[en] The sputtering yield of Mo honeycomb walls was compared with the yield of flat walls in a d.c. Ar glow discharge. Under the experimental condition where the mean energy is approximately 1 keV and the angle of incidence of primary ions strongly distributed around normal, the yield is reduced by a factor of 20 to 30. Before and after the bombardment, the surface topography of the honeycomb targets was observed by a scanning electron microscope. (author)

[en] A numerical method for treating one-dimensional compressible coolant dynamics is discussed, using the EULFCI (Eulerian type Fuel Coolant Interaction) code which has been developed for the fuel-coolant thermal interaction (FCI) under hypothetical core-disruptive accident condition of an LMFBR. The ICE (Implicit Continuous Eulerian) method is used to solve the Eulerian-type one-dimensional coolant flow dynamics. A special feature of present method is the utilization of an iterative procedure to solve the momentum and state equations. The influence brought by change in pressure convergence tolerance factor, time step width and number of mesh cells (or cell width) are discussed. Good stable solutions are obtained by this method. A new method of ''rezoning'' the Eulerian cells is proposed and successfully used to analyze the expansion of the FCI region when a small number of mesh cells is adopted. A comparison with corresponding results obtained with PLUTO code shows that the EULFCI code yields a much stabler solution though at the expense of longer computing time. (author)

[en] Stability is studied of a nuclear reactor system which is controlled by the concentration change of poison solution circulating through the pipe installed in the reactor. Particular attention is paid to: (1) nonlinearities due to the reactivity feedbacks, (2) rigorous treatment of nonlinear control elements without employing approximate methods such as the describing function and (3) nonlinear characteristics of the concentration change of poison solution. The stability of this complex reactor system is analyzed in the state space by applying the technique based on Lyapunov's method. A special technique is employed to cope with the difficulty such that the stability of a system with time lag depends on the present state as well as on the past history of the state which is usually indeterminable. Analysis is carried out for both simplified and realistic models. For the former model, one stability region is compared with another by varying the lag time, characteristics of nonlinear elements and the power at equilibrium point. Similar results are also obtained for the latter model. (author)

[en] A vibration monitoring technique has been developed which can be applied to continuous monitoring and to patrol checking of many kinds of rotating machines in nuclear power plants. In this method, the vibrating condition in such equipment are represented in terms of two parameters, i.e. a vibration amplitude (RMS value) and an average frequency. The average frequency is defined as the root value of the second moment of the vibration frequency weighted by the power spectrum. The average frequency can be calculated by simple analogue circuits and does not need the spectrum analysis. Using these two parameter, not only the occurrence of abnormal vibration but also the type of vibration can be detected. (author)

[en] The parameter identification and adaptive control schemes applied in a previous study to a nonlinear point reactor are extended to the case of a loosely-coupled-core reactor with internal feedbacks, constituting a nonlinear overall system. Both schemes are shown to be stable, with the system newly represented on the pattern of the Model Reference Adaptive System (MRAS) with use made of the Lyapunov's method. For either parameter identification or adaptive control of a loosely-coupled-core reactor, there exists no canonical form of multiple input-multiple output system which can be directly applied for deriving the MRAS with the matrix version of the Kalman-Yakubovich lemma as it was in the case of the point reactor. This difficulty is circumvented by the practical assumption that the neutron density can be directly measured on each core as reactivity change is applied as input into the coupled core as a whole. For parameter identification, the model parameters are adaptively adjusted to those of each core, while for the adaptive control, plant parameters of each core can be adaptively compensated, again through control inputs, to asymptotically reduce the output error between the model and the plant. The point reactor is shown to correspond to a special case. (author)

No abstract available

[en] A very simple model, as compared with those presented thus far, is developed to describe the stratified concurrent flow of gas-liquid mixtures in a horizontal pipe. Assuming densities of both phases are constant in location, mass and momentum equations are solved to obtain pressure gradient and volume fractions of both phases at steady state. Several experimental data by others are found in good agreements with the calculated results by the model. When the interface is smooth, i.e. the volumetric liquid flux J sub(l) < 0.1 ft/s, it is a good approximation to use the Blasius equation to estimate interfacial shear stress. For 0.1 <= J sub(l) <= 1.0 ft/s where the interface is not smooth but ripply or wavy, the Wallis correlation is found applicable. If we assume stratified flow geometry for J sub(l) <= 1.0 ft/s, agreements with experiment cannot be obtained, since the transition to slug or elongated bubble flow has already taken place. The transition from stratified to annular mist flow is found to occur at gas volume fraction α asymptotically equals 0.9 regardless of J sub(l). (author)

[en] Circumferential cracks detected in the JPDR (BWR) near welded joints connecting the nozzle safe-end to pipe (austenitic stainless steel) were studied in reference to the stresses applied in service, the conditions of welding, environment (O₂ and Cl^- concentration, water flow, temperature etc.), metallurgical structure and operating records, to determine the cause of cracking. Fatigue tests were also undertaken with simulated welded pipe of size to examine possible contribution of fatigue to the cracking. The analysis indicated stress corrosion to be the principal cause of cracking, and that it had initiated in the heat-affected zone which had been sensitized by the excess heat input of welding. The factors contributing to the stress corrosion were the presence of oxygen in the fluid, which had at times attained a level exceeding 0.2 ppm, and which combined with stress, at times exceeding the yield strength. This had caused the cracks once initiated, to propagate along the grain boundary. (author)

No abstract available

[en] Out-of-pile experiments were performed with Zircaloy-4 rods in subcooled water environment to study the basic phenomena occurring in the transient cooling process undergone by a fuel rod during a reactivity-initiated accident (RIA) affecting a light water reactor (LWR). The experimental results show that the cooling process of the fuel rod during an RIA can be divided into three phases separated by the quenching temperature T sub(q) and the rewetting temperature T sub(r). It is also noted from the experimental results that with increasing degree of subcooling, T sub(q) tends to rise to levels far exceeding the maximum liquid superheat temperature of water; T sub(r), on the other hand, is little affected by the cooling water temperature, and remains close to that of the maximum superheat temperature. Numerical calculations indicate conclusively that radial heat transfer to coolant water is the dominant factor that governs the transient cooling process in an RIA affecting the cold start-up of a BWR, rather than the axial heat conduction through rod which is considered to be the basic mechanism of cooling that governs the reflooding process during a LOCA. (author)