US3332884A - Disposal of radioactive waste using coal waste slag - Google Patents

Description

July 25, 1967 J. J. KELMAR 3,332,884

DISPOSAL OF RADIOACTIVE WASTE USING COAL WASTE SLAG Filed April 2, 1965 a X GAS HOLDER A mom-r012 22 JFILTEE 21 COAL WASHING WASTE.

.COAL on COKE LIMESTONE-1 a MIXER h .25

3 couvsvoz 35 3 7 19 Y MON 1'02 -27 necsrvms aarzsmremou a2- RADIOACTIVE MATEIIAL MOLTEN METAL 25 SLAG 26 5o 7 a; wnsrs 54 0 .sI- 1-"RL'1 INVENTOR. .fll/N J. KELMAK.

United States Patent 3,332,884 DISPOSAL OF RADIOACTIVE WASTE USING COAL WASTE SLAG John J. Kelmar, 2205 Cypress Drive, White Oak Borough, McKeesport, Pa. 15131 Filed Apr. 2, 1965, Ser. No. 445,110 4 Claims. (Cl. 252301.1)

This application constitutes a continuation-in-part of my application Serial No. 295,480 filed July 16, 1963, now abandoned.

This invention relates to the disposal of materials that are radioactive and therefore presents a potential health problem.

The disposal of radioactive waste material is becoming a serious problem in the utilization of atomic energy, especially as a consequence of the increased number of atomic power plants that are being built and placed in operation in and about major population centers. The wastes resulting from the Operation of such plants can be solid, liquid or gaseous. In addition to radioactive wastes produced in the reactors involved, other wastes are developed in operating and maintenance of these installations. For example, tools and equipment that are used in close proximity to these installations may themselves become radioactive. Similarly, protective clothing, paper and the like may also be contaminated as a consequence of use in the general area of a reactor. In reprocessing used fuel elements, waste materials are developed largely as sludge deposits in the recapturing of chemicals that may be used for that purpose.

There are known several methods for disposing of such radioactive materials. For example, radioactive waste has been diluted and then dispersed into rivers at a rate depending on the volume and speed of the river current. In instances, wastes have been concentrated and then encased in concrete or in stainless steel tanks and thereafter buried in zones where the public is not likely to come in contact with them. For small quantities of low contamination such as may be developed in medical laboratories, research centers and industrial plants that use radioisotopes, the method of incineration is a promising method of disposal.

Variousv methods are now employed for concentrating wastes vsuch as evaporating, ion exchange and similar processes. However, even after concentration there remains large volume of solution which must be stored for long periods until long lived radioactive isotope decay to a level safe enough for disposal. Some of the proposed process involve solid fixation in clay through cation ex- .change capacity. Other methods of fixation in clay process require preliminary removal of cladding agents of aluminum iron oxide and zirconium oxide, because the presence of these oxides severely reduces the fixation capacity of the clay in the process. Also the present fixation methods fail to incorporate ruthenium oxide in the product of the process.

It is the object of this invention to provide an improved 'method of disposing of radioactive fission products waste for permanent and safe disposal in a maximum permissible concentration for continuous exposure.

Another object of this invention is to provide a method of disposing radioactive fission products in permissible concentration for burial in soil as specified in Appendix C Atomic Energy Commission, Part 20-Standard For Protection Against Radiation.

3,332,884 Patented July 25, 1967 "ice Still another object of this invention is to utilize the properties of heat emitted electron of hot bodies in the slag constituents for dispersion and reaction of the radioactive components from the waste fission products.

The slag that is used in this invention is produced from coal waste washing operations in coal cleaning plants. This waste is mainly a shale product of weathering from volcanic rock and is one of the most highly stable substance known. As determined by actual experiment at the Brookhaven National Laboratory this shale has a material affinity or capacity for the exchange of Cs cations being in the order .of .0.Lmilliequivalent per gram of shale at room temperature. Since montmorillonite minerals have a much greater cation-exchange capacity, the ion-exchange process is not suitable for mine waste shale.

The shale product used in this production 'of slag is largely silica and ha a chemical analysis by weight as indicated in Table I.

The analysis of shale from diiferent sources will vary slightly, but the essential characteristic will be present in adequate levels for the purpose of this invention. In other words, shale in general has a composition that is not significantly different from the foregoing and therefore can be used without regards to source. 1 7

The minerals present in this shale are indicated in Table II.

TABLE II Approximately limit Mineral: percentage Clay 5 to Kaolinite 2.to 30 Chlorite 0m 15 Illite 3 to 60 Montmorillonite 0 to 10 Mica 5 to 60 Quartz 5 0 35 Siderite 0 to 12 Calcite 0 to 15 A conventional slagging type-gas producer furnace. is employed for gasifying the organic material and melting the inorganic substance into a silica-alumina-calciurn oxide slag. To produce one ton of slag the raw materials are melted at a temperature from 2700 F. to 3400 F. in a slagging-type furnace. The raw material charge-is indicated in Table III. Y

TABLE III Raw materials: p lbs.

Coal washing refuse (shale) -a ..e 1920 Limestone (CaCO 58,0

Coal s Oxygen 800 Moisture (H O) 550 The chemical composition by weight of the slag produced in the furnace is indicated in Table IV.

TABLE IV Percent by Component: weight SiO 51.30 A1 30.25 CaO 10.00 FeO 1.25

F6203 MgO 1.72 K 0 2.05 Nazoz S0 0.42 P 0 0.50

The density of the slag product is 192 lbs. per cubic foot.

The approximate chemical composition by volume of gas produced from raw material charged into the furnace is indicated in Table V.

TABLEV Component: Percent CO 3.5 CO 66.4 H 26.2 H O 3.2

Heating value of this gas is approximately 300 B.t.u. per cubic foot.

The slag product when melted and completely converted into a liquid is a fused mixture of the oxides as indicated in Table IV. These many complex compounds are capable of forming numerous chemical and physical combinations so that the properties of individual components may be no indication of the properties of the mixture as a whole. There is sufiicient evidence to lead to the belief that complex compounds most likely to exist and partly ionized at various stages of fusing and melting into the molecular species as indicated in Table VI.

TABLE VI 1 Calcium Orthosilicate 4 CaO.2SiO 2 Calcium Metasilicate 2 CaO.SiO 3 Lime CaO 4 Tetracalcium Phosphate 4 CaO.P O 5 Ferrous Oxide FeO 6 Monocalcium Ferrite CaO.Fe O 7 Monocalcium Aluminate CaO.Al O

2 C30-Al203 8 Calcium Phosphate 4 CaO.P O 9 Tricalcium Phosphate 3 CaO.P O 10 Iron Manganese Silicate 2 (FeO.MnO)SiO The oxides composing the slag are acid and basic and when in liquid form they are dissociated electrolytically and contains practically no neutral molecules as indicated by these reactions:

When an excess of silica is present the slag is acid and the orthosilicate 4CaO.2SiO is converted into a metasilicate 2CaO.SiO and a polymeric silicate ion is formed such as (SiO .O

In the process of heating and melting, the slag is raised to a high temperature and the atoms and molecules of the components may become ionized as the electrons are stripped off by the violent collisions consequent on the thermal agitation of the slag particles. Thus inorganic substances begin to emit electrons at 470 F., increasing materially at over 780 F. and the emission is quite large at over 1320 F. Chemical reactions between gases and alkali oxides in the slag also emit electrons. A great excess of electrons are emitted from high temperature fused solids as compared to gases. However, the denser the gas becomes the greater is the emission of electrons. The presence of such gases as carbon monoxide, oxygen and hydrogen contribute to the emission of electrons. The alkali elements of the slag have remarkable tendency to lose electrons and they possess the lowest ionization potential of the elements in the periodic table.

In fused and liquid slag, the element particles are readily compounded with opposite charged other particles. CaO at high temperature in the liquid slag emits electrons and itself becomes positively charged. Other constituents of the slag that emits electrons are; Fe in ferrous compounds (FeO), and in ferric compounds (Fe O Mg in magnesium compounds (MgO), Mn in manganese compounds (MnO), and K in potassium compounds (K 0). Therefore, these basic compounds of the slag become ionized with a positive charge.

Most fission products are unstable and decay by beta emission to the elements having the next higher atomic number. On the average radiocative fission products decay to stable nuclides through three stages of decay and after a short time there are about 250 radioactive species in a fission mixture. The most important fission products encountered in waste treatment and disposal operations are shown in Table VII.

TABLE VII Half Life Radiation 10.27 Years Beta.

Beta-G amma.

1.7Years Beta.

The beta particles are electrons which are emitted from the nuclei of radioactive atoms at speeds approaching the speed of light. They have a negative charge with the same mass as the electron. They exhibit a continuous energy distribution that is, each beta emitter is characterized by having a definite maximum energy for all beta particles emitted. Beta particles are created in the nuclei by conversion of the nuclear neutrons into protons. Nuclei which have a large neutron excess, that is a high ratio of neutrons to protons, are predisposed to beta particle emission, whereas, these nuclei with a low ratio of neutron to protons are predominantly apt to be positron emitters. The life time of a positron is usually short, since nearly every positron that is formed after being reduced in energy, it makes a final interaction with a negatron and the two particles unite and annihilate themselves in the fOrmation of gamma rays. Beta particles are so light they are easily deflected by other atoms. The distribution of beta particles is continuous with various energies, but at low energies the ionization losses and elastic scattering are very large and the particles are stopped by relatively thin layers of material.

Some radioactive nuclei emit gamma rays of discrete energies and the ray spectra consists of series of sharply defined wave length. Gamma rays frequently accompanying beta particles emission and at the end of beta particles range all the activity is due to gamma radiation.

Alpha particles are helium atoms which carry a double positive charge and produce dense ionization along their track by collision with electrons of the atoms. Fission product waste from heavy nuclei are in the order of uranium and thorium and these elements are extracted from fission products as completely as possible before leaving the reactor.

Accordingly my invention involves the process of reacting the radioactive components of the fission products with elements of the liquid slag. The liquid fission product waste is pressure sprayed into the heated raw material of the furnace burden. The raw material moves through drying zone at the temperature of 900 F. then into fusing and melting zone at 2700 F. and finally into the combustion'zone at the temperature of 3400 F. In the cornbustion zone all the charge is melted to liquid slag and it is held for a period of one hour at a temperature of 3400 F. and above so that all radioactive components are dispersed and comingled with the elements of the slag by thermal agitation from high temperature heat.

' The fission products are highly ionized and they interact With slag elements different from singly or doubly ionized particles such as protons or alpha particles. The heavy group fission product nuclei have an electron charge of 22 e. whereas the light group have an electron charge of 20 e. The fragment of the fission product along their path in the slag interact very strongly with the atoms of the slag producing excitation and ionization on the atoms. The energy changes that occur in the slag from the fragments are nuclear reactions which are in the order of million times greater than chemical reactions.

The swiftly moving fragment nucleus makes direct collision with sla-g atoms and transfers energy in the process, thus the fragments transfer their kinetic energy to the slag elements and thereby increasing the thermal energy of the slag. However, the elements of the slag are in the range of low atomic numbers and they have the capacity to absorb considerable energy from the decay of the nuclei. The alkali elements of the slag have a remarkable tendency to lose electrons making those atoms positively changed and therefore the beta particles of the fission products will be attracted to the ionized slag atoms.

When the slag is removed from the furnace and becomes solidified, the reacting pattern established in the liquid slag will continue but at a much lower rate, however, the atoms of the 'slag elements will now absorb considerable kinetic energy from the fragments of the fission products before they are excited and ionized..That is to ionize an atom in the cold slag it is necessary to add to it h an amount of energy required to remove an electron completely from the ground state of an atom to produce a positively charged ion and a free electron. Therefore,

.the cold slag becomes a stable medium for the series of radioactive transmutations in fission products known as the fission chains which usually involves three successive beta particle decays per chain.

Another phase of my invention involves the process of reacting the radioactive components of metallurgical waste products with the elements of the liquid slag. These solid wastes from fuel element fabrication may consist of steel and copper sheathing contaminated with uranium, also alumina, iron oxides and zirconium oxide cladding agents. The waste metal is charged with the furnace burden and as the metal descends through the drying and melting zone it undergoes oxidation from the water vapor carbon dioxide and oxygen and the ferrous elements of the charge and respond to these chemical reactions:

The Fe O is carried to the under surface of the slag next to the metal by either diffusion or convection currents in the slag itself and is then reduced to FeO by this reaction:

or it is reduced by carbon partly or completely by this reaction:

Fe O %+3C=3CO+2Fe This cycle in which Fe is being continually enriched in oxygen at the upper surface of the slag and loses it to the metalloids and iron at metal surface is the main method by which iron is being formed under the slag.

The disposal of radioactive aluminum, copper, zirconium and uranium will be along these lines; aluminum will go into oxide of slag as A1 0 copper compounds are readily reduced to metallic copper which alloys with the iron, zirconium metal will fuse in the slag unchanged, and uranium will go into slag as an oxide. The solubility of uranium in most metals is limited due to its large atomic diameter and the unique crystal structure of its alpha phase and the complex structure of its beta phase. The chemical activity of uranium is so strong that it combines with most elements of the periodic table. It exists in one of three allotropic phases depending on the temperature. The alpha phase which is stable at room temperature and exists up to 1234 F. and the beta phase is stable from 1234 F. to l426 F. while the gamma phase is stable from 1426" F. to the melting point. In the process of melting and passing through a zone of, chemically reacting slag elements and compounds which are electron emitting and ionized, the uranium atoms being electropositive and in the presence of greater concentration of reacting substances in the volume of slag, they will form into an oxide of the slag. Upon solidification of the slag the radioactive uranium becomes permanently fixed'in the slag.

of my invention for providing the methods for permanent disposal of radioactive waste in sla-g.

Example I In this method of the invention, the process comprises the spraying of 100 gallons of fission products waste.

producer gas with the volatiles absorbed in the slag com- I pounds. After one hour of melting period in the bottom of the furnace at temperatures of 3400 F. the slag is tapped and removed through the slag runner. p

The quantity of fission product present in 100 gallons .of waste solution resulting from the processing of lton of uranium irradiated to 2500 M.W. days per ton and 'decayed days has a concentration of significant radioisotopes as indicated in Table VIII.

The following examples will illustratethe effectiveness TABLE VIII Half life Concen- MPC, N uclide Years tration, uo./ml.

cJrnl.

0. 78 6. 9X10 lO- Total Microcuriesz 1, 551, 900

The radiation from 1,551,900 microcuries of disintegrations is confined in 4000 tons of slag. An equivalent radiation from 1 curie of disintegrations is confined in 2577 tons of slag.

Example II In this method the procedure is identical to the procedure described in Example I, except that 100 gallons of fission products waste solution is sprayed into 126 tons of raw material for the maximum permissible concentration (MPC) for disposal by burial in accordance to Appendix C, Atomic Energy Commission, Part 20Standards For Protection Against Radiation. Accordingly the concentration shall not exceed at the time of burial 1 000 times the amount specified. The burial being at a minimum depth of four feet and the successive burials are separated by distances of at least six feet; with not more than 12 burials being made in any one year. The specified concentration is indicated in Table IX.

TABLE IX MicrocuriesXlOOO For Burial In Soil Microeuries Specified Appendix G Nucllde PPP'PFPPP PP P case-maneuvcum 8 o o o Total Microcunes The radiation from 32,050 microcuries of disintegrations is confined into 84 tons of slag for disposal by burial. An equivalent radiation of 1 curie of disintegrations is confined in 57 tons of slag.

Example III This method involves the removal of radioactive components from fuel element metals through the process of melting the contaminated metals in the furnace burden and producing liquid slag and molten metal.

The wastes from fuel element fabrication may consist of steel and copper sheathing and cladding agents of alumina, stainless steel and zirconium oxides. Solid waste may also be charged in the furnace in the form of pot calcined Purex and Durex waste or calcined alumina imbedded in a tin-lead metal matrix. To facilitate the melting and refining by the slag, a quantity of hematite ore (55% Fe O equal in the amount to the weight of metallurgical waste, is charged with the raw materials. The quantity of radioactive solid waste to be disposed by melting is determined for (MPC) for continuous exposure, or (MPC) for disposal by burial. When suflicient quantity of molten metal is formed in the bottom of the furnace below the slag surface, the metal is removed by the iron runner. In the removal of slag only that portion is removed that has been held for one hour at the temperature of 3400 F.

The preferred embodiment of my invention is illustrated in the accompanying drawing which is a diagrammatical illustration of an apparatus including a slagging type furnace which is employed in carrying out the process of the present invention.

Referring to the drawing in detail, the slagging furnace 10, has a charging hopper 11, and a gas take off pipe 16, that leads into a gas washer 18. For admission of oxygen there are arranged circumferentially about the furnace oxygen burner nozzles 13, in the upper level and oxygen burner nozzles 14 in the lower level. Both rows of burners are connected to the manifold pipe 12 which extends around the furnace and is connected to an outside source for oxygen supply.

The raw materials consisting of coal washing waste, limestones, coal or coke are mixed in a suitable mixer 15 which also receives solid and metallurgical waste delivered by conveyor 19 from receiving and preparation building 28. After the raw materials and radioactive solids are thoroughly mixed, the material is delivered into the charging hopper 11, and thence into the furnace. The coke is ignited and burned to incandescence with proportioned quantity of oxygen and gasified in the combustion zone. As the charge is being melted, liquid hydrocarbon fuel is supplied by fuel lance 17 to decrease the consumption of coke. For the purpose of drying the raw material in the top of the furnace, oxygen is admitted by burner nozzle 13. A portion of the gas from the gas holder 23 is recirculated by line 35, properly controlled by valves, to the burner nozzle 13 for combustion with oxygen in the drying zone.

In the furnace operation, the normal burden charge capacity is approximately 35 tons of raw material. The material is melted in furnace 10, through these heating zones: (a) drying zone at the temperature of 900 F (b) melting zone at the temperature of 2700 F., and (0) combustion zone at the temperature of 3400 F In the fusing and melting phase, slag is formed in the bottom of the furnace and immediately below the slag, molten metal is accumulated. The slag is removed through notch 24 in 10 ton quantities after holding for one hour in the combustion zone. The molten metal is removed through notch The gas produced from the reacting carbon, oxygen and hydrogen rises through the furnace and leaves through take-off pipe 16 and is collected in gas washer 18 for primary removal of entrained solids and is then led by line 33, properly valved, to filter 21 for additional cleaning. Through monitor 22, the gas is sampled for (MPC) of radionuclides in air and then stored in gas holder 23 for recirculation and for plant use. The scrubbed liquid from gas washer 18 is led by line 26, properly valved, to the waste solution tank 31. Also into this tank low level and high level fission product waste solution is delivered from outside source. By pump 34 and line 32, with control valves, the waste solution is sprayed into the furnace through spray nozzle 20, at a pressure of 50 p.s.i.g.

The receiving and preparation burden 28, is equipped with monitor 27 for sampling the exhaust air which is discharged into stack 29. The metallurgical Waste from fuel fabrication process is mainly steel and copper sheathing and cladding agents of aluminum, zirconium and stainless steel. When the radioactivity of the cladding agents and the uranium core is too large for the capacity of the furnace then the core must be stripped from the cladding agents mechanically or by selective dissolution reagents which are then generally calcined at the reactor. The calcined radioactive waste in metal containers from outside source, and other solid materials are prepared in suitable size for delivery into the conveyor 19 for the furnace charge.

In the operation of the furnace, the utilization of the fission products in waste solution and the smelting and recovery of metallurgical waste is carried out in two separate operations. To carry out both processes jointly in one operation would require a very large furnace.

According to the provision of the patent statutes 1 have explained the principle of my invention and have illustrated and described what I now consider its best embodiment. However, I desire to have it understood that within the scoop of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of disposing of radioactive fission products waste, comprising thoroughly mixing a predetermined quantity of said waste with molten coal waste slag, cooling the mixture to solidify it, and then discarding it.

2. The method of disposing of radioactive fission products waste, comprising spraying a predetermined quantity of radioactive fission products Waste solution onto a burden of coal waste and combustible materials in a slagging furnace, raising the temperature of the sprayed burden to about 3400 F. to form molten coal waste slag, maintaining said slag in molten condition for a period of time long enough for all radioactive elements of said solution to be thoroughly dispersed and comingled with the slag, thereafter withdrawing the slag from the furnace and allowing the slag to cool and solidify, and then discarding the slag.

3. The method recited in claim 2, in which said period of time is about two hours.

4. The method of disposing of radioactive fission products Waste, comprising mixing with limestone and coal waste slag and combustible materials predetermined quantity of metal contaminated with radioactive fission products, charging the mixture into a slagging furnace, burning the combustible materials in the furnace to melt said slag and metal, whereby said fission products will mix with the molten slag, withdrawing said slag after about an hour to cool and solidify it, and then discarding the slag.

References Cited UNITED STATES PATENTS 2,943,059 6/1960 Beck et al. 252301.1 3,006,859 10/1961 Allemann et al 252301.1 3,008,904 11/1961 Johnson et al 252301.1 3,110,557 11/1963 Spector 252-301.1

BENJAMIN R. PADGETT, Primary Examiner.

CARL D. QUARFORTH, Examiner.

S. J. LECHERT, JR., Assistant Examiner.

Claims (1)

1. THE METHOD OF DISPOSING OF RADIOCACTIVE FISSION PRODUCTS WASTE, COMPRISING THOROUGHLY MIXING A PREDETERMINED QUANTITY OF SAID WASTE WITH MOLTEN COAL WASTE SLAG, COOLING THE MIXTURE TO SOLIDIFY IT, AND THEN DISCARDING IT.

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