Compilation of Existing Neutron Screen Technology

The presence of fast neutron spectra in new reactors is expected to induce a strong impact on the contained materials, including structural materials, nuclear fuels, neutron reflecting materials, and tritium breeding materials. Therefore, introduction of these reactors into operation will require extensive testing of their components, which must be performed under neutronic conditions representative of those expected to prevail inside the reactor cores when in operation. Due to limited availability of fast reactors, testing of future reactor materials will mostly take place in water cooled material test reactors (MTRs) by tailoring the neutron spectrum via neutron screens. The latter rely on the utilization of materials capable of absorbing neutrons at specific energy. A large but fragmented experience is available on that topic. In this work a comprehensive compilation of the existing neutron screen technology is attempted, focusing on neutron screens developed in order to locally enhance the fast over thermal neutron flux ratio in a reactor core

Preliminary Selection of Device Materials to Locally Transform Thermal into SFR Neutron Spectrum

The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require extensive testing of their components. This must be performed under neutronic conditions representative of those expected to prevail inside the new reactor cores when in operation. In a thermal Material Testing Reactor (MTR) such neutronic conditions can be achieved by tailoring the prevailing neutron spectrum with the utilization of a device containing appropriate materials. In this work various materials are investigated as candidate components of a device that will be required in case that a thermal MTR neutron energy spectrum must be locally transformed, so as to imitate Sodium cooled Fast Reactor (SFR). Many nuclides have been examined with respect to only their neutronic behavior, providing thus a pool of neutronically appropriate materials for consideration in further investigation, such as regarding reactor safety and fabrication issues. The nuclides have been studied using the neutronics code TRIPOLI-4.8 while the reflector of the Jules Horowitz Reactor (JHR) was considered as the hosting environment of the transforming device. The results obtained suggest that elements with important inelastic neutron scattering could be chosen at a first level as being able to modify the prevailing neutron spectrum towards the desired direction. The factors which are important for an effective inelastic scatterer comprise density and inelastic microscopic cross section, as well as the energy ranges where inelastic scattering occurs. All the above factors have been separately examined in order to suggest potential device materials, able to locally produce SFR neutron spectrum imitation in a thermal MTR

Assessment of off-site early countermeasures in the event of a LOCA in a research reactor

Off-site early emergency management actions due to a potential release from the Greek Research Reactor-1 are assessed with the aid of a modern decision support tool. To this end, a hypothetical loss-of-coolant accident has been assumed under two distinct ventilation schemes of the reactor building. Five, site-typical, meteorological scenarios have been applied based on observed conditions that demonstrate the effects the released radioactive plume has on the surrounding urban area. The JRODOS (Java-based Real-time On-line DecisiOn Support) system has been used to calculate gamma radiation doses, estimate the affected areas and assess early countermeasures in accordance with national legislation. The results indicate that the suggested countermeasures may need to be applied only to a very limited area in a few of the considered weather scenarios

Effects of onshore and offshore topography on sea breeze circulation: An observational study at eastern Attica, Greece

Field measurements of wind, air temperature and humidity were taken at the eastern part of the Attika district in June 1991, to examine the topographic influences exerted on the local sea breezes. These influences are due either to the elongated Evia island, faced by the northern half of Attica coastline some tens of kilometers offshore, or to the coast-parallel range of Hymettos mountain, rising steeply 12 km onshore. The instrumentation consisted mainly of three tethered meteorological balloons released at characteristic sires (i.e., the coast, a location between shoreline and mountain foot and the mountain top) and three autographic ground-based anemometers operating at selected locations. Data from the ground-based and upper air stations of the Hellenic National Meteorological Service, as well as the diurnal weather maps were also obtained and analyzed. Observations were made under different synoptic wind and the latter was found to determine remarkably the significance of the topographic effects. A preliminary two-dimensional numerical approach was also made concerning the sea breeze capability to reach the Hymettos mountain top in the case of a weak opposing geostrophic flow. © 1993 Birkhäuser Verlag

Criticality qualification of a new Monte Carlo code for reactor core analysis

International audienc

Building a dynamic code to simulate new reactor concepts

International audienc

Modeling And Simulating A Breeder Hybrid Soliton Reactor

International audienceUnderstanding and controlling early damage initiation and evolution are amongst the most important issues in nuclear power plants. Integranular cracking has been known to occur in both austenitic steels and nickel based alloys. Modelling efforts are under way to understand this phenomenon on the grain-level scale where the influence of the microstructure plays an important role. Here, the initiation and evolution of integranular cracking can be modelled using the advanced finite element approaches with explicit account of the grains, their crystallographic orientation and explicit inclusion of grain boundaries. The cohesive-zone approach, with damage initiation and evolution, can be used for grain boundaries. However, the stability of such an approach can be problematic, especially in cases where there are a number of inter-granular cracks. These cracks can form complex networks which can have a negative impact on the stability of the analysis. This work addresses some of the issues related to the stability. The influence of the finite element individual model parameters like convergence controls and numerical viscosity on the model convergence is looked at. The effects are demonstrated on a simple geometry containing 3 grains. It is shown that the numerical viscosity has the highest beneficial influence on the convergence. However values of numerical viscosity of more than 10 % of the time step should be avoided

Investigating the breeding capabilities of hybrid soliton reactors

International audienc