12 Radioactive Waste Management Development in Europe RAY D. WALTON, JR.
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0153.ch012
U. S. Energy Research and Development Administration, Wash., D.C. 20545
Germany, England, and France are vigorously developing technology and methodology for incorporating high-level radioactive waste into silicate glass. Germany is concentrating on a spray calcination vitrification system. England has selected a rising level glass process in which evaporation, calcination, and borosilicate glass vitrification all take place in a heated pot. France is operating a small-scale batch pot calcination-batch vitrification system and developing a new continuous system using a rotary calciner and melter with batchwise draw-off.
During the period M a y 4-18, 1973, several European sites were visited to observe waste management facilities and to discuss waste management development programs. Of primary interest was the technology for vitrification of high-level radioactive waste. The United
Kingdom
The U K has spent several years developing the F I N G A L Process and comparing it with other processes for vitrification of high-level waste. In this semicontinuous process liquid waste and borosilicate glass-making constituents are slowly added to a heated pot. Three layers exist i n the pot—a top liquid layer, a middle calcine layer, and a bottom molten glass layer. This is termed a rising level glass process because the glass level continues to rise during the process until the pot is filled to a designated level. Process and equipment development w i l l continue at Harwell with a concentrated effort on a modification of the F I N G A L Process called H A R V E S T which features an annular calcining and vitrification unit. 158 Campbell; High-Level Radioactive Waste Management Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
12.
WALTON
Waste Management in Europe
159
This unit w i l l be 13 ft high, with an external diameter of 30 i n . and an internal diameter of 16 in. Resistance heating w i l l be used for this annular space unit, and the design is primarily aimed at increasing the amount of heat input through the walls of the vessel. A l l gases w i l l be treated to prevent the deposition of ruthenium prior to entering a condenser/absorber where it, as well as a major fraction of the oxides of nitrogen, w i l l be removed by a caustic scrubber; the gases w i l l then be dehumidified and filtered prior to discharge to the atmosphere.
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0153.ch012
The Federal Republic of Germany In the F R G a great deal of attention is being given to basic chemical and physical research and development associated with glass-making processes. A process based on spray calcination at 450°C followed by semicontinuous incorporation in glass with batch drawoffs of glass-waste product, to be demonstrated i n a hot cell facility, is the primary candidate. Nonradioactive process testing is nearing completion, and radioactive testing is expected to be initiated early i n 1974. In the calciner, heat is supplied by recycled superheated steam to eliminate hot walls and to reduce greatly the volume of off-gas. Filters are used to separate solids from the off-gas stream, w i t h periodic blowback of superheated (400°C) steam to keep the filters clean. The current water balance around the spray calciner-melter is one 1. of high-level waste in and two to three 1. of low-level contaminated water out. This is no problem i n the current system as a low-level evaporator is available. However, for a production unit it appears that this balance w i l l have to be brought into line. Considerable effort is being expended in determining the characteristics of the waste glasses. Very sophisticated instrumentation is being used for differential thermal analysis and gravimetric thermal analysis of the waste glasses. One of the basic German thoughts is that devitrification or crystallization w i l l take place during storage at high temperatures and i n a radiation field. This crystallization may increase the solubility of the glass. However, by special heat treatment a microcrystalline ceramic material similar to Pyroceram can be formed. The Germans feel that this ceramic is superior to glass for very long storage of material. Thus, specially controlled cooling and heating cycles are being investigated in order to produce the superior microcrystalline structures. A thermite process with continuous addition of calcined waste and other dry constituents to the reactor vessel has also been developed on a nonradioactive basis. In a demonstration run approximately 2 kg of dry ingredients reacted in about 2 min at a temperature of approximately 2000 °C i n a ceramic crucible.
Campbell; High-Level Radioactive Waste Management Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
160
RADIOACTIVE WASTE MANAGEMENT
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0153.ch012
France France has developed and is operating on a small scale a process which involves batch calcination followed by batch mixing w i t h borosilicate glass additives, and melting to incorporate the waste i n a borosilicate glass. A l l Marcoule high-level waste, mostly from gas-cooled reactor fuel irradiated to approximately 4000 M w d / M T U and highly concentrated because it is relatively free of impurities such as iron or nitrate salts, is being processed through a pilot plant. The waste glass is being drawn into SS pots approximately 35 cm in diameter and 0.5 m high which are covered but not sealed. These containers are transported i n a shielded container to the nearby storage facility which is designed for 500 containers and is only 18 m square. Twenty containers of glass are stacked on top of each other i n a vertical underground shaft 45 cm i n diameter and 13 m long with a floor plug at the surface. Forced air, 25,000 m / h r with velocities up to 4 m/sec, is used for cooling. Although there are redundant systems to ensure that there w i l l not be a loss of cooling air flow, the worst possible consequence was assumed to be total melting of the glass. Current development is directed toward a continuous rotary calciner directly feeding into a borosilicate glass melter with batchwise drawoff of the waste glass. Full-scale nonradioactive engineering demonstration units are being tested. In order to reduce the requirements for radioactive tests, these units are designed for remote operation and maintenance. 3
Summary In summary, Germany, England, and France are vigorously developing technology and methodology for incorporating high-level radioactive waste i n silicate glass. RECEIVED November 27,
1974.
Campbell; High-Level Radioactive Waste Management Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
