The radiological impact of atmospheric emissions from oil shale retorts

Environment International, Vol. 11, pp. 57-64, 1985

0160-4120/85 $3.00 + .00 1985 Pergamon Press Ltd.

Printed in the USA. All rights reserved.

THE RADIOLOGICAL IMPACT OF ATMOSPHERIC EMISSIONS FROM OIL SHALE RETORTS Carl V. Gogolak, Environmental Measurements Laboratory, U.S. Department of Energy, 376 Hudson St., New York, New York 10014, USA

(Received 13 May 1984; Accepted 3 January 1985) The radionuclide content of various oil shales, shale oils, and retorting waste products has been studied to determine the extent to which the development of this energy resource may perturb the natural radiation environment. Nearly all of the radioactivity in the raw shale is found in the spent shale after retorting. A primary exposure pathway to the public from this radioactivity will be through the release of particulate matter to the atmosphere during various mining, crushing, and retorting operations. Since the activity of this material is close to that of normal soil, however, the expected radiological impact is small.

Introduction

nearly all of the radioactivity in the raw shale is found in the spent shale after retorting. For this reason, and because of the planned zero discharge of wastewaters to surface waters for most facilities (Mueller, 1981), it is likely that the primary exposure pathway to the public will be through the release of raw and spent shale dust to the atmosphere. This is the only pathway that will be considered in this paper. Using conservative estimates of particulate release rates and dilution factors for atmospheric emissions in the oil shale region of Colorado, the annual-average incremental inhalation exposure to the most exposed individual is calculated to be about 1°7o of that already received from natural sources.

Virtually all rock, including oil shale, contains trace quantities of the naturally occurring radionuclides ~38U, 232Th, and 4°K, together with their daughter products (NCRP, 1975; UNSCEAR, 1977). Although the concentrations o f these radionuclides may not be high, a commercial size oil shale retort of 50,000 barrel-per-day (85 kg sec-x, assuming a density of 922 kg m -3) capacity must process vast amounts of material and so the total amount of radioactivity involved is not negligible. When mining, crushing, and retorting some 70,000 tons (6.4 x 107 kg) of oil shale each day, the natural radioactivity contained in it is introduced to man's radiation environment. It then becomes part of what has been termed technologically enhanced natural radiation (Gesell and Prichard, 1975), which includes the dose to man from such diverse activities as the combustion of coal in generating electricity, the production and use of phosphate fertilizers, and air travel. We have examined the radionuclide contents of various oil shales, shale oils, and retorting waste products to determine the extent to which the development of this energy source may perturb the natural radiation environment. A literature review of trace metal studies on these materials yields a considerable body of information on potassium, uranium, and thorium. To obtain additional information on the state of equilibrium of the uranium and thorium series, gamma-ray spectrometry (Gogolak, 1982) was performed on samples obtained from the Fossil Fuels Research Matrix Program (Griest et al., 1980). The available information suggests that

Natural Radionuclide Concentrations in Oil Shale and Retort Products The radionuclide contents of raw oil shale are shown in Table 1. The concentrations found in typical soils and shales are also shown for comparison. For shale of the Green River formation, 23aUconcentrations are generally 1 to 2 pCi g-l, those for 232Th are 0.5 to 1.0 pCi g-1 and the 4°K content ranges from 5 to 26 pCi g-'. Within experimental error, the various members of the 238U and 232Th series are in secular equilibrium. Antrim shale from the eastern United States has the higher 238U activity which has previously been associated with these black Devonian shales (Gogolak, 1980). Moroccan shale is similar to Antrim shale in 238U content while Estonian shale from the Soviet Union appears similar to Green River shale in radionuclide content. 57

58

Carl V. Gogolak Table 1. Concentrations of natural radionuclides in raw oil shale.a Activity Concentration (pCi g-,)b Sample

Green River formation Paraho bulk, Anvil Pts., CO (ORNL #4204.6) Paraho baghouse (fine particles) (ORNL #4209.2) Occidental site Mahogany Zone, Utah and Colorado (10 samples) Saline Zone, CO (8 samples) Mahogany Zone, CO and Utah R-4 Zone, CO Paraho, Anvil Pts., CO bulk feedstock Baghouse (fine particles): > 105 # 74-105/~ 44-74 tt <44/~ Colony Mine Mahogany Zone, Utah and Colorado (21 samples) Other shales Estonian bulk (ORNL #4401.2) Antrim (Michigan Black Devonian) Moroccan (2 samples) Typical shale Typical soil average range

a3sU

226Ra

1.7 ±0.1

1.46 4-0.01

1.7 4- 0.2

1.23 4-0.03

1.7 4- 0.3 1.8 (0.6-2.4)

1.40 4- 0.02

% 222Rn Emanation

232Th

'°K

0.8 4-0.3

7

0.62 4-0.01

13.9 4-0.1

Gogolak (1982)

1.9 4-0.6

9

0.63 4-0.04

14.1 4-0.4

Gogolak (1982)

0.63 4-0.03 0.48 (0.13-1.32)

26.2 4-0.4 -

Gogolak (1982) Poulson et al. (1977)

21°Pb

Reference

1.3 (0.1-2.7) 1.6-2.3

0.80 (0.18-1.76) 0.56-1.19

1.5-2.8 1.55 +0.01

0.86-1.51 0.70 ±0.01

9.2-18.3 13.4 4-0.2

Desborough et aL (1976) Fruchter et al. (1979)

0.75 ±0.05 0.55 4-0.02 0.63 4-0.02 0.63 4-0.02 0.57 0.64 (0.51-0.76)

11.3 11.8 12.2 12.3 10.4 11.6 8.4-14.2)

Fruchter et aL (1979) Fruchter et al. (1979) Fruchter et al. (1979) Fruchter et al. (1979) Wildeman (1979) Fox (1980)

0.42 4-0.03

14.9 4-0.3

Gogolak 0982)

9.9

1.15

26.0

Fox (1980)

9.6 1.2 0.7 (0.3-1.4)

0.59 1.2 0.7 (0.2-1.3)

6.3 19 10 (2-20)

Fox (1980) UNSCEAR (1977) UNSCEAR (1977)

2.2 1.4 1.3 1.6

4-0.4 4-0.3 4-0.3 4-0.4 1.9 1.5 (1.2-1.7)

1.3 4-0.2

0.83 4-0.02

1.4 4-0.5

12

Poulson et aL (1977) 5.8-8.3

Desborough et aL (1976)

aIn this and succeeding tables, concentrations are given in pCi g-'. The conversions to mass concentrations are as follows: 23sU: 2.9 ppm per pCi g-~, 232Th: 9.1 ppm per Ci g-', 4°K: 0.12 percent K per pCi g-l. Although small amounts of other uranium and thorium isotopes are always present, 23sU and 2a2Th represent essentially all of the mass of these elements in these samples. bl pCi g-~ = 0.037 Bq g-t.

In general, the range o f concentrations of natural radionuclides in Green River shales corresponds fairly closely to that observed for typical soils, although the average 23sU concentration in oil shale is slightly higher than in the average soil. The data o f Fruchter et aL (1979) on fine particles collected from dust-control baghouses show no significant dependence o f radionuclide concentrations on particle size. The similarity of composition o f raw shale feedstock, rejects, and fines has been noted in other studies as well (Wildeman, 1979). G a m m a spectrometry (Gogolak, 1981) on bulk raw shale and baghouse fines confirm this. The emanation fraction for ZZ2Rn (i.e., the percent o f that produced

which escapes the rock particles) is slightly lower than that usually observed for soils. Consequently, the redistribution o f raw shale dust itself should cause no greater radiological impact than any large project that would displace or mobilize an equivalent quantity o f soil. As shown in Table 2, the concentrations o f natural radionuclides in spent shales are generally higher than in the corresponding raw shale. The increase is in about the same proportion as the ratio o f raw to spent shale total mass when both are observed for a given process. This has been found to be true for most trace metals (Fruchter et ai., 1979; Wildeman, 1979). From the available data, it appears that the enrichment o f ra-

59

Radionuclide content of oil shale retorts Table 2. Concentrations of natural radionuclides in spent oil shale. Activity Concentration (pCi g-t)a Sample Green River formation Surface retorts Paraho bulk, Anvil Pts., CO (ORNL #4205.5) Paraho haghouse (fine particles): exit flange (bulk) (ORNL #4213.6) >10# (ORNL #4212.1) 0-10 ~ (ORNL #4211.4) Paraho bulk Baghouse unscreened (fine particles): >841/z 420-841 /z 210-420/z 105-210/z 74-105/z 44-74 # <44/~ Colony Mine: TOSCO II Fischer Assay TOSCO II Paraho (direct mode): Pilot Plant Semiworks Simulated in situ retorts: LLL 125 kg retort LETC 10 t retort LETC 20 kg, LLL 125 kg and LLL-6000 kg retorts (21 samples) Other shales Surface retorts Estonian bulk (ORNL #4402.2) Simulated in situ retorts LETC 20 kg retort: Antrim shale Moroccan shale

% a2aRn Emanation

232Th

"OK

2

0.85 ±0.03

16.4 ±0.3

Gogolak (1982)

1.9 ±0.4

<2

0.72 ±0.02

14.6 ±0.1

Gogolak (1982)

2.9 ±0.5 3.7 ±0.6

<2 2

0.59 ±0.03 1.22 ±0.04 0.83 ±0.01

14.0 ±0.2 19.0 ±0.3 15.5 ±0.3

Gogolak (1982) Gogolak (1982) Fruchter et aL (1979)

0.71 ±0.07 0.75 ±0.02 0.76 ±0.02 0.75 ±0.02 0.68 ±0.02 0.73 ±0.02 0.96 ±0.03

13.8 19.9 17.8 16.4 14.4 14.7 13.3 13.6

Fruchter Fruchter Fruchter Fruchter Fruchter Fruchter Fruchter Fruchter

2.3 2.2 0.3

0.68 0.68 0.08

12.5 12.6 22.7

Wildeman (1979) Wildeman (1979) Lee et al. (1978)

1.7 2.4

0.77 0.44

-

1.5 4.4 2.1

1.05 0.09 0.92

-16.7

(1.6-2.4)

(0.57-1.15)

(11.5-20.9)

Fox (1980)

0.44 ~-0.01

15.7 ±0.1

Gogolak (1982)

1.25 0.66

28.0 7.2

238U

226Ra

a~°Pb

2.0 ±0.2

1.87 ±0.02

1.2 ±0.4

2.0 ±0.1

2.06 ±0.01

2.0 ±0.2 4.1 ±0.2 1.8 ±0.1

1.95 ±0.03 3.26 ±0.04

1.7 ±0.4 1.6 1.8 2.2 2.0 2.1 2.9

±0.3 ±0.4 ±0.5 ±0.5 ±0.5 ±0.7

1.0 ±0.1

1.04 ±0.01

0.7 ±0.2

10.7 11.3

12

Reference

et et et et et et et et

al. al. al. al. al. al. al. al.

(1979) (1979) (1979) (1979) (1979) (1979) (1979) (1979)

Cotter et aL (1978) Cotter et al. (1978) Fruchter et aL (1978) Fruchter et al. (1978) Fox (1980)

Fox (1980) Fox (1980)

al pCi g-' = 0.037 Bq g-t.

d i o n u c l i d e c o n c e n t r a t i o n s in the spent shale is a p p r o x i m a t e l y 30 ± 10°70. This factor will, o f course, vary with the grade o f shale a n d p e r h a p s also with the m e t h o d o f retorting. F o r samples a n a l y z e d in this study, the eman a t i o n f r a c t i o n o f 222Rn was r e d u c e d f r o m a b o u t 8070 to 2°70 or less. This indicates that the net effect o f a spent shale surface disposal area w o u l d p r o b a b l y be a decrease in local 222Rn e x h a l a t i o n . A n exception to the a b o v e is the shale f r o m Estonia, for which there are n o discernible e n r i c h m e n t a n d also n o decrease in e m a n a t i o n . I n c o n t r a s t to raw shale, there is a n increase in m o s t r a d i o n u c l i d e c o n c e n t r a t i o n s with decreasing spent shale

particle size, especially below 44/~m. T h e d a t a in T a b l e 2 o n spent shale b a g h o u s e fine particles show this trend. T h e limited d a t a available indicate that the respirable f r a c t i o n o f retorted shale fines ( < 10 # m diameter) m a y be enriched b y as m u c h as a factor o f 3 for 21°Pb, 2 for 238U, 1.7 for 226Ra, 1.5 for 232Th, a n d 1.2 for 4°K over the c o n c e n t r a t i o n s o f these radionuclides in bulk retorted shale. A significant e n r i c h m e n t o f stable lead in retorted shale b a g h o u s e fines over b u l k retorted shale has also b e e n observed ( F r u c h t e r e t a L , 1979; W i l d e m a n , 1979). T h e c o n c e n t r a t i o n s o f n a t u r a l r a d i o n u c l i d e s in crude shale oil, r e f i n e d shale oil p r o d u c t s , retort water, a n d

60

Carl v. Gogolak

retorting gases are generally quite low, often below detectable limits (Gogolak, 1982). An exception to this is the gaseous 22~Rn. For the purpose o f this study, it is assumed that essentially all o f the 222Rn contained in the raw shale escapes during retorting and is eventually released to the atmosphere with the retorting gases. Mass balance studies have been p e r f o r m e d for trace metals in both surface (Fruchter et ai., 1979) and simulated in s i t u (Fox, 1980) retorts. In each instance, the mobility o f potassium, uranium, and thorium (i.e., the percentage o f these metals present in the raw shale that is distributed into the oil, gas, and water phases) is substantially lower than 0.1 070. Thus, the available data show that the natural radioactivity associated with oil shale processing is primarily confined to the raw and spent shale. The m a j o r exposure pathways to the public will thus be through atmospheric releases o f raw and spent shale dust and 222Rn released with retort gases.

mation to the contrary, all other releases may be assumed to have a composition similar to spent shale. The projected percentage o f emissions f r o m mining and crushing operations varies f r o m 1070 to 90070 o f the total. Measurements made near the Colony site over a 9-month period indicate that background concentrations of suspended particulate matter in the oil shale region are about 10 #g m -3 (USDIB, 1977). Model dispersion calculations have been performed by several investigators to estimate the increase in ambient particulate concentrations due to oil shale operations. The peak annual average and worst-case 24-h average concentrations predicted by various models result in the ranges given in Table 3. The sources o f this information are the same as above for the particulate emissions. Where a range is shown for the model calculations (U.S. DOE, 1980) two different models were used, one for flat terrain and another for complex terrain. The dispersion calculations for the Colony site given by the Bureau of Land Management (USDIB, 1977) were verified by tracer studies conducted by Battelle Pacific Northwest Laboratories. It would appear that a single well-controlled facility of about 50,000 barrel-per-day (85 kg sec-' capacity) would not cause serious long-term increases in regional particulate concentrations. A possible exception m a y be the 5 /~g m -3 m a x i m u m permissible increment above background for the prevention o f significant deterioration of visibility in federally designated Class I parks and wilderness areas (U.S. DOE, 1980). The requirement of oil shale facilities to meet these air quality standards for particulate matter will simultaneously limit the population exposure due to the radionuclides released with it.

Atmospheric Release and Dispersion of Particulates from Oil Shale Facilities Estimates of the quantity o f particulate matter that m a y be released during various oil shale retorting operations with emission controls are listed for several different processes in Table 3. These data have been compiled from environmental impact analyses and prevention of significant deterioration (PSD) of air quality studies (U.S. DOE, 1980; U.S. E P A , 1981; USDIB, 1977). Emission estimates can vary considerably depending on the specific process and the extent o f control technology postulated. Releases f r o m mining and crushing operations should have the same composition as raw shale and are categorized separately. Lacking specific infor-

Table 3. Projected release and dispersion of particulates for specific oil shale technologies. Peak Conc. (#g m-3)

Emissions (g sec -~)

Site

Process

Mining Capacity and (bbl day-l)b Crushing

C-a tract

Combined in situ and TOSCO II (surface indirect) Colony TOSCO II Colony TOSCO II Colony TOSCO II Union surface Union Union B (Surface) Occidental modified in situ Eastern U.S. Hytort (surface) Federal limits for the prevention of significant deterioration (maximum permissible increments)

Other

Total

76,000

1.1

78.4

79.5

50,000 46,000 47,000 50,000 9,000 57,000 46,000

10.1 7 10 15.6 4.0 1.1 0.2

22.5 22.1 91 2.0 0.5 9.3 0,2

32.6 29.1 101 17.6 4.5 10.4 0.4

Class

aRatio of the release rate to the peak annual average concentration. bl bhl day-1 = 1.7 g sec-1.

I

II III

Dilution Factora (10' m3sec-1)

Annual Average

24-h Worst Case

0.32-0.9

2.5-200

9-25

3-5 18-214 --10 150-300 1-3 11-194 0.04-0.06 0.7-29 --

0.7-1.1

5

10

19 17

37 75

l 0.6-1.8 17-26

Reference USDOE (1980) USDOE (1980) U.S. EPA (1981) USDIB (1977) USDOE (1980) U.S. EPA (1981) USDOE (1980) U.S. EPA (1981)

Radionuclide content o f oil shale retorts

61

Radiological Impact From the data of the previous sections, we may estimate the radiological consequences of atmospheric releases of trace radioactivity with raw and spent shale particles from a model retorting facility. The major parameters used in this analysis and their values are shown in Table 4. The production capacity of the model plant is 50,000 barrels per day (85 kg sec -~) of oil from 70,000 tons per day (740 kg sec-~) of 30 gallons per ton (120 kg Mg -~) grade raw shale creating 56,000 tons per day (590 kg sec-~) of spent shale in the process. The data in Table 3 indicate that most oil shale retorts of this size, either in situ or surface, will release less than 100 g/sec of particulate matter, so this figure has been adopted for the model facility. A comparison between the ratios of the estimated release rates and projected peak annual average concentrations in Table 3 suggests that a dilution factor of about 10~ m ~sec-1 for these releases is appropriate. This would result in a peak annual average particulate concentration in the vicinity of the model facility of 10 /zgm-3 above background. Although this represents a significant increase for this region, the total will still be much lower than is observed in many populated areas (UNSCEAR, 1977). The concentration of natural radionuclides in this material will depend on whether it is primarily raw or spent shale particles, and if the latter, also on the particle size distribution. The average concentrations of natural radionuclides in raw and spent Green River formation shale, estimated from the data in Tables 1 and 2, are given in Table 4. The members of the ~38Uand 23~Th

Table 4. Parameters used to estimate the radiological impact o f oil shale facilities Production capacity Average ore grade Raw shale processed Spent shale produced Particulate release rate Peak a n n u a l average o f f site particulate concentration (above background)

50,000 barrels per day (85 kg sec-') 30 gal per ton (120 kg Mg -~) 70,000 tons per day (740 kg sec -1) 56,000 tons per day (590 kg sec -~) 100 g sec-1 10/~g m -~

Average radionuclide concentrations (pCi g-l):a 238U 2 2 6 R a 2 ~ o p b aa2Rn Raw shale Spent shale (hulk) Spent shale (respirable)

decay series are considered to be in secular equilibrium in the raw shale. For the respirable fraction of spent shale, we have estimated enrichment (based on the data in Tables 1 and 2) of 3 for lead, 2 for uranium, 1.7 for radium, 1.5 for thorium, and 1.2 for potassium. Since it is not certain what fraction of the airborne material carried off-site will be spent shale nor what fraction of it will be respirable, we have conservatively assumed that it is all spent shale and all of respirable size. This leads to the peak annual average off-site air concentrations of natural radionuclides shown in Table 5. Estimates of average background concentrations in the oil shale region and in populated areas are given for comparison. Except for 22~Rn, the incremental concentrations due to oil shale processing are comparable to the existing background concentrations from suspended soil and dust particles. The maximum off-site increase in 222Rn concentration, shown in Table 5, is < 1.0°70 of the normal concentration of this radionuclide in the lower atmosphere over continents, 0.1 pCiL-' (UNSCEAR, 1977). This background of ~2Rn is caused by the constant escape of this gas from the soil, where it is produced by the decay of 226Ra in the natural uranium series. At the typical exhalation rate for soil of 50 aCi cm -2 sec-1 (NCRP, 1975), the total release of 222Rn from a 50,000barrel-per-day (85 kg sec-1) facility corresponds to the normal exhalation from an area of < 2 km 2. The internal exposure due to the natural radionuclides inhaled with airborne spent shale particles was estimated using the same assumptions used for the study of fly-ash releases from coal-fired power plants by Beck et aL (1980) and dose conversion factors recommended by the NCRP (1975, 1977). This analysis assumes that oil shale particles, like fly-ash particles, are insoluble in body fluids and that the lung is the critical Table 5. M a x i m u m annual average air concentrations o f natural radionuclides during oil shale processing (fCi m-3)a Background

ZaaTh

4oK

1.5 2.0

1.5 2.0

1.5 2.0

1.5 2.0 b

0.64 0.80

13 17

4.0

3.4

6.0

3.4 b

1.20

20

al pCi g-i = 0.037 Bq g-1. bAlthough all 222Rn contained in the raw shale is released during retorting, this radionuclide will within a few weeks re-attain equilibrium with its parent 226Ra, less the 2% loss due to emanation.

Radionuclide

Maximum Off-site Increment

Populated Areas b

Oil shale Region c

238U 234U 23°Th 226Ra 2~Rn 2~°Pb 2'°Po 23~Th 228Th 228Ra 22"Ra "°K

0.04 0.04 0.03 0.034 110 0.06 0.06 0.012 0.012 0.014 0.014 0.2

0.07 0.07 0.07 0.07 105d 10-20 1-2 0.07 0.07 0.07 0.07 1

0.007 0.007 0.007 0.007 105d 1-2 0.1-0.2 0.007 0.007 0.007 0.007 0.1

al fCi m -3 = 3.7 x 10-5 Bq m-L bFrom Beck (1980). Clnferred from those in populated areas using a 10-1 ratio for the total dust loading in the two areas. dFrom U N S C E A R (1977).

62

Carl v. Gogolak

organ. The few studies o f leaching o f natural radionuclides from shale particles suggest that they are relatively insoluble (Fox, 1980; Heistand et aL, 1980; Stollenwerk and Runnells, 1980; Jackson et aL, 1975). Nevertheless, the doses estimated here would have to be modified should further studies show that oil shale particles are substantially soluble. The results o f this analysis are shown in Fig. 1, where the lung dose equivalent to the most exposed individual residing in the vicinity of a 50,000-barrel-per-day (85 kg sec -~) oil shale retort is compared to that of the most exposed individual residing near a modern well-controlled 1 GW(e) coal-fired power station (Beck et al., 1980). A coal plant o f this size burns the energy equivalent o f 31,000 barrels per day (53 kg sec -1) of shale oil. The total dose-equivalent due to the oil shale facility, 0.78 m r e m a -1, falls in the range projected for coal plants, 0.14-1.65 mrem a-', depending on stack height. These lung dose equivalents are low compared to the 100 mrem a-' received by the average U.S. resident from natural sources (NCRP, 1975). This is because the dose-

equivalent due to natural sources is dominated by the short-lived alpha-emitting daughters o f 222Rn, 2'8Po, and 2'4Po. The major incremental dose-equivalent from the energy production facilities is due to 2'°Po, whereas we have calculated that the dose-equivalent due to 222Rn and its short lived daughters is < 0.07 mrem for the oil shale retort and < 0.01 mrem for the coal plants. The food chain ingestion dose from deposited activity can be estimated by comparison with natural soil activity concentrations and the corresponding tissue dose rates. To calculate the increase in natural soil activity, a deposition velocity of 0.01 m sec -1 was used to account for both wet and dry deposition and was applied at the point o f maximum concentration, 10 /~g m -3. Over a period of 50 yr, this results in a deposit o f 150 g m -2, all o f which is assumed to contain the activity concentrations of natural radionuclides shown in Table 4 for respirable spent shale. Assuming that only the material in the first 15 cm of soil (240 k g m -2) is available to vegetation, the increases in soil activity shown in Table 6 are obtained. These increments were applied to the in-

LUNG DOSE EQUIVALENT MOST EXPOSED INDIVIDUAL (mrem/a) t GW(e) COAL

i.O

152m STACK

.9

OIL SHALE 50000 bbl/d

.8

.7 t 6W(e) COAL 52m STACK

.6 .5 .4 .3 .2 .t 0.0

U-238/234

Th-230

Ra-226

Pb-210 P o - 2 i O RADIONUCLIDE

Th-232

Th-22fl

~-228

Fig. 1. Lung dose equivalents to the most exposed individual from radionuclides released during oil shale retorting and coal combusion.

Radionuclide content of oil shale retorts

63

gestion dose equivalents to various organs estimated by the NCRP (1975) for natural background sources. The dose equivalents to the bone surfaces are nearly twice as high as those to all other organs combined and are shown in Table 6. The total, 0.16 m r e m a -~, is mostly due to 2~°Pb and 2~°Po. These dose estimates must be considered an upper limit, depending as they do on a number of quite conservative assumptions, including that the incremental increases in activity at the point of maximum concentration are applicable over a wide enough area to account for the production of a substantial portion of an individual's diet and that the uptake of natural radionuclides by plants from spent shale particles is the same as the uptake of these radionuclides from soil. In studies of revegetated spent shale beds (Schwab et al., 1983) lead was not detectable in the vegetation. This indicates that 2'°Pb, one of the major contributors to ingestion dose, may not be readily taken up by plants from spent shale. For these reasons, it is concluded that the inhalation pathway dominates the ingestion pathway and that the lung is the critical organ. Airborne shale particles deposited on the soil surface of the surrounding area can lead to an increase in the external gamma-ray exposure rate. The build-up of natural radionuclides that would occur over a 50-year operating period was calculated, as before, using the peak concentrations in Table 5 and an estimated deposition velocity of 1 cm sec-L However, in this case it is most conservative to assume that these radionuclides remain on the surface and the additional mass does not attenuate the existing radiation from the soil. The exposure rate conversion factors of Beck (1980) were used to find the exposure rate increase at 1 m above the ground. The result, 0.04 #R h-', is < 1°70 of typical terrestrial gamma-ray exposure rates (NCRP, 1975; UNSCEAR, 1977). Reclaimed spent shale disposal piles eventually be returned to public use. We have calculated the gammaray exposure rates expected over a thick ( > 2 0 cm) disposal pile assuming no soil cover. The concentrations of natural radionuclides in bulk spent shale were converted to the exposure rate at 1 m above using the uniform source conversion factors of Beck et al. (1972).

Table 6. Maximum annual dose-equivalent to bone surfaces from deposited activity after 50 yrs of operation. Dose Equivalent (mrem) Radionuclide

Increase in Top 15 cm Soil Activity (%)

238U 22eRa 21°Pb(2~°Po) 232Th 22'Ra Total aFrom NCRP (1975).

0.3 0.25 0.5 0.04 0.06

Backgrounda 4.8 6.6 24 0.7 8 44.1

Increment 0.014 0.017 0.12 0.003 0.005 0.16

The total exposure rate of 8.9 #R h -1 is within the range typically observed in undisturbed areas (UNSCEAR, 1977). From this we conclude that external gamma radiation exposure will not be an important factor in oil shale development.

Summary and Conclusions The radionuclide contents of oil shale, shale oil, and processing wastes have been studied. The concentrations of the 238U series, 232Th series, and 4°K in Green River shale differ little from that in average soil or rock. The naturally occurring radionuclides in the raw shale remain primarily with the spent shale during processing. Little radioactivity is redistributed to the product oil or retort water. The 222Rn in the raw shale escapes with the retort gases. During mining, crushing, and retorting operations, raw and spent shale particles are released to the atmosphere carrying trace quantities of natural radionuelides with them. The inhalation of this material is probably the major radiological impact associated with oil shale development. Strict emission control for this material is already required to meet various state and federal clean air standards. The lung dose equivalent from natural radionuclides in shale particles released from a 50,000-barrel-per-day (85 kg sec -1) facility meeting these requirements should not exceed 107o of that already received by the average US citizen from natural sources.

There are many complex and potentially serious environmental problems associated with the production of oil shale. These will require careful consideration as this energy resource is developed. It is the conclusion of this study, however, that radiological impacts will be relatively minor. They will be largely controlled by regulations already in place for nonradioactive pollutants, and will be of the same order of magnitude as those imposed by a well-controlled coal fired power plant of approximately the same energy production capacity. Acknowledgements-The author would like to thank his colleague Kevin Miller for his analysis of the ORNL samples. Kevin Miller and Harold Beck also provided many helpful insights during our discussions of this study. Wayne Griest of ORNL kindly supplied the samples for the analyses of trace radioactivity. Jon Fruchter of PNL and Dick Poulson of LETC either provided or helped in locating much of the data from other studies reviewed in this paper.

Refere nces Beck, H. L. (1980) Exposure rate conversion factors for radionuclides deposited on the ground. EML-378, U.S. Department of Energy, New York, NY. Beck, H. L., De Campo, J., and Gogolak, C. V. (1972) In situ Ge (Li) and NaI(TI) gamma-ray spectrometry. HASL-258, U.S. Department of Energy, New York, NY. Beck, H. L., Gogolak, C. V., Miller, K. M., and Lowder, W. M. (1980) Perturbations on the natural radiation environment due to the utilization of coal as an energy source, in Proceedings o f the Third International Symposium on the Natural Radiation Environment,

64 T. F. Gesell, W. M. Lowder, eds., pp. 1521-1558. CONF-780422, U.S. Department of Energy Report, New York, NY. Cotter, J. E., Prien C. H. Schmidt-Collerus, J. J., Powell, D. J., Sung, R., Habenicht, C., and Pressey, R. E. (1978) Sampling and analysis research program at the Paraho Oil Shale Demonstration Plant. Report 600/7-78-065, U.S. Environmental Protection Agency, Washington, DC. Desborough, G. A., Pitman, J. K., and Huffman, C., Jr. (1976) Concentration and mineralogical residence of elements in rich oil shale of the Green River formation, Piceance Creek basin, Colorado and the Uinta basin, U t a h - A preliminary report, Chem. Geol. 17, 13. Fox, J. P. (1980) The partitioning of major, minor and trace elements during simulated in-situ oil shale retorting, LBL-9062, U.S. Department of Energy, Berkeley, CA. Fruchter, J. S., Laul, J. C., Peterson, M. R., Ryan, P. W., and Turner, M. E. (1978) High precision trace element and organic constituent analysis of oil shale and solvent refined coal materials, in Analytical Chemistry of Oil Shales and Tar Sands, Advances in Chemistry Series No. 170. American Chemical Society, Washington, DC. Fruchter, J. S., Wilkerson, C. L., Evans, J. C., Sanders, R. W. and Abel, K. W. (1979) Source characterization studies of the paraho semiworks oil shale retort. PNL-2945, U.S. Department of Energy Report, Richland, WA. Gesell, T. F. and Prichard, H. M. (1975) The technologically enhanced natural radiation environment, Health Phys. 28, 361-366. Gogolak, C. V. (1980) Review of 222Rn in natural gas produced from unconventional sources. EML-395, U.S. Department of Energy, New York, NY. Gogolak, C. V. (1982) An evaluation of the potential radiological impact of oil shale development. EML-406, U.S. Department of Energy Report, New York, NY. Griest, W. H., Coffin, D. L., and Guerin, M. R. (1980) Fossil fuels research matrix program. ORNL/TM-7346, U.S. Department of Energy, Oak Ridge, TN. Heistand, R. N., Atwood, R. A., and Richardson, K. L. (1980) Paraho environmental data. USDOE Report EV-0086, Washington, DC. Jackson, L. P., Poulson, R. E., Spedding, T. J., Phillips, T. E., and Jensen, H. B. (1975) Characteristics and possible roles of various waters significant to in situ shale processing, Q. Colo. Sch. Mines 70, 105. Lee, H., Peyton, T. O., Steele, R. V., and White, R. K. (1977) Poten-

Carl V. Gngolak tial radioactive resulting from expanded energy programs. Report 600/7-77082, U.S. Environmental Protection Aency, Las Vegas, NV. Mueller, L. (1981) Effects of wastewater disposal on surface waters, in Environmental Perspectives on the Emerging Oil Shale Industry, R. Bates, and T. L. Thoem, eds., pp. 65-69. Report 600/2-80-205a, U.S. Environmental Protection Agency, Washington, DC. National Council on Radiation Protection and Measurements (1975) Natural background radiation in the United States. Report No. 45, NCRP, Washington, DC. National Council on Radiation Protection and Measurements (1977) Radiation exposure from consumer products and miscellaneous sources. Report No. 56, NCRP, Washington, DC. Poulson, R. E., Smith, J. W., Young, N. B., Robb, W. A., and Spedding, T. J. (1977) Minor elements in oil shale and oil shale products. LERC/R1-77/I, U.S. Energy Research and Development Administration, Laramie, WY. Schwab, A. P., Lindsay, W. L., and Smith, P. J. (1983) Elemental contents of plants growing on soil-covered resorted shale, J. Environ. Qual. 12, 301-304. Stollenwerk, K. and Runnels, D. (1980) Geochemistry of leaching of trace elements in oil shale, in Trace Elements in Oil Shale: Progress Report for 1979-1980; W.R. Chappell, ed., pp. 177-236. USDOE Report EV/10298-1, University of Colorado, Denver, CO. United Nations Scientific Committee on the Effects of Atomic Radiation (1977) Sources and effects of ionizing radiation. Report to the General Assembly, New York, NY. U.S. Department of Interior Bureau of Land Management (1977) Final environmental impact statement on the proposed development of oil shale resources by the colony development operation in Colorado, Vol. I. Government Printing Office USDIB 1977-799 536/206 Region 8, Washington, DC. U.S. Department of Energy (1980) Synthetic fuels and the environment: An environmental and regulatory impacts analysis. Report EV-0087, U.S. Department of Energy, Washington, DC. U.S. Environmental Protection Agency (1981) Environmental perspectives on the emerging oil shale industry, E. R. Bates, and T. L. Thoem, eds, pp. 277-324. Report 600/2-80-205a, U.S. Environmental Protection Agency, Cinncinati, OH. Wildeman, T. R. (1979) Chemical analysis of inputs and outputs of oil shale retorts, in Trace Elements in Oil Shale: Progress Report for 6/1/76 1/31/79, W. R. Chappell, ed., Chapter III, pp. 63-133. USDOE Report COO-4017-3, University of Colorado, Denver, CO.