The LANSCE proton beam hits a tungsten target, generating neutrons that travel along a flight path toward the Chi-Nu apparatus. The probability of subsequent reactions in the chain depends on the energy of the fission neutrons.Ĭonducted at the Weapons Neutron Research facility at the Los Alamos Neutron Science Center (LANSCE), the Chi-Nu experiment relied on a sophisticated apparatus testing several energy ranges. (Actinides are the 15 elements, all radioactive, with an atomic number from 89 to 103.) When a nucleus undergoes fission, or splits, several neutrons are released, potentially inducing fission in neighboring nuclei to create the chain reaction. The data inform nuclear models, Monte Carlo calculations, reactor performance calculations and more.Īctinide elements, and the chain reactions they can undergo, are important for nuclear weapons and energy reactors. Together with similar measurements on uranium-235 and plutonium-239, the results from the Chi-Nu experiments are now, in many cases, the dominant source of experimental data guiding modern efforts to evaluate the prompt-fission-neutron spectrum. Chi-Nu focuses on "fast-neutron-induced" fission, with incident neutron energies in millions of electron volts, where there have typically been very few measurements. The experiment measured uranium-238's prompt fission neutron spectrum: the energy of the neutron inducing the fission - the neutron that crashes into a nucleus and splits it - and the potentially wide-ranging energy distribution (the spectrum) of the neutrons released as a result. The Los Alamos team's final Chi-Nu study, on the isotope uranium-238, was recently published in Physical Review C. "Throughout the course of this project, we have observed clear signatures of fission processes that in many cases were never observed in any previous experiment." In the event of any runaway reactor event, NuScale says, the reactor quenches itself in its pool, making it “passively safe."Nuclear fission and related nuclear chain reactions were only discovered a little more than 80 years ago, and experimenters are still working to provide the full picture of fission processes for the major actinides," said Keegan Kelly, a physicist at Los Alamos National Laboratory. The pool portion of the reactor building is located below grade.” Nuclear Regulatory Commission (NRC) explains online: “The reactor vessel containment module is submerged in water in the reactor building safety related pool, which is also the ultimate heat sink for the reactor. “NuScale is a natural circulation light water reactor with the reactor core and helical coil steam generators located in a common reactor vessel in a cylindrical steel containment,” the U.S. And finally, the next wave of advanced reactors may involve fusion, embodied by ITER as well as much smaller tokamak and stellarator projects around the world. There’s an intermediate phase of new technology like molten salt. Most of the planned “advanced reactor” technology close to reality is like NuScale, in that it’s a new shape or application of an existing technology. small modular reactor design to be issued a FSER, NuScale is pioneering the way for additional innovative advanced nuclear technologies under development,” Nuclear Energy Institute (NEI) new reactor director Marc Nichol said in a statement. NuScale’s design uses classic nuclear fission water reactor technology in a much smaller form factor, which contrasts with the escalating sizes of most current nuclear plant construction around the world. Nuclear startup NuScale has received a landmark final safety evaluation report (FSER) for its modular reactor design, making it the first American modular design to reach this point. There are several more steps, including public feedback and the final road to building NuScale reactors.The reactor isn't technologically new, but has a much smaller form factor and new safety system.
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