WORK DONE

2.2.1. First Research Coordination Meeting: 1–5 December 2008

The participants offered experimental data for comparison and made brief presentations of the available experimental data and respective facilities. Discussions were held on the need to develop templates for the facility specification, for the experiment description and for the data submission for comparison of results.

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Discussions continued during the meeting and culminated in the participants defining the final proposal for the template documents. The last sessions of the meeting were dedicated to finalizing the summary of conclusions and recommendations.

The research coordination meeting (RCM) resulted in the following conclusions and recommendations:

 The CSIs agreed to focus on the improvement of safety, operation and utilization of research reactors while selecting the relevant data sets. The meeting aimed to classify the available data from participants and identified areas where experimental data was lacking. In some cases, the available experimental data was very broad and therefore an appropriate subset was selected and prepared by the providers;

 The various presentations described the available data for experimental comparison in order to allow judgement by participants on the applicability and potential quality of the submissions. That information was used to finalize the action matrix with regard to the list of benchmarks available for calculations. Participants indicated in the action matrix the data sets they found applicable and in which they had interest in performing specific calculations;

 The participants agreed to provide, when possible, the available uncertainty data, along with the benchmark specifications, whether the uncertainties were obtained from experimental conditions, calculations, judgment or from published literature.

 The participants agreed that submissions, irrespective of the availability of uncertainty data, would be initially accepted and used;

 The completeness and clarity of benchmark specification was critical for successful implementation of the CRP. Neutronic and thermal-hydraulic working groups within the meeting produced template documents to facilitate both benchmark specification and the submission of results. Those templates were integrated, finalized and submitted to the IAEA for further distribution to participants. Participants from South African Nuclear Energy Corporation (Necsa) and Investigaciones Aplicadas (INVAP) agreed to coordinate the inputs from participants to finalize the template documents and distribute them through the dedicated website for the CRP;

 The benchmark specifications were subject to an internal review process, in which participants who intended to calculate the specific benchmark analysis reviewed and commented on the specification prior to its final submission to the IAEA. The quality and applicability of the experimental sets was also evaluated;

 The data supplied to this CRP was restricted for use only within the activities of the CRP, unless otherwise agreed by the data provider;

 The available experimental data was sufficient to conduct this CRP. However, it was recognised that the data does not contemplate areas like fuel management, depletion, hydraulic data (core input data), heat transfer data (steady state and transient), gamma flux, neutron beam line characterization, shielding, etc. Therefore, it was recommended that the IAEA consider an extension of the CRP, envisaging the possibility to find such data and/or to promote experiments to obtain it.

2.2.2. Second Research Coordination Meeting: 14–18 June 2010

The meeting included review by the IAEA representatives of the CRP objectives and the expected results, the status of the relevant research contracts and agreements, and assessment of the results obtained to date in comparison with the CRP objectives.

5 The participants discussed the validity of the available computer codes for the prediction of specific phenomena and parameters, modelling approaches for various cases, and assumptions and approximations used in the calculations, as well as a preliminary comparison of the results.

The meeting also included presentations on the new experimental data provided to the CRP and were followed by the discussions to define the additional data needed for modelling and to revise the templates for results submission. It was agreed that the results of the CRP would be published in two separate IAEA documents. The first one dedicated to the description of the available experimental data, while the second dedicated to the detailed benchmarking results and the conclusions.

The individual participants progress reports, presentations and the associated discussions made by the participants during the second RCM on the status of their research contracts agreements showed that most of the tasks included in the individual work plans had been completed. The available sets of data covered different physical phenomena that was of concern for research reactor safety analysis, operation and utilization. The lack of uncertainty data associated with the experiment and measurement conditions was raised again as that data was vital for benchmarking analysis.

The thermal-hydraulic models and codes, including selection of appropriate correlations for prediction of different critical phenomena, involve larger uncertainties when compared to the codes used for neutronics modelling. In this regard, the CRP participants were encouraged to continue investigating the limitations of the thermal-hydraulic codes being benchmarked in this CRP for checking their validity for research reactor analysis.

The meeting recommended that in cases where multiple participants used the same codes for the same benchmarks, the most appropriate model parameters were to be distributed to all interested participants. These models could be run on a specific version of common codes to remove additional ambiguities. These benchmarks are also useful to evaluate the user effect influence which was one of the identified outputs of this CRP. In addition, a review process was incorporated into the CRP to assess the results obtained from all benchmark calculations, including identification of the discrepancies, their sources, and to suggest ways for further improvements.

The meeting recommended that since the work within this CRP involved application and analysis of methods and approaches (established and/or under development), the obtained results would be communicated to the code developers for further evaluation of the limitation of the codes.

2.2.3. Third Research Coordination Meeting: 5–9 December 2011

In addition to the CRP participants, this meeting was also attended by the Nuclear Engergy Agency (NEA)/ Organization for Economics Cooperation and Development (OECD). A technical visit was also organized to the construction sites of Jules Horowitz research Reactor and International Thermonuclear Experimental Reactor at Commissariat à L’Energie Atomique (CEA) Cadarache centre, France.

The meeting included several presentations from invited experts and observers. Topics included an overview of a set of tools developed by the NEA/OECD for describing, searching and analysing reactor neutronics benchmarks, an overview of the analysis performed following the Fukushima accident and various code systems and approaches used by the participants. The following was a summary of discussion:

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 The participants were requested to formulate preliminary technical conclusions based on analyses performed;

 The possibility to identify certain benchmarks as high quality reference benchmarks and as such include more extensive calculation data for future comparison was discussed;

 The need for establishing a database of thermal-hydraulic benchmark analysis, similar to that which existed at the NEA/OECD for criticality and reactor physics benchmark analysis, was highlighted.

Further activities during the meeting focussed on the review and finalization of important draft documents such as the two IAEA publications, as well as results templates needed for submission of benchmark results.

The status of facility and experiment descriptions (benchmark specifications) were reviewed and final comments and clarifications were gathered prior to drafting the first IAEA publication.

In addition, the following conclusions were drawn by participants:

 The CRP was helpful to the research reactor community and had provided a set of data and results which were clearly missing from literature;

 The various benchmark analysis had been challenging and had provided opportunity for good practice and lessons learned. Although the CRP had achieved a great deal in gathering relevant benchmarks and perform preliminary analysis on all of these, it was noted that interaction between neutronics and thermal-hydraulics components of benchmarks was still not optimal. In most cases these disciplines were treated rather independently and suggestions for improvement included either coupled calculations, or at least coupled approaches by neutronic and thermal-hydraulic analysts;

 The comparison planned within this CRP between individual submissions by the participants and joint benchmarking efforts was an added value of this CRP in terms of evaluating both user effects and models used in the codes employed;

 It was strongly recommended to include input models, i.e. input files, in the final publication (at least electronically) so that the intended users could build upon the lessons learned;

 The benchmarks performed in the CRP showed that static multi-dimensional neutronics, with point kinetics and multi-channel thermal-hydraulics was a commonly used approach for the reactor problems in benchmark analysis. 3D time-dependent solutions could be evaluated for selected transients to define the added value of such detailed modelling;

 The benchmarks performed also showed that neutronics modelling had proven to be reasonably accurate; obtaining good agreement for thermal-hydraulics analysis was more challenging as similar problems were experienced by many of the users.

2.2.4. Fourth Research Coordination Meeting: 17–21 December 2012

The meeting participants were informed by the IAEA representatives about the status of the first publication of the CRP. The participants discussed the consolidated results and made observations and comments regarding the capabilities of the various codes to provide reliable predictions of the experimental data. During the discussions there were possible explanations on the causes for the observed discrepancies. This assisted the participants to elaborate on follow-up activities necessary to optimize the outcome of the results consolidation for the

7 benefit of the research reactor community and prepare inputs for the second publication of the CRP (i.e. the present publication).

Further activities were focussed on the review and finalizsation of the consolidated results. The following were the highlighted:

 The distribution of ‘best’ input models for various benchmarks would be shared amongst participants at the end of the CRP;

 The user effect was identified as a major origin among code-to-code discrepancies. It was concluded that certain input parameters and nodalization methods affect significantly the results provided by the codes;

 The coupling between neutronics and thermal-hydraulics via the kinetic parameters and feedback coefficients seemed to be the major contributor to discrepancies between experimental measurements and codes estimates. It was recommended that harmonization efforts were to be made to improve the results of the models;

 The potential ways to reduce user effects were suggested by the participants. Among others, sensitivity analysis and adequate training through code benchmarking were the most prevalent.

The participants were informed that the second phase of this CRP was initiated by IAEA focusing on fuel burn-up and material activation.

Meeting participants suggested that the database and the benchmarking effort during the CRP would be made widely known throughout the research reactor community. Continuation of the benchmarking effort will be encouraged, and if there exist enough interested participants the IAEA was committed to organize and host a technical meeting to discuss the updated results.

Given the scope of this CRP, which includes eight benchmark analysis (with at least three experiments each) covering broad subjects related to research reactor safety, operation and utilization, the participants were informed of the status of the first publication of the CRP results (i.e. Ref. [1]).