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An Extreme Disposition Method For Low Level Radioactive Wastes Using Supercritical Water Wataru Sugiyama*, Tomoyuki Koizumi*, Akira Nishikawa*, Yuuji Sugita*, Ki Chul Park#, Hiroshi Tomiyasu# *Chubu Electric Power Co., Inc. #Shinshu University Introduction A large amount of radioactive wastes have been accumulated in nucl ear power plants. These are mostly fire retardant materials and at this moment stored in the 200L dram cans with mortar after the following p rocess. Combustibles (Paper, Wood etc.) Plastics (Fire retardant sheet etc.) Incombustibl

es (Metal etc.) Incineration Compression Melt 200L dram cans with mortar Figure The disposition process of low level radioactive wastes Introduction The present process has problems as follows: No significant decrease in total amounts of wastes Plastics, if involved in combustible wastes, may produce hazardous gases The effective disposition method for low level ra dioactive wastes has not been established yet The objective of the present study is to establish an extreme disposition method to minimize the wastes as close as to zero with zero addition during disposition. A disposition using supercritical water could be an Objective of the present study

Supercritical Water Oxidation method using oxygen as an oxidant in supercritical water are generally known and widely used. However, complete decomposition is not possible for stable materials such as aromatic compounds by this method. Recently, we have developed a new method using RuO2 as a catalyst in supercritical water. With this catalyst, the complete decomposition of fire retardant materials became possible without any other addition. The present study is to use this RuO2 catalyst for the disposition of low-level wastes to achieve an extreme disposition method. ref. 1. W. Sugiyama, K. C. Park, H. Tomiyasu, et. al., Super Green 2002,., Suwon, Korea, (2002) Residuals resulted from supercritical water oxidation treatment for p-dichlorobenzene using equivalent (right) and twice equivalent (left) H 2O2 as an oxidant under the following condition: 450 and 30 min. of reaction and 30 min. of reaction time. Solid residuals by the supercritical water oxidation treatment for p-di -chlorobenzene using equivalent (left) and twice equivalent (right) H 2 O2 under the following condition: 450 and 30 min. of reaction tim e. p-di-chlorobenzene is used for the simulation of PCB. Solid residual after the treatment by supercritical water oxidation (right) for polyvinylchloride powder (below). Solid residual by our new method (left) What is supercritical water? Critical Point

22 MPa and 374 This is the Critical Point of Water Supercritical Water Above the critical point (22 MPa and 374) in the phase diagram of water, water is no longer l iquid, but not gas either. A Characteristic of Supercritical Fluids Two phase Liquid Room temperature One phase Vapor High temperature L L L L Co L

Co L L octahedron L L L tetrahedron Critical point t Supercritical condition Lower viscosity, Higher diffusive(gaslike) Higher thermal conductivity(liquidlike) Lower dielectric constant, Larger ion produc Supercritical fluids can simultaneously control with slight variation in density. (from liquidlike to gaslike)

1H, 17O-NMR Chemical shift of water vs. Temp. O chemical shifts of water and the extent of hydrogen bonding as a function of temperature at 25 and 30MPa. 17 H NMR spectra of water measured in the the range of 25-400 at 30MPa. Increasin 1 g temperat Decreasing hy drogenbond Highfiel d shift Structure of 95% D2O H D O O

D D Structure of 95% CO3CD2OD DD C D C D D O D D D H O C D C D D Structure of 95% CO3OD D D C O D H D O

D C D D Fig. 5 Structure of water, ethanol and methanol (95%deuterations) Fig. 6 Proton spin-lattice relaxation times (T1) of water as a function of temperature. Spin-Lattice relaxation time T1 at temperatures from 25 to 400 T1 is controlled in low temperature (below 200) by the magnetic moments of adjacent atoms because of slow molecular motion (e.g. 1H gives larger magnetic influence than 2D) in high temperature under sub or supercritical conditions by the rate of intra-molecular rotation

Model compounds of coal Bridged aromatics O 1,3-Diphenylpropane O Phenyl ether Benzyl ether H N N-Phenylbenzylamine Condensed aromatics and heterocycles N H N Carbazole O Dibenzofuran

Benzene Phenanthrene Quinoline N Pyridine S Dibenzothiophene O Benzonaphtofuran Naphthalene S Benzo[b]thiophene Ref. Hayatsu, R., Scott, R. G. Nature, 1975, 257, 378. Decomposition of bridged aromatics by SCW CH3 SCW 390, 3 h

1,3-Diphenylpropane Toluene Ethylbenzene CH3 SCW O CH3 + OH + 390, 3 h Benzyl ether Benzyl alcohol H N SCW 390, 3 h

CH3 O + Benzaldehyde + N-Phenylbenzylamine Aromatic rings are highly stable in SCW OH NH2 + Aniline Aromatics Coal Polymers H C H

H C Biomass Polymers Hydrogenation ( H donor H2O ) Lower hydrocarbons with higher H/C ratio n Aromatics plastics Catalysts CO2 A nearly complete gasification of aromatics and polymers was achieved by stoichiometrically insufficient amounts of RuO2 in SCW to provide CH4, CO2 and H2 as major products. Experimental procedure HASTELLOY batchwise reactor

Sample : 150mg RuO2 : 30mg Water : 3mL Reaction Evaporate CHCl3 Decantati on Filter RuO2 and solid residue Time : 5,30,60 and 180min. Rinse Temp. : 673,723 and 773 K Cooling at room temp. Open Organic

residue Weigh Solid residue Weigh Water , CHCl3 Experimental procedure Figure Experiment equipment On-line gas chromatography apparatus Gas chromatographs Shimadzu, TCD-GC8APT, FID-GC8APF Analysis conditions Hydrocarbons Porapak Q, Col. Temp. 60 , He carrier CO2 Silica Gel, Col. Temp. 60 , He carrier H2 Molecular sieve 5A, Col. Temp. 50 , Ar carrier Table 2 Experimental results on RuO2-catalyzed gasification of naphthalene in SCW Atomic ratio Org. Molar ratio

H/C O/C [Org]/[RuO2] C-conv. (%) 0.80 0 5.12 96.7 Product distribution (%) Molar ratio CH4 CO2 H2 [O]CO2/[O]RuO2

[H]Gas/[H]Org 48.8 42.7 8.4 23.1 2.90 Carbon conversions of organic compounds (feed) to gaseous products were calculated according to the following equation; C-conv. (%) = 100[C] in gaseous products/[C] in feed, where [C] represents the moles of carbon. Table 3 Experimental results on RuO2-catalyzed gasification of polystyrene in SCW Atomic ratio Org. H C H H C Molar ratio H/C

O/C [Org]/[RuO2] C-conv. (%) 1.00 0 6.32 100.7 Product distribution (%) Molar ratio CH4 CO2 H2 [O]CO2/[O]RuO2 [H]Gas/[H]Org

53.7 39.4 6.9 21.5 2.47 Carbon conversions of organic compounds (feed) to gaseous products were calculated according to the following equation; C-conv. (%) = 100[C] in gaseous products/[C] in feed, where [C] represents the moles of carbon. Molar quantities of polymers are the apparent values calculated by assuming monomeric units to be molecules. Table 4 Summary of the experimental results on RuO2-catalyzed gasification of organic compounds in SCW Atomic ratio Org. Molar ratio a H/C O/C [Org]/[RuO2] C-conv.

(%) b 0.80 0 5.12 0.75 0 0.83 Product distribution (%) d Molar ratio CH4 CO2 H2 [O]CO2/[O]RuO2 [H]Gas/[H]Org g 96.7

48.8 42.7 8.4 23.1 2.90 3.94 87.9 c 52.7 40.6 6.7 18.1 2.86 0.08 3.87

99.9 45.8 48.8 5.4 23.9 (22.0) e 2.46 0.67 0.08 3.92 101.7 51.0 43.6 5.5 22.0 (20.1) e 3.46

PE 2.00 0 23.5 100.6 66.6 28.0 5.3 14.0 1.47 PP 2.00 0 15.7

99.9 66.5 26.9 6.5 13.5 1.49 PS 1.00 0 6.32 100.7 53.7 39.4 6.9 21.5

2.47 0.80 0.80 0.40 0.83 3.44 5.12 97.2 97.0 37.3 34.2 51.0 42.7 11.5 14.6 19.3 (12.6) e 14.0 (4.2) e 2.44 1.18

N H O O PET Cellulose PE = polyethylene, PP = polypropylene, PS = polystyrene, PET = poly(ethylene terephthalate) a Molar quantities of polymers are the apparent values calculated by assuming monomeric units to be molecules. b Carbon conversions of organic compounds (feed) to gaseous products were calculated according to the following equation; C-conv. (%) = 100[C] in gaseous products/[C] in feed, where [C] represents the moles of carbon. c The lower conversion is ascribed to the adsorption of CO2 by the resulting NH3; the wt.% conversion based on its feed and recovery was 98.6 wt.%. d C2H6 and C3H8 were detected as minor products, though the proportions (< 0.2%) are not listed here. e The values in parenthases were caluclated according to ([O]CO2 [O]Org)/[O]RuO2. g Molar ratios of hydrogen atoms in gaseous products ([H]Gas) to those in the organic compounds converted ([H]Org). In carbazole, Results Figure Decomposition of laminating sheet Reaction time : 180min. Reaction temperature : 723K

Results Figure Decomposition of fire retardant tape Results Figure Decomposition of anion exchange resin Results Figure Decomposition of rubber gloves Results The decomposition calculated using a formula as follows. a b a 100 (w%)

a : mass before experiment (mass of sample) b : mass after experiment (mass of decomposed sample) Results The samples, which are used in nuclear power plants, are commercially available ones from CHIYODA TECHNOL CORPORATION. Anion exchange resin was DOWEX 1-X8. Table Decomposition Basis Decomposition* (w%) Laminating sheet polyethylene 98 Cover sheet (ALARA sheet) polyethylene 98 Attention rope with tiger striping

polyethylene 99 nylon 99 polypropylen e 98 Samples Suit for controlled area (zipper) Fire retardant sheet polypropylen Fire retardant* tape 98 : Reaction time : 180min. e Reaction temperature : 723K Results Five typical samples are chosen to

determine the best condition Samples Laminating sheet Basis polyethylene Fire retardant sheet polypropylene Fire retardant tape polypropylene Anion exchange resin Rubber gloves polystyrene natural rubber Results Decomposition w% 100

75 50 : at 673K : at 723K : no catalyst at 723K 25 0 0 1 2 3 Timehr Figure Dependence of temperature and time for laminating sheet Results Decompositionw%

100 75 50 : at 673K : at 723K : no catalyst at 723K 25 0 0 1 2 3 Timehr Figure Dependence of temperature and time for fire retardant sheet Results

Decomposition w% 100 75 50 25 : at 673K : at 723K : no catalyst at 723K 0 0 1 2 3 Time hr Figure Dependence of temperature and time for fire retardant

tape Results Decompositionw% 100 75 50 : at 673K : at 723K : no catalyst at 723K 25 0 0 1 2 3 Time

hr Figure Dependence of temperature and time for anion exchange resin Results Decomposition w% 100 75 50 : at 673K : at 723K : at 773K : no catalyst at 723K 25 0 0 1 2

3 Timehr Figure Dependence of temperature and time for rubber gloves Discussion and Conclusion 1. Decompositions and gasification of fire retardant pl astics were performed nearly 100 by use of RuO2 as a catalyst in supercritical water, but a little residual s remained for anion exchange resin and natural ru bber Gases produced during the decomposition of all wa stes were CH4, CO2 and H2 and no hazardous gas suc h as CO was not observe Discussion and Conclusion 2. The catalytic effects by RuO2 are dependent on temperature and reaction time, but independent of ti me after 30 minutes Decomposition reactions are controlled by the cataly st rather than thermal decompositions Discussion and Conclusion

3. The best condition for the present catalytic reacti on is as follows Temp. : 450 Time : 30mi 4. Only rubber gloves n. showed lower decomposition rat io The reason is expected that the gloves contain C=C bonds originated from natural rubber and that these double bonds might prohibi t the decomposition Conclusion The present RuO2 catalytic disposition method in supercritical water enables nearly 100% decomposition for low-level wastes except natural rubber. Radioactive metals such as Fe, Co Ni were recovered as oxide precipitations. Nothing except the catalyst was added during the disposition.. Ruthenium can be recovered easily to be used recycled. In conclusion, this disposition might be close to the extreme method, that is, to make wastes zero with zero addition. Acknowledgement This study started at the beginning in Titech by the support of Future Program of

the Japan Society for the Promotion of Science. The author (HT) expresses his thanks to the following persons: Core members of Future Programs in JSPS: Prof. Yoshio Yoshizawa Prof. Yasuhiko Fujii Co-workers: Prof. Yasuhisa Ikeda Dr. Masayuki Hara Dr. Tomoo Yamamura, Dr. Yun-Yul Park, Dr. Seong-Yun Kim, Dr. Zsolt Fazekas, Dr. Norioko Asanuma, Dr. Takehiko Tsukahara, Dr. Varga Tamas, Dr. Yuichiro Asano, Dr. Koh Hatakeyama, Dr.Koji Mizuguchi, Prof. Gilvert Gordon (Volwiler Distinguish Professor of Miami University) Prof. Kunihiko Mizumachi (Emeritus Professor of Rikkyou University)

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