Patent Number: 043127746
Section: description

The following examples are presented. Unless otherwise specified all solutions are aqueous solutions. The "aqueous ammonium hydroxide" or "NH.sub.4 OH" used in the Examples contained about 28% NH.sub.3, ppm means parts per million parts of solution, ppb means parts per billion parts of solution, ppt means parts per trillion parts of solution, all parts and percentages are on a weight basis and all temperatures are given in degrees Centigrade. For reasons of safety all simulated radwaste solutions used in the Examples were actually non-radioactive; however, radioactive solutions of the same kind can be substituted and concentrated and encapsulated in accordance with the following Examples. EXAMPLE 1 Preparation of Glass Particles and Tubes A. A molten glass was formed in a platinum crucible at 1400.degree. C. from sand, boric acid, sodium carbonate and potassium carbonate, the glass having a nominal composition of 3.5 mole percent Na.sub.2 O, 3.5 mole percent K.sub.2 O, 33 mole percent B.sub.2 O.sub.3 and 60 mole percent SiO.sub.2. The molten glass was vertically updrawn and solidified into rods having a diameter of about 0.8 cm and a length of about 100 cm which were then crushed in a stainless steel cylinder with a stainless steel rod. The resulting powder was sieved and the fraction between 32 and 150 mesh screens was selected for use in certain of the following Examples. B. Tubes were formed by pulling the above-described molten glass and applying a small internal pressure. Tubes that were sealed at one end were formed by turning off the internal pressure during the drawing operation. Tubes open at both ends were formed by maintaining the internal pressure through the drawing and cut-off operation. The tubes were formed with an outside diameter of about 1 cm and a wall thickness of about 0.15 cm ad were cut to about 5 cm long. EXAMPLE 2 Preparation of Porous Glass Tubes A base glass tube having one sealed end and one open end was prepared as described in Example 1B. The tube was then heat-treated at 550.degree. C. for 110 minutes in an electric furnace to induce suitable phase separation. The tube after heat-treatment was annealed by cooling slowly down to room temperature, and was leached to form a porous tube by soaking it in a 3 N HCl solution saturated with NH.sub.4 Cl at 95.degree. C. for two days. The porous tube was then soaked in hot water for one day to wash out residue from the leaching operation and was then kept in a dessicator until the pores were dry of the washing water. The resulting porous glass tube had a nominal composition of 95 mole percent SiO.sub.2, 5 mole percent B.sub.2 O.sub.3 having interconnected pores, and an internal surface of about 100 m.sup.2 /gr. The surface of the resulting porous glass tube was saturated with .tbd.SiOH groups. EXAMPLE 3 Preparation of Porous Glass Powder Glass rods were prepared as described in Example 1A. Before crushing the glass rods, they were heat-treated at 550.degree. C. for 110 minutes and then crushed to form glass powder. Next the glass powder was sieved and the fraction passing through a 32 mesh screen but not through a 150 mesh screen was leached in a 3 N HCl solution at about 95.degree. C. for about six hours. The glass powder was washed with deionized water for about 24 hours at about 25.degree. C. The resulting porous glass powder had a nominal composition of 95 mole percent SiO.sub.2 ; 5 mole percent B.sub.2 O.sub.3, had interconnected pores, and had an internal surface of about 100 m.sup.2 /gr. The resulting glass surface was saturated with SiO H groups. The porous glass powder was dried in a beaker on a hot plate at about 150.degree. C. EXAMPLE 4 Use of a Porous Glass Tube to Concentrate and Encapsulate A dry porous tube having one open end and one closed end, prepared as described in Example 2, was impregnated with a solution containing dissolved CsNO.sub.3 and Al.sub.2 O.sub.3 particles simulating a nuclear waste fluid. The CsNO.sub.3 solution contained 67 grs of CsNO.sub.3 (which could be radioactive) dissolved in 23 ml water at 100.degree. C. and 10 grs of Al.sub.2 O.sub.3 representing suspended solids (which could be contaminated with radioactive isotopes). The interior of the tube was filled with the dopant solution, and the solution was allowed to penetrate into the pores. Some of the solution in the tube was allowed to pass through the tube walls to the outside of the tube and was collected for use in other tubes. This was continued until the interior of the tube was essentially empty of the solution. The Al.sub.2 O.sub.3 solids suspended in the solution, however, being much larger than the pore size of the tube walls were retained in the interior of the tube. Also, the solution containing the dissolved CsNO.sub.3 filled the pores of the glass tube walls. The resulting laden porous tube was then inserted in methanol at 0.degree. C. to cause the dissolved CsNO.sub.3 in the solution in the pores to precipitate in the pores. The inner and outer surfaces of the laden tube were soaked in clean methanol at 0.degree. C. for 24 hours, while changing the methanol often, resulting in thin layers on both the outside and inside surfaces of the tube in which the concentration of the precipitated CsNO.sub.3 was lower than the concentrations of precipitated CsNO.sub.2 deeper in the glass. (That is the inner and outer surface layers or regions contained approximately one fifteenth of the CsNO.sub.3 concentration of regions located deeper in the tube wall). The porous tube was then removed from the 0.degree. C. methanol bath and placed into a larger diameter (3.5 cm), substantially non-porous, fused silica glass tube having an open end and was dried under vacuum at 0.degree. C. for 24 hours. The fused silica glass tube containing the laden porous tube was then allowed to warm under vacuum to room temperature and was put into a furnace where it was slowly heated at 15.degree. C./hr up to 625.degree. C. This heating period allowed the pores of the glass to dry further. The laden porous tube inside the non-porous tube was held at 625.degree. C. for 16 hours to ensure that all the CsNO.sub.3 was decomposed and the resulting nitrogen oxides were expelled leaving Cs.sub.2 O. It was then heated to 875.degree. C. still under vacuum in order to fuse the pores and sinter the glass structure of the porous glass tube thus converting it into a substantially non-porous glass tube with the cesium (Cs.sub.2 O) trapped as a part of the glass structure. The solid (Al.sub.2 O.sub.3) remained deposited on the tube interior. The tube is placed horizontally on a graphite block in a ceramic tube furnace with another graphite block resting on top of it. It is heated to about 1350.degree. C. and the tube sags under the weight of the upper graphite block causing the interior surfaces of the tube to fuse and seal together, thus immobilizing and encapsulating both the Cs.sub.2 O from originally dissolved CsNO.sub.3 and the originally dispersed Al.sub.2 O.sub.3 solids. EXAMPLE 5 Use of Porous Powder in Non-Porous Tube to Encapsulate A non-radioactive aqueous solution simulating a radwaste stream projected for an existing spent nuclear fuel reprocessing plant and containing 3.06 grs Fe(NO.sub.3).sub.3.9H.sub.2 O, 1.68 grs Ce(NO.sub.3).sub.3.6H.sub.2 O, 0.78 grs La(NO.sub.3).sub.3.6H.sub.2 O, 0.78 grs CsNO.sub.3, 3.88 grs Nd(NO.sub.3).sub.3.5H.sub.2 O, 0.52 grs Ba(NO.sub.3).sub.2, 2.72 grs Zr(NO.sub.3).sub.4, 0.42 grs Sr(NO.sub.3).sub.2, 0.34 grs Y(NO.sub.3 0.sub.3.5H.sub.2 O and 5 ml water, with all elements in solution except Zr(NO.sub.3).sub.4 which was present as a precipitate, was poured into a 50 ml beaker which contained 5 grs of porous glass powder made as described in Example 3. The excess solution was decanted and the beaker was heated to 200.degree. C. on a hot plate to dry the glass powder and deposit the dissolved nitrates in the pores of the glass powder and the undissolved Zr(NO.sub.3).sub.4 on the outer surfaces of the glass powder. The laden glass powder was then placed in a Vycor tube (Corning 743170-4381) having a nominal composition of 96% SiO.sub.2 and 4% B.sub.2 O.sub.3, an inside diameter of 7 mm, an outside diameter of 9 mm and a length of 50 cm. The tube was sealed at one end and was connected to a vacuum pump. The tube containing the laden porous glass powder was then inserted into a furnace at room temperature under vacuum and heated at 15.degree. C./hr up to 600.degree. C. to evaporate any remaining water or other volatiles and to decompose the nitrates present into the corresponding metal oxide and nitrogen oxides and to expel the nitrogen oxides. After holding at 600.degree. C. for 24 hours., the tube was transferred to a second furnace capable of providing higher temperatures. Upon transferring from one furnace to the other, the temperature dropped to 530.degree. C. The temperature in the second furnace was increased gradually from 530.degree. C. to 1340.degree. C. over a period of three hours and 25 minutes. The tube was removed and was found to have collapsed above the level of the glass powder which had been impermeated with the simulated nuclear waste solution. This occurred because the furnace had a relatively large temperature gradient across it, and the tube had been inserted too far. Nevertheless, the final product was a partially collapsed tube completely sealing within it the glass powder with no cracks present in the tube. The uncollapsed lower portions of the tube contained the impermeated glass some of which was a loose powder, some of which had melted into chunks and some of which had melted and stuck to the interior walls of the tube. There were no breaks in the tube walls and no stress of the tube walls was observed under crossed polaroids. The resulting product effectively encapsulated the metal oxides resulting from the metal nitrates in the initial simulated nuclear waste stream and isolated them from the environment. EXAMPLE 6 Use of a Porous Glass Powder In a Non-Porous Glass Tube to Encapsulate Porous glass powder prepared in the manner described in Example 3 was poured into a 100 ml beaker and soaked at room temperature for 17 hours in a basic solution of 12 ml NH.sub.4 OH and 14 gr NaNO.sub.3 in 38 ml of water. Ion exchange took place as described in the above-mentioned concurrently filed application to form silicon-bonded sodium oxy groups on the outer surfaces of the glass powder particles and in the pores of the glass powder. The solution was then poured off and the porous glass powder was rinsed to a neutral pH. A simulated radwaste solution containing 12 grs Cu(NO.sub.3).sub.2 and 12 grs CsNO.sub.3 in 73 ml of water was poured into the beaker to cover the glass powder and the latter was allowed to soak for 16 hours. The solution was then removed leaving behind Cs and Cu ions bonded to the glass through silicon-bonded oxy linkages. The laden powder was rinsed in water and dried on a hot plate at about 200.degree. C. for one hour. It was then poured into a Vycor tube of the kind described in Example 5. The tube and contents were evacuated in vacuum and further dried in a furnace at room temperature and then heated to 450.degree. C. overnight in an electric furnace. It was then heated according to the schedule given in Table 1 below: TABLE 1 ______________________________________ Time (Hour:Minute) Temperature, .degree.C. Pressure, m Torrs ______________________________________ 9:12 450 4 9:25 680 -- 9:42 1230 4 9:50 1350 4 ______________________________________ Between 9:25 and 9:42, the porous glass beads sintered and became non-porous trapping both Cu ans Cs ions within the resulting glass structure. The glass tube was further heated while a mechanical vacuum pump was holding the pressure to 4 m torrs and at about 1350.degree. C. the tube collapsed. The tube was withdrawn from the furnace, and cooled. After sufficient time, both the outside Vycor glass and the inside sintered glass powder cooled below their respective glass transition temperatures and stress built up between both glasses. On further cooling the Vycor cracked. In order to prevent cracking, the original outside glass tube should have a higher thermal expansion coefficient to match or approximate the coefficient of the interior mass of sintered glass powder and Cu and Cs ions in it. Nevertheless, the tube did perform the important function of containing the potentially radioactive vapors, e.g., CsNO.sub.3, Cu, CuNO.sub.3 vapors, during processing. These vapors condensed on the interor upper surfaces of the tube and thus were prevented from entering the environment. EXAMPLE 7 Use of Cation Exchange Porous Glass Powder to Concentrate Dilute Radwaste and Encapsulate Radioactive Materials Removed Therefrom When handling low level nuclear waste, the concentrations of the dissolved and undissolved radioactive materials in the solution can be very low. Additives to prevent corrosion, often make such waste streams basic. A simulation of such a stream was performed by adding 0.011 g CsNO.sub.3, 0.018 g Cu(NO.sub.3).sub.2, 12.5 ml aqueous NH.sub.4 OH solution (28% NH.sub.3) to water to form 50 ml of solution. The porous glass powder prepared as described in Example 3 was added to the above solution and stirred for three hours. The cation exchange porous glass powder became pale blue due to the exchange of protons (of the hydroxyl groups on the internal and external surfaces of the porous glass powder) by copper cations which then became bonded to silicon through oxy linkages. The solution was removed from the glass powder which was then rinsed in water and dried on a hot plate at about 200.degree. C. for one hour. The powder was poured into a Vycor tube of the kind described in Example 5 and the tube and contents were evacuated under vacuum and gradually heated in a furnace from room temperature (about 20.degree.C.) to about 1350.degree. C. over a period of about three hours and 5 minutes. During heating the pores of the glass powder collapsed and the powder sintered into an integral mass trapping the Cs and Cu ions within it. During the last stages of heating the tube collapsed. Because the amount of simulated nuclear waste (Cs and Cu) encapsulated in the porous glass powder was small, the viscoelastic properties of the tube and the sintered glass powder matched each other more closely than in Example 6, and the final glass capsule did not crack. It remains monolithic and provided a continuous cladding around the mass of sintered glass powder containing the simulated radioactive Cs and Cu. EXAMPLE 8 Encapsulation of Calcined Nuclear Waste in a Vycor Tube for Burial About 1.5 ml of a non-radiactive aqueous solution simulating a radwaste stream projected for a spent nuclear fuel reprocessing plant and as described in Example 5 were placed in a 50 cm long Vycor tube which also is described in Example 5. The solution included dissolved nitrates as well as precipitated Zr(NO.sub.3).sub.4 as described in Example 5. No glass powder was added. The tube was connected to a vacuum pump by a rubber hose. In order not to have excessive bubbling, the tube was placed in an ice bath at 0.degree. C. and pumped overnight to dry its contents. The next day the temperature of the tube was 28.degree. C. and the interior pressure was 20 m Torrs. The tube was transferred to a furnace where it was heated under vacuum according to the heating schedule given in Table 2 below. TABLE 2 ______________________________________ Time (Hours:Minute) Temperature, .degree.C. Pressure, m Torr ______________________________________ 12:45 70 137 13:40 80 40 13:50 130 140 14:05 155 50 14:25 190 79 14:50 190 25 15:15 290 50 15:30 340 80 15:40 350 55 16:05 450 34 17:05 600 16 18:10 850 16 20:00 1340 14 ______________________________________ At 20:00, after seven hours and 15 minutes of heating, the tube which had collapsed during heating, was removed from the furnace. From the data in the above Table, it can be seen that pressure maxima occurred at 12:45, 13:50 and 14:25. This appears to have been due to the evaporation of water still in the tube when it was placed in the furnace and appears to have occurred each time when the temperature was significantly raised. If the temperature is held constant as at 13:40, 14:05 and 14:50, the pressure is reduced as the water vapor is taken off by the vacuum. Another maximum occurs around 15:30 at about 300.degree.-400.degree. C. which is apparently due to the decomposition of nitrates to form nitrogen oxides. The final product was a collapsed and sealed Vycor tube with calcined simulated nuclear waste (i.e., the oxides Fe, Ce, Ha, Cs, Nd, Ba, Zr, Sr and Y) encapsulated inside the collapsed and sealed tube. The surface of the collapsed and sealed tube showed no cracks. When the tube was examined under polarized light it was found to be free of stress. The resulting product was suitable for burial in the ground or sea and can be packaged with other like products in larger containers for such purposes. EXAMPLE 9 Use of Non-Porous Glass Powder in a Non-Porous Glass Tube For Incapsulating Nuclear Waste For Burial Pyrex glass (Corning 234030-510) having a nominal composition of 81%, SiO.sub.2, 2% Al.sub.2 O.sub.3, 13% B.sub.2 O.sub.3 and 4% Na.sub.2 O (given in wt. %'s) was crushed in a stainless steel cylinder using a stainless steel rod. The crushed glass was sieved and the fraction which passed through 60 mesh and was caught on 150 mesh was selected for use. 9.5 Gms of the selected fraction of Pyrex powder were mixed with 0.5 gm of porous glass powder impregnated with simulated nuclear waste stream and dried as described in Example 5. The mixed powder was further dried in a beaker on a hot plate at 110.degree. C. for about two hours. Part of this mixed powder was then placed in a 50 cm long Pyrex tube having the nominal composition given above, a 9 mm O.D. and a 7 mm I.D., so that it formed a column 10 cm high. Also, a piece of platinum wire, 1 cm long and 1.5 mm in diameter was added to the powder in the tube. The open end of the tube was attached to a vacuum pump and placed in a furnace where it was gradually heated from about 25.degree. C. to about 830.degree. C. in about four hours and 35 minutes. The finished product developed some cracks after it was pulled out of the furnace. The cracks appeared to be internal and did not extend to the outside surface of the collapsed Pyrex tube. The resulting product effectively encapsulated the glass powder containing simulated radioactive waste materials and platinum which represented the platinum group metals such as Pd, Ru and Rh that are commonly dispersed solids in nuclear waste streams. The cracking can be eliminated by more closely matching the thermal expansion coefficient of the tube and of the contents. The final product can be suitably buried underground or at sea, preferably with other like products and packaged in a larger container for convenience. EXAMPLE 10 Trapping Radioactive Vapors In A Porous Glass Rod The purpose of this example is to show that gas products emanating from the simulated nuclear waste being heated in a glass tube can be trapped in a porous glass rod. 6 Gms of porous glass powder prepared as described in Example 3, was mixed in a beaker with 2.76 gms of CsNO.sub.3, 3.17 gms of Cu(NO.sub.3).sub.2, 73 ml of H.sub.2 O and 25 ml of NH.sub.4 OH for 20.5 hours and washed for 24 hours. The impregnated porous glass powder was dried on a hot plate at a low temperature (about 200.degree. C. for about one hour). Then, the sample was placed in a Pyrex glass tube identical to the one described in Example 9 and having one end closed and a constricted neck located about 11 cm from the closed end. The powder formed a 4 cm high column in the tube. A 12.5 cm long porous glass rod, as prepared in Example 1A, having a diameter slightly less than 7 mm was inserted into the tube. The inner end of the rod had been ground down to a taper shape (which then was washed in a HF solution to free the pores) so that a fairly good seal was made between this end of the rod and the constricted neck section of the tube. The tube was placed upright partly inside a furnace so that the upper half of the rod was outside the furnace. Heating was carried out according to the time, temperature and pressure schedule shown in Table 3 below. At the end of the heating cycle, the tube was removed from the furnace. The bottom portions of the tube had collapsed up to 1 cm below the tapered end of the porous rod. The 5 cm section of the rod which was half inside and half outside the furnace was slighty yellow in color indicating the condensation of copper vapors, while all the other parts of the tube and the rod were substantially colorless. This indicates that the simulated radioactive vapor, i.e., copper vapors, escaping from the impregnating porous glass powder during tht heating process were trapped in the approximately 5 cm section of the porous rod and prevented from leaving the tube. The resulting collapsed tube product effectively encased the simulated radwaste in a strong glass structure. TABLE 3 ______________________________________ Time (Hours:Minute) Temperature, .degree.C. Pressure, m Torrs ______________________________________ 2:30 20 5 2:31 95 22 2:52 95 17 3:13 95 13 3:43 150 13 4:21 260 24 9:30 580 8 10:20 750 12 ______________________________________ The pressure maxima at 2:31 is due to water being expelled from the porous glass powder and the maxima at 4:21 is due to the nitrogen oxides produced by the decomposition of the cesium and copper nitrates. EXAMPLE 11 Porous Rod in Non-Porous Tube A porous rod having a length of 2.5 cm and a diameter of 0.7 cm and made in a manner similar to that described in Example 1A but not crushed and phase-separated and acid-leached as described in Example 2 was dried under vacuum, at room temperature, for 48 hours. The rod was then immersed (for 24 hours) in a 90.degree. C. solution comprising 15.28 g Fe(NO.sub.3).sub.3.9H.sub.2 O+2.16 g Sr(NO.sub.3).sub.2 +2.03 g (Y(NO.sub.3).sub.3.6H.sub.2 0+13.61 g Zr(NO.sub.3).sub.4 +3.98 g Cs(NO.sub.3)+2.67 g Ba(NO.sub.3).sub.2 +3.93 g La(NO.sub.3).sub.3.6H.sub.2 O+8.38 g Ce(NO.sub.3).sub.3.6H.sub.2 O+19.45 g Nd(NO.sub.3).sub.3.5H.sub.2 O67 ml H.sub.2 O. This solution simulates a projected waste stream of a nuclear reactor power plant. During the immersion, the solution diffused into the porous glass rod and filled its pores. The rod was then immediately transferred into a Pyrex test tube (nominal composition given in Example 9, 1.4 cm in O.D. and 15 cm long) containing a 110.degree. C. solution whose composition is similar to the one mentioned above. Vacuum was then applied to the tube in order to speed up the drying of the rod by evaporating the water which was present in the solutions. After a few minutes, the nitrates were observed to have precipitated inside the rod. A small amount of the nitrates precipitated on the surface of the rod forming a thin film which was later mechanically removed. To insure the completeness of the drying, the rod was left under vacuum at 110.degree. C. for about three hours. The dried impregnated rod was then placed under vacuum in a Vycor tube (having the nominal composition given in Example 5, 1 cm in O.D. and 50 cm long), at room temperature. The tube was then heated from room temperature to 625.degree. C. at 15.degree. C./hr., and from 625.degree. C. to 890.degree. C. at 50.degree. C./hr. (at which latter temperature the pores of the rod collapsed). The rod and first Vycor tube were then placed in a second Vycor tube (having the nominal composition given in Example 5, 50 cm long with a 15 mm O.D. and 12 mm I.D.) which was closed at one end. Then, the rod and tubes were placed in a furnace and heated from450.degree. C. to 1340.degree. C. over a period of two hours and 26 minutes. After this time, the tube and rod assembly were taken out of the furnace. The section of the tube around the stuffed rod had collapsed on the rod as well as an approximate 1.5" section above the rod. /The rod seemed to have some cracks in the rod which actually were there prior to heating, while the tube did not appear to have any cracks. EXAMPLES 12-19 Each of the Examples 4 through 11 are repeated, except that corresponding radioactive nitrates are used in place of the corresponding non-radioactive nitrates specified in Examples 4 through 11 and radioactive by contaminated Al.sub.2 O.sub.3 is used in place of non-radioactive Al.sub.2 O.sub.3 specified in Example 4. In each instance, the radioactive material is immobilized and encapsulated within the resulting glass product. EXAMPLES 20 and 21 In Example 20, silica gel purchased from DuPont as Ludox HS-40% is poured into a Vycor glass* tube plugged with glass wool at the top opening and a porous glass disc at the bottom opening to prevent the silica gel particles from escaping. Analysis of the silica gel (Ludox HS-40%) by atomic absorption before starting shows that it contains 40 wt.% SiO.sub.2, 0.41 wt. % titratable alkali as Na.sub.2 O, less than 0.1 wt. % Cs.sub.2 O, and a ratio of SiO.sub.2 to Na.sub.2 O of about 95 to 1. The silica gel contains about 0.4 mole percent silicon-bonded sodium oxy groups. The titratable sodium content is believed to be in the form of silicon-bonded surface sodium oxy groups and the surface to weight ratio is about 230 m.sup.2 /g. An essentially neutral solution containing 10 g CsNO.sub.3 per 100 ml of water is passed slowly through the silica gel. After several liters are passed through, the silica gel is dried and heated in vacuum above 100.degree. C. until the silica gel is observed to sinter (below 1000.degree. C.) and then it is heated further with a vacuum in the Vycor tube to collapse the tube on the sintered silica gel (which normally occurs below 1300.degree. C.). The final product, after cooling to room temperature is a solid rod with the outside surface consisting of at least 94% silica (e.g., the composition of the Vycor tube), and an interior containing Cs bonded to silicon through oxygen linkage and fused into the structure. Cesium oxide content is analyzed by atomic absorption spectroscopy to be at or above 2 weight percent based on the weight of silica gel. Sometimes the rods break into several pieces, but the immobilization and containment of the radwaste in the resulting glass product is still many times better than what is obtained by the prior art methods using cement. *Vycor brand silica glass No. 7913 made by Corning Glass Works and containing 96 wt. % silica and 4 wt. % B.sub.2 O.sub.3. Example 21 is carried out in exactly the same manner as described above with the only exception being that the CsNO.sub.3 is radioactive. There results a final product in which the radioactive Cs is chemically bonded through oxy linkages to silicon of the silica gel within the collapsed Vycor tube which effectively encapsulates and seals the radioactive Cs from the environment. EXAMPLES 22 and 23 Porous glass beads having an average diameter of about 50 to about 100 microns are prepared by the process described in Example 1A except that instead of pulling the molten glass into rods, it is quenched by pouring it into a cooling bath of water so as to form small fractured glass particles (frit) of varied shapes. The glass particles or frit are then formed into spheres by passing them through a radiant heating zone or high temperatue flame where they soften sufficiently to permit surface tension forces to form them into spheres while they are freely moving through the air. They are then cooled rapidly to prevent deformation or devitrification. There are thus formed beads or spheres averaging about 50 to about 100 microns in diameter. These beads or spheres are treated in the manner described in Example 3 to provide porous silicate glass beads and are subjected to a primary ion exchange treatment in a 3.2 M sodium nitrate-ammonium hydroxide solution for three days followed by rinsing well with deionized water until the pH of the rinse water is reduced to about 8. The beads so treated contain 2.0 wt. % silicon-bonded sodium oxy groups expressed as Na.sub.2 O, i.e., 4.0 mole percent sodium cations bonded to silicon through oxy linkages on the inner surfaces of the pores thereof. An ion exchange column of Vycor glass (Example 5) is plugged with a porous glass disc at the bottom and is filled with the treated spheres or beads, i.e., the beads having the silicon-bonded sodium oxy groups. A radioactive waste stream containing undissolved radioactive solids and dissolved radioactive Cs.sup.+ cations, in Example 27, or containing radioactive Sr.sup.2+ ions, in Example 23, is passed through the column. In each case, the aqueous solution coming from the bottom of the column is substantially free of radioactive cations. After a suitable period of time to provide an adequate loading of the radioactive material on and in the pores of the beads, the waste stream is diverted to a similar column. The loaded column is then heated by a heating zone traveling from the bottom up to first dry it, then to decompose the nitrates and drive off the nitrogen oxide decomposition products, then to close the pores of the beads, then to sinter the beads and finally to collapse the hollow Vycor column on the sintered beads to trap and encapsulate the sintered beads within the collapsed Vycor column. The radioactive cations are bound to the interior of the sintered bead mass and the undissolved radioactive solids are also trapped on the interior of the sintered bead mass as well as between the sintered bead mass and the interior collapsed Vycor column, thus providing a durable, leach-resistant glass product containing the radioactive waste materials and which is suitable for burial. EXAMPLE 24 This example illustraes a method for treating primary coolant from a pressurized water nuclear reactor plant. A mixture of powders of silica, boric acid, sodium carbonate and potassium carbonate is prepared in such proportions that yield a glass comprising 3.5 mole percent Na.sub.2 O, 3.5 mole percent K.sub.2 O, 33 mole percent B.sub.2 O.sub.3 and 60 mole percent SiO.sub.2. The mixture is heated in a platinum crucible up to 1400.degree. C. in an electric furnace to produce a molten glass which is pulled into rods about 8 mm in diameter and about 2.5 cm long. The glass rods are cooled and the glass is phase-separated by heat treating at about 550.degree. C. for about 110 minutes. The rods are then crushed to form a powder which is sieved through a 32 mesh screen onto a 150 mesh screen. The glass particles collected on the 150 mesh screen are leached in 3 N HCl at about 50.degree. C. for about 6 hours to remove the boron-rich phase and leave behind a porous glass comprising about 95 mole percent SiO.sub.2 and about 5 mole percent B.sub.2 O.sub.3. The porous glass has interconnected pores and contains at least about 5 mole percent silicon-bonded hydroxyl groups. The glass particles are then rinsed in deionized water until the rinse water reaches a pH of about 7. The porous glass powder is then immersed in an approximate 3.2 molar sodium nitrate-ammonium hydroxide aqueous solution for three days and then is rinsed in water until the pH of the rinse water is reduced to about 8. The resulting powder is then placed in an ion exchange column made of the Vycor glass as described in Example 5. A radioactive primary coolant from a pressurized water nuclear reactor plant utilizing UO.sub.2 fuel clad in stainless steel (containing 4.9 weight percent .sup.235 U) is passed through the column. The primary coolant has the composition given in Table 4 below which lists the radionuclide, the probable source, the probable form and the average concentration in microcuries per milliliter. The cationic radionuclides ion-exchange with sodium cations bonded to silicon through oxy groups in the porous silicate glass powder. TABLE 4 ______________________________________ Average Average Radio- Probable Probable Concentration Concentration nuclide Source.sup.a Form.sup.b (.mu.Ci/ml) (ppb) ______________________________________ 3.sub.H (1), (2) Water, gas 2.4 0.249 14.sub.C 1.2 .times. 10.sup.-5 2.69 .times. 10.sup.-3 24.sub.Na (1) Cation 1.9 .times. 10.sup.-2 2.18 .times. 10.sup.-6 32.sub.P 3.3 .times. 10.sup.-5 1.16 .times. 10.sup.-8 35.sub.S 3 .times. 10.sup.-6 7.08 .times. 10.sup.-8 51.sub.Cr (1) Anion 3.7 .times. 10.sup.-4 4.02 .times. 10.sup.-6 54.sub.Mn (1) Cation, s 2.7 .times. 10.sup.-4 3.38 .times. 10.sup.-5 55.sub.Fe (1) Cation, s 1.9 .times. 10.sup.-4 7.6 .times. 10.sup.-5 59.sub.Fe (1) Cation, s 1.0 .times. 10.sup.-5 2.03 .times. 10.sup.-7 57.sub.Co (1) Cation, s 1.2 .times. 10.sup.-6 1.42 .times. 10.sup.-7 58.sub.Co (1) Cation, s 4.7 .times. 10.sup.-4 1.48 .times. 10.sup.-5 60.sub.Co (1) Cation, s 7.7 .times. 10.sup.-5 6.81 .times. 10.sup.-5 63.sub.Ni (1) Cation, s 8.0 .times. 10.sup.-6 1.30 .times. 10.sup.-4 64.sub.Cu (1) Cation, anion, s 5.4 .times. 10.sup.-4 1.41 .times. 10.sup.-7 89.sub.Sr (2) Cation 2.8 .times. 10.sup.-6 9.93 .times. 10.sup.-8 90.sub.Sr (2) Cation 4 .times. 10.sup.-7 2.84 .times. 10.sup.-6 91.sub.Sr (2) Cation 9.8 .times. 10.sup.-5 2.76 .times. 10.sup.-8 90.sub.Y (2) s 91.sub.Y (2) s 92.sub.Y (2) s 95.sub.Zr (1), (2) s 1.7 .times. 10.sup.-5 8.06 .times. 10.sup.-7 95.sub.Nb (1), (2) s 1.9 .times. 10.sup.-5 4.83 .times. 10.sup.-7 99.sub.Mo (1), (2) Anion 1.2 .times. 10.sup.-4 2.54 .times. 10.sup.-7 103.sub.Ru (2) s 0 106.sub.Ru (2) s 0 122.sub.Sb (1) s 1.0 .times. 10.sup.-4 2.62 .times. 10.sup.-7 124.sub.Sb (1) s 2.0 .times. 10.sup.-5 1.16 .times. 10.sup.-6 132.sub.Te (2) Anion, s 131.sub.I (2) Anion 4.6 .times. 10.sup.-5 3.71 .times. 10.sup.-6 132.sub.I (2) Anion 133.sub.I (2) Anion 6.2 .times. 10.sup.-4 5.5 .times. 10.sup.-7 135.sub.I (2) Anion 9 .times. 10.sup.-4 2.60 .times. 10.sup.-7 134.sub.Cs (2) Cation 4.7 .times. 10.sup.-7 3.62 .times. 10.sup.-7 136.sub.Cs (2) Cation 0 137.sub.Cs (2) Cation 1.1 .times. 10.sup.-6 1.26 .times. 10.sup.-5 140.sub.Ba (2) Cation 4.7 .times. 10.sup.-6 6.45 .times. 10.sup.-8 141.sub.Ce (2) Anion, s 0 143.sub.Ce (2) Anion, s 0 144.sub.Ce (2) Anion, s 0 143.sub.Pr (2) Anion, s 110m.sub.Ag (1) s 1.2 .times. 10.sup.-5 2.52 .times. 10.sup.-6 181.sub.Hf (1) s 6 .times. 10.sup.-6 3.70 .times. 10.sup.-7 182.sub.Ta (1) s 2.5 .times. 10.sup.-5 4.01 .times. 10.sup.-6 183.sub.Ta (1) s 6.2 .times. 10.sup.-5 4.34 .times. 10.sup.-7 185.sub.W (1) s 1.2 .times. 10.sup.-5 1.28 .times. 10.sup.-6 187.sub.W (1) s 3.7 .times. 10.sup.-4 5.30 .times. 10.sup.-7 85m.sub.Kr (2) Gas 85.sub.Kr (2) Gas 88.sub.Kr (2) Gas 133.sub.Xe (2) Gas 8.9 .times. 10.sup.-5 4.78 .times. 10.sup.-8 135.sub.Xe (2) Gas 9 .times. 10.sup.-5 3.54 .times. 10.sup.-8 ______________________________________ .sup.a (1) Neutron activation products of nuclides from fuel cladding, construction material, and water. (2) Leakage from fuel. Mostly fission products. .sup.b Gas: presumably as dissolved gas. s: insoluble solids. The radioactive cations of the radionuclides listed in Table 4, cation-exchange with sodium cations bonded to silicon through oxy groups in the porous glass thereby binding the radionuclides to the porous glass through said silicon-bonded oxy groups and releasing non-radioactive sodium cations to the coolant solution. The insoluble radioactive solids in the coolant also filter out on the external surfaces of the porous glass particles. Additional porous glass particles can be added to increase the filtering capacity of the ion exchange column as the insoluble solids build-up on the column. The anionic radionuclides are not substantially removed in the column and pass with the coolant through the column. The anionic radionuclides can be subsequently removed by treatment with conventional anion exchange resins. Upon regeneration of the conventional anion exchange resin after it becomes loaded, the regenerant solution containing the anionic radionuclides can be concentrated by evaporation and the resulting concentrate can be molecularly stuffed pursuant to the procedures described in U.S. Pat. No. 4,110,096 into the pores of the porous glass in the ion exchange column after said porous glass had become substantially loaded with silicon-bonded radionuclide cation oxy groups. It is preferred to first dry the loaded porous glass so that the anionic radionuclide concentrate can readily enter the pores of the porous glass. The anionic radionuclides can be precipitated or deposited within the pores of the porous glass by the careful drying procedures disclosed in U.S. Pat. No. 4,110,096. Thereafter, columns containing the porous glass particles can be heated to drive off volatiles, to decompose decomposables and drive off non-radioactive decomposition products, to collapse the pores of the particles and sinter same into a unitary mass and to collapse the Vycor glass column around the sintered mass thereby enveloping the filtered solids and the sintered mass glass particles containing the cationic and anionic radinuclides within the collapsed Vycor glass column. While the glass column cracks because of differential thermal contraction it still contains and further immobilizes the radioactive materials and forms a product that is many times more durable than cement or metal drum presently in use. There is thus provided a durable package of concentrated radionuclides which is highly resistant to leaching by water or other fluids. As illustrated in Example 24, liquid radwaste that must be satisfactorily treated and disposed of can be highly dilute. The volume of dilute radwaste treated with a given amount of ion exchange porous glass pursuant to Example 24 can be practically unlimited before all the available exchange sites (i.e. silicon-bonded sodium oxy groups) in the porous silicate glass are filled by radioactive cations. For example, the weight of the dilute liquid radwaste described in Example 24 that could be expected to be treated befoe exhausting all exchange sites would be of the order of 10.sup.9 or more times the weight of the ion exchange porous glass employed. Furthermore, it could be expected that other parts of the system would require overhaul, e.g., repair or replacement of pumps or piping or other equipment, before the ion exchange silicate glass becomes exhausted. Consequently, it is quite possible, if not probable, that the radioactivity of the resulting porous glass when sintered for storage may never reach 1 millicurie or even 1 microcurie per cc. of the glass. In the absence of malfunction requiring overhaul of the other parts of the radwaste treatment system, 100 or less to 10.sup.9 or more, preferably 100 to 10.sup.6, weight parts of radwaste can be treated for each weight part of porous silicate glass within the Vycor tube ion exchange column. EXAMPLE 25 Use of Porous Powder in Non-Porous Tube to Encapsulate A non-radioactive nitrate mixture was used to similate the United Kingdom UKM-22 commercial waste whose composition is reported in terms of oxides in Table 5. Various amounts of nitrates were mixed together in such a proportion as to yield the appropriate oxide concentrations given in Table 5. Appropriate amounts of nitrates whose total weight corresponds to a total of 2 g oxides were placed in a 250 ml beaker; 20 ml H.sub.2 O was added; the solution was stirred and heated up slowly to 80.degree. C. at which temperature a light brown solution containing some undissolved salts was obtained. 18 g of porous glass prepared as in Example 3 was then added to the solution as to give a 10% loading of waste oxides with respect to the final glass. The volume ratio of solution to glass powder was close to 1:1. The mixture was dried at 90.degree. C. Approximately 3 g of the dry mixture was heated under vacuum in a Vycor tube similar to the one described in Example 5 according to the following schedule: ______________________________________ Time (hour:minute) T (.degree.C.) Pressure, m Torrs ______________________________________ 9:45 AM 25 25 10:15 AM 65 30 11:15 AM 278 26 11:30 AM 342 38 11:40 AM 383 32 11:50 PM 403 68 12:05 PM 520 44 3:20 PM 1300 36 3:45 PM 1310 16 4:15 PM 1310 16 ______________________________________ The finished glass product showed that the pores of the powder and the grains inside the tube were all sintered. In addition, the tube was completely collapsed but cracked during air quenching. The finished product was powdered to increase its surface area and was subjected to a leaching test at pH 5.6 and at 70.degree. C. for various exposure times. The results as reported in Table 6 show that the glass sample possesses an excellent chemical durability. TABLE 5 ______________________________________ United Kingdom, UKM-22 composition. Reported Simulated Reported Simulated Oxide wt % wt % Oxide wt % wt % ______________________________________ Al.sub.2 O.sub.3 19.89 19.89 ZrO.sub.2 5.57 5.57 Rb.sub.2 O 0.43 0.43 PO.sub.4 0.93 0.93 Cs.sub.2 O 3.00 3.00 Cr.sub.2 O.sub.3 2.18 2.18 MgO 24.68 24.68 MoO.sub.3 6.89 6.89 SrO 1.25 1.25 Fe.sub.2 O.sub.3 10.63 10.63 BaO 1.48 1.48 RuO.sub.2 2.65 2.65 Y.sub.2 O.sub.3 0.66 0.66 NiO.sub.2 1.40 1.40 La.sub.2 O.sub.3 1.71 1.71 PdO 1.71 1.71 Pr.sub.6 O.sub.11 1.67 -- ZnO 1.71 1.71 Nd.sub.2 O.sub.3 7.08 7.08 U.sub.3 O.sub.8 0.23 Replaced by CeO.sub.2 CeO.sub.2 3.85 3.85 SO.sub.4 0.39 0.39 ______________________________________ TABLE 6 ______________________________________ Chemical Durability Of Product Obtained In Example 25 In Deionized Water Having An Initial pH of 5.6* Glass Component and Leach Rate** Sample SiO.sub.2 Ln*** Fe Na Cs Sr ______________________________________ Core and Clad 295 32 &lt;1 &lt;4 &lt;20 &lt;1 Powdered Core Powdered 127 42 11 17 3 8 ______________________________________ *Data taken between Day 12 and Day 15, 70.degree. C., 71 hrs. **Leach rates are in ng of waste dissolved per cm.sup.2 of surface area o powdered product per day. ***Includes all lanthanides. The leach rates reported in Tables 7 and 9 below have been normalized by the amount of the component present in the glass. Thus, they represent the leach rate the glass would have it the measurement was made only on that component. The glass is dissolving at the silica leach rate. The sodium, strontium and cesium diffuse to the surface and are initially leached at a faster rate. Iron and lanthanites concentrate at the surface. Eventually, the whole glass will leach at the silica rate. EXAMPLE 26 Use of Porous Powder in Non-Porous Tube To Encapsulate A non-radioactive nitrate mixture similar to the one described in Example 25 to simulate the UKM-22 waste was prepared. However, in the preparation of this nitrate mixture, Zr(NO.sub.3).sub.4 and K.sub.2 MoO.sub.4 was dissolved separately from the other nitrates with sufficient amount of concentrated HNO.sub.3, the others being dissolved in a 3MHNO.sub.3 solution or in water. The two solutions were then mixed together and no precipitate was observed. Phosphoric acid and sulfuric acid were subsequently added to the solution to yield appropriate amounts of PO.sub.4.sup..tbd. and SO.sub.4.sup..tbd.. A white gelatinous precipitate appeared and did not dissolve upon heating up to 70.degree. C. About 50% of the nitrates precipitated out when the solution was evaporated down to about 15 ml. Eight grams of porous glass prepared as in Example 3 were then added to the solution to give a 20% loading of waste oxides with respect to the final glass. The volume ratio of solution to glass powder was about 1:1. The mixture was dried at 90.degree. C. for about 16 hrs. Approximately 3 g of the dry mixture was placed under vacuum in a Vycor tube having an outside diameter of 13 mm and a wall thickness of 1.5 mm. The mixture was heated to 600.degree. C. at 50.degree. C./hr. After holding at 600.degree. C. for 48 hrs, the tube was subjected to a temperature jump to 1240.degree. C. where the pores and the grains inside the tube were well sintered. The tube, however, did not collapse and bubbles were formed in the waste-glass matrix. Moreover, the tube cracked during air quenching. Leaching tests were performed on the core of the sample. The results reported in Table 7 show that it has an excellent chemical durability. TABLE 7 ______________________________________ Chemical Durability Of Product Obtained In Example 26 In Deionized Water Having An Initial pH of 5.6* Time Glass Component and Leach Rate** (Days) SiO.sub.2 Fe Ln*** Na Sr Cs ______________________________________ 0.34 6,190 1150 737 3.61 .times. 10.sup.5 3,260 &lt;1000 1.3 963 120 344 &lt;2,500 6,340 300 2.2 550 30 400 &lt;2,500 2,200 &lt;300 3.3 370 49 550 &lt;2,500 2,300 1,400 5.7 200 12 &lt;80 &lt;2,500 1,400 120 9.3 260 &lt;13 50 &lt;2,500 680 &lt;320 12.2 220 3 210 &lt;2,500 1,900 150 15.2 230 &lt;13 56 -- 2,000 &lt;320 ______________________________________ *Data taken at 70.degree. C. **Leach rates are in ng of waste dissolved per cm.sup.2 of surface area o powdered product per day. ***Includes all lanthanites. EXAMPLE 27 Use of Porous Powder In Ion-Exchanged Tube To Encapsulate A mixture containing non-radioactive nitrates and porous glass was prepared as in Example 26 but with only 5% loading of oxides with respect to the final glass. Approximately 3 g of the dry mixture was introduced in an ion-exchanged tube which was prepared as follows: an opened porous tube having an outside diameter of 10 mm, a wall thickness of .about.1 mm and a length of 20 cm was prepared as in Example 2. The porous tube was then soaked in a solution containing 200 ppm Cs with enough NH.sub.4 OH to give a pH of 10 for 18 hrs, and washed in room temperature water until a pH of 7 was obtained. The Cs exchanged tube was subsequently dried under vacuum and was heated from room temperature to 600.degree. C. at 15.degree. C./hr and from 600.degree. C. to 870.degree. C. at 50.degree. C./hr to collapse the pores. One end of the tube was then sealed using a torch prior to the introduction of the mixture of simulated wastes and porous glass. The mixture was then heated under vacuum in the tube according to the following schedule: ______________________________________ Time (hour:minute) T (.degree.C.) Pressure, m Torrs ______________________________________ 11:00 AM 22 15 11:20 AM 180 100 11:25 AM 200 100 11:35 AM 252 50 12:02 PM 330 48 12:10 PM 470 36 12:53 PM 547 28 1:00 PM 775 25 1:20 PM 875 24 1:30 PM 927 24 1:35 PM 1010 24 1:47 PM 1075 24 2:00 PM 1100 24 ______________________________________ The finished glass article showed that the collapsing of the tube was complete and there were no cracks. The grains inside the tube, however, did not completely sinter. Here the thermal expansion coefficients of the tube and powder were matched. However, complete sintering was not achieved because the collapsing temperature of the tube (about 1100.degree. C.) was too low for the nuclear waste composition and loading level utilized. The composition of the ion exchange tube was measured to be 0.5 weight percent Cs. EXAMPLE 28 Use of Porous Powder In Non-Porous Tube To Encapsulate A non-radioactive nitrate mixture was used to simulate the West-Valley PW-8a waste whose composition is reported in terms of oxides in Table 8. Various amounts of nitrates were first dissolved separately in 3 M HNO.sub.3 or in water and then were mixed in such a proportion as to yield the appropriate oxide concentrations given in Table 8. The solution containing appropriate amounts of nitrates plus some undissolved salts whose total weight corresponds to a total of 4 g oxides was evaporated down to near dryness and was then mixed with 16 g of porous glass prepared as in Example 3 as to yield a loading of 20% waste oxides with respect to the final glass. The mixture was subsequently dried at 90.degree. C. Approximately 3 g of the dry mixture was heated under vacuum in a Vycor tube similar to the one described in Example 5. The mixture was heated to 600.degree. C. then was subjected to a temperature jump to about 1250.degree. C. at which temperature the waste porous glass mixture sintered completely. The Vycor tube did not fully collapse and cracked during air quenching. Leaching tests were performed on the core of the sample. The results reported in Table 9 show that it has an excellent chemical durability. TABLE 8 ______________________________________ West-Valley PW-8a Composition Reported Simulated Reported Simulated Oxide wt % wt % Oxide wt % wt % ______________________________________ Na.sub.2 O 16.62 16.62 TeO.sub.2 0.86 -- Fe.sub.2 O.sub.3 34.29 34.29 Cs.sub.2 O 1.14 1.14 Cr.sub.2 O.sub.3 1.36 1.36 BaO 1.85 1.85 NiO 1.74 1.74 Y.sub.2 O.sub.3 0.05 0.05 P.sub.2 O.sub.5 1.58 1.58 La.sub.2 O.sub.3 6.05 6.05 Rb.sub.2 O 0.21 0.21 CeO.sub.2 12.09 12.09 SrO 1.25 1.25 Pr.sub.6 O.sub.11 1.06 1.06 ZrO.sub.2 5.84 5.84 Nd.sub.2 O.sub.3 3.62 3.62 MoO.sub.3 7.54 7.54 Sm.sub.2 O.sub.3 0.64 0.64 Rh.sub.2 O.sub.3 0.36 0.36 Eu.sub.2 O.sub.3 0.17 0.17 Ag.sub.2 O 0.104 0.104 Gd.sub.2 O.sub.3 0.43 0.43 CdO 0.15 0.15 ______________________________________ 9 ______________________________________ Chemical Durability Of Product Obtained In Example 28 In Deionized Water Having An Initial pH of 5.6* Time Glass Component and Leach Rate** (Days) SiO.sub.2 Fe Ln*** Na Sr Cs ______________________________________ 0.34 2800 62 &lt;32 6500 560 223 1.3 905 8 370 2500 2000 &lt;630 2.2 550 25 440 1400 240 370 3.25 430 12 440 1360 1200 670 5.7 200 100 150 870 880 340 9.3 280 &lt;25 150 780 600 630 12.2 313 &lt;1 200 780 780 770 15.2 300 3 120 840 -- 620 ______________________________________ *Data taken at 70.degree. C. **Leach rates are in ng of waste dissolved per cm.sup.2 of surface area o powdered product per day. ***Includes all lanthanites. EXAMPLE 29 Use Of Porous Powder In Ion-Exchanged Tube To Encapsulate The porous powder mixed with nuclear waste described in Example 28 was used in a tube made according to Example 27. The mixture was heated in vacuum to 600.degree. C. then subjected to a temperature jump to about 1100.degree. C. at which temperature the waste porous glass mixture sintered conpletely. The ion exchanged tube did collapse completely. However, it cracked during air quenching. Upon examination of the core material it was found that it had been completely sintered and that it was a good quality glass. Thus, by increasing the loading level of nuclear waste from Example 27, we were able to lower the sintering temperature to below the collapsing temperature of the ion exchanged tube. However, we put an excessive amount of nuclear waste in this experiment and the expansion coefficient was slightly too high causing a small number of cracks. To achieve a completely sintered uncracked product with ion exchanged tubes used in Example 27 and 29, intermediate loading levels should be used. For example, loading levels between 8 and 12%.