2024-01-07 23:10:00
In the field of nuclear safety and the design of fast neutron reactors, the Chi-Nu experiment at Los Alamos National Laboratory (USA) provides essential and new data. This multi-year research is expected to influence the understanding and application of nuclear fission reactions.
The Chi-Nu project, which spanned several years, measured the energy spectrum of neutrons emitted during neutron-induced fission. This experiment recently concluded the most detailed and extensive uncertainty analysis on the three major actinide elements:uranium-238l’uranium-235 and the plutonium-239.
« Nuclear fission and associated chain reactions were only discovered just over 80 years ago, and experimentalists are still working to provide a complete picture of fission processes for major actinides “, commented Keegan Kelly, physicist at Los Alamos National Laboratory. “ During this project, we observed clear signatures of fission processes that, in many cases, had not been observed in any previous experiment. »
Crucial data for fission and reactor design
The experiment measured the spectrum of fast fission neutrons of uranium-238: the energy of the fission-inducing neutron – the neutron that crashes into a nucleus and splits it – and the potentially extended energy distribution (the spectrum) of neutrons released following this fission.
Chi-Nu focuses on fission induced by “ fast neutrons ”, with incident neutron energies numbering in the millions of electron volts, where measurements have traditionally been rare.
In conjunction with similar measurements on uranium-235 and plutonium-239, the results of the Chi-Nu experiments now constitute, in many cases, the primary source of experimental data guiding modern efforts to evaluate the neutron spectra of prompt fission.
This data informs nuclear models, Monte Carlo calculations, reactor performance calculations and more.
Jaime Gomez (left) and Keegan Kelly work to set up the Chi-Nu experiment, calibrate distances between detectors, and install gas lines for the fision counting target (at center).Credit: Los Alamos National Laboratory
Future Applications of Chi-Nu Skills
Researchers continue to build a complete picture of actinide isotopes. In related work funded by the Nuclear Safety and Criticality Program, the Chi-Nu experimental team is currently collecting and analyzing data on plutonium-240 and uranium-233.
With the conclusion of the Office of Experimental Sciences measurements, the team plans to apply the skills and methodologies learned in fission neutron measurements to a range of other isotopes. They are also directing their efforts toward measurements of neutrons emitted during neutron diffusion reactions, where neutrons transport through a material while depositing energy. The energy and angular spectra of the emitted neutrons and gamma rays are measured, as well as the probability of the reaction occurring, usually referred to as the neutron scattering cross section.
Synthetic
The data provided by the Chi-Nu experiment at Los Alamos National Laboratory constitute a significant contribution to the understanding of nuclear fission and to the improvement of applications related to nuclear safety and reactor design. These results, which are part of a rigorous and detailed scientific approach, promise to positively influence technological advances in the field of nuclear energy.
For a better understanding
What is the Chi-Nu Experience?
The Chi-Nu experiment is a research project at Los Alamos National Laboratory that measured the energy spectrum of neutrons emitted during neutron-induced nuclear fission.
What are the actinide elements studied by Chi-Nu?
Chi-Nu analyzed the major actinide elements such as uranium-238, uranium-235 and plutonium-239.
How important is the data collected by Chi-Nu?
Chi-Nu data is essential for guiding nuclear models, reactor performance calculations and other nuclear security applications.
What are the future applications of the skills acquired by the Chi-Nu team?
The Chi-Nu team plans to apply their skills in measuring fission neutrons to other isotopes and the study of neutron diffusion reactions.
What’s next for Team Chi-Nu?
The team continues to analyze isotopes such as plutonium-240 and uranium-233 and is looking toward new measurements in the field of neutron scattering.
References
Main illustration caption: Physicist Keegan Kelly sets up a fision counting target containing regarding 100 milligrams of an interesting actinide for a Chi-Nu experiment. The device includes 54 liquid scintillation neutron detectors and 22 lithium glass detectors to measure neutrons in different energy ranges.
Article : “Measurement of the 238U(n, f) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons with 1.5–20 MeV energy.” Physical Review C. DOI: 10.1103/PhysRevC.108.024603
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