Potential Radiation Doses from 1996 Hanford Operations
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Potential Radiation Doses from 1996 Hanford Operations |
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In 1996, potential doses to the public resulting from exposure to Hanford Site liquid and gaseous effluents were evaluated to determine compliance with pertinent regulations and limits. These doses were calculated from reported effluent releases and environmental surveillance data using Version 1.485 of the GENII computer code and Hanford-specific parameters.
The potential dose to the maximally exposed individual in 1996 from site operations was 0.007 millirem (0.00007 millisievert) compared to 0.02 millirem (0.0002 millisievert) calculated for 1995. The radiological dose to the population within 80 kilometers (50 miles) of the site, esti- mated to be 380,000 persons, from 1996 site operations was 0.2 person-rem (0.002 person-sievert), which is slightly less than the 1995 calculated population dose of 0.3 person-rem (0.003 person-sievert). The average per-capita dose from 1996 site operations was 0.0005 millirem (0.000005 millisievert). The national average dose from background sources is 300 millirem per year (3 millisievert per year), and the current DOE radiological dose limit for a member of the public is 100 millirem per year (1 millisievert per year). Therefore, the average individual potentially received 0.0005% of the DOE standard and 0.0007% of the national average background.
Special exposure scenarios not included in the dose estimates above include the ingestion of game animals residing on the site, exposure to radiation at a publicly accessible location with the maximum exposure rate, and consuming drinking water at the Fast Flux Test Facility. Doses from these scenarios would have also been small compared to the DOE dose limit. Radiological dose through the air pathway was 0.005% of the EPA limit of 10 millirem per year.
The "boundary" radiation dose rate is the external radiation dose rate measured at publicly accessible locations on or near the site. The boundary dose rate was determined from radiation exposure measurements using thermoluminescent dosimeters at locations of expected elevated dose rates onsite and at representative locations offsite. These boundary dose rates should not be used to calculate annual doses to the general public because no one can actually reside at any of these boundary locations. However, these rates can be used to determine the dose to a specific individual who might spend some time at that location.
The dose rate at the location with the highest exposure rate along the 100-N shoreline (Figure 21) during 1996 was 0.02 millirem per hour (2 x 10-4 millisievert per hour), or about twice the average background dose rate of 0.01 millirem per hour (1 x 10-4 millisievert per hour) normally observed at offsite shoreline locations. Therefore, for every hour someone spent at the 100-N Area shoreline during 1996, the external radiological dose received from Hanford operations would be approximately 0.01 millirem (1 x 10-4 millisievert) above the natural background dose. If an individual spent an hour at this location, a dose would be received that is similar to the annual dose calculated for the hypothetical maximally exposed individual at Sagemoor. The public can approach the shoreline by boat but they are legally restricted from stepping onto the shoreline. Therefore, an individual is unlikely to remain on or near the shoreline for an extended period of time.
Figure 21. The N Reactor complex is located along the Columbia River shoreline.
Wildlife have access to areas of the site that contain radioactive materials, and some do become contaminated. Sometimes contaminated wildlife travel offsite. Sampling is conducted onsite to estimate the maximum contamination levels that might possibly exist in animals hunted offsite. Because this scenario has a relatively low probability of occurring, these doses are not included in the maximally exposed individual calculation.
Listed below are estimates of the radiological doses that could have resulted if wildlife containing the maximum concentrations measured in onsite wildlife in 1996 migrated offsite, were hunted, and were eaten.
During 1996, groundwater was used as drinking water by workers at the Fast Flux Test Facility. Therefore, this water was sampled and analyzed throughout the year in accordance with applicable drinking water regulations. All annual average radionuclide concentrations measured during 1996 were well below applicable drinking water standards, but concentrations of tritium were detected at levels greater than typical background values. Based on the measured concentrations, the potential dose to Fast Flux Test Facility workers (an estimate derived by assuming a consumption of 1 liter per day [0.26 gallon per day] for 240 working days), the worker would receive an effective dose equivalent of <0.2 millirem (<0.002 millisievert). The doses calculated here are well below the drinking water pathway dose limit of 4 millirem for public drinking water supplies operated by DOE.
Regulations that control radiation dose from airborne emissions from DOE facilities specify that no member of the public shall receive a dose of more than 10 millirem per year (0.1 millisievert per year) from exposure to airborne radionuclide effluents, other than radon, released at DOE facilities.
The 1996 air emissions from monitored Hanford facilities, including radon-220 and radon-222 releases from the 300 Area, resulted in a potential dose to a maximally exposed individual across from the 300 Area of 0.005 millirem (5 x 10-5 millisievert), which represents 0.05% of the standard. Of this total, radon emissions from the 327 Building contributed 0.003 millirem (3 x 10-5 millisievert); nonradon emissions from all monitored stack sources contributed 0.002 millirem (2 x 10-5 millisievert). Therefore, the estimated annual dose from monitored stack releases at the Hanford Site during 1996 was well below the Clean Air Act standard.
During 1996, the estimated dose from diffuse sources to the maximally exposed individual across the river from the 300 Area was 0.03 millirem (3 x 10-4 millisievert), which was greater than the estimated dose at that location from stack emissions (0.005 millirem or 5 x 10-5 millisievert). Doses at other locations around the Hanford Site perimeter ranged from 0.02 to 0.06 millirem (2 x 10-4 to 6 x 10-4 millisievert). Based on these results, the combined dose from stack emissions and diffuse and unmonitored sources during 1996 was well below the EPA standard.
The average per capita dose from 1996 Hanford operations based on a population of 380,000 within 80 kilometers (50 miles) of the site was 0.5 microrem (5 x 10-3 microsievert). To place this dose from Hanford activities into perspective, the estimate may be compared with doses from other routinely encountered sources of radiation such as natural terrestrial and cosmic background radiation, medical treatment and x rays, natural radionuclides in the body, and inhalation of naturally occurring radon. The national average radiation doses from these other sources are illustrated in Figure 22. The estimated average per capita dose to members of the public from Hanford sources is only approximately 0.0002% of the annual per capita dose (300 millirem) from natural background sources.
Figure 22. National annual average radiation doses from various sources (millirem).
Although no increase in the incidence of health effects from low doses of radiation has been confirmed by scientists, some accept the hypothesis that low-level doses might increase the probability of cancer or other health effects. Regulatory agencies conservatively (cautiously) assume that the probability of these types of health effects at low doses (down to zero) is proportional to the probability per unit dose of these same health effects observed historically at much higher doses (in atomic bomb victims, radium dial painters). Under these assumptions, even natural background radiation (which is hundreds of times greater than radiation from current Hanford releases) increases each person's probability or chance of developing a detrimental health effect.
Not all scientists agree on how to translate data on health effects into the numerical probability (risk) of detrimental effects from low-level radiation doses. Some studies have indicated that low doses may cause beneficial effects. Because cancer and hereditary diseases in the general population may be caused by many sources (e.g., genetic defects, sunlight, chemicals, background radiation), some scientists doubt that the risk from low-level radiation exposure can ever be conclusively proved. In developing Clean Air Act regulations, EPA uses a probability value of approximately 4 per 10 million (4 x 10-7) for the risk of developing a fatal cancer after receiving a dose of 1 millirem (0.01 millisievert). Additional data support the reduction of even this small risk value, possibly to zero, for certain types of radiation when the dose is spread over an extended time.
Government agencies are trying to determine what level of risk is safe for members of the public exposed to pollutants from industrial activities (e.g., DOE facilities, nuclear power plants, chemical plants, and hazardous waste sites). All of these industrial activities are considered beneficial to people in some way such as providing electricity, national defense, waste disposal, and consumer products. These government agencies have a complex task in establishing environmental regulations that control levels of risk to the public without unnecessarily reducing needed benefits from industry.
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