ABSTRACT Time-sequence count data of a neutron counter were acquired at subcritical states of UTR-KINKI reactor and then a Feynman-α analysis considering delayed neutrons was carried out to determine a measured ratio of delayed to prompt neutron contribution to the correlation amplitude Y. The zero-power reactor was driven by a neutron source inherent in highly enriched uranium fuels to reduce any

ABSTRACT We perform energy-dependent calculations of independent and cumulative fission product yields for  235U,  238U, and  239Pu in the first chance fission region. Starting with the primary fission fragment distributions taken from available experimental data and analytical functions based on assumptions for the excitation energy and spin-parity distributions, the Hauser-Feshbach statistical decay

ABSTRACT Thick corrosion oxide (Fe3O4) layers containing radioactive metals are generated in a carbon steel heat transport system (HTS) of pressurized heavy water reactors during operation. It is necessary to decontaminate the oxide layers to reduce radiation exposure to workers before maintenance and decommissioning. Since the oxide layer thickness in the HTS is about 75 μm, a considerable amounts

ABSTRACT Non-premixed combustion of hydrogen jets containing sodium vapor and mist reduces threats to reactor containment integrity in sodium-cooled fast reactors (SFRs) because it gradually consumes hydrogen gas generated mainly by a reaction between sodium and concrete. Previous studies have been limited to experimentally determining ignition thresholds on the jet temperature and the sodium concentration

ABSTRACT Defense in depth is a pillar of nuclear power plant design and it also plays an important factor for the reliability of fuel supply. While most safety systems of a classical light water reactor usually remain unchanged for many years of operation the first and second fission product barrier – the fuel and the cladding – are regularly exchanged by loading fresh fuel assemblies into the reactor

ABSTRACT Neutron capture cross-section measurements for  237Np have been conducted with the Accurate Neutron Nucleus Reaction Measurement Instrument (ANNRI) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC) using neutrons with energy ranging from thermal energy to 1 MeV. A time-of-flight (TOF) method using a NaI(Tl) detector was employed and

ABSTRACT Thermodynamic analysis and optimization for the steam methane reforming (SMR) hydrogen production system using the high temperature gas-cooled reactor pebble-bed module power plant (HTR-PM) are investigated in this work. Based on the thermodynamic-equilibrium model, parameters of thermal efficiency (η), hydrogen production (YH2/methane), methane conversion rate (X1) and carbon monoxide conversion

ABSTRACT The F82H, which is one of reduced activation ferritic/martensitic steels, is a strong candidate structure material for fusion reactor because of its satisfactory mechanical property and high swelling resistance in the operating temperature range. One disadvantage of F82H would be its low thermal conductivity as a structural material for divertor. In this study, we have fabricated several F82H-based

ABSTRACT Radon in soil is a valuable radioactive tracer in earth science, especially for earthquake and volcanic precursors. For the purpose of continuous measurement of radon-in-soil concentration in-situ, a new-designed measurement system was developed. Calibration and experiments for humidity response correction were carried out in details, and field measurement of vertical profile with 7 radon

ABSTRACT It is investigated for the nuclear security following the cyber terrorism of the Kudankulam nuclear power plant (KNPP) in Tamil Nadu, India. The relationship between arbitrary data and the invasion scenario is analyzed by the designed algorithms. In the study, the system dynamics (SD) can be used for the non-linear matters in the terrorism. There are two kinds of results in this modeling.

ABSTRACT The applicability of Monte–Carlo calculations is examined for the analyses of light-water-moderated and light-water-reflected cores at the Kyoto University Critical Assembly with the use of the experimental data of criticality, reactivity, and reaction rates. For the well-thermalized cores, criticality demonstrates the dependence of eigenvalue bias on the neutron spectrum at a critical state

ABSTRACT After the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP), the Nuclear Regulation Authority (NRA) has adopted measures based on radiation monitoring in residential areas, instead of making decisions based on predictive radioactive material diffusion to protect residents in emergency preparedness and response. Protective actions such as sheltering and evacuation based on the measured

ABSTRACT To judge whether an application system is a subcritical state or not based on numerical results of the effective neutron multiplication factor keff, an evaluation method of the estimated criticality lower-limit multiplication factor (ECLLMF) using the bootstrap method is newly proposed. By utilizing numerical results of keff for critical benchmark-problems that are selected depending on neutronic

ABSTRACT The risk of criticality accidents by fuel debris in the decommissioning of Fukushima Dai-ichi Nuclear Power Station is unlikely to be negligible. Therefore, an estimation of the consequences of such accidents is important. According to the latest study, estimating the energy that would be released if fuel debris became supercritical while falling into water is thought to be important. In falling

ABSTRACT In the design process of a steam generator, a porous-media-approach computational code is utilized for simulating three-dimensional two-phase flow behavior in the secondary side of steam generators. For the design of next-generation steam generators, the advanced thermal-hydraulic analysis code based on the two-fluid model has been developed by implementing constitutive equations into the

ABSTRACT A steam generator is one of the essential components in Pressurized Water Reactors. One of its critical design issues is to prevent heat transfer tube damage caused by corrosion and flow-induced vibration. When designing a U-tube bundle of steam generators, a thermal hydraulic simulation code is used to predict velocity and density distribution along tubes, especially porous-media-based code

ABSTRACT Fuel debris removal is the most challenging part of damaged nuclear power station decommissioning. It is important to carry out nuclear safety calculations accurately and quickly enough. Here, it was clarified that modern codes based on the Monte Carlo method were capable of performing neutronic analysis with the same accuracy and without significant differences in the results. The benchmark

ABSTRACT Bearings are widely applied in rotating machinery of nuclear power plants (NPPs). Data-driven fault diagnosis technology is critical to ensuring the reliable operation of rotating machinery. Aiming at the problem of poor model generalization ability caused by discrepant data distribution of monitoring signals under various working conditions, a deep transfer learning method based on fully

ABSTRACT Atmospheric transport, dispersion, and deposition models (ATDMs) can support decision-making during nuclear emergencies; however, uncertainties in the ATDM results need to be carefully evaluated. To investigate the uncertainties derived from meteorological forecast inputs, we conducted three-day forecast simulations every day for one year with hypothetical releases of radionuclides (one-hour

ABSTRACT A Compton camera system for use on an unmanned helicopter was previously developed to characterize the distribution of radioactive materials in highly contaminated areas. For this study, a Compton camera system was equipped with a small camera, laser distance meter, an attitude angle sensor, temperature sensors, and real-time monitoring software for better measurement of flight parameters

ABSTRACT In order to develop models regarding subcooled boiling flow and its heat transfer, we conducted subcooled boiling experiments to investigate subcooled bubble formation and measured development process of the bubbles using a test loop with a vertical annulus flow path under atmospheric conditions. Two-phase flow parameters regarding subcooled boiling, such as instantaneous bubble velocity,

ABSTRACT Supercritical CO2 (S-CO2) Brayton cycle is one of the alternative energy conversion technologies for generation IV nuclear energy systems. Printed circuit heat exchanger (PCHE) is one of the key components in S-CO2 Brayton cycle. Although PCHE has dedicated steady-state models, transient models that can be applied to precise analysis of systems remain to be developed. The deviations brought

ABSTRACT To extend the information on the validation of the JENDL-4.0 nuclear data library, continuous-energy Monte Carlo calculation was applied to the analysis of the measured core radial fission rate distributions in the light-water-moderated cores loaded with mixed oxide (MOX) and UO2 fuel rods. The measured results were taken from the reports of the critical experiments performed using the Tank-type

ABSTRACT The present study performed integral experiments of 99Tc by an activation method using a fast-neutron source reactor ‘YAYOI’ of the University of Tokyo to validate evaluated nuclear data libraries: JENDL-4.0, ENDF/B-VII and VIII. Technetium-99 samples were irradiated with reactor neutrons using a pneumatic system, and repeated 74 times to accumulate statistics. Reaction rates of 99Tc were

ABSTRACT A ‘transXend’ detector measures X-rays as electric current and yields an X-ray energy spectrum after analysis. Response functions are necessary for the analysis and are previously estimated using material details of the X-ray detector. The detector specifics, however, are not always available to users. Here, a ‘response-function-less’ transXend detector is described that relies on transmission

ABSTRACT The neutron capture cross section of 243Am was measured by the time-of-flight method with a pulsed neutron beam from a spallation neutron source of the Japan Proton Accelerator Research Complex. An Fe neutron beam filter was used to make the incident neutron beam quasi-monoenergetic around 23.5 keV. The neutron capture γ-rays were detected with a NaI(Tl) detector. The pulse height weighting

ABSTRACT An adaptive setting method of background cross sections is implemented to FRENDY/MG, which is a multi-group neutron cross section generation module, for accurate interpolation of self-shielding factors with a minimum number of background cross sections. Since the dependence of self-shielding factors on background cross section is significantly different among energy group, reaction type, and

ABSTRACT The accident in Fukushima Dai-ichi nuclear power plants reconfirms the necessity of the safety assessment considering multiple nuclear reactor units. However, consideration of the interdependency among safety systems or events in multiple units as well as the time dependency of accident progressions is difficult in the conventional event tree method, which is widely used in probabilistic risk

ABSTRACT Laboratory experiments and model estimates were carried out to evaluate the effectiveness of sorbent for construction of the Permeable Reactive Barrier (PRB) at downstream of H4 tank area in Fukushima-Daiichi Nuclear Power Station in September 2014. Measurement of cation exchange capacity and X-ray diffraction analyses of crystal structures were carried out for natural zeolites. The Sr adsorption

ABSTRACT To systematically examine the relationship between the fuel fragmentation during a loss-of-coolant accident (LOCA) and the pellet microstructure, heating tests were conducted on micro fuel samples obtained from various radial positions of high-burnup fuel. The extent of the fuel fragmentation was evaluated via fission gas release rate and post-test microscopies. The results provide direct

ABSTRACT While evaluating the secondary impact of transport casks under the oblique drop tests based on the IAEA transport regulation, it is important to find the most severe condition defined with respect to the oblique angle of the cask attitude during its fall.Currently the costly finite element method is generally used for this purpose.In this study, a simplified theoretical method has been proposed

ABSTRACT In-vessel retention (IVR) is a viable method of preserving reactor pressure vessel integrity in severe reactor accidents. Accurate knowledge of the bubble lift-off diameter for a downward-facing inclined heating surface is vital for successfully implementing IVR following the critical heat flux (CHF). A research facility was designed to visualize bubble lift-off for different heating surface

ABSTRACT Boiling water reactors have internal components manufactured with stainless-steel type 304. Some relevant cracks have been detected through the periodic inspections of their internal components. Regarding the core shroud, cracks have been observed along the circumferential welds. The causes of such cracks are: radiation, vibration, stress corrosion cracking (SCC) and residual stresses, acting

ABSTRACT This paper presents a Bayesian-estimation-based seismic fragility assessment method that can significantly reduce the computational burden. The likelihood function and prior distribution used in the Bayesian estimation were enhanced. A probability density function of the seismic capacity was adopted as the likelihood function, although previous studies have generally used the fragility curve

ABSTRACT Early public protection measures play an important role in reducing the health effects of radiation exposure. In particular, a staged evacuation is recognized as the most important strategy. However, studies on segmenting an evacuation region with non-uniform population density are lacking; therefore, the purpose of this study is to gain insight regarding this topic. First, the evacuation

ABSTRACT Determining the completeness of nuclear reactor decommissioning is an important step in safely utilizing nuclear power. For example, 137Cs from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident can be treated as background radioactivity, so determining the origin of 137Cs is essential. To accomplish this, measuring the 135Cs/137Cs isotope ratio can be useful, so this study optimized

ABSTRACT A new burnup calculation method for burnable absorber-containing fuels called the Advanced Optimally-Weighted Predictor-Corrector (AOWPC) method is proposed based on the OWPC method. The AOWPC method can effectively reduce the time discretization errors in the burnup calculation. Verification calculations comparing with the conventional predictor-corrector (PC) and projected PC (PPC) methods

ABSTRACT The impact of disposal of mixed oxide (MOX) fuel from light water reactors (LWRs) has been considered from the viewpoint of the thermal properties and the number of the vitrified waste for various conditions of the nuclear fuel cycle. In addition, the effect of separation of the minor actinides (MAs) (Np, Am, Cm) that potentially influence the geological disposal area has been evaluated quantitatively

ABSTRACT CBZ is a general-purpose reactor physics analysis code system, and FRBurner, which focuses on fast reactor burnup calculations, was developed recently with diverse combinations of available methodologies. Verification of this module is conducted with the OECD/NEA fast rector benchmark since this benchmark provides various types of fast reactors. Four key reactor physics parameters, effective

ABSTRACT The multi-group cross-section generation capability for neutrons is implemented in the FRENDY nuclear data processing code. ACE-formatted files are used as the source of nuclear data instead of ENDF-formatted files since FRENDY already has the capability to generate pointwise cross sections in the ACE format. The several distinguished features are implemented for the multi-group generation

ABSTRACT A safety assessment was performed on the second-phase disposal facility of the Gyeongju low – and intermediate-level radioactive waste repository using the RESRAD-OFFSITE code. On the basis of the acceptance criteria of the repository, 13 radionuclides and gross alpha were selected as the radionuclides to be evaluated. In addition, the thermodynamic database of Japan Atomic Energy Agency and

ABSTRACT The reactor pressure vessel (RPV) failure timing in Unit 1–3 of the Fukushima Daiichi Nuclear Power Plant was estimated by considering the metallic interactions in the lower plenum. The re-molten core materials could attack and penetrate the weld and, hence, the materials science aspect is expected to provide insights that can assist in the estimation of RPV failure. First, to examine the

ABSTRACT Using an activation method with a well-thermalized neutron field, it is principally possible to drive a thermal-neutron capture cross-section without considering an epithermal neutron component. We demonstrated neutron capture cross-section measurements using the graphite thermal column (TC-Pn) of the Kyoto University Research Reactor. First, in order to confirm that the graphite thermal column

ABSTRACT Nuclear grade 316 stainless steel (SS) is the main material of core internals for liquid sodium-cooled fast reactor (SFR). However, very limited mechanical properties of nuclear grade 316SS under elevated-temperature liquid sodium, including yield strength (YS), ultimate tensile strength (UTS) and total elongation (TE), can be obtained due to long-time consumption and extreme testing condition

ABSTRACT Pool scrubbing is one of the promising means for mitigating radioactive aerosol release into the environment in nuclear severe accident scenarios. The influence of operational conditions on its performance is therefore of much interest. This paper focuses on the influence of particle number density found in our experiments. The experiments, conducted for insoluble monodispersed (0.5 µm) particles

ABSTRACT Human reliability analysis (HRA) for severe accidents is an important component of a Level 2 probabilistic risk assessment (PRA) for nuclear power plants. In this study, a Bayesian network (BN) is used to construct a qualitative causal model of human error during severe accidents by identifying the main cognitive functions (MCFs), crew failure modes (CFMs), and performance influencing factors

ABSTRACT The mechanism of crystallographic orientation dependent on helium-induced blister formation in plasma-facing tungsten was studied by helium implantation, scanning electron microscopy (SEM) observation, and molecular dynamics (MD) simulation. In the present work, the electropolished high-purity tungsten was exposed to 18 keV helium ions to a fluence of 1.1 × 1018 He·cm-2at room temperature

ABSTRACT For an university training and research reactor of Kindai University, the Feynman-α analyses based on several formulae are carried out to examine the applicability of these formulae to the subcritical thermal reactor system. The original formula, in which the effect of delayed neutrons is neglected, results in a prompt-neutron decay constant sensitive to an upper limit of the gate time range

ABSTRACT A cross-section adjustment method based on Bayesian theory was derived for adjusting the specific cross-section set. The present method gives the ‘a posteriori’ distribution of the specific cross-section and does not require the adjustment of the other cross-sections. In the derivation, the experimental error, calculation error, and cross-section error are assumed to distribute normally and

ABSTRACT Performance improvement of the printed circuit heat exchanger (PCHE) plays a vital role in improving the comprehensive performance of the supercritical carbon dioxide (S-CO2) Brayton cycle. In this study, three design parameters are selected to improve the comprehensive performance of a PCHE, including channel type, channel number, and channel length. The thermal effectiveness and the total

ABSTRACT The paper summarizes the results of the control blade degradation test CLADS-MADE-02 performed in the Japan Atomic Energy Agency . The test focused on the beginning phase of the accident at Fukushima Dai-Ichi Nuclear Power Plant (1F) Unit 3. The investigation provided important data, especially on the temperature history, exhaust gas measurement, and in situ video of metallic debris formation

ABSTRACT Dissolution behavior of Sr and Ba is crucial for evaluating secondary source terms via coolant water from ex-vessel debris accumulated at Fukushima Daiichi Nuclear Power Station. To understand the mechanism, knowing the distribution of Sr and Ba in the ex-vessel debris is necessary. As a result of reaction tests between simulated corium and concrete materials, two-layered structures were observed

ABSTRACT Cesium-enriched particles released from the Fukushima Daiich Nuclear Power Plant (NPP1) exist in the Fukushima coastal waters and offshore, and they possibly affect the wide-area distribution of the radioactive cesium measured by the towed spectrometer. Therefore, the distribution of them in marine sediment was measured near NPP1 in November, 2016. We scanned the seafloor using a remotely

ABSTRACT A modeling calculation methodology for estimating the radionuclide composition in the wastes generated at the Fukushima Daiichi nuclear power station has been upgraded by introducing an approach using Bayesian inference. The developed stochastic method describes the credible interval of the regression curve for the log-normal distribution of the measured transport ratio, which is used to calibrate

ABSTRACT Understanding the pathways of 137Cs transfer to spiders as generalist predators is useful to assess the long-term recycling of 137Cs through the food chain in forest ecosystems. Approximately 6.5 years after the Fukushima Dai-ichi Nuclear Power Plant accident, we collected spider samples at two different habitats (in a forest interior and along a river) in a forest and determined their 137Cs

ABSTRACT The occurrence of common cause failures poses a critical threat to the seismic safety of nuclear power plants. The installation of diverse components such as isolation systems is believed to be a promising strategy to avoid such failures, especially in the context of disasters such as the Fukushima accident. Although the effectiveness of implementing diverse components in enhancing the seismic

ABSTRACT 6Li and 10B contents in the nuclear graphite need to be calculated and evaluated for 4He and the gaseous nuclear radioactive waste 3H, which should be eliminated to an acceptable low level. Furthermore, it will help analyze the diffusion and adsorption behavior as precursors of 3H and 4He. Based on reactions of 6Li(n,α)3H and 10B(n,α)7Li, we employ Neutron Depth Profiling (NDP) as a non-invasive

ABSTRACT The latest ENDF/B-VIII library adapted new porosity-dependent cross-section data of graphite. However, the porosity of the actual graphite does not necessarily correspond to the porosity given in the data. We have proposed a method to perform neutronic calculations at the desired porosity on the basis of the pseudo-material method. We have also compared the keff values calculated by the pseudo-material

ABSTRACT In this work, a hybrid Monte Carlo/sensitivity-based uncertainty contribution estimation approach is derived and tested. The approach is based on using the statistical samples used in the Monte Carlo uncertainty quantification combined with the subspace analysis to define and solve a set of linear equations to estimate the first-order sensitivities whenever the adjoint and forward sensitivity

ABSTRACT The ‘perturbation source method’ (PSM) is a Monte Carlo perturbation method that calculates an exact k-eigenvalue change caused by cross-section changes. Although the PSM, which can consider the effect of fission source perturbation, was proposed long ago, it has garnered minimal interest as a Monte Carlo perturbation method. The applicability of the PSM has not been thoroughly elucidated