. A setpoint change to 11% *wil 1 maintain ex is ting safety margins.. No other setpoint changes are required for the steam generator levels.

The safety analysis does not take credit for the pressurizer water level trip function following a high energy line rupture inside the containment.

It should be noted that the coincident pressurizer low level-low pressure safety injection actuation was revised to delete low level as described in our response to Bulletin 79-06A.

Setpoi nt changes will be made prior to Unit 1 returning to service from the present refueling outage and prior to startup for Unit 2.

The setpoint change may be temporary pending the results of an engineer-ing study of methods to eliminate the erroneous level indication through suitable design changes.

Potential solutions that are being considered are insulating the reference legs, sealed measurement systems that are not susceptible to the temperatures of interest, or temperature compensa-tion of the instruments. A timetable for implementation of other potential changes has not been established.

The present corrective action of setpoint revisions is adequate for maintaining safe plant operations.

Supplemental infonnation will be forwarded concerning this bulletin topic if any other corrective action is contemplated.

4.

Post accident operating procedures which require the operator to use steam generator level and pressurizer level indication will be revised to re-flect the infonnation presented above.

Cautionary statements will be included alerting the operators of the potential erroneous level indica-tion and actions that should be taken.

Correction curves will be provided for the operator's use.

Procedure revisions for this item will be com-pleted prior to Unit 1 returning to service from the present refueling outage.

Operator training concerning this particular topic will be com-pleted within one month, by November 5, 1979.

The changes in procedures and operator training will be completed prior to startup of Unit 2.

JPG:gmv

SALEM GENERATING STATION NOS. l AND 2 UNITS RESPONSE TO NRC BULLETIN 79-21 TABLE A STEAM GENERATOR LEVEL INSTRUMENTATION REFERENCE LEG HEATUP COMPENSATION Reference Leg Ambient Temperature Correction to Steam Generator Level

% of Span 120°F 200°F 240°F 300°F 350°F oi

].5i 5.7~

9.6i 13.4%

Basis:

Reference Leg Calibration Temperature Pressure 120°F 805 psia Example:

Calculations assumed constant steam pressure with varying reference leg temperature.

0 Containment ambient temperature is 240 F.

Instrument indicates a level of 33~.

Assuming reference leg has reached containment ambient temperature, the actual level in the steam generator is lower at 27.3%.. Steam pressure is assumed to remain approximately the same (no large changes).

SALEM GENERATING STATION NOS. l AND 2 UNITS RESPONSE TO NRC BULLETIN 79-21 TABLE. B STEAM GENERATOR LEVEL INSTRUMENTATION REFERENCE LEG COMPENSATION DUE TO STEAM PRESSURE Steam Generator*

Instrument Indicated Pressure Level 1000 psia

5. 7'fo 32.5'{o

48. 7'fo 805 psi a 5%

33%

50%

600 psi a 4.3%

33.73 51.5%

400 psi a 3.73 34.6%

53.3'fo 200 psi a 3.2%

36.0%

55°9%

Basis:

Reference Leg-Calibration Temperature 120°F Pressure 805 psia Calculations assumed constant reference with varying steam pressure.

Actual Level 5~

331' 5o'{o 5%

33~

50%

5%

33%

50%

5%

33%

50%

5%

33%

50%

leg temperature

1--**-.--.

I I

SALEM GENERATING STATION NOS. l AND 2 UNITS RESPONSE TO NRC BULLETIN 79-21 TABLE C Pressurizer Level Instrumentation Reference Leg Heatup Compensation Reference Leg Ambient Temperature Correction to Pressurizer Level

% of Span 120°F 200°F 240°F 300°F 350°F Basis:

Example:

Reference Leg Calibration Temperature Pressure O°/c 5.33 8.7%

14.6%

20.3%

120°F 2250 psia Calculations assumed constant pressure with varying reference leg temperature.

Containment ambient temperature is 24o°F Instrument indicates a level of 30%.

Assuming reference leg has reached containment ambient temperature, the actual level in the pressurizer is lower at 21.33.

Pressurizer pressure is assumed to remain approximately the same (no large change).

SALEM GENERATING STATION NOS. l AND 2 UNITS RESPONSE TO NRC BULLETIN 79-21 TABLE D Pressurizer Level Instrumentation Reference Leg Compensation Due to Pressurizer Pressure Pressurizer Instrument Indicated Actual Pressure 2500 2250 2000 1500 1000 500 100 Basfs:

Level 21.83 48.53 20%

503 18.63 5.5 16.93 55.0%

lE.1%

59.13 16.23 64.63 18%

72.93 Reference Leg Calibration Temperature Pressure Level

201, 50%

20%

50%.

20%

503 20%

50%

20%

50%

20%

50'%

20%

50~

2250 psia Calculations assumed constant reference leg temperature with varying pressurizer pressure.

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