The primary pathway by which radionuclides can move off the INL Site is through the air and for this reason the air pathway is the primary focus of monitoring on and around the INL Site. Samples for particulates and iodine-131 (131I) gas in air were collected weekly for the duration of the quarter at 16 locations using low-volume air samplers. Moisture in the atmosphere was sampled at four locations around the INL Site and analyzed for tritium. Air sampling activities and results for the fourth quarter of 2018 are discussed below. A summary of approximate minimum detectable concentrations (MDCs) for radiological analyses and DOE Derived Concentration Standard (DCS) (DOE 2011b) values is provided in Appendix B.
Radioactivity associated with airborne particulates was monitored continuously by 18 low-volume air samplers (two of which are used as replicate samplers) at 16 locations during the fourth quarter of 2018 (Figure 2). Three of these samplers are located on the INL Site, seven are situated off the INL Site near the boundary, and eight have been placed at locations distant to the INL Site. Samplers are divided into INL Site, Boundary, and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INL Site. Each replicate sampler is relocated every other year to a new location. At the start of 2018, one replicate sampler was moved to Blue Dome (a Boundary location) and one was moved to Atomic City (also a Boundary location). An average of 20,615 ft3 (584 m3) of air was sampled at each location, each week, at an average flow rate of 2.05 ft3/min (0.06 m3/min). Particulates in air were collected on membrane particulate filters (1.2 µm pore size). Gases passing through the filter were collected with an activated charcoal cartridge.
Filters and charcoal cartridges were changed weekly at each station during the quarter. Each particulate filter was analyzed for gross alpha and gross beta radioactivity using thin-window gas flow proportional counting systems after waiting about four days for naturally-occurring daughter products of radon and thorium to decay.
The weekly particulate filters collected during the quarter for each location were composited and analyzed for gamma-emitting radionuclides. Selected composites were also analyzed by location for 90Sr, 238Pu, 239/240Pu, and 241Am as determined by a rotating quarterly schedule.
Charcoal cartridges were analyzed for gamma-emitting radionuclides, specifically for iodine-131 (131I). Iodine-131 is of particular interest because it is produced in relatively large quantities by nuclear fission, is readily accumulated in human and animal thyroids, and has a half-life of eight days. This means that any elevated level of 131I in the environment could be from a recent release of fission products.
Gross alpha results are reported in Table C-1. Gross alpha data were tested for normality prior to statistical analyses, and generally showed no consistent discernible distribution. The data are graphically shown in Figures 3 through 6. Box and whiskers plots were used to present the non-parametric data. As shown in the figures all data were below were well below the DCS for 239/240Pu, the most conservative value for a human-made alpha-emitting radionuclide that might be detected at the INL Site. Nothing unusual was noted in the gross alpha data and all were well within measurements taken within the last ten years (2008-2017).
Outliers and extreme values were retained in subsequent statistical analyses because they are within the range of measurements made in the past ten years, and because these values could not be attributed to mistakes in collection, analysis, or reporting procedures.
Because there is no discernible distribution of the data, the nonparametric Kruskal-Wallis test of multiple independent groups was used to test if there are statistical differences between INL Site, Boundary, and Distant locations. The use of nonparametric tests, such as Kruskal-Wallis, gives less weight to outlier and extreme values thus allowing a more appropriate comparison of data groups. A statistically significant difference exists between groups if the p-value is less than 0.05. Values greater than 0.05 translate into a 95 percent confidence that the groups are statistically the same. The p-value for each comparison is shown in Table D-1. The results show that there were no differences between location groups during the fourth quarter and during the months of October, November and December.
Gross beta results are presented in Table C-1 and displayed in Figures 7 through 10. The data are tested quarterly and generally are found to be neither normally nor log-normally distributed. Box and whiskers plots were used to present the non-parametric data. Outliers and extreme values were retained in subsequent statistical analyses because they are within the range of measurements made in the past ten years, and because these values could not be attributed to mistakes in collection, analysis, or reporting procedures. There was no statistically significant difference in the data between groups for the quarter as a whole using the Kruskal-Wallis analysis of variance by ranks test (Table D-1). There were also no statistical differences between location groups during any month of the quarter.
Iodine-131 was not detected in any of the 26 sets of charcoal cartridges measured during the fourth quarter. Weekly 131I results for each location are listed in Table C-2 of Appendix C.
The results of analyses of quarterly composited filters are presented in Table C-3 of Appendix C. No 137Cs or other human-made gamma-emitting radionuclides were found in quarterly composited filters. Srontium-90, a beta-emitting radionuclide, was not detected in any composite sample. Americium-241, Plutonium-238 and -239/240, alpha-emitting radionuclides, were also not detected in any composite sample.
Atmospheric moisture is collected by pulling air through a column of absorbent material (molecular sieve material) to absorb water vapor. The water is then extracted from the absorbent material by heat distillation. The resulting water samples are then analyzed for tritium using liquid scintillation.
Results were available for eleven atmospheric moisture samples collected at the INL Site, Boundary, and Distant locations during the fourth quarter of 2018 (Figure 11). Five of the results exceeded the 3s uncertainty level for tritium, with similar results to those reported during the past ten years (2008-2017). Results also remain similar between the four sampling locations. All samples were significantly below the DOE DCS for tritium in air of 1.4 x 10-8 μCi/mLair with a maximum reported value of 14.0 x 10-13 μCi/mLair at EFS. Results are shown in Table C-4, Appendix C.
Radiation has always been a part of the natural environment in the form of cosmic radiation, cosmogenic radionuclides [carbon-14 (14C), Beryllium-7 (7Be), and tritium (3H)], and naturally occurring radionuclides, such as potassium-40 (40K), and the thorium, uranium, and actinium series radionuclides which have very long half lives. Additionally, human-made radionuclides were distributed throughout the world beginning in the early 1940s. Atmospheric testing of nuclear weapons from 1945 through 1980 and nuclear power plant accidents, such as the Chernobyl accident in the former Soviet Union during 1986, have resulted in fallout of detectable radionuclides around the world. This natural and manmade global fallout radioactivity is referred to as background radiation. MORE
The primary concern regarding radioactivity is the amount of energy deposited by particles or gamma radiation to the surrounding environment. It is possible that the energy from radiation may damage living tissue. When radiation interacts with the atoms of a given substance, it can alter the number of electrons associated with those atoms (usually removing orbital electrons). This is called ionization. MORE