ENS 51331
ENS Event | |
|---|---|
15:00 Aug 20, 2015 | |
| Title | Personnel Overexposure |
| Event Description | At about 0900 MDT on Thursday August 20, 2015, [the CEO of International Isotopes] was informed by our area manager that one of our technicians had been exposed to a 'flash' of radiation while handling a Co-60 source drawer. They reported his electronic dosimeter was reading 5.62 Rem. [The CEO of International Isotopes] immediately went to the work area and verified the Co-60 source (approximately 4000 Curies of Co-60) was in a secure shielded position and interviewed the technicians involved. All of the other technicians in the area reported their pocket or electronic dosimeters were reading normally (e.g. doses in the range of 1 to 5 mRem). The initial investigation indicates there was only one technician performing the work and in the immediate vicinity of the cask and source drawer at the time of the exposure.
The technicians were preparing to transfer the Co-60 source drawer into another shielded container (a therapy head). A special handling tool had been bolted to the end of the source drawer for positioning the source drawer within a therapy head. This special handling tool needed to be removed from the source drawer in order to transfer the source back into the therapy head. The technician attempted to move the source drawer just enough to expose the bolts on the special handling tool so it could be removed. The technician stated that the drawer was sticking and when he pulled harder on the drawer it slid out of the cask about 9 inches, bringing the source to within an estimated 2 inches of the cask external surface. The technician immediately pushed the source drawer back into the cask into a fully shielded position. The technician then noted that his electronic dosimeter was reading 5.62 [Rem] and he left the work area. The electronic Dosimeter reading was at 26 inches from the source. The TLD was approximately 15 inches from the source and a dose calculation resulted in a whole body dose of 16.9 Rem. Dose calculations for the hand (extremity) is 237 to 950 Rem depending on various assumptions. The technician was not wearing any finger rings. His dosimetry is being sent off for emergency reading. The technician is being restricted from work on radioactive materials.
The follow-up investigation continues at INIS. We have completed several simulated walk-throughs of the event and compared to personnel statements and descriptions of the event. We have been able to retrieve security camera footage of the event as well from two different angles. The security video footage reveals that the technician did, in fact, momentarily completely remove the source drawer containing the cobalt source from the shield. This video is being used to carefully model estimated exposures to both the individuals extremity and whole body. Dosimetry results were obtained from Landauer and indicated whole body readings of 201.875 Rem. Blood sampling from the individual does not support this high of an exposure and a review of the security video indicates the individuals TLD (on a lanyard around his neck) swung out away from his body, very near the source drawer, and was not in a position to accurately represent whole body exposure. Additional modeling using the security camera footage and additional data obtained from the electronic dosimeter will be used to estimate a more accurate whole body dose to the individual. The exposed individual has been providing blood samples at the local hospital per the sampling protocol prescribed by the DOE Radiation Emergency Assistance and Training Center. All blood samples are normal with no indication of radiation exposure. This sampling will continue through today (August 22) until a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> period of testing from the event has been completed. Closer modeling to more accurately determine the individuals extremity dose are still in progress. This modeling is using both security camera footage as well as video footage from the mock-up of the event. While this modeling is not complete it appears that extremity dose may be closer to 50 Rem or less rather than the 250 - 950 Rem initially estimated. Daily photographs are being taken of the individuals hands and lower extremities to monitor for the development of any edema or signs of radiation damage to tissues. At this time there are no indications of radiation effects to any extremity. Additional data was extracted from the electronic dosimeter worn by the individual. This dosimeter was the device that initially read 5.62 Rem after the event. Analysis of the dosimeter data indicates it was exposed to a peak dose rate of about 3,739 R/hr. This is significantly less than the 10,166 R/hr initially estimated to have caused the 5.62 Rem ED reading at an estimated 2 seconds of exposure time. Using dose and dose rate information from this ED it appears the actual exposure time was about 5.4 seconds and this correlates with the security camera video time stamp. Additional information will be reported as it becomes available. Notified R4DO (Hay), NMSS EO (Habighorst), and NMSS (McIntosh), NSIR (Milligan), and NMSS_Events_Notification via email.
The following update was received from International Isotopes via email: Blood testing for the technician involved in the exposure event has been completed and all results are normal. Complete documentation is to be provided to the company by the medical provider on Monday and an additional follow-up discussion will be held directly between the company and the physicians at REAC/TS [National Nuclear Security Administration - Radiation Emergency Assistance / Training Site] on Monday, 8/24 to see what additional, if any, testing is recommended. Notified R4DO (Hay), NMSS EO (Habighorst), and NMSS (McIntosh), NSIR (Milligan), and NMSS_Events_Notification via email.
Dose modeling of the technician's extremity (left hand) and whole body exposures have been completed. These models estimate 49.1 Rem to the left hand. The whole body dose has been calculated to be 7.245 Rem. Both models were completed using micro shield and based upon a 3664 curie source in a 5.5 second exposure period. The whole body model assumed 3 worker positions and all times and distances are based upon our observations of the security video and supplemented by the mock-up of the event. Additional modeling will be performed of the lower extremities to confirm whether the left hand was likely to have been the most exposed extremity. The whole body model will also be validated by repeating the calculations and assumptions used against the known position of the electronic dosimeter and comparing calculated results of this modeling to the 5.62 Rem indicated on that dosimeter after the event. Over the coming weeks the company plans to acquire an expert in this type of dose reconstruction and have them independently verify the company's models and exposure calculations. The completed report of all lab work on the exposed technician is expected to be obtained on Monday, August 23. The company also plans to contact DOE's REAC/TS on Monday and confer with them on all blood test results and discuss whether any additional precautionary sampling or testing is advised. Visual examination of the exposed technicians hands and lower extremities will continue to be performed daily at least through August 28 unless REAC/TS recommends a longer monitoring period. At this time there are still no indications of radiation effects to any extremity of the exposed technician. Notified the R4DO (Hay), NMSS EO (Habighorst), IAEA Contact (Milligan & McIntosh via e-mail), and NMSS Events Resource (via e-mail).
REAC/TS has been contacted to discuss and review the results of laboratory work of the exposed technician. [The] Associate Director, Radiation Emergency Assistance Center/Training Site confirms that all blood work appears normal. [The Associate Director REACTS/TS] recommended that we continue CBC once daily through Friday this week and continue to forward them the results. She also agreed with our plan for continued daily examination of extremities through 8-28 but recommended further that we continue this examination every other day for up to 3 weeks post event (Sept. 10). The company has contracted with [the] Associate Dean for Idaho State University, to perform an independent dose assessment of the event. This work is expected to begin this week with a goal of including this report with the formal 30 day report on this event. Notified the R4DO (Campbell), NMSS EO (Habighorst), IAEA Contact (Milligan & McIntosh via e-mail) and NMSS Events Resource (via email).
The following report was received via e-mail: International Isotopes received the cytogenetic biodosimetry analysis for this event. "The results are dated September 2, 2015 but were just made available through the ordering physician and the individual to the Company today. The result of 0.504 Gy (50.4 Rad) is much higher than our previous whole body dose estimates but does not change the Company's current course of action and corrective actions. REAC/TS was contacted to discuss the results and does not recommend any re-testing to validate the results. REAC/TS still confirms they do not consider this a 'clinically significant dose.' Notified the R4DO (Drake), IAEA (Milligan and McIntosh), NMSS EO (Silva), and NMSS Events Resource via e-mail. |
| Where | |
|---|---|
| International Isotopes Idaho Falls, Idaho (NRC Region 4) | |
| License number: | 11-27680-01 |
| Organization: | International Isotopes |
| Reporting | |
| 10 CFR 20.2202(a)(1) | |
| Time - Person (Reporting Time:+-1.93 h-0.0804 days <br />-0.0115 weeks <br />-0.00264 months <br />) | |
| Opened: | Steve Laflin 13:04 Aug 20, 2015 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Sep 9, 2015 |
| 51331 - NRC Website | |
International Isotopes with 10 CFR 20.2202(a)(1) | |
WEEKMONTHYEARENS 513312015-08-20T15:00:00020 August 2015 15:00:00
[Table view]10 CFR 20.2202(a)(1) Personnel Overexposure 2015-08-20T15:00:00 | |