A reactor noise monitor has been developed to provide a tool that serves the real time routine function of detecting anomalous states of operation in power reactors. In this monitor, RMS (root mean square) values and average frequencies of noise signals are calculated on a real time basis. The average frequency is defined as the frequency averaged by weighting with PSD (power spectral density) of the noise signal and proved to be equivalent to the ratio of an RMS value of the differentiated noise signal to an RMS value of the noise signal itself. Thus, the average frequency can be obtained on a real time basis by using a differentiator, an RMS calculator and a divider. The fre-quency components of 12 kinds of signals ranging of 0.0136 Hz are divided into two or three frequency regions by band-pass filters and the RMS value and the average frequency of each frequency region are obtained by the digital calculation method. The performance of this monitor was tested by using a simulated anomalous signal with a peak on its PSD. From the test, it is proved that this monitor can detect more than 10% changes of the RMS value and average frequency. The functions of this monitor were also confirmed at the actual BWR power plant.
In addition, a method to detect peak location of PSD is developed and the accuracy of the peak frequency measurement of the proposed method is investigated to be satis-factory.

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A very simple model, as compared with those presented thus far, is developed to describe the stratified cocurrent flow of gas-liquid mixtures in a horizontal pipe. Assum-ing 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 calcu-lated results by the model. When the interface is smooth, i.e. the volumetric liquid flux J_ι<0.1 ft/s, it is a good approximation to use the Blasius equation to estimate inter-facial shear stress. For 0.1 ?? J_ι ?? 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 geom-etry for J_ι>1.0 ft/s, agreements with experiment cannot be obtained, since the transi-tion 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 ?? 0.9 regardless of J_ι.

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An experimental study was made in a cocurrent downflow for air-water system in tube on flow pattern, void fraction and pressure drop. In addition to wetted wall flow which is a distinguished feature in downflow, the same kinds of flow patterns as in up-flow were observed. They were represented on the flow map of downflow with the same variables as those of upflow. The flow maps showed that gas phase is relatively hard to exist in the form of bubble in the cocurrent downflow.
General correlations of the void fraction and the pressure drop in a cocurrent down-flow were obtained by applying the following equations which have been established in upflow, i.e. (1-α)(1-Kα)=β/(1-β) for void fraction and φ_ι=(1-α)^-z for pressure drop. The determined values of K and Z by using the experimental results in the pre-sent study and other experimental works in cocurrent downflow were K=2.0-0.4/β for β ?? 0.2, K=-0.25+1.25β for β ?? 0.2 and Z=0.90.
Comparisons between the predicted values by the presented correlations and experi-mental data showed satisfactory agreement.

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In the liquid metal boiling with the incipient boiling superheat, the pressure transient is large enough to be measured. In this paper the time constant of pressure transient τ in the growing stage of the vapor bubble is measured and its dependence on the channel geometry, the dynamic constraint and the liquid temperature is made clear. The evap-oration coefficient C is also obtained by measuring the vapor pressure and the liquid column velocity. For potassium C is constant in our experiment and its value is (3.8±0.6) ×10^-3. Using the measured C, the τs are computed with the momentum equation, the state equation and the Hertz-knudsen equation in the kinetic theory.

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The fracture strength of two kinds of UO₂ specimens possessing pores of different maximum sizes (60 and 140 μm) was measured in the range of room temperature 1, 300°C by means of diametral compression testing. The fracture strength thus obtained proved to be smaller than any of the values reported by previous authors who mainly used bending tests. Finite element analysis showed that the method used in the present study should logically yield results close to the true tensile fracture strength. The des-crepancies noted with the results reported from the other studies were attributable to the differences in the methods used for the measurements.
The fracture strength was found to remain almost constant in the relatively low temperature region (R.T.800°C) beyond which the value increased with temperature (intermediate temperature region of 1, 0001, 300°C). Electron-microscopic observations of the fractured surface indicated that the brittle-to-ductile transition temperature (T_c) was situated between 800 and 1, 000°C when the strain was applied slowly. Raising the strain rate proved to affect both fracture strength and T_c. These dependences of tem-perature and strain rate on the fracture strength are explained from the relation between dislocation velocity and deformation rate. Griffith's theory is cited to describe the rela-tion between the largest pore size and fracture strength.

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The NO₂ decomposition by electron beam irradiation was studied in the NO₂-N₂ and NO₂-rare gas mixtures. The NO₂ decomposition yields, G(-NO₂), at low doses in the case of the 500 ppm NO2 initial concentration were 2.9, 10.4 and 5.9 for the NO₂-N₂, NO2-He and NO2-Ar mixtures respectively. A large amount of NO was formed by irradiation of these mixtures. The G(NO) was almost equal to the G(-NO₂). The N₂O was also formed in the NO₂-N₂ mixture. The NO₂ decomposition is mainly attributable to the attack of N, formed by the radiolysis of N₂, on NO₂ in the NO₂-N₂ mixture, and to the attacks of R⁺ and R^*, formed by the radiolysis of a rare gas (R), on NO₂ in the NO₂-rare gas mixture. The NO₂ decomposition in the NO₂-N₂ mixture was depressed markedly by the addition of a small amount of O₂. This may be mainly attributable to the regeneration of NO₂ by the reaction of NO with O.

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Transient sodium boiling experiments were conducted in an electrically heated 7-pin bundle under transient overpower conditions. In each run the heater power was gradually raised at almost constant rate under forced convection.
The observed coolant voiding was initially limited to the central subchannel on ac-count of an appreciable time lag in temperature rise occurring between the central and peripheral subchannels. This would appear to call for calculations with two-dimensional voiding model.
The bulk pressure rises registered upon initial vaporization were markedly lower than the vapor pressure corresponding to the incipient-boiling (IB) wall superheat. The pressure pulse generated upon vapor bubble collapse correlated reasonably well with the re-entrant liquid velocity, but the measured value was very much smaller than predicted theoretically from sodium hammer analysis.

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Albedo data were calculated by ANISN for iron-covered concrete slab as well as for iron and concrete single layer slabs. Neutron is allowed to be incident on a slab with each of 14 energy groups ranging from 10 MeV to 1 keV and reflected with energy between and including the incident group and the lowest group. Neutron direction is described with 8 discrete angles for incidence and reflection respectively. Discussion was made for the dependency on slab thickness and on angle and energy of incidence and reflection. As a result, albedo data calculated by ANISN showed good agreement with the other similar data and consequently they were concluded to be sufficiently valid for use in shield design calculation.

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