29 Apr (NucNet): Research into the antineutrino spectrum of uranium-238 has “opened the door” to independent monitoring of reactor core contents from outside the pressure vessel or reactor container using a new generation of smaller antineutrino detectors, physicists in Germany have said.
Physicists at Technische Universität München (Munich Technical University, TUM) have successfully carried out an experiment to determine the cumulative antineutrino spectrum of the fission products of uranium-238.
In the 1980s, physicists determined the antineutrino spectra of three main fuel isotopes, uranium-235, plutonium-239 and plutonium-241. But the antineutrino spectrum of the fourth main nuclear fuel, uranium-238, which accounts for approximately 10 percent of the total antineutrino flux, remained unclear. It had only been estimated using inaccurate theoretical calculations and thus limited the accuracy of the antineutrino predictions.
TUM physicists say they have now “closed this gap” after using fast neutrons in an experiment to determine the cumulative antineutrino spectrum of the fission products of uranium-238.
They say antineutrino detectors could provide a more precise method to confirm that reactors are operating according to International Atomic Energy Agency (IAEA) standards and that fissile materials are not being diverted for use in an undeclared nuclear weapons programme.
Nils Haag, chair of experimental particle astrophysics at TUM, developed an experimental setup that allowed researchers to determine the missing spectrum of uranium 238. He located his experimental setup at the Heinz Maier Leibnitz Neutron Research Facility, which has a source of fast neutrons.
The antineutrino spectrum can be used to monitor the status, performance and even composition of reactor cores, Dr Haag said. These new results open the door to predict the expected antineutrino spectrum emitted by a reactor with significantly higher accuracy.
This means that antineutrino detectors might be developed to help the IAEA safeguard fissile materials within nuclear reactors. The IAEA is responsible for monitoring nuclear facilities for nonproliferation compliance, but for some of its assessments, the agency must rely on operator declaration.
According to TUM, smaller prototype antineutrino detectors measuring one cubic metre have become available and would allow for the antineutrino spectrum analysis of a nuclear fission reactor from about 10 metres from the reactor core.
In a project funded by the US National Nuclear Security Administration’s Office of Nonproliferation Research and Development, scientists from Lawrence Livermore and Sandia have developed autonomous detectors that continuously and accurately monitor antineutrinos in real time throughout the one- to two-year fuel cycle of a standard pressurised water reactor.
Details are online: www.tum.de/en/about-tum/news/press-releases/short/article/31486
For details of the US Lawrence Livermore and Sandia project: www.llnl.gov/str/JulAug08/pdfs/07.08.4.pdf
