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).
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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
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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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