17 juin 2013
Découverte d’un problème générique sur des soupapes qui n’assureraient pas leur fonction de limitation de pression. Les réacteurs équipés de ce type de soupape et donc potentiellement à risque sont : Limerick 1 & 2 avec 28 soupapes de ce type et Pilgrim avec 4 soupapes et FitzPatrick avec trois soupapes.
Available in english only.
CURTISS WRIGHT FLOW CONTROL CO.
Event Date : 05/03/2013 Event Time : [EDT] Last Update Date : 06/17/2013 Emergency Class : NON EMERGENCY 10 CFR Section : 21.21(a)(2) - INTERIM EVAL OF DEVIATION
Event Text
INTERIM PART 21 REPORT OF POTENTIAL DEFECT IN A RELIEF VALVE BELLOWS
The following was excerpted from a fax :
(ii) Identification of the basic component supplied for such facility or such activity within the United States which may fail to comply or contains a potential defect.
Target Rock P/N : 303480-1, Bellows, Manufactured by Target Rock.
(iii) Identification of the firm supplying the basic component which fails to comply or contains a defect.
Target Rock, Business Unit of Curtiss-Wright Flow Control Corporation 1966E Broadhollow Road East Farmingdale, NY 11735
(iv) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such defect or failure to comply.
During as-found steam testing on March 5, 2013 of a Pilgrim Main Steam Safety Relief Valve (MS-SRV) (TR Model 09J-001, valve assembly S/N 5, pilot assembly S/N 23, bellows PIN 303480-1 S/N 607) a loud pop was heard and as-found testing was secured. Subsequently, the pilot assembly was removed from the valve assembly and subjected to a leak test and would not hold pressure. The pilot assembly was disassembled and a visual inspection of the P/N 303480-1 bellows convolutions revealed a through wall failure in one of the convolutions. It is noted the steam testing was performed at an offsite test facility and the valve did not fail installed in the plant.
The bellows acts as a pressure sensor responsible for initiating the opening of the MS-SRV at set pressure. Failure of the bellows does not directly impact the integrity of the Reactor Coolant System (RCS) pressure boundary, which is maintained by the bonnet assembly that surrounds it, but does impair the ability of the MS-SRV to provide over-pressure protection of the RCS. This technology has an extensive history of reliability in nuclear power systems and has been used in Commercial Nuclear Power Plants (NPPs) since the 1970s. This is the first reported incident regarding a thru wall bellows failure.
Target Rock initiated a comprehensive root cause evaluation pursuing several areas of investigation. In parallel, Entergy is conducting an independent investigation and we are cooperating with them. A complete review of our paperwork confirms all manufacturing procedures and processes were performed in accordance with all specified requirements. This includes :
Raw material analysis
Dimensional inspections
Cleaning
Heat Treatment
Manufacturing processes
Testing
Review of design stresses
Preliminary metallurgical analysis of the failed bellows indicates cracks forming in an inter-granular manner as would be expected from Inter Granular Stress Corrosion Cracks (IGSCC) originating at pit like location on the interior pressurized surface. The source of this cracking is the focus of on going investigations. Target Rock has also visually inspected two other bellows of the same part number, one manufactured from the same material lot and another manufactured from an earlier material lot. Both of these bellows were installed in valves steam tested at Target Rock. One of these valves bellows was also full flow tested at Wyle Labs. Neither of these additional bellows contained pit-like locations and may indicate this potential failure mechanism is an isolated incident. However, to date, neither Target Rock nor Pilgrim can draw final conclusions with the information collected and analyzed.
The mode of failure has not been determined ; however, in order to address the potential for a common mode failure, Target Rock is continuing metallurgical testing of the failed bellows and the two other bellows with the same part number. Based on these results, it is likely we will need to evaluate bellows that have been installed in other NPP as they become available.
(v) The date on which the information of such defect or failure to comply was obtained.
The as-found steam test and identification of the potential defect occurred on March 5, 2013.
(vi) In the case of a basic component which contains a defect or fails to comply, the number and location of these components in use at, supplied for, being supplied for, or may be supplied for, manufactured, or being manufactured for one or more facilities or activities subject to the regulations in this part.
The following plants are running with bellows P/N 303480-1 installed : Limerick 1 & 2, Pilgrim, and J.A. Fitzpatrick.
(vii) The corrective action which has been, is being, or will be taken ; the name of the individual or organization responsible for the action ; and the length of time that has been or will be taken to complete the action.
The root cause of the potential defect is not yet known as of the date of this report. Therefore, no specific corrective actions have been initiated. Target Rock Corrective Action Request CAR 13-013 will document the corrective actions when they are determined. This determination will be based on further mechanical and material evaluations. TR anticipates completing these evaluations within 45 days ; however, in the event the evaluations are not completed, TR will forward another interim report within 45 days.
(viii) Any advice related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or will be given to purchasers or licensees.
Target Rock will recommend that the end user perform a detailed visual inspection of the interior convolutions of installed bellows P/N 303480-1 at the next opportunity to determine if any areas of pitting or cracking exist on the interior walls of the bellows. This is a difficult inspection to perform due to the following : internal geometry of the convolutions, a trained inspector is required and specific inspection technology is needed to yield reliable results.
* * * UPDATE FROM JOHN DEBONIS TO HOWIE CROUCH VIA EMAIL AT 1109 EDT ON 6/17/13 * * *
The following are excerpts from an email sent by Target Rock, a business unit of Curtiss-Wright Flow Control Corporation :
Our [Target Rock] investigation indicates the bellows failed due to in-situ hydrogen embrittlement and this hydrogen embrittlement may have been promoted by inadequate cleaning of the bellows. The inadequate cleaning may have induced formation of surface pits during heat treatment providing for localized concentration of hydrogen.
Based on these results, we [Target Rock] are notifying end users with the P/N 303480-1 bellows in service (listed below) to perform field inspections at the next available opportunity. Note, the ASME Code requires these valves to be as-found tested at a maximum 5-year interval. A procedure to inspect the bellows will be forwarded to the applicable plants in parallel with this notification.
In addition to this inspection Target Rock recommends, as a preventive measure, the P/N 303480-1 bellows be replaced with a P/N 300083-1 or -3 bellows, as applicable, to negate the effects of hydrogen embrittlement. Finite element analysis of the P/N 300083-1 or -3 bellows shows significantly lower stresses at plant operating conditions. The lower stress levels provide an incremental increase in safety margin so that hydrogen embrittlement need not be considered a significant degradation mechanism.
Target Rock is implementing corrective actions to improve in-process cleaning and inspection, with emphasis on cleaning prior to heat treatment, to address this root cause.
The corrective actions will be completed within 60 days of this letter.
Should you have any questions regarding this matter, please contact Steven Pauly, Vice President Energy Products at (631) 293-3800, ext. 4640.
Limerick 1 & 2 has 28, Pilgrim has 4, and FitzPatrick has 3 of these items.
Notified NRR Part 21 Group (email), R1DO (Rogge) and R3DO (Daley) via email.
Event Number : 48996
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130618en.html
La boutique
Informez vous