Information Notice 1980-43, Failures of Continuous Water Level Monitor for Scram Discharge Volume at Dresden Unit No.2

Failures of Continuous Water Level Monitor for Scram Discharge Volume at Dresden Unit No.2

ML031180523
Person / Time
Site:	Dresden, 05000000
Issue date:	12/05/1980
From:	NRC/OI
To:
References
IN-80-043, NUDOCS 8008220279
Download: ML031180523 (3)

SSINS NO.: 6835 Accession No.

8008220279 IN 80-43 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 December 5, 1980

IE Information Notice No. 80-43: FAILURES OF THE CONTINUOUS WATER LEVEL

MONITOR FOR THE SCRAM DISCHARGE VOLUME

AT DRESDEN UNIT NO. 2 Descriotion of Circumstances:

On December 2, 1980, following a reactor scram at Dresden Nuclear Power

Station Unit 2, the licensee discovered that the recently installed scram

discharge volume (SDV) continuous water level monitoring system had failed

to respond as expected. The continuous water level monitoring system was

designed and supplied by Nortec Corporation, and utilizes a single transmit/

receive transducer for each of the four level monitoring channels. Following

installation of the continuous level monitoring system, the licensee verified

its operability by tripping each alarm channel while its sensor was connected

to a calibration standard consisting of a section of 4 inch pipe identical to

the SDV piping. No in situ test of the equipment was accomplished.

The expected high level annunciator alarms were not received in the control

room following scram when the SDV filled with water. An investigation

to determine the cause was initiated and once per shift checks of the

SDV level on both Units 2 and 3 were re-instituted. The reactor scram

system functioned normally and post scram manual ultrasonic tests on the

SDV verified proper system drain.

Investigations by the licensee determined that the ultrasonic detectors

were inadequately coupled to the SDV piping. The coupling was improved

and testing performed to show that the system could detect water flow

into the SDV during single control rod scram tests. The unit was taken

critical and was heating up on December 4, 1980, at approximately 400

psig when a reactor scram occurred. The expected SDV high level annunciator

alarms were not received in the control room immediately following the

scram, but were received about 10-15 minutes later when the SDV was draining.

Following an additional scram at approximately 20 psig with control rods

inserted these alarms were received properly. Investigation identified

level detection system operability problems as evidenced by a low signal

to noise ratio. Arrannements are being made for replacement components

(including transducers to improve the signal characteristics and reduce

system noise. Until the improvements are installed and demonstrated

adequate by in situ testing, use of the ultrasonic detection system is

being augmented with manual ultrasonic checks of level in the SDV, using

the previously required once per shift check. A manual check will be

performed after each reactor scram. At Dresden Unit 2 the licensee will

IN 80-43 December 5, 1980 complete the system improvements and required testing within 7 days in

accordance with the Immediate Action Letter issued by Region III on

December 4, 1980.

The above operating experience indicates the need for a demonstration

of the operability of ultransonic systems recently installed to continuously

monitor for water in the SDV. Until demonstrated operable by in situ

testing, these systems should not be solely relied on for detection of

water in the SDV. Use of new ultrasonic detection systems should be

augmented by manual checks for water in the SDV each shift and after

reactor scram until in situ testing is performed.

It is important that a high degree of reliability be established in

operability of these continuous water level monitoring systems in order

to support plant operations in the interim until final scram discharge

system modifications are performed.

This IE Information Notice is provided as an early notification of a

possibly significant matter that is still under review bv the NRC staff.

Recipients should review the information for possible applicability

to their facilities. No specific response is requested at this time.

Pending further NRC evaluations, we expect licensee actions will be

requested or required.

No written response to this IE Information Notice is required. If you have

any questions regarding this matter, please contact the Director of the

appropriate NRC Regional Office.

IN 80-43 December 5, 1980

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