Presentation on theme: "An Extreme Disposition Method For Low Level Radioactive Wastes Using Supercritical Water Wataru Sugiyama*, Tomoyuki Koizumi*, Akira Nishikawa*, Yuuji Sugita*,"— Presentation transcript:
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 nuclear power plants. These are mostly fire retardant materials and at this moment stored in the 200L dram cans with mortar after the following process. Combustibles (Paper, Wood etc.) Plastics (Fire retardant sheet etc.) Incombustibles (Metal etc.) IncinerationMeltCompression 200L dram cans with mortar Figure The disposition process of low level radioactive wastes
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 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 only method for this purpose. Introduction The effective disposition method for low level radioactive wastes has not been established yet
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 RuO 2 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 RuO 2 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) 2. K. C. Park, H. Tomiyasu;, ChemComm. (2003) 694
Residuals resulted from supercritical water oxidation treatment for p-di- chlorobenzene using equivalent (right) and twice equivalent (left) H 2 O 2 as an oxidant under the following condition: 450 ℃ 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 O 2 under the following condition: 450 ℃ and 30 min. of reaction time. 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 liquid, but not gas either.
Supercritical condition Critical point Room temperatureHigh temperature L Co L L L LL L L L L tetrahedron octahedron VaporLiquid Two phaseOne phase A Characteristic of Supercritical Fluids ● Lower viscosity, Higher diffusive(gaslike) ● Higher thermal conductivity(liquidlike) ● Lower dielectric constant, Larger ion product Supercritical fluids can simultaneously control with slight variation in density. (from liquidlike to gaslike)
1 H NMR spectra of water measured in the the range of ℃ at 30MPa. 【 1 H, 17 O-NMR Chemical shift of water vs. Temp. 】 17 O chemical shifts of water and the extent of hydrogen bonding as a function of temperature at 25 and 30MPa. Increasin g temperat ure Decreasing hydrogenbond Highfiel d shift
Fig. 6 Proton spin-lattice relaxation times (T 1 ) of water as a function of temperature. Structure of 95% D 2 O Structure of 95% CO 3 CD 2 OD Structure of 95% CO 3 OD Fig. 5 Structure of water, ethanol and methanol (95%deuterations)
Spin-Lattice relaxation time T 1 at temperatures from 25 to 400 ℃ T 1 is controlled in low temperature (below 200 ℃ ) by the magnetic moments of adjacent atoms because of slow molecular motion (e.g. 1 H gives larger magnetic influence than 2 D) in high temperature under sub or supercritical conditions by the rate of intra-molecular rotation
Model compounds of coal Ref. Hayatsu, R., Scott, R. G. Nature, 1975, 257, ,3-Diphenylpropane Benzyl ether N-Phenylbenzylamine Phenyl ether Bridged aromatics Benzene Naphthalene Phenanthrene Dibenzofuran Benzonaphtofuran Pyridine Quinoline Carbazole Dibenzothiophene Benzo[b]thiophene Condensed aromatics and heterocycles
1,3-Diphenylpropane 390 ℃, 3 h SCW 390 ℃, 3 h SCW 390 ℃, 3 h SCW Benzyl ether N-Phenylbenzylamine TolueneEthylbenzene Benzyl alcohol Benzaldehyde Aniline Aromatic rings are highly stable in SCW Decomposition of bridged aromatics by SCW
Aromatics Lower hydrocarbons with higher H/C ratio Catalysts Polymers n Hydrogenation ( H donor ： H 2 O ) CO 2 PolymersAromaticsplasticsCoal Biomass A nearly complete gasification of aromatics and polymers was achieved by stoichiometrically insufficient amounts of RuO 2 in SCW to provide CH 4, CO 2 and H 2 as major products.
Sample : 150mg RuO 2 : 30mg Water : 3mL Experimental procedure HASTELLOY batchwise reactor Reaction Time : 5,30,60 and 180min. Temp. : 673,723 and 773 K Cooling at room temp. Water, CHCl 3 Open Decantation Evaporate CHCl 3 Solid residue Organic residue Weigh Rinse Filter RuO 2 and solid residue
On-line gas chromatography apparatus Gas chromatographs ： Shimadzu, TCD-GC8APT, FID-GC8APF Analysis conditions Hydrocarbons ： Porapak Q, Col. Temp. 60 ℃, He carrier H 2 ： Molecular sieve 5A, Col. Temp. 50 ℃, Ar carrier CO 2 ： Silica Gel, Col. Temp. 60 ℃, He carrier
Table 2 Experimental results on RuO 2 -catalyzed gasification of naphthalene in SCW Org. Atomic ratioMolar ratio C-conv. (%) Product distribution (%)Molar ratio H/CO/C[Org]/[RuO 2 ] CH 4 CO 2 H2H2 [O] CO 2 /[O] RuO 2 [H] Gas /[H] Org 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.
Org. Atomic ratioMolar ratio C-conv. (%) Product distribution (%)Molar ratio H/CO/C[Org]/[RuO 2 ] CH 4 CO 2 H2H2 [O] CO 2 /[O] RuO 2 [H] Gas /[H] Org Table 3 Experimental results on RuO 2 -catalyzed gasification of polystyrene in SCW 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 RuO 2 -catalyzed gasification of organic compounds in SCW Org. Atomic ratioMolar ratio a C-conv. (%) b Product distribution (%) d Molar ratio H/CO/C[Org]/[RuO 2 ] CH 4 CO 2 H2H2 [O] CO 2 /[O] RuO 2 [H] Gas /[H] Org g c (22.0) e (20.1) e 3.46 PE PP PS PET (12.6) e 2.44 Cellulose (4.2) e 1.18 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 CO 2 by the resulting NH 3 ; the wt.% conversion based on its feed and recovery was 98.6 wt.%. d C 2 H 6 and C 3 H 8 were detected as minor products, though the proportions (< 0.2%) are not listed here. e The values in parenthases were caluclated according to ([O]CO 2 − [O] Org )/[O] RuO 2. g Molar ratios of hydrogen atoms in gaseous products ([H] Gas ) to those in the organic compounds converted ([H] Org ). In carbazole, [H] Org was calculated using the wt.% conversion. PE = polyethylene, PP = polypropylene, PS = polystyrene, PET = poly(ethylene terephthalate)
Results Figure Decomposition of laminating sheet Reaction time : 180min. Reaction temperature : 723K
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. × 100 (w%) a － b a a : mass before experiment (mass of sample) b : mass after experiment (mass of decomposed sample)
Results SamplesBasis Decomposition* (w%) Laminating sheetpolyethylene98 Cover sheet (ALARA sheet)polyethylene98 Attention rope with tiger stripingpolyethylene99 Suit for controlled area (zipper)nylon99 Fire retardant sheetpolypropylene98 Fire retardant tapepolypropylene98 Anion exchange resinpolystyrene94 Rubber glovesnatural rubber79 Table Decomposition * : Reaction time : 180min. Reaction temperature : 723K The samples, which are used in nuclear power plants, are commercially available ones from CHIYODA TECHNOL CORPORATION. Anion exchange resin was DOWEX 1-X8.
Results Five typical samples are chosen to determine the best condition SamplesBasis Laminating sheetpolyethylene Fire retardant sheetpolypropylene Fire retardant tapepolypropylene Anion exchange resinpolystyrene Rubber glovesnatural rubber
Figure Dependence of temperature and time for laminating sheet Results ▲ : at 673K ◆ : at 723K ■ : no catalyst at 723K
Figure Dependence of temperature and time for fire retardant sheet Results ▲ : at 673K ◆ : at 723K ■ : no catalyst at 723K
Figure Dependence of temperature and time for fire retardant tape Results ▲ : at 673K ◆ : at 723K ■ : no catalyst at 723K
Figure Dependence of temperature and time for anion exchange resin Results ▲ : at 673K ◆ : at 723K ■ : no catalyst at 723K
Figure Dependence of temperature and time for rubber gloves Results ▲ : at 673K ◆ : at 723K ● : at 773K ■ : no catalyst at 723K
Discussion and Conclusion 1.Decompositions and gasification of fire retardant plastics were performed nearly 100 by use of RuO 2 as a catalyst in supercritical water, but a little residuals remained for anion exchange resin and natural rubber Gases produced during the decomposition of all wastes were CH 4, CO 2 and H 2 and no hazardous gas such as CO was not observe
Discussion and Conclusion 2. The catalytic effects by RuO 2 are dependent on temperature and reaction time, but independent of time after 30 minutes Decomposition reactions are controlled by the catalyst rather than thermal decompositions
Discussion and Conclusion Temp. : 450 ℃ Time : 30min. 3. The best condition for the present catalytic reaction is as follows 4. Only rubber gloves showed lower decomposition ratio The reason is expected that the gloves contain C=C bonds originated from natural rubber and that these double bonds might prohibit the decomposition
Conclusion The present RuO 2 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)