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Information Notice No. 94-89: Equipment Failures at Irradiator Facilities
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS WASHINGTON, D.C. 20555 December 28, 1994 NRC INFORMATION NOTICE 94-89: EQUIPMENT FAILURES AT IRRADIATOR FACILITIES Addressees All U.S. Nuclear Regulatory Commission irradiator licensees. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to several equipment failures -- some of which have generic implications -- that involve wet source storage irradiators. It is expected that all recipients (including dry source storage irradiator licensees) will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not new NRC requirements; therefore, no specific action or written response is required. Description of Circumstances The first equipment failure involved the time delay system required in 10 CFR 36.23(f). The second equipment failure involved two incidents where the control console provided false indications of irradiator condition. The final equipment failure involved a source rack that failed to return to its shielded position after the command was initiated at the control console. 1. Fault in the Operational Time Delay Reset Power Supply. In this incident, a fault in the control console circuitry occurred at a licensee's facility when an external electrical power surge caused a fuse to blow in the operational time delay reset power supply. This circuit had been recently installed to meet the requirements of 10 CFR Part 36. The operational time delay circuit prevents the control console from activating for a preset time after being initiated by the operator in the irradiation room, thereby preventing source rack movement per 10 CFR 36.23(f). In addition, the operational time delay circuit of this irradiator must be operational for the audible and visual warning circuit and the door interlock circuit to function properly. The audible and visual warning systems are designed to activate whenever the irradiator door is opened and source movement is initiated. Nevertheless, the audible and visual warning systems did not activate when the operator left the irradiation room, until the control console was turned "ON" with the console key. The planned irradiation was performed, however, since the audible warning system did activate before irradiation, per the requirement in 10 CFR 36.31(a). 9412210186. IN 94-89 December 28, 1994 Page 2 of 5 The operational time delay circuit was also designed to reset after an irradiation to prevent the control console from being re-energized and allowing additional source movement. The control console should not re- energize until the circuit is again initiated by the operator in the irradiation room. However, in this incident, the control console was able to be re-energized before the time delay circuit was initiated. The blown fuse in the reset power supply prevented the time delay circuit from resetting as designed. To prevent reoccurrence, a surge protector was installed to protect the entire system from external power surges, and the time delay circuit was redesigned to disable the control console, audio and visual safety circuits, and the source positioning system, in case the fuse blows again. This alerts the operator to a fault and prevents source movement until the fuse is replaced. 2. False Indications of Source Rack Position. A false indication of source rack position (rack not in the fully down position) was received at the control console of a wet source storage licensee when the wire that carries the source position signal shorted because of worn insulation. Vibration in the system caused the wire to rub against nearby metal and wore away the insulation. The short-circuit also caused an initial intermittent false indication of a collision between the source rack and the carrier. The licensee verified that the sources were in the shielded position and traced the fault to the damaged wire. The wire was replaced and rerouted through a flexible conduit to reduce the possibility of additional wear. A second false indication of source rack position occurred at the same facility when the plunger of a source rack down-position switch failed to extend and thereby did not properly indicate the true position of the source rack. The plunger failed to extend because of corrosion between the plunger and sleeve causing increased friction. The irradiator licensee received conflicting signals when the lower position switch indicated that the source rack was not fully down, but the upper position switch indicated that the source rack was fully down. The installed radiation monitors and subsequent surveys performed outside of the cell indicated that the source rack was shielded. Further visual analysis confirmed that the source racks were in the fully shielded position. The licensee concluded that the lower source rack position switch was malfunctioning and replaced the switch. On further analysis of the switch, it was determined that green corrosion deposits on the brass sleeve and steel plunger of the switch caused the plunger to stick in the retracted position, preventing it from springing back to the extended position. With the plunger in the retracted position, the switch indicates the source rack is not in the fully down position. The irradiator vendor, Nordion International, Inc. (NII), was notified and has issued Service Bulletin IND-93-2, which is included as Attachment 1 to this information notice. Service Bulletin IND-93- 2 advises all users of NII pool type irradiators containing these plunger-type position indicators to check the switches for evidence of corrosion, clean the switches if corrosion is found, and replace the switches as soon as possible. IN 94-89 December 28, 1994 Page 3 of 5 In addition, NII has provided replacement switches constructed of corrosion- resistant materials (porcelain sleeve and stainless steel plunger) to all users whose irradiators contain the non-corrosion-resistant switches, and has provided instructions for installation and initial testing of the new switches. 3. Failure of Source Rack to Return to the Shielded Position. In this incident, a source rack at a licensee's facility failed to return to the shielded position. This occurred when an air solenoid valve failed to fully return to the exhaust position and stuck in an intermediate position that blocked any air passage through the valve, thereby trapping air pressure in the line between the valve and source rack hoist. During a typical irradiation, the licensee noted an irregular reading on the control console (not related to source rack position) and pressed the emergency stop button. The source rack position indication on the control console indicated that one of the two irradiator source racks failed to return to the fully down/shielded position. The installed radiation monitors, the position of the source rack cable on the roof of the irradiator building, and subsequent radiation surveys performed outside the irradiation cell confirmed that one source rack had remained in the up/unshielded position. Further investigation revealed that pressure remained in the air line to the source rack hoist, keeping the rack in the exposed position, when this pressure should have been released. The licensee cut the air line to release the pressure, and the source rack returned to the fully down/shielded position. The licensee determined that one or both of the air solenoid valves in the supply line failed to move to the exhaust position when the source down command was initiated, thereby not lowering the source rack. Both valves were replaced and the source hoist system operated normally. The irradiator vendor, NII, was notified and both solenoid valves were returned to NII for further investigation. NII determined that the solenoid valves that were indicated to be four-way, two-position (exhaust/pressurize), five-port valves could in certain circumstances, operate as four-way, three- position (exhaust/pressurize/neutral), five-port valves. A two-position valve would exhaust pressure in the air line to the source rack hoist upon loss of supply air pressure, regardless of valve position. The neutral position of a three-position valve would maintain pressure in the air line to the source rack hoist regardless of supply air pressure. Therefore, a three-position valve would not allow for a fail-safe operation. The circumstance that allowed the valve to operate as a three-position valve was attributed to the deterioration and hardening of the seals in the valve spool, causing the valve spool to stick in the "neutral" position. NII's investigation showed that it is unlikely that the ingress of contaminants caused the valve spool to stick in the "neutral" position. However, NII did not rule that out as a contributing factor. According to NII, harding of the seals is thought to be caused by oxidation over time of the seal material. One of the spools, in use for over 5 years, showed considerable hardening of the seal material, whereas the seals of the other spool, in use for only 14 months, had become hardened, but not as hard as the first valve's seals. IN 94-89 December 28, 1994 Page 4 of 5 As a result of this incident, NII issued Service Bulletin IND-94-1, which is included as Attachment 2 to this information notice. To preclude future failures of this nature, NII recommends that Norgren part 54237-56 valve spools no longer be used in Norgren Nugget 200 Series Source Hoist Valves, part K71EA00 KSI AECKGI, and that Norgren part 54237-58 spools be used as replacement spools in existing and all new valves of this type used in NII pool type irradiators. The 54237-58 spools allow for the exhaust of air in all positions, thus eliminating the possibility of pressure remaining in the air line to the source rack hoist on removal of supply air pressure. In addition, NII recommended in their report to the licensee, that the spools be replaced periodically to reduce the possibility of additional failures because of seal hardening. NII's investigation revealed that detectable hardening of the seal material has occurred, in at least one case, within 14 months of use. However, the valve in that case continued to operate without failure. In addition, NII reports that licensees who have ordered replacement valves for the original installed valves (part K71EA00 KSI AECKGI), may have received replacement valves labeled with Norgren's "off-the-shelf" part numbers. Therefore, Norgren Nugget 200 Series Source Hoist Valves with part numbers K71EA00 KS6 KQ1, K71EA00 KS6 AECKGI, and any other variants of the K71EA00 valves used for these operations should have their valve spools replaced also. NII asserts that the construction and operation of these valves are identical to the K71EA00 KSI AECKGI valves. Discussion: The failures of the audible and visual warning systems and operational time delay to initiate properly were caused by a blown fuse in the operational time delay reset power supply, failing to cause the timer to reset. This allowed the control console to be energized and source movement to occur before the operational time delay being re-initiated, contrary to Part 36 requirements. The redesigned circuit prevents this situation from occurring by not allowing the control console to re-energize if this fuse blows again. The control console is designed such that source movement cannot occur unless the control console is energized. Irradiator users should evaluate all possible failure modes of source positioning control circuitry and interlocks, or circuitry that supports these systems, upon installation and whenever modifications are made. The worn insulation that caused the short in the source rack position indication circuit did not cause a situation in which the source racks were in the exposed position unintentionally. However, the licensee was required to bypass safety interlocks (using appropriate safety measures) to verify the true position of the source rack. Users should be aware of and take precautions against conditions (e.g., wear caused by vibration, excessive heat, embrittlement caused by high radiation, etc.) which could cause the failure of essential electrical components and indicators. IN 94-89 December 28, 1994 Page 5 of 5 Users of NII pool-type irradiators containing source down-position indication switches constructed of non-corrosion-resistant materials should be aware that if the recommendations contained in NII Service Bulletin IND-93-2 are not followed, the potential for false or conflicting source rack position signals exists. If a false signal is received, the operator may be required to bypass safety interlocks (using appropriate safety measures) to verify the true position of the source rack. The most likely cause of the corrosion was the close proximity of the switch to the water line and high humidity in the irradiation room. To date, NII is not aware of any indications of corrosion developing in the upper source position switch, which is constructed using materials similar to the original bottom source down-position switches. The upper switch is located away from the water line and is exposed to higher temperatures and lower humidity when the source rack is in the raised/exposed position. However, if conditions exist in the area around the upper switch that are favorable to corrosion (e.g., high humidity or a caustic atmosphere), this switch could corrode also. Users of NII pool-type irradiators containing Norgren part 54237-56 valve spools used in Norgren Nugget 200 Series Source Hoist Valves, part K71EA00, should be aware that if they do not follow the NII recommendation to replace the 54237-56 spools with 54237-58 spools, the source racks may become stuck in the exposed position. Licensees may have to cut the air line to the source rack hoist to return the source rack to the shielded position. In addition, the licensees should consider NII's recommendation that the spools be replaced on a periodic basis to reduce the possibility of failure, according to their specific operation. If not replaced, the replacement valve spools could fail because of seal material hardening, although such failure would not cause pressure to remain trapped in the air line. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contact listed below or the appropriate regional office. /s/'d by CJPaperiello Carl J. Paperiello, Director Division of Industrial and Medical Nuclear Safety Office of Nuclear Materials Safety and Safeguards Technical contact: Douglas Broaddus, NMSS (301) 415-5847 Attachments: 1. Nordion International Inc., Service Bulletin IND-93-2 2. Nordion International Inc., Service Bulletin IND-94-1 3. List of Recently issued NMSS Information Notices 4. List of Recently issued NRC Information Notices. Attachment 1 IN 94-89 December 28, 1994 Page 1 of 1 NORDION INTERNATIONAL INC. 1993 November 25 United States Regulatory Commission Washington DC USA 2055 Mail Stop 5H6 Service Bulletin IND-93-2 Source Down Detector Switch (Pool Type) Dear Sir/Madam: This is to advise you of a recent failure of the Pool Type Source Down Switch in a wet storage irradiator facility. The Pool Type Source Down Switch failed to provide the required signal when the source was fully down in the safe position. The failure was found to be due to green corrosion deposits on the metal plunger of the switch actuator assembly. The deposits caused the plunger to stick in the retracted position and prevented it from springing back to the source down position when the actuating lever indicated that the source was down. The switch failure resulted in the machine stopping in a safe condition. Access to the radiation room is denied until a source down signal is obtained. The correct procedure in this event is to call Nordion International Inc. for instructions on gaining access so that the problem can be corrected. Nordion will be sending you a replacement switch actuator made from corrosion resistant materials together with instructions for the replacement. We expect to be able to ship these by the end of December 1993. In the meantime we ask you to inspect your switch. If you see evidence of corrosion, remove the switch actuator and have it cleaned free of corrosion before having it reinstalled and continuing normal service. If you have any questions regarding this information, please do not hesitate to call me. Yours sincerely, R.G.McKinnon Chief Engineer . Attachment 2 IN 94-89 December 28, 1994 Page 1 of 6 1994 June 21 SERVICE BULLETIN IND-94-1 IRRADIATORS WITH NORGREN SOURCE VALVES Dear Sir/Madam: This Service Bulletin is being used to advise you of a source hoist pneumatic valve failure. Although there is no substantial risk of injury in this event, it is Nordion policy in the interest of safety and reliability of our products to recommend and implement where possible the necessary corrective action. During a normal shutdown of an irradiator, the source failed to return to the storage position and only returned after the air supply line to the source hoist was disconnected. The valve was a Norgren model K71EA00-KS1-AECKG1. Evaluation showed that this valve requires a spool which would always be open to exhaust should it jam in any intermediate position. The failed valve had a standard spool which blocked all ports when it jammed in an intermediate position thereby preventing the source from going down. The action required to prevent this occurrence is to remove the standard spool (Norgren Part No. 54237-56) from the valve and replace it with a new spool (Norgren Part No. 54237-58) that will allow air to exhaust if it jams in any intermediate position. You will find the replacement spools enclosed. To install these parts please follow the instructions provided, fill out the enclosed inspection form and return it to Nordion in the envelope provided. Yours sincerely, R.G.McKinnon Chief Engineer Quality Assurance Department. Attachment 2 IN 94-89 December 28, 1994 Page 2 of 6 NORDION INTERNATIONAL INC. DECLARATION OF ORIGIN AND VALUE TO (CONSIGNEE): UNIT DESCRIPTION OF GOODS QUANTITY Norgren Spools (Part No. 54237-58) COMMERCIAL VALUE: $30.00Cdn. COUNTRY OF ORIGIN: United States of America CHARGE POINT #: NR200K00 SIGNATURE: DATE: 1994 June 23 Graham Rose . Attachment 2 IN 94-89 December 28, 1994 Page 3 of 6 NORGREN NUGGET 200 SERIES SOURCE HOIST VALVE SPOOL REPLACEMENT INSTRUCTIONS June 22, 1994 This document pertains to the modification of Norgren valves with a part number K71EA00-KS1-AECKG1 in source hoist use. The modification details the replacement of the old norgren part number 54237-56 spool with a norgren part number 54237-58 spool supplied in this kit. The spool replacement kit contains: 1-One new spool (Norgren part number 54237-58) and one spool number label for each source hoist valve in your source hoist pneumatic assembly(ies). 2-A Nordion service bulletin regarding the source hoist valve spools, this instruction sheet/packing list, the Norgren valve inspection form and a return shipping label. If any of these items are missing, please call Nordion at 1 800 465 3666 from the United States or (613) 592 2790 from elsewhere in the world and ask for Graham Rose in Irradiator Engineering or the Installation and Service department. NOTE: Read the service bulletin and all instructions before starting the spool replacement. Spool Replacement Procedure 1-Shut down the irradiator. 2-Enter the personnel access and disconnect the air supply to the source hoist valve panel (disconnect the chain across the personnel access corridor). 3-Close the personnel access door and take the machine key with you to the source hoist valve panel. This will prevent inadvertent machine startup. 1 . Attachment 2 IN 94-89 December 28, 1994 Page 4 of 6 NOTE: Steps 4 through 7 must be performed for each source hoist valve in the source hoist pneumatic assembly(ies). 4-Remove the solenoid valve operator from the end of the valve (two (2) phillips screws). Be careful to note the orientation of the solenoid operator and insure you do not loose the small O-ring and plug which are between the valve body and operator. 5-Remove the spool from the valve body. 6-Grease the new spool using the grease in the package and install the spool. Spool orientation is not important. 7-Replace the solenoid valve operator, noting the observations made in step 4. 8-Repeat steps 4 to 7 on all source hoist valves. Test Procedure 1-After the spool replacements are complete, start the machine using the normal startup procedure. Raise all source racks. 2-Confirm that all source racks were raised. 3-Shut down the machine and confirm that all source racks return to the fully shielded position. 4-Start the machine again, using the normal startup procedure. 5-At the source hoist valve panel, remove the electrical coil connector from one of the source hoist valves. The rack should return to the fully shielded position. 6-Re-install the coil connector and repeat steps 4 to 6 for the remaining source hoist valves. 2 . Attachment 2 IN 94-89 December 28, 1994 Page 5 of 6 Old Spools Please return the old spools which were removed from the source hoist valves with the valve inspection form in the shipping envelope, to Nordion for analysis. Validation The 54237-58 spool has been tested in a K71EA00-KS1-AECKG1 valve. All flow paths and spool movement failure modes were tested. The valve performed correctly. If any difficulties or questions arise, please call Nordion at 1 800 465 3666 from the United States or (613) 592 2790 from elsewhere in the world, and ask for the Installation and Service department. Sincerely, Graham Rose Project Engineer 3 . Attachment 2 IN 94-89 December 28, 1994 Page 6 of 6 Norgren valve inspection form Did the system pass the test procedure Date Approximately how old are the spools How old are the valve bodies Approximately what was the valve rebuild interval Was lubricated air used in the valves How easily was the spool removed(ie. slid out,notchy,difficult) Approximate number of source movements per day(0.1,1,10,50) Have any symptoms of a possible valve failure been noticed in the past This history of spool change will go on the unit history file for each irradiator at Nordion for future reference. The valve data will be used to determine if any further action needs to be taken regarding the Norgren K71EA00-KS1-AECKG1 source hoist valves. Spools were changed and labels affixed by Date I thank you in advance for your input. Anyone who would like results of this survey may call Graham Rose at Nordion at 1 800 465 3666 from the United States or (613) 592 3400 Ext. #2545 from elsewhere in the world. Please allow 4 to 6 weeks after you receive this to allow for response return and return processing.
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