Projects / Programmes
Development of methodology for calibration of neutron detectors with a 14.1 MeV neutron generator - JET fusion reactor case
| Code |
Science |
Field |
Subfield |
| 2.03.00 |
Engineering sciences and technologies |
Energy engineering |
|
| Code |
Science |
Field |
| T160 |
Technological sciences |
Nuclear engineering and technology |
| Code |
Science |
Field |
| 2.03 |
Engineering and Technology |
Mechanical engineering |
Fusion, JET, Joint European Torus, fusion reactor, low carbon energy sources, sustainable energy, calibration of neutron detectors, stochastic neutron transport methods
Researchers (16)
Organisations (2)
Abstract
Joint European torus (JET), presently the world's largest magnetic confinement nuclear fusion research facility, has gone under major refurbishment in 2009 and started operating with the new configuration in 2011. The major change was the replacement of reactor Carbon wallwith the ITER-like wall (ILW) made of Beryllium, Tungsten and Carbon. This significantly affects the neutron yield measurements which are the basis for the determination of the absolute fusion reaction rate and the operational monitoring with respect to the neutron budget during any campaign.
After refurbishment, we calibrated the two main systems which carry the JET calibration, i.e. the external Fission Chamber detectors and the Activation System. This was the first direct calibration of the Activation system in JET. We used the existing JET remote-handling system to deploy the Cf-252 neutron source and developed the compatible tooling and systems necessary to ensure safe and efficient deployment in these cases.
Extrapolation to 14 MeV neutron energy would lead to larger uncertainties, which would demand the adoption of large safety margins in the consumption of the available neutron budget. In order to fully exploit the nominal neutron budget available and to obtain a full scientific return for the investment in the DT campaign at JET, an accurate calibration at 14 MeV neutron energy is needed.
The 14 MeV neutron calibration would serve also as a benchmark for the calibration procedure envisaged for ITER, where a large DT neutron generator remotely moved inside the plasma chamber will be used, similarly to what will be done at JET. ITER is presently designing and optimising the calibration procedure in order to reduce the uncertainty to unprecedented low values ((10 %) required for accurate tritium accountancy. The JET calibration would provide a valuable validation of the ITER’s strategy and an assessment of the sources of uncertainties.
The calibration will be carried out with a 14 MeV neutron generator (NG) with suitable intensity (≈5×10E8 n/s). The NG intensity and energy spectrum of neutron emission will have to be accurately pre-characterized at different emission angles.
In order to significantly improve the accuracy of the calibration, a whole suite of calculations is required to support the JET neutron calibration project. Due to complex geometry of the fusion device and asymmetrical structure, the only reasonable method to be used for neutron transport calculation is the Monte Carlo method. As the detectors are very small compared to the tokamak, various Monte Carlo variance reduction techniques should be used to speed up the calculations and reduce the statistical uncertainty of the calculated result. The type of method and the way the method is used, strongly depend on the type of problems under investigation, hence it is essential to verify the calculated results by comparison with benchmark experiments.
The scope of the project is to develop computational model of the JET tokamak, to choose and apply appropriate Monte Carlo variance reduction calculational methods, verify them by comparing the experimental values and use the calculations to support the calibration. Calculations will support the calibration process by evaluating all possible sources of errors, uncertainties and biases. This will then allow application of appropriate correction to the measurements, which will significantly improve the accuracy of the neutron yield measurements at JET. The results will also be useful for other tokamak reactors. Moreover, in the future the knowledge and experience gained in the project can be applied to neutron transport calculations in fission reactors.
Significance for science
The continuation of JET tokamak operation will depend, among other conditions, on reliable measurements of the neutron yield, which must be within operational limits. All scientific projects require precise neutron yield measurements for the characterization of individual pulses. The verification of the neutron yield measurements is therefore of high importance for future operation in D-D and D-T modes. The utilization of experimental and computational methods which we have developed, and their future development, will apply to the planned operation in D-T mode in 2020 and will strongly contribute to the planning of future JET activities. Understanding the process of neutron yield measurement and expanding the knowledge is highly important for the future ITER fusion reactor, in which the methods used for the calibration of neutron detectors are to be finally defined. Accurate knowledge of the fusion power of the reactor, attainable only through neutron measurements, is crucial for the approval of the operating license for the fusion device. Neutron measurements serve as a basis for the determination of the consumption of tritium fuel, and consequently also the quantity of tritium remaining in the walls of the reactor vessel. This quantity represents one of the most important operational limits of the reactor for the radiation protection standpoint, as in the case of a severe accident the remaining tritium could be released to the environment. The quantity of remaining tritium in the vessel must be known with an uncertainty of less or equal to 10 %, which translates into the requirement that the precision in the neutron detector calibration should be to within 10 %. The methodology developed in the course of the research project has demonstrated that a precision to within 10 % in the neutron detector calibration is attainable. This is an important result, which will strongly affect the development of nuclear fusion as a sustainable and environmentally friendly source of energy in the future. Additionally, the evaluated experiment results will serve as a benchmark for the verification and validation of computational methods and nuclear data in fusion devices and other similar systems, as classical fission reactors, in which similar materials and neutron detectors are employed. We will make use of the benchmark for the verification and validation of Monte Carlo computational methods and variance reduction techniques and nuclear data libraries. It will be possible at a later stage to make use of the developed methodology in other fusion reactor as ITER, DEMO, etc.
Significance for the country
The collaboration with the Joint European Torus (JET), the largest research fusion device in the world, has granted Slovenia with access to state-of-the-art knowledge in the field of fusion technology, which will increase Slovenia’s involvement in European research projects. Slovenian researchers who have worked on the research project have collaborated with the greatest scientists in the field of Physics, experimental and computational techniques, and have greatly enriched their knowledge. Knowledge gained in neutron detection and neutron transport calculations will be passed on to Slovenian scientists and students, which is crucial for sustaining and improving nuclear science in Slovenia. The opportunity of collaboration in a project of such a large scale represents an important recognition for Slovenian science and a favourable promotion for Slovenia. The Slovenian contribution will be especially notable In the near future, when the JET machine will achieve and surpass a fusion gain factor of Q=1, an important milestone in the development of nuclear fusion as a sustainable and environmentally-friendly energy source for the future. This research project is an important step towards this goal. The performance of the activities in the research project has opened new research fields, most importantly multi-physics coupling of Plasma Physics and Neutronics. New collaborations have been initiated in the scope of ITER and JET research projects, which will further contribute to Slovenian knowledge and research funding. Knowledge gained in light ion transport calculations will be utilized in the development and validation of computational methods for proton transport, applicable to proton therapy, a relatively new method for cancer treatment which has significantly lower side-effects compared to classical radiotherapy using gamma ray sources. Preparations for the construction of a centre for proton therapy in Slovenia are currently under way. Our knowledge will therefore also contribute to the improvement of cancer treatment techniques. For Slovenia, the smallest nuclear country in the world with little natural resources, collaboration in the development and the exploitation of nuclear fusion is of great importance for future sustainable development.
Most important scientific results
Annual report
2014,
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2015,
final report
