For the conditioning of spent resins contaminated with radionuclides, such as: 137Cs, 134Cs, 60Co, 58Co, 57Co, 54Mn, etc., techniques of direct immobilization in cement, bitumen and organic polymers have been tested. The selected process was the bituminization using industrial bitumen, I 60-70, made in Romania, which had very good characteristics. The paper presents stages of the research project, technical conditions for the process and advantages of the bituminization of spent resins

Andrei, Veronica

Arsene, Carmen

Negoiu, Dumitru

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WM’03 Conference, February 23-27, 2003, Tucson, AZ    1CONDITIONING TECHNOLOGY FOR RADIOACTIVE WASTE  RESULTED FROM THE TREATMENT OF LIQUID WASTE  FROM THE ROMANIAN NUCLEAR POWER PLANT  CARMEN ARSENE, VERONICA ANDREI, DUMITRU NEGOIU Institute for Nuclear Research, P.O Box 78, 0300 Pitesti, Romania Nuclearelectrica, Bucharest, Romania Bucharest University, Romania    ABSTRACT  For the conditioning of spent resins contaminated with radionuclides, such as: 137Cs, 134Cs, 60Co, 58Co, 57Co, 54Mn, etc., techniques of direct immobilization in cement, bitumen and organic polymers have been tested. The selected process was the bituminization using industrial bitumen, I 60-70, made in Romania, which had very good characteristics. The paper presents stages of the research project, technical conditions for the process and advantages of the bituminization of spent resins.   INTRODUCTION  One of the main directions from the Romanian R&D radioactive waste management program, initiated in 1992, four years before the start-up of the Cernavoda Nuclear Power Plant (NPP) was to establish treatment and conditioning technologies for low and intermediate radioactive waste generated by plant operation.  Researches for treatment of the liquid radioactive wastes from the Decontamination Center of the plant (1) have showed that the best solution is ion-exchange method. As a result of the process, secondary solid wastes -spent ion exchangers- is generated. In terms of disposal, the work was focused on the conditioning of the secondary waste.  Spent resins treatment or conditioning technologies have to consider the presence of the large number of radionuclides and the organic base of the ion exchangers. Also, any solution for conditioning and disposal of spent resins package has to take into account both nuclear safety and economic aspects. The adopted solution should not increase significantly the costs of waste management but should limit at a maximum practicable extent the contamination and irradiation of the operating staff, population and the environment.  In Romania dose limits for workers and population are established within the Romanian Regulations for Radiological Safety and those are in accordance with the recommendations of International Commission for Radiological Protection.  For the conditioning of spent resins contaminated with Cs-137, Cs-134, Co-60, Co-58, Co-57, Mn-54 etc techniques of direct immobilization in cement, bitumen and organic polymers have been experimented. The selected process was the bituminization using industrial bitumen, I 60-70, made in Romania, which have had very good characteristics.  The research project (2) was implemented in few stages, as follows:   selection of the conditioning process of spent resins WM’03 Conference, February 23-27, 2003, Tucson, AZ    2 conceiving, design and building of a pilot plant for conditioning of spent resins  immobilization experiments of spent resins at pilot scale  determination of the optimum process parameters within which the plant operates  long standing leaching studies on the bitumen products   GENERAL TECHNOLOGICAL CONCEPT  The bituminization technology of ion exchangers contaminated with 14C consists in a homogeneous dispersion of the resins in the molten bitumen and solidification of the mixture by cooling. The main stages of the technological process are:  Filtration of resin The filtration of resin is applied for removing the excess water from resin suspension with intentions to decrease the time for mixing bitumen and resin and to avoid foaming during the bituminization process. The filtrated resin is temporary stored in a container.  Resin embedding in molten bitumen The effective conditioning process is as follows: in the installation molten bitumen is added, in portions, in a controlled manner and under stirring of the filtrated resin. The temperature variation must be surveyed the entire process; when the temperature decreases under 1100C the heating is started until the operating optimum temperature is reached (1200C). After the last portion was fed, the stirring is continued till a fluid homogenous mass is obtained. The bituminized mixture is heated to a final temperature of 1300C and it is drained into an 80 L stainless steel drum. After filing and cooling, the 80 L container is cemented and confined in other with a bigger capacity (220 L). Thus, in terms of final disposal, the final product presents two confinement barriers: the bitumen matrix and the concrete layer, ensuring long-term stability.  Off-gases decontamination During the bituminization process, because of the high temperature, a significant amount of gas is produced. Besides water vapours, it contains degradation products of resin and bitumen (3) (CO2, SO2, amines, n-paraffins C6 - C32, isoparaffins and aromatic hydrocarbons). For decontamination, the generated gases are passed through a heat exchanger in which water vapours and condensable gases are condensed. The gases decontaminated are taken over by the filtration installation of the box in which the bituminization pilot plant is fixed. The flowsheet of bituminization of spent ion exchangers is presented in Figure 1.  The components of the pilot plant for ion exchangers conditioning are: - filter dewatering- constructed according to principle of  Nuce filter - bitumen-resin blender - represents the main component of the conditioning pilot plant in which the mixing process of resin with molten bitumen takes place. It is a cylindrical tank made of stainless steel, it is disposed horizontally; its capacity is 62 l and operates discontinuously. The blender is equipped with feeder port, for bitumen and resin, tap of bitumen-resin mixture, helicoid stirrer, which homogenizes the mixture during the process, electric heating system, temperature control system, off-gases system - heat exchanger - collecting vessel for condensate WM’03 Conference, February 23-27, 2003, Tucson, AZ    3bitumen-resin mixtureDECANTATIONMELTINGALIMENTARErasina umedabitumenDOSAGEFILTRATIONDOSAGEFEED MOLTENBITUMENCONDENSATIONBITUMINIZATIONCONFINEMENTin 70L drumSOLIDIFICATIONFILTRATIONCONDENSATESEPARATIONWaste WaterTankoff-gasgases +condensateREPOSITORYSTACKexcess waterspent resin  - aggregate  - cement milkpHadjCONFINEMENTin 220L drumcondensunabs. gases Fig. 1  Flowsheet of bituminization of spent ion-exchange resins    WM’03 Conference, February 23-27, 2003, Tucson, AZ    4TECHNOLOGICAL PARAMETERS OF THE BITUMINIZATION PROCESS  As a result of the experiments carried out with anionite, carbonate anionite, cationite and resin mixtures in various ratios, the optimum operational plant parameters were found:  - bitumen type:     I60/70 - mixing temperature:    1200C - feed type of resin:     discontinuously - molten bitumen volume added for a charge: 20 L - wet resin volume added for a charge:  36.7 L - rotational speed of the stirrer:   25±5 rot/min - pouring temperature of a bituminized mixture: 125-1300C - embedding rate of dry resin:   40% - homogenization time for a resin portion:  20 min - resin volume added for a portion:   1.5 L   CHARACTERISTICS OF ION-EXCHANGE RESINS USED IN EXPERIMENTS  In order to obtain the most appropriate results cationite C100H and anionite A600 Romanian resins, having form and structure similar to IRN-77 and IRN-78, were used. C 100H resin is a strong-acid cationite in the –SO3H form, based on styrene-divinylbenzene, contains minimum 99.9% ion exchangers in the R-H form and it is similar to IRN-77. A600 resin is a strong-base anionite, based on same support and it has linked –N(CH3)3+ functional groups; it contains minimum 95% ion exchangers in the R-OH form, max.0.1% in R-Cl form, max. 5% R2CO3, max. 0.3% in R2SO4 form and is similar to IRN-78. The physico-chemical characteristics (4) of these ion exchangers are presented in Table I.  Table I. The characteristics of ion-exchange resins used for treatment of liquid radioactive waste at the Decontamination Center  Trade name C 100H A 600 Manufacturer Purolite Co., Ro. Purolite Co., Ro. Functional group -SO3- -N(CH3)3+ Ion form H+ OH- Size (mm) 0,3 - 1,2 0,3 - 1,2 Moisture (%) 54 48 Density (g/cm3) 0,76 - 0,8 0,68 -0,71 Exchange capacity (meq/g / meq/mL) 4,5   /   2 3,9   /   1,4 pH range 0 - 14 0 - 14 Max.oper. temp(0C) 120 60 Remarks Nuclear grade, min.99.9% R-H form Nuclear grade min.95% R-OH form max. 0.1% in forma R-Cl max. 5% R2CO3 max. 0,3% in forma R2SO4   WM’03 Conference, February 23-27, 2003, Tucson, AZ    5CHARACTERISTICS OF SPENT ION-EXCHANGE RESINS GENERATED FROM THE DECONTAMINATION CENTER  In Table II there are presented activities of radionuclides from the spent resins. Values are estimative.   Table II Spent resins activities  Radionuclid activity (Bq/kg wet resin) Crt. No. Spent resin type 54Mn 57Co 58Co 60Co 134Cs 137Cs 1. CAN DECON 7000 900 4300 504200 29900 7559002. POD 6300 700 4000 482700 26200 6667003. CAN DECON:POD (1:1) 4200 400 2000 253300 17800 4503004. CAN DECON* 10900 1300 9023 263077 - 55692  CHARACTERISTICS OF BITUMEN  In order to find the most suitable bitumen type, immobilization experiments of spent resins were carried out using a variety of Romanian bitumen sorts: D60/80, I60/70, H82/92, Acumulator, I85/95, E110, and ARPECHIM-Pitesti. As a result of collected data (7), I60/70 bitumen type was determined to be the most suitable. I60/70 bitumen is direct-distilled bitumen and its properties are presented in Table III.   Table III. Characteristics of I60/70 bitumen  Characteristics  Softening point From 60 to 700C Penetration at 250C from  1.5 to 4.0mm Flash point Min.2400C Density at 250C 1.02-1.03 g/cm3 Paraffin content Max. 2% Water content Traces Mineral acidity and alkalinity Absence Solubility in organic solvents Min. 99% Paraffin with min. 450C softening point Max. 1.8%   LEACHING TESTS  The leaching test consisted in the immersion of the bitumen-resin products in deionized water (considered to be representative for disposal medium) so that whole surface came in contact with it. The ratio between the leachant volume and the surface area of each specimen was 10/1. The specimens were kept in the leaching medium for 365 days, and changed with frequencies recommended by international agreed standards (IAEA, ISO). In table IV the specimens characteristics are presented.   6Table IV. The characteristics of the bituminized ion-exchange resin specimens used in leaching tests  Pr. no. Spent resin type Bitumen  (g) Dry resin in specimen (g) Embedding resin (%) Specim.mass (g) Specim.volume (cm3) Density (g/cm3) Specim. surface area(cm2) Leachant volume (cm3) 0. Inactive resin 13.32 8.88 0.667 22.20 19.8 1.121 40.5 405 1. CAN DECON 13.14 8.76 0.667 21.90 19.8 1.106 40.5 405 2. POD 12.91 8.61 0.667 21.52 19.8 1.087 40.5 405 3. CAN DECON:POD (1:1) 13.56 9.04 0.667 22.60 19.8 1.141 40.5 405 0.* Inactive resin 11.57 3.86 0.333 15.43 18.0 0.857 36.9 370 4.* CAN DECON 14.17 4.72 0.333 18.9 18.0 1.050 36.9 370 5.* CAN DECON 13.87 4.62 0.333 18.5 16.0 1.156 33.3 370   Table V. Activity of bitumen-resin specimens  Activity of radionuclide (Bq/specim.) Total activity  (Bq/specim) Pr. N0. Tip rasina uzata 54Mn 57Co 58Co 60Co 134Cs 137Cs  0. Inactive resin - - - - - - - 1. CAN DECON 122.64 15.77 75.34 8833.6 523.8 13243.0 22814.552. POD 108.46 12.05 68.86 8310.1 451.06 11477.0 20428.55. CAN DECON:POD (1:1) 75.94 7.23 36.12 4579.6 321.82 8141.4 13162.230.* Inactive resin - - - - - - - 4.* CAN DECON 102.89 12.27 85.18 2483.4 - 525.7 3209.475.* CAN DECON 100.71 12.01 83.37 2430.8 - 514.6 3141.49    7The radionuclide releases in leaching medium and the corresponding leach rates were determined.  Table VI. Leaching rates for the different radionuclides. R (kg/m2s)  after 365 leaching days after 714 leaching days Radionuclide Leaching Rate Specim. 1 Specim. 2 Specim. 3 Specim. 4 Specim.a 5 137Cs Bq/specim. 13243 11477 8141 526 515  R (kg/m2s) 6.21E-10 4.81E-9 1.02E-9 1.36E-9 1.51E-9 134Cs Bq/specim. 524 451 322 - -  R (kg/m2s) 3.43E-9 3.91E-9 5.76E-9 - - 60Co Bq/specim. 8833 8310 4579 2483 2431  R (kg/m2s) 3.03E-10 3.17E-10 6.04E-10 3.35E-10 3.71E-10 58Co Bq/specim. 75.34 68.86 36.12 85.18 83.37  R (kg/m2s) 2.67E-8 2.87E-8 5.75 E-8 7.37E-9 8.17E-9 57Co Bq/specim. 15.77 12.05 7.23 12.27 12.01  R (kg/m2s) 5.43E-8 6.99E-8 1.22E-7 2.16E-8 2.40E-8 54Mn Bq/specim. 122.64 108.46 75.94 102.89 100.71  R (kg/m2s) 1.48E-8 1.64E-8 2.46E-8 5.47E-9 6.06E-9   The leaching rates were calculated using the following equation (according to SR ISO 6961)  R = xxtSaa××0 (Eq.1)   where, R - leach rate (kg/m2s) ax  - activity, per secunda, of the leached radionuclide at tx time  a0 -initial activity of x radionuclide, per secunda kilogram, present in specimen  S  - exposed surface area of specimen (m2)  tx    - leaching duration (seconds)   SUMMARY AND CONCLUSIONS  Without being the best solution and giving the best matrix, the direct immobilization in bitumen was proposed like an optimum solution due to certain advantages:   The embedding rate of resin in bitumen is high (until 50% dry resin).   At operating temperature, 1200C, the waste volume is significantly reduced (about 70% from water contained in wet resin is collected as condensation product)   The leaching tests, performed on bitumen products, led to low cumulative leaching rates: for 137Cs and 60Co <10-7, for 134Cs, 58Co, 57Co and 54Mn<10-6 g/cm2day (for all cases the losses were under detection limit of γ spectrometer)   The bituminization pilot plant required a simple operation, it was safe for the environment, easy for maintenance and, from the economic point of view, it has been accessible.   8REFERENCES  1. M. BALASOIU, The technology for treatment of liquid radioactive waste from the Decontamination Center of the NPP-Cernavoda, Institute for Nuclear Research, Pitesti, 2000. 2. C. ARSENE, Establishing of conditioning technology for conditioning of radioactive waste from treatment of liquid radioactive waste from the Decontamination Center of the NPP-Cernavoda, IRN/IR-6308, Institute for Nuclear Research, Pitesti, 2002. 3. C. ARSENE, D. NEGOIU, "Degradation products of resin and bitumen during the bituminization process of spent resin”, Chemistry Review no.2, Bucharest, pag.115, 2002 4. The Purolite Company, Ion exchangers – characteristics, Purolite International Ltd. Anglia, 1996   

Conditioning Technology for Radioactive Waste Resulted From the Treatment of Liquid Waste From the Romanian Nuclear Power Plant

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