The radioisotope 99mTc, used in greater than 80% of nuclear medicine applications, has traditionally been produced and supplied to radiopharmaceutical companies in the form of its precursor 99Mo. Nuclear fission produced 99Mo had been supplied by Nordion International of Canada and Cintichem, Inc. of New York, USA. With the shutdown of Cintichem's reactor in 1989, a need was recognized for a US supply, and the US Department of Energy recently published a record of decision designating Sandia National Laboratories (SNL) to meet that need. A recent campaign was launched which utilized the SNL Annular Core Research Reactor to irradiate UO 2 coated targets fabricated by Los Alamos National Laboratory to produce 99Mo. The irradiated targets were chemically processed in the SNL Hot Cell Facility to separate and purify the 99Mo. The campaign also included final product quality analysis, and process waste handling. The campaign was accomplished with high 99Mo recovery. Final product quality was assessed at SNL, and samples were sent to an outside laboratory for independent verification. The campaign provided data and experience useful in pursuing US Food and Drag Administration and radiopharmaceutical company approval.

A series of in-pile experiments that addresses the phenomenology associated with Late-Phase processes in Light Water Reactors (LWRs) has been performed in the Annular Core Research Reactor (ACRR) at Sandia National Laboratories. The Melt Progression (MP) experiments were designed to provide information as part of the effort to develop and verify computer models for the analysis of LWR core damage during severe accidents. The MP-2 experiment is the second experiment in the series. The MP experiments examine the formation and movement of ceramic molten pools that form in the disrupted regions of a reactor core and migrate through the disrupted and intact regions of the core toward the core boundaries. The late phase of a reactor accident evolves as a consequence of early phase core degradation processes that include cladding oxidation, melting, core blockage formation, and general loss of fuel rod geometry. The MP-2 experiment assembly consisted of three regions: (1) a rubble bed composed of enriched U02 and Zr02 that simulated the severely disrupted regions of the reactor core, ( 2 ) a composite ceramic/metallic crust which represented the blockage formed by the early phase melting, relocation, and refreezing of mostly metallic core components, and (3) an intact rod stub region that remained in place below the blockage region. The test assembly was fission heated in the central cavity of the ACRR at an average rate of -0.2 K/s ultimately achieving a peak temperature in the molten pool of -3400 K. Melting of the debris bed ceramic components was initiated near the center of the bed. The molten material relocated downward under the influence of gravity, refreezing to form a ceramic crust near the bottom of the rubble bed. As ACRR power levels were increased over time, the crust gradually remelted and reformed at progressively lower positions in the bed until late in the experiment when it penetrated into and attacked the ceramic/metallic blockage. The metallic components of the blockage region melted and relocated downward to the bottom of the intact rod stub region prior to the time at which the ceramic melt penetrated the blockage region from above. The ceramic pool had penetrated halfway into the blockage region at the end of the experiment. The measurements of thermal response and material relocation are discussed and compared to the results of the computer simulations. Postexperiment examination of the assembly with the associated material interactions and metallurgy are also discussed in detail together with the analyses and interpretation of the results.

The post-irradiation examination (PIE) of the NET-1.2 fuel element was completed in December, 1993. The goal of the PIE work was to gather data regarding the fracture of the hot frit during the experiment. Five cracks were observed in the hot frit at various locations although only two were believed to have initiated the overall component failure. These two cracks were complete circumferential failures and were located near the open and closed ends of the frit within the active flow region. The location and orientation of these fractures suggested that failure was the result of thermally -induced stresses that exceeded pre-test predictions. The cause of the failure was the temperature difference between the coolant flowing through the hot frit and the thermally massive end fittings. The resulting axial temperature gradients in the hot frit imposed thermal stresses that exceeded failure in the frit coating material. This coating fracture then propagated through the graphite substrate. Post-test analyses of the frit response based on measured data from the experiment verified that the frit coating failure stresses were exceeded.Additionally, the cold frit behaved unexpectedly. The PIE inspection of this component showed that a majority of the compliant panels were permanently deformed against the cold frit inner wall even though the transients that the bed was exposed to were not thought to be capable of creating this magnitude of bed expansion. No evidence of bed locking was observed. A calculational error in the prediction of the total bed expansion was found (post-PIE) which certainly contributed to the under-estimation of the bed displacement. Additionally, temperature differences between the bulk of the frit and the panels created a bowing force which may have allowed some amount of bed settling at relatively low temperatures while particle thermal expansion was minimal. These panel deformations then became permanent when larger temperature changes in the capsule created stresses which exceeded yield. .. DISCLAIMER Portions-11-NET-1.2 PIE Report EXECUTIVE SUMMARYThe apparent failure of the hot frit in the NET-1.2 fuel element which was observed in the test series that occurred in June of 1993 in Sandia's Annular Core Research Reactor prompted the Space Nuclear Thermal Propulsion Program (SNTP) sponsor, the USAF Phillips Laboratory, to perform a minimal post irradiation examination (PIE). This PIE effort was intended to gather and evaluate data on the failure of the hot frit. That information could then be used by researchers to generate informed estimations regarding issues that could have bearing on the fuel element or experiment capsule design process (such as timing of the failure, modality of the fractures and reasons for the overstressed situations that led to failure).The NET-1.2 PIE activities occurred during the months of November and December 1993 in the Hot Cell Facility (HCF) at Sandia. Detailed disassembly procedures were developed to satisfy the safety concerns with the operation (i...