Part 21 Report - 1996-020

 
 

ACCESSION #: 9511080110



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                              UNIVERSITY OF

                                WISCONSIN

                                 MADISON



                                                       September 18, 1995



U.S. Nuclear Regulatory Commission, Region III

Inspection and Enforcement Section

ATTN: Ms. B. J. Holt

801 Warrenville Rd.

Lisle, Illinois 60532



RE:  Incident Involving J.L. Shepherd Model 109 Irradiator, BML 48-09843-

     28



Dear Ms. Holt:



Background



The UW Madison has 5 closed-beam irradiators under license number 48-

09843-28.  Three of these are J.L. Shepherd irradiators, two Mark Is and

one Model 109.  The Model 109 located in Rm. K4/358B Clinical Sciences

Center, is relatively unique in that the radiation source is actually

about 12 Cs-137, each nominally about 240 Ci for a total current activity

of 2880 Ci.



Because this incident involved authorized repairs to the door/cover to

the sample chamber, a description of that system may be in order.  In the

Model 109, the sample chamber is a cylinder approximately 6 inches in

diameter and about 12 inches long.  It is stainless steel with shielding

at both the bottom (or base) and the top.  Because there is scatter

radiation, two thick scatter shields in the shape of French doors.  There

is a solenoid interlock at the top of the left-hand door which is

activated by an arm from the right-hand door depressing the interlock

when the two doors are together.  The interlock prevents irradiation of

the sample chamber while the scatter shield is open.



There is a door/cover (Figure 1) which provides access to the sample

chamber.  It is a machined piece of stainless steel with a thumb hole

centered approximately 1 inch from the top which is used to remove the

door.  When in place, the door is secured at the top by a spring loaded

screw fastened to the column through a tang on the door and at the bottom

by a small (approximately 1/4 x 1/4 tab welded to the door which is

inserted into a groove in the bottom of the sample chamber.  The entire

cylindrical sample chamber is lowered into the source chamber for the

irradiation.  Tolerances between the sample chamber and chamber housing

and the walls of the irradiator are less than 1 mm.



Approximately 1 month ago the tab on the bottom of the door broke off

(perhaps the second time in 15 years).  The door/cover was removed (as it

must be to insert



                            Safety Department



        University of Wisconsin-Madison   103 North Lake Street 

    Madison, Wisconsin 53715-1212   608/262-8769   FAX: 608/262-6767





samples into the chamber) and a new tab was welded on to the door. 

Unfortunately, this tab was not quite aligned with the slot causing the

door to be slightly out of plumb.  When the chamber was lowered, it would

drag and stick, resulting in the sloshing and spilling of some sample

liquids in the sample chamber.  To reduce the drag on the system, the it

was decided to file / grind down portions of the door which were sticking

out and rubbing.  This maintenance had the concurrence of J.L. Shepherd

and could be performed by taking the door to a machine shop.



Description of the Event (attached letter of 12 Sept)



Tim Sailor, a maintenance worker was contacted to perform the grinding

operation.  Because he did not know what was actually wrong and where the

misalignment points were, he desired to be shown the problem in action. 

On 11 September, Jim Refsguard, the maintenance manager in Human Oncology

brought the worker into the irradiator room to demonstrate the problem.



Because the scatter shield doors hide the movement of the sample chamber

column, Mr. Refsguard decided to by-pass the interlock using a screw

driver and watch the column descend, noting the areas of contact.  The

two persons stood about 1 meter from the front of the unit (Figure 2) to

observe the transit, Mr. Refsguard selected a time of 0.1 minutes on the

timer and pressed the "irradiate" button.  The sample chamber column

began descending.  Within a second or so the Prime Alert area monitor

(set to alarm at 1 mR/hr) alarmed.  Knowing that the alarm indicated

radiation exposure, Mr. Refsguard immediately pressed the "load" button

and the sample chamber returned.  The door was then removed, the high

points ground down, and the door replaced.



Discussion



Although the Jim Refsguard had been responsible for proper functioning

and certain routine maintenance of this system since about 1981 and was

familiar with its operation, there is no documentation of his receiving

formal training on the system.  As Mr. Refsguard noted in his report,

this lack of formal radiation safety training resulted in his assuming

that the radiation would shoot up the column and not scatter. 

Additionally, neither he nor Tim Sailor wore any dosimeters when in the

room.





Thus, none of the workers involved had dosimetry nor documented training. 

Since September, 1993, it is Safety's policy that all new closed-beam

irradiator workers first receive the 4-hour Radiation Safety for

Radiation Workers training (offered weekly) followed by an irradiator

training block which has both a 2-hour academic portion (usually offered

monthly) and a hands-on, irradiator specific (e.g., Mark I or Model 109)

portion.  These workers then apply for dosimetry to monitor radiation

exposure.  As noted in Item 8 of the 48-09843-28 license renewal packet

(control No. 398620) Safety is in the process of extending this program

to include the Model 109.  Additionally, whenever maintenance workers

enter an irradiator room, our policy is



                                                   Model 109 Incident - 2





to provide that worker with training commensurate with the potential

hazard, but as a minimum one that covers the radiation hazard and any

alarms present, and to provide oversight while the worker is in the room.



On 12 September, we attempted to obtain some relatively firm exposure

numbers.  We taped 3 TLD chips on the inside of the left scatter shield

approximately 6.5, 15, and 18 cm from the bottom of the scatter shield. 

We then ran the system through the scenario outlined by Mr. Refsguard

(i.e., timer set for 0.1 min, irradiate button pressed, sample column

went to irradiate position, load button was pressed -- a total TLD

exposure time of approximately 9.8 seconds, 0.024 minutes exposure and

about 0.07 minutes chamber travel).  These chips were then sent to our

dosimeter vendor for reading.  The exposures to the chips next to the

sample column were 350, 45, and 27 milliroentgen, respectively.



Because the sources are stationary, we determined that the persons could

not have been exposed to the primary beam, however, it is possible that

the bottom chip (at 6.5 cm) may have been exposed partly to the primary

beam.  Assuming a worst case scenario, that the exposure to this chip was

due entirely to scatter (assuming part exposure to the primary beam would

reduce the exposure to the persons involved), we calculated (attached

letter from Bruce Thomadsen dated 18 Sept) a maximum exposure at the 1

meter distance where both workers were standing to be approximately 0.4

m.R.



Corrective Action



Although calculated exposures are trivial, we believe that the bypassing

of a safety interlock by persons not completely aware of the potential

radiation hazards involved is a significant safety issue.  Therefore, our

corrections are addressed to insuring such safety incidents do not occur

with this system, nor with the other closed-beam irradiator systems we

have on campus.  Specifically:



1.   Safety is currently integrating the training for all irradiator

     workers into a single program which will enable us to implement a

     uniform program with appropriate personnel controls for all three

     research irradiators.  The first of these classes is scheduled for

     20 September.  Mr. Refsguard indicated that he had always intended

     taking these classes and would make attendance a priority.  He did

     attend the 4-hour training block on 13 Sept.



2.   Mr. Refsguard was informed that all maintenance requests would need

     to be staffed through the Safety Department (much as is done for the

     other irradiators on campus).  Safety will coordinate any necessary

     training and on-site supervision.  We have been communicating with

     J.L. Shepherd and have tentatively arranged to have J.L. Shepherd

     train and certify several of our workers to perform certain (non-

     source handling) maintenance functions on these irradiators.



                                                   Model 109 Incident - 3





3.   All irradiator owners on campus were appraised of the incident and

     the need to channel maintenance functions through the Safety

     Department to insure proper training and dosimetry are provided.



If you have any questions pertaining to this information, please call me

at (608) 262-9178 or FAX me at (608) 262-6767.



Sincerely,





Ronald R. Bresell

Radiation Safety Officer



xc

NRC Operations Center



                                                   Model 109 Incident - 4





Figure omitted.





Figure omitted.





                         UNIVERSITY OF WISCONSIN

                              COMPREHENSIVE

                              CANCER CENTER



TO:   Ron Bresell

      UW Safety

From: Jim Refsguard

      UW Cancer Center

RE:   K4/358 Alarm

                                                       September 12, 1995



     Per our conversation, this is my report on the incident in CSC

K4/358 on September 11th.



     I had received word that the drawer of the Cesium Irradiator was

again running roughly and needed to be checked.  We have had our best

results working with the machine shop at the Physical Sciences Lab, and

Tim Sailor arrived to work on the unit.



     We discovered that both the outer surface of the door to the sample

chamber and the inner surface of the lead outer doors were scratched and

grooved, apparently because the sample chamber door was out-of-round and

binding as the drawer was lowered.



     In an attempt to determine what portion of the sample chamber door

was catching we manually closed the interlock switch for the lead doors,

leaving them open while the drawer descended.  I assumed since the source

was buried in the stack the only escape of radiation would be directly up

and did not anticipate the scattering effect.



     When the drawer was about half lowered the alarm went off for about

1 second then silenced as the drawer finished its descent.  As soon as I

heard the alarm I pressed the load button to bring the drawer back up. 

As the drawer returned the alarm again was heard for about 1 second. 

When the drawer reach the load position we immediately closed the outer

doors.  I understand now that the alarm occured when the hollow sample

section of the drawer was situated above the source and did not offer any

shielding.  I now understand that some of this radiation scattered off

the insides of the lead stack until it exited the stack and scattered

about the room, thus activating the alarm.



     Both of us were about 3 feet away from the unit positioned to look

horizontally at the level of the sample chamber cover as it descended.



     I immediately reported the alarm to Dr. Thomadsen for his

evaluation.  If you have any questions or need clarification, please

contact me.



                                   Jim Refsguard

                                   CSC K4/566   263-5365



                          Facilities Management



         K4/566, 600 Highland Avenue o Madison, WI 53792-0001 o

                    (608)263-5363 o FAX (608)263-6062



                 UNIVERSITY OF WISCONSIN MEDICAL SCHOOL





                              UNIVERSITY OF

                            WISCONSIN-MADISON

                             MEDICAL SCHOOL



Date:     18 September 1995



To:       Ron Bresell

          Radiation Safety Officer



From:     Bruce Thomadsen





re:       Exposure from the cesium Hot Box



Based on the information gathered from Jim Refsguard and from

measurements on the cesium unit, we have calculated the exposure that he

and the worker from PSL might have received.  As can be seen on the

scaled figure, neither person could have been in the primary beam. 

Considering scattered radiation, the hand-written sheet contains some

detailed calculations based on the TLD results.  Note that the TLD

measurements should be divided by 1.87 as the backscatter factor for Lif

in contact with lead.  From that analysis, the dose to the workers is

likely to be approximately 0.00124 mrem.



Ignoring the likely assumptions, and instead assuming that all of the

dose to the TLD chip was due to scatter from the top lead plug of the

drawer, the dose to the closest worker would be



                D= 187 mR (7.65 cm/165.5 cm)**2 = 0.4 mR.



These two values probably bracket the true dose, with lower value being

more realistic.



                      Department of Human Oncology



          K4/B100 Clinical Science Center   600 Highland Avenue

           Madison, WI 53792   608/263-8500   FAX 608/263-9167





Figure "Landauer Glow Curve Report Process #U8142A Card #0644955"

omitted.





Handwritten page omitted.





Graph omitted.





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