A Review on Immobilization of Phosphate Containing High Level Nuclear Wastes Within Glass Matrix

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<ul><li><p>R</p><p>Aw</p><p>PM</p><p>h</p><p>a</p><p>ARRAA</p><p>KHIPR</p><p>C</p><p>0h</p><p>Journal of Hazardous Materials 235 236 (2012) 17 28</p><p>Contents lists available at SciVerse ScienceDirect</p><p>Journal of Hazardous Materials</p><p>jou rn al h om epage: www.elsev ier .com/ loc ate / jhazmat</p><p>eview</p><p> review on immobilization of phosphate containing high level nuclear wastesithin glass matrix Present status and future challenges</p><p>ranesh Senguptaaterials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085, India</p><p> i g h l i g h t s</p><p>Technical review.High level nuclear waste immobilization within phosphate glasses.Integration of data from laboratory scale experiments, plant scale observations and natural rock information.</p><p> r t i c l e i n f o</p><p>rticle history:eceived 10 April 2012eceived in revised form 12 July 2012ccepted 18 July 2012</p><p>a b s t r a c t</p><p>Immobilization of phosphate containing high level nuclear wastes within commonly used silicate glassesis difficult due to restricted solubility of P2O5 within such melts and its tendency to promote crystalliza-tion. The situation becomes more adverse when sulfate, chromate, etc. are also present within the waste.To solve this problem waste developers have carried out significant laboratory scale research works in</p><p>vailable online 27 July 2012</p><p>eywords:igh level nuclear waste</p><p>mmobilizationhosphate glasseview</p><p>various phosphate based glass systems and successfully identified few formulations which apparentlylook very promising as they are chemically durable, thermally stable and can be processed at moderatetemperatures. However, in the absence of required plant scale manufacturing experiences it is not pos-sible to replace existing silicate based vitrification processes by the phosphate based ones. A review onphosphate glass based wasteforms is presented here.</p><p> 2012 Elsevier B.V. All rights reserved.</p><p>ontents</p><p>1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182. Generation of phosphate rich HLW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20</p><p>2.1. Bismuth process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.2. PUREX process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.3. P2O5-HLWs storage as neutralized solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.4. P2O5-HLWs storage as calcined powder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21</p><p>3. Phosphate in silicate melts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.1. Lessons learnt from natural melts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.2. Difficulties associated with phase separations within HLW loaded silicate melts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21</p><p>4. Networking within phosphate melt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225. Immobilization of phosphate containing HLW within glass matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23</p>6. Future challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<p>Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</p><p>E-mail address: praneshsengupta@gmail.com</p><p>304-3894/$ see front matter 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jhazmat.2012.07.039</p><p> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26</p><p> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26</p>dx.doi.org/10.1016/j.jhazmat.2012.07.039http://www.sciencedirect.com/science/journal/03043894http://www.elsevier.com/locate/jhazmatmailto:praneshsengupta@gmail.comdx.doi.org/10.1016/j.jhazmat.2012.07.039</li><li><p>1 ous M</p><p>1</p><p>fa</p><p>(</p><p>afisZ(cst</p><p>8 P. Sengupta / Journal of Hazard</p><p>. Introduction</p><p>Eco-friendly and proliferation resistant management of spentuels is one of the most sensitive issues in the world today. Optionsvailable at the back-end of nuclear fuel cycles are either</p><p>(i) direct disposal of spent fuel within suitable deep geologicalrepositories (better known as open fuel cycle), or</p><p>ii) reprocessing it to extract valuables, followed by immobilizingthe process generated nuclear high level liquid wastes (HLWs)within suitable inert matrice(s) for its interim storage anddisposal inside deep geological repositories (better known asclosed fuel cycle). Reaserch is also being pursued to segregateand separately irradiate long lived minor actinides and fissionproducts within critical and subcritical reactors to convert theminto shorter lived radionuclides (partitioning and transmuta-tion; advanced fuel cycle; Fig. 1).</p><p>Recently, closed fuel cycle option has gained more importances it is environment friendly and economical [1]. In a simpli-ed way, reprocessing begins with dismantling of water cooledpent fuel bundles into pins and separating irradiated pellets fromircaloy (ZrSn alloys)/Al/stainless steel (FeCrNi alloys) clads</p>protective metal jacket surrounding the fuel pellets) throughhopping (mostly by mechanical shearing) and dissolving themall slices within concentrated acids (Fig. 2). The resultant solu-ions so obtained are highly hazardous as they contain various<p>Fig. 1. Schematic diagram showing basic differences betw</p><p>aterials 235 236 (2012) 17 28</p><p>radioisotopes (radioactivity more than few Ci/litre and possesnearly 99% of the total radioactivity witnessed in a given nuclearfuel cycle) of fissile and fertile materials, minor actinides, fissionelements, activation products, etc. extracted from the spent fuels(Table 1; [2]). Needless to say, the actual compositions (chem-istry and radiochemistry) of HLWs depend on reprocessing routeadopted as well as on spent fuel compositions [37] and their irra-diation history (type of reactors, pellet-cladding interactions [8],neutron flux, burn up, cooling period, etc. [9]). Fig. 3 shows the fourdifferent possible modes of occurrences of radionuclides within aspent fuel. For example they can occur (i) within the irradiatedmatrix fuel, (ii) along the grain boundaries, pores, cracks, dislo-cations, etc., (iii) diffused inside clad and (iv) within the gap inbetween fuel and clad. With passage of time, relative contributionsof each of the radionuclides on the overall radioactivity of the spentfuel changes due to differences in their respective half-lives (T1/2;Table 2). Among all the radioisotopes present, those having T1/2 ofthe order of years to decades and capable of getting incorporatedwithin tissues or organs (e.g. 90Sr) are biologically most dangerousones. On the other hand, radionuclides having high radiotoxicity,geochemical mobility, and long half-lives (e.g. 99Tc, 129I, 79Se, 135Cs,239Pu, 237Np, 235U, 36Cl, and 14C) are elements of deep concern fromenvironmental pollution point of view [10,11]. Therefore, for pro-</p>tection of biosphere, HLWs need to be concentrated and contained.<p>In general, HLWs are concentrated by evaporation and neutral-ized by addition of alkali (NaOH), and stored in large undergroundsteel tanks. Although such storage is acceptable for few years, but</p><p>een open and closed (advanced) nuclear fuel cycles.</p></li><li><p>P. Sengupta / Journal of Hazardous Materials 235 236 (2012) 17 28 19</p><p>Cooled </p><p>spent fuel </p><p>Shearing Chopping and </p><p>dissolution Reprocessing Product </p><p>conversion</p><p>U storage/ </p><p>disposal </p><p>U oxide</p><p>Compacti on/ Alloy formation </p><p>U nitrate solutio n</p><p>Vitri fic ati on </p><p>Np, Am, Cm, re maining fission products</p><p>Pu nitrate solutio n</p><p>Product </p><p>conversion</p><p>Pu oxideMOX fuel </p><p>fabricatio n </p><p>Repository </p><p>s in th</p><p>opeaFaRrccmaddfimedtmc</p><p>TR</p><p>Fig. 2. Schematic diagram showing major step</p><p>n long time scale the wastes need to be immobilized within appro-riate inert host matrices (wasteform), stored and disposed offxtremely carefully within suitable deep geological repositories sos to isolate them from biosphere for as many as 104106 years.or conditioning of the HLWs, various amorphous (borosilicatend aluminosilicate glasses), crystalline (synthetic rock SYN-OC, titanate ceramics, phosphate ceramics (monazite, apatite andelated phases), calcines, alloys, etc.) and crypto-crystalline (glasseramics based on sphene, zirconolite, monazite, zircon, etc.) matri-es [1224] have been proposed but the final selection of wasteformaterials depends on several scientific and technological merits</p><p>nd demerits associated with HLW compositions [25,26], producturability factors, processing constraints [2733], service conditionemands [34,35], etc. Thus identification of a suitable wasteformor any given HLW is a difficult task, and too much of expectationsn terms of its long term performance within geological repository</p><p>ake the selection procedure even tougher. It is argued that thenvironment within deep geological repository (constructed at a</p>epth of 5001000 m from the surface) is expected to be harsh dueo simultaneous interplay between (i) thermal field, (ii) thermo-<p>echanical field, (iii) biological field, (iv) hydrological field, (v)hemical field and (vi) radiation field [36].</p><p>able 1adionuclides commonly found within spent nuclear fuel.</p><p>Major actinides 234U, 235U, 236U, 237U, 238U232Th236Pu, 237Pu, 238Pu, 239Pu, 240Pu, 241Pu, 242Pu</p><p>Minor actinides 237Np, 239Np241Am, 242Am, 243Am242Cm, 243Cm, 244Cm, 245Cm, 246Cm</p><p>Fission materials 79Se, 85Kr, 87Rb, 89Sr, 90Sr, 93Zr, 95Zr, 95Nb 99Tc, 107Pd, 115In149Sm, 151Sm, 133Xe, 140Ba, 134Te, 93Mo, 106Ru, 106Rh, 107</p><p>Activation products 3H, 10Be, 14C, 24Na, 36Cl, 39Ar, 55Fe, 59Ni, 60Co, 63Ni, 93Mo,</p><p>e back-end part of closed nuclear fuel cycles.</p><p>Of the various matrix-options available, sodium borosilicateglasses are mostly favored as they offer wide compositional flexibil-ities, high order of product durabilities and are easy to manufacturethrough remote and robotic operations. Extensive scientific andtechnological database already exist for the system and the glassesare well accepted by general public. However in reality, borosili-cate glasses cannot be considered as a universal wasteform matrixas in many cases HLWs contain elements having poor solubilitywithin it [37,38]. A good example of this is phosphate rich HLWs(P2O5-HLWs) which have only 23 wt% (P2O5) solubility withinborosilicate melts [39]. The only possible way to condition suchHLWs within conventional borosilicate glass metrices is to dilutethem to a level so that the concentration(s) of the troubleshootingelement(s) become lower than their respective solubility limits. Butsuch an approach finally increases the volume of the vitrified wasteproducts and makes the waste management procedure more costly.An alternative approach to this is to find out a novel amorphousmatrix having higher solubility for P2O5-HLWs. Toward this a num-</p>ber of efforts have been made across the world over the last fiftyyears, but so far limited progresses have been made to produce suchmatrices in actual plant scale on regular basis. The probable reasonbehind this is lack of complete comprehensions of the problem, its<p>, 126Sn, 129I, 131I 135Cs, 137Cs, 141Ce, 142Ce, 144Ce, 144Pr 144Nd, 147Sm, 147Pm, 148Sm,Pd, 140La, 154Eu</p><p>93mNb, 94Nb, 99Tc, 108mAg, 113mCd, 121mSn, 205Pb, 210Po</p></li><li><p>20 P. Sengupta / Journal of Hazardous M</p><p>Ff</p><p>aubwbhdittfimStc</p><p>2</p><p>t(d</p><p>TT</p><p>ig. 3. Schematic diagram (not to scale) showing elemental distribution within auel-clad assembly after irradiation.</p><p>ssociated difficulties and bottle neck situations. Hence for betternderstanding of the subject and to take right steps towards feasi-le solutions it is absolutely necessary to put together the lessonse have learnt from past experiments. So far no such attempt has</p><p>een made and the present article tries to fill up this lacuna. Itas compiled all relevant past experimental results, from 1950s tillate, in a single source so as to enable the researchers, the waste</p><p>mmobilizers and the policy makers to judge the current state-of-he-art. The review starts by summarizing the various reprocessingechniques leading to P2O5-HLW generations, followed by the dif-culties encountered while immobilizing the same in bo...</p></li></ul>

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