05000354/LER-2009-004
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Initial Reporting | |
| ENS 45074 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation |
| 3542009004R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor (BWR/4) Essential Instrument Air System — {LE} Tubing — {TBG} *Energy Industry Identification System {El IS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: May 17, 2009 Discovery Date: May 17, 2009
CONDITIONS PRIOR TO OCCURRENCE
Hope Creek was in Operational Condition lat 100% reactor power. No structures, systems or components were inoperable at the time of discovery that contributed to the event.
DESCRIPTION OF OCCURRENCE
At 0335 on May 17, 2009, the control room received indication of CRD motion into the core. The control room crew noted several CRDs inserting into the left side of the core and a corresponding lowering of reactor power. While the operator at the controls was taking action to insert a manual scram, an automatic RPS scram signal was received due to a low RPV level condition caused by the collapse of voids as CRDs inserted, lowering reactor power.
Subsequent investigation revealed that a solder joint on the scram air header {LE/TBG} at HCU 22-11 separated and depressurized the scram air header which caused the multiple control rod insertions by removing air from the scram pilot valves of the HCUs.
The solder joint had been previously identified in September 2008 as having an air leak. Supplemental personnel were used to perform the diagnostic testing to identify air leaks on the scram air header. 39 items were identified and provided in the test results to the system manager. The supplemental personnel did not submit a CAP notification other than as a report of the conditions found. The system manager, generated CAP notifications to repair the identified discrepancies, however the solder leak at HCU 22-11 was missed and no CAP notification was generated.
During RF15, repairs commenced on the identified leaks from the September testing. The leak at HCU 22-11 was not repaired because no CAP notification was written to repair the leak. On May 17, 2009, the leaking solder joint failed, causing multiple CRD movement and reactor scram.
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SAFETY CONSEQUENCES AND IMPLICATIONS
The air leak caused CRD movement into the core and a resultant reactor scram. All systems performed as designed and there was no challenge to other plant systems. There was no impact to the health and safety of the public as a result of this event.
A review of this event determined that a Safety System Functional Failure (SSFF) has not occurred as defined in Nuclear Energy Institute (NEI) 99-02.
CAUSE OF OCCURRENCE
The RCE identified the following root causes:
(1) Failure of improperly soldered joint; (2) Communication of the test discrepancies not added to the corrective action program (CAP) by the individual who discovered the condition; and (3)Supplemental personnel expectations not clearly communicated with regards to reporting deficiencies found.
The testing in September of 2008 identified that the solder joint at HCU 22-11 had an air leak that was "beyond bubbling". The leak was blowing air out of the fitting almost one-half way around the 1/2 inch fitting at a rate that did not allow bubbling of the snoop solution. The specific details of the leak were not communicated to the system manager directly. The leak was described in a note in the remarks portion of the work plan (CAP number 30164922) as "North HCU 1.5 inch header has a large leak at the 1/2 inch bull, feeding the H1BF-2211-V116 valve". This note was not detected by the system manager when compiling the notifications for addressing the discrepancies noted during the test.
A review of the pictures of the failed connection revealed that there was inadequate insertion of the tubing at the connection and that there was inadequate solder wetting along the connection as well. The review indicates that the joint was poorly made at the time of construction.
PREVIOUS OCCURRENCES
The RCE noted that there were two previous events at Hope Creek Generating Station (HCGS).
In 1989 a similar connection failed at HCU 34-59, also causing a reactor scram. The corrective actions included physically testing each similar connection, leak checking connections and radiography of similar joints prior to re-start. Long term corrective actions were to implement a testing program for instrument air piping during the current refuel outage.
In 1997 a similar connection separated during maintenance on a nearby fitting. The corrective action instituted was the performance of a single point vulnerability study that resulted in the surveillance that was being performed in September 2008 — perform periodic sonic inspections of the scram air header.
CORRECTIVE ACTIONS
The RCE identified the following corrective actions to preclude recurrence (CAPRs):
(1) The separated joint was re-soldered and re-tested satisfactorily.
(2) Revise the supplemental contractor procedure (AP-1) to include the requirements for writing CAP notifications.
Additional corrective actions (CAs) reviewed and addressed include:
(1) Implement recurring PM to monitor the leaks in Technical Evaluation 80098784. Future threaded fitting leaks that cannot be repaired will use this Technical Evaluation.
(2) Present to the Plant Health Committee (PHC) for creation of a temporary modification or design change package that may be used if future leaks are identified on soldered joints (i.e. apply a clamp). This will be used for compensatory action for all future soldered fitting leaks that cannot be immediately repaired.
(3) Revise Maplewood Testing Services (MTS) Orientation and Certification Program to include training of MTS personnel on procedure AP-1. Add this specific OE to the orientation Training.
(4) Conduct Stand Down with MTS employees to clearly communicate requirements of the CAP.
(5) Review all orders assigned to MTS to ensure clear concise direction is given in terms of writing a CAP notification or supplying the data to the client organization.
COMMITMENTS
This LER contains no commitments.
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