05000321/LER-2010-004
| Edwin I. Hatch Nuclear Plant | |
| Event date: | 06-03-2010 |
|---|---|
| Report date: | 07-30-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212010004R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS EK)
DESCRIPTION OF EVENT
On June 03, 2010, at approximately 1443 EDT, with Unit 1 operating at 2799 CMWTh, 99.8 percent rated thermal power, a section of one-quarter inch tubing in EDG 1A' s fuel system separated from the fitting that secured it to a discharge check valve. The discharge of diesel fuel oil from the subject tubing on to the surfaces of the EDG exhaust manifold and into its environs created the potential for unsafe conditions for continued EDG operation, and the EDG lA was secured at approximately 1448 EDT. The EDG had been in operation for planned monthly surveillance at the time of the tubing separation. Based on the information available at the time, it was judged that EDG lA would not be capable of performing its intended safety function for its applicable mission time, and it was declared to be inoperable. Actions required by Technical Specification Limiting Condition for Operation (LCO) 3.8.1 were taken, including the verification of operability of the remaining Unit 1 EDGs.
The subject tubing is one quarter inch in diameter. It functions to direct "waste" diesel fuel oil from the EDG's fuel injectors to a fuel oil collection tank on the EDG skid. In the subject line is a check valve which prevents possible back flow of the fuel oil in the line. The separation of the tubing occurred at the point of connection of the tubing and the outlet side of that check valve. That connection is secured by a typical flared-compression-type fitting of the tubing being attached to the check valve's tapered threaded fitting by a compression nut.
CAUSE OF EVENT
The direct cause of the tubing separation was judged to be degradation of the flared compression-type fitting due to apparent tubing wall thinning likely produced by repeated stressing of the material through repetitive removal and re-assembly of the fitting connecting the failed tubing and the associated check valve as part of planned diesel generator maintenance. The repeated application of the stress from torquing the fitting's compression nut upon re-assembly can thin the material and in some cases can lead to cracking of the tubing wall.
A precursor to the tubing failure was noted on April 01, 2010, when a small amount of leakage from this same portion of tubing was noted. An attempt to stop the leakage by torquing the compression nut of the fitting to the check valve was unsuccessful, and an evaluation of continued operation of the EDG was made. Due to nature of the leak (dripping onto the floor area), the limited leak rate and the fact that the surface onto which the fuel oil was leaking was well below the diesel fuel oil ignition temperature (a margin on the order of 300 degrees Fahrenheit), EDG operation was judged to be operable. A work order for repair of the leakage was initiated but had not been worked prior to the June 3, 2010 event.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable under 10CFR 50.73(a)(2)(i)(B), in that an event and an associated condition occurred and existed that was prohibited by the technical specifications. It is reportable since surveillance testing indicated that equipment (e.g., one train of a multiple train system) was not capable of performing its specified safety functions from the time of the discovery of the precursor leak on April 01, 2010, and, thus would have been inoperable for a period of time longer than allowed by technical specifications (i.e., the 72 hour LCO allowed outage time). The June 03, 2010 testing was conducted within the required time (i.e., the � surveillance interval plus any allowed extension), however there was firm evidence, based on a review of relevant information drawn from equipment history and the Condition Reporting system (i.e., CR 2010104391) that the causative condition that resulted in the tubing separation existed previously.
By virtue of the fact that the condition revealed by the April 01, 2010 leak that led to the separation which occurred during the June 03, 2010 surveillance was documented at the time of that discovery, this event meets the reporting criteria for 50.73(a)(2)(i)(B).
This event occurred during routine maintenance / surveillance operation of EDG lA with Unit 1 at approximately full power with electrical power for the unit's auxiliary loads connected to 4.16-kV buses being supplied from off-site sources through the unit's auxiliary transformers and startup transformers. Thus, the cessation of the operation of EDG lA due to the dispersal of fuel oil from the failed tubing did not result in any plant transient or loss of operating equipment function other than EDG lA itself.
Upon the declaration of the inoperable status of EDG lA due to the perceived risk of fire from the fuel oil released to the environs by the separated tubing, the Technical Specification Limiting Condition for Operation (LCO) 3.8.1 applied and the appropriate Actions (specifically, those Actions required for Condition B — "One Unit 1 or the swing DG inoperable") were taken.
The design of the plant's electrical power systems and compliance with the associated technical specifications provide assurance of independent and redundant available sources of power to the Engineered Safety Feature (ESF) systems during all anticipated operational occurrences and accident conditions. Thus, the electrical power required to safely shut down the reactor, maintain the shutdown condition, and operate all auxiliaries necessary for plant safety was available throughout this event. Based on this information, this event had low safety significance.
CORRECTIVE ACTIONS
Short term corrective actions implemented in response to the subject separation of a section of the tubing of the EDG lA fuel oil system were the following.
EDG lA was shutdown to stop the release of diesel fuel oil to the EDG's environs upon discovery of the tubing failure.
EDG IA was declared inoperable and LCO 3.8.1 was entered and applicable Actions for Condition B were taken.
The separated tubing in the diesel fuel oil system of EDG lA was repaired and the EDG returned to available status on June 04, 2010 at 1535 EDST. The EDG was restored to operable status and the associated action statement was cleared at 0130 on June 05, 2010.
The corresponding portions of tubing in each of the other four EDGs in the plants electrical power system were inspected and showed no degradation or cracking. There was slight wear noted at the tips of the flares on EDGs 1B and 1C. As a preemptive measure the applicable tubing on all EDGS was replaced since the subject tubing on all EDGs was of a like design and had experienced a similar service and maintenance history.
� It should be noted that at the time of the April 01, 2010 observation of a fuel leak on EDG lA noted above, an inspection of the other four EDGs was conducted to verify that there were no evidence of current leakage or residue that would indicate past leakage at the corresponding fuel line connections.
That inspection determined that the leakage noted on EDG lA was unique to that diesel generator.
A cause determination for the failed tubing was initiated and is near its conclusion. Depending of the findings of that cause determination and any associated recommendations, additional longer term corrective or preventative actions may be enacted. If the circumstances or conclusions described herein are significantly revised through the review of that cause determination by staff and management, a supplemental Licensee Event Report will be submitted for the NRC's information and files.
ADDITIONAL INFORMATION
Failed Component Information:
Other Systems Affected: 4.16 kV ESF buses lE (lost onsite standby power source when EDG 1A declared inoperable) EIIS System Code: EK EIIS Component Code: DG Manufacturer: Fairbanks Morse Model Number: 3800TD Type: one quarter inch diameter steel tubing — skid mounted EDG vendor supplied sub-component Manufacturer Code: F010 Commitment Information: This report does not create any new permanent licensing commitments Previous Similar Events: None