an extreme disposition method for low level radioactive wastes using supercritical water wataru...
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.)
Incineration MeltCompression
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 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)
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) H2O2 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) H2
O2 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 conditionCritical pointRoom temperature High temperature
L
Co
L
L
L
LL Co
L
L
LL
tetrahedronoctahedron
Vapor Vapor Liquid Liquid Two phase One phase
A Characteristic of Supercritical Fluids 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)
1H NMR spectra of water measured in the the range of 25-400 at 30MPa. ℃
【 1H, 17O-NMR Chemical shift of water vs. Temp.】
17O chemical shifts of water and the extent of hydrogen bonding as a function of temperature
at 25 and 30MPa.
Increasing temperature
Decreasing hydrogenbond
Highfield shift
Fig. 6 Proton spin-lattice relaxation times (T1) of water as a function of temperature.
Structure of 95% DStructure of 95% D22OO
Structure of 95% COStructure of 95% CO33CDCD22ODOD
Structure of 95% COStructure of 95% CO33ODOD
D
O
H O
D D
CD
DD
CD D
O
H C
DD
DCD D
O
D
CD
DD
O
HC
DD
D
O
D
Fig. 5 Structure of water, ethanol and methanol (95%deuterations)
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
Ref. Hayatsu, R., Scott, R. G. Nature, 1975, 257, 378.
O
HN
O 1,3-Diphenylpropane
Benzyl ether
N-Phenylbenzylamine
Phenyl ether
Bridged aromatics
N
ONH
ON
Benzene
Naphthalene
Phenanthrene
Dibenzofuran
BenzonaphtofuranPyridine
Quinoline
Carbazole
S
S
Dibenzothiophene
Benzo[b]thiophene
Condensed aromatics and heterocycles
O
HN
CH3
NH2OHCH3
CH3
CH3
OH O
1,3-Diphenylpropane
390℃, 3 h
SCW
390℃, 3 h
SCW
390℃, 3 h
SCW
Benzyl ether
N-Phenylbenzylamine
Toluene Ethylbenzene
+
+
+
+
+
Benzyl alcohol Benzaldehyde
Aniline
Aromatic rings are highly stable in SCW
Decomposition of bridged aromatics by SCW
Aromatics
Lower hydrocarbons with higher H/C ratioCatalysts
Polymers
CC
H
H
H
n
Hydrogenation ( H donor : H2O )
CO2
PolymersAromatics plasticsCoal Biomass
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.
Sample : 150mg
RuO2 : 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
,
CHCl3
Open
Decantation
Evaporate CHCl3
Solid residue
Organic residue
Weigh
Weigh
Rinse
Filter RuO2
and solid residue
On-line gas chromatography apparatus
Gas chromatographs : Shimadzu, TCD-GC8APT, FID-GC8APFAnalysis conditions
Hydrocarbons : Porapak Q, Col. Temp. 60 ℃, He carrier
H2 : Molecular sieve 5A, Col. Temp. 50 ℃, Ar carrier
CO2 : Silica Gel, Col. Temp. 60 ℃, He carrier
Table 2 Experimental results on RuO2-catalyzed gasification of naphthalene in SCW
Org.Atomic ratio Molar ratio
C-conv.(%)
Product distribution (%) Molar ratio
H/C O/C [Org]/[RuO2] CH4 CO2 H2 [O]CO2/[O]RuO2 [H]Gas/[H]Org
0.80 0 5.12 96.7 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.
Org.Atomic ratio Molar ratio
C-conv.(%)
Product distribution (%) Molar ratio
H/C O/C [Org]/[RuO2] CH4 CO2 H2 [O]CO2/[O]RuO2 [H]Gas/[H]Org
1.00 0 6.32 100.7 53.7 39.4 6.9 21.5 2.47CC
H
H
H
Table 3 Experimental results on RuO2-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 RuO2-catalyzed gasification of organic compounds in SCW
Org.Atomic ratio Molar ratio a
C-conv.(%) b
Product distribution (%) d Molar ratio
H/C O/C [Org]/[RuO2] CH4 CO2 H2 [O]CO2/[O]RuO2 [H]Gas/[H]Org g
0.80 0 5.12 96.7 48.8 42.7 8.4 23.1 2.90
0.75 0 3.94 87.9 c 52.7 40.6 6.7 18.1 2.86
0.83 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
PET 0.80 0.40 3.44 97.2 37.3 51.0 11.5 19.3 (12.6) e 2.44
Cellulose 0.80 0.83 5.12 97.0 34.2 42.7 14.6 14.0 (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 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, [H]Org was calculated using the wt.% conversion.
O
O
NH
PE = polyethylene, PP = polypropylene, PS = polystyrene, PET = poly(ethylene terephthalate)
Results
Figure Decomposition of laminating sheet
Reaction time : 180min.
Reaction temperature : 723K
Results
The decomposition calculated using a formula as follows.
×100 (w%)a -
ba
a : mass before experiment (mass of sample)
b : mass after experiment (mass of decomposed sample)
Results
Samples BasisDecomposition*
(w%)
Laminating sheet polyethylene 98
Cover sheet (ALARA sheet) polyethylene 98
Attention rope with tiger striping
polyethylene 99
Suit for controlled area (zipper)
nylon 99
Fire retardant sheetpolypropylen
e98
Fire retardant tapepolypropylen
e98
Anion exchange resin polystyrene 94
Rubber glovesnatural rubber
79
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
Samples Basis
Laminating sheet polyethylene
Fire retardant sheet polypropylene
Fire retardant tape polypropylene
Anion exchange resin
polystyrene
Rubber gloves natural rubber
0
25
50
75
100
0 1 2 3
Time(hr)
Dec
ompo
sitio
n(w
%)
Figure Dependence of temperature and time for laminating sheet
Results
▲ : at 673K◆ : at 723K■ : no catalyst at 723K
0
25
50
75
100
0 1 2 3
Time(hr)
Dec
ompo
sitio
n(w
%)
Figure Dependence of temperature and time for fire retardant sheet
Results
▲ : at 673K◆ : at 723K■ : no catalyst at 723K
0
25
50
75
100
0 1 2 3
Time(hr)
Dec
ompo
sitio
n(w
%)
Figure Dependence of temperature and time for fire retardant tape
Results
▲ : at 673K◆ : at 723K■ : no catalyst at 723K
0
25
50
75
100
0 1 2 3
Time(hr)
Dec
ompo
sitio
n(w
%)
Figure Dependence of temperature and time for anion exchange resin
Results
▲ : at 673K◆ : at 723K■ : no catalyst at 723K
0
25
50
75
100
0 1 2 3
Time(hr)
Dec
ompo
sitio
n(w
%)
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 RuO2 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 CH4, CO2 and H2 and no hazardous gas such as CO was not observe
Discussion and Conclusion
2. The catalytic effects by RuO2 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 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)