Projects / Programmes
Neutron calculations for use with neutron diagnostics - application to the JET fusion reactor
| Code |
Science |
Field |
Subfield |
| 2.03.02 |
Engineering sciences and technologies |
Energy engineering |
Fuels and energy conversion technology |
| Code |
Science |
Field |
| T160 |
Technological sciences |
Nuclear engineering and technology |
| Code |
Science |
Field |
| 2.02 |
Engineering and Technology |
Electrical engineering, Electronic engineering, Information engineering |
Fusion, JET, Joint European Torus, neutron diagnostics, fusion reactor, low carbon energy sources, sustainable energy, Monte Carlo neutron transport, Monte Carlo variance reduction
Researchers (13)
Organisations (2)
Abstract
The Joint European Torus - JET is currently the largest and most powerful magnetic containment fusion device to study nuclear fusion. JET started operation in 1983; its configuration did since then continuously evolve due to upgrades and addition of new components. The most comprehensive upgrade of the torus so far was made in 2010, when the carbon first wall was replaced with an ITER-like wall, made of graphite, tungsten and beryllium.
The only calibration of neutron detector systems with a 252Cf neutron source was at JET performed before the start-up of the reactor in 1983. Only the KN1 system, i.e. fission cells in the exterior of the torus, were calibrated at that time. The remaining systems were only cross-calibrated with respect to KN1. A recalibration with a neutron source, located inside the tokamak vacuum vessel, is at JET scheduled again for December 2012.
Upgrades of the JET torus affect the neutron field and hence the calibration factors for individual neutron detection systems. The most problematic is the calibration of KN1 fission cells, which are located in the exterior of the torus. During the first calibration of JET, its surrounding was relatively empty. Later a lot of experimental equipment has, however, accumulated there, especially in the space around KN1.
It is therefore imperative to understand the response of detectors with the help of calculations. Accurate knowledge of detector response due to the neutron yield in the plasma is particularly important, since experimental calibrations of detector systems with neutron sources are in tokamaks performed very rarely; the torus configuration is, however, constantly upgraded and does change.
The project is aimed at a comprehensive analysis of neutron diagnostics for the example of the JET fusion reactor. A lot of experimental data exists at JET which is unique, since JET is the worlds largest such facility. A complete evaluation of this information was not yet performed in terms of their comparison with calculations for each past configuration of the torus and with results of the initial calibration. The change due to the latest upgrade of the torus in 2010 will be specifically analyzed. The recalibration in 2012 offers a unique opportunity to compare the computational results with data, obtained with a well characterized source. This will be a rare opportunity for evaluation and validation of the calculation results.
Within the project we will pursue the understanding of the calibration factors for the three different diagnostic systems at JET. Due to the small size of the detectors with respect to the size of the tokamak, variance reduction techniques will have to be used in order to speed up calculations and to reduce the statistical errors. Type and method of the variance reduction techniques is highly dependent on the problem addressed.
The ability to compare calculations with experimental results and the cooperation with experimenters in such a complex device, as the JET tokamak, is invaluable to acquire new skills which can not be obtained with theoretical work at the home institution.
The applicant for the project leader have been for many years working with the group for neutron diagnostics at JET, and I have lead, or am leading, projects for Monte Carlo transport calculations for JET . The proposed project team has access to all relevant information at JET. The proposed project also includes all necessary topics for a comprehensive understanding of the neutron transport in large tokamaks (like JET) including their detection, for which all our experience, gained so far, will be used. We will choose and use appropriate methods for variance reduction which will be verified through comparison with measurements. The results will be useful also for other tokamaks and similar devices. The knowledge and experience gained during this project will also be used to calculate neutron transport in fission reactors.
Significance for science
For a successful operation of the JET Tokamak excellent diagnostics and the related correct determination of the fusion power are necessary, as the operating conditions of the JET torus are connected to it. A successful evaluation of the calibration data was therefore important both from the scientific and applicable point of view. We confirmed the assumption that it is possible to reduce the degree of uncertainty of calibration to the level below 10%. At the same time the difficulty of comparison with the numerical results was evident. We namely compared 250 individual measurements for four different detectors, of which three were in outside of the torus and thus highly dependent on the slowing down and attenuation of the neutron flux. It turned out that the existing computational capabilities reach its limits for a successful description of the experimental data. The mentioned findings will make an important contribution to the planned calibration with a DT source at JET and at ITER. The obtained data will be particularly important for a similar planned calibration on the future reactor ITER, which will be, due to its much higher fusion power, licensed under the more stringent regulations. The uncertainty of calibration, and thus the absolute fusion power, must not exceed 10%. The calibration, carried out at JET, is expected to be the last one before the more demanding calibration at ITER. Members of the project team are in contact with researchers from ITER for cooperation and share of experience. We have developed a method, by which we upgraded the MCNP model, which had previously consisted of an sector of only 90° of the torus and was suitable for calculations with a circular-symmetrical plasma source, but not for the much less frequent calculations with a point source, as during the calibration. The problem was solved by modifying the MCNP source code and we effectively acquired the ability to trace particles, as if transported in 360 °geometry. The approach was then used for the much more sophisticated model of the future ITER reactor, and it is now the only method for similar calculations for ITER, supported also by the administrator of the ITER model. We tested different techniques for variance reduction and concluded that the use of energy-dependent weight windows is most suitable for such complex systems, as the JET torus. The most suitable is the FENDL 3.0 library. Comparisons of experimental and calculated values will serve as benchmark experiments in the areas of shielding and fusion neutronics.
Significance for the country
The offer to participate in such an important project is a recognition for Slovenian scientists and the successful completion did pave us the way to future projects and expansion of our work in the wider field of fusion. JET torus is currently the largest operational fusion experiment and during the work we constantly faced and cooperated with the most renowned experts in the field of neutronics for fusion reactors. The experience gained will be passed to the following generations of Slovenian researchers through lectures and mentoring. Through the successful cooperation we have paved the way for the acquisition of additional projects in the field of transport calculations for fusion reactors, primarily in the continuation of existing work on the largest project for JET so far, which was launched by the new organization EuroFusion, namely "Activities for the DT calibration for JET" for the years 2014-2018. Within the framework of the project we cover the same responsibilities, as we have so far, in addition our work has expanded. In this way, the presence of Slovenian researchers at JET continued and expanded. In 2014 two young researchers, whose mentors participated in the current project, visited jet and successfully joined the work. The project leader has, also on the basis of successful work for JET, in 2015 obtained the leadership on two sub-projects for the Radial Neutron Camera project for the future fusion reactor ITER; the scope of work is similar then for JET. We also participate in the work for a future demonstration fusion power plant DEMO, with a project entitled "Tritium breeding ratio assessment." International connections on such a level have a significant impact on the Slovenian scientist’s access to knowledge in the field of fusion reactor neutronics at the highest level. The focus of the current project were transport calculations for the purposes of neutron diagnostics. A very similar problem is encountered also in the work for the fission reactor in the Krško Nuclear Power Plant. The possibilities for the implementation of experiments at NEK are very limited or non-existent, as it is a fully commercial type of reactor, unlike JET. Each experience acquired elsewhere is therefore welcome. The accomplished knowledge in the field of neutron diagnostics can be used in current and future projects for the Krško NPP, with which nuclear safety will increase. The choice of nuclear data libraries significantly contributes to the quality of each transport calculation. A collaborator on the project, Andrej Trkov, finished his work on the project early, since also due to his successful cooperation at JET, he received a high position at the IAEA - Nuclear Data Section, as a trustee for some of the most important data libraries. Through this link, Slovenian researchers have a direct access to the latest libraries and high-quality advice on their use.
Most important scientific results
Annual report
2013,
2014,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2013,
2014,
final report,
complete report on dLib.si
