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

Abstract

This paper presents a nuclear data sensitivity and uncertainty analysis of the effective delayed neutron fraction b eff for critical and subcritical cores of the MYRRHA reactor using the continuous-energy Monte Carlo N-Particle transport code MCNP. The b eff sensitivities are calculated by the modified k-ratio method proposed by Chiba. Comparing the b eff 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 b eff . Using the calculated b eff sensitivities and the JENDL-4.0u covariance data, the b eff 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 239 Pu and 238 U. *

Simulation of the Measured Reactivity Distributions in the Subcritical MYRRHA Reactor

“…Figure 5 presents the flowchart of the developed method. -320 [33] 0.95944 ± 0.00018 - [34] system, the reference values of kkcode and βeff obtained in MCNP6.2 modeling are 0.956 0.00002 and 335.0 ± 2.0 pcm (percent mille, one-thousandth of a percent), respectiv These values are quite close to those published by other authors, especially by Romo et al [31]; see Table 1. The obtained kkcode and βeff values were fixed for further evalua of differences (Δ = kexp − kkcode), which are considered to be the final result.…”