b'the order of 10-6) were used in the upper regions of the model where part-length rods would end. This workaround allows for MPACT and CTF to accurately predict power and temperature distributions, although the coolant flow patterns predicted in CTF are affected. Other features of BWRs are included in the models, such as cruciform control blades that are inserted from the bottom of the core and large water rods. A 2-D cross-section of a single fuel assembly model is shown in Figure 1 with key characteristics highlighted, including a quarter of a control blade. The different colored fuel pins indicate different levels of fuel enrichment and gadolinia content. Each fuel assembly in the mini-core model is identical to the one shown in Figure 1, but the control blade is located in the center of the 4x4 array of assemblies. Fast neutron flux and temperature distributions were obtained in the channel box for varying degrees of control blade insertion. Examples of the distributions are shown in Figures 2 and 3, which show the temperature and fast flux distributions in the single assembly model channel box with the control blade fully withdrawn Figure 4. Temperature and fastcontaining different fuel loadingand halfway inserted, respectively. neutron flux distributions in apatterns and gadolinia content, leadAdditionally, the temperature and fast control cell with the controlto nonuniform fast neutron fluxneutron flux is shown in Figure 4 for blade fully inserted. in the core. Multiple axial regionsa control cell (four fuel assemblies) with different fuel loading patternsfrom the mini-core model. Obtaining are able to be modeled in VERA-CS,these distributions under varying and the coupled codes predict voidoperating conditions is important fraction distributions representa- for informing deformation studies tive of real BWRs. Part-length rodthat will determine the feasibility of modeling is still under developmentusing SiC/SiC as a BWR channel box by CASL, but a workaround wasmaterial since too much deformation used in which extremely low fuelcould lead to interference with control density and enrichment (both onblades or stress-induced failures.164 2019|AFC ACCOMPLISHMENTS'