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dose estimates for Toaki accident
Here is the latest section from Valarie Putnam's accident summary on dose
estimates. Her final report should be out in December or
January. Her draft report, including references for the material
below, will be available for downloading at the following web site:
http://www.ans.org/PI/japan.html
soon.
Mike ... mcbaker@lanl.gov
--------------------------------------------
News reports indicate approximately 7000 people were checked for radiological exposure using various techniques. Apparently most doses were estimated from sodium activation levels, measured with whole-body counters or through blood samples. Dose estimates were completed for all plant workers, in-field responders, nearby people [evacuees?], and, at their personal request, others in the region. Some estimates are being revised based on further information, such as estimated fission yields and additional medical tests ordered for some overexposed persons. To ensure all data is gathered, invited medical experts from around the world recommended a second test for up to 1800 people, to be conducted after October 30th because blood changes due to low doses are slow to develop.
Significant unplanned exposures were apparently limited to 69 people:
· The three workers in the building received severe exposures. Initially estimated doses of 17, 10, and 3Gy were revised in mid-October to 18, 10, and 2.5GyEq (1800, 1000, 250rad, gamma equivalent) respectively, apparently based on fission yield estimates (Soda 91026; IAEA 991115). By November 15th dose estimates were revised to 9.06, 4.96, and 1.19GyEq (906, 496, and 119 rad, gamma equivalent) based on four estimation methods: 24Na activation in blood, 24Na from whole body counts, lymphocyte count, and chromosome aberration (Kato 991115). News articles reported that, in violation of requirements, these three men were not wearing their personal dosimeter badges, which were found 150 or 160 yards from the tank (CNN News;Asia Now 991016). http://www.nirs.go.jp/jco/jco_no3.html indicated for the third patient, NIRS monitored clothing, nasal smear, and vomit, confirming the presence of 24Na, 80Br, 82Br and 42K and detecting 139Ba, 91Sr, 139Xe, and 91Kr. For this patient NIRS also detected 56Mn, 64Cu, 65Ni, and 24Na activity in coins, blood sample, and a cell phone.
· Of 123 radiation workers on site during the first pulse, 56 JCO workers outside the accident building received doses from 0.1 to 23mGy (0.01 to 2.3rad), based on analyses of film badges whole body counts. Of these 56 workers, only 22 were wearing film badges (http://atmimg.tokyo.jst.go.jp:8090/jco02/siryo7-2.htm; Kato 991115; IAEA 991115). Table 3 lists initial dose estimates for 42 of the 93 workers subjected to whole body counting, including the 36 initially listed as potentially overexposed workers. Twenty workers were added to the initial list of 36 potentially overexposed workers on October 15th. CNN news indicated these workers were initially overlooked because they failed to turn-in their dosimeter badges (CNN News;Asia Now 991016). (http://atmimg.tokyo.jst.go.jp:8090/jco02/siryo7-1.htm and http://atmimg.tokyo.jst.go.jp:8090/jco03/siryo3-2-1.htm (first map) show approximate locations for 123 on-site people during the first pulse. http://atmimg.tokyo.jst.go.jp:8090/jco02/siryo7-2.htm shows initial exposure estimates for the 93 persons. http://atmimg.tokyo.jst.go.jp:8090/jco03/siryo3-2-1.htm (third map) shows movements of on-site persons who apparently did not go to or stay in evacuation staging or muster areas.)
· Three municipal emergency service workers received doses from 0.5 to 3.9mGy (0.05 to 3.9rad) when they rescued the three severely exposed workers and, apparently, accompanied these workers to the hospital. Table 4 lists their initial dose estimates based on whole body count results. These initial dose estimates were revised to 0.4 to 4.1mGy (0.04 to 41rad) on October 22nd (IAEA 91116). These men apparently entered the area without appropriate PPE because they were not advised of conditions or accident type before entry. [Respirators and anti-contamination suits would help protect wearers from some fission products, splashed solution, etc., but not from neutron radiation. Also, news reports might include protective measures such as limiting time and using routes that might be better shielded than other routes. Nobody I talked with knows of PPE to protect from direct neutron radiation exposure (body suits with thick water lining?)]
· Up to seven members of the public, who were near site boundaries at the time, received doses initially estimated as 0.4 to 9.1mGy (0.04 to 0.91rad). Table 5 lists their initial dose estimate information. These estimates were revised to 0.5 to 9.4mGy (0.05 to 0.94rad) on October 22nd (IAEA 991115). These people are construction workers who were working at or near the plant (BBC 991004; IAEA 99116). They are identified here as construction workers because they were not necessarily residents and they might have been contractor or temporary plant employees. [Apparently these people were near the point B marked in Figure 1. Early news reports of exposures to golf course employees apparently confused a golf course with this construction-related area.].
Significant planned-during-emergency-response exposures were apparently limited to 27 JCO workers (IAEA 991115; Kato 991115):
· Of 35 people responding during efforts to drain the water jacket, 21 JCO workers received doses initially estimated as between 0.04 to 119mSv (0.004 to 11.9rem). Table 4 lists initial dose estimates for these 35 people. These estimates were revised to 0.05 to 120mSv (0.005 to 12.0rem) on October 22nd. Planning for these 21 exposures included dividing responders into ten two-man teams, and having each responder wear [clip-on?] gamma and neutron dose rate meters.
· Apparently six JCO workers received doses from 0.03 to 0.61mSv (0.003 to 0.061rem) while feeding boric acid into the precipitation tank. Planning for these exposures included dividing responders into three two-man teams. These responders apparently wore gamma, but not neutron, dose rate meters, a decision based on data from radiation monitoring points within and around the site.
Area radiation level estimates were also completed based on other information:
· on-site personal film badges which were not worn at the time of the accident (for example, an employee was absent, was not working in an area requiring a badge, or neglected to wear the required badge). Effective dose from gamma radiation ranged from 0.2 to 6.2mSv (0., with most in the range of 0.1 to 1.0mSv. (IAEA 991115)
· neutron activation of various metals on- and off-site, such as zinc coins and gold jewelry. Locations within 100, 150, and 500m of the subject building are estimated to have received 100, 40, and 1mSv neutron radiation, respectively (Daily Yomuiri 991104; KnoxNews 991115). Apparently one or more off-site locations received approximately 1.4mSv over the first few hours, exceeding a 1mSv limit for the public.
Two Greenpeace activists measured radiation and/or contamination levels around the facility and Tokaimura. Greenpeace charges that hundreds, rather than about 50, were overexposed in the accident. However, evidence to date indicates these claims are exaggerated.