Automatic and remote-controlled measuring devices are required to detect liquid leakage from structures in reactor containment vessels.
A new device has been developed to measure a droplet diameter based on the distance between two brilliant spots formed on a droplet surface by the reflection and refraction of a collimated light beam. The device is composed of a collimated beam source, a linear CCD (Charge Coupled Device) camera and a data processor.
The measurement error is less than 1% in volume for a 5 mm diameter BK7 ball lens falling within a 200 mm horizontal width at a distance of 1. 75 m.
This device is applicable to the measurement of droplet volume within a 200 mm diameter horizontal area with 10% accuracy.

View full abstract

This paper investigates the control problem of xenon spatial oscillations in the axial direction during load following operations of a nuclear reactor. The system model is described by a one-group diffusion equation with xenon and power feedbacks and iodine-xenon dynamic equations and controlled by full-length and part-length control rods. In order to achieve the control purpose we formulate the control model as the design problem of robust servo systems for distributed parameter reactor systems. Hence the total thermal power and the axial offset are chosen as outputs to be controlled. The control law is designed based upon finite-dimensional systems which are constructed by linearizing around steady states, approximating by the Galerkin approximate method and reducing dimensions via the singular perturbation method. From a computational point of view a simple computational algorithm to obtain an approximate solution of the steady state neutron balance is developed via the perturbation method. Some results of numerical simulations are represented to show effectiveness of the theory developed in this paper. Particularly it is shown that the designed servo systems are robust against model errors with the linearization and the modal truncation.

View full abstract

Uranium-dioxide particles coated by pyrocarbon (BISO), which were irradiated at 1, 3001, 400°C to burnups of ca. 1% FIMA, were heated isochronally and isothermally at temperatures between 1, 600 and 2, 300°C. Release fractions of ¹³⁷Cs, ¹⁵⁵Eu and ¹⁰⁶Ru were larger than 10^-2 after heating at 2, 000°C for 2 h; the results were in contrast to much smaller release fractions from TRISO particles with intact silicon-carbide (SiC) coating. The release of ¹³⁷Cs and ¹⁴⁴Ce from the BISO particle was controlled by diffusion in the dense pyrocarbon layer at temperatures between 1, 600 and 2, 300°C, while that of ¹⁵⁵Eu and ¹⁰⁶Ru was controlled by diffusion in the fuel kernel above 1, 800°C. These results can be used as reference data on release behavior of the fission products from TRISO particles with defective SiC layers.

View full abstract

The surface morphology and composition changes of a Mo fixed limiter used in the High-Field Tokamak TRIAM-1 after about 70, 000 hydrogen plasma discharges have been investigated by means of optical microscope, SEM-EDS and AES. Significant difference in surface damage is observed between the electron drift side and the ion drift side.
The damage on the electron drift side is characterized by melting, cracking, cone-like protuberance, droplet, eutectic and impurity accumulation. This is considered to be caused by the overlapped effects of the heat load from the plasma, which decreases with increasing distance from the plasma center, and the impurity accumulation which originated from the stainless steel vacuum vessel and the limiter itself.
The kinds of damage on the ion drift side are melting due to arcing, sputtering, blistering and color change of the surface due to impurity accumulation. The distribution of these damages changes with the distance from the limiter edge. The damage observed on the ion drift side is considered to be caused by the synergistic effects of sputtering due to ion bombardment, impurity accumulation and heat load due to arcing.

View full abstract

Rates of He release from two kinds of simulated high-level radioactive waste glasses were measured in the temperature range from 573 to 753 K by a mass spectrometric method. Diffusion coefficients of He in the glasses were determined from the fractional release data. The diffusion coefficients were given as a function of temperature by the equations :
D/(m²•s^-1) =2.3×10^-6 exp (-71.1±2.1 kJ/RT) for P0798 glass,
=9.8×10^-7 exp (-60.2±2.1 kJ/RT) for P0504 glass.
In addition, solubilities of He in the glasses were determined from the measurement of the total amount of released He and found to be
S/(atoms/m³)=2.0×10²² for P0798 glass
=2.2×10²² for P0504 glass, at 693 K and 1.7×10⁵ Pa He.
The diffusivities and solubilities of He in the glasses were, respectively, several and an order of magnitude lower than silica, alkali silicate and Pyrex glasses, which properties are notable for the radioactive waste glasses.

View full abstract

An analytic polynomial nodal method using partial currents has been derived for the solu tion of multigroup neutron diffusion equations in three-dimensional (3-D) cartesian geometry. This method is characterized by expressing the source and leakage terms in an auxiliary 1-D diffusion equation by quadratic polynomials and solving it analytically. Based on this method, we have developed a 3-D multigroup diffusion code ANDEX, and applied to 2-D LWR and 3-D FBR models. The results of ken, power distributions and computing time have been compared with those of finite difference method calculations.

View full abstract

A computer code TERFOC-N has been developed to calculate doses to the public due to atmospheric releases of radionuclides in normal operations of nuclear facilities. The code calculates the highest individual dose and the collective dose from four exposure pathways ; internal doses due to ingestion and inhalation, external doses due to cloudshine and groundshine.
A foodchain model, which is originally referred to the U. S. NRC Regulatory Guide 1.109, has been improved to apply to not only LWRs but also other nuclear facilities.
This report describes the models employed and gives a sample run performed by the code. The parameters which were sensitive to ingestion dose were identified from the results of sensitivity analysis. The models which significantly contributed to the dose were identified among the models improved and extended here.

View full abstract