Overview of the RPV-2 and INTERN-1 packages: From primary damage to microplasticity

In the framework of the European project PERFECT, four multiscale simulation packages dedicated to the prediction of evolution of material properties were developed. Among them, the RPV-2 and INTERN-1 are two simulation sequences of similar structure dealing with radiation damage in the reactor pressure vessel and the reactor internal structures, respectively. Both start at the atomic scale, where the neutron spectrum of the specified reactor is used to determine the energy distribution of the primary knocked-on atoms (PKA). A database of molecular dynamics results is then used to integrate the instantaneous production of defect clusters resulting from the displacement cascades initiated by each PKA. Depending on the type of calculation chosen to model long-term diffusion and reactions of defect clusters, precipitates and mixed-clusters, this primary damage enters either in rate equations or in Object Kinetic Monte Carlo simulations. The later correspond to a more accurate (but also more computationally demanding) physical model for diffusion as positions of objects on a lattice are explicitly treated. Finally, the increase of critical resolved shear stress is estimated from these cluster distributions either using an analytical model, taking into account the self and mutual dipole interactions of dislocations pinned on randomly dispersed unshearable obstacles, or by simulating the glide of a single dislocation line in its main slip system. Dislocation dynamics simulations were already used to validate some of the assumptions of the latter models, and will be fully integrated in the next versions of the packages.     

The evaluation of a reactivity insertion due to the group motion of FBR core subassemblies beyond Design Basis Ground Motion

The seismic probabilistic safety assessment (PSA) for fast breeder reactors (FBRs) has been carried out to confirm that the seismic safety is equivalent to that of light water reactors (LWRs). The seismic response on the reactor structure of FBRs causes seismic reactivity. The group motion of fuel assemblies is one of a typical seismic response. Therefore, much attention has been paid on the reactivity insertion mechanism due to the group motion of fuel assemblies and its consequence during the earthquake over the Design Basis Ground Motion (DBGM) condition. When the displacement of each subassembly is moving toward the same direction, each gap reduces coherently and the radial core compaction occurs, which results in positive reactivity insertion. We evaluate the gap reduction characteristics at the mid-plane of core by using a correlation coefficient. As a result, the fuel subassemblies are most concentrated when the input seismic motion of about 5 Hz frequency and 40 m/s² acceleration is applied. The amount of reactivity insertion is estimated approximately 1$ that corresponds to prompt criticality.     

中美核电厂流出物监测与排放管理要求对比分析

对我国和美国核电厂流出物的监测和排放管理要求进行了对比分析,指出我国在法规标准方面需要进行修订和完善之处,提出参考借鉴美国的经验对我国核电厂流出物监测和排放管理要求进行规范的建议。     

Response of nuclear materials in storage and transport to malevolent environments

Abstract

Work related to the assessment of radiological health consequences resulting from a sabotage attack on nuclear fuel storage or transport casks has been continuing since the late 1970s. While the level of effort in this area has been uneven over these three decades due to policy priorities, funding levels and programmatic priorities of the countries funding this type of work, substantial progress has been made. From phenomenology of in cask transport processes to development of aerosol production in high energy attack environments, the analytical and experimental work performed provides substantial justification to consequence assessments that heretofore have had to rely on conservative assumptions in lieu of empirical data. One constant since the late 1990s in addressing this problem has been an international working group whose primary focus has been to develop source term data from experimental simulations of sabotage types of attacks. This working group, titled the International Working Group for Sabotage Concerns of Transport and Storage Casks (WGSTSC) is comprised of experts mainly from the USA, France and Germany. Technical support has also been provided, on an intermittent basis, from the UK and Japan. The WGSTSC has pooled resources and expertise to design and conduct experiments to produce the data needed to perform radiological consequence assessments. In addition to the experimental programme, this group also has coupled modern analytical techniques with experimental results to understand the effects of high energy density devices on nuclear materials. This paper reviews the paradigm that has guided the WGSTSC effort and shows how the results from the experimental programmes of the past three decades have brought us to the current level of understanding of the potential consequences from a malevolent attack on nuclear transport and storage facilities. In addition, the paper provides an update on the status of the work of the WGSTSC and describes what additional experimental and analytical efforts would be most productive in further narrowing of uncertainty in consequence prediction.     

Isolation and identification of bacteria able to form biofilms from deep subsurface environments

Migration radionuclides in an underground environment are one of the major concerns in the safety assessment of a geological repository. Biofilms can have an impact on the transport of radionuclides in several ways: (1) by acting as a barrier to radionuclide sorption onto geological surfaces, or (2) by providing a sorption site for radionuclides, or (3) by trapping many things, including radionuclides. Little is known about bacterial effects on the biofilm formation deep underground. In this study, we isolated bacterial strains from deep groundwater and evaluated the biofilm formation abilities of these strains by crystal violet assay. Bacterial strains were isolated from ground-water collected at –140 m in the 07-V140-M01 borehole at the Horonobe Underground Research Center, Japan. The crystal violet assay showed that 98% of the isolated strains had biofilm formation abilities under tested conditions. This result suggested that biofilm formation must not be neglected in the study of migration radionuclides in nuclear waste repositories. The isolated strains produced differential amounts of biofilm, although they were identified as the same Pseudomonas species, suggesting that biofilm formation abilities varied at different strain levels. These results support the conclusion that the assessment of biofilm impact on the transport of radionuclides in a geological repository must consider the variation in biofilm formation as a function of strain level.     

An overview of 20 years' Romanian experience on packaging and components testing according to national and international regulations

Abstract

More than 20 years ago, the Institute for Nuclear Research (INR) Pitesti in Romania, through its Reliability and Testing Laboratory, was licensed by the Romanian Nuclear Regulatory Body – CNCAN to carry out qualification tests for packages intended for the transport and storage of radioactive materials. The radioactive material is placed in packaging which are designed in accordance with national and the International Atomic Energy Agency's (IAEA's) Regulations for safe transport to the disposal centre. A broad range of verification and certification tests are performed at INR on radioactive material packages or component sections, such as packages used for the transport of radioactive sources to be used for industrial or medical purposes. This paper describes some of the various tests, which have been performed, and how they relate to normal conditions and minor mishaps during transport. Quality assurance and quality control measures taken in order to meet technical specification provided by design there are also presented.     

High heat load tests on W/Cu mock-ups and evaluation of their application to EAST device

Tungsten has been considered as the primary candidate plasma-facing materials (PFM) for the EAST device. Three actively cooled W/Cu mock-ups with an interlayer made of tungsten-copper alloy (1.5 mm) were designed and manufactured. The tungsten armors, pure sintered tungsten plate (1 mm) and plasma-sprayed tungsten coatings (0.3 and 0.9 mm), were bonded to the interlayer by brazing and depositing respectively. All mock-ups can withstand high heat flux up to 5 MW/m² and no obvious failure was found after tests. The thermal performance experiments and microstructure analyses indicated the structure of mock-ups possess good thermal contact and high heat transfer capability. WCu alloy as an interlayer can largely reduce the stress due to the mismatch and improve the reliability. The mock-up with 0.9 mm coating had the highest surface temperature than the other two mock-ups, delaminations of this mock-up were found in the near surface by SEM. The primary results show that pure sintered tungsten brazed to WCu alloy is a possible way, and thick plasma-sprayed coating technique still need to be improved.     

Calculation and evaluation of cross-sections for p+Fe reactions up to 250 MeV

All cross-sections of proton-induced reactions, angular distributions and the energy spectra of neutron, proton, deuteron, triton, helium and alpha-particle emission are consistent calculated and analyzed for p+^{54,56,57,58,nat}Fe at incident proton energies below 250 MeV by using nuclear theoretical models which integrate the optical model, the intra-nuclear cascade model, direct, preequilibrium and equilibrium reaction theories. Especially, the cross-sections of the light composite particle (d, t, ³He and α) emissions are improved based on the exciton model including the pick-up mechanism. Theoretical calculated results are compared with existing experimental data.     

中低放固体放射性废物处置中的α废物在线检测及位置判定方法初探

根据在核废料回取分类、压缩减容的处置工艺及部分专用设备开发等方面的研究和初步实践,提出了利用现代测试技术和自动控制原理对a型废物进行在线探测、位置判定、目标成像、定性分析、比活度粗测的方法。     

Design and setup of a testing device to investigate a reduced sized attachment system mock up for the ITER EU HCPB-TBM under different mechanical loading conditions

In order to determine the forces acting on the EU-Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) during operation, a measurement system is developed. Therefore, two force reconstruction (FR) methods using measured strain signals are selected that are suitable for the application to the TBM. The first one, the augmented Kalman filter is a combined deterministic-stochastic approach. A second FR method based on the concept of a model predictive controller is proposed in this paper, which uses an optimization algorithm. In order to test the selected methods a testing device has been built which can be used to apply different force excitations on a reduced sized TBM mock up and measure the resulting strain signals of 16 strain gages. A simple tube mock up has been designed and manufactured to test and calibrate the FR algorithms. In addition, a second TBM mock up with attachment system is described. Finally, first results of the FR of a worst-case test case from simulated strain data of the simple tube mock up are presented.