Development of reference benchmark neutron field in LR-0 reactor
Type of document
habilitační prácehabilitation thesis
Author
Košťál, Michal
Metadata
Show full item recordAbstract
A neutron reference field is defined as a permanent reproducible neutron field with well defined
neutron fluence rate and neutron energy spectra. The standard reference field has neutron spectra
characterized employing neutron spectra measurements by means of time-of-flight measurements.
Historically there was only one standard neutron reference field, 252Cf(s.f.). In 2017 into neutron
standards, there was also included
235U(n_th, fiss), which becomes secondary neutron standard.
Reference neutron benchmark fields are defined as permanent and reproducible neutron fields, less
well characterized as a standard field, but still acceptable as a measurement reference by a community
of users. This work deals with the development of a reference neutron benchmark field in a special
core placed in an LR-0 reactor. In this reference neutron benchmark field, there were precisely
measured neutron and gamma spectra using stilbene spectrometry. This is very important in the case
of this reactor benchmark field because it was observed that neutron spectra above 6 MeV are nearly
identical with 235U PFNS, and also it was confirmed that the gamma has a negligible effect on measured
neutronic quantities. Namely, the impact of the photo-nuclear reactions (γ,n) competing with (n,2n) in
the production of the same residual nucleus was shown to be negligible. To confirm the spatial
distribution of the field, there was also validated the fission density distribution across the driver core.
This precise characterization of the core is important and well usable also in other issues. It’s worth
noting it is an excellent tool for validation of neutronic properties of materials inserted in the center
of the special core, or surrounding it, for example, sand, whose neutronic parameters are important
not only in space programs but also in used fuel storage management, because major material of earth
crust is SiO2. The most recent also interesting application was validation of neutronic description of
stainless steel, which is important in criticality safety issues as stainless steel is the major component
of water moderated reactors internals.
The essential results, namely criticality, flux distribution, neutron spectra and also some of the
measured spectral averaged cross section evaluated as SACS averaged in 235U PFNS were benchmarked
in the IRPhEP database. This database is the most reliable one, which is used in improvements of
nuclear cross sections. The field became one of the IRDFF-II reference benchmark neutron fields, and
the measured data were used for improving the newly developed IRDFF-II neutron dosimetry library.
Collections
The following license files are associated with this item: