05000272/LER-1979-050, Forwards Updated LER 79-050/01X-1

Forwards Updated LER 79-050/01X-1

ML18081A659
Person / Time
Site:	Salem
Issue date:	11/10/1979
From:	Librizzi F Public Service Enterprise Group
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML18081A660	List: 05000272/LER-1979-050, Forwards Updated LER 79-050/01X-1 05000272/LER-1979-050-01, Westinghouse Notified Util That Heatup of S/G Level Measurement Ref Legs Presents Potential Safety Problem During Accident Conditions.Caused by Design Deficiency.Changed low-low Setpoint
References
NUDOCS 7912040338
Download: ML18081A659 (5)

LER-1979-050, Forwards Updated LER 79-050/01X-1

Event date:
Report date:
2721979050R00 - NRC Website

text

e OPS~G Public Service Electric and Gas Company 80 Park Place Ne1Nark. N.J. 07101 Phone 2011430-7000 Mr. Boyce H. Grier Director of USNRC November 10, 1979 Off ice of Inspection arid Enforcement Region 1 631 Park Avenue King of Prussia, Pennsylvania 19406

Dear Mr. Grier:

LICENSE NO. DPR-70 DOCKET NO. 50-272 REPORTABLE OCCURRENCE 79-50/0lT SUPPLEMENTAL REPORT Pursuant to the requirements of Salem Generating Station Unit No. 1 Technical Specifications, Section 6.9.1, we are submitting supple-mental Licensee Event Report 79-50/0lX-l.

Sincerely yours,

,*}

• /).L,~-~\\. ---

F. P. Libriz*z.J General Manager -

Electric Production CC:

Director, Office of Inspection and Enforcement (30 copies)

Director, Office of Management Information and Program Control (3 copies)

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s 1!1 95-2001 (200M) 2-78

Report Number:

Report. Date:

Occurrence Date:

Facility:

79-50/0lX-l 11/10/79 7/10/79 Salem Generating Station Public Service Electric & Gas Company Hancock's Bridge, New Jersey 08038 IDENTIFICATION OF OCCURRENCE:

Steam Generator Water Level Instrumentation Deficiency CONDITIONS PRIOR TO OCCURRENCE:

Operational Mode 5 DESCRIPTION OF OCCURRENCE:

Westinghouse has notified PSE&G that a potential safety problem exists with the heatup of the steam generator level measurement reference legs during accident conditions.

Pipe breaks inside t.he containment resulting in elevated containment ambient temperatures could cause heatup of the steam generator level reference legs.

This would result in a decrease in water column density and an increase in the indicated steam generator water level.

The actual water level will be lower than the level indicated by the instruments.

The erroneous indication of level could result in delayed protection system actuation (reactor trip and auxiliary feedwater initiation) and could affect operator response for post accident recovery.

DESIGNATION OF APPARENT CAUSE OF OCCURRENCE:

The cause of this occurrence is an apparent design deficiency which was not sufficiently analyzed for post accident conditions during the initial design phase of the steam supply system.

ANALYSIS OF OCCURRENCE:

Level measurement of the steam generators at Salem employ an open column reference leg.

Only steam generator narrow range level is utilized in a protective function.

Three separate instruments and reference leg measurement systems are provided for each steam generator.

The instrument lines are not insulated and, therefore, are subject to potential heatup and subsequent indication errors due to increased containment ambient temperatures.

Large steam generator pressure changes caused by high energy line* pipe ruptures could also cause indication errors.

The steam generator narrow range level instruments provide information for the following protective functions:

~.

LER 79-50/0lX-l 1.

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

2.

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

3.

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

4.

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

5.

Post accident monitoring for operator action.

The potential error bias in instrument indication due to reference leg heatup is on the high side.

The first two protective functions of high-high level trip and low level trip are not required for plant protection during postulated high energy line breaks.

These items are primarily for feedwater control system malfunctions.

The potential error bias for the remaining three items could result in a less conservative *analysis of high energy line break events.

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 leg heatup effects.

The backup trip function for the f~edwater 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, revisions to the level setpoints are only required to compensate for reference leg heatup up to the temperature at which the containment high pressure signal is received.

A conservative upper bound for reference leg temperature would be at the peak containffient temperature reached following a 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 chacteristics 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 setpoint would be reached prior to a containment temperature of 240°F.

LER 79-50/0lX-l An analysis has been performed of potential indication errors assum-ing different reference leg ambient temperatures compared with the entire reference leg calibration data.

Assuming that the reference leg is at an 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 particular 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% will maintain existing safety margins.

No other setpoint changes are required for the steam generator levels.

With regards to post-accident monitoring, the existing operating procedures require the use of steam generator level indication in accident recovery as an aid in controlling auxiliary f eedwater flow to the unaffected steam generators for primary to secondary heat transfer.

The indication errors associated with reference leg heatup should not have an adverse effect on operator actions.

Existing procedures at Salem direct the operator to maintain steam generator level at 33%.

The maximum containment design temperature for Salem is 350°F, which occurs for a very short period of time (one minute with only an additional two minutes above 300°F).

The probable maximum heatup of the reference legs will be to some temperature less than 300°F, which.would result in indication errors of less than 10%

of span.

Even assuming this error and the errors in indication from the expected pressure fluctuations in the unaffected steam generators, the steam generators would be maintained at an actual level sufficient to maintain the unit in a safe condition.

The indication bias will decrease as the containment ambient and reference leg temperatures decrease during the course of the postulated accident.

CORRECTIVE ACTION

The low-low steam generator water level setpoints have been changed to 11% to account for indication bias due to reference leg heatup.

A change of 6% is based on the preceding analysis of containment temperature, steam generator level, and the containment high pressure signal.

The Salem operating procedures and training program for post-accident recovery will be revised to address the concerns discussed herein.

Cautionary statements will be added to the procedures alerting the operators of the potential errors in steam generator level indications.

Correction curves will be provided for the operator's use in deter-mining actual level for reference leg heatup and fluctuating steam pressure.

LER 79-50/0lX-l The setpoint change may be temporary pending the results of an engineering study of methods to eliminate the erroneous level indication through suitable design changes.

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

Prepared By A. W. Kapple Manager -

Salem Generating Station SORC Meeting No.

82-79