A unified approach for numerical calculation of space-dependent kinetic equation

A unified numerical method based on the factorization approach is developed to solve the space-dependent neutron kinetic equation. Various numerical methods for solving the space-dependent kinetic equation have been developed so far. These methods can be classified into two categories, i.e., the direct and the factorization methods. The factorization method is known as an effective numerical method. In the present study, a new factorization method named the multigrid amplitude function (MAF) method is developed. Unlike the improved quasi-static (IQS) method, an independent amplitude function is assigned for each spatial region and energy group in the MAF method. The MAF method is a generalization of conventional methods, e.g., the frequency transform, IQS, and Theta methods. To evaluate the amplitude function in the MAF method, the time-dependent coarse-mesh finite difference (TCMFD) method is developed. The MAF method is implemented into a space-dependent kinetic code on the basis of the analytical polynomial nodal method. In order to verify the effectiveness of the MAF method, the TWIGL, Langenbuch, Maurer, and Werner (LMW), and Laboratorium für Reaktorregelung and Anlagensicherung (LRA) benchmark problems are analyzed. The calculation results show the effectiveness of the present method.     

A MAUT approach for selecting a dismantling scenario for the thermal column in KRR-1

In this paper, an evaluation methodology for selecting an optimal dismantling scenario at the stage of a decommissioning planning is presented. The selection of a dismantling scenario is critical for an entire decommissioning project because by the selected dismantling scenario, the dismantling schedule, the dismantling cost, a worker’s exposure, and the work safety level are determined. So it is necessary that an optimal scenario for dismantling an object is selected through an evaluation of the relevant scenarios in consideration of several evaluation items. In this research, as an evaluation model, the multi-attribute utility theory (MAUT) is quantitatively and qualitatively applied to assess these scenarios. Quantification of an evaluation item in the MAUT method has been performed by using a single utility function as well as a multi-utility function for each item. As an implementation, the MAUT method is applied to select the best scenario for the thermal column in Korea Research Reactor-1 (KRR-1) and its advantages and disadvantages compared with the (analytic hierarchy process) AHP method about the application to a decommissioning project.     

Using thermionic nuclear power systems with a thermal reactor for interorbital space flights

Conclusion The use of a thermionic NPS with a thermal reactor in space technology to supply power to the RMPS offers broad possibilities for interorbital delivery of payloads while using comparatively cheap launch rockets to place spacecraft in a fixed orbit. The flight time from a fixed to a geostationary orbit ranges from several months to half a year, and the mass of the payload in a geostationary orbit for optimal RMPS parameters may reach 7–8 tons (not counting the mass of the NPS).It should be noted that after the flight is completed, the NPS can serve as a source of electrical power for spacecraft in geostationary orbit.Red Star Scientific-Production Organization. Translated from Atomnaya Énergiya, Vol. 70, No. 4, pp. 221–224, April, 1991.     

A data-driven approach for predicting failure scenarios in nuclear systems

A data-driven approach is presented for the on-line identification of the system Failure Mode (FM) and the prediction of the available Recovery Time (RT) during a failure scenario, i.e., the time remaining until the system can no longer perform its function in an irreversible manner. The FM identification and RT prediction modules are linked in a general framework that recognizes the patterns of dynamic evolution of the process variables in the different system failure modes. When a new failure scenario develops, its evolution pattern is compared by fuzzy similarity analysis to a library of reference multidimensional trajectory patterns of process variables evolution; the failure mode of the developing scenario is identified by combining the modes of failure of the reference patterns, weighed by their similarity to the developing pattern; the similarity weights are then fed to the RT prediction module that estimates the time remaining before the developing trajectory pattern hits a failure threshold.     

Merits and limits of thermalhydraulic plant simulations - towards a unified approach to qualify plant models

The paper describes the problems associated with building a Nuclear Plant Model for simulation of transients under the light of recent Spanish and Belgian experience and suggests an approach to qualify plant models based on post-processing and scaling techniques.     

Structural response function approach for evaluation of thermal striping phenomena

A rational analysis method for thermal stress induced by fluid temperature fluctuation is developed, by utilizing frequency response characteristics of structures. High frequency components of temperature fluctuation are attenuated during a transfer process from fluid to structures. Low frequency components hardly induce thermal stress, since temperature homogenization in structures. Based on investigations of the frequency response mechanism, a frequency response function of structures was derived, which can predict stress amplitudes on structural surfaces from fluid temperature amplitudes and frequencies. It is formulated by multiplication of the effective heat transfer and the effective thermal stress functions. The frequency response function was applied to fatigue analysis of nuclear components, and clarified relation of fatigue damage to thermal hydraulic and structural design parameters.     

Evaluation on a double-chamber gas-liquid phase discharge reactor for benzene degradation

A double-chamber gas-liquid phase DBD reactor (GLDR), consisting of a gas-phase discharge chamber and a gas-liquid discharge chamber in series, was designed to enhance the degradation of benzene and the emission of NOx. The performance of the GLDR on discharge characteristics, reactive species production and benzene degradation was compared to that of the single-chamber gas phase DBD reactor (GPDR). The effects of discharge gap, applied voltage, initial benzene concentration, gas flow rate and solution conductivity on the degradation and energy yield of benzene in the GLDR were investigated. The GLDR presents a higher discharge power, higher benzene degradation and higher energy yield than that of the GPDR. NO₂ emission was remarkably inhibited in the GLDR, possibly due to the dissolution of NO₂ in water. The benzene degradation efficiency increased with the applied voltage, but decreased with the initial concentration, gas flow rate, and gas discharge gap, while the solution conductivity presented less influence on benzene degradation. The benzene degradation efficiency and the energy yield reached 61.11% and 1.45 g kWh^–1 at 4 mm total gas discharge gap, 15 kV applied voltage, 200 ppm benzene concentration, 0.2 L min⁻¹ gas flow rate and 721 μS cm⁻¹ water conductivity. The intermediates and byproducts during benzene degradation were detected by FT-IR, GC-MS and LC-MS primarily, and phenols, CO_x, and other aromatic substitutes, O₃, NO_x, etc, were determined as the main intermediates. According to these detected byproducts, a possible benzene degradation mechanism was proposed.     

Characteristics of gas-liquid two-phase flow in a capillary tube

Gas-liquid two-phase phenomena in capillary tubes were investigated with special attention on the flow patterns, the time varying void fraction and pressure loss. The directions of flow were vertical upward, horizontal and vertical downward. Pipe inner diameters used were 1 mm, 2.4 mm and 4.9 mm. As a result it is made clear that due to the strong effects of surface tension the flow pattern is not severely affected by the direction of flow, the smaller the pipe inner diameter, the easier the formation of liquid slug and the pressure loss in a unit length takes much larger than the estimated value by the Chisholm equation.     

Development of a unified technological process for cementing solid radwastes

The results of research on cementing finely dispersed, mixed, closely packed, and coarsely fragmented solid radioactive wastes by mixing, flow-through, and impregnation to create a unified complex of technological processes are presented. A new method of impregnation which consists of feeding under pressure through a probe into the bottom of a container with solid wastes a cement solution with a high penetrating power is shown. The drawbacks of flow-through are eliminated, the integrity of the pouring is guaranteed, and the quality is monitored by determining the degree of impregnation and density of the cement solution which has passed through the layer of solid wastes. This method of cementing can be used for all solid wastes considered and the equipment and cement compositions are basic for the works cementing solid radioactive wastes.     

Development of a unified technological process for cementing liquid radioactive wastes

The possibility of cementing liquid wastes with different compositions by a unified method is examined. Methods of cementing are studied in order to determine the similarity of the parameters for preparing the cement solution under the conditions of reliable (accident free) execution of the technological process. The possibility of using a unified composition for the cement mixture and the type of equipment that permits the maximum incorporation of different wastes in the final product meeting the regulations is determined.     

Use of local approach for predicting fatigue cracks in sleeves subjected to repeated thermal shocks

In pressurized-water nuclear plants, certain parts of the circuits have special zone where, for construction reasons, there is a slot that causes a high concentration of stresses. This is the case in particular of nozzles, protected by sleeves, which are subjected to numerous transients and thermal shocks. Loop tests have been carried out on models to evaluate the risk of the initiation or propagation of cracks in these structures. These appear after a few hundred cycles (500) of 210°C amplitude and attain a depth of the order of one milli-metre at 3000 cycles. To analyse how these fatigue cracks begin, an original method based on local approach has been developed in France. A law giving the number of cycles to initiate a crack in terms of the stress σ_θθ has been determined experimentally by numerous rupture mechanics tests on samples. Concordance of calculation and tests has been very satisfactory and has validated this method for thermal shocks on axisymmetrical structures. It is however desirable that an analogous method should be developed and validated for situations in which the plasticity is not confined.     

An integral CFD approach for the thermal simulation of the PBMR Reactor Unit

A CFD method was developed to conduct integral thermal reactor analysis for the complete Reactor Unit of the Pebble Bed Modular Reactor (Pty) Ltd (PBMR). The requirement was however also to include very detailed aspects such as leakage and bypass flow paths through the reflector blocks and sleeves. The aim was therefore to investigate the influence of leakage and bypass flow on the thermal performance of the Reactor Unit in an integral fashion.The focus of this paper is to discuss the methodology that was developed. The discussion will firstly highlight all the required inputs, elaborate briefly on the underlying theory and how this was implemented into the CFD modeling capability. Results will be discussed briefly, but the focus is on the methodology.     

Safety approach in the EU test blanket systems design

This paper reveals the safety strategy and approach developed and followed in the design of the two EU TBS describing its objectives, components and implementation. Addressing the safety in the early stage of the conceptual design of nuclear facilities is a well recognized international practice and industrial project-level requirement for the successful completion of the licensing process within expected project cost and schedule. The impact of the early development of the safety approach, its implementation and monitoring in the design of nuclear device like the TBS is not limited to the safety assessment and licensing activities only. Safety approach plays indispensible role in reducing the overall project risk. It infiltrates the entire design process through the unavoidable interfaces between the design features and its safety level. In reality the entire process of the TBS development, design, technological demonstration and implementation is affected by the project team safety culture.     

Prediction method for thermal stratification in a reactor vessel

The prediction method for thermal stratification phenomena in a fast breeder reactor is described. The focus of attention is placed on the applicability of water test results to predict thermal stratification phenomena in a real plant. The basic feature of thermal stratification was examined in a cylindrical plenum, using water and sodium as test fluids. The similitude relationship between a small-scale test and a real plant is discussed in order to understand the experimental results. The scale-model experiments for LMFBRs (liquid metal-cooled fast breeder reactors) were also performed to see the effects of a reactor configuration and reactor-trip operation condition. Then the magnitudes of the temperature gradient and the ascending speed of stratified interface in the hot plenum of LMFBRs were predicted, based on the results of the water scale-model.     

Approximation analytical solutions for a unified plasma sheath model by double decomposition method

A unified plasma sheath model and its potential equation are proposed.Any higher-order approximation analytical solutions for the unified plasma sheath potential equation are derived by double decomposition method.