Health Physics Pergamon Press 1975. Vol. 29 (October), pp. 481-488.
Printed in Northern Ireland
WASTE MANAGEMENT H. F. SOULE U.S. Atomic Energy Commission, Washington, D.C. (Received 10 February 1975)
Abstract-Current planning for the management of radioactivewastes, with some emphasis on plutonium contaminated wastes, includes the provision of repositories from which the wastes can be safkly removed to permanent disposal. A number of possibilities for permanent disposal are under investigation with the most favorable, at the present time, apparently disposal in a stable geological formation. However, final choice cannot be made until all studies are completed and a pilot phase demonstrates the adequacy of the chosen method. The radioactive wastes which result from all portions of the fuel cycle could comprise an important source of exposure to the public if permitted to do so. The objectives of the AEC waste management program are to provide methods of treating, handling and storing these wastes so that this exposure will not occur. This paper is intended to describe some of the problems and current progress of waste management programs, with emphasis on plutoniumcontaminated wastes. Since the technology in this field is advancing at a rapid pace, the descriptions given can be regarded only as a snapshot at one point in time. However, even at the risk of rapid obsolescence, it appears worthwhile to include these considerations in a symposium on plutonium.
FIGURE1 is a qualitative schematic of the nuclear fuel cycle which is used to point out four different kinds of radioactive waste which will be contaminated with plutonium. The first of these is waste in which the contaminant is primarily plutonium. As plutonium recycle grows and increased amounts of isotopes other than zsOPuare present,,the penetrating radiation from this kind of contaminant will be much higher than that from weapons-grade plutonium. However, it will still1 be relatively low level compared to that from mixed fission products. The primary places where these wastes will occur are a t the tail end of the reprocessing plant after fission products have been chemically separated and in the fciel fabrication plant where the plutonium is recycled into the system. The waste matrices here will be plugged-up HEPA filters, ion exchange resins from the clean-up of liquid effluents, plastic bags, obsolete equipment, scrap which is not profitable for reprocessing, and similar materials. The second kind of plutonium-contaminated waste will be that with a substantial admixture of fission products so that there is significant beta-gamma radiation affecting occupational safety during the handling of the waste. This waste will come primarily from the reprocessing plant up-stream of the point where the final separation is made.
However, it can also come from the reactor if there are cladding problems allowing fuel to erode into the coolant system. Of course, from occupational safety considerations at the reactor, the integrity of that cladding is very important. The two remaining types are unique to the reprocessing plant. Figure 2 is a schematic of a fuel reprocessing plant. One of the places where a plutonium-contaminated waste is generated is in the chop-leach step. The metallurgists have made fuel cladding which is very difficult to dissolve. Therefore, the reprocessing people chop the fuel, spread it out thin, and dissolve the fuel material in acid, leaving behind little shreds of the original cladding which are called “hulls.” There are traces of‘ fuel, including plutonium, clinging to this material. There are also, of course, fission products associated with the fuel plus induced activity. This makes a plutonium-contaminated waste which has rather high levels of betagamma activity. The remaining plutoniumcontaminated waste comes from the first solvent extraction where, in all the reprocessing plants in the world today, tributyl phosphate is used to extract the uranium and plutonium from the nitric acid solution. This is the source of the so-called “high-level” wastes which contain some 99+ % of the fission products. There are
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FIG. 2. Typical reprocessing plant. Simplified flow sheet.
estimates ranging as high as 99.995% of the non-volatile fission products going into this stream. There is an anomaly here in the chemical technology of this entire system. At present, we can make plutonium and uranium which have been purified from one another to a very high degree-something like one part in lo8 by weight. We also separate the fission products from these two valuable streams to a very high degree, but we do not have a parallel efficiency at recovering the plutonium and keeping a trace of it from going into this system. As Dr. Pigford mentioned earlier this morning, 0.5 % is a nominal plutonium loss which people very often use in predictions of process efficiency. Now, because of the intense radiation from fission products, high-level liquid wastes and the prospective solids prepared from them comprise potentially extreme gamma radiation hazards occupationally if anybody is permitted near them. Hence, they must be handled remotely. From a very long-range point of view, when the fission products have decayed, the 0.5% of the plutonium which was lost will be the controlling factor in the potential hazard, and Dr. Pigford's many slides of the actinides in the high-level wastes bear this out. I n Fig. 3, some predicted nuclear electric generating capacities are outlined. The volume of high-level liquidwaste if not solidified is purely academic. The regulations now require that this be kept no longer than 5 yr before it is solidified a t the reprocessing plant, and with the sizable reduction in volume by even present
solidification processes, whatever the confinement problems may be, the high-level solidified waste will not be a volume problem. There will be something like 25 x 106 1. of solid by the year 2000 for the entire United States, and this includes some predictions for the growth of the breeder program. These numbers were derived from work by Blomeke, Key and Nichols a t the Oak Ridge National Laboratory. Figure 4 is a companion diagram to Fig. 3, showing for the same years the accumulated activity. The key figure here is the 1.9 MCi of 239Puaccumulated at a repository by the year 2000. The next question logically is what is the AEC's high-level waste program for managing this material? I would like to mention briefly the two essential parts of the program and then go into a little bit of detail on each one. We frequently describe it as a two-part or a twophase or a two-prong program. One prong of the effort is that, by using the technology which
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FIG. 4. Estimated activity in waste from civilian nuclear power industry.
FIG. 1. The nuclear fuel cycle.
FIG.5. Retrievable surface storage facility. Water basin concept. Cutaway view.
FIG.10. Retrievable storage a t thc Idaho Transuranic Storage Area.
H. F. SOULE
is readily available right now and does not require any research and development effort, we will provide a t some central place engineered storage or fully retrievable storage. Any term denoting that the waste is under complete control and that we can get it back and move it somewhere else whenever we want to is appropriate. The second part of the program is that, during the time the retrievable facility is in operation, we will evaluate several of the most promising geological formations and go ahead with a pilot program to put the material into the most promising of these formations. The pilot program provj ng successful, this will become the so-called permanent disposal technique where there would be no further maintenance or replacement of equipment required and surveillance woulld be extremely nominal. Now the fact that there are two parts to this program is an extremely important one. When technical problems with acceptance of a specific geological site arose a t Lyons (Kansas) several years ago, many people came to the conclusion that geological storage had been dropped completely. I n fact, one environmentalist group has stated that the AEC told Congress that the best. thing for extraordinarily long periods of time was to keep this material in retrievable storage. The quote that was taken out of context by this group was apparently a statement that a retrievable surface storage facility, using present technology, could be used to store ithe waste for as long as we cared to maintain the facility and to hold surveillance over it. The difference, of course, between being able to do something and feeling that it is necessary to do it is quite significant. We have not said that it is necessary or desirable to keep this waste in retrievable storage for as far ahead as anybody acan see and to do nothing else. With that brief loolc at the two parts of the program, let us review the operation of the retrievable surface storage facility (RSSF). We would anticipate that the liquid waste would be converted to a solid, probably calcined, a t the licensed reprocessing plants using a variation of the process that has operated quite successfully at the Idaho site for alimost 10 yr. The encapsulated material would then be shipped to the central AEC repository in shipping containers
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which are very similar in nature to the so-called1 Type B shipping containers which have been used safely to ship highly irradiated fuels from reactors to the reprocessing sites. At the RSSF,, the cannisters will be inspected for compliance: with the acceptance criteria in a hot cell. These: hot cells will be very similar to those used for. radiometallurgy. They will have measuring equipment, facilities for decontamination and rejacketing of an occasional damaged cannister, and will be used in any one of the three basic engineering concepts currently considered. These concepts are basically a water-basin, an air-cooled vault, and a sealed cask. Figure 5 is an artist’s concept of the water-basin concept. This is a variation of the water-filled basins which have been used at reactors and reprocessing plants since the beginning of the Manhattan Project to store highly irradiated fuel elements. The difference is that the storage would be over a period of some years and, hence, the quality inspection and periodic re-inspection program would have to be somewhat different in its nature. The heat, which would be dissipated from the cannisters into the basin, would be disposed of through cooling towers to a secondary system. By the year 2000, if all of the U.S. material were stockpiled in one repository of this kind, the total heat load to be dumped to the air would be something like 200 MW. This occasionally excites people who would like this heat to be used, but the heat per cannister is on the order of 5 kW, and 5 kW from a metal object l o f t long and 1 ft in diameter has not been attractive. A second concept under consideration is an air-cooled vault (shown in Fig. 6). In this particular case, conduction through the wall of the cannister and convection to the air with a natural draft discharge would be used to dissipate the heat. Employees would be protected by an overstructure. This facility would look somewhat like the deck of a typical fuel reprocessing plant except that where the process cells are we would have the cannisters. The advantage of the water-basin concept is that it is very similar to the spent fuel storage we have been doing for many years. Since it does require a mechanical cooling system which can go wrong, it has a certain possibility of error or
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HEPl FILTERS
FOR
RECEIVING CELL E
HIGH INTEGRITI OVERPACK
AIR FLOW BAFFLES
FIG.6 . RSSF air cooled vault concept.
mechanical failure. I n the air-cooled vault, the material could not be visually inspected while in storage position, and the periodic re-inspection program of the cannisters would require more maneuvering and manipulating of the cover blocks. The advantage, of course, is that, by using a passive cooling system, there is literally no coolant circulating equipment to go wrong. Figure 7 illustrates the projected growth curve in the numbers of these cannisters and a step-wise modular construction program which would be anticipated. For either of the two preceding concepts, the inspection facilities would be built to the maximum throughput, but the individual sections of the water-basin or air-cooled basin could be built step-wise to minimize the original capital. By putting
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proper stubs on the original construction, you could put on additional wings to give the full storage capacity needed for the year 2000. Figure 8 is a different storage concept in which a vault is not needed. The same inspection facilities as before would be provided, but each waste cannister would be placed in a n outer container. One possibility would be a n all-steel container, but with the higher actinides that are anticipated, some neutron shielding would be needed because of alpha-neutron reactions and spontaneous fission. Thus, there are, in addition to the steel, various combinations of steel and concrete. I n one of the variations of this concept, the containers are placed on their ends with chimney effect betwekn the steel and the concrete to provide natural convection. The sealed-cask concept has the advantages of the air-cooled vault concept in that it is entirely passive in its cooling. Also, because of its very massive nature, it is almost as sabotageproof as anything can be. One possible disadvantage is that it does tie up a rather substantial amount of steel for a fairly long period. T o give a feel for the quantity, if we were to use entirely steel with nominal dose rates of a few mR/hr a t contact with the outside, by the year 2000 we would be tying up about 5 % of one year’s steel production at present rates. With proper jacketing and a sacrificial liner, chances of being able to recover this steel eventually would be quite good. Thus, this use would not be an irretrievable loss but, rather,
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FIG.8. RSSF sealed storage cask concept.
H. F. SOULE
a temporary tie-up of material. This use must be weighed against the steel that would be used up in a reinforced concrete vault if we go that other route. Another feature of the RSSF is the form of the stored wastes. The reprocessing plants now appear to be planning upon calcining, which produces a fairly powdery oxide. The chances of a catastrophic accident, where a guillotine break in a cannister would result in losing powder onto the floor of a hot cell, appear to be very low. However, if such a n accident were to occur, the margin of safety would be much higher if the material were in a monolithic solid, preferably a low solubility solid. There is now work in progress at the Waste Solidification Engineering Prototype at Hanford in making various forms of glass out of calcine. I n addition, if this looks promising, a glassmaking plant at the RSSF itself will be included. The experts, people in the glass industry, feel that the oxide powder could be a suitable starting material to produce glass directly and that it would not be necessary to redissolve the calcine into liquid form. For the siting of the RSSF, we have reviewed a number of federally owned sites, not all of them AEC sites, for katures such as logistics, availability of land, and rail support. Not all of these appear equally promising, and at the present time the three sites which appear most suitable for an RSSF are the three western sites of the AEC with their rather large areas of unused land: the Nevada Test Site, the Idaho Nuclear Engineering Laboratory* and Hanford. The AEC has not taken a firm position as to which of these three engineering concepts and which site we intend to recommend. We are preparing a draft environmental statement which will not take a position; it will simply lay out the alternatives and solicit comments from industry, from environmentalists, and from the public. We hope to publish this draft statement the latter part ofJune7 and, after the comment period and public hearing-only after that period-will the Commission make a firm decision on what to propose in the budget. One
* Formerly the National Reactor Testing Station. t The draft EIS was is:iued in September 1974 as
WASH-1539.
485
of the alternatives to be mentioned in this impact statement is the one Commissioner Larson touched on briefly (i.e. providing the equivalent of a n RSSF for reprocessing plants). ALs Commissioner Larson said, the official regulatory policy is still a central repository, but in the spirit of cooperation, we are going to cover this particular alternative and give people a chance to express their opinions. T o return now to the geological storage, the Lyons site, which is in bedded salt, was not acceptable because of problems which were specific a t that site. The problems there did not involve the integrity of the salt. There i.3 now a program of looking at several other likely formations: domed salt as distinct from bedded salt, granite, limestone, possibly certain type:: of very tight shale. The goal here is that, within a few years, there would be available as much data about these other formations as there is now about bedded salt. A fresh decision could then be made along with some site considerations which could lead to selection of a proposed site for a pilot geological repository. Figure 9 is a schematic of the way the casks would be lowered into a salt mine, moved through tunnels, and placed in the floors of the tunnels. Probably a similar approach would be used in other geological formations. The two main aspects of the pilot approach, and I stress the word pilot, is that during the first years of operation of the facility the waste cannisters would only be inserted in some kind of special fittings so that there would be assurance that, if the geological community decided that the approach was wrong, the material could be removed from the mine and leave no contamination behind. This was done some years ago with irradiated fuel elements in Lyons, and this feature would be repeated. A second feature of the pilot concept is that the RSSF would be built first, and there would always be enough reserve capacity within the RSSF to receive the entire inventory of the pilot geological facility if the consensus should go that way. The belief, of course, is that the consensus would go the other way and that, after the advisory panel of geologists had done all of the additional tests and studies they felt were necessary, they would give an approval and that this would be considered permanent disposal.
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TRANSFEAGALLERY
FIG.9. Bedded salt pilot plant handling schematic.
Let us now consider the other kinds of plutonium-contaminated waste mentioned previously: the hulls, the trash and obsolete equipment. From the beginning of the Manhattan Project, this kind of material has been buried in relatively shallow trenches and pits in so-called burial grounds. They are somewhat analogous to sanitary land-fill except they were picked with more care than a typical municipal or industrial sanitary land-fill. In 1969, the AEC became involved in a controversy over the safety of this kind of burial at the Idaho Nuclear Engineering Laboratory, which is where all this kind of material from the Rocky Flats weapons fabrication plant had been sent. The Bureau of Radiological Health reviewed the situation and gave a relatively clean bill of health, qualified by some very reasonable recommendations for closer monitoring a t the burial trenches. Even so, the thought of maintaining surveillance over a rather large inventory (namely, some 350 kg of plutonium dispersed through some 3,000,000 fts of solid waste) for a n indefinite period of time was still troublesome. It bothered the Idaho authorities, and a commitment was made that, when a high-level repository in salt was available, the fresh Rocky
Flats wastes would be sent directly to that salt mine. I n addition, at the time a salt repository became available, the Rocky Flats waste at Idaho would be removed and sent to the salt mine. Of course, there was a caveat understood that this would be a major job and would take some years to accomplish. With this commitment, it became a n obvious advantage to store the plutonium-contaminated solid waste in such a way that it could be readily retrieved without major exhumation and decontamination. At the Idaho Nuclear Engineering Laboratory since about 1971, wastes have been stored by a concept which is called a “covered pad.” This is no longer burial pits or trenches; instead, the various casks and drums of plutoniumcontaminated waste from Rocky Flats are carefully stacked and are essentially used to make a small structure which is then covered with plywood and tarpaulins and a modest amount of earth backfill. Figure 10 shows a closeup of how these crates are used to make an outer barrier, and when the drums are stacked within, these are grouped with a n air-break between them for safety purposes. T h e entire structure is then covered with tarps, plywood and plastic.
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of the so-called tectonic plates will carry it deeper beneath the earth’s crust. All of these things have the rather common drawbacks that the basic scientific knowledge to evaluate their safety is lacking, and there would be much research and development required to come to a point of deciding whether they were safe. Another type of advanced concept is space disposal, and with the help of NASA, BattelleNorthwest looked at this. One of the uncertainties is that the space people do not feel confident that they can predict high earth orbits or solar orbits for the very great length of time required. A path which would take the material out of the solar system is perhaps feasible, but there would still be the problems of designing a container that would have a useful payload and would stand the maximum launch pad accident. Therefore, space disposal is something which, if ever, will be possible only after a great deal of research and development. One of the interim things that would almost necessarily have to be done is partitioning which means taking out the worst offenders in the waste (plutonium, other actinides, and possibly strontium) and putting them in a separate package, for which more sophisticated or expensive treatment would be feasible. Another kind of advanced concept, which almost certainly requires partitioning, is transmutation : the nuclear bombardment of waste to convert it into shorter lived material. There is one very special case of transmutation which does not appear at all out of reason. This is the case where the separations technology is improved to keep that 0.5% of plutonium from getting into the high-level waste in the first place and putting it back through the system as fuel. DWMT has approximately doubled the fiscal year 1975 proposals for this type of work, which also includes looking at the possibilities of taking the material out of the old wastes. A group of top chemical technology people, including our previous speaker, Bill Maraman, is being formed into a research and development steering committee to advise the Division of Waste Management and Transportation right now as * Proposed rulemakingwas published in September to what could be done even further to improve this separations technology. The 0.5% loss so 1974. t The full study has since been published as far has not proved objectionable, but this is BNWL- 1900. probably because the true, long-term costs, both
Of course, if this were to continue for a longer pcriod of time, volume reduction would be very desirable. Plutonium-contaminated scrap has been successfully incinerated for some years at both Rocky Flats and Hanford for scrap recovery purposes. However, for simply reducing the volume of waste, this has not yet been done. ‘Thcxre is a facility being designed a t Los Alamos to develop the techniques for volume reduction. In the near future, the regulatory arm of the AEC will undoubtedly publish proposed rules* which will essentially take the position for commercial plutonium-contaminated wastes that the operating side took several years ago after the Idaho problem. Namely, that above a certain contamination level, which tentatively is 10 nCi/g of waste, the material would be turned over to the AEC for storage. For a short timc we would probably store it in a manner similar to what has been done with AEC wastes, and then after incineration or volume reduction it would probably go into some kind of storage. Of course, the long-range goal would be geological storage which, potentially, is just as applicable to this kind of waste as it is to the high-level waste. As Commissioner Larson indicated, there are studies of possibilities even beyond geological storage. Battelle-Northwest, with the help of outside consultants, has completed a study which is not yet completely published. A short summary document, WASH-1297, is available. t The geological storage which has been discussed is at depths which can be reached by conventional mining methods-I 000-2000 ft deep. There is another family of disposal concepts which use unusual geological formations, very greath depths, uncoventional mining approaches, or a combination of all of these. These include such cmcepts as a nuclear detonation to make a cavity to receive liquid haste, allowing it to melt the rock and then refreeze; burying in the ice on the Antarctic Continent; and burying it beneath the ocean at a very great depth where the slow movement
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financial and environmental, of this disposal have not been realized. To conclude, these problems cannot be belittled. They are quite great. O n the other hand, we i n the Division of Waste Management and Transportation think that none of them are insoluble. We believe we have the top management’s attention within the Commission. We seem to have the approval of the Joint Committee on Atomic Energy, and we have received all of our requested budget money i n the last several years. In conclusion, with the understanding and the help of knowledgeable people like yourselves, this will help get the job done. DISCUSSION
PIGFORD, T. H.: From the emphasis you have placed on the very careful approach toward highlevel wastes, I gather that the losses of plutonium in the solid wastes in conversion and fabrication tend to be greater than 0.5%. It seems to me that we will end up with more plutonium in those other wastes than we will in the wastes from reprocessing and that we will have the same kind of long-term environmental problems on those. SOULE,H. F.: Your point is certainly very well taken. Improving efficiencies in the fabrication plant is very important, and whatever can be done to keep the plutonium out of the waste and from getting back into the system, improved scrap recovery technology, for instance, should be looked at. PIGFORD, T. H.: I mean the technique of burying those wastes themselves. They have more plutonium than the high-level wastes. SOULE,H. F.: With the prospective change in rules, they would get the same kind of geological disposal as the high-level wastes.
PICFORD, T. H. : I can see the logic of trying to cut this 0.5 % loss of plutionium to the high-level wastes down to zero, but that doesn’t stop the plutonium because most of the plutonium in high-level wastes after a few hundred years comes instead from americium, and you can forget about the 0.5 %-you still have the plutonium problem. SOULE,H. F.: I t might also be necessary to improve the technology and to get the americium out instead of letting it go to the waste. CALDWELL, C. S.: In your proposed regulation change, have the tariffs for the interim engineered storage and the legal aspect of title to the plutonium contained in the waste been resolved? SOULE, H. F. : My prediction is that the regulation will contain the same type of title provision as the regulation of high-level wastes-namely, that at the time of physical transfer of the wastes, title and custody would go also. Also, the schedule of fees is being worked up. We would hope to have it ready for publication when the proposed rule-making is published. WALSKE, C. : In the AEC’s long-term program for storage in salt beds, there is a problem with public understanding. The public sees that the Lyons facility was attempted sometime ago and then cancelled. If I understand the AEC’s program, there will be several more years in investigating quite a number of salt mines, during which time I believe, for one, that the industry is going to continue to be wrapped over the knuckles for not having a proven example to show people. SOULE, H. F.: The geological evaluation program will be described in the impact statement, and if the thrust of the comments is not to wait any longer but to go ahead with a single geological depository, the change may very well come about.
Printed in Northern Ireland
WASTE MANAGEMENT H. F. SOULE U.S. Atomic Energy Commission, Washington, D.C. (Received 10 February 1975)
Abstract-Current planning for the management of radioactivewastes, with some emphasis on plutonium contaminated wastes, includes the provision of repositories from which the wastes can be safkly removed to permanent disposal. A number of possibilities for permanent disposal are under investigation with the most favorable, at the present time, apparently disposal in a stable geological formation. However, final choice cannot be made until all studies are completed and a pilot phase demonstrates the adequacy of the chosen method. The radioactive wastes which result from all portions of the fuel cycle could comprise an important source of exposure to the public if permitted to do so. The objectives of the AEC waste management program are to provide methods of treating, handling and storing these wastes so that this exposure will not occur. This paper is intended to describe some of the problems and current progress of waste management programs, with emphasis on plutoniumcontaminated wastes. Since the technology in this field is advancing at a rapid pace, the descriptions given can be regarded only as a snapshot at one point in time. However, even at the risk of rapid obsolescence, it appears worthwhile to include these considerations in a symposium on plutonium.
FIGURE1 is a qualitative schematic of the nuclear fuel cycle which is used to point out four different kinds of radioactive waste which will be contaminated with plutonium. The first of these is waste in which the contaminant is primarily plutonium. As plutonium recycle grows and increased amounts of isotopes other than zsOPuare present,,the penetrating radiation from this kind of contaminant will be much higher than that from weapons-grade plutonium. However, it will still1 be relatively low level compared to that from mixed fission products. The primary places where these wastes will occur are a t the tail end of the reprocessing plant after fission products have been chemically separated and in the fciel fabrication plant where the plutonium is recycled into the system. The waste matrices here will be plugged-up HEPA filters, ion exchange resins from the clean-up of liquid effluents, plastic bags, obsolete equipment, scrap which is not profitable for reprocessing, and similar materials. The second kind of plutonium-contaminated waste will be that with a substantial admixture of fission products so that there is significant beta-gamma radiation affecting occupational safety during the handling of the waste. This waste will come primarily from the reprocessing plant up-stream of the point where the final separation is made.
However, it can also come from the reactor if there are cladding problems allowing fuel to erode into the coolant system. Of course, from occupational safety considerations at the reactor, the integrity of that cladding is very important. The two remaining types are unique to the reprocessing plant. Figure 2 is a schematic of a fuel reprocessing plant. One of the places where a plutonium-contaminated waste is generated is in the chop-leach step. The metallurgists have made fuel cladding which is very difficult to dissolve. Therefore, the reprocessing people chop the fuel, spread it out thin, and dissolve the fuel material in acid, leaving behind little shreds of the original cladding which are called “hulls.” There are traces of‘ fuel, including plutonium, clinging to this material. There are also, of course, fission products associated with the fuel plus induced activity. This makes a plutonium-contaminated waste which has rather high levels of betagamma activity. The remaining plutoniumcontaminated waste comes from the first solvent extraction where, in all the reprocessing plants in the world today, tributyl phosphate is used to extract the uranium and plutonium from the nitric acid solution. This is the source of the so-called “high-level” wastes which contain some 99+ % of the fission products. There are
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PLUTONIUM URANIUM EFFLUENT TO TO RECYCLE TO RECYCLE DISCHARGE
FIG. 2. Typical reprocessing plant. Simplified flow sheet.
estimates ranging as high as 99.995% of the non-volatile fission products going into this stream. There is an anomaly here in the chemical technology of this entire system. At present, we can make plutonium and uranium which have been purified from one another to a very high degree-something like one part in lo8 by weight. We also separate the fission products from these two valuable streams to a very high degree, but we do not have a parallel efficiency at recovering the plutonium and keeping a trace of it from going into this system. As Dr. Pigford mentioned earlier this morning, 0.5 % is a nominal plutonium loss which people very often use in predictions of process efficiency. Now, because of the intense radiation from fission products, high-level liquid wastes and the prospective solids prepared from them comprise potentially extreme gamma radiation hazards occupationally if anybody is permitted near them. Hence, they must be handled remotely. From a very long-range point of view, when the fission products have decayed, the 0.5% of the plutonium which was lost will be the controlling factor in the potential hazard, and Dr. Pigford's many slides of the actinides in the high-level wastes bear this out. I n Fig. 3, some predicted nuclear electric generating capacities are outlined. The volume of high-level liquidwaste if not solidified is purely academic. The regulations now require that this be kept no longer than 5 yr before it is solidified a t the reprocessing plant, and with the sizable reduction in volume by even present
solidification processes, whatever the confinement problems may be, the high-level solidified waste will not be a volume problem. There will be something like 25 x 106 1. of solid by the year 2000 for the entire United States, and this includes some predictions for the growth of the breeder program. These numbers were derived from work by Blomeke, Key and Nichols a t the Oak Ridge National Laboratory. Figure 4 is a companion diagram to Fig. 3, showing for the same years the accumulated activity. The key figure here is the 1.9 MCi of 239Puaccumulated at a repository by the year 2000. The next question logically is what is the AEC's high-level waste program for managing this material? I would like to mention briefly the two essential parts of the program and then go into a little bit of detail on each one. We frequently describe it as a two-part or a twophase or a two-prong program. One prong of the effort is that, by using the technology which
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FIG. 4. Estimated activity in waste from civilian nuclear power industry.
FIG. 1. The nuclear fuel cycle.
FIG.5. Retrievable surface storage facility. Water basin concept. Cutaway view.
FIG.10. Retrievable storage a t thc Idaho Transuranic Storage Area.
H. F. SOULE
is readily available right now and does not require any research and development effort, we will provide a t some central place engineered storage or fully retrievable storage. Any term denoting that the waste is under complete control and that we can get it back and move it somewhere else whenever we want to is appropriate. The second part of the program is that, during the time the retrievable facility is in operation, we will evaluate several of the most promising geological formations and go ahead with a pilot program to put the material into the most promising of these formations. The pilot program provj ng successful, this will become the so-called permanent disposal technique where there would be no further maintenance or replacement of equipment required and surveillance woulld be extremely nominal. Now the fact that there are two parts to this program is an extremely important one. When technical problems with acceptance of a specific geological site arose a t Lyons (Kansas) several years ago, many people came to the conclusion that geological storage had been dropped completely. I n fact, one environmentalist group has stated that the AEC told Congress that the best. thing for extraordinarily long periods of time was to keep this material in retrievable storage. The quote that was taken out of context by this group was apparently a statement that a retrievable surface storage facility, using present technology, could be used to store ithe waste for as long as we cared to maintain the facility and to hold surveillance over it. The difference, of course, between being able to do something and feeling that it is necessary to do it is quite significant. We have not said that it is necessary or desirable to keep this waste in retrievable storage for as far ahead as anybody acan see and to do nothing else. With that brief loolc at the two parts of the program, let us review the operation of the retrievable surface storage facility (RSSF). We would anticipate that the liquid waste would be converted to a solid, probably calcined, a t the licensed reprocessing plants using a variation of the process that has operated quite successfully at the Idaho site for alimost 10 yr. The encapsulated material would then be shipped to the central AEC repository in shipping containers
483
which are very similar in nature to the so-called1 Type B shipping containers which have been used safely to ship highly irradiated fuels from reactors to the reprocessing sites. At the RSSF,, the cannisters will be inspected for compliance: with the acceptance criteria in a hot cell. These: hot cells will be very similar to those used for. radiometallurgy. They will have measuring equipment, facilities for decontamination and rejacketing of an occasional damaged cannister, and will be used in any one of the three basic engineering concepts currently considered. These concepts are basically a water-basin, an air-cooled vault, and a sealed cask. Figure 5 is an artist’s concept of the water-basin concept. This is a variation of the water-filled basins which have been used at reactors and reprocessing plants since the beginning of the Manhattan Project to store highly irradiated fuel elements. The difference is that the storage would be over a period of some years and, hence, the quality inspection and periodic re-inspection program would have to be somewhat different in its nature. The heat, which would be dissipated from the cannisters into the basin, would be disposed of through cooling towers to a secondary system. By the year 2000, if all of the U.S. material were stockpiled in one repository of this kind, the total heat load to be dumped to the air would be something like 200 MW. This occasionally excites people who would like this heat to be used, but the heat per cannister is on the order of 5 kW, and 5 kW from a metal object l o f t long and 1 ft in diameter has not been attractive. A second concept under consideration is an air-cooled vault (shown in Fig. 6). In this particular case, conduction through the wall of the cannister and convection to the air with a natural draft discharge would be used to dissipate the heat. Employees would be protected by an overstructure. This facility would look somewhat like the deck of a typical fuel reprocessing plant except that where the process cells are we would have the cannisters. The advantage of the water-basin concept is that it is very similar to the spent fuel storage we have been doing for many years. Since it does require a mechanical cooling system which can go wrong, it has a certain possibility of error or
484
WASTE MANAGEMENT
HEPl FILTERS
FOR
RECEIVING CELL E
HIGH INTEGRITI OVERPACK
AIR FLOW BAFFLES
FIG.6 . RSSF air cooled vault concept.
mechanical failure. I n the air-cooled vault, the material could not be visually inspected while in storage position, and the periodic re-inspection program of the cannisters would require more maneuvering and manipulating of the cover blocks. The advantage, of course, is that, by using a passive cooling system, there is literally no coolant circulating equipment to go wrong. Figure 7 illustrates the projected growth curve in the numbers of these cannisters and a step-wise modular construction program which would be anticipated. For either of the two preceding concepts, the inspection facilities would be built to the maximum throughput, but the individual sections of the water-basin or air-cooled basin could be built step-wise to minimize the original capital. By putting
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CONSTRUCTION TIME
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BASINS CONSTRUCTED 0 No(I BASIN 500 CANISTERS) -
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proper stubs on the original construction, you could put on additional wings to give the full storage capacity needed for the year 2000. Figure 8 is a different storage concept in which a vault is not needed. The same inspection facilities as before would be provided, but each waste cannister would be placed in a n outer container. One possibility would be a n all-steel container, but with the higher actinides that are anticipated, some neutron shielding would be needed because of alpha-neutron reactions and spontaneous fission. Thus, there are, in addition to the steel, various combinations of steel and concrete. I n one of the variations of this concept, the containers are placed on their ends with chimney effect betwekn the steel and the concrete to provide natural convection. The sealed-cask concept has the advantages of the air-cooled vault concept in that it is entirely passive in its cooling. Also, because of its very massive nature, it is almost as sabotageproof as anything can be. One possible disadvantage is that it does tie up a rather substantial amount of steel for a fairly long period. T o give a feel for the quantity, if we were to use entirely steel with nominal dose rates of a few mR/hr a t contact with the outside, by the year 2000 we would be tying up about 5 % of one year’s steel production at present rates. With proper jacketing and a sacrificial liner, chances of being able to recover this steel eventually would be quite good. Thus, this use would not be an irretrievable loss but, rather,
SK
CANISTER STORAGE CAPACITY OF FACILITY
TEST
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-
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FIG.8. RSSF sealed storage cask concept.
H. F. SOULE
a temporary tie-up of material. This use must be weighed against the steel that would be used up in a reinforced concrete vault if we go that other route. Another feature of the RSSF is the form of the stored wastes. The reprocessing plants now appear to be planning upon calcining, which produces a fairly powdery oxide. The chances of a catastrophic accident, where a guillotine break in a cannister would result in losing powder onto the floor of a hot cell, appear to be very low. However, if such a n accident were to occur, the margin of safety would be much higher if the material were in a monolithic solid, preferably a low solubility solid. There is now work in progress at the Waste Solidification Engineering Prototype at Hanford in making various forms of glass out of calcine. I n addition, if this looks promising, a glassmaking plant at the RSSF itself will be included. The experts, people in the glass industry, feel that the oxide powder could be a suitable starting material to produce glass directly and that it would not be necessary to redissolve the calcine into liquid form. For the siting of the RSSF, we have reviewed a number of federally owned sites, not all of them AEC sites, for katures such as logistics, availability of land, and rail support. Not all of these appear equally promising, and at the present time the three sites which appear most suitable for an RSSF are the three western sites of the AEC with their rather large areas of unused land: the Nevada Test Site, the Idaho Nuclear Engineering Laboratory* and Hanford. The AEC has not taken a firm position as to which of these three engineering concepts and which site we intend to recommend. We are preparing a draft environmental statement which will not take a position; it will simply lay out the alternatives and solicit comments from industry, from environmentalists, and from the public. We hope to publish this draft statement the latter part ofJune7 and, after the comment period and public hearing-only after that period-will the Commission make a firm decision on what to propose in the budget. One
* Formerly the National Reactor Testing Station. t The draft EIS was is:iued in September 1974 as
WASH-1539.
485
of the alternatives to be mentioned in this impact statement is the one Commissioner Larson touched on briefly (i.e. providing the equivalent of a n RSSF for reprocessing plants). ALs Commissioner Larson said, the official regulatory policy is still a central repository, but in the spirit of cooperation, we are going to cover this particular alternative and give people a chance to express their opinions. T o return now to the geological storage, the Lyons site, which is in bedded salt, was not acceptable because of problems which were specific a t that site. The problems there did not involve the integrity of the salt. There i.3 now a program of looking at several other likely formations: domed salt as distinct from bedded salt, granite, limestone, possibly certain type:: of very tight shale. The goal here is that, within a few years, there would be available as much data about these other formations as there is now about bedded salt. A fresh decision could then be made along with some site considerations which could lead to selection of a proposed site for a pilot geological repository. Figure 9 is a schematic of the way the casks would be lowered into a salt mine, moved through tunnels, and placed in the floors of the tunnels. Probably a similar approach would be used in other geological formations. The two main aspects of the pilot approach, and I stress the word pilot, is that during the first years of operation of the facility the waste cannisters would only be inserted in some kind of special fittings so that there would be assurance that, if the geological community decided that the approach was wrong, the material could be removed from the mine and leave no contamination behind. This was done some years ago with irradiated fuel elements in Lyons, and this feature would be repeated. A second feature of the pilot concept is that the RSSF would be built first, and there would always be enough reserve capacity within the RSSF to receive the entire inventory of the pilot geological facility if the consensus should go that way. The belief, of course, is that the consensus would go the other way and that, after the advisory panel of geologists had done all of the additional tests and studies they felt were necessary, they would give an approval and that this would be considered permanent disposal.
48 6
WASTE MANAGEMENT
TRANSFEAGALLERY
FIG.9. Bedded salt pilot plant handling schematic.
Let us now consider the other kinds of plutonium-contaminated waste mentioned previously: the hulls, the trash and obsolete equipment. From the beginning of the Manhattan Project, this kind of material has been buried in relatively shallow trenches and pits in so-called burial grounds. They are somewhat analogous to sanitary land-fill except they were picked with more care than a typical municipal or industrial sanitary land-fill. In 1969, the AEC became involved in a controversy over the safety of this kind of burial at the Idaho Nuclear Engineering Laboratory, which is where all this kind of material from the Rocky Flats weapons fabrication plant had been sent. The Bureau of Radiological Health reviewed the situation and gave a relatively clean bill of health, qualified by some very reasonable recommendations for closer monitoring a t the burial trenches. Even so, the thought of maintaining surveillance over a rather large inventory (namely, some 350 kg of plutonium dispersed through some 3,000,000 fts of solid waste) for a n indefinite period of time was still troublesome. It bothered the Idaho authorities, and a commitment was made that, when a high-level repository in salt was available, the fresh Rocky
Flats wastes would be sent directly to that salt mine. I n addition, at the time a salt repository became available, the Rocky Flats waste at Idaho would be removed and sent to the salt mine. Of course, there was a caveat understood that this would be a major job and would take some years to accomplish. With this commitment, it became a n obvious advantage to store the plutonium-contaminated solid waste in such a way that it could be readily retrieved without major exhumation and decontamination. At the Idaho Nuclear Engineering Laboratory since about 1971, wastes have been stored by a concept which is called a “covered pad.” This is no longer burial pits or trenches; instead, the various casks and drums of plutoniumcontaminated waste from Rocky Flats are carefully stacked and are essentially used to make a small structure which is then covered with plywood and tarpaulins and a modest amount of earth backfill. Figure 10 shows a closeup of how these crates are used to make an outer barrier, and when the drums are stacked within, these are grouped with a n air-break between them for safety purposes. T h e entire structure is then covered with tarps, plywood and plastic.
H. F. SOULE
487
of the so-called tectonic plates will carry it deeper beneath the earth’s crust. All of these things have the rather common drawbacks that the basic scientific knowledge to evaluate their safety is lacking, and there would be much research and development required to come to a point of deciding whether they were safe. Another type of advanced concept is space disposal, and with the help of NASA, BattelleNorthwest looked at this. One of the uncertainties is that the space people do not feel confident that they can predict high earth orbits or solar orbits for the very great length of time required. A path which would take the material out of the solar system is perhaps feasible, but there would still be the problems of designing a container that would have a useful payload and would stand the maximum launch pad accident. Therefore, space disposal is something which, if ever, will be possible only after a great deal of research and development. One of the interim things that would almost necessarily have to be done is partitioning which means taking out the worst offenders in the waste (plutonium, other actinides, and possibly strontium) and putting them in a separate package, for which more sophisticated or expensive treatment would be feasible. Another kind of advanced concept, which almost certainly requires partitioning, is transmutation : the nuclear bombardment of waste to convert it into shorter lived material. There is one very special case of transmutation which does not appear at all out of reason. This is the case where the separations technology is improved to keep that 0.5% of plutonium from getting into the high-level waste in the first place and putting it back through the system as fuel. DWMT has approximately doubled the fiscal year 1975 proposals for this type of work, which also includes looking at the possibilities of taking the material out of the old wastes. A group of top chemical technology people, including our previous speaker, Bill Maraman, is being formed into a research and development steering committee to advise the Division of Waste Management and Transportation right now as * Proposed rulemakingwas published in September to what could be done even further to improve this separations technology. The 0.5% loss so 1974. t The full study has since been published as far has not proved objectionable, but this is BNWL- 1900. probably because the true, long-term costs, both
Of course, if this were to continue for a longer pcriod of time, volume reduction would be very desirable. Plutonium-contaminated scrap has been successfully incinerated for some years at both Rocky Flats and Hanford for scrap recovery purposes. However, for simply reducing the volume of waste, this has not yet been done. ‘Thcxre is a facility being designed a t Los Alamos to develop the techniques for volume reduction. In the near future, the regulatory arm of the AEC will undoubtedly publish proposed rules* which will essentially take the position for commercial plutonium-contaminated wastes that the operating side took several years ago after the Idaho problem. Namely, that above a certain contamination level, which tentatively is 10 nCi/g of waste, the material would be turned over to the AEC for storage. For a short timc we would probably store it in a manner similar to what has been done with AEC wastes, and then after incineration or volume reduction it would probably go into some kind of storage. Of course, the long-range goal would be geological storage which, potentially, is just as applicable to this kind of waste as it is to the high-level waste. As Commissioner Larson indicated, there are studies of possibilities even beyond geological storage. Battelle-Northwest, with the help of outside consultants, has completed a study which is not yet completely published. A short summary document, WASH-1297, is available. t The geological storage which has been discussed is at depths which can be reached by conventional mining methods-I 000-2000 ft deep. There is another family of disposal concepts which use unusual geological formations, very greath depths, uncoventional mining approaches, or a combination of all of these. These include such cmcepts as a nuclear detonation to make a cavity to receive liquid haste, allowing it to melt the rock and then refreeze; burying in the ice on the Antarctic Continent; and burying it beneath the ocean at a very great depth where the slow movement
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financial and environmental, of this disposal have not been realized. To conclude, these problems cannot be belittled. They are quite great. O n the other hand, we i n the Division of Waste Management and Transportation think that none of them are insoluble. We believe we have the top management’s attention within the Commission. We seem to have the approval of the Joint Committee on Atomic Energy, and we have received all of our requested budget money i n the last several years. In conclusion, with the understanding and the help of knowledgeable people like yourselves, this will help get the job done. DISCUSSION
PIGFORD, T. H.: From the emphasis you have placed on the very careful approach toward highlevel wastes, I gather that the losses of plutonium in the solid wastes in conversion and fabrication tend to be greater than 0.5%. It seems to me that we will end up with more plutonium in those other wastes than we will in the wastes from reprocessing and that we will have the same kind of long-term environmental problems on those. SOULE,H. F.: Your point is certainly very well taken. Improving efficiencies in the fabrication plant is very important, and whatever can be done to keep the plutonium out of the waste and from getting back into the system, improved scrap recovery technology, for instance, should be looked at. PIGFORD, T. H.: I mean the technique of burying those wastes themselves. They have more plutonium than the high-level wastes. SOULE,H. F.: With the prospective change in rules, they would get the same kind of geological disposal as the high-level wastes.
PICFORD, T. H. : I can see the logic of trying to cut this 0.5 % loss of plutionium to the high-level wastes down to zero, but that doesn’t stop the plutonium because most of the plutonium in high-level wastes after a few hundred years comes instead from americium, and you can forget about the 0.5 %-you still have the plutonium problem. SOULE,H. F.: I t might also be necessary to improve the technology and to get the americium out instead of letting it go to the waste. CALDWELL, C. S.: In your proposed regulation change, have the tariffs for the interim engineered storage and the legal aspect of title to the plutonium contained in the waste been resolved? SOULE, H. F. : My prediction is that the regulation will contain the same type of title provision as the regulation of high-level wastes-namely, that at the time of physical transfer of the wastes, title and custody would go also. Also, the schedule of fees is being worked up. We would hope to have it ready for publication when the proposed rule-making is published. WALSKE, C. : In the AEC’s long-term program for storage in salt beds, there is a problem with public understanding. The public sees that the Lyons facility was attempted sometime ago and then cancelled. If I understand the AEC’s program, there will be several more years in investigating quite a number of salt mines, during which time I believe, for one, that the industry is going to continue to be wrapped over the knuckles for not having a proven example to show people. SOULE, H. F.: The geological evaluation program will be described in the impact statement, and if the thrust of the comments is not to wait any longer but to go ahead with a single geological depository, the change may very well come about.
