05000454/LER-2005-002

LER-2005-002, One of Two Trains of Hydrogen Recombiners Inoperable Longer Than Allowed by Technical Specifications Due to Inadequate Procedure

Docket Number
Event date:	09-26-2004
Report date:	04-15-2005
4542005002R00 - NRC Website

A. Plant Condition Prior to Event:

Event Date/Time: September 26, 2004 / 0936 hours0.0108 days <br />0.26 hours <br />0.00155 weeks <br />3.56148e-4 months <br /> Unit 1 and Unit 2 - Mode 1 — Power Operations, Reactor Power 100% Reactor Coolant System [AB]: Normal operating temperature and pressure.

No structures, systems or components were inoperable at the start of the event that contributed to the event.

Background

The Containment Combustible Gas Control System (OG) [BB] at Byron Station consists in part, of two 100% capacity independent hydrogen recombiner trains (i.e., OA and OB) and are shared between the two units.

B. Description of Event:

On February 14, 2005, during the performance of a scheduled gaseous leakage test of the OA OG train, the System Engineer (non-licensed) discovered a flow transmitter test tap pipe cap was not installed. This condition rendered the OA OG train inoperable due to inaccurate flow indication. The OA train was declared inoperable and Technical Specification (TS) 3.6.8, "Hydrogen Recombiners" action condition "A" was entered for both units at 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br />. This condition allows one train of OG to be inoperable for 30 days. A cap was installed and TS 3.6.8 condition "A" exited at 1700 the same day. The OB OG train was checked and found to have its corresponding cap installed.

An investigation ensued and the review of historical work records identified that the last maintenance activity on the OA OG train was the August 27, 2004 execution of the 18-month calibration procedure, Byron Instrument Maintenance Surveillance Requirement (BISR) Z.6.A.1-202, "Surveillance Calibration Of Hydrogen Recombiner Inlet Flow Loop." It was determined that during this calibration activity, the flow transmitter test tap pipe cap was removed as setup for the calibration activity and not replaced at the conclusion of the calibration procedure.

As a result, the OA OG train was unknowingly inoperable since 0936 hours0.0108 days <br />0.26 hours <br />0.00155 weeks <br />3.56148e-4 months <br /> on August 27, 2004. TS 3.6.8 condition "A" allows for one train of OG to be inoperable for 30 days and if the train is not restored to operable status then condition "C" requires both units to be in Mode 3 in the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

Consequently, on September 26, 2004 at 1536 hours0.0178 days <br />0.427 hours <br />0.00254 weeks <br />5.84448e-4 months <br />, (i.e., 30 days plus 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) both units were inadvertently in a condition prohibited by TS 3.6.8 in that both units were in Mode 1 and not in Mode 3.

(B. Description cont.) This condition existed from September 26, 2004 until February 14, 2005. A review of Operator logs indicates the OB train was always operable in this time period.

C. Cause of Event:

The calibration procedure BISR Z.6.a.1-202 was inadequate in that it failed to contain the explicit procedural steps to ensure the test tap pipe caps were properly re-installed.

In addition, the Maintenance Management enforcement of the use of human performance tools within the maintenance departments was inadequate. The IM technicians involved in the August 27, 2004 calibration and other IM technician involved in previous calibrations using this procedure should have recognized the procedural inadequacies prior to execution and revised the procedure accordingly. The IM technicians involved accepted the inadequate procedure and relied on their craft capabilities to properly conduct the calibration.

D. Safety Analysis

The current licensing basis for the hydrogen recombiners is to provide the capability of controlling bulk hydrogen concentration in containment to less than the lower flammable concentration of 4.0 volume percent following a design basis accident. This capability was still maintained with the 100% redundant OB train. However, for this approximate six-month period the reliability of the overall system function of hydrogen control inside containment was reduced in that one train was inoperable.

The NRC has recently revised 10 CFR 50.44, "Combustible gas control for nuclear power reactors" to eliminate, in part, the requirements for hydrogen recombiners in gas controls in light water cooled power reactors. Consequently, Byron Station has submitted to the NRC a license amendment request (LAR) (reference 1) to eliminate the hydrogen recombiner Technical Specifications requirements. This LAR is in accordance with the NRC's consolidated line item improvement process for Technical Specification Task Force Standard Technical Specification Change Traveler 447, "Elimination of Hydrogen Recombiners and Change to Hydrogen and Oxygen Monitors.

Based on a preliminary engineering assessment using the Alternate Source Term methodology with known containment and control room leakage rates, the total doses for the Main Control Room, Exclusion Area Boundary and the Low Population Zone are within regulatory limits. A conservatively high value of leakage from the missing fitting on the recombiner was used as input to the dose calculations. In addition to the dose effects, the following were reviewed with acceptable consequences:

(D. Safety Analysis cont.) 1. Effects of venting hydrogen to the Auxiliary Building, 2. Effects of venting high temperature/high humidity vapor to the Auxiliary Building.

3. Effects of the jet impingement on nearby components, 4. Effects on required Operator access to equipment.

Based on the above, the leakage from the recombiner has minimal safety significance.

E. Corrective Actions

BISR Z.6.A.1-202 will be revised prior to the next calibration to address the procedural deficiencies that led to this event.

The Instrument Maintenance Department will implement, within the standard work preparation process, a requirement six weeks prior to work execution, to conduct a review of the adequacy of involved procedures.

An extent of condition review will be conducted of instrument maintenance procedures related to TS systems to identify any similar inadequacies.

Maintenance Management's expectations will be re-enforced to use human error prevention tools in reviewing procedures and to revise procedures when found to be inadequate.

Maintenance Management will develop and institutionalize specific annual training for the Maintenance organization on human error events involving complacency/overconfidence and the failed defense of procedure adherence.

F. Previous Occurrences

There have been no LERs within the past two years of a similar nature.

G. Component Failure Data:

Manufacturer Nomenclature Model N/A H. Reference/s 1. Keith Jury (Exelon) to U.S. NRC Document Control Desk, "Request for Amendment to Technical Specifications to Eliminate Requirements for Hydrogen Recombiner and Hydrogen/Oxygen Monitors Using the Consolidated Line Item Improvement Process," dated September 15, 2004.