Part 21 Report - 1996-020

ACCESSION #: 9511080110 NOTE: This text document was processed from a scanned version or an electronic submittal and was processed as received. Some tables, figures, strikeouts, redlines, and enclosures are not included with this submittal, and are omitted due to ASCII text conversion limitations. In order to view this document in its entirety, you may wish to use the NUDOCS microfiche in addition to the electronic text. 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. *** END OF DOCUMENT ***

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