25 research outputs found
Graphical Visualisation of the MCNP Mesh Tally File
This paper presents an updated version of the MTV3D (Mesh Tally Visualization in 3D) program with Windows graphical user interface for visualization of the MCNP-based mesh tally files. Several improvements over the previous program version are addressing better figure export functionality ("Save as" option), switching between linear and logarithmic values on axes, dynamic figure scaling in active window, inversion of relative errors from āmaxā to āminā values, etc. MCNP is a well known and widely used general purpose Monte Carlo computer code for neutron, photon and electron transport simulation through arbitrary three-dimensional configurations. An important feature of the MCNP code is a graphical display of the simulation model using auxiliary program, such as X-window server, which is useful for geometry error-checking during model setup and visualisation of Monte Carlo results from a mesh tally file (i.e. meshtal file) over a structured xyz mesh. Such inspection of the model is useful for the end user, providing an insight of the Monte Carlo convergence process in a phase space and effectiveness of the selected variance reduction parameters in shielding calculations. Basic features and functionalities of the updated MTV3D program are presented on some selected hybrid-shielding problems involving ADVANTG3.0.3 and MCNP6.1.1b codes
Characterization of Fast Neutron Transmission Through an Iron Shield
In this paper we give an analysis of the neutron transmission through an iron sphere using Monte Carlo and transport theory methods based on ENDF/B-VII.1 general purpose library. The motivation for this investigation comes from a well-known deficiency in the iron inelastic data from the older library evaluation (ENDF/B-V), giving a concern for a fast neutron flux underestimation within the reactor pressure vessels. In order to benchmark the next-generation ENDF/B-VI iron data, the U.S. Nuclear Regulatory Commission and the former Czechoslovakian National Research Institute have jointly preformed several experiments in 1990s, addressing neutron leakage spectra obtained for a 252Cf fission source in a centre of an iron sphere. It was shown that the ENDF/B-VI iron cross section, containing several improvements over previous evaluations, will not entirely resolve the neutron spectrum discrepancies observed at high neutron energies. Since safety analyses of reactor pressure vessel embrittlement are often based on neutron transport calculations using specific multigroup cross section libraries, simulation of this benchmark was performed using a hybrid shielding methodology of ADVANTG3.0.3 and MCNP6.1.1b codes. Comparison of calculated and referenced dosimeter activation rates are presented for several "standard" nuclear reactions, often used in reactor pressure vessel dosimetry. For that purpose, the new IRDFF-II special library from the IAEA Nuclear Data Services was used as a reference source of dosimetry cross sections. The MCNP6.1.1b code was used for calculation of reaction rates, which were also compared with previous IRDFF-1.05 special library and general purpose ENDF/B-VII.1 library
Monte Carlo Codes for Neutron Buildup Factors
The point-kernel method is a widely used practical tool for gamma-ray shielding calculations.
However, application of that method for neutron transport simulations is very limited. The accuracy
of the method strongly depends on the accuracy of buildup factors used in the calculations. Buildup
factors are usually obtained using appropriate computer codes, either based on discrete ordinates
transport method or Monte Carlo approach. Since these codes put strong demands on computer
resources, they are applied on a limited number of shielding configurations and an attempt is made
to use these results and formulate an empirical expression for buildup factors estimation. Due to
high physical complexity of neutron transport through shielding material it is very hard to perform
parameterisation in order to establish adequate empirical formula. Existing formulas are very
limited and are usually applicable to a narrow neutron energy range for few commonly used
shielding materials, mostly in monolayer configuration.
Recently, a new approach has been proposed for determination of gamma ray buildup factors
for mono-layer, as well as multi-layer shielding configurations covering a wide gamma ray energy
range. The new regression model is based on support vector machines learning technique, which
has theoretical background in statistical learning theory. Development of named regression model
required a large number of experimental data obtained by Monte Carlo computer code. More than
7000 Monte Carlo runs were required. Due to physical complexity neutron transport is likely to
require even more experimental data in order to generate a model of reasonable accuracy.
Therefore, the choice of appropriate Monte Carlo code is a very important question. One has to take
into account the accuracy as well as the time required for input preparation and running the code.
What also has to be considered is the possibility of the code to be incorporated in an algorithm for
automated generation of experimental data.
In this paper three Monte Carlo codes are analysed, namely SCALE4.4 code package (SAS3
sequence), SCALE6.0 code package (MAVRIC sequence), and MCNP5. Two simple experimental
setups based on a point isotropic source in spherical and slab-like shield are modelled, and the
codes are examined on previously mentioned issues.
The comparison results show that each one of the examined codes has potential to be used for
neutron buildup factor model generation. However, some aspects of their utilization require further
analysis prior to final selection
Point Kernel Modification Including Support Vector Regression Neutron Buildup Factor Models
This work presents the results of radiation shielding calculations using modified point kernel
code QAD-CGGP. The modification includes a new approach to neutron buildup factor estimations
based on machine learning technique called Support vector regression (SVR). SVR neutron buildup
factor models for common shielding materials are developed and built into the QAD-CGGP. The
development of the models consisted of acquiring the data to be used for learning the model,
optimizing the SVR parameters, and application of active learning methods for improving the
learning process. The modified code is tested, and the results are compared with the MCNP6 results
Full Core Criticality Modeling of Gas-Cooled Fast Reactor using the SCALE6.0 and MCNP5 Code Packages
The Gas-Cooled Fast Reactor (GFR) is one of the reactor concepts selected by the Generation
IV International Forum (GIF) for the next generation of innovative nuclear energy systems. It was
selected among a group of more than 100 prototypes and his commercial availability is expected by
2030. GFR has common goals as the rest GIF advanced reactor types: economy, safety,
proliferation resistance, availability and sustainability. Several GFR fuel design concepts such as
plates, rod pins and pebbles are currently being investigated in order to meet the high temperature
constraints characteristic for a GFR working environment. In the previous study we have compared
the fuel depletion results for heterogeneous GFR fuel assembly (FA), obtained with TRITON6
sequence of SCALE6.0 with the results of the MCNPX-CINDER90 and TRIPOLI-4-D codes.
Present work is a continuation of neutronic criticality analysis of heterogeneous FA and full core
configurations of a GFR concept using 3-D Monte Carlo codes KENO-VI/SCALE6.0 and MCNP5.
The FA is based on a hexagonal mesh of fuel rods (uranium and plutonium carbide fuel, silicon
carbide clad, helium gas coolant) with axial reflector thickness being varied for the purpose of
optimization. Three reflector materials were analyzed: zirconium carbide (ZrC), silicon carbide
(SiC) and natural uranium. ZrC has been selected as a reflector material, having the best
contribution to the neutron economy and to the reactivity of the core. The core safety parameters
were also analysed: a negative temperature coefficient of reactivity was verified for the heavy metal
fuel and coolant density loss. Criticality calculations of different FA active heights were performed
and the reflector thickness was also adjusted. Finally, GFR full core criticality calculations using
different active fuel rod heights and fixed ZrC reflector height were done to find the optimal height
of the core. The Shannon entropy of the GFR core fission distribution was proved to be useful
technique to monitor both fission source convergence (stationarity) and core eigenvalue
convergence (keff) to fundamental eigenmode with MCNP5. All calculations were done with
ENDF/B-VII.0 library. The obtained results showed high similarity with reference results
PCA Benchmark Analysis with ADVANTG3.0.1. and MCNP6.1.1b Codes
The Pool Critical Assembly Pressure Vessel (PCA) benchmark is a well known benchmark in
the reactor shielding community which is described in the Shielding Integral Benchmark Archive
and Database (SINBAD). It is based on the experiments performed at the PCA facility in the Oak
Ridge National Laboratory (ORNL) and it can be used for the qualification of the pressure vessel
fluence calculational methodology. The measured quantities to be compared against the calculated
values are the equivalent fission fluxes at several experimental access tubes (A1 to A8) in front,
behind, and inside the pressure-vessel wall simulator. This benchmark is particularly suitable to test
the capabilities of the shielding calculational methodology and cross-section libraries to predict invessel
flux gradients because only a few approximations are necessary in the overall analysis. This
benchmark was analyzed using a modern hybrid stochastic-deterministic shielding methodology
with ADVANTG3.0.1 and MCNP6.1.1b codes. ADVANTG3.0.1 is an automated tool for
generating variance reduction (VR) parameters for Monte Carlo (MC) calculations with
MCNP5v1.60 code (and higher versions). It is based on the multigroup, discrete ordinates solver
Denovo, used for approximating the forward-adjoint transport fluxes to construct VR parameters for
the final MC simulation. The VR parameters in form of the weight windows and the source biasing
cards can be directly used with unmodified MCNP input. The underlining CADIS methodology in
Denovo code was initially developed for biasing local MC results, such as point detector or a
limited region detector. The FW-CADIS extension was developed for biasing MC results globally
over a mesh tallies or multiple point/region detectors. Both CADIS and FW-CADIS are based on
the concept of the neutron importance function, which is a solution of the adjoint Boltzmann
transport equation. The equivalent fission fluxes calculated with MCNP are based on several highenergy
threshold reactions from international dosimetry libraries IRDF-2002 and IRDFF-2014,
distributed by the IAEA Nuclear Data Section. The obtained results show a good agreement with
referenced PCA measurements. Visualization of the deterministic solution in 3D was done using the
VisIt code from the Lawrence Livermore National Laboratory (LLNL)
24-Month Operating Cycle Containing Gadolinium Integral Burnable Absorbers for NPP KrŔko
A few years ago Westinghouse innovations in PWR technology resulted in a proposal for a
new type of integral fuel burnable absorbers containing Gadolinium. Preliminary designs of loading
patterns for NPP KrŔko were made for 18 month fuel cycles with standard VANTAGE+ fuel type
containing Integral Fuel Burnable Absorbers (IFBA) with enriched Boron, as well as newly
proposed Gadolinium based absorbers. In this paper we investigate the possibility to design 24
month cycle for the NPP KrŔko with VANTAGE+ fuel type and Gadolinium based integral
absorbers. The key fuel cycle parameters are compared to the one based on IFBAs. The analysis is
performed by the latest version of FUMACS code package capable of simulating Gadolinium based
integral fuel burnable absorbers