Nuclear data-induced uncertainty of k_eff using highly-enriched uranium at Kyoto University critical assembly

To evaluate the validation of the k_eff in the experimental analysis at the Kyoto University Critical Assembly (KUCA), the modeling of the core configuration is examined in the comparison of measured and calculated reactivities, as well as, the uncertainty induced by nuclear data and originated from the manufacturing variation in highly-enriched uranium (HEU) plates. For the evaluation of k_eff, eigenvalue calculation by MCNP6.1 and Scale-6.2/Keno-Vi are performed to obtain the calculation bias in k_eff values. With the use of standard model with averaged values of the core materials, calculation bias shows about 350 pcm in EE-1 core and about 600 pcm in E-3 core with the dependence on the spectrum. Further, the uncertainty induced by the nuclear data indicates about 1000 pcm in the k_eff evaluation with the variation of the control rod position and the core spectrum. In the breakdown of the uncertainty induced by the nuclear data, the impact of ²³⁵U shows significantly dominant for over 90% in EE-1 and E-3 cores. For the manufacturing variation of HEU plates, the uncertainty is evaluated for of the enrichment, length of the plates and thickness as around 10%, 5%, and 10%, respectively. Accordingly, the uncertainty of the nuclear data is considered dominant on the k_eff evaluation in the experimental analysis at KUCA. (Author)