Nea Committee on Reactor Physics Reactor Physics Activities in Nea Member Countries

The only significant development of the AUS system has been an extension.of the available cross-sections. That portion of the ENDF/B V data files which is unrestricted has been acquired from the IAEA Nuclear Data Section and the data processed for the AUS.ENDF2006 group library as required. In particular, a large set of fission product data has been processtid, sufficient for calculations of both reactivity effects and fission product inventories. Some limited tests of the revised fission product data have been made in applications to heat generation in nuclear fuel waste and to the AAFX's research reactor HIFAR. Only minor differences from results using gDF/B IV data were noted. Strategy A neutronics study c&the conversion of HIFAR to the use of fuel with 20% 235u enrichment (LEU) was completed. Earlier studies had established the 235U loading required to match the fuel element consumption rate obtained with HEU fuel and the effect on performance of using this fuel. The current study was mainly concerned with the effect of varying the 235U loading to establish the most appropriate performance/economics compromise for use of LEU U.?Siz-Al fuel in HIFAR. The study established the fuel consumption rates to be expected for a range of rig burdens and the effects on radioisotope production and neutron beam facilities. The neutronics models used had been previously established in studies such as those described in NRACRP-L 273. Fuel element power peaking and reactivity swing over a fuel cycle were also investigated. It was concluded that an increase in 255U loading and reactor power was the preferred option. The result of these performance and fuel-cycle cost studies for a range of possible LEU conveI%ion options and operational modes for HIFAR were used in developing recommenda,tions on conversion strategy to low enrichment fuel. 5 2.2 Low Enrichment Fuel in HIFAR : Consequences for Irradiation Facilities~ Although fuel cycle, reactivity and safety aspects of research reactor conversion to operation with LEU fuel of <20% 235U enrichment have been very extensively studied in many centres, the influence of the conversion on the experimental facilities and services provided by the reactors has received little detailed examination. Reactor neutronics calculations which specifically model the HIFAR production on facilities for some commercially important radioisotopes were undertaken. The following three radioisotope production reactions, routinely used in HIFAR. in-core hollow fuel element (HFE) irradiation facilities, were selected for study: (i) "MO production by (n,y) reaction in natural MOO) …