Reactor physics - Cross sections modeling and evaluation

This article is the first part of a two part review presenting the nuclear data evaluation process. It describes the present state of the theoretical knowledge of the nuclear physics processes involved in reactor physics. During the evaluation process, the theoretical and experimental knowledge is distilled and synthesized into the files used by simulation codes. After an overview of the content of the evaluated files, the different methods used for nuclear data evaluation are described. We will mainly focus on modeling. This review is illustrated by examples chosen from everyday practice of nuclear data evaluation