Neutronic analysis for the fission Mo-99 production by irradiation of a LEU target at RECH-1 reactor

For the purpose of developing the capability to produce fission Mo, the Chilean Nuclear Energy Commission is participating in the IAEA Coordinated Research Project: “Developing Techniques for Small Scale Indigenous Mo-99 Production using LEU Fission or Neutron Activation”. Fission Mo will be produced irradiating, at RECH-1 reactor, a target made of a LEU metallic uranium foil held between two concentric aluminum tubes. KAERI will provide the LEU foil. Neutronic calculations were performed to estimate the fission products activity for a 13 grams LEU foil annular target, which will be irradiated at the level power of 5 MW during 48 hours. 1.Introduction The RECH-1 research reactor is a pool type reactor with a nominal thermal power of 5 MW. This reactor is operated by the Chilean Nuclear Energy Commission (CCHEN) at La Reina Nuclear Center. The RECH-1 is a light water-moderated, water-cooled and beryllium-reflected reactor and it employs a flat plate MTR-type fuel with low enriched uranium. Six blade-plates control absorbers pass through the core in three groups of two. The present core configuration of the RECH-1 reactor, No 62 (Fig. 1), has 32 LEU fuel elements containing U3Si2-Al. These LEU fuel elements were built by the Chilean Fuel Fabrication Plant with a uranium density of 3.4 g/cm [1]. The technical specifications of these fuel elements were developed by the Chilean Manufacturer based on the original HEU assembly and approved by the reactor operator. 2.Description of the preliminary target irradiation system The preliminary target irradiation system is formed by a LEU (19.75% of U) metallic uranium foil of 13 grams of 50 mm x 100 mm and 130 microns of thickness wrapped in a thin nickel fission product-recoil barrier of 15 microns thickness. KAERI will provide the LEU foil. The metallic uranium foil with its nickel coating surrounds an aluminum tube of 152 mm in length, 27.99 mm outer diameter and 26.42 mm inner diameter. This inner tube has an undercut to position the foil. This set, as well, is surrounded by an aluminum tube of 28.22 mm inner diameter, 30.15 mm outer diameter and 152 mm in length. Outer and inner cylinders are swaged to give good thermal contact. By means of a tool specially designed, the inner tube is become deformed to produce a good contact between the different materials that constitute the target. The design of the target irradiation system was done to maximize the target heat dissipation by the coolant flow inside the target. The Fig. 2 shows the preliminary target irradiation system [2]. J. Medel and G. Torres 2 1 2 3 4 5 6 7 8 9 10 G Bk Be Be Be Be Be Be Be Be Bk F Bk Al LR60 4.183 LR61 5.143 LR56 6.691 LR57 6.791 LR62 5.153 LR63 4.198 Al LREX1 E Be LR53 5.359 LR51 7.632 LR45 15.936 LR01L 41.110 LR02L 41.882 LR46 16.543 LR50 7.880 LR55 5.447 Be D Al Be LR47 9.567 LR41 20.744 CI CI LR42 21.833 LR48 10.310 Be Al C Be LR52 5.352 LR49 7.177 LR44 15.703 LR03L 37.931 LR04L 37.837 LR43 16.755 LR82 7.710 LR54 5.644 Be B Be Be LR66 3.974 LR67 4.610 LR58 5.863 LR59 6.145 LR64 4.721 LR65 4.399 Be Be A R 11/8” Al Be Be CI CI Be Be TI Be H Al Bk R 1 1⁄2” CI PIBM PIBM CI Pb Pb Al Fn Fig. 1.Present core configuration, No 62, of the RECH-1 reactor with the average burnup, in percent, at beginning of cycle (BOC) for each fuel element 3.Neutronic and activity calculations The neutronic calculations were performed using WIMS-D [3], [4], [5] and CITATION [6] codes, neutronic programs used routinely in the fuel management of this reactor. Different cell models were needed to generate appropriate cross sections for the various reactor regions in structures of three and five energy groups. The WIMS-D code was used to generate the multigroup nuclear constants library for different regions as a function of burnup. The main transport calculation was performed in 20 and 36 energy groups, condensing to 5 and 3 groups respectively for the diffusion theory calculations in two and three dimensions (Table 1). Fig. 2.Preliminary target irradiation system Proyecto M o de fis ión C onjun to Irrad iación de blancos