NRC Generic Letter 80-66, IEB 80-17 Supplement 1 Failure of Control Rods to Insert During a Scram at a BWR

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GL80066 SSINS No. 6820 Accession No.:

8006190027 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555

July 18, 1980 IE Bulletin No. 80-17 Supplement No. 1

FAILURE OF 76 OF 185 CONTROL RODS TO FULLY INSERT DURING A SCRAM AT A BWR

Description of Circumstances

Please refer to IE Bulletin 80-17, issued July 3, 1980, for complete details of the initiating event. Although we are essentially confident that the event was caused by water in the Scram Discharge Volume (SDV) system we do not yet have a complete explanation as to why the water was present. The best estimate is that some type of blockage existed in the vent and/or drainage system for the SDV, precluding adequate drainage. To ensure that the SDV is empty, Browns Ferry (BF-3) has installed instrumentation to continuously monitor the water in the scram discharge volume. Such instrumentation is being considered by other plants.

Since issuance of IE Bulletin 80-17, additional information has been identified. Specifically:

a) At Browns Ferry a discrepancy was found between the "as-built" scram discharge system and the "as-designed" system. An unused one-inch (1")

instrument line was found uncapped on the four-inch (4") drain header on the west side (the side whose rods scrammed) scram discharge volume vent system of Unit No. 3. It is believed that this line improved the venting, and therefore the drain time for that system.

b) It has been determined that the vent systems on some scram discharge volumes interconnect with vent headers that are also common with and are connected to other systems. The interconnected "vent" system may contain water drained or being drained from those other systems. This water could potentially affect performance of the SDV. Also, both the vent and drain systems for the scram discharge system may contain long lengths of relatively small bore piping. Designs specify a very gradual slope, such that small errors in the "as-installed" piping could result in degraded performance (for example, due to loop seals).

c) Concerns have been expressed within the NRC Staff regarding potential delays that may occur before start of injection of boron into the BWR system from the Standby Liquid Control System (SLCS) when this manual operator action is required. The potential delays could be caused by unavailability of the SLCS key which is required to initiate this system, and/or administrative delays which require supervisory approval before the SLCS can be manually initiated by the control room licensed operator.

In view of the above items, the following actions in addition to those specified in IE Bulletin 80-17 are to be taken by BWR licensees.

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A. Action to be Taken by BWR Licensees Upon Receipt and to be Reported Within 20 Days of the Date of This Letter:

1) Provide to the NRC Regional Office an analysis of the adequacy of the "as-built" SDV system and associated vent and drain systems, including any identified design deficiencies. Include copies of verified "as-built" isometric drawings of the SDV and detailed descriptions of the system, verified to be correct, as part of this analysis.

2) Revise and implement Operating Procedures as necessary to provide clear guidance to the licensed operator in the control room regarding when he should initiate the SLCS without obtaining prior supervisory approval. Provide a description of the implemented procedural requirements.

3) Assure that procedures exist and are implemented for specifying remedial action to be taken if water is found in the SDV system at times when it should be free of water. Provide a description of the implemented procedural requirements.

4) Revise and implement administrative procedures as necessary to ensure that the SLCS key shall be readily available to the licensed operator in the control room. Provide a description of the implemented procedural requirements.

5) Continue daily monitoring of water levels in all scram discharge volumes until continuous monitoring system(s) (discussed in B.1 below) is (are) installed and operational (this requirement supersedes the requirements of Item 5 of IE Bulletin 80-17 which required daily surveillance for only 6 days).

B. Action to be Taken by BWR Licensees and Completed by September 1, 1980:

1) Install a system to continuously monitor water levels in all scram discharge volumes. Continuous recording and alarm features must be included in the design. Consideration should be given to use of diverse level sensors in this (these) system(s). The design installed should represent the design with the highest level of reliability compatible with completion of installation by September 1, 1980. Provide a written description of the system design to the NRC Regional Office.

If installation by September 1, 1980 is not possible, by August 15, 1980, submit to the NRC Regional Office:

1) Documentation in detail why the installation cannot be completed by 9/1/80.

2) A Commitment to a firm schedule for installation.

3) A commitment to equipment changes and/or surveillance requirements in addition to those now in effect that will provide adequate assurance of SDV operability in the interim until installation is completed.

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2) Perform a study of potential designs for improving the venting system for the scram discharge volumes and submit a description to NRC by September 1, 1980. Improvements such as providing a redundant, independent vent for each significant volume in the system or locally installed vacuum breakers close to each such volume should be considered (some plants already include a design which vents locally to atmosphere). Include an estimate of the time that would be required to accomplish these modifications in your report to be submitted to the NRC Regional Office. We have been told that meetings have already been scheduled by GE to discuss their proposals in this area with licensees.

Additional requirements are under consideration and will be the subject of further communication from NRC.

Licensees of all operating BWRs shall submit the information requested within the specified allowable times. This information is requested under the provisions of 10 CFR 50.54 (f). Accordingly, you are requested to provide within the time periods specified above, written statements of the above information signed under oath or affirmation. Reports shall be submitted to the Director, Division of Reactor Operation Inspection, NRC. Office of Inspection and Enforcement, Washington DC 20555.

Approved by GAO, B180225 (R0071); clearance expires 7-31-80. Approval was given under a blanket clearance specifically for identified generic problems.