Research at the CEA in the field of safety in 2nd and 3rd generation light water reactors

The research programs at the CEA in the field of safety in nuclear reactors are carried out in a framework of international partnerships. Their purpose is to develop studies on:

• –The methods allowing for the determination of earthquake hazards and their consequences;
• –The behaviour of fuel in an accident situation;
• –The comprehension of deflagration and detonation phenomena of hydrogen and the search for effective prevention methods involving an explosion risk;
• –The cooling of corium in order to stop its progression in and outside the vessel thereby reducing the risk of perforating the basemat;
• –The behaviour of the different fission product families according to their volatility for the UO₂ and MOX fuels.

     

Learning lessons from five electrostatic incidents

It is well known that electrostatic discharges can ignite mixtures of flammable gases with air and suspensions of combustible dust in air. For this reason, the prevention of electrostatic discharges is an essential part of measures to prevent explosions and fires. Incendive electrostatic discharges occurred in five cases in various chemical plants.The incidents involved were:

• 1.Spark type electrostatic discharges from a leaking steam pipe.
• 2.Spark type electrostatic discharges inside a charging chute for a solid.
• 3.A spark type electrostatic discharge whilst transferring a solid powder from a bin, which led to ignition of the powder.
• 4.A propagating brush discharge during pneumatic transfer of solid, which caused a severe electric shock to a process operator.
• 5.A brush discharge inside an electrostatic precipitator which caused ignition of an aerosol of hydrocarbon.

To avoid explosions and fires it is important to prevent incendive electrostatic discharges from occurring in industrial facilities. To help managers of chemical plants to do this, the incidents above are presented in the form of learning lessons including:

• •the mechanism of the generation and separation of electrical charges,
• •the mechanism of the electrostatic discharge,
• •the root causes of the incident,
• •the safety measures which are necessary to avoid a repetition.

     

Theory of magnetostriction in amorphous and polycrystalline ferromagnets: I. Description of the formalism

Magnetostriction of amorphous and polycrystalline ferromagnets is discussed with special emphasis to the following questions:

• 1.1. Is magnetostriction in these systems totally determined by the conventional mechanism via the strain-derivative of the local
• 2.anisotropy tensor as in crystalline materials, or is there also a contribution from the reorientation mechanism due to stiff
• 3.rotations of local structure units?
• 4.2. What is the effect of the elastic coupling of the structural units on the effective magnetostruction tensor in disordered
• 5.ferromagnets? An iterative solution for the effective magnetostriction tensor is derived from two method, the balance-of-force
• 6.method and the incompatibility method.

     

Relativistic thermodynamics of gases

Relativistic thermodynamics of degenerate gases is presented here as a field theory of the 14 fields of

• particle density—particle flux, and
• stress—energy—momentum.

The field equations are based on the conservation laws of particle numbers, and energy-momentum and on a balance of fluxes. The necessary constitutive equations are strongly restricted by the

• principle of relativity,
• entropy principle,
• requirement of hyperbolicity.

It turns out that the resulting field equations contain only viscosity, bulk viscosity and heat conductivity as unknown functions. All other constitutive coefficients may be calculated from the equilibrium equations of state that are known from statistical arguments.The paper offers a more systematic version of relativistic thermodynamics of gases than the earlier papers by Müller and Israel. At the same time the present version contains less unknown functions than those earlier papers. All speeds of propagation are finite.The relation between the present theory and the classical one formulated by Eckart is described.     

Etude de l'énergie de désorption des substances polaires

Polar substance energy desorption study. This study suggests an extension of the Dubinin-Radushkevich and Gibbs-Helmholtz equations, by using adsorption forces in microporous composites. These forces, mainly those of Van der Waals, have been set up in three groups of components according to their effects :

• •unspecified forces,
• •dispersion-perturbation forces,
• •quadrupole and dipole interaction forces.

The suggested models take into account the different forces and present a good coherence with the experiment.     

Mesure de la diffusivité longitudinale de matériaux anisotropes

Measurement of in-plane diffusivity of anisotropic solid samples. Survey of the techniques developed at LEMTA. Three techniques for the measurement of in-plane diffusivity of anisotropic solid samples have been developed at the Laboratory and are presented here :

• •the two directional heat pulse (flash) method with local contact measurement of two temperatures;
• •the fin method with local contact or contactless measurement of two temperatures;
• •the two directional heat pulse method with measurement of the temperature field by an infrared camera and data processing through integral transformations.

     

An improved flipped SU(5)×U(1) model from the four-dimensional string

We discuss a four-dimensional string model whose effective field theory is a supersymmetric flipped SU(5)×U(1) GUT with the following properties.

• •- The quark and lepton mass matrices have a hierarchical structure and all Cabibbo-Kobayashi-Maskawa mixing angles can be non-zero.
• •- There is a natural splitting of Higgs doublets and triplets.
• •- A novel seesaw mechanism gives light left-handed neutrinos.
• •- The gauge group is reduced to the standard model SU(3)_C×SU(2)_L×U(1)_Y at a large mass scale close to M_P.

Extensive use is made of non-renormalizable superpotential couplings which may arise from couplings to identifiable massive modes, and are restricted by an R symmetry and the requirements of flatness is some field directions.     

Effect of operating temperatures on the coefficient of performance of active carbon-methanol systems

Experimental and predicted results of an active carbon (AC35)-methanol pair as a function of operating temperatures are discussed.Experimental COP's higher than 0.5 are obtained when the evaporating temperature lift is less than 25°C. The COP is seen to be very sensitive to the evaporating and adsorbing temperatures. The regenerating temperature is of the order of 100°C which makes that pair a good candidate for solar cooling applications.A comparison between the results obtained with that pair and predicted performances of three other pairs (NH₃H₂O, ZeoliteH₂O and another active carbon-methanol pair) shows that:

• 1.(1) two adsorber cycles give higher COP's than the NH₃H₂H₂O continuous cycle;
• 2.(2) intermittent adsorptive cycles give higher COP's than the NH₃H₂O continuous cycle as long as the evaporating temperature lift is less than 50°C;
• 3.(3) among the solid adsorbents, the active carbon-methanol pairs seem to be the most promising for cooling applications. The choice of the active carbon depends on the evaporating temperature lift: AC35 is very well adapted for temperature lifts larger than 30°C; ACLH could be better adapted to smaller evaporating temperature lifts, as suggested by Passos et al.

     

Confinement thermique d'une enceinte par jet d'air en convection forcée

A global model is proposed for the heat transfer through a plane air jet which is used as a thermal seal of a case at temperatures higher than the ambient one. The model considers that forced convection predominates over the natural convection and uses an analogy between heat and mass transfers. The heat balance calculation is based on an estimation of the velocity and temperature profiles at returning slot of the jet. Hydrodynamically, the jet is assimilated to a free jet. Thermally, a new formulation for the temperature profile in the jet is proposed for the most general case whatever the temperatures at the blowing slot and on each side of the jet — room and case —. The predictions by the model are in good agreement with experimental results from the point of view of:

• •- the changes in longitudinal and transversal temperature in the jet;
• •- the flux exchanged between all compartments;
• •- the energy consumption required to assure a given difference between the case temperature and the ambient one.

     

Über die gewünschte hörerlautstärke bei kammermusik

One of the acoustic criteria that have a major influence on the auditory experience during a concert is that of volume. This is something that is not always felt to be satisfactory, especially among chamber music audiences. It is not yet known, however, which volume levels listeners of chamber music pieces consider to be desirable. By means of suitable listening experiments, an attempt was made to find an answer to this question.In a medium-sized auditorium, comparable in size to a small chamber music hall, individual listeners were played excerpts from various pieces of chamber music. Each listener was requested to adjust the volume to what he or she felt to be the optimal level. The following values were then measured for each excerpt: the equivalent continuous sound level L_eq, the mean maximum level L_1% and the lower limiting level L_95%. The measurements, which covered a sample of 24 people, show that:

1. 1.1.|There are clear upper and lower limits for acceptable sound volume levels.
2. 2.2.|The preferred volume levels can differ considerably within these limits.
3. 3.3.|There is an individual volume range for each individual listener.
4. 4.4.|A volume with an equivalent continuous sound level L_eq around 70 dB(A) is the single most satisfactory level for listeners overall.

     

Optimisation of glass cover inclination for maximum yield in a solar still

In this communication, a thermal analysis of solar distillation has been developed to optimise the inclination of the glass cover for maximum yield. Further, the effect of inclination on the internal heat and mass transfer relation, the water and the glass cover temperature have also been carried out. Based on numerical computation for winter and summer climate conditions, it is infered that:

• 1.(i) the yield increases with increase of inclination in winter and vice-versa in summer;
• 2.(ii) there is a significant reduction in evaporative heat transfer co-efficient with increase of inclination in summer and winter.

     

Boiler fuel savings by heat recovery and reduced standby losses

This paper is concerned with an investigation into the fuel savings that can be achieved in a fuel-fired package boiler by the use of an economiser which incorporates a flue damper, linked via a controller, to the burner. The fuel savings are accomplished by two means.

• 1.1. By direct heat recovery from the flue gases leaving the boiler and
• 2.2. By a reduction in boiler draught and cooling losses by closing the flue damper which is activated on burner shut down. These losses occur during normal burner cycling and standby periods.

Experimental heat recovery data were obtained from a hot gas boiler simulation test rig, and shown to be dependent on the exhaust temperature, excess air level and boiler size. Standby savings were predicted from a boiler cooling model, based on measured boiler cooling rates and draught conditions. Details of the cooling model are given in the paper. The standby savings were found to depend on boiler operating time, the number of burner cycles during boiler operation and the boiler cooling rate time constant, burner purge time and flue gas damper delay time. Overall the fuel savings that can be achieved were found to be in the range 6–16% depending on the operating conditions prevailing, and additional tests on boilers confirmed these findings.     

Diffuse reflection by rough surfaces: an introduction

In this introductory paper, we present with some details the (mathematically) simplest methods proposed to compute the electromagnetic field scattered by a rough surface separating two homogeneous media. These methods remain largely used both in propagation and remote sensing problems. The methods described in the paper are:

• –the geometrical optics approximation, in which the wave is considered as a set of rays obeying the laws of reflection and refraction;
• –the small perturbation method, due to Rayleigh and Rice, in which the field is given as an expansion on a set of elementary harmonic plane waves, the coefficients of which are determined so as to satisfy the boundary conditions;
• –the Kirchhoff approximation, in which the field is given as an integral on the rough surface; in this method one needs to know some components of the field on the surface, and an approximation is substituted to the unknown true value.

We end with a short discussion of some problems not adequately solved by these methods, namely self-shadowing, multiple scattering and some inadequacies of the Gaussian model for random surfaces. To cite this article: M. Sylvain, C. R. Physique 6 (2005).     

Texture in NdFeB magnets analysed on the basis of the determination of Nd2Fe14B single crystals easy growth axis

We have shown by X-ray analysis and magnetic measurements, that the easy growth axis of Nd₂Fe₁₄B crystals corresponds to the “a” axis of the tetragonal structure while the easy magnetization axis is the “c” axis at temperatures above 135K. This correlation allows to understand some interesting features in NdFeB magnets:

• •-anisotropic contraction during sintering in magnets obtained by classical powder metallurgy,
• •-orientation mechanism during hot pressing (“die upset”) of magnets based on melt spun ribons.

     

Optimisation d'un cycle de Brayton moteur en contact avec des capacités thermiques finies

Optimization of a Brayton cycle engine in contact with fluid thermal capacities. Finite time thermodynamics studies have recently been devoted to all kind of cycles. Some works have been done on Brayton engine cycles.The proposed model is a synthesis of the preceding ones; this model completes the preceding papers, particularly regarding the two following aspects:

• 1.it takes into account the thermal losses occurring between heat source and sink, that are finite time reservoirs;
• 2.it influences the two limiting conditions for fluids at source and sink (four cases). The study is performed with partial and total regeneration, and without regeneration of heat. Influence of global internal irreversibility of the engine is also included in the sensitivity analysis of the proposed model.

Results are presented in a nondimensionnal form useful for design project. Limiting cases are enlightened by the proposed method, and allow us to disuss the whole set of previously obtained results.     

Cohomogeneity-one Einstein–Weyl structures: a local approach

We analyse in a systematic way the (non-) compact n-dimensional Einstein–Weyl spaces equipped with a cohomogeneity-one metric. In that context, with no compactness hypothesis for the manifold on which lives the Einstein–Weyl structure, we prove that, as soon as the (n−1)-dimensional space is a homogeneous reductive Riemannian space with a unimodular group of left-acting isometries G:

• •there exists a Gauduchon gauge such that the Weyl-form is co-closed and its dual is a Killing vector for the metric;
• •in that gauge, a simple constraint on the conformal scalar curvature holds;
• •a non-exact Einstein–Weyl structure may exist only if the (n−1)-dimensional homogeneous space G/H contains a non-trivial subgroup H′ that commutes with the isotropy subgroup H;
• •the extra isometry due to this Killing vector corresponds to the right-action of one of the generators of the algebra of the subgroup H′.

The first two results are well known when the Einstein–Weyl structure lives on a compact manifold, but our analysis gives the first hints on the enlargement of the symmetry due to the Einstein–Weyl constraint.We also prove that the subclass with G compact, a one-dimensional subgroup H′ and the (n−2)-dimensional space G/(H×H′) being an arbitrary compact symmetric Kähler coset space, corresponds to n-dimensional Riemannian locally conformally Kähler metrics. The explicit family of structures of cohomogeneity-one under SU(n/2) being, thanks to our results, invariant under U(1)×SU(n/2), it coincides with the one first studied by Madsen; our analysis allows us to prove most of his conjectures.     

Dependence of lattice hadron masses on external magnetic fields

We study the variation of the hadron masses in the presence of external magnetic fields of strength of the order of the masses themselves.We identify the main factors affecting the lattice simulation results:

• •- the boundary discontinuities for eB ⪡ 2π/L²a².
• •- the SU(6) choice of the hadron wave function.

We confirm qualitatively the earlier theoretical ansatz on the linear behaviour of the masses with the magnetic field and, as a by-product, we improve the lattice measurements of the nucleon magnetic moments.However our systematic and statistical errors preclude us from measuring the theoretically predicted field strength at which the proton becomes heavier than the neutron.     

Nachwirkungsmechanismen in Ferriten

In ferrites a large number of after-effects are found, with time constants between nano-seconds and years. In this review the after-effects due to ion-and electron motion will be treated. One finds:

1. single-ion effects in combination with lattice deformations, e.g. Mn³⁺;
2. ion effects caused by mobile vacancies, e.g. Co²⁺;
3. effects due to electron transfer:
4. Co²⁺?Co³⁺
5. Me²⁺?Fe³⁺, in combination with Me⁴⁺ and vacancies.
6. Me⁴⁺?Fe²⁺, with Me=Si, Ti (photomagnetic effect).

The electron transfer is found to be related to electrical effects. In analogy to the photoelectric effect, one has found that illumination produces changes in magnetic properties. Generally speaking, one has in ferrites as many problems with donors and acceptors as in other semiconductors. Information from magnetic measurements helps to elucidate their nature.