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The Pebble Bed Modular Reactor is a particular design of pebble bed reactor under development by South African company PBMR Ltd since 1994. The project entails the construction of a demonstration power plant at Koeberg near Cape Town and a fuel plant at Pelindaba near Pretoria. Wikipedia.

Stempniewicz M.M.,Nuclear Research and Consultancy Group | Goede P.,Pbmr Pty Ltd.
Nuclear Engineering and Design | Year: 2016

This paper describes the work performed to find the sorption coefficients that represent well the available experimental data for cesium, iodine, and silver on dust particles. The purpose of this work is to generate a set of coefficients that may be recommended for computer code users. The following data was correlated:. •I-131 on AVR dust.•Ag-110m on AVR dust.•Cs-134 and Cs-137 on AVR dust. The results are summarized as follows:. •The available data can be correlated. The data scatter is about 4 orders of magnitude. Therefore the coefficients of the Langmuir isotherms vary by 4 orders of magnitude.•Sorption rates are higher at low temperatures and lower at high temperatures. This tendency has been observed in the data compiled at Oak Ridge. It is therefore surmised that the highest value of the sorption coefficients are appropriate for the low temperatures and the lowest value of the sorption coefficients are appropriate for the high temperatures. The recommended sorption coefficients are presented in this paper.•The present set of coefficients is very rough and should be a subject for future verification against experimental data. © 2015 Elsevier B.V. Source

Boer B.,Technical University of Delft | Lathouwers D.,Technical University of Delft | Kloosterman J.L.,Technical University of Delft | Van Der Hagen T.H.J.J.,Technical University of Delft | Strydom G.,Pbmr Pty Ltd.
Nuclear Technology | Year: 2010

The DALTON-THERMIX code system has been developed for safety analysis and core optimization of pebble-bed reactors. The code system consists of the new three-dimensional diffusion code DALTON, which is coupled to the existing thermal-hydraulic code THERMLX. These codes are linked to a database procedure for the generation of neutron cross sections using SCALE-5. The behavior of pebble-bed reactors during a loss of forced cooling (LOFC) transient is of particular interest since the absence of forced cooling could lead to a significant increase of the temperature of the coated particle fuel. Therefore, the reactor power may be constrained during normal operation to limit the temperature. For validation purposes, calculation results of normal operation, an LOFC transient, and a control rod withdrawal transient without SCRAM have been compared with experimental data obtained in the High Ternperature Reactor-10 (HTR-10). The code system has been applied to the 400-MW(thermal) pebble bed modular reactor (PBMR) design, including the analysis of three different LOFC transients. Theses results are verified by a comparison with the results of the existing TINTE code system. It was found that the code system is capable of modeling both small (HTR-10) and large (PBMR) pebble-bed reactors and therefore provides a flexible tool for safety analysis and core optimization of future reactor designs. The analyses of the LOFC transients show that the peak fuel temperature is only slightly elevated (less than +100°C) as compared to its nominal value in the HTR-10 but reaches a maximum value of 1648°C during the depressurized LOFC case of the PBMR benchmark, which is significantly higher than the peak fuel temperature (976°C) during normal operation. Source

Roberts D.E.,South African Council for Scientific and Industrial Research | Du Plessis A.,South African Council for Scientific and Industrial Research | Du Plessis A.,Stellenbosch University | Steyn J.,South African Council for Scientific and Industrial Research | And 4 more authors.
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2010

The detection of metallic silver on Chemical Vapour Deposited (CVD) grown silicon carbide and in Pebble Bed Modular Reactor (PBMR) supplied tri-structural isotropic (TRISO) coated particles (with 500 μm diameter zirconium oxide surrogate kernel) has been studied with femtosecond Laser Induced Breakdown Spectroscopy (femto-LIBS). The SiC layer of the TRISO coated particle is the main barrier to metallic and gaseous fission products of which 110mAg is of particular interest for direct cycle high temperature reactors. This work is a feasibility study for diagnosing and profiling silver transport through the silicon carbide layer of fuel particles for a high temperature gas reactor in out-of-reactor experimentation. The zirconium oxide is a surrogate for the enriched uranium oxide fuel. The conclusion reached in this study was that femto-LIBS can achieve good surface spatial resolution and good depth resolution for studies of silver in experimental coated particles. The LIBS technique also offers a good alternative for a remote analytical technique. © 2010 Elsevier B.V. All rights reserved. Source

Fontanet J.,CIEMAT | Herranz L.,CIEMAT | Ramlakan A.,Pbmr Pty Ltd.
International Congress on Advances in Nuclear Power Plants 2010, ICAPP 2010 | Year: 2010

A break in the Helium Pressure Boundary (HPB) in a HTGR will result in the primary depressurization and the transport, by the helium, of circulating and resuspended particles into the confinement building. Uncertainties associated with the characterization of these aerosols could potentially have a substantial impact on its behavior in the building and, consequently, in the source term leaked to the environment. Therefore, sensitivity studies in aerosol source entering the confinement are of utmost relevance in the safety analysis performed in HTGRs. This paper analyses the effect of the break location, inlet mass flow rate and size distribution to the aerosol mass fraction leaked outside the confinement. In order to do so, three HPB break size accidents (small, large and very large) have been modeled with the ASTEC vl.3 code. The results have highlighted that the variable that has the most significant effect in the external release is the rate at which aerosol enters the confinement. The effect of other variables depends on the scenario. For small break, the particle size has a moderate effect whereas it is negligible in large breaks. Moreover, the break location plays a significant role for large breaks although the net released mass is hardly affected. Finally, the released mass fraction is shown to be correlated with the in-confinement residence time by a simple expression. Source

Van Rooyen I.J.,South African Council for Scientific and Industrial Research | Van Rooyen I.J.,Nelson Mandela Metropolitan University | Van Rooyen I.J.,Pbmr Pty Ltd. | Van Rooyen I.J.,Idaho National Laboratory | And 6 more authors.
Nuclear Engineering and Design | Year: 2012

The integrity and property behavior of the SiC layer of the Tri-isotropic (TRISO) coated particle (CP) for high temperature reactors (HTR) are very important as the SiC layer is the main barrier for gaseous and metallic fission product release. This study describes the work done on un-irradiated SiC samples prepared with varying phosphorus levels to simulate the presence of phosphorus due to transmutation. 30Si transmutes to phosphorous ( 31P) and other transmutation products during irradiation, which may affect the integrity of the SiC layer. The P-doping levels of the SiC samples used in this study cover the range from 1.1 × 10 15 to 1.2 × 10 19 atom/cm 3 and are therefore relevant to the PBMR operating conditions. Annealing from 1000 °C to 2100 °C was performed to study the possible changes in nanostructures and various properties due to temperature. Characterization results by X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM), are reported in this article. As grain boundary diffusion is identified as a possible mechanism by which 110mAg, one of the fission activation products, might be released through intact SiC layer, grain size measurements is also included in this study. Temperature is evidently one of the factors/parameters amongst others known to influence the grain size of SiC and therefore it is important to investigate the effect of high temperature annealing on the SiC grain size. The ASTM E112 method as well as electron back scatter diffraction (EBSD) was used to determine the grain size of various commercial SiC samples and the SiC layer in experimental PBMR Coated Particles (CPs) after annealing at temperatures ranging from 1600 °C to 2100 °C. The HRTEM micrograph of the decomposition of SiC at 2100 °C are shown and discussed. Nanotubes were not identified during the TEM and HRTEM analysis although graphitic structures were identified. The preliminary conclusion reached is that the P-content at these experimental levels (1.1 × 10 15 to 1.2 × 10 19 atom/cm 3) does not have a significant influence on the nanostructure of SiC at high temperatures without irradiation. © 2011 Elsevier B.V. Source

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