Monte Carlo neutron-kinetics analysis in continuous time and energy

To get more insights into the neutron-kinetics processes with affordable cost in both computing time and storage and to provide other researches with the reference solution, a weighted Monte Carlo kinetics (wMCk) method has been derived, verified and employed to analyze neutron-kinetics processes in continuous-time and continuous-energy phase-spaces in this paper. Firstly, after deriving the integral form of neutron-kinetics equations, the integral expressions of the neutron and precursor densities can be obtained. To improve the computing efficiency, the wMCk method is formulated with no branch in all particle histories. A new tally formula has been derived to provide the spectra at user-specified timepoints. Secondly, a code named NECP-Dandi has been developed to simulate neutron-kinetics cases. The code is then verified by a series of test problems. Thirdly, neutron-kinetics processes caused by the nuclide-density perturbation or the initial-source distortion are analyzed to show the spectrum variation during the entire kinetics processes.