Solute transport by radiation-induced segregation (RIS) leads to local changes of alloy composition. We have studied RIS in a binary Ni-8 at. % Si alloy by 7-MeV-proton and 28-MeV-alpha particle irradiations. Damage levels varied between 0.1 and 0.3 dpa. The irradiations were carried out at 475/sup 0/C, the expected peak RIS temperature; preimplantation of helium at 700/sup 0/C was carried out in some specimens. Solute segregation was studied by energy-dispersive x-ray analysis (EDX). Using very fine electron-beam probes of 2 nm diameter from a high-brightness field-emission source, microchemical profiles across the grain boundaries were measured. Radiation-induced precipitation of Ni/sub 3/Si was investigated by dark-field transmission electron microscopy (TEM).
This report summarizes the early results of the post irradiation examination of the 50 GWd/MT MOX Test Fuel Capsule 5. This is the only test capsule that participated in every irradiation phase and individual Advanced Test Reactor cycle. Capsule 5 occupied low flux test assembly positions during most of its irradiation and hence linear heat generation rates and fuel temperatures were low compared to those of all other weapons-derived MOX test capsules. The purpose of this preliminary examination is to document and monitor the progress of the MOX Test Fuel Irradiation. Capsule 5 and its Fuel Pin 8 were found to be in excellent condition. The gas pressure measurement yielded a pin pressure of 70 psia and the fission gas release was 3.1% based on 85Kr activity measurement, within the European experience for similar irradiation histories. Preliminary fuel stack gamma scan measurements and fuel pin diameter measurements indicate that this fuel has behaved as expected for the irradiation conditions experienced.
The post irradiation examination (PIE) of the Advanced Test Reactor (ATR) MOX capsules containing MOX fuel fabricated from weaponsderived plutonium irradiated to 30 GWd/MT has shown excellent fuel performance. Two test capsule types were examined; one contained fuel that underwent a special thermal gallium removal process (TIGR) and the other contained fuel that did not undergo any special processing. Initial gamma scanning revealed normal capsule and fuel pin behavior. Fission gas measurements of the capsules and fuel pins demonstrated the integrity of the fuel pins and showed the fission gas release to be between 1.5 and 2.3%, within the expected range. Metallographic mounts were prepared from the fuel pins and fuel behavior was found to be in accordance with expectations, with no indications of significant fuel restructuring or abnormal swelling. As was expected from earlier PIE work, large plutonium agglomerates were present. Some were as large as 600 microns, several times that expected in contemporary commercial MOX fuel. No irradiation difficulties were noted with these agglomerates. The grain structure of the pellet was observed to change over the radius of the pellet, with larger grains in the pellet center. This effect was more pronounced in the TIGR treated material that also appeared to have a greater fission gas release. A SEM/Microprobe examination of the fuel and clad showed no adverse interactions and confirmed that the pellet grain structure of the TIGR treated material is behaving somewhat differently. Elemental mapping confirmed that the agglomerates were rich in plutonium and that fission products were localized in the agglomerates. Radiochemical analysis of the fuel confirmed the expected burnup values and showed no indications of significant migration of gallium to the clad.
