IAEA Coordinated Research Program Research Articles

The IAEA CRP on HTGR uncertainties: Sensitivity study of PHISICS/RELAP5-3D MHTGR-350 core calculations using various SCALE/NEWT cross-section sets for Ex. II-1a

Uncertainty and sensitivity analysis is an indispensable element of any substantial attempt in reactor simulation validation. A Coordinated Research Program (CRP) supervised by the International Atomic Energy Agency was started to investigate the various uncertainty quantification methodologies for High Temperature Gas-cooled Reactors. The first phase of the CRP is dedicated to the estimation of cell and lattice model uncertainties due to the neutron cross sections. Phase II is oriented towards the investigation of propagated uncertainties from the lattice to the coupled neutronics/thermal hydraulics core calculations. Best-estimate results for the prismatic single block (Ex. I-2a) and super cell models (Ex. I-2c) were obtained using the SCALE 6.2.0 two-dimensional lattice code NEWT. A reference spectrum was obtained with Serpent 2.1.27 for the single block, super cell and core models. The flux spectrum in the system of interest plays a primary role in the quantification of uncertainties caused by cross sections. In this work, the TRITON/NEWT-flux-weighted cross sections obtained for Ex. I-2a and various models of Ex.I-2c are utilized to perform a sensitivity analysis of the MHTGR-350 core power densities and eigenvalues. The core solutions are obtained with the Idaho National Laboratory (INL) coupled code PHISICS/RELAP5-3D. It is observed that axial shape of the core power density does not vary significantly with the various lattice cell libraries utilized. The use of cross section libraries originating from super cells induces changes of the core power density by 1–10% radially as compared to the Ex.I-2a cross sections. The magnitude of these variations increases as the moderator-to-fuel ratio increases in the super cell lattice models. A lattice flux spectrum resembling the core spectrum is hence necessary for correct predictions in nodal core calculations.

Challenges associated with the behaviour of radioactive particles in the environment

A series of different nuclear sources associated with the nuclear weapon and fuel cycles have contributed to the release of radioactive particles to the environment. Following nuclear weapon tests, safety tests, conventional destruction of weapons, reactor explosions and fires, a major fraction of released refractory radionuclides such as uranium (U) and plutonium (Pu) were present as entities ranging from sub microns to fragments. Furthermore, radioactive particles and colloids have been released from reprocessing facilities and civil reactors, from radioactive waste dumped at sea, and from NORM sites. Thus, whenever refractory radionuclides are released to the environment following nuclear events, radioactive particles should be expected.Results from many years of research have shown that particle characteristics such as elemental composition depend on the source, while characteristics such as particle size distribution, structure, and oxidation state influencing ecosystem transfer depend also on the release scenarios. When radioactive particles are deposited in the environment, weathering processes occur and associated radionuclides are subsequently mobilized, changing the apparent Kd. Thus, particles retained in soils or sediments are unevenly distributed, and dissolution of radionuclides from particles may be partial. For areas affected by particle contamination, the inventories can therefore be underestimated, and impact and risk assessments may suffer from unacceptable large uncertainties if radioactive particles are ignored. To integrate radioactive particles into environmental impact assessments, key challenges include the linking of particle characteristics to specific sources, to ecosystem transfer, and to uptake and retention in biological systems. To elucidate these issues, the EC-funded COMET and RATE projects and the IAEA Coordinated Research Program on particles have revisited selected contaminated sites and archive samples. This COMET position paper summarizes new knowledge on key sources that have contributed to particle releases, including particle characteristics based on advanced techniques, with emphasis on particle weathering processes as well as on heterogeneities in biological samples to evaluate potential uptake and retention of radioactive particles.

The IAEA coordinated research programme on HTGR uncertainty analysis: Phase I status and Ex. I-1 prismatic reference results

The quantification of uncertainties in design and safety analysis of reactors is today not only broadly accepted, but in many cases became the preferred way to replace traditional conservative analysis for safety and licensing analysis. The use of a more fundamental methodology is also consistent with the reliable high fidelity physics models and robust, efficient, and accurate codes available today. To facilitate uncertainty analysis applications a comprehensive approach and methodology must be developed and applied, in contrast to the historical approach where sensitivity analysis were performed and uncertainties then determined by a simplified statistical combination of a few important input parameters. New methodologies are currently under development in the OECD/NEA Light Water Reactor (LWR) Uncertainty Analysis in Best-Estimate Modelling (UAM) benchmark activity. High Temperature Gas-cooled Reactor (HTGR) designs require specific treatment of the double heterogeneous fuel design and large graphite quantities at high temperatures. The IAEA has therefore launched a Coordinated Research Project (CRP) on HTGR Uncertainty Analysis in Modelling (UAM) in 2013 to study uncertainty propagation specifically in the HTGR analysis chain.Two benchmark problems are defined, with the prismatic design represented by the General Atomics (GA) MHTGR-350 and a 250MW modular pebble bed design similar to the Chinese HTR-PM. Work has started on the first phase and the current CRP status is reported in the paper. A comparison of the Serpent and SCALE/KENO-VI reference Monte Carlo results for Ex. I-1 of the MHTGR-350 design is also included. It was observed that the SCALE/KENO-VI Continuous Energy (CE) k∞ values were 395pcm (Ex. I-1a) to 803pcm (Ex. I-1b) higher than the respective Serpent lattice calculations, and that within the set of the SCALE results, the KENO-VI 238 Multi-Group (MG) k∞ values were up to 800pcm lower than the KENO-VI CE values. The use of the latest ENDF-B-VII.1 cross section library in Serpent lead to ∼180pcm lower k∞ values compared to the older ENDF-B-VII.0 dataset, caused by the modified graphite neutron capture cross section. The fourth beta release of SCALE 6.2 likewise produced lower CE k∞ values when compared to SCALE 6.1, and the improved performance of the new 252-group library available in SCALE 6.2 is especially noteworthy. A SCALE/TSUNAMI uncertainty analysis of the Hot Full Power variant for Ex. I-1a furthermore concluded that the 238U(n,γ) (capture) and 235U(v¯) cross-section covariance matrices contributed the most to the total k∞ uncertainty of 0.58%.

Benchmarking RSG-GAS reactor thermal hydraulic data using RELAP5 code

The present work is developed within the frame of the IAEA Coordinated Research Program 1496, “Innovative methods in research reactor analysis: Benchmark against experimental data on neutronics and thermal-hydraulic computational methods and tools for operation and safety analysis of research reactors”.The objective of this work is to test the credibility of RELAP5 code in simulating the research reactor behavior during transients. Where, the code’s results were compared to the experimental measurements taken from Instrumented (thermocouple) Fuel Elements (IFE), installed at several positions in the core.The research reactor used in this study is the RSG-GAS reactor, located in the Serpong in Indonesia. Both the steady state and the transient simulation results performed using RELAP5 code for, are presented in this work.The calculated values for the coolant and clad surface temperature, at different locations in the core, showed an agreement with the experimental values with a difference less than 7% for the steady state, and with a difference less than 10% for transient conditions. However, RELAP5 was unable to predict the measured value of the coolant output temperature after the natural convection begins especially after stagnation occurred. In this case, the difference between the code results and experimental data was about 23%.

Investigation of the Capability of REALP5 to Solve Complex Fuel Geometry

This work is developed within IAEA Coordinated Research Program 1496, “Innovative methods in research reactor analysis: Benchmark against experimental data on neutronics and thermal-hydraulic computational methods and tools for operation and safety analysis of research reactors”. The study investigates the capability of Code RELAP5/Mod3.4 to solve complex geometry complexity. Its results are compared to the results of PARET, a common code in thermal hydraulic analysis for research reactors, belonging to MTR-PC groups. The WWR-SM reactor at the Institute of Nuclear Physics (INP) in the Republic of Uzbekistan is simulated using both PARET and RELAP5 at steady state. Results from the two codes are compared. REALP5 code succeeded in solving the complex fuel geometry. The PARET code needed some calculations to obtain the final result. Although the final results from the PARET are more accurate, the small differences in both results makes using RELAP5 code recommended in case of complex fuel assemblies. Keywords—Complex fuel geometry, PARET, RELAP5, WWRSM reactor.

THE USE OF NUMERICAL MODELS IN SUPPORT OF SITE CHARACTERIZATION AND PERFORMANCE ASSESSMENT STUDIES FOR GEOLOGICAL REPOSITORIES

The paper is describing work being developed in the frame of a 5-year IAEA Coordinated Research Programme (CRP) started in late 2005. Participants gained knowledge of modelling methodologies and experience in the development and use of rather sophisticated simulation tools in support of site characterization and performance assessment calculations. These goals were achieved by a coordinated effort, in which the advantages and limitations of numerical models are examined and demonstrated through a comparative analysis of simplified, illustrative test cases. This knowledge and experience should help them address these issues in their own country’s nuclear waste program. Coordination efforts during the first three years of the project aimed at enabling this transfer of expertise and maximizing the learning experience of the participants as a group. This was accomplished by identifying common interests of the participants (i.e., Process Modelling and Total System Performance Assessment methodology), and by defining complementary tasks that are solved by the members. Synthesis of all available results by comparative assessments is planned in the coming months. The project will be completed end of 2010. This paper is summarizing activities up to November 2009.

Complex Model to Study Long Term Environmental Tritium Behavior

ABSTRACTTo assess long-term environmental safety of a tritium facility, prediction of consequences of potential tritium releases in the environment is needed both during routine operations and in case of accidents. Modeling is the only method to obtain such assessment without any environmental contamination.The current paper describes the TRIEF model designed to assess consequences of long-term atmospheric tritium emission for such environmental compartments as atmosphere, soil, plants; tritium contamination of ground and underground water is also included. The model takes into account tritium transport among all of the compartments. The model has been successfully validated in model-experiment intercomparison study in framework of the IAEA co-ordinated research programme “BIOMASS” on assessment of environmental contamination from the continuous source of atmospheric tritium release. The experimental data included tritium concentrations in the atmospheric moisture, vegetation, soil and the overlying snow cover. The modelling period was 20 years. Most of the predicted values agreed with observations within experimental uncertainties, which were a factor of 2.The TRIEF model is based on both HTO equilibrium and material balance approach in all the compartments. Average concentrations in atmosphere are calculated by using the Gauss-type model for primary and secondary source. HT and HTO behavior are modeled separately. Both wet and dry deposition of HTO is taken into account in case of HTO emission. HTO concentration in soil moisture is determined by the moisture balance equation. HTO concentration in plant tissue free water and organically bound tritium are estimated as a combination of HTO content in soil moisture and atmospheric humidity. HTO contamination of aquifer is modeled using available finite-differences codes within 12 hydro-geological strata.

Application of Isotope Dilution Technique in Vitamin A Nutrition

The isotope dilution technique involving deuterated retinol has been developed to quantitatively estimate total body reserves of vitamin A in humans. The technique provided good estimates in comparison to hepatic vitamin A concentrations in Bangladeshi surgical patients. Kinetic studies in the United States, Bangladesh, and Guatemala indicated the mean equilibration time of 17 to 20 days irrespective of the size of hepatic reserves. Due to the controversy surrounding the efficacy of a carotene-rich diet on improvement of vitamin A status, the isotope dilution technique was proposed to pursue this research question further (IAEA's coordinated research program). In the Philippines, schoolchildren with low serum retinol concentrations showed significant improvement in total body vitamin A stores following intake of carotene-rich foods (orange fruits and vegetables), using a three-day deuterated-retinol-dilution procedure. When Chinese kindergarten children were fed green and yellow vegetables during the winter, their total body vitamin A stores were sustained as compared to a steady decline of vitamin A stores in the control children. Likewise, daily consumption of purified beta-carotene or diet rich in provitamin A carotenoids were shown to prevent a loss in total body vitamin A stores among Thai lactating women during the rice-planting season. These studies demonstrate potentials of the isotope dilution technique to evaluate the impact of provitamin A carotenoid intervention programs.

A computer program with graphical user interface to plot the multigroup cross sections of WIMS-D library

As a result of the IAEA Co-ordinated Research Programme entitled “Final Stage of the WIMS Library Update Project,” new and updated WIMS-D libraries based upon ENDF/B-VI.5, JENDL-3.2 and JEF-2.2 have become available. A project to prepare an exhaustive handbook of WIMS-D cross sections from old and new libraries has been taken up by the authors. As part of this project, we have developed a computer program ‘XnWlup’ with user-friendly graphical interface to help the users of WIMS-D library to enable quick visualization of the plots of the energy dependence of the multigroup cross sections of any nuclide of interest. This software enables the user to generate and view the histogram of 69 multi-group cross sections as a function of neutron energy under Microsoft Windows environment. This software is designed using Microsoft Visual C++ and Microsoft Foundation Classes Library. The current features of the software, on-line help manual and future plans for further development are described in this paper.

「マイナーアクチニド核廃棄物の核変換のために要求される核分裂生成物収率データ」ＩＡＥＡ協力研究計画 第１回検討会合報告

The first research coordinate meeting (RCM) for IAEA Coordinated Research Program (IAEA/CRP) on fission product yield data required for transmutation of minor actinide nuclear waste was held on Nov. 57, 1997 at the IAEA headquarter at Vienna. Systematic data for fission product yield (FPY) are required to estimate feasibility, neutron economy and environmental safety of actinide burner reactor and accelerator-driven system for transmutation of minor actinide nuclear waste. On the other hand, the current energy-dependent data exist only up to 14 MeV and data set of FPY for minor actinide nuclei and calculation tools for FPY are incomplete. The purpose of this CRP is to develop systematics and/or models to evaluate energy-dependent FPY. This RCM was held to review the current status of experimental data and models and to share the needed tasks among CRP participants. In this report, the reviewed results are mentioned as well as the shared tasks expected to Japan. This status review is useful for the discussion of Japanese contributions.

Nuclear techniques applied to air particulate matter studies

The most important fraction of aerosols with respect to human health is the respirable fraction, which has particles less than 10 μm in equivalent aerodynamic diameter (EAD), the so called PM 10 fraction. The collection of these respirable particles and the determination of their trace element composition is the focus of an IAEA Co-ordinated Research Programme (CRP). The IAEA Laboratory participated in this Programme and established collection sites for the air particulate samples on the grounds of the Atominstitute of the Austrian Universities in Vienna and the IAEA Laboratories, Seibersdorf, representing an urban residential site and a rural site. The collected samples as well as samples of simulated air filters (used also for blind controls) and control materials were analyzed sequentially and/or in sections by X-ray fluorescence (XRF), proton induced X-ray emission (PIXE), instrumental neutron activation analysis (INAA), and atomic absorption spectrometry (AAS). Results demonstrate the applicability of the PM-10 sampling approach, provided PIXE and/or INAA are used in the determinations. Reliable results can be obtained that will lead in comparable air pollution data for many regions in the world through CRP.

Correlation among the Changes in Mechanical Properties due to Neutron Irradiation for Pressure Vessel Steels.

Irradiation hardening and embrittlement of reactor pressure vessel (RPV) steels having different contents of copper and nickel have been investigated as a part of the phase III of IAEA Coordinated Research Program (CRP). Seven kinds of materials which were made by Japanese steel manufacturers for the CRP were used. Neutron irradiation was conducted in Japan Materials Testing Reactor (JMTR). Mechanical properties of the materials were examined by conducting the hardness, tensile, Charpy impact and fracture toughness tests before and after irradiation. Some relationships between the changes of the mechanical properties due to irradiation were established. The increase in yield strength was correlated with hardness increase and the shift of Charpy transition temperature. In the upper shelf temperature range, the decrease in fracture toughness was well correlated with the degree of the increase in yield strength.

IAEA-coordinated research programme on radon in the human environment

IAEA-coordinated research programme on radon in the human environment

Calorimetric and transport properties of Zircalloy 2, Zircalloy 4, and Inconel 625

This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured properties include thermal diffusivity, specific heat, and electrical resistivity. Thermal diffusivity was measured by the laser pulse technique. Specific heat and electrical resistivity were measured using a millisecond-resolution direct electrical pulse heating technique. Thermal conductivity was computed from the experimentally determined thermal difusivity and specific heat functions and the room temperature density values. Measurements were performed in the 20 to 1500°C temperature range, depending on the material and property concerned.

Coordinated research efforts for establishing an in international radiotherapy dose intercomparison service based on the alanine/ESR system

The IAEA has long been active in the field of high-dose standardization. In cooperation with the Gesellschaft für Umwelt und Gesundheit (GSF), Germany, an International Dose Assurance Service (IDAS) was established based on alanine/ESR dosimetry. This service operates over the range of 100 Gy to 100 kGy and is directed towards industrial radiation processing in IAEA Member States. In complements the IAEA/WHO TLD postal dose intercomparison service for dose assurance in hospital radiotherapy departments. Experience with the alanine high dose service suggests that the alanine dosimeter might provide superior performance to TLD in the therapy dose range. Preliminary test measurements with the participation of GSF/Germany, Istituto Superiore di Sanità/Italy (both providing alanine dosimeters and their evaluation) and IAEA (providing) reference irradiations traceable to BIPM) seems to justify research efforts through an IAEA Coordinated Research Programme (CRP). This CRP, entitled “Therapy Level Dosimetry with the Alanine/ESR System” is presently under set-up. It will include general work common to all assigned/potential contract holders as well as some specific research topics in accordance to individual proposals of each participant.

The significance of hair mineral analysis as a means for assessing internal body burdens of environmental pollutants: Results from an IAEA Co-ordinated Research Programme

During a five-year period, the International Atomic Energy Agency supported a Coordinated Research Programme (CRP) to investigate the quantitative relationship between internal body burdens of a number of elements of environmental health significance and their respective concentrations in hair. The use of nuclear-related analytical techniques, such as neutron activation analysis, X-ray fluorescence, particle-induced X-ray emission and radiotracers, was emphasized. One aspect of the CRP focused on studies in man, using autopsy cases, of mineral distribution in five tissues, i.e. liver, kidney, lung, brain and bone in addition to hair, and the elements of primary importance were As, Cd, Cu, Hg, Pb, Se and Zn. Emphasis was placed on analytical quality assurance. Hair and internal tissue samples were obtained from subjects from Bulgaria, China, the former German Democratic Republic, Hungary, Japan, Norway and Sweden.

The half-life of 192Ir

The current interest in the use of 192Ir for brachytherapy prompted a re-evaluation of existing half-life values. Using the evaluation criteria adopted in a recent IAEA-Coordinated Research Programme, it was determined that the uncertainty in the half-life obtained by evaluating published data spanning the last 20 years is too large.Further measurements of the half-life have been carried out using high-pressure re-entrant ionization chambers. The results of these latest measurements are presented together with a re-evaluation of the half-life using the IAEA-CRP criteria. The recommended half-life of 192Ir is 73.830 ± 0.018 d.

The IAEA Coordinated Research Programme on the Performance of High-Level Waste Forms and Packages Under Repository Conditions

ABSTRACTThe IAEA initiated, in 1991, a Coordinated Research Programme (CRP), with the aim of promoting the exchange of information on the results obtained by different countries in the performance of high-level waste forms and waste packages under conditions relevant to final repository. These studies are being undertaken to obtain reliable data as input to safety assessments and environmental impact analyses, for final disposal purposes. The CRP includes studies on waste forms that are presently of interest worldwide: borosilicate glass, Synroc and spent fuel.Ten laboratories leading in investigation of high-level waste form performance have already joined the programme. The results of their studies and plans for future research were presented at the first Research Coordination Meeting, held in Karlsruhe, Germany, in November 1991. The technical contributions concentrated on effecting an understanding of dissolution mechanisms of waste forms under simulated repository conditions. A quantitative interpretation of the chemical processes in the near field is considered a prerequisite for long-term predictions and for the formulation of a "source term" for performance assessment studies.

Study of the correlation of trace elments in human hair and internal organs by NAA

24 male autopsy cases aged 35–60 years have been collected from Shanghai China to study the relationships between human hair and internal tissues. Autopsy samples of hair, kidney-cortex, liver and lung were analyzed. A radiochemical neutron activation analysis (RNAA) based on a simple group extraction scheme was used for measuring the trace elements As, Cd, Hg, Cu and Zn. Zinc diethyldithiocarbamate Zn(DDC)2 and methly isobutyl ketone-iodide have been chosen as reagent. Trace element of Se was determined by instrumental neutron activation analysis (INAA). A SLOWPOKE reactor with a thermal neutron flux of 8·1011 n·cm−2·s−1 and a swimming pool type reactor with a thermal neutron flux of 1·1013 n·cm−2·s−1 were used for short and long irradiation of samples, respectively. The reliability of methods has been checked by analyzing biological standard reference materials Horse Kidney (IAEA H8), Tomato Leaves (NBS 1573) and Human Hair (NIES-5). The analytical results show that toxic elements As, Cd and Hg exist in a larger individual variability than the essential elements of Cu, Se and Zn for each tissue. A linear regression analysis related to the six elements of primary interest for the IAEA Coordinated Research Program (CRP) has been done by a computer program for each pair of hair-tissue. A positive correlation is found between concentration of As in hair and kidney-cortex, the correlation coefficient r is 0.751 (p<0.01). Positive correlations between concentration of Se in hair and liver, kidney-cortex and lung are also observed in this study. It shows that the elements As and Se in hair may be useful indicators for assessing certain internal tissues of normal persons. A comparison of Cd concentration in lung shows a significant difference between smokers and non-smokers. A significant correlation between element Cd and Zn in kidney-cortex is also presented in this paper.

Survey on the activities in Switzerland in the field of HTGR-development

The activities of the Swiss industry and of the “Paul Scherrer Institute” in the development and production of components and systems for the nuclear industry are reviewed. For the HTGR, major programs include the German HTR-500 project, the gas-cooled district heating reactor (GHR) and the PROTEUS critical experiments. The experiments are being performed in the framework of an IAEA coordinated research program.