Abstract and subjects
The 'K-effective of the World' problem was introduced nearly 30 years ago by G. E. Whitesides [1]. The general theme was to caution Monte Carlo code users that, despite the sophistication of the codes for representing realistic geometry and physics interactions, correct results can be obtained only if users pay attention to source convergence in the Monte Carlo iterations and to running a sufficient number of neutron histories to adequately sample all significant regions of the problem. From [1]: The extreme example, which defines a situation in which this difficulty can exist, is the 'k-effective of the World' problem. That is, if one attempts to calculate the k(eff) of the world using a Monte Carlo calculation, what k(eff) would be computed assuming that there are several critical assemblies located around the world? The answer would likely be the k(eff) of the world with no critical assemblies present. The cause of the erroneous result is the fact that the volume of fissile material in the world would be so large relative to the volume of fissile material in the critical assemblies that most commonly used forms of sampling would almost never 'see'the critical assemblies. Hence, this would not reflect their existence in the computed keff...The erroneous results for these types of problems are the result of the failure of the calculation to converge the source to the fundamental source mode.