In this report the final computational model with results of the effect of ex-core neutron detector position on their response is presented. The aim of this work is to analyze the change in the ex-core detector signal, if they are moved by an earthquake. In the first part of the report the final computational model of the Krško NPP core and containment building model with explicitly added ex-core neutron detectors is presented. In the second part of the report the results of final calculations of thermal and total neutron flux at the ex-core detector locations and their change if ex-core detectors are moved for 5 cm in radial, axial or azimuthal direction are given. It was shown that change in power range nuclear instrumentation position does not have a significant effect on thermal neutron flux inside active part of the detector, while for intermediate range nuclear instrumentation the radial movement of 5 cm contributes to ?7.3 %-8.6 % change in thermal neutron flux inside the active detector part. In addition, horizontal, radial, axial or azimuthal gradient of thermal and total neutron flux at ex-core detector positions are presented. In the third part of the report, the effect of core barrel movement on power and intermediate range nuclear instrumentation response is analysed. It was demonstrated that core barrel movement during an earthquake can lead to significant change in the ex-core detector signal. The core barrel radial movement of 5 mm leads to 8 %-9 % change in the thermal neutron flux inside the active detector region.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 57535235The rod insertion method presents an efficient way of measuring the reactivity worth of control rods in a nuclear reactor. This is an inherently dynamic method, which is why we highlighted the differences between the static and the dynamic reactivity. Direct comparison of results based on the static and the dynamic reactivity relies heavily on adequate time-resolved three-dimensional numerical simulation. In the present work, this is achieved by updating the Gnomer computer program to support such calculation and verifying it on representative test cases. In the following, improvements of the rod insertion method are based on experimental data from the Krško nuclear power plant. Due to the results of the analysis, some of the methodological assumptions are retained (e.g. continuous insertion), while others are ameliorated (e.g. flux redistribution correction). A new correction is added, namely the reactivity overshoot compensation. It takes into account the dynamic effects after the control rod has reached its fully inserted state, and as such increases the total rod worth measurement consistency. Lastly, conversion from dynamic to static reactivity worth is established by following the examples in the literature and by using kinetic simulation. Thus – with the updated methodology – the rod insertion method is proven to yield excellent results in comparison to the well-established boron dilution method, and can be used as replacement.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 3170404In this master thesis a validation and evaluation of the recently released ADVANTG code, which combines a well-known Monte Carlo (MC) transport code MCNP with a deterministic transport code Denovo, is presented. The aim of ADVANTG is to automate the process of generating the variance reduction parameters (weight-windows) for the fixed source MCNP calculations, which consequently accelerate the simulations in terms of the required CPU time. Reliability and consistent performance of the ADVANTG code were tested on two computationally demanding benchmarks from the ICSBEP handbook: the “Labyrinth” experiment where neutron fluxes were measured and calculated in a three-section concrete labyrinth for a 252Cf neutron source and the “Skyshine” experiment where neutron and photon scattering in the air above an open operating reactor are simulated. The efficiency of each simulation has been obtained by the statistical test FOM. Compared to the analog MCNP simulations, the speed-up factors or the increases in relative efficiency of up to 1400 (neutrons), for the “Labyrinth” case, and up to 30000 (neutrons) and 1400 (photons), for the “Skyshine” case, were achieved using the ADVANTG-generated variance reduction parameters. As the mean values obtained by the ADVANTG-accelerated simulation sit within the statistical uncertainties of the analog simulation for both cases, it was shown that no additional bias is introduced by the ADVANTG code. Because of its reliability and consistent performance the ADVANTG code was used to analyse ? dose rates from the future Slovenian silo type low and intermediate level waste (LILW) repository. Using ADVANTGs variance reduction technique different detailed calculations of ? dose rates were once again achievable in reasonable time. Contrary, all previous calculations used rough geometric models or other different kind of approximation, which did not take into account the effect of backscattering in the air properly. For the optimized ADVANTG settings the maximum speed-ups up to 10000 were achieved compared to the analog MCNP simulation. Within the framework of the study we analysed the influence of different repository configurations on the values of the annual photon dose rates for different measurement positions on the surface. For all configurations of the repository, with the exception of using LILW from NPP Krško, the annual photon dose rates, due to ? rays, were for all measurement positions lower than the prescribed limit values (worker: 20 mSv/year). For the latter, an additional analysis was made, where the concrete N2b disposals, in which the LILW is stored, were modelled in more detailed. To ensure that the photon dose rates are lower than the prescribed limit values, the required thickness of the additional grout was determined by varying the additional quantity of the grout. The ADVANTG code has proven to be a powerful and reliable tool for generating effective variance reduction parameters and to greatly accelerate analog MCNP simulations. Therefore, in even more complex cases, it will be necessary or the only option for simulations with the statistically relevant results.
D.11 Other
COBISS.SI-ID: 3313508