The Analytical and Experimental Research of In-Vessel Corium Retention in CPR1000

The analytical and experiment research of In-Vessel Corium Retention (IVR) in the Chinese Pressurized-water Reactor 1000 MWe (CPR1000) are introduced. The IVR research consists of preliminary phase and detailed phase. The analysis of thermal failure, structural failure and penetration failure of Reactor Pressure Vessel (RPV) and the experimental research of External Reactor Vessel Cooling (ERVC) are performed at preliminary phase. Analysis results show that the RPV failure is the dominated by thermal failure mode and the probability of the thermal failure is very low. Test results show that the IVR success probability for CPR1000 is about 99% if the Critical Heat Flux (CHF) of CPR1000 is the same as that of AP600. Further works, including the ERVC enhancement design, the CHF test of the RPV outer wall and the recalculation of the IVR success probability for CPR1000, will be performed at detailed phase in the near future.

Research of Radon Transportation Model to Investigate Buried Fault

How to get the position, direction and width of buried fault effectively is still very difficult when finding buried faults by measuring 222Rn radioactivity. In this paper we established a technique to carry out buried fault investigation. It was based on Fick’s fist law, Darcy’s law and theory of clusters to analyze radon transportation and simulate 222Rn transportation in ideal conditions. The feasibility indicates that measuring or investigating the concentration of radon to find abnormal region can help people find buried faults. 218Po and 214Po, daughter products of 222Rn, are generally considered to be proportional to initial concentration of 222Rn. 218Po and 214Po have short half-life of 3.05 min and 164us respectively which is very suitable for actual measure work. So in order to accumulate alpha particles effectively, soil gas sampling period is set about twice half-life of 218Po. The established model is applied to analyze two buried fault areas in Southwest China and the results are really much better.

Apply Performance Evaluation Matrix on Investigating Human Error Events in the Main Control Room

Digitalized nuclear instruments and control systems have become the main stream design for the main control room (MCR) of advanced nuclear power plants (NPPs) nowadays. Digital human-system interface (HSI) could improve human performance and, on the other hand, could reduce operators’ situation awareness as well. It might cause humans making wrong decision during an emergency unintentionally. Besides, digital HSI relies on computers to integrate system information automatically instead of human operation. It has changed the operator’s role from mainly relating operational activity to mainly relating monitoring. However, if operators omit or misjudge the information on the video display units or wide display panel, the error of omission and error of commission may occur. Therefore, how to avoid and prevent human errors has become a very imperative and important issue in the nuclear safety field. This study applies Performance Evaluation Matrix to explore the potential human errors problems of the MCR. The results show that the potential problems which would probably affect to the human performance of the MCR in advanced NPPs are multiple accidents, pressure level, number of operators, and other factors such as working environmental.

Simulation of CCD Degradation Induced by Protons Irradiation

The mechanisms of charge coupled devices (CCD) irradiated by protons are analyzed. The simulation models of ionization damage and displacement damage are developed. The charge transfer efficiency (CTE) decreased by proton irradiation is numerically simulated. The CTE degradation caused by different traps and by protons with different energies has been studied respectively. Both surface dark signals induced by proton ionization damage and bulk dark signals induced by proton displacement damage are numerically simulated. The variability of surface dark signals, bulk dark signals, and total dark signals with proton fluence is compared. The simulation results are in agreement with the experimental results of the relevant literatures.

Fracture Strength Estimation of SiC Block for IS Process

The Japan Atomic Energy Agency has been conducting R&D on thermochemical water-splitting Iodine-Sulfur (IS) process for hydrogen production to meet massive demand in the future hydrogen economy. A concept of sulfuric acid decomposer was developed featuring a heat exchanger block made of SiC. Recent activity has focused on the reliability assessment of SiC block. Although knowing the strength of SiC block is important for the reliability assessment, it is difficult to evaluate a large-scale ceramics structure without destructive test. In this study, a novel approach for strength estimation of SiC structure was proposed. Since accurate strength estimation of individual ceramics structure is difficult, a prediction method of minimum strength in the structure of the same design was proposed based on effective volume theory and optimized Weibull modulus. Optimum value of the Weibull modulus was determined for estimating the lowest strength. The strength estimation line was developed by using the determined modulus. The validity of the line was verified by destructive test of SiC block model, which is small-scale model of the SiC block. The fracture strength of small-scale model satisfied the predicted strength.

Visualization Study of Cavity Tone in Closed Tandem Side-Branches Using a High Time-Resolved PIV Technique

Flow-induced acoustic resonance in a piping system containing closed tandem side-branches was investigated experimentally in this study. Velocity perturbation was induced at the mouth of the cavity using two pumps and a block. An uncommon acoustic mode change, from a higher mode to a lower mode, was observed when the flow rate in the main pipe increased. This phenomenon was examined by high-time-resolved Particle Image Velocimetry (PIV). The instantaneous velocity field in a cross section was visualized two-dimensionally using PIV technique, simultaneously with the pressure measurement at multi-points around the cavity by microphones. The fluid flows at different points in the cavity interact, with some phase differences between them, and the relation between the fluid flows was clarified. The phase difference of the acoustic pressure fluctuation at different points around the cavity was also obtained. Consequently, phase delays of oscillation at different points were obtained two-dimensionally. 2-D phase map was helpful to discuss the feedback mechanism of the self-induced vibration. This is the first research which can obtain this kind contour map using the time sequential instantaneous velocity fields for closed tandem side-branches system which has long side-branches (L/D ≫1) and high inflow velocity at high resonant frequency.

Application of Neutron Radiography to Observe Water Absorbtion of Concrete

It has been experienced that service life of reinforced concrete structures is often limited due to lack of durability of cement-based materials. One major reason for this durability problem is the penetration of water and compounds dissolved in water into concrete. Therefore, there is an urgent need to study water penetration into concrete in order to better understand deterioration mechanisms. Neutron radiography provides an advanced non-destructive technique with high spatial resolution. In this contribution, neutron radiography was successfully utilized to study the process of water absorption of two types of concrete with different water-cement ratios namely 0.4 and 0.6. It is shown that it is possible to visualize migration of water into concrete and to quantify the time-dependent moisture distribution with accurately and with high spatial resolution by means of neutron radiography. In concrete with high water-cement ratio, water penetrates much quicker than in concrete with lower water cement ratio. Water penetration depth obtained from neutron radiography is in good agreement with corresponding values obtained from capillary suction tests. Experimental results obtained by means of neutron radiography on water penetration into concrete will be presented and discussed in this contribution. Results will provide us with a solid basis for a better understanding of deteriorating processes in concrete and other cement-based materials. These results may be considered to be a first step to improve durability of concrete.

The Design of a Neutron Dosimeter

At present, most of the developed neutron dosimeters that have a moderator with a single counter, applied in neutron radiation fields within large range energies from thermal to MeV neutrons, are not a satisfaction to energy response. The purpose of the article is designing a suitable neutron dosimeter for the radiation protection purpose. In order to overcome the disadvantage of the energy response of the neutron dosimeters combined a single sphere with a single counter, three spheres and three 3He counters were combined for the detector design. The response function of moderators with different thicknesses combined with SP9 3He counters were calculated with MCNP program MCNP4C [1]. The selection of three different thicknesses of the moderating polyethylene sphere was done with a Matlab program [2]. A suitable combination of three different thicknesses was confirmed for the detector design. The electronic system of the neutron dosimeter was introduced. The fluence to ambient dose-equivalent conversion coefficient were calculated, analyzed and compared with the values recommended in the ICRP 74 Publication [3]. The calculated result explain that it is very significance to this design of neutron dosimeter, it may be applied to the monitor of the ambient dose in the neutron radiation fields, improving at present the status of the energy response of neutron dosimeters.

Study of Template Measurement of Plutonium Pit Based on Gamma-Ray Detection

Template measurement is an important method in deep nuclear disarmament. The gamma-ray spectrum of Plutonium pit shows unique property due to age, abundance, amounts and thickness of the Plutonium pit; that is, same designed pits yield similar gamma-ray spectra while different design give distinct spectra. Useful information is extracted from gamma-ray spectrum generated by the reliable Plutonium pit radiation as ‘template’. Comparison of the data from inspected objects with the template can give conclusion whether they are of the same type. This paper studies how to choose template data from gamma-ray spectrum and discusses the limits of the gamma-ray measurement. Because of the strong self-absorption of Plutonium, some characteristics of Plutonium pit can’t be identified only by gamma spectrum. MCNP simulation was employed to prove that in some cases, template depending on gamma-ray spectrum from the reliable Plutonium pit alone can’t effectively distinguish the spurious objects. And a further approach indicates that enhancing neutron counting rate of spontaneous fission of Plutonium can improve the problem. Neutron counting rate can be indirectly acquired by spontaneous fissile neutrons bombarding a 10B target. 478 keV γ rays are concomitant with the nuclear reaction 10B(n,α)7Li* from 7Li* nuclei’s deexcitation. Neutron information is gathered by detecting 478 keV γ photons. Using HPGe γ detector can both detect γ-ray spectrum and acquire neutron counting rate. This method efficiently increases confidence of template measurement and also ensures the dismantling process without revealing sensitive nuclear warhead design information.

Neutron Diffraction and SEM Study on CaO-Al2O3-SiO2(ZnO-BaO-Na2O) Glass-Ceramics Prepared Under Different Cooling Conditions

Neutron diffraction and Scanning Electron Microscope (SEM) were employed to study complex two-phase coexistence structure and surface morphology of CaO-Al2O3-SiO2(ZnO-BaO-Na2O) glass ceramics prepared under different cooling conditions. With the rapid cooling temperature decreasing from above 850°C to 750°C and 300°C, the length of the needle-like precipitated β-wollastonite crystal decreased from 30 μm to 15 μm and 5 μm, respectively. Meanwhile, the transgranular fracture appeared and the grain boundary became indistinct in the sample rapidly cooled to 750°C, and the microcracks appeared in the samples rapidly cooled to 300°C and below. These phenomena contribute to the decrease of bending strength for the rapid cooling. Neutron diffraction revealed that the unit cell of precipitated β-wollastonite crystal elongated along its three axes and its volume increased at different cooling conditions. With the decrease of the cooling temperature, the elongation of axes and increase of volume were enhanced, implying that the tensile stress of the β-wollastonite crystal increased. At the same time, intensity of the crystal diffraction peaks increased and atomic temperature factors decreased, which revealed that defects inside a smaller size of crystal granular were less than that in larger one. Amorphous peaks at low diffraction angle did not changed with cooling temperature, showing that the middle-range-order inside residual glass phases were almost the same for all cooling conditions, while intensity of amorphous peaks at high diffraction angle increased notably for samples rapidly cooled to below 850°C, showing that rapid cooling may result in severe short-range-order in residual glass phase, which induced tensile stress of crystalline phase from around amorphous phase and therefore lead to occurrence of transgranular fracture and microcracks. This study suggests that rapid cooling to below 850°C should be avoided in order to obtain preferable mechanical properties for CaO-Al2O3-SiO2(ZnO-BaO-Na2O) glass ceramics.