1. Extented scope and objectives Not only focused on Monte Carlo difficulties and issues Focused on tools/codes and associated methodologies to support criticality safety studies/assessment The goal of this Expert Group could be to transfer knowledge on new stochastic techniques to criticality safety practitioners EG title: EG on Advanced Stochastic Simulations and Modelizations Or The goal of this Expert Group could be to transfer knowledge on methodologies implemented in codes to criticality safety practitioners EG title: EG on Criticality Codes and Associated Methodologies Proposed modifications to mandate and discussion EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

2. This Expert Group shall: Survey recent advances in the development of new stochastic techniques (including Monte Carlo) for criticality analysis codes. Identify new techniques as high-priority for further detailed study, and solicit EG members to investigate each technique. For each selected technique, designated EG members will review the methodology, survey the literature, assess the verification/validation status, possibly establish benchmark tests that could be used by EG member Monte Carlo codes, and suggest guidelines for applying the new techniques to problems of importance to practitioners. Draft recommendations to practitioners for using the improved methodology in their work, and to guide its employment. Review of mandate, proposed modifications to mandate and discussion EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

3. The activities of the Expert Group could be selected from (but are not limited to) the following list: Analysis of sub-critical experiments. Transient suppression (ie, convergence acceleration). Convergence of adjoint calculations for criticality. Under-prediction of statistical uncertainties for tallies. Uncertainties propagation with Monte Carlo codes Surrogate based techniques Algorithm-assisted assessment in criticality safety (Mathematical methods to identify penalysing parameters and their range that guaranty sub-criticality of systems…) Optimizations Uses of Metamodels Tools to support evaluation of the hazard in CSA Random geometry (particles in solution, TRISO fuel, etc.). Geometric perturbations (eg, tolerances, absorber reactivity worth, ...). Monte Carlo perturbation theory - review methodology and, if necessary, revisit benchmarks. Monte Carlo depletion - (Burn-up credit) methodology, approximations, review, benchmark. Review of mandate, proposed modifications to mandate and discussion EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

4. Algorithm-assisted assessment in criticality safety: example EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

5. Algorithm-assisted assessment in criticality safety: example EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

6. Status The group takes part in the WPNCS => activities should be focused on Criticality “Draft recommendations to practitioners for using the improved methodology in their work, and to guide its employment” => find a way to have a more important participation of practitioners Different codes and tools used to perform CSA CS studies are mainly perform with MC codes - but not only New MC devts often performed for reactor applications. Not for criticality Different practices/learning in different countries Different codes sequences: deterministic(generation of homogenized MG constant/Self shield.) - MC, deterministic(standards), depletion-MC, depletion-deterministic… New techniques to improve MC issues are often only available in codes developments versions (not available for standard users)=> difficult for “standard users” to participate to benchmarks By experience it is today difficult to maintain activities for a group only focus on MC codes usage (for criticality issues)=> more difficulties to maintain 2 groups => extend scope of the group => activities towards users => gather developers and users contributions & points of view Scope: Criticality codes and their best practices to assist CS studies Review of mandate, proposed modifications to mandate and discussion EGAMCT meeting sept, 2012 J. Miss NEA WPNCS

7. Identification/proposal of first studies and deliverables: Parametric benchmarking on Monte Carlo depletion convergence (IRSN will collect contributions) State of the art report on codes and methodologies to support CS studies(based for example on one simple benchmark from the EGSC phase 1 report ?) Obviously MC codes but also other sequences/approaches used in the different countries. How to treat the geometry (with or without homogeneization) => pure Monte Carlo or hybrid deterministic-MC or mixed fixed source – eigenvalue MC (CAAST…)? How many energy groups if deterministic calculations (group structure)? How to treat self-shielding issues (Dancof factors…)? Which methods to manage the Monte Carlo transient? Which statistical test to check Monte Carlo convergence calculations? How to use their results => Is it interesting to apply them on one or several keff estimators? How to calculate criticality standards: by using MC, deterministic, mixed(det-MC) calculations? … Scope: Codes and their best practices to assist CS studies Define clear and simple deliverables Review of mandate, proposed modifications to mandate and discussion EGAMCT meeting sept, 2012 J. Miss NEA WPNCS