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Microstructure of high-level radioactive waste glass heavily irradiated in a high-voltage electron microscope
NUCLEAR AND CHEMICAL WASTE MANAGEMENT, Printed in the USA. AU rights reserved.
Vol. 4,
pp. 147-151<1983 Copyright
0391-815X/83 $3.00 + .oO Q 1983 Pergamon Pres Ltd.
MICROSTRUCTURE OF HIGH-LEVEL RADIOACTIVE WASTE GLASS HEAVILY IRRADIATED IN A HIGH-VOLTAGE ELECTRON MICROSCOPE Seichi Sato Koichi Asakura Hiro taka Furuya Department of Nuclear Engineering, Faculty of Engineering, Kyushu University,Hakozaki, Higashi-ku, Fukuoka 812, Japan
ABSTRACT. Simulated radioactive waste glass has been irradiated in high voltage electron microscope up to 1.O x 10Z3 e/cm2 or 2.5 displacement per atom (dpa) in order to clarify change of microstructure and the cause for radiation effects.
Void formation by electron irradiation has been indicated more than the displacement atom concentration at saturation of radiation effects by a-accelerated test. It is likely that the void formation is important to understand the behavior of radiation effects of waste glass especially in heavy irradiation.
INTRODUCTION Dissolution and transport of radionuclides in ground water are the main threats to the isolation of high leve1 radioactive waste glass in deep geologie formation. A large volume of data affecting the release properties have been obtained in an attempt to estimate the technical safety. Among them, much attention is now being given to clarification of radiation effects of waste glasses because the glasses are irradiated up to 0.1-1 dpa for such a long period of time as 104- 1O6years. To realize the high radiation exposure in laboratory experiments within a short period of time, accelerated tests by doping
There are two interesting subjects to be clarifïed for the purpose of further understanding of radiation effects in waste glass. One is the change of microstructure of irradiated glass with increase of radiation exposure which must be closely related to the radiation effects and is very important when discussing the mechanism of its evolution. The other is the property of glass irradiated far beyond the 5 x lol8 a-decay/cm3 or 0.1 dpa. For these purposes, high voltage electron microscope is one of powerful and interesting instruments because heavy irradiation and observation of microstructure of a specimen can be simultaneously carried out. In the present study, irradiation and observation of microstructures of radioactive waste glass were carried out, using high voltage electron microscope up to 1 x 10Z3e/cm*, which corresponds to 2 x 10z3 displacement atoms/cm’ or 2.5 dpa.
EXPERIMENTAL Specimen glass, developed by Power Reactor and Nuclear Fuel Development Corporation (Japan) whose chemical composition is given elsewhere (4) was prepared as follows. Simulated waste glass G-2-30 containing 27.3 wt.% waste was melted in Pt crucible at 1200 “C and was casted in a cylindrical carbon mold placed in an electric furnace at about 600 “C and then cooled 6 “C/h to make the glass to be stressfree. The glass was cut to a thickness of 0.3 mm by a diamond cutter. After being mechanically polished 147
148
FIGURE 1.
S. SATO, K. ASAKURA, AND H. FURUYA
The bright field electron micrographs of simulated waste glass (G-2-30) irradiated by 1.O MeV electron. Flux of electron is 3.82 x lol9 e/(cm’*s). Years after disposal were calculated using Eq. 1 and the number of displacement atoms given by Roberts et al. (2).
149
MICROSTRUCTIJRE OF RADIOACIIVE WASTE GLASS by 3.0 Pm alumina powder up to 0.1 mm, it was chemically polished by 0.2 wt.% hydrofluoric acid and was washed by an ultrasonic machine to eliminate precipitants on the specimen surface. The thickness of the edge of the specimen glass was 0.5-2 pm. The specimen glass was then set in 3 mm mesh for high voltage electron microscope by means of Bioden Meshcement. Thereafter, carbon coating was carried out on the both side of the specimen to avoid the accumulation of electric charge. Electron irradiation and observation of specimen glass were performed, using high voltage electron microscope (HVEM JEM-1000 at Kyushu University). Electron fluence was determined by Faraday cup and was from lO*Oto 1023e/cm*, while flux was from 101s to lol9 e/(cm**s). The energies of electron beam were 1.00, 0.75, and 0.5 MeV. RESULTS AND DISCUSSION Microstructure of the specimen irradiated by 1.0 MeV electron are typically shown in Fig. 1 as a function of fluence at flux 3.82 x lol9 e/(cm**s). Two types of white spots are found in the microstructures. One, called type A, is a fine white spot of about 0.005 Pm in diameter. In Fig. lb, the aggregate of only this type of white spot can be seen. The other, called type
B, is a large white spot of above 0.03 Pm in diameter which can be seen in the aggregate of type A spot in Figs. IC-1 f. With increase of fluence, type A spot becomes clear and the size of type B spot increases. The diameters of the isolated type B spots in the specimens irradiated at 0.75 and 1.O MeV are given in Fig. 2 as a function of fluence. In order to know what the type B spot is, several irradiations and observations were performed in many specimens. Two typical microstructures characteristic of the type B spot are shown in Figs. 3a and 3b. At the fluence of 9.7 x lO*l e/cmz given in Fig. 3a, a number of type B spots of 0.1 Pm in diameter appeared in irradiated glass. At the fluence of 4.5 x 102* e/cm*, a microstructure including aggregate of several large type B spot of -0.3 pm in diameter was seen as is shown in Fig. 3b, where the microstructure was obtained when the specimen was tilted by 30 degrees. As is indicated by an arrow, a smooth curved surface can be definitely seen. Since the definite white spot means the lack of glass components, compared with the residual region of the specimen, it is likely that the smooth curved surface appears as a result of the swelling due to the evolution of the aggregate of the spots under the surface. Therefore, the white spots of type B are voids existing in bulk of specimen glass. In Figs. 1, 3a, and
0.1
0.01
IPa
Fl_UX(e.crñ2.seS') I
@
04.77x1018 @ 3.82x10'9 1000keV a2.20x10'9 A 3.82~10"
0.6
l 0
750keV H 1.43x1o'g
1 1020 FIGURE 2.
I
I
102’
f
I
I
Il1lli
1022 FLUENCE(eañ2)
I
I
I
111111
1
LI
1023
Duse dependence of void diameter (type B) as a function of flux and energy of incident electron. Dashed line shows the number of displacement atoms where the radiation effect by cY-accelerated test reaches saturation.
150
S. SATO, K. ASAKURA, AND H. FURUYA damage rate (dpa/s) of specimen, although other factors such as the species of incident particle, impurity content of specimen have some effects. When the temperature of specimen is too low or high, no void nucleates. In the connection of damage rate, Kuramoto et al. (7) recently showed that the irradiation at the smaller damage rate makes the void nucleus in iron at the smaller displacement atom concentration. In the case of lower flux, the waste glass specimen was likely placed under a more favorable condition to void nucleation, although the temperature of specimen was not known because of experimental difficulty. It is important to compare concentration of displacement atoms formed by HVEM irradiation with the one obtained in a-accelerated test, because HVEM has an excellent advantage to irradiate the specimen beyond the concentration of displacement atoms which can be reached using a-accelerated test. The number of atoms per unit volume of glass N is 8 x 10Z2/cm3 (4) and average mass number of this waste glass is 22. Displacement energy Ed is assumed to be 25 ev. The cross section u, for primary displacement by incident electron at 1.0 MeV can be taken to be constant value, 2.5 x 10eZ3cm2 for thin specimen used in the present study. Thus, the concentration of displacement atoms N,(e) in the specimen irradiated to fluence C$by 1.0 MeV electron is given by the equation, N,(e) = Nu&.
bf FIGURE 3. Microstructures including voids; (a) fluence 9.7 x 10” e/cm’ and (b) fluence 4.5 x 10” e/cm2. Specimen is tilted by 30 degrees in(b). Swelling due to void formation can be seen in (b), while it was not found in (a).
3b, various sizes of void from -0.03 to 0.3 Pm in diameter exist continuously. Taking into account both the continuous existente and the size of type A spot of -0.005 Pm in diameter, it is suggested that type A spot is also a very smal1 void. With respect to behavior of nucleation and growth of the void, two interesting points can be seen in Fig. 2. First, at the energy of 1.O and 0.75 MeV, both type A and type B void appeared, while at the energy of 0.5 MeV, only type A void was observed. The reason is not clean but it should be noted that the energy of more than -0.2 MeV is needed to displace atoms in waste glass (5) and cross section for primary displacement increases remarkably with energy (6). Secondly, in the case of constant energy of incident electron, void appeared and grew more easily in lower flux. Void nucleation depends mainly on the temperature,
(1)
If C#Iis 1.0 x 10Z3 e/cm’, which is the maximum fluence in the present experiment, N,(e) = 2 x 10Z3/cm3, or 2.5 dpa.
(2)
On the other hand, in the case of
(3)
This value is 20 times less than the value obtained in the present experiment as given in Eq. 2. The fluence at 1.O MeV electron which corresponds to the value of 1 x 1022/cm3 is plotted in Fig. 2 by a dashed line. The line is included in the region in which a void generated by the present irradiation exists. It is interesting to discuss the saturation of radiation effects and incubation dose of void formation in waste glass in the comparison with those in metals and ceramics. Table 1 shows the dependenties of typical radiation effects in waste glass and some radiation effects in metals and actinide oxides on the displacement atom concentration. It should be noted that the saturation of al1 radiation effects begins in the range of displacement atom concentration from
MICROSTRUCTURE
151
OF RADIOACTIVE WASTE GLASS
TABLE 1 The Saturation of Radiation Effects and Incubation Dose of Void Formation as a Function of Displacement Atom Concenlration Displacement Atom Concentration (Cd in dpa)
Waste Glass
Actinide Oxide
Metal Lattice hardening in Ni (10) Cd = 0.001-0.05 (increase) (c) Cd > 0.5 (saturation)
10-1
10.’
Density change (8) (a) Cd = 0.01-0.1 (increase or decrease) Cd > 0.1 (saturation) Stored energy (9) (a) Cd = 0.01-0.1 (increase) Cd > 0.1 (saturation)
10-1
Void nucleation (b) Cd = 0.1-1.0
FP gas diffusion coefficient in UO, (11) (d) Cd = 0.001-1 (decrease) Cd > 1 (no change) Lattice expansion in UO, (12) (d) Cd = 0.001-0.5 (increase) Cd > 0.5 (decrease) Lattice expansion in PuO, (13,14) (a) Cd = 0.01-0.1 (increase) Cd > 0.1 (saturation)
100
Void nucleation in Fe (7)
FP gas bubble nucleation (15) (d)
10
Cd = 1-10 (c)
Cd = 1-10
(a) cY-decay radiation; (b) High voltage electron microscope (this work) irradiation; (c) neutron irradiation; (d) fission. It is assumed that au-decay, neutron irradiation and fission produce 2000, 500, and 20,000 displacement atoms per an event, respectively.
0.1 to 1.O dpa in three kinds of materials (waste glass, metal, actinide oxide). This fact suggests that the cascade regions (volume distorted by the cascade which an incident particle produces) created by ion bombardment and simple defects by electron irradiation begin to overlap, respectively, in the range of displacement atom concentration from 0.1 to 1.O dpa. Then the atom displacements by an additional irradiation changes little extent of lattice distortion beyond the above range. The displacement atom concentration for the void nucleation in waste glass in about 10 times smaller than the ones in metal and actinide. This differente implies that “vacancy” in glass moves more easily in amorphous waste glass than in crystalline solid.
REFERENCES Technical Report Series No. 187, Characteristics of solidified high-leve1 waste products compiled by Grover J.R. International Atomic Energy Agency, Vienna (1979). Mendel, J. E., Nelson, R. D., Turcotte, R. P., Gray, W. J., Merz, M. D., Roberts, F. P., Weber, W. J., Westrik, J. H., Jr. and Clark, D. E. A state-of-the-art review of materials properties of nuclear waste forms. PNL-3802, Battelle, Pacific Northwest Laboratory, Richland, WA (1981). Furuya, H. and Sato, S. Radiation Damage on High-leve1 Radioactive Waste Glass. Genshiryoku-kogyo 27~ 65 (1981). Sato, S., Nishino, Y., Nishikawa, H. and Furuya, H. Determination of Heat Capacity of Simulated Radioactive Waste Glass by Drop Calorimetry. J. Nucl. Sci. Technol. 18: 540
(1981). 5. Lanza, F., Manara, A., and Rutten, F. V. Simulation possibilities of radiation effects in glasses used for conditioning high activity waste. EUR 556Oe, Commission of the European Communities, Luxembourg (1976). 6. Ishino, S. Syosha-sonsyo. University of Tokyo Press, Tokyo (1979). 7. Kuramoto, E., Yoshida, N., Tsukuda, N., Kitazima, K., Packan, N. H., Lewis, M. B., and Nansur, L. K. Simulation irradiation studies on iron. J. Nucl. Mater. 103 & 104: 1091 (1981). 8. Roberts, F. P., Turcotte, R. P., and Weber, W. J. Material characterization workshop on the irradiation effects in nuclear waste forms. PNL-3588, Battelle, Pacific Northwest Laboratory, Richland, WA (1981). 9. Roberts, F. P. Irradiation effects on borosilicate waste glasses. PNL-SA-8182, Battelle, Pacific Northwest Laboratory, Richland, WA (1980). 10. Markin, M. J. and Minter, F. J. Irradiation hardening in copper and nickel. Actu Met. 8: 691 (1960). ll. MacEwan, J. R. and Stevens, W. H. Xenon diffusion in UO,. J. Nucl. Mater. 11: 77 (1964). 12. Nakae, N., Harada, A., Kirihara, T., and Nasu, S. Irradiation Induced Lattice Deffects in UOI. J. Nucf. Mater. 71: 314 (1978).
13. Mendelssohn, K., King, E., Lee, J. A., Rand, M. H., Griffin, C. S., and Street, R. S. Self-Irradiation Damage in Transuranic Elements and Compounds in Plutonium A. E., Kay and M. B., Waldron, eds., pp. 189-204. Chapman Hall, London (1965). 14. Chikalla, T. D. and Turcotte, R. P. Self-radiation damage ingrowth in ‘3’Pu02. Radiation Effects 19: 93 (1973). 15. Turnbull, J. A. The distribution of intragranular fission gas bubbles in UO, during irradiation. J. Nucl. Muter. 38: 203 (1971).
Vol. 4,
pp. 147-151<1983 Copyright
0391-815X/83 $3.00 + .oO Q 1983 Pergamon Pres Ltd.
MICROSTRUCTURE OF HIGH-LEVEL RADIOACTIVE WASTE GLASS HEAVILY IRRADIATED IN A HIGH-VOLTAGE ELECTRON MICROSCOPE Seichi Sato Koichi Asakura Hiro taka Furuya Department of Nuclear Engineering, Faculty of Engineering, Kyushu University,Hakozaki, Higashi-ku, Fukuoka 812, Japan
ABSTRACT. Simulated radioactive waste glass has been irradiated in high voltage electron microscope up to 1.O x 10Z3 e/cm2 or 2.5 displacement per atom (dpa) in order to clarify change of microstructure and the cause for radiation effects.
Void formation by electron irradiation has been indicated more than the displacement atom concentration at saturation of radiation effects by a-accelerated test. It is likely that the void formation is important to understand the behavior of radiation effects of waste glass especially in heavy irradiation.
INTRODUCTION Dissolution and transport of radionuclides in ground water are the main threats to the isolation of high leve1 radioactive waste glass in deep geologie formation. A large volume of data affecting the release properties have been obtained in an attempt to estimate the technical safety. Among them, much attention is now being given to clarification of radiation effects of waste glasses because the glasses are irradiated up to 0.1-1 dpa for such a long period of time as 104- 1O6years. To realize the high radiation exposure in laboratory experiments within a short period of time, accelerated tests by doping
There are two interesting subjects to be clarifïed for the purpose of further understanding of radiation effects in waste glass. One is the change of microstructure of irradiated glass with increase of radiation exposure which must be closely related to the radiation effects and is very important when discussing the mechanism of its evolution. The other is the property of glass irradiated far beyond the 5 x lol8 a-decay/cm3 or 0.1 dpa. For these purposes, high voltage electron microscope is one of powerful and interesting instruments because heavy irradiation and observation of microstructure of a specimen can be simultaneously carried out. In the present study, irradiation and observation of microstructures of radioactive waste glass were carried out, using high voltage electron microscope up to 1 x 10Z3e/cm*, which corresponds to 2 x 10z3 displacement atoms/cm’ or 2.5 dpa.
EXPERIMENTAL Specimen glass, developed by Power Reactor and Nuclear Fuel Development Corporation (Japan) whose chemical composition is given elsewhere (4) was prepared as follows. Simulated waste glass G-2-30 containing 27.3 wt.% waste was melted in Pt crucible at 1200 “C and was casted in a cylindrical carbon mold placed in an electric furnace at about 600 “C and then cooled 6 “C/h to make the glass to be stressfree. The glass was cut to a thickness of 0.3 mm by a diamond cutter. After being mechanically polished 147
148
FIGURE 1.
S. SATO, K. ASAKURA, AND H. FURUYA
The bright field electron micrographs of simulated waste glass (G-2-30) irradiated by 1.O MeV electron. Flux of electron is 3.82 x lol9 e/(cm’*s). Years after disposal were calculated using Eq. 1 and the number of displacement atoms given by Roberts et al. (2).
149
MICROSTRUCTIJRE OF RADIOACIIVE WASTE GLASS by 3.0 Pm alumina powder up to 0.1 mm, it was chemically polished by 0.2 wt.% hydrofluoric acid and was washed by an ultrasonic machine to eliminate precipitants on the specimen surface. The thickness of the edge of the specimen glass was 0.5-2 pm. The specimen glass was then set in 3 mm mesh for high voltage electron microscope by means of Bioden Meshcement. Thereafter, carbon coating was carried out on the both side of the specimen to avoid the accumulation of electric charge. Electron irradiation and observation of specimen glass were performed, using high voltage electron microscope (HVEM JEM-1000 at Kyushu University). Electron fluence was determined by Faraday cup and was from lO*Oto 1023e/cm*, while flux was from 101s to lol9 e/(cm**s). The energies of electron beam were 1.00, 0.75, and 0.5 MeV. RESULTS AND DISCUSSION Microstructure of the specimen irradiated by 1.0 MeV electron are typically shown in Fig. 1 as a function of fluence at flux 3.82 x lol9 e/(cm**s). Two types of white spots are found in the microstructures. One, called type A, is a fine white spot of about 0.005 Pm in diameter. In Fig. lb, the aggregate of only this type of white spot can be seen. The other, called type
B, is a large white spot of above 0.03 Pm in diameter which can be seen in the aggregate of type A spot in Figs. IC-1 f. With increase of fluence, type A spot becomes clear and the size of type B spot increases. The diameters of the isolated type B spots in the specimens irradiated at 0.75 and 1.O MeV are given in Fig. 2 as a function of fluence. In order to know what the type B spot is, several irradiations and observations were performed in many specimens. Two typical microstructures characteristic of the type B spot are shown in Figs. 3a and 3b. At the fluence of 9.7 x lO*l e/cmz given in Fig. 3a, a number of type B spots of 0.1 Pm in diameter appeared in irradiated glass. At the fluence of 4.5 x 102* e/cm*, a microstructure including aggregate of several large type B spot of -0.3 pm in diameter was seen as is shown in Fig. 3b, where the microstructure was obtained when the specimen was tilted by 30 degrees. As is indicated by an arrow, a smooth curved surface can be definitely seen. Since the definite white spot means the lack of glass components, compared with the residual region of the specimen, it is likely that the smooth curved surface appears as a result of the swelling due to the evolution of the aggregate of the spots under the surface. Therefore, the white spots of type B are voids existing in bulk of specimen glass. In Figs. 1, 3a, and
0.1
0.01
IPa
Fl_UX(e.crñ2.seS') I
@
04.77x1018 @ 3.82x10'9 1000keV a2.20x10'9 A 3.82~10"
0.6
l 0
750keV H 1.43x1o'g
1 1020 FIGURE 2.
I
I
102’
f
I
I
Il1lli
1022 FLUENCE(eañ2)
I
I
I
111111
1
LI
1023
Duse dependence of void diameter (type B) as a function of flux and energy of incident electron. Dashed line shows the number of displacement atoms where the radiation effect by cY-accelerated test reaches saturation.
150
S. SATO, K. ASAKURA, AND H. FURUYA damage rate (dpa/s) of specimen, although other factors such as the species of incident particle, impurity content of specimen have some effects. When the temperature of specimen is too low or high, no void nucleates. In the connection of damage rate, Kuramoto et al. (7) recently showed that the irradiation at the smaller damage rate makes the void nucleus in iron at the smaller displacement atom concentration. In the case of lower flux, the waste glass specimen was likely placed under a more favorable condition to void nucleation, although the temperature of specimen was not known because of experimental difficulty. It is important to compare concentration of displacement atoms formed by HVEM irradiation with the one obtained in a-accelerated test, because HVEM has an excellent advantage to irradiate the specimen beyond the concentration of displacement atoms which can be reached using a-accelerated test. The number of atoms per unit volume of glass N is 8 x 10Z2/cm3 (4) and average mass number of this waste glass is 22. Displacement energy Ed is assumed to be 25 ev. The cross section u, for primary displacement by incident electron at 1.0 MeV can be taken to be constant value, 2.5 x 10eZ3cm2 for thin specimen used in the present study. Thus, the concentration of displacement atoms N,(e) in the specimen irradiated to fluence C$by 1.0 MeV electron is given by the equation, N,(e) = Nu&.
bf FIGURE 3. Microstructures including voids; (a) fluence 9.7 x 10” e/cm’ and (b) fluence 4.5 x 10” e/cm2. Specimen is tilted by 30 degrees in(b). Swelling due to void formation can be seen in (b), while it was not found in (a).
3b, various sizes of void from -0.03 to 0.3 Pm in diameter exist continuously. Taking into account both the continuous existente and the size of type A spot of -0.005 Pm in diameter, it is suggested that type A spot is also a very smal1 void. With respect to behavior of nucleation and growth of the void, two interesting points can be seen in Fig. 2. First, at the energy of 1.O and 0.75 MeV, both type A and type B void appeared, while at the energy of 0.5 MeV, only type A void was observed. The reason is not clean but it should be noted that the energy of more than -0.2 MeV is needed to displace atoms in waste glass (5) and cross section for primary displacement increases remarkably with energy (6). Secondly, in the case of constant energy of incident electron, void appeared and grew more easily in lower flux. Void nucleation depends mainly on the temperature,
(1)
If C#Iis 1.0 x 10Z3 e/cm’, which is the maximum fluence in the present experiment, N,(e) = 2 x 10Z3/cm3, or 2.5 dpa.
(2)
On the other hand, in the case of
(3)
This value is 20 times less than the value obtained in the present experiment as given in Eq. 2. The fluence at 1.O MeV electron which corresponds to the value of 1 x 1022/cm3 is plotted in Fig. 2 by a dashed line. The line is included in the region in which a void generated by the present irradiation exists. It is interesting to discuss the saturation of radiation effects and incubation dose of void formation in waste glass in the comparison with those in metals and ceramics. Table 1 shows the dependenties of typical radiation effects in waste glass and some radiation effects in metals and actinide oxides on the displacement atom concentration. It should be noted that the saturation of al1 radiation effects begins in the range of displacement atom concentration from
MICROSTRUCTURE
151
OF RADIOACTIVE WASTE GLASS
TABLE 1 The Saturation of Radiation Effects and Incubation Dose of Void Formation as a Function of Displacement Atom Concenlration Displacement Atom Concentration (Cd in dpa)
Waste Glass
Actinide Oxide
Metal Lattice hardening in Ni (10) Cd = 0.001-0.05 (increase) (c) Cd > 0.5 (saturation)
10-1
10.’
Density change (8) (a) Cd = 0.01-0.1 (increase or decrease) Cd > 0.1 (saturation) Stored energy (9) (a) Cd = 0.01-0.1 (increase) Cd > 0.1 (saturation)
10-1
Void nucleation (b) Cd = 0.1-1.0
FP gas diffusion coefficient in UO, (11) (d) Cd = 0.001-1 (decrease) Cd > 1 (no change) Lattice expansion in UO, (12) (d) Cd = 0.001-0.5 (increase) Cd > 0.5 (decrease) Lattice expansion in PuO, (13,14) (a) Cd = 0.01-0.1 (increase) Cd > 0.1 (saturation)
100
Void nucleation in Fe (7)
FP gas bubble nucleation (15) (d)
10
Cd = 1-10 (c)
Cd = 1-10
(a) cY-decay radiation; (b) High voltage electron microscope (this work) irradiation; (c) neutron irradiation; (d) fission. It is assumed that au-decay, neutron irradiation and fission produce 2000, 500, and 20,000 displacement atoms per an event, respectively.
0.1 to 1.O dpa in three kinds of materials (waste glass, metal, actinide oxide). This fact suggests that the cascade regions (volume distorted by the cascade which an incident particle produces) created by ion bombardment and simple defects by electron irradiation begin to overlap, respectively, in the range of displacement atom concentration from 0.1 to 1.O dpa. Then the atom displacements by an additional irradiation changes little extent of lattice distortion beyond the above range. The displacement atom concentration for the void nucleation in waste glass in about 10 times smaller than the ones in metal and actinide. This differente implies that “vacancy” in glass moves more easily in amorphous waste glass than in crystalline solid.
REFERENCES Technical Report Series No. 187, Characteristics of solidified high-leve1 waste products compiled by Grover J.R. International Atomic Energy Agency, Vienna (1979). Mendel, J. E., Nelson, R. D., Turcotte, R. P., Gray, W. J., Merz, M. D., Roberts, F. P., Weber, W. J., Westrik, J. H., Jr. and Clark, D. E. A state-of-the-art review of materials properties of nuclear waste forms. PNL-3802, Battelle, Pacific Northwest Laboratory, Richland, WA (1981). Furuya, H. and Sato, S. Radiation Damage on High-leve1 Radioactive Waste Glass. Genshiryoku-kogyo 27~ 65 (1981). Sato, S., Nishino, Y., Nishikawa, H. and Furuya, H. Determination of Heat Capacity of Simulated Radioactive Waste Glass by Drop Calorimetry. J. Nucl. Sci. Technol. 18: 540
(1981). 5. Lanza, F., Manara, A., and Rutten, F. V. Simulation possibilities of radiation effects in glasses used for conditioning high activity waste. EUR 556Oe, Commission of the European Communities, Luxembourg (1976). 6. Ishino, S. Syosha-sonsyo. University of Tokyo Press, Tokyo (1979). 7. Kuramoto, E., Yoshida, N., Tsukuda, N., Kitazima, K., Packan, N. H., Lewis, M. B., and Nansur, L. K. Simulation irradiation studies on iron. J. Nucl. Mater. 103 & 104: 1091 (1981). 8. Roberts, F. P., Turcotte, R. P., and Weber, W. J. Material characterization workshop on the irradiation effects in nuclear waste forms. PNL-3588, Battelle, Pacific Northwest Laboratory, Richland, WA (1981). 9. Roberts, F. P. Irradiation effects on borosilicate waste glasses. PNL-SA-8182, Battelle, Pacific Northwest Laboratory, Richland, WA (1980). 10. Markin, M. J. and Minter, F. J. Irradiation hardening in copper and nickel. Actu Met. 8: 691 (1960). ll. MacEwan, J. R. and Stevens, W. H. Xenon diffusion in UO,. J. Nucl. Mater. 11: 77 (1964). 12. Nakae, N., Harada, A., Kirihara, T., and Nasu, S. Irradiation Induced Lattice Deffects in UOI. J. Nucf. Mater. 71: 314 (1978).
13. Mendelssohn, K., King, E., Lee, J. A., Rand, M. H., Griffin, C. S., and Street, R. S. Self-Irradiation Damage in Transuranic Elements and Compounds in Plutonium A. E., Kay and M. B., Waldron, eds., pp. 189-204. Chapman Hall, London (1965). 14. Chikalla, T. D. and Turcotte, R. P. Self-radiation damage ingrowth in ‘3’Pu02. Radiation Effects 19: 93 (1973). 15. Turnbull, J. A. The distribution of intragranular fission gas bubbles in UO, during irradiation. J. Nucl. Muter. 38: 203 (1971).