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Post-irradiation examination has started and initial results are available for the varying temperature irradiation experiment conducted in the high flux isotope reactor (HFIR), carried out in the framework of the Japan–USA Fusion Cooperation Program (JUPITER project). This experiment is an unprecedented controlled irradiation experiment designed for symmetrical comparison of isothermal and temperature-variant neutron irradiation effects. This paper summarizes the irradiation experiments and initial results obtained from the post-irradiation examination of an austenitic alloy, vanadium, a vanadium alloy and copper. These preliminary results extend the trends observed in earlier, lower fluence experiments, with some effects of the low temperature phase of variable temperature irradiation on evolving microstructures.

A temperature controlled instrumented capsule has been irradiated in the RB* position of the high flux isotope reactor (HFIR) at the Oak Ridge National Laboratory in order to perform in situ thermal conductivity measurements of monolithic ceramics and composite materials during neutron irradiation. This determination of thermal conductivity utilizes a temperature gradient technique whereby two thermocouples measure the absolute temperature along a cylindrical sample which is constrained to one-dimensional thermal conduction. The heat source is the intrinsic gamma heating of the core region of the HFIR. This paper provides an overview of the experiment and gives preliminary results on the degradation in thermal conductivity of a few ceramic specimens measured as a function of irradiation temperature (200–700°C) and fast neutron fluence up to ∼3.4 × 1025 n/m2 (E>0.1 MeV ) .

An experiment to directly compare the effects of neutron fluence received at steady temperature on microstructure and mechanical properties of candidate fusion reactor structural materials to the effects of receiving 10% of the fluence at reduced temperature has been designed. The Varying Temperature Experiment is being fabricated for irradiation in a large Removable Beryllium (RB) position of the High Flux Isotope Reactor (HFIR). For this experiment, specimen temperatures are elevated and controlled whenever there is substantial neutron fluence to the specimens (reactor power > 10%). Half of the specimens are irradiated at two distinct temperatures, and half are irradiated at constant temperature. The capsule features to meet these requirements are described. The experiment will operate for ten reactor cycles beginning in early 1998. This project is a collaborative effort under the Japan-USA cooperative program (Jupiter Project).

A capsule has been designed that permits four specimen sets to be irradiated in an RB* location in the High Flux Isotope reactor (HFIR) with distinct temperature histories. During the reporting period critical component prototyping was completed. The results have lead to some design and operational changes from that previously reported. The primary design changes are (1) compression seals in the specimen holes of the beryllium holders, and (2) oxide-dispersion strengthened aluminum alloy (DISPAL) specimen sleeves in all holders. Details of the capsule design are presented in the previous issue of this publication. Four, axially displaced temperature zones are independently controlled. Holder temperatures are monitored by thermocouples and controlled by a combination of adjustable temperature control gas mixtures and auxiliary heaters. The high temperature holders are located in the center of the experimental region, which is centered on the reactor mid-plane, and the low temperature holders are located at the ends of the experimental region.

The purpose of this experiment is to determine effects of temperature variation during irradiation on microstructure and mechanical properties of potential fusion reactor structural materials. A varying temperature irradiation experiment is being performed under the framework of the Japan-USA Program of Irradiation Tests for fusion Research (JUPITER) to study the effects of temperature variation on the microstructure and mechanical properties of candidate fusion reactor structural materials. An irradiation capsule has been designed for operation in the High Flux Isotope Reactor at Oak Ridge National Laboratory that will allow four sets of metallurgical test specimens to be irradiated to exposure levels ranging from 5 to 10 dpa. Two sets of specimens will be irradiated at constant temperature of 500{degrees}C and 350{degrees}C. Matching specimen sets will be irradiated to similar exposure levels, with 10% of the exposure to occur at reduced temperatures of 300{degrees}C and 200{degrees}C.

The TRIST-ERI capsule was assembled and irradiated in a large Removable Beryllium (RB{star}) position of the High Flux Isotope Reactor (HFIR) during this reporting period. Irradiation began on March 8, 1996, was completed on June 20, 1996, during operating cycles 344, 345, and 346. This report describes the thermal operation of the capsule.

A collaborative DOE/Monbusho series of irradiation experiments is being implemented to determine, in situ, the effects of irradiation on the electrical resistivity of ceramic materials. The first experiment, TRIST-ER1, has been designed to irradiate 15 Al{sub 2}O{sub 3} test specimens at 450{degrees}C in an RB position of the High Flux Isotope Reactor (HFIR). Each test specimen is located in a sealed vanadium subcapsule with instrumentation provided to each subcapsule to measure temperature and resistance, and to place a biasing voltage across the specimen. Twelve of the specimens will be biased with 200 V/mm across the sample at all times, while three will not be biased, but can be if so desired during the irradiation. The experiment design, component fabrication, and subcapsule assembly have been completed. A three cycle irradiation, to a fast neutron (E>0.1 MeV) fluence of about 3x10{sup 25}n/m{sup 2} ({approx}3 dpa in Al{sub 2}O{sub 3}), is expected to begin early in March 1996.