scholarly journals Homogenization in the energy variable for a neutron transport model

2020 ◽  
Vol 117 (1-2) ◽  
pp. 1-25
Author(s):  
Harsha Hutridurga ◽  
Olga Mula ◽  
Francesco Salvarani
Keyword(s):  
Transport Model ◽  
Neutron Transport ◽  
Energy Variable

Penetration depth of Cosmic-ray neutron sensing for soil moisture under extreme vertical soil moisture gradients in measurements and modelling

2021 ◽  
Author(s):  
Lena M. Scheiffele ◽  
Jannis Weimar ◽  
Daniel Rasche ◽  
Benjamin Fersch ◽  
Sascha E. Oswald
Keyword(s):  
Soil Moisture ◽  
Sensor Network ◽  
Penetration Depth ◽  
Transport Model ◽  
Neutron Transport ◽  
Soil Column ◽  
Weighted Average ◽  
Monitoring Network ◽  
Cosmic Ray ◽  
Soil Moisture Monitoring

<p>Cosmic-Ray Neutron Sensing (CRNS) delivers an integral value of soil moisture over a radial footprint of 150 to 240 m and a penetration depth of 15 to 83 cm. The support volume, especially in the vertical extent, decreases with increasing soil moisture. As the sensor is most sensitive to upper soil layers and the signal contribution decreases with increasing depth, the vertical distribution of moisture influences the signal received by the neutron detector. Additional soil moisture measurements are required to estimate the penetration depth of the CRNS measurement. These may be provided by profile measurements of a soil moisture monitoring network equipped with buried electromagnetic sensors. Different horizontal and vertical weighting schemes exist to compare the integrated CRNS value to an integrated (weighted) average value from a sensor network by adjusting reference measurements to the spatial sensitivity of the sensor. The vertical weighting was developed based on hydrodynamic modelling of a soil column and a neutron transport model (MCNPx). Since then the development of the Ultra Rapid Adaptable Neutron-Only Simulation (URANOS) opened up the possibilities for more complex neutron simulations to understand and interpret the CRNS signal. Simulations confirmed the large influence of soil moisture on the penetration depth of the sensor for homogeneous vertical soil moisture distributions, rarely occurring in natural environments. While in recent years the influence of horizontal heterogeneities on the signal generation was the focus of several studies, the influence of vertical gradients achieved less attention.</p><p>Against this background, we evaluate data from a field site in southern Germany with clayey soils and influence of shallow groundwater, where a CRNS is operated in parallel to a soil moisture monitoring network. We observe a good match between the time series of CRNS derived soil moisture and the weighted soil moisture from the sensor network during infiltration events. Several times during summer, however, topsoil dries and a strong vertical gradient develops (0.20 m³ m<sup>-</sup>³ in 5 cm to 0.50 m³ m<sup>-</sup>³ in 20 cm depth). During these periods the weighted sensor network underestimates CRNS derived soil moisture by up to 0.25 m³ m<sup>-</sup>³. We hypothesize, that the estimation of the penetration depth does not hold for these extreme soil moisture gradients and that neutrons penetrate deeper into the soil and probe the wetter layers. The combination of observed neutron intensities as well as dedicated neutron transport simulations using the URANOS and MNCP6 model code will help to understand the site-specific signal behavior, explain differences observed in the data and lastly, gain information on the behavior of neutron intensities under vertically varying soil moisture contents.</p>

Calculations and Measurements of Pressure Vessel Thermal Neutron Fluxes in the VVER-1000 Mock-Up in the LR-0 Research Reactor

2015 ◽  
Vol 1 (2) ◽  
Author(s):  
Michal Košťál ◽  
Vlastimil Juříček ◽  
Ján Milčák ◽  
Vojtěch Rypar ◽  
Antonín Kolros
Keyword(s):  
Thermal Neutron ◽  
Pressure Vessel ◽  
Reaction Rate ◽  
Gas Transport ◽  
Transport Model ◽  
Neutron Transport ◽  
Reactor Pressure Vessel ◽  
Attenuation Coefficients ◽  
Free Gas ◽  
Reactor Pressure

This paper deals with measured as well as calculated parameters of thermal neutron transport in the reactor pressure vessel model, located behind the LR-0 reactor vessel. A VVER-1000 mock-up core placed in the LR-0 reactor is the source of neutrons, whose transport through heavy steel structures surrounding the core (i.e., the side reflector up to the area behind LR-0 vessel), is studied. The change of neutron distribution due to the variable thickness of the steel reactor pressure vessel (RPV) layers was measured and calculated using MCNPX code. The experimental results are compared with calculations performed with CENDL 3.1 and ENDF/B VII using both the thermal scattering law sublibrary with the S(α,β) model and the free gas transport model. When steel thickness increases, the measured reaction rate attenuation coefficients show a considerable decrease in thermal neutron flux, while measured Cd ratios show a faster decrease in the thermal part of the neutron spectra than the epithermal part. The calculation to experiment (C/E) for the Cd ratio shows in most cases better correspondence when the thermal neutron transport is described by means of a free gas transport model than with the thermal scattering law (TSL) model. Significantly better agreement of reaction rates is observed for the epithermal reaction rate attenuation coefficients than for thermal ones. The results are similar for both the free gas and TSL models at these energies.

scholarly journals APPLICATION OF RECENT DEVELOPMENTS IN INTEGRAL DATA ASSIMILATION TO IN-DEPTH ANALYSIS OF UH1.2 EXPERIMENT AND TRANSPOSITION TO WHOLE PWR CORE

2021 ◽  
Vol 247 ◽  
pp. 15001
Author(s):  
J.-M. Palau ◽  
A. Rizzo ◽  
P. Tamagno ◽  
C. De Saint Jean
Keyword(s):  
Data Assimilation ◽  
Transport Model ◽  
Neutron Transport ◽  
Information Criteria ◽  
Adjustment Process ◽  
Technological Parameters ◽  
Fission Rate ◽  
Depth Analysis ◽  
Recent Developments ◽  
Integral Data

Recent developments in the Integral Data Assimilation (IDA) methods within Bayesian framework have been achieved at CEA to tackle the problem of correlated experiments (through technological uncertainties) and neutron transport model numerical effects. Hence, reference Monte-Carlo and deterministic calculations (TRIPOLI4® and APOLLO3®) are used together to solve neutron transport equations and get the sensitivity profiles. Furthermore, the analysis of the mock-up experiments technological parameters is performed to get accurate uncertainties and correlations between the experiments (finally the covariance experimental matrix required for IDA). We apply here the IDA approach with a new, extend set of statistical indicators (Cook’s distance, Bayesian and Aikike Information criteria (BIC, AIC)) implemented in the nuclear physics CEA CONRAD code, to the integral experiments UH1.2 in reference and voided configurations (standard PWR fuel assembly in the EOLE mock-up reactor). The adjusted multigroup cross-sections and posterior covariances are compared by choosing different ingredients in the assimilation process. Finally, the investigated key neutron parameters; reactivity, reactivity worth (void effects) and fissions rates are transposed (with the same CONRAD code) to a standard PWR core. This in-depth analysis enables us to predict the residual uncertainties and biases due to the multigroup cross-section adjustments assessing at the same time the similarity of these integral experiments for the main PWR neutronic safety parameters. In addition, technological parameters uncertainties and their impact on Bayesian adjustment process are taken into account through a global experimental covariance matrix. We point out that the UH1.2 experiments bring relevant additional information to PWR keff calculations reducing significantly the posterior results but are less relevant for fission rate distribution in reference and voided configurations.

Neutron transport model based on the transmission probability method

2013 ◽  
Vol 72 ◽  
pp. 33-38
Author(s):  
Kunpeng Wang ◽  
Andrei Rineiski ◽  
Werner Maschek ◽  
Hongchun Wu ◽  
Liangzhi Cao
Keyword(s):  
Transport Model ◽  
Neutron Transport ◽  
Transmission Probability ◽  
Probability Method ◽  
Model Based
Sign in / Sign up

Export Citation Format

Share Document