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A full and heterogeneous model of the ITER tokamak for comprehensive nuclear analyses


ITER is the flagship fusion project, conceived as an experiment to select and develop the technologies for the first demonstration reactor, DEMO. Nuclear analysis is a core discipline in support of the design, commissioning and operation of the machine. To date, it has been conducted with increasingly detailed partial models, which represented toroidal segments of the tokamak. However, the limitations of this methodology became evident as estimates of quantities relevant to design, safety and operation showed unquantifiable uncertainties, which is a risk. Here, we present a detailed and realistic 360° MCNP model of the ITER tokamak called E-lite. We demonstrate the model’s usability and practicality. Two examples are used to illustrate qualitatively and quantitatively how it solves previously intractable problems with marked benefits for the future nuclear analysis of ITER, with applications to DEMO and future reactors. E-lite constitutes a milestone in the field of nuclear analysis in terms of realism in the evaluation of key quantities.

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Fig. 1: E-lite model representing the 360° of the ITER tokamak.
Fig. 2: Description of the calibration exercise.
Fig. 3: Representation of the neutron flux computed with E-lite.
Fig. 4: Neutron flux impinging on the inner face of the bio-shield.

Data availability

Data and the model are the intellectual property of the ITER Organization. Data of the main text and the supplementary information will be made available upon reasonable request after the recipients confirm in writing that the purpose of obtaining the data is only to reproduce the results and after the recipients have signed and returned a non-disclosure agreement confirming that no part of the data will be distributed in any way. Data for the tritium breeding module ports will not be made available, as they are subject to additional intellectual property restrictions.

Code availability

The MCNP5 v.1.60 code2 is distributed by the Radiation Safety Information Computational Center (RSICC, Oak Ridge National Laboratory) under user licences, following the procedure provided online ( The D1SUNED v.3.1.4 code11, which is developed by UNED, is a proprietary patch-code to MCNP5 v.1.60. The code will be made available on reasonable request after the recipients confirm in writing that the purpose of obtaining the code is only to reproduce the results and after the recipients have signed and returned a non-disclosure agreement confirming that no part of the code will be distributed in any way.


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This work was carried out using an adaption of the C-model MCNP model that was developed as a collaborative effort between the Amec company (international), Culham Centre for Fusion Energy (United Kingdom), Frascati Research Centre of the National Agency for New Technologies, Energy and Sustainable Economic Development (Italy), FDS Team of the Institute of Nuclear Energy Safety Technology (People’s Republic of China), ITER Organization (France), Japan Atomic Energy Agency in Naka (Japan), National Distance Education University (UNED) (Spain), Fusion for Energy (Spain) and University of Wisconsin – Madison (United States). This work was performed under ITER contract IO/CT/13/6-141 between the ITER Organization and the consortium consisting of UNED and the IDOM Corporation. We appreciate the support given by MINECO for the funding of the Juan de la Cierva-incorporación 2016 programme and funding under I+D+i-Retos Investigación (project ENE2015-70733R), by the Comunidad de Madrid for funding under I+D en Tecnologías (TECHNOFUSIÓN (III)-CM, project S2018/EMT-4437), by the Escuela Técnica Superior de Ingenieros Industriales-UNED 2019 programme, and by UNED for funding of the predoctoral contract (Formación Personal Investigador). We thank L. Bertalot from the ITER Organization for his support and indications in relation to ITER neutron calibration. The views expressed in this publication are the sole responsibility of the authors and do not necessarily reflect the views of Fusion for Energy or of the ITER Organization. Neither of these institutions nor any person acting on their behalf is responsible for the use that might have been made of information in this publication. The content of this paper does not commit the ITER Organization to being a nuclear operator.

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Authors and Affiliations



R.J. and G.P., with M.J.L., E.P., R.P. and M.F., conceived the model. G.P. created the model with the support of P.M., M.D.P., J.A., A.J.L.-R. and A.K. R.J. and G.P. conceived the analysis, executed it with the support of P.S. and F.O., and interpreted the data with the support of M.J.L., R.P. and J.S.

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Correspondence to R. Juarez.

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The authors declare no competing interests.

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Peer review information Nature Energy thanks Paul Wilson, Yican Wu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–4, Table 1, discussion and references

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Juarez, R., Pedroche, G., Loughlin, M.J. et al. A full and heterogeneous model of the ITER tokamak for comprehensive nuclear analyses. Nat Energy 6, 150–157 (2021).

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