Particulars of radiolysis and mass transfer in two-phase water coolant of a nuclear power facility with steam generation at an interphase surface

A model of an interphase transfer of stable products of the radiolysis of water in boiling coolant is developed taking account of the intensity of their delivery to the interphase boundary in the liquid phase and removal into the vapor phase with vapor generation on the interphase surface. A computational study is made of the radiolysis of the coolant and interphase transfer of the products of the radiolysis of water in the core and on the pulling section of BWR of the Oskarshamn-2 nuclear power plant in Sweden. A comparison of the computational data with the results of the technical measurements of the coolant composition of the BWR at the Oskarshamn-2 nuclear power plant showed that the accumulation of stable products of the radiolysis of water in the vapor-gas phase of the coolant is determined by the kinetics of radiolysis in the liquid phase, the concentration of the oxygen-containing components in the liquid phase is due to the present of hydrogen peroxide in it.     

Particulars of the simulation of experiments on supercritical pressure water using other media

Post-reactor investigations have been performed on BN-600 fuel-element cladding, made of 0Kh16N15M3BR steel, after irradiation to maximum burnup of 10% h.a. and higher. It is shown that the highest degradation of the operating properties of the fuel-element cladding is observed in the zone of maximum increase of its diameter and is expressed as total embrittlement of the cladding material and appearance of cracks of substantial depth on the inner surface. The processes resulting in the degradation of the properties of fuel-element cladding are directly related either with swelling or with radiation-induced segregation, occurring in the same temperature range and under the action of the same driving forces as swelling. The most important stresses, from the standpoint of the serviceability of fuel elements, turn out to be those arising in cladding as a result of the gradient of the swelling along the thickness of the cladding. The level of these stresses is also determined by the form of the temperature dependence of the swelling of the steel used for the fuel-element cladding. Translated from Atomnaya énergiya, Vol. 106, No. 4, pp. 188–195, April, 2009.     

Evaluation of dosimetric functions for Ir-192 source using radiochromic film

Ir-192 source is widely used in high dose rate brachytherapy. The aim of this study was to derive the brachytherapy dosimetric functions described in AAPM TG-43 to characterize the dosimetric properties of commercially available microselectron HDR Ir-192 source. All the measurements were carried out with GAFCHROMIC EBT radiochromic film in water equivalent solid phantom and the grey values were analyzed using Omnipro IMRT film dosimetry software with Vidar VXR-16 scanner. Optical density of the film was converted to dose using calibration film established in this study. Measurements were carried out by measuring the dose at radial distances from 0.5 cm to 5.0 cm with interval of 0.5 cm and at polar angle 0°-180° in 10° intervals. Dosimetric functions such as dose rate constant, radial dose functions and anisotropy of the dose distribution were found to be in good agreement with Monte Carlo calculations. This study confirms the feasibility of radiochromic EBT film dosimetry in characterization of the TG-43 parameters for Ir-192 HDR source.     

Reliability analysis of a passive cooling system using a response surface with an application to the flexible conversion ratio reactor

A risk-informed methodology is applied to the selection of an ultimate heat sink for a Passive Secondary Auxiliary Cooling System. The reliability of the chosen design during the bounding transient, a station blackout, is calculated. The methodology considers both active component failures and the potential for inadequate cooling due to adverse thermal-hydraulic conditions. A response surface is developed as a surrogate for the thermal-hydraulic code and used for uncertainty propagation. The uncertainty introduced by the use of the response surface itself is explored. Two sensitivity studies are performed. The first study measures the sensitivity of peak clad temperature to initial ambient conditions and system degradation. The second study explores the sensitivity of system reliability to code error.     

Effect of surface mechanical finishes on charging ability of electron irradiated PMMA in a scanning electron microscope

Charging of Polymethyl Methacrylate insulators (PMMA), in a scanning electron microscope (SEM) is studied owing to a time resolved current method. This method allows the evolution of trapped charge versus time and the charging time constant to be deduced. The effect of surface roughness change on the ability of PMMA to trapped charge is highlighted. The results show that the trapped charge at the steady state decreases when the roughness increases in the micrometer range while the time constant of charging increases with surface roughness. This behaviour is due to the increase of leakage current and/or enhanced secondary electron emission (SEE). On the one hand, surface mechanical finishes allows, the build up charge in insulators submitted to an electron bombardment to be lowered. On the other hand this treatment allows the secondary electron emission to be raised for some specific applications.     

Determination of water equivalent ratio for some dosimetric materials in proton therapy using MNCPX simulation tool

The water equivalent ratio(WER) was calculated for polypropylene(PP), paraffin, polyethylene(PE), polystyrene(PS), polymethyl methacrylate(PMMA), and polycarbonate materials with potential applications in dosimetry and medical physics. This was performed using the Monte Carlo simulation code, MCNPX, at different proton energies. The calculated WER values were compared with National Institute of Standards and Technology(NIST) data, available experimental and analytical results,as well as the FLUKA, SRIM, and SEICS codes. PP and PMMA were associated with the minimum and maximum WER values, respectively. Good agreement was observed between the MCNPX and NIST data. The biggest difference was 0.71% for PS at 150 MeV proton energy. In addition, a relatively large positive correlation between the WER values and the electron density of the dosimetric materials was observed. Finally, it was noted that PE presented the most analogous Depth Dose Characteristics to liquid water.     

Probing cytotoxicity of nanoparticles and organic compounds using scanning proton microscopy, scanning electron microscopy and fluorescence microscopy

Scanning proton microscopy, scanning electron microscopy (SEM) and fluorescence microscopy have been used to probe the cytotoxicity effect of benzo[a]pyrene (BaP), ethidium bromide (EB) and nanoparticles (ZnO, Al₂O₃ and TiO₂) on a T lymphoblastic leukemia Jurkat cell line. The increased calcium ion (from CaCl₂) in the culture medium stimulated the accumulation of BaP and EB inside the cell, leading to cell death. ZnO, Al₂O₃ and TiO₂ nanoparticles, however, showed a protective effect against these two organic compounds. Such inorganic nanoparticles complexed with BaP or EB which became less toxic to the cell. Fe₂O₃ nanoparticles as an insoluble particle model scavenged by macrophage were investigated in rats. They were scavenged out of the lung tissue about 48 h after infection. This result suggest that some insoluble inorganic nanoparticles of PM (particulate matters) showed protective effects on organic toxins induced acute toxic effects as they can be scavenged by macrophage cells. Whereas, some inorganic ions such as calcium ion in PM may help environmental organic toxins to penetrate cell membrane and induce higher toxic effect.     

Diagnosis of surface degradation of flame-retardant ethylene propylene diene copolymer by scanning probe microscopy

Most electric cables installed in nuclear power plants use organic polymers for their electrical insulation. Regarding this, degradation of the polymers could lead to fatal accidents. However, no truly reliable diagnostic methods that can detect the degradation of polymer insulation in electric cables have been established. Therefore, development of a reliable diagnostic method is very important. The present research shows that scanning probe microscopy can be a good tool to evaluate microscopic changes induced on the surface of flame-retardant ethylene propylene diene copolymer by its degradation.     

Study of image reconstruction using dynamic grids in tomographic gamma scanning

In this paper, a new image reconstruction algorithm employing dynamic grids technique is proposed for tomographic gamma scanning. The key feature of the algorithm is the use of adaptive grid refinement in areas that indicate large values. Simulation results show that the application of dynamic grids has a good performance in emission reconstruction with a distinct advantage in the accurate positioning of the ’hot spots’ and reducing the number of grids, but doesn’t achieve a tangible improvement in transmission reconstruction.     

Fracture mechanics analysis of a pressure vessel with a semi-elliptical surface crack using elastic-plastic FEM-calculations

Results of an elastic-plastic three dimensional finite element analysis for a semi-elliptical surface crack inside a pressure vessel is presented. The calculations were performed by the finite element program ADINA, incorporating von Mises yield condition and isotropic hardening. The calculations were performed up to that pressure level where general yield of the ligament takes place. The results of the finite element analysis are compared with figures obtained from analytical procedures of elastic as well as of elastic-plastic fracture mechanics.     

Application of a remote-controlled collimated dosimetric system for surveying spent MR fuel storage facilities

The results of using a specially developed collimated dosimetric system, placed on a Brokk-90 remotecontrolled machine, to survey a spent fuel storage facility are presented. The measuring block of the system consists of collimated and uncollimated γ-ray detectors, video cameras, and headlights. The range of the dose-rate measurements of the γ-ray detectors varies from 0.4 mSv/h to 8.5 Sv/h. The collimation angle of the collimated detector is 12° and the lead shielding is 30 mm thick. The system made it possible to perform this work in large radiation fields by remote means. The dose rate distribution along extended elements, extracted from the spent fuel storage facility in the MR hall, is obtained. The contents of the storage facility were visualized in all details. Using the results of the survey, the contents of the storage facility were repacked and removed from the MR room.     

Calibration of laser tomography as a new optical diagnostic tool applied to dosimetric polymer gels

Numerous medical applications, as radiotherapy for example, require accurate and reproducible three-dimensional dose measurements with high spatial resolution. A solution of great interest and which has been exploited for many years is the use of dosimetric gels based on different physico-chemical principles, as Fricke’s gels or polymer gels. Fricke’s gels take advantage of the oxidation of ferrous ions in ferric while polymer gels are the result of the synthesis of polyacrylamide hydrogel from monomer and cross-linking agent. Fricke’s gels have particular limitations not encountered with polymer gel dosimeters: the time delay between irradiation and measurement must be reduced in order to limit the diffusion of ferric ions which may remove the spatial dose information. That’s why, during the past decade, many compositions of polymer gels have been studied (PAG, MAGIC, …), elaborated and even commercialized (BANG gels). However the gel composition remains of great interest regarding its physical properties. In this work, the authors propose a new optical diagnostic tool more flexible and less expensive in comparison with existing techniques like magnetic resonance imaging (MRI) and Optical-CT. This technique is based on light scattering behaviour occurring in an irradiated polymer gel (note that light scattering in Fricke’s gels is very feeble, the latter being essentially absorbant).     

Numerical simulation of binary collisions using a modified surface tension model with particle method

The binary collision of liquid droplets is of both practical importance and fundamental value in computational fluid mechanics. We present a modified surface tension model within the moving particle semi-implicit (MPS) method, and carry out two-dimensional simulations to investigate the mechanisms of coalescence and separation of the droplets during binary collision. The modified surface tension model improves accuracy and convergence. A mechanism map is established for various possible deformation pathways encountered during binary collision, as the impact speed is varied; a new pathway is reported when the collision speed is critical. In addition, eccentric collisions are simulated and the effect of the rotation of coalesced particle is explored. The results qualitatively agree with experiments and the numerical protocol may find applications in studying free surface flows and interface deformation.     

Development of an in-air RBS technique using a metal capillary

We have developed a simple Rutherford backscattering spectroscopic (RBS) method to analyze sample depth profiles in air. To avoid excessive energy loss of projectile ions in air, we have used a 3 MeV proton beam extracted into air with a metal capillary. Using this capillary, we were able to extract a sufficiently large proton beam current to perform in-air RBS and in-air PIXE without requiring any window, such as a thin film, between a vacuum chamber and air. We have validated our technique by analyzing the depth profiles for Au foils of various thicknesses, 0.25, 0.75, and 2.5 μm. A comparison of the experimental results with a simple theoretical calculation indicates that this technique is useful for analyzing the depth profile of any specimen in air.     

等离子氧化面垒探测器的研制

本文报道了一种制备面垒探测器的新工艺——等离子氧化工艺。初步的实验结果表明,探测器制作周期短、性能稳定、制作重复率高。灵敏面积直径为20mm的探测器(电阻率1000Ωcm)在室温下对α粒子的能量分辨率为0.7％(~(241)Am(α))。     

Elastic-plastic fracture mechanics analysis of a pressure vessel with an axial outer surface flaw

The stress and strain state in pressure vessel containing an axial semi-elliptical surface flaw is analyzed by elastic-plastic finite element (FE) calculations. The variation of J along the crack front is presented. Stresses and strains in the vicinity of the surface flaw are compared with those of a compact specimen of the same material at a similar J level. The FE results are taken to examine the ductile crack growth obtained in a vessel test and to discuss the validity of J-controlled crack growth. It is shown that the local constraint of the component affects the crack resistance significantly and that, therefore, J_R-curves have to account for the varying triaxiality of the stress state. This improved two parameter approach yields a much better prediction of the stable crack growth and, especially, is able to describe the canoe shape of the surface crack.     

Fracture initiation and propagation in a cylindrical shell containing an initial surface flaw

The paper deals with the problem of fracture initiation, propagation, and arrest in a pressurized cylindrical vessel which contains an initial surface flaw. It is assumed that the flaw has the most unfavorable geometry and orientation, namely, it is a relatively long part-through axial crack.First we consider the problem of a crack which is sufficiently ‘shallow’ so that the plastic deformations are confined to the neighborhood of the crack border and part of the net section near the inner wall is still elastic. The plasticity-corrected stress intensity factor obtained from this analysis is the controlling load factor in failure considerations related to fatigue crack propagation, stress corrosion cracking, and static fracture (with the use of fracture toughness, COD, or a K_R curvetype failure criterion).The problem of relatively deep crack with fully-yielded net ligament is then considered. Plastic deformations are also assumed to spread around the crack ends through the entire wall thickness. A perfectly plastic strip model (with an eight order shell theory) is used to calculate the plastic zone size and the crack opening displacement along the crack border. Previous studies indicate that for the analysis of the type of stable and subsequent unstable crack propagation problems under consideration, the crack opening displacement δ is a more suitable load factor than the stress intensity factor K, or the crack extension force G. Thus, in this paper a ‘crack opening stretch’ type material characterization will be used.After the rupture of the net ligament under the crack, the axial crack propagation is accompanied by the depressurization of the vessel caused by leakage. From this point on the fracture problem is coupled with the related fluid mechanics or gas dynamics problem where the primary unknowns are the pressure and the crack length as functions of time. In the present study it is assumed that the volume of the vessel is finite and the crack propagation is quasi-static (this assumption, which is necessary to keep the problem within manageable proportions, is justified by the relatively low crack velocities, i.e. v_c < 0.25 c₂, c₂ being the shear wave velocity).