Since the early 2000s there is an increasing demand from nuclear research, industry, safety and regulation for best-estimate predictions to be provided with their confidence bounds. Consequently, an in-depth discussion on uncertainty analysis in modelling was organised at the June 2005 Nuclear Science Committee (NSC) meeting of the Nuclear Energy Agency (NEA). Furthermore, discussions were held at the 2005 International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C) in Avignon and the Washington American Nuclear Society (ANS) meetings. A workshop on uncertainty analysis in modelling (UAM) was held in April 2006 at the University of Pisa, Italy, to define future actions and a programme of work. This resulted in the endorsement of the NEA Expert Group on Uncertainty Analysis in Modelling (EGUAM) under the auspices of the Working Party on Scientific Issues in Reactor Systems (WPRS) by the NSC at its June 2006 meeting.
This report summarises the final results of Phase I, which consists of exercises at the three different scales of pin cell, fuel pin lattice, and reactor core with the aim of examining the propagation of neutronics uncertainties from small to full scale modelling. Altogether, 48 results were submitted by 20 organisations, from 12 countries. This extraordinarily large participation reflects the success of the benchmark activity in creating a community of practice that has advanced uncertainty analysis and modelling methods, fulfilling the initial purpose to share best practices and lessons learnt throughout the course of the activity. This report on the Phase 1 results provides important insights into best practices in the domain of uncertainty analysis, and provides important feedback to the nuclear data community in its burgeoning efforts to improve and complement uncertainty information in the nuclear data evaluations.