Evaluation of irradiation damage and structural integrity assessment of the HIFAR reactor aluminium tank

This paper describes the experimental program aimed at assessing more accurately the changes in mechanical properties which have occurred in the RAT aluminium, and the effect these changes may have on the structural integrity of the RAT. Details will include information on the sectioning of the irradiated components and production of appropriate test pieces, the measurement of tensile, fracture toughness and hardness properties using conventional techniques and the use of small punch testing for the determination of fracture properties. Also included will be details of microscopic examination using optical, SEM and TEM techniques. Further discussion will be made on the structural integrity assessment of the RAT, including assumptions about mechanical loadings on the tank, mechanical properties of the tank material, and defect distributions within the RAT structural welds. Preliminary results are consistent with previously reported studies in the literature and provide confidence in earlier assessments of the RAT's condition. Chemical analysis of transmutation produced silicon confirms a model of fluence distribution in the reactor. The partially worked structure of the aluminium revealed evidence of some radiation induced recovery, however no evidence was found for dislocation loops or voiding. Hardness measurements, tensile strength and small punch test results were related to the extent of transmutation silicon precipitation resulting from thermal neutrons and were found to be consistent with data reported in the literature. The program of continuing evaluation of the RAT is described, including the continuing structural integrity assessment and the range of non-destructive inspection activities due to be undertaken during the extended shut down of HIFAR scheduled for late 1995. (orig./HP)