Management and Disposition of Excess Weapons Plutonium (1994) / Chapter Skim
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Appendix C
Appendix C
Pages 245-275
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From page 245... ...
Consistent with the discussion in Chapter 6, options should: ~ Management and Disposition of Excess Weapons Plutonium: Report of the Panel on ReactorRelated Options (Washington, D.C.: National Academy Press, 1994)
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From page 246... ...
The nominal stock of excess weapons plutonium is 50 tons each for the United States and Russia, which could in principle be stored in a single large warehouse. The global stock of spent fuel by the year 2000 will amount to more than 150,000 tons (containing over 1,400 tons of plutonium)
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From page 247... ...
to retrieve the plutonium for use in weapons as it would be to separate a similar amount of plutonium in spent fuel for the same purpose. DISPOSAL IN DEEP BOREHOLES Description Disposal in deep boreholes has been considered in several countries for spent fuel or HLW (generally as a backup to the currently preferred approach of disposal in mined geologic repositories nearer the surface)
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From page 248... ...
For example, a detailed Swedish study on HEW disposal in deep holes focuses on a "preferred option" that would involve a hole 80 centimeters in diameter at depth, into which would be placed canisters with a length of 4.4 meters and a diameter of 50 centimeters, centered in the hole.4 Each canister would be separated from the next by sealing plugs of compressed bentonite clay. After the "deployment zone" was filled, an additional long length of bentonite clay would be used to seal the hole.
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From page 249... ...
Although boreholes have not received anything like the technical scrutiny that has been applied to mined repositories, the great depth of the hole and the very low permeability of crystalline rock (granite) suggest that the risks of radioactive releases from such holes might be even lower than those from mined repositories.
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From page 250... ...
would probably involve casting the fuel rods themselves in copper. This would reduce the otherwise large void volume within canisters containing spent fuel assemblies, which (if undisplaced)
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From page 251... ...
If the material to be disposed of generated substantial quantities of heat (as is the case with HEW and spent fuel) , the decrease in density resulting from the warming of the surrounding water could lead to upward convection in the absence of such saline water, though it would still not rise through a major salinity gradient.
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From page 252... ...
There is clearly less processing necessary to transform weapons plutonium to a suitable waste form and to handle the resulting canisters than is the case for HEW or spent fuel, because of the intense gamma radioactivity of these latter products. In any case, it appears certain that in the United States, the costs of development of the borehole option, and particularly of gaining the needed licensing and approvals (if they were eventually obtained)
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From page 253... ...
Still, if the location of the hole were known, it could eventually be found. If the goal of retrieval were only to acquire a few tons of plutonium, and reactors and reprocessing facilities were available, it might turn out to be easier to make new plutonium or to separate reactor-grade plutonium from spent fuel; ~ Svensk Karnbranslehantering AB, op.
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From page 254... ...
Thus, a substantial additional research and development effort would have to be focused on the deep-hole approach if this were to be a leading contender for plutonium disposal. The Swedish study suggests a future work plan that includes: · continued review of data from past deep boreholes in crystalline rock; · drilling-related research; · research on plugging and sealing; · modeling of water convection in and around the hole; · pilot studies to determine the depth to saline water, using electromagnetic methods; and · drilling of a 3-kilometer borehole, to test the geological assumptions.
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From page 255... ...
SUB-SEABED DISPOSAL Description As described in Chapter 6, disposal in the sub-seabed has long been the leading alternative to mined geologic repositories for disposal of spent fuel and high-level wastes. A detailed 1988 study by the Nuclear Energy Agency (NEA)
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From page 256... ...
Environmental Impact As with deep boreholes, the first question to consider is reliable isolation of plutonium from the environment. The mud of the abyssal plains has several advantages.
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From page 257... ...
The mud's capability to bind plutonium might be saturated at a concentration of something like 1 kilogram of plutonium per cubic meter of mud, even if the plutonium concentration in the pore water is well below the solubility limit. At that concentration, the 10 kilograms of plutonium that might be held in a single canister would be sorbed in 10 cubic meters of mud' so the saturation zone would extend less than 1.5 meters from the canister itself.
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From page 258... ...
19) has a significantly lower diffusion time in the absence of sorption than calculated above, indicating that radionuclides that were not sorbed in the mud would reach the surface "on the order of 104 years after their release from waste packages emplaced at a depth of 50 +/- 20 meters in the sediment because of the time required for diffusion through the sedimentary pore water." The calculation in the text would have reached a similar conclusion had it used a diffusion coefficient equal to that of water, rather than the lower diffusion coefficient of plutonium.
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From page 259... ...
Studies to date suggest that "the thermally-induced movement of the pore waters, the waste package, and the sediments is small,"~5 but a major field test to assess this conclusion, the In-Situ Heat Experiment, was canceled in the late 1980s. In the case of excess weapons plutonium, this is not an issue because the heat output from the weapons plutonium would be only about 30 watts per canister (assuming 10 kilograms of plutonium could be placed in each canister)
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From page 260... ...
As noted above, because of the extremely slow predicted movement of radionuclides through the mud, some studies have concluded that plausible human doses of radioactivity from spent fuel or HLW correctly emplaced in the sub-seabed would be many thousands of times lower than doses from natural background radiation. Doses to maximally exposed individuals from a worstcase accident, however, such as a ship bearing spent fuel or HLW that sank near shore with none of the canisters recovered, could be several times normal background.
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From page 261... ...
. Retrievability As with deep boreholes, retrievability would be desirable from the point of view of ensuring that the disposal concept was working as expected, but undesirable if the goal was to create substantial barriers to recovery and use of this material in weapons.
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From page 262... ...
For less-developed countries and subnational groups, recovering plutonium by such means might be more costly and time-consuming than recovering plutonium from spent fuel, thus meeting the spent fuel standard. To limit such recovery possibilities, the area in which the plutonium-bearing canisters had been deposited could be monitored for an indefinite time, if that were agreed on.
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From page 263... ...
At the time the U.S. program was canceled in the mid-1980s, it was estimated that another 25 years would be required before a sub-seabed disposal approach could be operational.22 Development and emplacement costs are likely to be lower for the sub-seabed approach than for deep boreholes, but licensing and policy questions are much more problematic, whether a site in the broad ocean is contemplated or one in the 200-nautical-mile exclusive economic zone.
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From page 264... ...
In addition to this legal framework, any proposal for disposal in or below the oceans is likely to provoke intense public and political opposition, both within the United States and internationally. In short, gaining approval from a majority of the parties to the London Dumping Convention for sub-seabed disposal of plutonium, and overcoming the political, legal, and regulatory hurdles (including providing experimental data that do not yet exist)
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From page 265... ...
Environmental Impact Existing regulations, national and international, provide a framework in which to consider the environmental impact of diluting 100 tons of excess weapons plutonium in the ocean. In the United States, new regulations enter into force on January 1, 1994, limiting the allowable plutonium concentration in water to which members of the public might be exposed to 2 x 10-8 curies per cubic meter.26 These limits were set with the goal of ensuring that a person drinking 2 liters a day of this water would receive a radiation dose of no more than 50 millirem per year.
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From page 266... ...
As noted above, the London Dumping Convention forbids all disposal of high-level radioactive waste into the sea, and a majority of the parties to the convention have recently voted to bar low-level dumping as well. Any proposal to dispose of tens of tons of weapons plutonium in the ocean would surely be seen as directly contrary to the intent of the convention, even if the material could be diluted enough that it would meet current standards for disposal of low-level waste.
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From page 267... ...
Moreover, in Chapter 6, the committee argues that if options for eliminating weapons plutonium nearly completely from international human access involve substantial additional risks, costs, or delays compared to options that make it as inaccessible as plutonium in spent fuel as the ocean dilution option would-these additional problems should not be borne unless global stocks of civil plutonium are to be treated in a similar way. The excess global stock of civil plutonium is drastically larger than the excess weapons plutonium stock (some 800 tons compared to 100 tons)
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From page 268... ...
As noted, the majority of the parties to the London Dumping Convention, including the United States, have voted to bar dumping of low-level radioactive waste as well as high-level waste. Such a ban would make all the preceding calculations concerning IAEA regulations on low-level waste disposal academic, unambiguously forbidding an ocean dilution approach.
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From page 269... ...
Thus, the inevitable risk of launch accidents is a fundamental problem for the space disposal approach. Launching the plutonium into low-earth orbit (which requires a velocity of about 8 kilometers per second)
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From page 270... ...
First, one must consider that the plutonium should be in a form that will reliably be noncritical even if, for example, an accident results in it being immersed in ocean water. Thus, the plutonium must be combined with some neutron-absorbing material.
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From page 271... ...
At this cost, launching the 238-kilogram payload to LEO would cost some $2.4 million, or about $240 per gram of plutonium. The launch costs for disposing of 100 tons of excess weapons plutonium in this way not including any other costs, such as development and licensing-would come to $24 billion.
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From page 272... ...
DESTRUCTION WITH UNDERGROUND NUCLEAR EXPLOSIONS Description Shortly after the dissolution of the former Soviet Union, the Russian firm CHETEK, associated with the Russian nuclear weapons laboratory Arzamas-16 and the Ministry of Atomic Energy, proposed that plutonium could be disposed of by using underground nuclear explosions.34 A single 50-kiloton device could be surrounded by some 5,000 plutonium pits. The 50-kiloton blast would melt both the pits and 50,000 tons of the surrounding rock, into which the plutonium from the pits would be dissolved and distributed.
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From page 273... ...
For example, concerns over potential long-term criticality of the underground plutonium, after possible differential leaching of different constituents in the rock, would be far more difficult to address than in the case of the vitrification or spent fuel options, since there would be no opportunity to engineer the resulting waste form with this problem in mind. Furthermore, a much larger surface area of plutonium-bearing material would ultimately be exposed to water than is the case in an engineered repository.
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From page 274... ...
The only fission products in this rock would come from the single nuclear explosion, and thus the rock would be much easier to handle than spent fuel, even if that fuel were many decades old. Since gold can be mined profitably at a level of 1 ounce per ton (at a market price of some $10 per gram)
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From page 275... ...
The crucial aspects of subseabed disposal are the policy implications, and these questions can be explored on the assumption that the technical aspects can be resolved satisfactorily. The policy issues may differ somewhat depending on whether the plutonium would be emplaced within the exclusive economic zone with 200 nautical miles of the United States or Russia, or in international waters- though the two zones are strongly coupled by ocean circulation and both are covered by the London Dumping Convention.
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