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Characteristics of microstructural evolution of radiation damage in ceramics under fusion environment
Discussion on invited papers
158
Paper on page
31
Radiation damage and irradiation effects in solid breeders K. Noda R. Behrisch: Is there an effect of radiation on hydrogen trapping and retention ?
any irradiation test, therefore assessment of damage of that layer by thermal neutrons is appropriate. Furthermore, beryllium/ceramic compacts quite similar to the SIBELIUS have been placed in a closed capsule in BEATRIX-II so both thermal and fast neutron environments will be tested.
damage Paper on page
K. Noda: Hydrogen (tritium) trapping and retention are very important. The objectives of ion conductivity measurements are focused on the effects of irradiation on the diffusion process. Studies by another method are needed to obtain information about trapping and retention. E. R. Hodgson: 1) What is the ionizing dose rate? 2) For the increase in 0 observed for irradiation below 450 K is the effect electronic or ionic? K. Noda: I) Detailed calculation is needed to evaluate ionization energy deposited in the specimens. Such evaluation is very important, since electronic excitation process are considered to contribute damage production in the case of LizO. 2) In the examined temperature range, the conductivity depends strongly on concentration level of impurities such as OH- ions. The increase of conductivity below 450 K was an irradiation effect in the post irradiation condition. So, such an effect is an irradiation effect on ionic conductivity. Paper on page
42
Research and development status of ceramic breeder materials C. E. Johnson K. R. Kummerer: In future fusion power reactors the blanket temperature will be well above 300°C. Why do you ask to extend the investigation of breeder ceramics to temperatures below 3OO”C? C. E. Johnson: The ITER fusion reactor design has selected ceramics as a first option blanket maThe breeder blanket will be inserted into terial. ITER will proceed the reactor on construction. through a physics operational phasebefore the technology phase. In both phases low temperature operation will be stressed so it appears prudent to expand the ceramics breeder data base to include low temperatures. H. Watanabe: SIBELIUS experiment is conducted in SILOE reactor, it is a thermal reactor. In blanket environment Be is exposed to higher energy neutrons. How do you think about the different conditions between thermal neutron irradiation and blanket environmcnt ? C. E. Johnson: Thr presumed Be0 protective layer on metallic beryllium has never been subjected to
Characteristics microstructural
53
of
evolution
of radiation damage in ceramics under fusion environment C. Kinoshita R. R. Hasiguti: Concerning TiCI-x, you mentioned only structural vacancies. But I think you may have interstitials and vacancies of both Ti and C when it is irradiated. How do you consider the roles of these different defects ? C. Kinoshita: In crystals with low ionicity, stoichiometry and electrical neutrality are not important factors for nuclei of loops. In this sense, Ti and C might behave as identical species for nucleation sites. In order to get conclusive results, however, furlher studies on the nucleation process are required under preferential displacements of Ti or C. E. R. Hodgson: 1) For MgO, Al203 and MgAl204 the EM c!Dse rates are very high, will this not invalidate your results? 2) Do you take into account radiation enhanced impurity aggregation in MgO? C. Kinoshita: 1) The EM dose rates are corresponding to more than 10e6 dpa and 108 Cy/s and much higher than expected in fusion environment. In this sense I agree with you. The EM studies, however, give critical insights into mechanisms, factors and parameters which should be considered in the fusion 2) Impurities are taken into account environment. only for nucleation sites of loops through the electron flux and temperature dependence of loop density, and they provided a much smaller number of nucleation sites than expected. The reason has not been made clear, but may be due to purified matrix through the irradiation induced impurity segregation. H. Wiedersich: Is the high loop concentration persisting to high temperature in the case of Fe and Cr doping of MgO related to the possibility that these dopents may be present in the tri-valcnt state? C. Kinoshita: From the dependences of temperature and electron flux on the volume density and the growth rate of loops above ~600 K, trivalent impurities stem to be affecting the mobility of vacancies rather than providing nucleationsites of interstitial loops.
158
Paper on page
31
Radiation damage and irradiation effects in solid breeders K. Noda R. Behrisch: Is there an effect of radiation on hydrogen trapping and retention ?
any irradiation test, therefore assessment of damage of that layer by thermal neutrons is appropriate. Furthermore, beryllium/ceramic compacts quite similar to the SIBELIUS have been placed in a closed capsule in BEATRIX-II so both thermal and fast neutron environments will be tested.
damage Paper on page
K. Noda: Hydrogen (tritium) trapping and retention are very important. The objectives of ion conductivity measurements are focused on the effects of irradiation on the diffusion process. Studies by another method are needed to obtain information about trapping and retention. E. R. Hodgson: 1) What is the ionizing dose rate? 2) For the increase in 0 observed for irradiation below 450 K is the effect electronic or ionic? K. Noda: I) Detailed calculation is needed to evaluate ionization energy deposited in the specimens. Such evaluation is very important, since electronic excitation process are considered to contribute damage production in the case of LizO. 2) In the examined temperature range, the conductivity depends strongly on concentration level of impurities such as OH- ions. The increase of conductivity below 450 K was an irradiation effect in the post irradiation condition. So, such an effect is an irradiation effect on ionic conductivity. Paper on page
42
Research and development status of ceramic breeder materials C. E. Johnson K. R. Kummerer: In future fusion power reactors the blanket temperature will be well above 300°C. Why do you ask to extend the investigation of breeder ceramics to temperatures below 3OO”C? C. E. Johnson: The ITER fusion reactor design has selected ceramics as a first option blanket maThe breeder blanket will be inserted into terial. ITER will proceed the reactor on construction. through a physics operational phasebefore the technology phase. In both phases low temperature operation will be stressed so it appears prudent to expand the ceramics breeder data base to include low temperatures. H. Watanabe: SIBELIUS experiment is conducted in SILOE reactor, it is a thermal reactor. In blanket environment Be is exposed to higher energy neutrons. How do you think about the different conditions between thermal neutron irradiation and blanket environmcnt ? C. E. Johnson: Thr presumed Be0 protective layer on metallic beryllium has never been subjected to
Characteristics microstructural
53
of
evolution
of radiation damage in ceramics under fusion environment C. Kinoshita R. R. Hasiguti: Concerning TiCI-x, you mentioned only structural vacancies. But I think you may have interstitials and vacancies of both Ti and C when it is irradiated. How do you consider the roles of these different defects ? C. Kinoshita: In crystals with low ionicity, stoichiometry and electrical neutrality are not important factors for nuclei of loops. In this sense, Ti and C might behave as identical species for nucleation sites. In order to get conclusive results, however, furlher studies on the nucleation process are required under preferential displacements of Ti or C. E. R. Hodgson: 1) For MgO, Al203 and MgAl204 the EM c!Dse rates are very high, will this not invalidate your results? 2) Do you take into account radiation enhanced impurity aggregation in MgO? C. Kinoshita: 1) The EM dose rates are corresponding to more than 10e6 dpa and 108 Cy/s and much higher than expected in fusion environment. In this sense I agree with you. The EM studies, however, give critical insights into mechanisms, factors and parameters which should be considered in the fusion 2) Impurities are taken into account environment. only for nucleation sites of loops through the electron flux and temperature dependence of loop density, and they provided a much smaller number of nucleation sites than expected. The reason has not been made clear, but may be due to purified matrix through the irradiation induced impurity segregation. H. Wiedersich: Is the high loop concentration persisting to high temperature in the case of Fe and Cr doping of MgO related to the possibility that these dopents may be present in the tri-valcnt state? C. Kinoshita: From the dependences of temperature and electron flux on the volume density and the growth rate of loops above ~600 K, trivalent impurities stem to be affecting the mobility of vacancies rather than providing nucleationsites of interstitial loops.