4. Monte Carlo method applied to reactor physics

The Monte-Carlo probabilistic approach simulates "reality" on a microscopic scale, and traces it back to macroscopic quantities: neutrons are tracked individually, and the events considered are the interactions to which they give rise with the various atomic nuclei that make up the medium through which they pass: diffusions, captures, fissions, (n, 2n) reactions, etc. This sequence of events is referred to as the "story". This sequence of events is referred to as a history. By calculating enough neutron histories, we can quantify the macroscopic physical quantity of interest. The population of neutrons in the core of a PWR in normal operation present at a given instant is some 10 ¹⁵ . Current technology does not yet allow this many particles to be processed. With a representative sample of one billion (10 ⁹ ...