Showing papers in "Journal of Nuclear Science and Technology in 2014"
TL;DR: In this article, the safety design requirements of the advanced loop-type fast reactor, so-called JSFR, are the prevention of severe accidents and the mitigation of severe-accident consequences.
Abstract: As the most promising concept of sodium-cooled fast reactors, the Japan Atomic Energy Agency (JAEA) has selected the advanced loop-type fast reactor, so-called JSFR. The safety design requirements of JSFR for Design Extension Condition (DEC) are the prevention of severe accidents and the mitigation of severe-accident consequences. For the mitigation of severe-accident consequences, in particular, the In-Vessel Retention (IVR) against postulated Core Disruptive Accidents (CDAs) is required. In order to investigate the sufficiency of these safety requirements, a CDA scenario should be constructed, in which the elimination of power excursion and the in-vessel cooling of degraded core materials are evaluated so as to achieve IVR. In the present study, the factors leading to IVR failure were identified by creating phenomenological diagrams, and the effectiveness of design measures against them were evaluated based on experimental data and computer simulations. This is an unprecedented approach to the construct...
73 citations
TL;DR: To inspect the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi nuclear power plant (F1-NPP), a transportable fiber-coupled laser-induced breakdown spectroscopy (LIBS) instrument h...
Abstract: To inspect the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi nuclear power plant (F1-NPP), a transportable fiber-coupled laser-induced breakdown spectroscopy (LIBS) instrument h...
64 citations
TL;DR: In this article, Monte Carlo transport simulations assuming exponential distributions in the ground were performed to obtain ambient dose equivalent for mono-energetic gamma-ray sources having different relaxation depths; on the basis of the simulated data, conversion coefficients for radionuclides were composed considering recent nuclear decay data.
Abstract: Conversion coefficients of radionuclide deposition density to the ambient dose equivalent rate at 1 m height above ground were calculated for exponentially distributed sources in the ground. First, Monte Carlo transport simulations assuming exponential distributions in the ground were performed to obtain ambient dose equivalent for mono-energetic gamma-ray sources having different relaxation depths; next, on the basis of the simulated data, conversion coefficients for radionuclides were composed considering recent nuclear decay data. The ambient dose equivalent rates were then compared to the effective dose rates for reference adults and a new-born baby as well as to air kerma rates quoted from previous studies. It was confirmed that the ambient dose equivalent sufficiently overestimates effective doses, independently of age, for sources exponentially distributed in the ground. Furthermore, the air kerma was found to also overestimate the effective doses for all ages in the same conditions. In order to ve...
55 citations
TL;DR: In this paper, the isotopic ratios of 134Cs/137Cs and 135C/137C were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator.
Abstract: Cesium was recovered from plant samples obtained from Fukushima prefecture. The isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator. Samples containing 5 Bq of 137Cs were analyzed with typical analytical errors of approximately 0.5% for 134Cs/137Cs and approximately 0.1% for 135Cs/137Cs. Measurements of both ratios showed profiles that were characteristic of the measurements of among other environmental samples reported in the literature. The results showed the isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were applicable for the source analysis of radioactive Cs in Fukushima prefecture.
50 citations
TL;DR: In this article, the fundamental phase relationships in the solidified core melt of the Fukushima Daiichi nuclear power plant were predicted by using core materials [B4C, stainless steel, etc.
Abstract: To predict the fundamental phase relationships in the solidified core melt of the Fukushima Daiichi Nuclear Power Plant, solidified melt samples of the various core materials [B4C, stainless steel,...
43 citations
TL;DR: To characterize the rubble and trees contaminated by radionuclides released by the recent accident at the Fukushima Daiichi Nuclear Power Station, the radiochemical analysis protocols were modified in this paper, which is the only work we are aware of.
Abstract: To characterize the rubble and trees contaminated by radionuclides released by the recent accident at the Fukushima Daiichi Nuclear Power Station, the radiochemical analysis protocols were modified...
39 citations
TL;DR: F fuzzy TOPSIS and generalized Choquet fuzzy integral algorithm for evaluation and selection of optimal locations for NPP in Turkey are proposed and Inceburun–Sinop was selected as a study site due to its highest performance and meeting most of the investigated criteria.
Abstract: The location selection for nuclear power plant (NPP) is a strategic decision, which has significant impact on the economic operation of the plant and sustainable development of the region. This pap...
35 citations
TL;DR: In this paper, a double-sensor conductivity probe was used to measure void fraction and bubble velocity in each subchannel in a 4×4 rod bundle, and the results showed that the distribution of void fraction in inner and side subchannels depend not only on lift force acting on bubbles but also on geometrical constraints on bubble dynamics, i.e., the effects of rod walls on bubble shape and rise v
Abstract: Lack of local void fraction data in a rod bundle makes it difficult to validate a numerical method for predicting gas–liquid two-phase flow in the bundle Distributions of local void fraction and bubble velocity in each subchannel in a 4×4 rod bundle were, therefore, measured using a double-sensor conductivity probe Liquid velocity in the subchannel was also measured using laser Doppler velocimetry (LDV) to obtain relative velocity between bubbles and the liquid phase The size and pitch of rods were 10 and 125 mm, respectively Air and water at atmospheric pressure and room temperature were used for the gas and liquid phases, respectively The volume fluxes of gas and liquid phases ranged from 006 to 015 m/s and from 09 to 15 m/s, respectively Experimental results showed that the distributions of void fraction in inner and side subchannels depend not only on lift force acting on bubbles but also on geometrical constraints on bubble dynamics, ie the effects of rod walls on bubble shape and rise v
33 citations
TL;DR: In this article, the radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000ppm in pure silica fiber, and the improved optical fibers were irradiated with γ-ray up to 1 × 106 Gy using a 60Co source.
Abstract: In the Fukushima Daiichi Nuclear Power Station, it is necessary to survey the locations and conditions of fuel debris inside reactor pressure vessels or primary containment vessels under water and radiation environment in preparation for removing fuel debris. An optical fiber is well known for features such as signal transmission, light weight, superior insulation performance, water resistance and electromagnetic noise resistance. These features allow the optical fiber to simplify the instrumentation systems for in-vessel inspection, as long as provide that the optical fiber can be used under high radiation dose environment. The radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000 ppm in pure silica fiber. The improved optical fibers were irradiated with γ-ray up to 1 × 106 Gy using a 60Co source. They indicated a large peak around 600 nm and a peak tail from ultraviolet region, but no large absorption in infrared region except a hydroxyl absorption peak of...
33 citations
TL;DR: In this paper, the integrated sorption and diffusion (ISD) model was developed based on the consistent combination of clay-water interaction, sorption, and diffusion models, which can aid in the prediction of the long-term performance of geological disposal systems of radioactive waste.
Abstract: It is important to understand the coupled processes of sorption and diffusion of radionuclides (RNs) in compacted bentonite, and to develop mechanistic models that can aid in the prediction of the long-term performance of geological disposal systems of radioactive waste. The integrated sorption and diffusion (ISD) model was developed based on the consistent combination of clay–water interaction, sorption and diffusion models. The diffusion model based on the electrical double layer theory describing relative ionic concentrations and viscoelectric effects at the negatively charged clay surface was coupled with porewater chemistry and sorption models. This ISD model was successfully tested for various actinides with a complex chemistry (Np(V), Am(III), U(VI) under conditions where variably charged carbonate complexes are formed) considered in Part 1, by using published diffusion and sorption data (Da, De, Kd) as a function of partial montmorillonite density. Quantitative agreements were observed by consider...
32 citations
TL;DR: The analysis results show that reliability of AP1000 passive safety systems (PXS and PCCS) is increased due to redundancies and diversity of passive safety subsystems and components, and four stages automatic depressurization system is the key subsystem for successful actuation of PXS-PCCS system.
Abstract: The passive safety systems utilized in advanced pressurized water reactor (PWR) design such as AP1000 should be more reliable than that of active safety systems of conventional PWR by less possible opportunities of hardware failures and human errors (less human intervention). The objectives of present study are to evaluate the dynamic reliability of AP1000 plant in order to check the effectiveness of passive safety systems by comparing the reliability-related issues with that of active safety systems in the event of the big accidents. How should the dynamic reliability of passive safety systems properly evaluated? And then what will be the comparison of reliability results of AP1000 passive safety systems with the active safety systems of conventional PWR.For this purpose, a single loop model of AP1000 passive core cooling system (PXS) and passive containment cooling system (PCCS) are assumed separately for quantitative reliability evaluation. The transient behaviors of these passive safety systems are ta...
TL;DR: In this paper, a cross section adjustment method based on the random sampling technique is proposed, where correlations among cross sections and core parameters are used instead of sensitivity c... and the proposed method uses correlation among cross-sections and core parameter correlations to improve cross-section adjustment.
Abstract: A cross section adjustment method based on the random sampling technique is proposed. In the proposed method, correlations among cross sections and core parameters are used instead of sensitivity c...
TL;DR: In this article, the displacement cross-sections, implemented in the particle and heavy ion transport code system (PHITS), have been calculated to estimate the radiation damage in structural materials used at accel
Abstract: The displacement cross-sections, implemented in the particle and heavy ion transport code system (PHITS), have been calculated to estimate the radiation damage in structural materials used at accel...
TL;DR: A technical demonstration of cosmic-ray muon radiography of a UO2 fuel assembly was performed at Toshiba Nuclear Critical Assembly (NCA) as mentioned in this paper, where the fuel assembly in the NCA was imaged through obstacles s...
Abstract: A technical demonstration of cosmic-ray muon radiography of a UO2 fuel assembly was performed at Toshiba Nuclear Critical Assembly (NCA). The fuel assembly in the NCA was imaged through obstacles s...
TL;DR: In this article, a series of experiments using non-spherical particles was performed within a recently developed comparatively larger scale experimental facility, and an extension scheme was suggested with the intention to extend the base model to cover the particle shape influence.
Abstract: Studies on debris bed self-leveling behavior with non-spherical particles are crucial in the assessment of actual leveling behavior that could occur in core disruptive accident of sodium-cooled fast reactors. Although in our previous publications, a simple empirical model (based model), with its wide applicability confirmed over various experimental conditions, has been successfully advanced to predict the transient leveling behavior, up until now this model is restricted to calculations of debris bed of spherical particles. Focusing on this aspect, in this study a series of experiments using non-spherical particles was performed within a recently developed comparatively larger scale experimental facility. Based on the knowledge and data obtained, an extension scheme was suggested with the intention to extend the base model to cover the particle-shape influence. The proposed scheme principally consists of two parts – with one part for correcting the terminal velocity of a single non-spherical particle, wh...
TL;DR: The chemistry of the process and coolant systems in water-cooled nuclear reactors is tightly controlled to minimise material degradation and, for some systems, to regulate reactor power as mentioned in this paper, which is the case in all nuclear power plants.
Abstract: The chemistry of the process and coolant systems in water-cooled nuclear reactors is tightly controlled to minimise material degradation and, for some systems, to regulate reactor power. Tight cont...
TL;DR: To support the design and operation of the decontamination system using KURION media for the treatment of highly contaminated water accumulated in Fukushima Daiichi Nuclear Power Station, Central R....
Abstract: To support the design and operation of the decontamination system using KURION media for the treatment of highly contaminated water accumulated in Fukushima Daiichi Nuclear Power Station, Central R...
TL;DR: In this paper, the critical heat flux (CHF) of an oxidized zircaloy surface and its enhancement were investigated during saturated water pool boiling at atmospheric pressure, and the results showed that the oxidized surface (OS) specimens increased the CHF, which could be because the oxidised surface improves the surface wettability.
Abstract: In the present experimental study, the critical heat flux (CHF) of an oxidized zircaloy surface and its enhancement were investigated during saturated water pool boiling at atmospheric pressure. Three kinds of zircaloy specimens, oxidized at three different temperature conditions (i.e., 300, 450, and 600 °C), were prepared with a non-treated (i.e., fresh) zircaloy surface. The surfaces of the test specimens were characterized by an energy dispersive spectroscopy analysis, scanning electron microscopy image, and water contact angle measurement. The oxidized surface (OS) specimens increased the CHF, which could be because the oxidized surface improves the surface wettability (i.e., decreases the water contact angle). The OS specimens showed the similar water contact angles, and their CHF values became almost the same. In the present experimental conditions, the water contact angle could be considered as a reasonable parameter to explain the CHF data of test specimens. The CHF enhancement of the OS specimens...
TL;DR: In this paper, an X-type hot-film anemometry and a multi-sensor optical probe were used to study gas-water bubbles in a noncircular duct.
Abstract: In nuclear engineering fields, gas–liquid bubbly flows exist in channels with various shape and size cross-sections. Although many experiments have been carried out especially in circular pipes, those in a noncircular duct are very limited. To contribute to the development of gas–liquid bubbly flow model for a noncircular duct, detail measurements for the air–water bubbly flow in a square duct (side length: 0.136 m) were carried out by an X-type hot-film anemometry and a multi-sensor optical probe. Local flow parameters of the void fraction, bubble diameter, bubble frequency, axial liquid velocity and turbulent kinetic energy were measured in 11 two-phase flow conditions. These flow conditions covered bubbly flow with the area-averaged void fraction ranging from 0.069 to 0.172. A pronounced corner peak of the void fraction was observed in a quarter square area of a measuring cross-section. Due to a high bubble concentration in the corner, the maximum values of both axial liquid velocity and turbulent kine...
TL;DR: For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, a study investigated the fundamental properties of h....
Abstract: For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of h...
TL;DR: In this article, an energy-resolved computed tomography (CT) using a transXend detector was proposed to estimate the effective atomic number (EZF) in a human body.
Abstract: For ion radiation therapy, the measurement of effective atomic numbers, Zeff, is necessary to know the material distribution in a human body; the range of ions entering the human body is influenced by the material distribution along their paths. Zeff, however, cannot be measured at hospitals because monochromatic X-rays with different energies are necessary and are used only at synchrotron facilities. To make Zeff measurements at hand, we propose energy-resolved computed tomography (CT) using a “transXend detector”. By assigning two narrow energy ranges in the unfolding process of the data obtained by the transXend detector, Zeff for acrylic and aluminum can be estimated by energy-resolved CT. The estimated Zeff are compared with those obtained by dual-energy and monochromatic X-ray CT.
TL;DR: Severe accident analysis for Small Break (SB), Middle Break (MB), and Large Break (LB) Loss-OfCoolant Accident (LOCA), Station Black Out (SBO), Total Loss ofFeed-Water (TLOFW) was performed and e...
Abstract: Severe accident analysis for Small Break (SB), Middle Break (MB), and Large Break (LB) Loss-Of-Coolant Accident (LOCA), Station Black Out (SBO), Total Loss-Of-Feed-Water (TLOFW) was performed and e...
TL;DR: In order to estimate the state of reactor pressure vessel of Fukushima Daiichi nuclear power plant, it is important to clarify the breakup and fragmentation of molten material jet in the lower plenum of boi... as mentioned in this paper.
Abstract: To estimate the state of reactor pressure vessel of Fukushima Daiichi nuclear power plant, it is important to clarify the breakup and fragmentation of molten material jet in the lower plenum of boi...
TL;DR: In this paper, the authors developed a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergency situations resulting from accidental or deliberate releases of radioactive materials (e.g., a terrorist attack in an urban area).
Abstract: We have developed a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergency situations resulting from accidental or deliberate releases of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavior of a plume dispersing over a flat terrain was successfully simulated. In Parts 2 and 3, LESs of turbulent flows and plume dispersion around an isolated building and in building arrays with different obstacle densities were performed, which showed the basic performance comparable to wind tunnel experimental technique. In this study, we apply the LES model to turbulent flows and plume dispersion in an actual urban area. Although some of the turbulence and dispersion characteristics are quantitatively different from the wind tunnel experimental data, the distribution patterns are generally similar to those of the experiments. It is concluded that our LES model si...
TL;DR: In this paper, a feasibility study of gamma spectrometry of molten core material from the Fukushima Daiichi Nuclear Power Station unit 1, 2, and 3 cores for special nuclear material accountancy is presented.
Abstract: The technologies applied to the analysis of the Three Mile Island accident were examined in a feasibility study of gamma spectrometry of molten core material from the Fukushima Daiichi Nuclear Power Station unit 1, 2, and 3 cores for special nuclear material accountancy. The focus is on low-volatile fission products and heavy metal inventory analysis, and the fundamental characteristics of gamma-rays from fuel debris with respect to passive measurements. The inventory ratios of the low-volatile lanthanides, 154Eu and 144Ce, to special nuclear materials were evaluated by the entire core inventories in units 1, 2, and 3 with an estimated uncertainty of 9%–13% at the 1σ level for homogenized molten fuel material. The uncertainty is expected to be larger locally owing to the use of the irradiation cycle averaging approach. The ratios were also evaluated as a function of burnup for specific fuel debris with an estimated uncertainty of 13%–25% at the 1σ level for units 1 and 2, and most of the fuels in unit 3, ...
TL;DR: In this article, an experimental study in a 6×6 rod bundle has been performed to investigate the effects of spacer grids on the single-phase convective heat transfer enhancement.
Abstract: The spacer grids within a fuel assembly of a nuclear reactor core disrupt and re-establish the momentum and thermal boundary layers so that they enhance the local heat transfer within and downstream of the spacer grids. An experimental study in a 6×6 rod bundle has been performed to investigate the effects of spacer grids on the single-phase convective heat transfer enhancement. The experimental data showed that the Reynolds number has a significant impact on the heat transfer enhancement only when the Reynolds numbers are lower than about 10,000. The conventional correlations showed poor predictions of the heat transfer enhancement by spacer grids at low Reynolds numbers; in particular, the maximum heat transfer rate at the top end of the spacer grids was significantly overestimated. Furthermore, the conventional correlations did not properly account for the effects of the Reynolds numbers on the heat transfer enhancement. Therefore, more systematic experiments should be performed using various spacer gr...
TL;DR: The integrated sorption and diffusion (ISD) model for compacted bentonite was developed to achieve a consistent combination of clay-water interaction, sorption, and diffusion models.
Abstract: To predict the long-term migration of radionuclides (RNs) under variable conditions within the framework of safety analyses for geological disposal, thermodynamic sorption models are very powerful tools. The integrated sorption and diffusion (ISD) model for compacted bentonite was developed to achieve a consistent combination of clay–water interaction, sorption, and diffusion models. The basic premise considered in the ISD model was to consistently use the same simple surface model design and parameters for describing RNs sorption/diffusion as well as clay surface and porewater chemistry. A simple 1-site non-electrostatic surface complexation model in combination with a 1-site ion exchange model was selected to keep sorption model characteristics relatively robust for compacted systems. Fundamental parameters for the proposed model were evaluated from surface titration data for purified montmorillonite. The resulting basic model was then parameterized on the basis of selected published sorption data-sets ...
TL;DR: In this paper, a series of experiments which consisted of three out-of-pile tests and one inpile test were conducted to obtain experimental knowledge of the upward discharge of molten fuel.
Abstract: In order to eliminate the energetic potential in the case of postulated core-disruptive accidents (CDAs) of sodium-cooled fast reactors, introduction of a fuel subassembly with an inner-duct structure (FAIDUS) has been considered. Recently, a design option of FAIDUS which leads molten fuel to upward discharge has been considered as the reference core design of the Japan Sodium-Cooled Fast Reactor (JSFR). In this study, a series of experiments which consisted of three out-of-pile tests and one in-pile test were conducted to obtain experimental knowledge of the upward discharge of molten fuel. Experimental data which showed a sequence of upward fuel discharge and effects of initial pressure conditions on upward discharge were obtained through the out-of-pile and in-pile test. Preliminary extrapolation of the present results to the supposed condition in the early phase of the CDA in the JSFR design suggests that the sufficient upward flow rate of molten fuel is expected to prevent the core melting from progr...
TL;DR: Clean Burn as mentioned in this paper is an innovative plutonium burner concept based on high temperature gas cooled reactor (HTGR) technology, which is expected to be as an effective and safe method to consume surplus plutonium accumulated in Japan.
Abstract: An innovative plutonium burner concept based on high temperature gas cooled reactor (HTGR) technology, “Clean Burn”, is proposed by Japan Atomic Energy Agency (JAEA). That is expected to be as an effective and safe method to consume surplus plutonium accumulated in Japan. A similar concept proposed by General Atomics (GA), Deep Burn, cannot be introduced to Japan because of its adopting highly enriched plutonium, which shall infringe on a Japanese nuclear nonproliferation policy according to Japan–US reprocessing negotiation. The Clean Burn concept can avoid this problem by employing an inert matrix fuel (IMF) and a tightly coupled fuel reprocessing and fabrication plants. Both features make it impossible to extract plutonium alone out of the fabrication process and its outcomes. As a result, the Clean Burn can use surplus plutonium as a fuel without mixing it with uranium matrix. Thus, surplus plutonium alone will be incinerated effectively, while generation of plutonium from the uranium matrix is avoide...
TL;DR: Since the start of the severe accidents at the Fukushima Daiichi Nuclear Power Plant in March 2011, concrete surfaces within the reactor buildings (RBs) have been exposed to radioactive contaminant as mentioned in this paper.
Abstract: Since the start of the severe accidents at the Fukushima Daiichi Nuclear Power Plant in March 2011, concrete surfaces within the reactor buildings (RBs) have been exposed to radioactive contaminant...