IN2P3 and Framatome have just signed a collaboration protocol involving three IN2P3 laboratories, the LPSC in Grenoble, the IJCLab in Orsay, Subatech in Nantes, and Framatome's Design School, a new entity created in early 2020 and integrated into Framatome's Advanced Reactor Competence Centre.
The Subatech researchers involved: Axel Laureau and Lydie Giot from the Nuclear Structure and Energy (SEN) team
Access to the IN2P3 press release, coordinated by Sébastien Incerti, IN2P3 Deputy Scientific Director:
Participants : from left to right, Sébastien Incerti (IN2P3), Axel Laureau (Subatech), Patrice Verdier (IN2P3), Elsa Merle (LPSC),
Jean-Marie Hamy (Framatome), Bernard Carluec, Florian Vaiana, Alexandre Dauphin (Framatome) and in distance : Lydie Giot (Subatech) and Jean-Christophe Blanchon (CORYS)
Nuclear physicists from Subatech have participated in an international research collaboration to show how the spin of two fragments from the fission of an atomic nucleus is generated.
A series of experiments at the ALTO accelerator at the IJC lab in Orsay revealed that fragments from nuclear fission obtain their intrinsic angular momentum (or spin) after fission, and not before as was previously widely assumed. This result was made possible by the 'nu-ball' collaboration, an international group of nuclear physicists whose aim is to study the structure of many nuclei. This group includes researchers from 37 institutes and 16 countries, among them members of Subatech, and is led by the Irène-Joliot-Curie laboratory in Orsay. The results are presented in the new Nature publication entitled 'Angular momentum generation in nuclear fission'.
Not only do these results provide new insight into the role of angular momentum in the fission mechanism, but they also have implications for other fields of research such as the study of the structure of neutron-rich nuclei, the synthesis of superheavy elements, and applications such as the residual power of nuclear reactors.
The beta radioactivity of fission products in nuclear reactors is responsible for their very high production of antineutrinos. In 2011, the revision of the theoretical model of electron/antineutrino conversion revealed a 6% deficit between the predicted antineutrinos and those measured in the vicinity of reactors. Two hypotheses were considered at the time: there were other types of sterile neutrinos whose properties had to be characterised, or the model was imperfect. The SEN group is working on the only alternative model to conversion: the summation method, as well as on experimental measurements to improve its predictivity. The model consists of a careful study of the nuclear decay of the main contributors to the antineutrino emission in the fuel and to sum their contributions. Associated with the TAGS collaboration, the group has so far been able to measure and analyse 15 major nuclei for the prediction of antineutrino spectra. The inclusion of these Pandemonium-corrected nuclei in the calculation of the flux of produced antineutrinos shows a systematic effect: the predicted flux is consistently closer to the measured flux (see figure) and seems to confirm the results of the neutrino experiments regarding the imperfection of the conversion model. The flux discrepancy narrows to 2% with the measurements of flux of the Daya Bay collaboration and the impact of other TAGS nuclei on the model will be assessed soon.
Caption: In 2011 the summation model (Greenwood) then compatible with the conversion model predicted 6% more antineutrinos than measured by Daya Bay (DB). The improvement of the nuclear model in 2012, 2015, 2017 and 2018 thanks to the TAGS data allowed to reduce the gap to 2%. Figure M. Estienne et al. Phys. Rev. Lett. 123 (2019) 022502.
Decay heat is the heat released after the reactor shutdown as a result of radioactive decays of the fuel isotopes and delayed fissions. The determination of decay heat is a major safety issue for a reactor in operation or in accidental conditions but also for the transport of burnt fuel and nuclear waste management. It is in particular a key parameter for the design of the Generation IV reactors safety systems but also for the use of innovating fuels. Few decay heat measurements are available. Hence there is a real need to have reliable codes to estimate the decay heat associated with its uncertainty. The calculation of decay heat relies on the combination of reactor simulations to estimate the fuel inventory and on nuclear data
used as an input : decay properties of the fission products and actinides, fission yields and cross sections.
The Nuclear Structure and Energy group of the SUBATECH laboratory performs decay heat calculations with the Monte Carlo depletion code SERPENT2 developed by the VTT in Finland for fission pulses, PWR fuel assemblies but also Gen IV concepts.
Since 2015, the impact of new TAS measurements of the β- and γ mean decay energies of some key fission products
on the decay heat calculation of thermal/fast fission pulses has been calculated with the SERPENT2 code.
The radioactivity of fission products in a nuclear reactor releases a large amount of energy. Some of this energy escapes from the reactor with the antineutrinos. Understanding their number and energy has kept the physics community on tenterhooks for some years with the reactor anomaly, a deficit of antineutrinos detected at short distances from nuclear reactors compared to predictions that could be explained by the existence of sterile neutrinos. The way in which the nuclei produced in the reactor core decay could perhaps also provide the key to this enigma. The study of some of these fission products remained a challenge, but the combination of the most advanced production, detection and analysis techniques allowed the radioactive properties of two niobium isotopes with isomeric states to be measured. The results show a major impact on the prediction of reactor antineutrino spectra by the summation method.
Publication: Large Impact of the Decay of Niobium Isomers on the Reactor ¯νe Summation Calculations, V. Guadilla et al., Phys. Rev. Lett. 122, 042502 – Published 30 January 2019.
Contacts: V. Guadilla, M. Fallot (Subatech)
Beta decay of 100Nb isomers (left). Impact of the results on the energy spectrum of antineutrinos from 239Pu fission (right).