United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9709250208

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3M Health Physics Services    3M Center, Building 220-3W-06

                              PO Box 33283

                              St. Paul, MN 55133-3283

                              612 736 0498

                              612 736 2285 Fax

September 18, 1997

U.S.  Nuclear Regulatory Commission

Document Control Desk

Washington, D.C. 20555


Subject:  Failure of Co-60 Source to Lower in Response to Fault

          Indications and Emergency Stop Signals

Description of the August 12 Event Resulting in 3M's Decision to Notify

the NRC Under 10CFR21

This letter constitutes 3M's notification to the NRC that the source rack

containing approximately 1.5 MCi of doubly encapsulated Co-60 in 3M's

AECL Model JS-7500 gamma irradiator located in Brookings, SD failed to

lower in response to fault indications and emergency stop signals on

August 12, 1997.  The letter follows 3M's telephone notification to the

NRC on August 20, 1997 about this event.

The following fault indications and stops, although activated, failed to

return the source to the storage pool:

1.  Internal Conveyor

2.  Safety Timer

3.  Machine Safety Stop

4.  Emergency Stop

The source rack was returned to the storage pool without further incident

by turning off the machine key.  Personnel safety was never compromised

during the approximately 20 minutes the source remained raised.  The

personnel access door remained locked until the source was returned to

the pool.

Despite multiple fault indications at approximately 2:35 p.m. on August

12, the source remained raised.  Upon noting the condition, the operators

on shift first verified that the source was up by noting the position of

the cable sheaves in the penthouse.  They then compared this information

to the source position indications on the control console.  All

indications from the penthouse and the control console consistently and

correctly indicated that the source was in the irradiate position.  At

approximately 2:55 p.m., one of the operators turned the keyswitch to the

"off" position, thereby returning the source to the storage pool.


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September 18, 1997

3M's Investigation into the Root Cause

Once the source was securely stored in the pool, 3M electricians examined

and tested circuits and relays in the maze and the control console on

August 13 and 14.  The electricians found electrical grounds in the maze

wiring that caused current to bypass relay K50 which opens in response to

control panel faults and normally de-energizes solenoid valves SV39 &

SV40 controlling the source hoist operation.  (See Attachment 1).  The

ground fault indicator, located in the rear of the control console, was

illuminated.  All available evidence indicates the failure was

electrically induced and not mechanical.

3M's Corrective Actions and their Present Status

On August 14, 3M Brookings personnel initiated a conference call with

members of 3M's corporate Health Physics Services staff and

representatives of Nordion International (formerly AECL).  All parties

agreed to the following immediate corrective actions:

Corrective Action #1

3M Brookings would activate the 10CFR21 Committee to determine (1)

whether a defect or a deviation existed in the irradiator design or

components, and (2) whether this must be reported to the NRC.

Status: Corrective Action #1

The 10 CFR 21 committee met on August 19.  The committee concluded that

because the defective electrical design may have resulted in a major

degradation in irradiator safety, i.e.  the temporary loss of the

emergency stop potentially created a substantial safety hazard, a

reportable defect existed.  The committee concluded that 3M should notify

the NRC so that the NRC could choose to trend data from similar

irradiators to determine whether a generic design defect existed in

similar facilities.  3M concluded it was important to facilitate the

NRC's opportunity to notify other owners of similar irradiators.

Consequently, 3M informed the NRC about the defect by telephone on August


Corrective Action #2

3M would write a license amendment request to make the following

electrical changes to the control circuitry:


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September 18, 1997

(1)  Change the ground fault indicator to a ground fault detector with an

     associated control circuit.

(2)  Change the control panel machine stop push button S50 to a

     detented/latched push button with additional contacts wired in

     series with solenoid valves SV39 & SV40 controlling the source


(3)  Install additional contacts on customer stop push button S59 wired

     in series with SV39 and SV40.

(4)  Add circuitry normally open K30 and K50A into the K61 fault

     detection circuit, resulting in a final system check of the internal

     conveyer, safety timer, source rack, area monitor, air pressure,

     exhaust fan, high temperature and smoke detectors, and radiation

     monitor indications as well as those checked prior to start up.

     (See Attachment 2).

Status: Corrective Action #2

3M will submit this license amendment to the NRC within the next week.

3M is currently waiting for written endorsement from Nordion

International for these enhancements.

Corrective Action #3

3M would replace both K50 relays with new ones.

Status: Corrective Action #3

The K50 relays and the K28 relay were replaced on September 2, 1997.

Corrective Action #4

3M operators would check the machine safety and emergency stops once per

shift to ensure they are functioning correctly until all changes listed

in Corrective Action #2 have been made.

Status: Corrective Action #4

The operators are currently checking the machine safety and emergency

stops once per shift They will continue their checks until the plant

Radiation Safety Officer instructs them otherwise.


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September 18, 1997

3M's August 20 Telephone Notification per 10CFR21

On August 20, 3M notified representatives of Region III that the source

had failed to respond to the internal conveyor, safety timer, machine

safety stop and emergency stop signals and faults.  3M informed the NRC

that 3M would be formally reporting the event in accordance with the

applicable reporting provisions of 10CFR21.  Later on August 20th,

representatives of Region III responded by indicating that the electrical

fault should have been reported under 10CFR36.83 (a), "Source stuck in an

unshielded position." Although 3M did not agree with this assessment, 3M

formally reported the event under 10CFR36.83 (a) on the same day.

10CFR36.83 requires telephone reporting within 24 hours of the event.

Requiring licensee notification within 24 hours indicates that the NRC

views this situation as an emergency, with the potential to produce

sickness or even death in exposed personnel.  3M did not report under

this regulation because 3M interpreted 10CFR36.83(a) as applying to a

mechanically stuck source, i.e., a source that was jammed or wedged in

the unshielded position inside the cell and which could not be freed

without assistance from Nordion and/or NRC personnel.  Such a loss of

control would indeed constitute an emergency; however, this situation did

not occur on August 12 in 3M's Brookings, SD plant Instead, the source in

3M's irradiator remained in the up position for approximately twenty

minutes before the operator turned the machine key to "off".  The

personnel access door remained locked.  As a result, the 3M situation

never posed a threat to the health and safety of operating personnel or

the general public.

3M's interpretation of "stuck" is based on the NRC's regulatory guidance.

Appendix C of Draft Regulatory Guide DG-0003 "Guide for the Preparation

of Applications for Licenses for Non-Self-Contained Irradiators" gives

examples of dangerous or potentially dangerous incidents that have

occurred at irradiators.  In every example involving a stuck source, the

source was mechanically wedged or jammed against the source pass

mechanism or the product totes.  In NUREG-1345, "Review of Events at

Large Pool-Type Irradiators", all examples of stuck source racks involve

racks which were jammed or wedged due to problems with source cables and

product carriers.


Because 3M felt that 10CFR36.83(a) did not apply, 3M did not notify the

NRC by telephone within 24 hours of the event.  Instead, a 10CFR21

investigation was initiated and completed, and the NRC was notified by

telephone informally upon completion of the investigation.  Because the

NRC requested reporting under 10CFR36.83(a), a formal telephone report

was made in accordance with 10CFR36.83 that same day.  This


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September 18, 1997

occurred on August 20, eight days after the event.  Since the NRC

preferred that 3M report the above-described incident under

10CFR36.83(a), this letter constitutes the written component of the

report required under 10CFR36.83.  However, we emphasize our conclusion

that NRC's regulatory guidance indicates that 10CFR36.83(a) does not

apply to the August 12 event.

3M has requested written agreement from Nordion for the changes specified

in Corrective Action #2 above.  Once the Nordion documentation arrives,

3M will write a license amendment request separate from this letter

requesting permission to effect these changes.  The license amendment

request will then be mailed to Region III.

Questions or comments regarding this report may be directed to Deborah A.

Loeser or Frederick B.  Entwistle of 3M's Health Physics Services at

(612) 733-3199 or (612) 736-0740, respectively.


Duane C.  Hall, Manager

Health Physics Services

c:   R. J. Stangeland - Brookings Mfg. Engineering - Brookings, SD -


Figure "Attachment 1" omitted.

Figure "Attachment 2" omitted.


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