Radioactive
wastes , must for the protection of mankind be stored or Disposed in
Such a Manner That isolation from the biosphere is assured until they
have decayed to innocuous levels . If this is not done , the world could face severe physical problems to living species living on this planet .
Some atoms can disintegrate spontaneously . As they do , they emit ionizing radiation . Atoms having this property are called radioactive . By far the greatest number of uses for radioactivity in Canada relate not to the fission , but to the decay of radioactive materials - Radioisotopes . These are unstable atoms emit energy That period of time for a That varies with the isotope . During this active period , while the atoms are ' decaying ' to a stable state Their energies can be used accordion thing to the kind of energy they emit .
Since the mid 1900 's radioactive wastes have been stored in different manners , but since several at years new ways of disposing wastes and failure thesis have been developed so they no longer May be harmful . A very advantageous way of interference radioactive wastes is by a process called " vitrification " .
Vitrification is a semi - continuous process thatenables the following operations to be carried out with the same equipment : evaporation of the waste solution mixed with the-------------------------------------------------- ---------- 1 ) borosilicate : any of several at salts derived from both boric acid and Silicic acid and found in certain minerals zoals tourmaline .
necesary additives for the production of borosilicate glass ,calcination and elaboration of the glass . These operations arecarried out in a metallic pot thats heated in an inductionfurnace . The vitrification of one load of wastes comprises of the following stages . The first step is 'Feeding ' . In this step the vitrification these receives a constant flow or mixture of wastes and additives , or until it is 80 % full or calcination . The feeding rate and heating power are adjusted so That an aqueous phase or several at Permanently liters is maintained at the surface of the pot. The second step is the " calcination and glass evaporation . In this step when the pot is practically full of calcination , the temperature is Progressively Increased up to 1100 to 1500 ° C and then was maintained for several at hours so to allow the glass to elaborate . The third step is " Glass casting " . The glass is cast in a special container . The heating of the output of the vitrification pot causes the glass to melt plug , osmanthus -allowing the glass to flow into containers All which are then transfered into the storage . Although part of the waste is transformed into a solid product there is still treatment of gaseous and liquid wastes . The gases That escape from the pot during feeding and calcination are collected and sent to ruthenium filters , condensers and scrubbing columns . The ruthenium filters Consist of a bed or-------------------------------------------------- ----------2 ) condensacate : product or condensation .
glass pellets coated with ferrous oxide and maintained at atemperature of 500 C. In the treatment of liquid wastes , thecondensates collected containerization about 15 % ruthenium . This isthen concentrated in an evaporator where nitric acid is destroyed by formaldehyde so as to maintain low acidity . The concentration is then Neutralized and enters the vitrification pot.
Once the vitrification process is finished , the containers are stored in a storage pit . This pit has leg designed so That the number of containers That May Be Stored is equivalent to nine years of production . Powerful fans providence air circulation to cool down glass .
The glass produced has the advantage of being stored as solid rather than liquid . The advantages of the solids are thatthey have almost complete insolubility , chemical inertias , absence of volatile products and good radiation resistance . The ruthenium That escapes is absorbed by a filter. The amount of ruthenium likely to be released into the environment is minimal .
Another method thats being used today to get rid of radioactive waste is the ' self placement and processing radioactive wastes in deep underground cavities . This is the disposing of toxic wastes by Incorporating them into molten silicate rock , with low permeability . By this method , liquidwastes are injected into a deep underground cavity with mineral treatment and allowed to self -boil . The result ting
steam is processed at ground level and recycled in a closed system . When waste addition is terminated , the chimney is allowed to boil dry . The heat generated by the radioactive wastes then melts the surrounding rock , osmanthus dissolving the wastes . When waste water and stop addition , the cavity temperature would rise to the melting point of the rock . As the molten rock mass Increases in size , so does the surface area . This results in a higher rate of conductive heat loss to the surrounding rock . Concurrently the heat production rate of radioactivity diminishes Because Of decay . When the heat loss rate Exceeds That of input , the molten rock will start to cool and solidify . Finally the rock refreezes , trapping the radioactivity in an insoluble matrix rock deep underground . The heat surrounding the radioactivity would preventinfo the intrusion of ground water . After all , the steam and vapor are no longer released . The outlet hole would be sealed . To go a little deeper into this concept , the treatment of the wastes before injection is very important . To avoid breakdown of the rock that constitutes the formation , the acidity or he wastes has to be reduced . It has established experimentally That leg pH values of 6.5 to 9.5 are the best for all receiving formations . With Such a pH range , breakdown of the formationrock formation and dissociation of the water are avoided . The stability of waste containing metal cations All which become hydrolysed in acid can be guaranteed only by complexing agents All which form " water - soluble complexes ' with cations in the
relevant pH range . The importance of complexing in the preparation of wastes Increases Because raising of the waste solution pH to neutrality , or slight alkalinity results in Increased sorption by the formation rock or Radioisotopes present in the form of free cations . The incorporation of cations Such causes a pronounced change in Their distribution between the liquid and solid phases and weakens the bond between isotopes and rock formation . Now preparation of theEqually important is ash formation . To reduce the Possibility of chemical interaction between the waste and the formation , the waste is first flushed with acid solutions . This operation removes the principal minerals likely to become Involved in exchange reactions and the soluble rock particles , Thereby creating a porous area capable of accommodating the waste . In this case the required acidity of the flushing solution is established experimentally , while the required amount of radial dispersion is Determined using the formula :
R = Qt
2 mnR is the waste dispersion radius ( meters )Q is the flow rate ( m / day )t is the solution pumping time (days )m is the effective thickness of the formation ( meters )n is the effective porosity of the formation ( % )
In this concept , the storage and processing are minimized . There is no surface storage of wastes required . The permanent binding of radioactive wastes in rock matrix gives assurance of its permanent elimination in the environment .
This is a safe method of disposal from the effects of earthquakes , floods or sabotage .
With the development of new ion exchangers and the advances made in ion technology , the field of application of thesis materials in waste treatment continues to grow . Decontamination factors Achieved in ion exchange treatment of waste solutions vary with the type and composition of the waste stream , the radionuclides in the solution and the type of exchanger .
Waste solution to be processed by ion exchange shouldhave a low suspended solids concentration , less than 4ppm , since this material will interfere with the process by coating the exchanger surface . Generally the waste solutions Should containers less than 2500mg / l total solids . Most of the dissolved solids would be ionized and would compete with the radionuclides for the exchange sites . In the event where the waste can measure specifications thesis , two principal techniques are used: batch operation and column operation .
The batch operation Consists of placing a given quantityor waste solution and a Predetermined amount of exchanger in a vessel , mixing them well and permit ting them to stay in contact until equilibrium is Reached . The solution is then filtered . The Extent of the exchange is limited by the selectivity of the resin . Therefore , Unless the selectivity for the radioactive ion is very favored- , the efficiency ofremoval will be low .
Column application is Essentially a large number of batch operations in series. Column operations become more practical. In many waste solutions , the radioactive ions are cations and a single column or series of columns or cation exchanger willprovide decontamination . High capacity organic resins are used Often Because their fiduciary good flow rate and rapid rate of exchange .
Monobed or mixed bed cation and anion exchangers columns containerization in the same vessel . Synthetic organic resins , or the strong acid and strong base type are Usually used . During operation of mixed bed columns , cation and anion exchangers are mixed to ensure That the ACIS formed after contact with the H -form cation resins : immediately Neutralized by the OH -form anion resin . The monobed or mixed bed systems are normally more economical to process waste solutions .
Against background of growing concern over the exposure of the population or any portion of it to any level orradiation , However small , the methods All which have been successfully used in the past to dispose of radioactive wastes must be reexamined . There are two comm only used methods , the storage of highly active liquid wastes and the disposal of low- activity liquid wastes to a natural environment : sea , river or ground . In the case of the storage of highly active wastes , no absolute guarantee can ever be given . This is Because of a possible vessel deterioration or catastrophe All which would cause a release of radioactivity . The only alternative to dilution
That is and dispersion or concentration and storage . This is implied for the low activity wastes Disposed into the environment . The alternative May Be to evaporate off the bulk of the waste to Obtain a small concentrated volume . The aim is to develop more efficient types of evaporators . At the same time the decontamination factors obtained in evaporation must be high to ensure That the activity of the condensate is negligible , though there remains the problem of accidental dispersion . Much effort has been current in many countries on the establishment of the ultimate disposal methods . These are defined to Those Who fix the fission product activity in a non -leak bootable solid state , so That the general dispersion can never occur. The most promising outlines in the near future are , 'the absorption of montmorillonite clay' Which is Comprised of natural clays thathave a good capacity for chemical exchange of cations and can store radioactive wastes , " fused salt calcination ' whichwill Neutralize the wastes and high temperature processing. Even though man has made many breakthroughs in the processing , storage and disintegration of radioactive wastes , there is still much work ahead to render the wastes absolutely harmless .
Some atoms can disintegrate spontaneously . As they do , they emit ionizing radiation . Atoms having this property are called radioactive . By far the greatest number of uses for radioactivity in Canada relate not to the fission , but to the decay of radioactive materials - Radioisotopes . These are unstable atoms emit energy That period of time for a That varies with the isotope . During this active period , while the atoms are ' decaying ' to a stable state Their energies can be used accordion thing to the kind of energy they emit .
Since the mid 1900 's radioactive wastes have been stored in different manners , but since several at years new ways of disposing wastes and failure thesis have been developed so they no longer May be harmful . A very advantageous way of interference radioactive wastes is by a process called " vitrification " .
Vitrification is a semi - continuous process thatenables the following operations to be carried out with the same equipment : evaporation of the waste solution mixed with the-------------------------------------------------- ---------- 1 ) borosilicate : any of several at salts derived from both boric acid and Silicic acid and found in certain minerals zoals tourmaline .
necesary additives for the production of borosilicate glass ,calcination and elaboration of the glass . These operations arecarried out in a metallic pot thats heated in an inductionfurnace . The vitrification of one load of wastes comprises of the following stages . The first step is 'Feeding ' . In this step the vitrification these receives a constant flow or mixture of wastes and additives , or until it is 80 % full or calcination . The feeding rate and heating power are adjusted so That an aqueous phase or several at Permanently liters is maintained at the surface of the pot. The second step is the " calcination and glass evaporation . In this step when the pot is practically full of calcination , the temperature is Progressively Increased up to 1100 to 1500 ° C and then was maintained for several at hours so to allow the glass to elaborate . The third step is " Glass casting " . The glass is cast in a special container . The heating of the output of the vitrification pot causes the glass to melt plug , osmanthus -allowing the glass to flow into containers All which are then transfered into the storage . Although part of the waste is transformed into a solid product there is still treatment of gaseous and liquid wastes . The gases That escape from the pot during feeding and calcination are collected and sent to ruthenium filters , condensers and scrubbing columns . The ruthenium filters Consist of a bed or-------------------------------------------------- ----------2 ) condensacate : product or condensation .
glass pellets coated with ferrous oxide and maintained at atemperature of 500 C. In the treatment of liquid wastes , thecondensates collected containerization about 15 % ruthenium . This isthen concentrated in an evaporator where nitric acid is destroyed by formaldehyde so as to maintain low acidity . The concentration is then Neutralized and enters the vitrification pot.
Once the vitrification process is finished , the containers are stored in a storage pit . This pit has leg designed so That the number of containers That May Be Stored is equivalent to nine years of production . Powerful fans providence air circulation to cool down glass .
The glass produced has the advantage of being stored as solid rather than liquid . The advantages of the solids are thatthey have almost complete insolubility , chemical inertias , absence of volatile products and good radiation resistance . The ruthenium That escapes is absorbed by a filter. The amount of ruthenium likely to be released into the environment is minimal .
Another method thats being used today to get rid of radioactive waste is the ' self placement and processing radioactive wastes in deep underground cavities . This is the disposing of toxic wastes by Incorporating them into molten silicate rock , with low permeability . By this method , liquidwastes are injected into a deep underground cavity with mineral treatment and allowed to self -boil . The result ting
steam is processed at ground level and recycled in a closed system . When waste addition is terminated , the chimney is allowed to boil dry . The heat generated by the radioactive wastes then melts the surrounding rock , osmanthus dissolving the wastes . When waste water and stop addition , the cavity temperature would rise to the melting point of the rock . As the molten rock mass Increases in size , so does the surface area . This results in a higher rate of conductive heat loss to the surrounding rock . Concurrently the heat production rate of radioactivity diminishes Because Of decay . When the heat loss rate Exceeds That of input , the molten rock will start to cool and solidify . Finally the rock refreezes , trapping the radioactivity in an insoluble matrix rock deep underground . The heat surrounding the radioactivity would preventinfo the intrusion of ground water . After all , the steam and vapor are no longer released . The outlet hole would be sealed . To go a little deeper into this concept , the treatment of the wastes before injection is very important . To avoid breakdown of the rock that constitutes the formation , the acidity or he wastes has to be reduced . It has established experimentally That leg pH values of 6.5 to 9.5 are the best for all receiving formations . With Such a pH range , breakdown of the formationrock formation and dissociation of the water are avoided . The stability of waste containing metal cations All which become hydrolysed in acid can be guaranteed only by complexing agents All which form " water - soluble complexes ' with cations in the
relevant pH range . The importance of complexing in the preparation of wastes Increases Because raising of the waste solution pH to neutrality , or slight alkalinity results in Increased sorption by the formation rock or Radioisotopes present in the form of free cations . The incorporation of cations Such causes a pronounced change in Their distribution between the liquid and solid phases and weakens the bond between isotopes and rock formation . Now preparation of theEqually important is ash formation . To reduce the Possibility of chemical interaction between the waste and the formation , the waste is first flushed with acid solutions . This operation removes the principal minerals likely to become Involved in exchange reactions and the soluble rock particles , Thereby creating a porous area capable of accommodating the waste . In this case the required acidity of the flushing solution is established experimentally , while the required amount of radial dispersion is Determined using the formula :
R = Qt
2 mnR is the waste dispersion radius ( meters )Q is the flow rate ( m / day )t is the solution pumping time (days )m is the effective thickness of the formation ( meters )n is the effective porosity of the formation ( % )
In this concept , the storage and processing are minimized . There is no surface storage of wastes required . The permanent binding of radioactive wastes in rock matrix gives assurance of its permanent elimination in the environment .
This is a safe method of disposal from the effects of earthquakes , floods or sabotage .
With the development of new ion exchangers and the advances made in ion technology , the field of application of thesis materials in waste treatment continues to grow . Decontamination factors Achieved in ion exchange treatment of waste solutions vary with the type and composition of the waste stream , the radionuclides in the solution and the type of exchanger .
Waste solution to be processed by ion exchange shouldhave a low suspended solids concentration , less than 4ppm , since this material will interfere with the process by coating the exchanger surface . Generally the waste solutions Should containers less than 2500mg / l total solids . Most of the dissolved solids would be ionized and would compete with the radionuclides for the exchange sites . In the event where the waste can measure specifications thesis , two principal techniques are used: batch operation and column operation .
The batch operation Consists of placing a given quantityor waste solution and a Predetermined amount of exchanger in a vessel , mixing them well and permit ting them to stay in contact until equilibrium is Reached . The solution is then filtered . The Extent of the exchange is limited by the selectivity of the resin . Therefore , Unless the selectivity for the radioactive ion is very favored- , the efficiency ofremoval will be low .
Column application is Essentially a large number of batch operations in series. Column operations become more practical. In many waste solutions , the radioactive ions are cations and a single column or series of columns or cation exchanger willprovide decontamination . High capacity organic resins are used Often Because their fiduciary good flow rate and rapid rate of exchange .
Monobed or mixed bed cation and anion exchangers columns containerization in the same vessel . Synthetic organic resins , or the strong acid and strong base type are Usually used . During operation of mixed bed columns , cation and anion exchangers are mixed to ensure That the ACIS formed after contact with the H -form cation resins : immediately Neutralized by the OH -form anion resin . The monobed or mixed bed systems are normally more economical to process waste solutions .
Against background of growing concern over the exposure of the population or any portion of it to any level orradiation , However small , the methods All which have been successfully used in the past to dispose of radioactive wastes must be reexamined . There are two comm only used methods , the storage of highly active liquid wastes and the disposal of low- activity liquid wastes to a natural environment : sea , river or ground . In the case of the storage of highly active wastes , no absolute guarantee can ever be given . This is Because of a possible vessel deterioration or catastrophe All which would cause a release of radioactivity . The only alternative to dilution
That is and dispersion or concentration and storage . This is implied for the low activity wastes Disposed into the environment . The alternative May Be to evaporate off the bulk of the waste to Obtain a small concentrated volume . The aim is to develop more efficient types of evaporators . At the same time the decontamination factors obtained in evaporation must be high to ensure That the activity of the condensate is negligible , though there remains the problem of accidental dispersion . Much effort has been current in many countries on the establishment of the ultimate disposal methods . These are defined to Those Who fix the fission product activity in a non -leak bootable solid state , so That the general dispersion can never occur. The most promising outlines in the near future are , 'the absorption of montmorillonite clay' Which is Comprised of natural clays thathave a good capacity for chemical exchange of cations and can store radioactive wastes , " fused salt calcination ' whichwill Neutralize the wastes and high temperature processing. Even though man has made many breakthroughs in the processing , storage and disintegration of radioactive wastes , there is still much work ahead to render the wastes absolutely harmless .
No comments:
Post a Comment