Environ. Sci. Technol. 1985, 19, 1128-1131
(33) Greenland, D. J. Soil Sci. 1971, 111, 34-41.
Received for review September 11, 1984. Revised manuscript received February 1,1985. Accepted June 7,1985. This research was sponsored by the U S . Air Force Officeof Scientific Research
through its Summer Faculty Graduate Student Research Program under Contract F-49620-82-C-0035 and through Subcontract SCEEE 83RIP/O2. The research was undertaken at the Air Force Engineering and Services Laboratory, Tyndall, AFB, FL, and the Environmental Engineering Laboratories at Cornell University.
Concentrations of Krypton-85 near the Nevada Test Site R. Frank Grossman" and Robert W. Holloway
Environmental Monitoring Systems Laboratory, US. Environmental Protection Agency, Las Vegas, Nevada 89 1 14 Since 1972, the Environmental Monitoring Systems Laboratory has operated a network of noble gas samplers around the Nevada Test Site (NTS). For 10 of those years, the network also included several samplers on the NTS. The network was established to measure the concentrations of noble gases released to the atmosphere by underground nuclear detonations, by posttest operations, and by seepage from the ground from previous underground tests. During this 12-year period, the concentrations of krypton-85 measured in samples collected around the NTS gradually increased with time from 16 pCi/m3 in 1972 to 25 pCi/m3 in 1983. This increase was not found to be due to nuclear testing activities at the NTS but to the worldwide use of nuclear technology, a trend that has been predicted by previous investigators. The observed trend of increasing concentration was considerably less than had been projected by other authors, being only one-eighth to one-fifth of that projected. It is suggested that the difference from predictions is due to a decrease in the rate of growth in the number of nuclear power plants and, more significantly, the slow growth of nuclear fuel reprocessing activities. W
Introduction Since April 1972, a network of air samplers has been operated on and around the Nevada Test Site to monitor the concentrations of noble gases released to the atmosphere by underground nuclear detonations, postshot operations, and seepage through the ground. The first year of continuous operation of this network was reported earlier by this laboratory (1). Also, a series of environmental monitoring reports since 1972 (2-13) have summarized the data from the noble gas sampling network for each calendar year to assess any radiation exposures to off-site residents. For the first time, this report reviews the results of the noble gas network collected over a 12-year period to identify long-term trends and to present descriptive statistics of the data. Network Operations The initial network that was established around the Nevada Test Site included samplers at four on-site and six off-site locations. Over the years, additional stations were added, both on site and off site, to improve coverage. In 1982, the operation and analysis of the onsite samplers were turned over to the Reynolds Electrical and Engineering Co., a contractor at the Nevada Test Site for the U.S. Department of Energy. Also, the off-site network was expanded to 16 stations, 15 of which were part of the Community Radiation Monitoring Program, which is described in ref ll. Figure l shows the location of all the off-site stations relative to the Nevada Test Site. This laboratory was also involved in the environmental monitoring conducted around the Three-Mile Island Nu1128
Environ. Scl. Technol., Vol. 19, No. 11, 1985
clear Power Station shortly following the accident in March 1979. Noble gases were monitored by collecting compressed air samples from one station 0.4 mile from the reactor and several stations in nearby towns. The samples were analyzed at the EMSL-LV Laboratory through Oct 1983 and subsequently by personnel of the Office of Radiation Programs, EPA. Analytical Procedures During the period 1972-1982, air-compressing units designed to collect 1 m3 of air, as described by Andrews (14),were used throughout the network to collect weekly air samples in dual pressure tanks. Continued operation of the compressors resulted in a deterioration of the design pressure of 400 psi; however, the analytical laboratory was able to adapt to a smaller sample size of 0.6-0.7 m3 instead of the desired 1 m3, In 1982, an air sampler that liquified air by cryogenic techniques was fielded; however, some compressor-type samplers continued to be used as replacements for the cryogenic units during breakdowns. The cryogenic samplers were adjusted to collect the same size air sample each week as the compressor units. All samples were returned to the Las Vegas Laboratory for analysis. The analytical procedure was described by Johns et al. (17). The procedure involves the separation and purification of krypton and xenon by adsorption on chromatographic columns and the subsequent analysis of the radioactivity in the krypton and xenon fractions by liquid scintillation counting. Data Analysis The accuracy of the krypton-85 measurements is evaluated periodically with samples of known radioactivity. The bias of the measurements has been within 8% of the standard samples. As an estimate of the precision of the krypton-85 analyses, at least 30 samples per year are split and analyzed separately. The precision of the measurements, expressed as percent coefficient of variation, as determined during the years 1978 and 1981-1983 has been 8-14%. A correlation goodness of fit test was applied to the krypton-85 data grouped by year. The results of the test indicated that the data could generally be separated into either normal, log-normal, or mixed distributions with each year showing a unique pattern. As the distribution of the data varied between normal and log normal, normal statistics was used for convenience to summarize the data for this report. Table I summarizes the data by listing the annual mean concentrations of krypton-85 for each station for the years 1972-1983. As shown by the annual means, the concentration of kryton-85 has been gradually increasing. From the data in Table I, the relationship of off-site krypton-85 concentration with time is pCi/m3 = 14.88 + 0.83t and the
Not subject to US. Copyright. Published 1985 by the American Chemical Society
Table I. Mean Annual Krypton-85 Concentration (pCi/mJ) by Station and Network, 1972-1983
1972 off site Alamo Austin Beatty Cedar City Death Vally Jct Diablo/Rachel" Goldfield Hika Indian Springs Las Vegas Lathrop Wells Overton Pahrump Salt Lake City Shoshone St. George Tonopah network average on site area 12 area 15 area 51 area 400 BJY Desert Rock gate 700 Mercury area 5 area 20 network average
1973
1974
1975
1976
1977
1978
1979
1980
1982
1983
26.1
24.4 24.2 24.6 24.6
24.6 25.2 24.4 24.3 24.9 24.5
24.0
16.0
16.3
17.2
18.7
20.2
20.0
20.3
18.7
15.7 16.3
15.3 16.2
17.5 17.1
16.9 18.3
19.6 19.4
19.7 19.1
19.8 19.9
20.6
15.7
15.6
17.4
15.8
15.6
17.3
17.3 20.0 17.7
17.0 19.6 18.2
19.0 19.9 19.5
19.9 20.2 20.1
19.3 18.9 19.2 18.6
21.3 20.9 18.7 21.6
23.9 24.4 24.0 23.5 26.2 23.2
16.1 15.9
16.0 15.8
17.5 17.3
16.9 17.9
19.2 19.0
19.2 19.5
20.0 20.0
18.4 18.8
21.3 21.0
24.6 24.0
24.1 24.7 26.4 24.2 24.1 24.2 24.1 24.1 24.6 24.8 23.5 23.7 24.4
15.6
15.8
17.6
18.0
19.5
19.2
20.0
18.4
18.1
19.8
19.3
20.0
19.3 18.0 17.4 18.7
18.7 13.6 13.4 17.6
20.5
21.3
22.0
19.0 19.2 19.0 18.4 21.0
21.0 21.4 20.6 21.0 23.2
24.1 24.6 24.2 22.9 26.0
24.5b 25.0b 23Ab 24.4b 25.4*
18.8
19.5
19.9
18.9
21.4
23.0
24.2b
16.8 15.9 15.8
16.0
18.3 16.0 16.1
16.6
18.2
20.8
1981
18.8
24.8 24.0 25.7 24.8 23.7 25.4 25.3 24.8 25.5 24.8 24.gb 24.gb 25.3b 26.5b 25.6b
17.9
19.6
TMI networkC
19.8
20.4
19.3
21.5
24.2
24.6
25.3b 25.5b 25.0
22.7
25.1
25.0
25.9
25.7
astation at Diablo was moved to Rachel in March 1979. *Measurements made by Reynolds Electrical Engineering Co., Inc., and reported by Scoggins (14, 15). CAverageconcentrations were derived from data distribution less than 60 pCi/m3.
I
Nevada
Salt Lake City @,Pyramid
c a Austm
I I I
m
Lake
5 V;
I
I
I
N
I
St George
Shoshone 0
25
50
75 100
Soalain Miles
V
Sampling Location
Flgure 1. Sampling locations used around the Nevada Test Site to monitor for noble gases.
relationship of on-site concentrations with time is pCi/m3 = 15.42 + 0.81t, where t is the number of years after Jan 1, 1972. The correlation coefficient for both linear regressions is 0.96. From Table I, one can also observe that the on-site mean krypton45 concentrations were consistently higher than
those off site, except for 1975, when the means, both on site and off site, were the same. When the on-site and off-site means were tested to determine if they were statistically different for each year, the hypothesis that the means were statistically the same was rejected at the 0.01 significance level for the years 1973 and 1974 and at the 0.05 significance level for the years 1976 and 1978-1980. The on-site station at BJY was consistently higher than all other on-site stations. This station was located in an area that received drainage winds from all the test areas. As a check on seasonal variations of the krypton-85 concentrations, the monthly mean concentrations for the off-site network were plotted with time. No identifiable variation was observed other than the gradual increase in concentration with time.
Discussion Since the beginning of the nuclear industry in the 1950s, krypton-85 has been released to the atmosphere by nuclear weapons tests, operating nuclear power reactors, and nuclear fuel reprocessing plants, the latter one being the greatest contributor to tpe present atmospheric burden of krypton-85 (18). As the half-life of krypton45 is relatively long (10.76 years) and there is no removal process from the atmosphere, the releases of krypton-85 by the nuclear industry results in a cumulative buildup in the troposphere. This buildup is supported by the data in this report, however, the linear regression followed by the trend in concentrations does not agree with the second degree polynomial expressions found by Rozanski (19) to fit the krypton45 measurements he obtained for the Northern and Southern Hemispheres from a data review for the period 1950-1977. However, the linear regression is similar Environ. Sci. Technol., Vol. 19, No. 11, 1985
1129
210-
Table 11. Krypton-85 Releases from Nuclear Facilities within the United States
I
200-
i
190-
Ii
180170160150-
year
curies
year
curies
1972 1973 1974 1975 1976 1977
1060 000 754 000
1978 1979 1980 1981 1982 1983
545 000 495 000 682 000 905 000 531 000 598 000
774 000 567 000 779 000 560 000
“E 140\
0,
130-
Bernhardt
i
E u
120-
g u0
110-
g
100-
c ..; 0
90-
8070-
- 4- ;* ’i’” ,’ t ,
Nlcholsand Binford 11971) Machta et .a ( 1 9 7 4 )
I
*/’
60-
0
50-
0
40-
0
‘4 ,0 0.*
30-
20-,) W
-
0 72
I
Grossman and Holloway pCi/m3 1 4 8 8 * 0 8 3 t R 096
/*
. - = - * . - l -
7
73
I 74 I
75
I 76 I
77
78
I 79
80
I
81
I
82
I
83
I
84
I
85
There is generally fair agreement between the EPA network averages and the krypton-85 concentrations measured in the Northern Hemisphere and reported by other individuals. Wardaszko (27) reported a value of 18 pCi/m3 at Warsaw, Poland, for 1973. The EPA off-site network average was 15.8 pCi/m3 for the same year. Janssens et al. (28) reported background concentrations of 0.7-0.8 Bq/m3 (18.9-21.6 pCi/m3) for the years 1979 and 1980, while the EPA network averages were 18.8 and 21.0 pCi/m3 for the same years. Csongor (25)also reported that the krypton-85 concentration in Hungary was 17 pCi/m3 in 1975 and was increasing at a rate of 1 pCi/m3 annually; the EPA network average for 1975 was 17.9 pCi/m3 with an annual increase of 0.83 pCi/m3. A comparison of the NTS off-site network averages with those for the Three-Mile Island (TMI) network shows the Three-Mile Island network to have a higher background for each of the years 1979-1983, by as much as 0.9-3.9 pCi/m3. The lack of a seasonal variation in krypton-85 concentrations is in contrast to the annual springtime increase in concentration of particulate airborne radioactivity normally resulting from downward-mixing radioactive debris that was injected into the stratosphere by past atmospheric nuclear tests. This suggests that the concentrations of krypton-85 that we observe are directly from sources on the earth’s surface. Table I1 lists the total quantities of krypton-85 released to the atmosphere during the years 1972-1983 by nuclear facilities under the management of the U.S. Department of Energy (29). As these facilities include all the locations of nuclear fuel processing by the Federal Government within the United States, all major sources of krypton-85 should be included. From the total annual releases, which ranged from 500 000 to 1000 000 Ci for this 12-year period, the krypton-85 concentration within the Northern Hemisphere resulting from the releases was estimated to be about 3 pCi/m3, assuming a correction for radioactive decay, homogeneous mixing throughout the Northern Hemisphere, and a volume of 4.3 X lox8m3 for the earth’s troposphere estimated by Poldervaart (30). As the average annual network concentration of krypton-85 for 1983 (Table I) was 25 pCi/m3, the contributions of krypton-85 to the Northern Hemisphere by other countries appears to be more significant than that of the United States.
Conclusions The concentrations of krypton-85 measured in air samples collected on and around the Nevada Test Site over the last 1 2 years have shown that the on-site seepage of krypton-85 is only rarely detectable on site, although the on-site station averages were consistently higher than the off-site averages by 0.1-0.9 pCi/m3. The trend of the concentrations year to year has been increasing in accordance with the linear regression: annual off-site average concentration in pCi/m3 = 14.88 + 0.83t and annual on-site average concentration = 15.42 + 0.81t, where t is the number of years after 1972. The correlation coefficient 1130
Environ. Sci. Technol., Vol. 19, No. 11, 1985
for both e q u a t i o n s is 0.96. The observed trend i n concentrations has resulted in levels that have been one-eighth of levels predicted b y others. No seasonal variation i n krypton-85 concentrations was observed d u r i n g t h i s 12-year period. This is i n sharp contrast t o the well-known spring peak of fission p r o d u c t radioactivity from atmospheric weapons testing. Since the s p r i n g p e a k is k n o w n t o be caused b y the i n t r u s i o n of d e b r i s f r o m the stratosphere, it seems clear that the stratosphere is not a significant source of krypton-85. T h i s suggests that the annual increases in krypton-85 observed in this work are the result of sources o n the earth’s surface which we suspect t o be nuclear fuel reprocessing facilities. The contribution b y the federally operated nuclear fuel processing facilities i n the U n i t e d States to the 1983 ambient krypton-85 concentration of 25 pCi/m3 was estimated to be only 1 2 % , leaving nuclear fuel processing i n foreign countries as the major source of the worldwide inventory of krypton-85. Registry No. @Kr, 13983-27-2.
Literature Cited (1) Andrews, V. E.; Wruble, D. T. In “Noble Gases”; Stanley, R. E.; Moghissi, A. A., Eds.; National Technical Information Service, U S . Department of Commerce: Springfield, VA, 1973; CONF-730915, p p 281-289. (2) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1972”; National Technical Information Services, U S . Department of Commerce: Springfield, VA, 1973; NERC-LV-539-23. (3) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1973”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1974; NERC-LV-539-31. (4) U S . EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1974”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1975; NERC-LV-539-39. (5) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1975”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1976; EMSL-LV-539-4. (6) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1976”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1977; EMSL-LV-539-12. ( 7 ) U S . EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1977“; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1978; EMSL-LV-0539-18, (8) U S . EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1978”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1979; EMSL-LV-0539-31. (9) U S . EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1 9 7 9 ; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1980; EMSL-LV-0539-36. (10) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1980”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1981; EPA-600/4-81-047. (11) U S . EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground
Unuclear Detonations, January-December 1981”;National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1982; EPA-600/4-82-061. (12) U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1982”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1983; EPA-600/4-83-032. U.S. EPA “Environmental Monitoring Report for the Nevada Test Site and Other Test Areas for Underground Nuclear Detonations, January-December 1983”; National Technical Information Services, U.S. Department of Commerce: Springfield, VA, 1984; EPA-600/4-84-040. Andrews, V. E. “Noble Gas Sampling System”; National Technical Information Service: Springfield, VA, 1977; EMSL-LV-539-7. Scoggins, W. A. “Environmental Surveillance Report for the Nevada Test Site (January through December 1982)”; DOE/NV/00410-76, National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1983; p 33. Scoggins, W. A. “Environmental Surveillance Report for the Nevada Test Site (January through December 1983)”; National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1984; DOE/NV/ 10327-4, p 29. Johns, F. B.; Hahn, P. B.; Thome, D. J.; Bretthauer, E. W. “Radiochemical Analytical Procedures for Analysis of Environmental Samples”; National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1979; EMSL-LV-0539-17. NCRP “Krypton-85 In The Atmosphere - Accumulation, Biological Significance, and Control Technology”. Washington, DC, National Council on Radiation Protection and Measurements Report 44. Rozanski, K. Environ. I n t . 1979, 2, 139-143. United Nations Scientific Committee on the Effects of Atomic Radiation “Ionizing Radiation: Levels and Effects”; United Nations: New York, 1972; Vol. 1, p 72. Bernhardt, D. E.; Moghissi, A. A,; Cochran, J. A. In “Noble Gases”; Stanley, R. E.; Moghissi, A. A,, Eds.; National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1973; CONF-730915, pp 4-19. Coleman, J. R.; Liberace, R. Radiol. Health Data Rep. 1966, 7, 615. Nichols, J. P.; Binford, F. T. “Status of Noble Gas Removal and Disposal”; Oak Ridge National Laboratory: Oak Ridge, TN, 1971; ORNL-TM-3515 (as presented in NCRP, 1975, P 34). Machta, L.; Ferber, G. J.; Heffter, J. L. “Regional and Global Scale Dispersion of Krypton-85 for Population-Dose Calculations”; Physical Behavior of Radioactive Contaminants in the Atmosphere, International Atomic Energy Agency: Vienna, 1974; p 411 (as presented in NCRP, 1975, P 34). Csongor, E. Low Radioact. Meas. Appl. Proc. I n t . S y m p . 1977,-471-474. Boeck, W. L. Science (Washington, D.C.) 1976, 193, 195-198. Wardaszko, T. In “Noble Gases”; Stanley, R. E.; Moghissi, A. A., Eds.; National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1973; CONF730915, pp 20-23. Janssens, A,; Raes, F.; Cottens, E.; Eggermont, G.; Beuysse, J. (1981), “Measurement of Low-Level Activity of K r y p ton-85 in Air”; International Atomic Energy Agency: Berlin, West Germany, 1981, CONF-810409, pp 447-458. Effluent Information System, managed by EG&G, Idaho, Inc., for the U.S. Department of Energy, Idaho Falls, ID 83415. Poldervaart, A., Ed. “Crust of the E a r t h , Geological Society of America: New York, 1955; p 121-123. Recei‘ved far review September 27, 1984. Revised manuscript receiiled April 15, 1985. Accepted May 24, 1985. Environ. Sci. Technol., Vol. 19, No. 11, 1985
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