Chapter 6. CONCLUSIONS
6.3. Estimation of radiation damage accumulated in the neutron absorber
Helium ion irradiation tests on Al 6061 alloys and commercial neutron absorbers were conducted to emulate the radiation damage accumulated in neutron absorbers and the following conclusions were determined; (1) threshold damage level for bubble nucleation in the Al 6061 alloy lies within the range of 0.1–1 dpa, (2) The average size of bubbles in the eight-year-old neutron absorber (25.9 ± 7.4 nm) was the most similar to that of 10-dpa irradiated Al 6061 alloy specimens (28.4 ± 13.8 nm), which indicates that the radiation damage accumulated in the absorber was estimated to be ~10 dpa, and (3) preferential cavity formation was observed along the grain boundaries in Al matrix and Al cladding of neutron absorbers, which resulted in the reduced average size of cavities.
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114
APPENDIX A: Aluminum powder particles
Aluminum powder particles on the surface of 8.25 yr neutron absorber.
Cracked aluminum powder particles.
116
Hollow sphere formation on the surface of 4.33 yr neutron absorber.
Hollow sphere formation below the oxide layer of 4.33 yr neutron absorber after the corrosion tests.
118
APPENDIX B: Surface corrosion
Hollow sphere formation on the surface of 8.25 yr neutron absorber after the corrosion tests.
Microcracked aluminum oxide film on the surface of 8.25 yr absorber after the corrosion tests.
120
Discontinuous oxide layer on the surface of 8.25 yr neutron absorber after the corrosion tests.
APPENDIX C: Radiation-induced bubbles
Gas bubble formation in the Al matrix of 2.75 yr neutron absorber.
122
Gas bubble formation in the Al matrix of 4.33 yr neutron absorber.
Gas bubble formation in the Al matrix of 4.33 yr neutron absorber.
124
Gas bubble formation in the Al matrix of 8.25 yr neutron absorber.
Gas bubble formation in the Al matrix of 8.25 yr neutron absorber.
126
Gas bubble formation in the Al matrix of 8.25 yr neutron absorber.
Gas bubble formation in the Al matrix of 8.25 yr neutron absorber.
128
Gas bubble agglomeration in the Al matrix of 8.25 yr neutron absorber.
Gas bubble agglomeration in the Al matrix of 8.25 yr neutron absorber.