Simulation of pellet-cladding thermomechanical interaction and fission gas release

This paper summarizes the present status of a computer code that describes some of the main phenomena occurring in a nuclear fuel rod throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, gas mixing, swelling, and densification are modeled. The modular structure of the code allows for the incorporation of models to simulate different phenomena and material properties. Collapsible rods can be also simulated.The code is bidimensional, assumes cylindrical symmetry for the rod and uses the finite element method to integrate the differential equations. The stress–strain and heat conduction problems are nonlinear due to plasticity and to the temperature dependence of the thermal conductivity. The fission gas inventory is calculated with a diffusion model, assuming spherical grains and using a one-dimensional finite element scheme. Pressure increase, swelling and densification are coupled with the stress field.Good results are obtained for the simulation of the irradiation tests of the first argentine prototypes of MOX fuels, where the bamboo effect is clearly observed, and of the FUMEX series for the fuel centerline temperature, the inside rod pressure and the fractional gas release.     

An algebraic approach to data languages and timed languages

Algebra offers an elegant and powerful approach to understand regular languages and finite automata. Such framework has been notoriously lacking for timed languages and timed automata. We introduce the notion of monoid recognizability for data languages, which includes timed languages as special case, in a way that respects the spirit of the classical situation. We study closure properties and hierarchies in this model and prove that emptiness is decidable under natural hypotheses. Our class of recognizable languages properly includes many families of deterministic timed languages that have been proposed until now, and the same holds for non-deterministic versions.     

Conquering Uncertainty in Multiple-Valued Logic Design

In modern science, significant advances are typically made atcross-roads of disciplines. Thus, many optimization problems inMultiple-valued Logic Design have been successfullyapproached using ideas and techniques from ArtificialIntelligence. In particular, improvements in multiple-valuedlogic design have been made by exploiting information/uncertaintymeasures. In this paper, we review well-known information measuresin the multiple-valued domain and consider some methods of findinginformation measures for completely or incompletely specifiedfunctions with multiple-valued and continuous attributes. In thisrespect, the paper addresses the problem known as discretizationand introduces a method of finding an optimal representation ofcontinuous data in the multiple-valued domain. We also propose atechnique for efficient calculation of different informationmeasures using Multiple-valued Decision Diagrams. As oneapplication of our technique, we outline an approach tosynthesizing digital circuits derived from decision diagrams thatcan yield to reduction in power dissipation. The paper also showsthe impact in several important areas of multiple-valued systemdesign including (i) fuzzy logic, (ii) quantum computing systems,and (iii) data mining.     

Analysis of the Polonium Hazard in Nuclear Power Systems with Lead–Bismuth Coolant

Polonium presents no danger under normal operating conditions when the coolant loop is sealed. In our country, we have almost 40 years of experience in working with radioactive lead–bismuth coolant in the reactors used in nuclear-powered submarines and ground-based testing prototypes. This experience has made it possible to study how the polonium radiation conditions inside working enclosures are produced and to develop effective safety measures for different operating regimes, including irregular situations and accidents.Data are presented on the polonium radiation conditions in certain typical operating and accident situations in a nuclear submarine: spillage of a substantial amount of coolant directly into the reactor bay, the consequences of an interloop leak in a steam generator, and refueling with fresh nuclear fuel.Regular medical-biological examinations of the workers participating in the operation of the system, repair work, and liquidation of the consequences of accidents did not show any cases of irradiation by polonium above the established health norms.Inferences are drawn from studies performed in this and other countries of polonium emission from lead-based polonium-containing media when such media are heated in vacuum and in an inert-gas atmosphere in the temperature range 300–800°C.     

The ВД-12НФП Eddy-Current Flaw Detector and Methods for Processing a Measured Signal Produced by a Flaw

The field of application, the features of operation, and the main performance characteristics of a -12 eddy-current flaw detector are considered. Methods of digital data processing for improving the recognition of flaw-produced signals against the background noise are presented.     

A Hadamard transform electron ionization time-of-flight mass spectrometer

We describe the first Hadamard transform time-of-flight mass spectrometer (HT-TOFMS) that incorporates an electron (impact) ionization source. This implementation was realized in an existent TOF instrument using commercially available components and simple modifications to the ion source. In the present apparatus, a Hadamard mask is expressed by modulating the ion generation process within the ion source; thus, the present approach differs from previous designs that use external electrostatic devices to modulate a continuous ion stream. The present implementation may be operated in conventional TOF mode at 12.5 kHz and in HT-TOF mode at 20-40 MHz. In Hadamard mode the design can operate using any circulant simplex code, allowing the operator much flexibility for optimizing resolution and mass range and for eliminating nonstochastic fluctuations, e.g., encoding errors and signal hum. We demonstrate typical performance of the HT-TOFMS in standard and reflectron geometries using sequences of three constructions and of varied length, generating HT-TOF mass spectra of molecules that match conventional reference spectra. The auxiliary material includes an electrical schematic for the floating high-speed encoding amplifier, which is also of use in other high-speed electrostatic optics applications, and a list of 537 validated vectors comprising the first row of each circulant simplex sequence (S(n)=3-8219) derived using maximal shift register (n=2(m)-1), quadratic residue (n=4m-3), and twin prime constructions [n=p(p+2)].     

Method for determining critical pressure in assembling hybrid MCT focal plane arrays

A simple method is proposed for determining the critical pressure that does not destroy Cd _x Hg_1?x Te diodes in hybrid assembling. The method allows obtaining a set of data that reliably define the critical parameter (the value of force) of the flip-chip hybrid FPA process. The method was tested on Cd _x Hg_1?x Te samples (x = 0.21). It is found that the abrupt change in the electrophysical properties of the material occurs when the diameter of indium bumps increases 2 times and more during compression at a pressure of about 3 kg/mm². The obtained gage load/bump deformation dependences show that this pressure corresponds to the beginning of the region of indium strengthening on the deformation curve.