Combining disparate sources of information in the safety assessment of software-based systems

The main topic of the paper is a discussion on how to combine disparate sources of information in the safety assessment of software-based systems. This is based on experience gained through the licensing process of a programmable system in the Swedish nuclear power plant Ringhals, where a guideline for reviewing software in safety-related systems was applied. One lesson learned from this activity is that the approval of a programmable safety critical system, in particular one which is based on Commercial-Off-The-Shelf software, is based on a combination of disparate sources of information. This combination of information is made in a diagrammatic framework. An emerging methodology to combine information about disparate evidences in a systematic way is based on Bayesian Belief Networks. The objective is to show the link between basic information and the confidence one can have in a system.     

Study of spray cooling of a pressure vessel head of a boiling water reactor

The present paper deals with a theoretical analysis of the spray cooling of a Reactor Pressure Vessel (RPV) head in a Boiling Water Reactor (BWR). To this end a detailed computational model has been developed. The model predicts the trajectories, diameters and temperatures of subcooled droplets moving in saturated vapor. The model has been validated through comparison with experimental data, in which droplet temperatures were measured as functions of the distance that they cover in saturated vapor from the moment they leave the sprinkler outlet to the moment they impact on the RPV head inner wall. The calculations are in very good agreement with measurements, confirming the model adequacy for the present study. The model has been used for a parametric study to investigate the influence of several parameters on the cooling efficiency of the spray system. Based on the study it has been shown that one of the main parameters that govern the temperature increase in a subcooled droplet is its initial diameter. Comparisons are also made between conclusions from the theoretical model and observations made through flow and temperature measurements in the plant (Forsmark 1 and 2). One of these observations is that the rate at which the RPV head temperature decreases on the way down from hot to cold standby is constant and independent of the sprinkling flow rate as long as the flow rate is above a certain minimum value. Accordingly, the theoretical model shows that if one assumes that the cooling of the RPV head is through a water film built on the inner wall due to sprinkling, the heat removal rate is only very weakly dependent on the sprinkling flow rate.     

装机量圆整对刚性级联流体性能影响初步理论分析

建立刚性级联在投资回报率、稳定运行等方面具有一定优势。刚性级联更接近理想级联形式,理想级联对各级的供料流量有着严格的要求,因此在组成级联的单个分离设备供料流量一致的情况下,就对级联各级的装机量有严格的要求。而实际生产级联中无法完全满足理想级联对装机量的要求,装机量往往需要圆整,因此研究装机量圆整对级联性能的影响具有实际意义。本文提出一个圆整参数,并通过对级联流体性能分析得出:任一个级联只要给出运行边界条件,就能获得在保证级联安全运行前提下所允许的圆整范围。本文还确定一种能使实际级联性能更接近理想级联的装机量圆整方法。     

Simulation study of the influence of leak electrons on the discharge characteristics of a cusped field thruster

Previous studies have shown that leak electrons in cusped field thrusters can move along the channel axis to the anode after crossing the magnetic cusp on the exit. In this paper, a one- dimensional fluid model is built along two typical electron paths to study the influence of leak electrons on the discharge characteristics of a cusped field thruster, considering the electron temperature equation. It is found that the frequencies of low-frequency oscillations increase with a decrease in the proportion of leak electrons, which is related to an increase in the ion speed in the channel. Simulation results show that the position of the peak electron temperature is near the magnetic cusp on the exit and the position of the peak electron density is located downstream from the middle magnetic tip. With a decrease in the proportion of the leak electrons, the peak electron temperature and peak electron density decrease and the position of the peak electron density moves away from the exit, which is related to a decrease in the potential fall on the exit and an increase in confinement of electrons to the middle magnetic cusp.     

Theory of Natural Frequencies of Two Pulsating Bubbles in Infinite Liquid

The volume oscillation of bubbles is a fundamental problem associated with the behavior of coolant in nuclear reactors and with reactor safety. Many studies have been reported on the oscillation frequency of a single bubble. Based on theory governing the behavior of single bubble, an accurate theory is derived on the natural frequencies of two pulsating spherical bubbles placed in an infinite liquid. The problem is reduced to calculation of the effect of a bubble on the inertial constant of the other bubble. Bispherical coordinates are introduced to calculate the velocity potential. The effects of liquid compressibilty and viscosity on the natural frequency are shown to he negligible. The most prominent result is that two kinds of frequencies are found to exist when two bubbles oscillate in phase and 180° out of phase. Examination further reveal that the analysis presented here includes Shima's solution as a special case. Numerical calculations substantiate the prediction that the resonant frequency of many bubbles is smaller than that of a single bubble.     

The experimental investigation of the impact of a particle or a rigid body on a cylindrical shell

This paper is devoted to the investigation of the impact of loose or detached parts and components on the body of a primary system of nuclear power plants or in pipelines.

The model task of an impact of a particle or a rigid body on a cylindrical shell is solved. The dependences of force of the impact and the acceleration of a point of the shell on time are received. Theoretical calculations are confirmed with the experiments.

The solution of these tasks and the theoretical calculations are the base for the solution of the inverse problem of the detection of the location of an impact by a particle on the shell and its mass and velocity.

The method of the solution of inverse problem for the impact of a particle is presented below. The experimental installation for measurement parameters of the oscillations of a point of the shell is created. An analogue-to-digital converter is used in the installation, and structural schema is drawn. The installation includes a hardware-software complex based on a personal computer.     

反应堆保护系统可靠性指标的评价方法研究

反应堆保护系统的性能水平对核电厂安全、经济、可靠运行有很大影响。而实践中如何正确评价反应堆保护系统的可靠性指标,业界并未形成一致方法。本文选取简化的典型反应堆保护系统为研究对象,主要讨论拒动概率故障树分析和误动率马尔科夫方法的适用性,分析拒动概率、误动率两个指标分别适用的评价方法,并对示例系统的可靠性指标进行定量计算。本研究对进一步澄清国内反应堆保护系统可靠性评价中的方法问题,具有重要的参考价值。     

Cross-sectional investigation of radiation damage of 2 MeV proton-irradiated silicon carbide

Cross-sectional investigation is an important method to study ion irradiation effects in the depth direction. In this study, 2 Me V H~+was implanted in 6 H-SiC single crystals to investigate the effects of light ion irradiation on SiC. Raman spectroscopy and scanning electronic microscopy(SEM) were carried out on crosssectional samples to reveal the in-depth damage states and dopant behavior. The most damaged region is a little shallower than that predicted by the SRIM procedure,owing to the uncertainty in SRIM simulations. Layered structures representing zones of varying damage after2 MeV H ion irradiation are clearly observed. Two bands are observed in SEM images, of which on band corresponds to the damage peak, while the other band at the end of the H ion-affected area is probably a result of H diffusion propelled by a hydrogen-rich layer during irradiation.A charge accumulation effect related with conductivity on the sample surfaces during SEM tests is observed in theH-implanted area. A model is proposed to explain these phenomena.     

Effect of hydrocarbons on the efficiency of catalytic reactor of detritiation system in an event of fire

Detritiation system of a nuclear fusion plant is mandatory to be designed and qualified taking carefully into consideration all the possible extraordinary situations in addition to that in a normal condition. We focused on the change in the efficiency of tritium oxidation of a catalytic reactor in an event of fire where the air accompanied with hydrocarbons, water vapor, and tritium is fed into a catalytic reactor at the same time. Our test results on the effect of these gases on the efficiency of tritium oxidation of the catalytic reactor indicated; (1) tritiated hydrocarbon produces significantly by reaction between tritium and hydrocarbons in a catalytic reactor; (2) there is little possibility of degradation in the detritiation performance because the tritiated hydrocarbons produced in the catalyst reactor are combusted; (3) there is no possibility of uncontrollable rise in the temperature of the catalytic reactor by heat of reactions; and (4) saturated water vapor could temporarily poison the catalyst and degrades the detritiation performance. Our investigation indicated a saturated water vapor condition without hydrocarbons would be the dominant scenario to determine the amount of catalyst for the design of catalytic reactor of the detritiation system.     

Study of the influence of surface roughness in the PIXE analysis of pottery

The PIXE analysis of pottery is possible by operating in air with basically no limits on the size and shape of the goods. The analysis of the clay body in valuable goods of archaeological and historical value is, however, limited to exposures along pre-existent rough fractures whose surface could alter the transmission of X-rays to the detectors and create artefacts. We have studied the effect on a homogeneous metal slab where grooves of different shape and depth have been milled and compared the data with a Monte Carlo (MC) calculation for our typical set-up and with data on a few potsherds from archaeological excavations.     

Transient Heat Transfer Analysis of a Layer by Considering the Effect of Radiation

The transient heat transfer analysis of a layer has been studied much less than the steady state. However, transient temperature distribution resulted from including radiation and conduction simultaneously, is significantly different from those obtained by considering conduction alone. In order to include the effect of radiation heat transfer, we must insert the gradient of radiative flux in the energy equation. For this purpose, a variety of multi-flux methods have been suggested. A simplified procedure is the two-flux method, which is the one used in the present paper. This paper is focused on one-dimensional transient heat transfer of a layer using Finite Difference Method. To this end, a computer implementation has been written, which is based on implicit finite difference formulation and is capable of considering effect of radiation. By subjecting the layer to various boundary conditions, the effect of variation of refractive index and scattering on transient temperature distribution is discussed.     

Experimental Results of Bremsstrahlung Shielding from Dielectric Trapping with the Use of Tl-204

A method is described for investigating the effects on bremsstrahlung of charge buildup in a dielectric from betas emitted by a radionuclide. Data is also reported of bremsstrahlung attenuation as a function of days of irradiation with point of maximum attenuation depending on magnitude of charge current. Cyclic behavior is indicated. Effects of charge buildup in dielectric on bremsstrahlung have applications as shielding against radiations from energetic electrons.     

Influence of oxide structure on the elevated temperature pitting behaviour of Fe-Cr-Ni alloys

The influence of temperature, potential, alloy and electrolyte composition on the growth of hot water oxide layers on stainless steel type AISI 321 and Fe-Cr-model alloys is presented. The correlation between the oxide layer properties and the pitting corrosion behaviour is discussed. In situ electrochemical investigations have been carried out in aqueous electrolytes (pH 8) on hydrothermal conditions varying from 150 to 250°C. After hot water exposition the steel surfaces were examined microscopically. The porosity of these layers increases with rising temperature due to a change in crystallinity from a fine-crystalline to a coarse-crystalline structure. It is shown that the pitting initiation mechanism is strongly dependent on the morphology of the oxide layers. At 150°C pitting corrosion occurs, whereas at 250°C the formation of extended hollow shaped corrosion has been observed. The cause of the detected inhibiting effect of sulphate ions on the chloride induced pitting is discussed. Furthermore, evident dependencies of the pitting susceptibility on the chromium content of the alloy and on the oxide layer preformation potential have been observed.     

Investigation of the Mixing of Coolant Flows in a VVÉR Vessel

The mixing of flows in a flow-through channel of a VVÉR-1000 reactor in the case where a flow with high or low boron concentration and a flow whose temperature is different from the temperature in the reactor are fed into the same circuit is studied. To this end investigations were performed on a bench at the Special Design Office Gidropress with a model VVÉR-1000 reactor on a 1:5 scale. Regimes with the main circulation pump switched on and with natural circulation restored for an accident with a small leak are studied.Intercircuit mixing in the VVÉR-1000 reactor setup is also studied in the case where the temperature of the coolant changes in one of the circuits (regimes with a break in a steam pipe and closure of the steam channel of the turbine) or with asymmetric feeding of boron into the first loop when one of the tanks in the system for rapid introduction of boron fails. An analytical solution of the problem and the results of measurements performed on units with VVÉR-1000 reactors are presented.     

Recent Development of Data Acquisition System on HL-2A

This paper introduced recent development of data acquisition system(DAS) on the HL-2A tokamak. The existing DAS has to be remodeled because of the evident improvement on HL-2A itself and the increasing amount of corresponding experimental data. First, the experimental network on HL-2A Tokamak as a communication center is described in detail. Secondly, "The File's Format & Criterion of Experimental Data on HL-2A Tokamak" as the core of the new software is also presented. Thirdly, not only a multi-screen image display system on HL-2A is discussed, but also the build-up of a new display wall system is dealt with. Finally, on the graphical WINDOWS platform and on the basis of the new Data File's Format & Criterion, the new software on HL-2A is described, including a new multi-layer database management program, a real-time processing program, a common interactive analytic processing program and a data post-processing program, which is now under development.     

Calculation of AC Losses of CICC for Superconducting Outsert Coils in a Hybrid Magnet

This paper is devoted to predict AC loss of Cable in Conduit Conductor (CICC) which is of importance in the design of conductors. The consideration for the conductor’s design and main parameters for the magnets are introduced. In order to attain a good accuracy in the calculation of AC losses, the field distribution within superconducting outsert should be considered. Calculation of the AC losses, including hysteresis losses and coupling losses, is conducted. An emphasis is put on the hysteresis loss during the ramp up of the current to the operational current (15.3 kA) and the coupling loss of the conductor in a power-down condition for insert. The results are obtained to be 74.9kJ and 950J for 40 T hybrid magnets, respectively. Based on the calculation, a brief analysis of losses effect on the conductor design and the operation of magnet is given for the purpose that the capacity of the cryogenertor can be evaluated and the stability regime can be improved in our future work on the hybrid magnets.     

Economic competitiveness of the new generation of NPPs with NP-500 units in Russia

An economic analysis of NPPs with the new design of the average capacity unit (NP-500) developed in Russia is carried out. The design is characterized by the application of passive safety systems, and a double protective containment, that allows a decrease in the probability of a severe accident by 2 or 3 orders of magnitude in comparison with present VVER units, operated at modern NPPs. The NP-500 unit has a capacity of 635 MWe; it is more compact, and therefore it has a smaller specific consumption of materials and a smaller number of regular staff. Licensing of the design on the basis of international practice is now nearing completion. The published data on costs by the Joint Parallel Nuclear Alternatives Study (JPNAS), executed for the US-Russia Joint Commission on Economic and Technological Cooperation, as well as recent forecasts by different authors for the period 1995–2010 on power consumption, specific investments in thermal power plants and the costs of organic fuels for different regions of Russia are used. An original methodology for analysis of equilibrium prices of energy (marginal costs), competition for developing power technologies and accounting for a factor of inertia in power systems is described. The total self-sufficiency of Russia with nuclear fuel for the forecasting period and the necessity of adequate development of the organic power infrastructure are taken into account. The individual rates of development of the different competitive energy technologies and appropriate returns on capital are determined. The competitiveness of NPPs with NP-500 units in different regions of Russia is analyzed. The attractiveness of investment in this objective is emphasized.