Porous Alumina Silicate Matrix Gubka for Solidification of 137Cs Strip Product
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0985-NN11-02
Porous Alumina Silicate Matrix Gubka for Solidification of 137Cs Strip Product Albert Aloy, Alexander Strelnikov, and Vyacheslav Essimantovskiy "V.G. Khlopin Radium Institute", 2nd Murinskiy str., 28, Saint Petersburg, 194021, Russian Federation ABSTRACT Separated liquid highñlevel radioactive waste (HLW) fractions, in particular, about 100 liters of a 137Cs strip product with activity up to ~ 100 Ci/l (3.7 TBq/l) have been produced during the development and testing of partitioning technology and temporarily stored at V.G. Khlopin Radium Institute (KRI) (SaintñPetersburg, Russia). The benchñ scale experimental unit designed for operation in the hot cell was developed for 137Cs strip product solidification using an alumina silicate porous inorganic material (PIM) called Gubka. Conditions of saturation, drying, and calcinations of the salts into Gubka pores were optimized, and the operations under a remote control regime were executed during tests using a simulated strip product doped with 137Cs. The volume reduction coefficients were equal by a factor of 3.2ñ3.9 and a 137Cs discharge into an offñgas system was not detected. 137Cs leach rates from Gubka blocks after calcination at 800°C were 1.0ñ1.5⋅10-3 g/m2⋅per day. INTRODUCTION At present, a number of countries are investigating partitioning technology of liquid HLW. This technology produces relatively small volumes of the strip products like 137Cs, 90 Sr, transuranic elements (TUE), and rare earth elements (REE) [1]. The solidification of these strip products allows decreased cost and increased safety in its transport to the near by repository. To solve this problem, PIMs like silica gel [2, 3], porous glass [4], porous shamotte [5], and so on can be used. A new PIM called Gubka was suggested for use in 137Cs strip product solidification at KRI. Gubka is the porous blocks on bases of alumina silicate cenospheres (hollow microspheres) [6, 7]. The radiochemical composition of the real 137 Cs strip product stored at KRI is as follows (Bq/l): 137Cs up to 3⋅1012; 90Sr up to 1010; 154 Eu up to 109; Σα up to 108. The chemical composition is (g/l): NH4NO3 up to 300, HNO3 up to 250. In previous work [8] it was shown that cesium was distributed in the composition between two crystalline phases: CsAlSiO4 and CsAlSi2O6, and in the glassy phase during solidification of the simulated solution using Gubka. When Н3РО4 was added with a molar ratio of Cs2O:P2O5= 1:2 to the solution, the Gubka poresí filling was increased 4ñ5 times without salting-out and decreased the cesium discharge ~ 50times. EXPERIMENT The following stages of the 137Cs strip product solidification process, using Gubka, were suggested:
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repeated cycles: Gubka saturation by strip product with the addition of (Н3РО4) or without it ñ drying with periodical NH4NO3 thermal destruction; • CsNO3 or СsH5(PO4)2 calcination into Gubka pores; • containerization of Gubka saturated by 137Cs for transportation to the repository. The benchñscale unit was developed and fabricated to realize the process in the
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