Advanced Computer Codes Research Articles

Safety researches on LWR loss-of-coolant accident.

On the LWR LOCA safety, many experimental and analytical works were performed in the governmental organization and the nuclear industries. The works covers not only LOCA ECCS studies but also studies on containment spray, hydrogen diffusion in the containment, pressure suppression and pipe behavior. The reactor safety is demonstrated with many large scale test facilities in the works. The results were applied to improve the design, operation procedure and guide-line of regulation of LWRs and also to develop advanced computer codes. In this paper described are the major research accomplishments in Japan on engineered safety features of the LWRs for a LOCA. Also described are the studies on coolability of a severed damaged core.

Application of Advanced Computational Codes in the Design of an Experiment for a Supersonic Throughflow Fan Rotor

Increased emphasis on sustained supersonic or hypersonic cruise has revived interest in the supersonic throughflow fan as a possible component in advanced propulsion systems. Use of a fan that can operate with a supersonic inlet axial Mach number is attractive from the standpoint of reducing the inlet losses incurred in diffusing the flow from a supersonic flight Mach number to a subsonic one at the fan face. The data base for components of this type is practically nonexistent; therefore, in order to furnish the required information for assessment of this type fan, a program has been initiated at the NASA Lewis Research Center to design, build, and test a fan rotor that operates with supersonic axial velocities from inlet to exit. This paper describes the design of the experiment using advanced computational codes to calculate the unique components required. The fan rotor has constant hub and tip radii and was designed for a pressure ratio of 2.7 with a tip speed of 457 m/s. The rotor was designed using existing turbomachinery design and analysis codes modified to handle fully supersonic axial flow through the rotor. A two-dimensional axisymmetric throughflow design code plus a blade element code were used to generate fan rotor velocity diagrams and blade shapes. A quasi-three-dimensional, thin shear layer Navier–Stokes code was used to assess the performance of the fan rotor blade shapes. The final design was stacked and checked for three-dimensional effects using a three-dimensional Euler code interactively coupled with a two-dimensional boundary layer code. A translating nozzle was designed to produce a uniform flow parallel to the fan up to the design axial Mach number of 2.0. The nozzle was designed with the three-dimensional Euler/interactive boundary layer code. The nozzle design in the expansion region was analyzed with a three-dimensional parabolized viscous code, which corroborated the results from the Euler code. A translating supersonic diffuser was designed using these same codes.

Simulation of the chernobyl accident

Abstract An analysis of the April 26, 1986 accident at the Chernobyl-4 nuclear power plant in the Soviet Union is presented. The peak calculated core power during the accident was 550 000 MW t . The analysis provides insights that further understanding of the plant behavior during the accident. The plant was modeled with the RELAP5/MOD2 computer code using information available in the open literature. RELAP5/MOD2 is an advanced computer code designed for best-estimate thermal-hydraulic analysis of transients in light water reactors. The Chernobyl-4 model included the reactor kinetics effects of fuel temperature, graphite temperature, core average void fraction, and automatic regulator control rod position. Preliminary calculations indicated the effects of recirculation pump coast down during performance of a test at the plant were not sufficient to initiate a reactor kinetics-driven power excursion. Another mechanism, or “trigger” is required. The accident simulation assumed the trigger was recirculation pump performance degradation caused by the onset of pump cavitation. Fuel disintegration caused by the power excursion probably led to rupture of pressure tubes. To further characterize the response of the Chernobyl-4 plant during severe accidents, simulations of an extended station blackout sequence with failure of all feedwater are also presented. For those simulations, RELAP5/MOD2 and SCDAP/MOD1 (an advanced best-estimate computer code for the prediction of reactor core behavior during a severe accident) were used. The simulations indicated that fuel rod melting was delayed significantly because the graphite acted as a heat sink.

Simplified thermal-hydraulic methods for analyzing light water reactor event sequence families

A simplified method for obtaining thermal-hydraulic plant responses for light water reactors is described. The method combines the application of detailed and simplified plant models, using an advanced computer code (such as RELAP5), to simulate plant responses to accident or operational transient events. Calculations using a simplified plant model are performed to extend the results obtained with a detailed plant model. The simplified model is then used to investigate the effects of minor changes in event sequences. The method is an accurate, economical means of determining thermal-hydraulic plant responses for groups of sequences that share common controlling thermal-hydraulic phenomena. The methods described here are therefore valuable in assisting probabilistic risk assessments that typically require deterministic evaluation of large numbers of sequences grouped in this manner.

Introductory aerothermodynamics of advanced space transportation systems

The aerothermodynamic problems associated with hypervelocity flight at high altitudes (low ambient density) are considered. The physical phenomena are described and their severity in terms of aerodynamic heating for advanced space transportation systems are estimated. Flight domains corresponding to various physical phenomena are mapped. Approximate methods of analysis for conceptual studies are noted and preliminary results and estimates are presented. Problem areas that need both theoretical and experimental research are highlighted. The development of advanced computational codes that need to be prepared for use when approximate conceptual studies have defined advantageous configurations is discussed. Two advanced space transportation systems are considered: the aeroassisted orbital transfer vehicle concept and the small, rapid-response, manned, maneuverable concept that takes off from Earth or a conventional aircraft, enters a near-Earth orbit, and finally re-enters the atmosphere with lift and cross-range capability to land on an airstrip. Nomenclature g = gravitational constant GO = geosynchronous orbit k = catalycity coefficient p = pressure q = heating rate r = distance from the center of the Earth R = body nose equivalent body radius, surface reflectivity T = temperature U = velocity relative to the Earth's atmosphere V = inertial velocity or speed F = ratio of radiative flux to freestream energy flux A = shock standoff distance e = surface emissivity X = mean free path p = gas density a = Stephan-Boltzmann constant

Comparison of two modeling methods for three‐dimensional current systems

Three‐dimensional current systems in high latitudes are obtained by two independent methods on the basis of magnetic field data obtained from the IMS Alaska meridian chain of observatories. In spite of the totally different principles used, the two methods result in similar large‐scale distributions of the ionospheric currents and field‐aligned currents, and the estimated values are in reasonable agreement with those observed more directly by radar and satellite techniques. Thus ground‐based magnetic field records, together with an advanced computer code for separating the contribution from ionospheric and field‐aligned currents, are proven to be a powerful tool in studying the substorm current system, providing a complete set of information on the global distribution of ionospheric currents, electric fields and of field‐aligned currents as well as the convection pattern. There are, however, some differences which are mostly intrinsic to each method. These are discussed in detail in terms of advantages and disadvantages of each method.

One-dimensional two-fluid equations for horizontal stratified two-phase flow

Advanced computer codes for water reactor loss-of-coolant analysis are based on the use of the two-fluid model of two-phase flow, in which conservation equations are solved for the gas and liquid phases separately. The standard two-fluid equations, however, sometimes predict the growth of instabilities in the flow, and occasionally become improperly posed. These difficulties have in the past led to the proposal of several different forms for the conservations equations. To help resolve these uncertainties a widely accepted form of the one-dimensional two-fluid equations is used to calculate wave propagation speeds, and stability limits, for the illustrative case of a frictionless horizontal stratified gas-liquid flow. Calculated propagation velocities are shown to agree with the appropriate limit of an exact solution, and the predicted stability limits are found consistent with available observations on the stability of the stratified flow regime. These comparisons help improve confidence in the ability of the two-fluid equations to analyse more complex problems in transient two-phase flow.