(last updated 15 Sep 1996)
Radioactive Waste Management Associates
March 30, 1992
(Updated November 14, 1995)
(reproduced here with permission)
Radioactive Waste Management Associates
526 W. 26th Street Rm.517, New York, NY 10001, USA
Tel. +1-212-620-0526, Fax: +1-212-620-0518, E-Mail: email@example.com
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In projecting complex events and circumstances far into the future, large uncertainties are unavoidable, and some of these uncertainties are indicated by the range we present for each physical quantity. For the radiation dose commitments, the uncertainty is in large part due to the uncertain physical future of the piles: will they be drained and barren, vegetated or saturated and swampy? We develop estimates for each scenario in the appropriate sections, and in this summary we bracket the possibilities by giving the lowest and the highest results of these separate calculations, as explained in Section 2.3. In addition, as explained in Section 2.4, the range of responsible opinion on how many deaths will result from a given dose gives rise to further variation in expected deaths within each column. Although not presented here, genetic effects and non-fatal cancers are each expected to be of about the same magnitude as the fatal cancers.
Aquatic releases from Elliot Lake tailings result in the projected health effects shown in Table 1-1. The projected health effects are separately listed for residents of the Serpent River Basin and the global community, which includes the entire North Atlantic region. The Serpent River Basin (which includes the North Channel) is assumed to have a constant population of 10,000. As seen, the fatal cancers due to all Elliot Lake tailings, range between 170 and 2200 over a 500-year period. This does not include fatal cancers incurred by uranium miners and other persons directly exposed by walking on the tailings piles. The global health effects range between 1,600 and 22,200, calculated over a 1000-year period, again assuming a constant population density. As discussed below, the range of responsible opinion on how many deaths will result from a given dose is then the source of the variation in expected deaths within each column. Genetic effects and non-fatal cancers are each expected to be about the same magnitude as the fatal cancers.
As we discuss later, because the Beak model does not correctly model the ingrowth of radium due to the decay of thorium downstream, the likely health effects due to aquatic releases are expected to be greater.
Table 1-1. Aquatic Releases from Elliot Lake Uranium Tailings. Projected Radiation Dose Commitments and Health Effects - Base Case Serpent River Basin Global ------------------------------------------------------------------ Radiation Dose Commitment (million person-rems) 0.74 - 0.86 6.8 - 8.4 Fatal Cancers 170 - 2200 1600 - 22,000
RADON, a decay product of radium, is an inert, radioactive gas which escapes the tailings pile. Though radon has a half-life of only 3.8 days, it will distribute itself throughout the Northern Hemisphere. Assuming 4 billion inhabitants, Beak estimates can be projected to give the radiation doses shown in Table 1-2, and from them we estimate the global health effects, primarily fatal lung cancer. Again, the uncertainty presented arises both from including the largest and smallest results from the three scenarios and from different estimates of how many deaths will be produced by a given dose commitment. The first column shows that per year, the number of health effects are quite low, with the saturated case producing very low rates of radon release, while the vegetated case produced the greatest rate. By "saturated" tailings, we mean the tailings are completely covered with water; "vegetated" means grass and other vegetation covers the tailings pile. Beak's calculations only extend for 1000 years, at the end of which all three scenarios indicate continued high levels of radon being released. For the barren and vegetated cases the decline in radon release was exponential, and we integrated this declining rate to obtain the amounts indicated under "Integrated Total". For the saturated case we could not make an estimate, since although low, the release rate was still increasing at the end of 1000 years. Also, all of Beak's calculations assume the piles retain their physical integrity. If erosion or other events allow some redistribution of the material, the releases will be considerably larger. The column titled "Maximum Release" attempts to estimate an upper limit for these possibilities by combining the first year's release rate with the half-life of the parent thorium as described in Section 4. These estimates of millions of deaths would result only if the piles are substantially redistributed.
Table 1-2. Radon Releases from Elliot Lake Uranium Tailings, Projected Global Health Effects Integrated Maximum First Year Total Release -------------------------------------------------------------------------- Radon Released (1 - 110) x 10^3 (84 - 110) x 10^6 1.2 x 10^10 (Curies) Global Radiation 85 - 10,000 (8 - 10) x 10^6 1.1 x 10^9 Dose (person-rems) Global Fatal Cancers 0 - 26 (2.3 - 26) x 10^3 2.8 x 10^6
Airborne radioactive particulates and radon from the tailings pile suspended by the wind produce the dose commitments and health effects to local residents shown in Table 1-3, assuming a constant population of 50,000 persons within 80 km of Elliot Lake and looking at the first 1000 years after creation of the tailings. As discussed below, we include two estimates, one ("Partial Shielding") based on Beak's assumption that radionuclides are largely contained within the tailings pile, and one ("Maximum Release") which assumes that erosion and other effects allow the radionuclides to escape. In addition a modelling parameter, the "small particle enhancement factor", gives rise to substantial uncertainty as shown by including results from both ends of its normal range of values. The overall expectation then ranges from 1 to 2200 fatalities among the local population. The very small numbers arise from the "saturated" case where the radionuclides are trapped beneath water in the piles. If the piles lose their structural integrity during the several hundred-thousand year lifetime of the radionuclides, the effects could be closer to those indicated in the "Maximum Release" column.
Table 1-3. Particulate Releases from Elliot Lake Uranium Tailings: Projected Doses and Health Effects Within 80 Km of Tailings, Over 1000 years. Normal Release Maximum Release SPEF = 1* SPEF = 2.5 SPEF = 1 SPEF = 2.5 --------------------------------------------------------------------------- Radiation Dose (person-rems) 1100 - 72,300 1100 - 120,000 400,000 860,000 Fatal Cancers 1 - 190 1 - 310 1050 2200 * SPEF = small particle enhancement factor; see text.
Comparing the three primary pathways of radioactivity from the uranium mill tailings pile to humans, we note that the health effects within 80 km are somewhat greater from aquatic releases than from wind suspension of particulates. However, when the global health effects are compared, radon produces by far the largest number of health effects.
An important finding of our study is that, for the disposal possibilities considered by Beak, the total dose to Serpent River Basin residents and to the global population is almost independent of the method of disposing of mill tailings, although the time period over which doses are received will depend on the method of tailings disposition. That is, the range of different decommissioning methods considered by Beak and others only serve to spread or narrow the dose over time. We discuss this issue and offer other possible waste disposal methods in the section on Comparative Methods of Tailings Disposition, below.
If one assigns an undiscounted dollar value to human life (the numbers we have seen range from $20,000 to $10 million), the nuclear option becomes quite pricey. But also, the range of remediation methods that are cost-effective is quite large. However, it is imperative that these costs be included in the price of nuclear electricity now, rather than leaving it to future generations to clean up or suffer the consequences.
Two decommissioning methods have been examined. The benefits achieved in terms of reducing hazardous release as well as the difficulties and uncertainties pertaining to those options are summarized below and detailed in Section 7. Comparative costs are also estimated. The two methods considered and compared with the base case, are earth cover and vegetation, and flooding the tailings.
Earth cover and vegetation: The cover could be achieved with various layers. First rock, or peat or any material available locally would provide the necessary isolation; second a layer of top soil would allow vegetation to grow. Flooding: The option presented by Beak consultants refers to the construction of an impervious dam, maintaining the water table above the tailing surface.
Table 1-4. Comparison of Decommissioning Options Objectives Earth cover and vegetating Flooding ------------------------------------------------------------------------ Tailings stabilization and isolation intrusion and misuse prevention can be achieved if cover is at good solution if flooding can be least 10 feet maintained and lake is not used in the future as a recreational area prevention of tailing spreading by wind erosion and surface thick cover necessary. Vegetation wind erosion avoided as long as would protect the earth cover from flooding maintained; before water runoff erosion flooding, clay or bentonite could placed on the tailings in case of lake drain. Surface water runoff will erode the watershed and provide the tailings with a naturally protecting layer of sediments prevent spreading by flood barriers should be constructed can dams and spillways be properly built and maintained ? Control of radon and gamma emission radon earth cover provides control if greatly reduced, if maintained thick and compact enough; but forever veget. might enhance radon release gamma same conditions as for radon control ? Prevention of leachate contamination of surface water or groundwater Since oxygen is necessary for the production of pyrite-generated acid, and oxygen transport is via both diffusion and water percolating through the tailings, the most promising approach to the problem is to minimize those two factors: Oxygen penetration is reduced No more unsaturated zone due to the earth cover. Vegetating enhances transpiration Oxygen penetration is limited due and thus reduces the hydraulic to reduced diffusion of O2 in input by 32%. water, thus pyrite oxidation is greatly reduced.
An important finding of our study is that the total dose to Serpent River Basin residents and to the global population is almost independent of the method of disposing of mill tailings, although the time period over which doses are received will depend on the method of tailings disposition. That is, the range of different decommissioning methods considered by Beak and others only serve to spread or narrow the dose over time. We discuss this issue and offer other possible waste disposal methods in the section on Comparative Methods of Tailings Disposition, below.
Table 1-5. Collective dose commitment for different management options for the Serpent River area t integration 1,000 5,000 10,000 time (yrs) --------------------------------------------------- Base case 610,463 * * Cover +Veget. 599,513 * * Flooding 77,471 514,650 692,588 * no change from previous value; t - radiation dose in person-rems
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