ENS 47580
ENS Event | |
|---|---|
22:05 Jan 9, 2012 | |
| Title | Nut on Hold-Down Stud Was Found Loose |
| Event Description | On January 9, 2012, at 1405 [PST], plant personnel notified the Diablo Canyon shift manager that a nut on a hold-down stud on an Independent Spent Fuel Storage Installation(ISFSI) HISTORM spent fuel storage cask was loose to the touch. Plant personnel hand tightened the nut and verified that none of the other 16 casks in the facility had nuts that were loose to the touch.
The Diablo Canyon ISFSI design requires that each spent fuel storage cask be installed with the cask compressed against the embedment plate using 16, two-inch diameter, anchor studs. Each stud is pre-loaded to approximately 157,000 lbf. This design ensures the cask will remain stable during a seismic event. A manufacturer's analysis of the stability of the cask with all of the 16 hold down stud nuts installed with no pre-load concluded that the cask would maintain its stability during a seismic event. PG&E has contracted the vendor to re-tension the stud and expect[s] completion [by] 1/13/2012. PG&E will assess the need to verify tension of the remaining studs based on the extent of condition evaluation. Cause of the loose nut has not yet been determined. The NRC Senior Resident Inspector has been informed.
On January 11, 2012, at 1325 PDT, plant personnel notified the Diablo Canyon shift manager that two additional nuts on hold-down studs for other ISFSI HISTORM spent fuel storage casks were discovered to be loose. The two additional nuts (one per cask) were discovered when the full effort of two hands was used on the nuts while performing an extent-of-condition evaluation. All 16 nuts on all 16 casks were tested for tightness using the full effort of two hands (i.e., no pre-load). NRC senior resident inspector has been informed. Notified the R4DO (Powers), NRR EO (Cheok), and NMSS EO (Mohseni).
On February 29, 2012, at 1610 PST, plant personnel notified the Diablo Canyon shift manager that cause analysis of loose nuts on hold-down studs of ISFSI HISTORM spent fuel storage casks determined the cause is not a defect and this occurrence is not reportable. Accordingly, the reporting criteria for Event Notification 47580 is changed from '72.75(c)(1) Non-emergency condition' to 'Voluntary Report.' Pacific Gas and Electric (PG&E) plans to submit a voluntary, written report (licensee event report) to the NRC. PG&E personnel informed the NRC resident inspector. Notified R4DO (Lantz), NRR EO (Lee), and NMSS EO (Rubenstone). |
| Where | |
|---|---|
| Pacific Gas & Electric Co. Avila Beach, California (NRC Region 4) | |
| License number: | SNM-2511 |
| Organization: | Diablo Canyon |
| Reporting | |
| Information Only | |
| Time - Person (Reporting Time:+1.65 h0.0688 days <br />0.00982 weeks <br />0.00226 months <br />) | |
| Opened: | Michael Quitter 23:44 Jan 9, 2012 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Feb 29, 2012 |
| 47580 - NRC Website
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Pacific Gas & Electric with Information Only | |
WEEKMONTHYEARENS 475802012-01-09T22:05:0009 January 2012 22:05:00
[Table view]Information Only Nut on Hold-Down Stud Was Found Loose 2012-01-09T22:05:00 | |