Sensitivity and uncertainty analysis of betaeff for MYRRHA using a Monte Carlo technique

This paper presents a nuclear data sensitivity and uncertainty analysis of the effective delayed neutron fraction betaeff for critical and subcritical cores of the MYRRHA reactor using the continuous-energy Monte Carlo N-Particle transport code MCNP. The betaeff sensitivities are calculated by the modified k-ratio method proposed by Chiba. Comparing the betaeff sensitivities obtained with different scaling factors a introduced by Chiba shows that a value of a=20 is the most suitable for the uncertainty quantification of betaeff. Using the calculated betaeff sensitivities and the JENDL-4.0u covariance data, the betaeff uncertainties for the critical and subcritical cores are determined to be 2.2±0.2% and 2.0±0.2%, respectively, which are dominated by delayed neutron yield of 239Pu and 238U.