Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Ueki, Taro
Progress in Nuclear Energy, 159, p.104630_1 - 104630_9, 2023/05
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)In this work, the methodology of Generalized Extreme Value (GEV) is applied to criticality tallies in Monte Carlo fission source cycles in order to evaluate the utility value of the distribution tail ends. Numerical results obtained under a sufficiently large number of particles per cycle show that the extreme value index (EVI) in GEV falls within the range of Weibull distribution including the EVI of Gumbel distribution as the role of a boundary value layer. GEV is also applied to a historically-challenging loosely-coupled system for demonstrating population diagnosis under an insufficient number of particles per cycle. It turns out that the transition from one equilibrium to other equilibrium makes the EVIs of upper and lower distribution tail ends depart from each other so that one of them falls in the range of Weibull distribution and the other in that of Frechet distribution.
Ueki, Taro
no journal, ,
In the Monte Carlo criticality calculation of a loosely-coupled system, when the sampling from the fission source distribution (FSD) is conducted for small neutron population, the convergence of FSD toward stationarity occurs in an ill-conditioned manner and yields the biased estimate of the neutron effective multiplication factor (keff). This phenomenon is known as the keff-of-the-world problem and has been upgraded to a challenging problem under the current computing power. Based on this upgraded problem, the methodology of generalized extreme value statistics is shown to effectively detect the transition from one stationary FSD to other stationary FSD under small population size.
