[en] The first rod cluster used to control the reactor is connected to a first drive shaft which is moved by a mechanism; this drive shaft comprises locking thimbles which are actionned by a device sliding on the end of the shaft; this device ensures the locking of thimbles by means of a spring or their opening moving to the top of the shaft. The second cluster, keeping inserted completely in the assembly during a part of the reactor operation cycle, is connected to a second drive shaft. This second shaft mounted coaxialy inside the first shaft, acts as a piston actionned for its displacement to the top by the opening a pressure reducing valve of the tight shell in which the two drive shafts move. The second shaft, in high position, can be connected to the first one by the thimbles fitting into a groove of the second drive shaft. The invention applies, more particularly, to nuclear reactor with improved efficiency utilizing neutron spectra shift control clusters

[en] The present invention proposes a spectral-shift rod designed to be introduced in a classical guide tube able besides to receive an absorber rod, without the spectral-shift rod being subject, to important shocks or vibrations. Most time, the spectral-shift rod is a fertile rod comprising a stack of fertile pellets

[en] The present cap is for a PWR fuel assembly. The fuel assembly has a lower cap integral with the upper cap by means of guide tubes receiving the control rod assemblies. The cap has a support for a cluster of control rods. Sliding spacers allow the support to slide in a direction parallel to the guide tubes one. A spring or several springs are integrated to the cap and arranged between the upper cap and the support to slowdown the control assembly at the end of their drop. One sliding spacer at least comprises stop motion devices fixing the rest position of the support plate. The invention finds an application in variable spectrum reactors

No abstract available

[en] France is considering plutonium recycling in existing PWR's. Development of FRAMATOME's spectral shift reactor is described and preliminary results of core studies are communicated

[en] A method of operating a nuclear reactor having a core and coolant displacer elements arranged in the core wherein is established a reactor coolant temperature set point at which it is desired to operate said reactor and first reactor coolant teperature band limits are provided within which said set point is located and it is desired to operate said reactor characterized in that said reactor coolant displacer are moved relative to the reactor core for adjusting the volume of reactor coolant in said core as said reactor coolant temperature approaches said first band limits thereby to maintain said reactor coolant temperature near said set point and within said first band limits

[en] This paper presents Framatome studies concerning the optimization of water power reactors. Three fuel models have been taken into account: fuel with grid and stainless steel cladding; fuel with grid and zircaloy cladding; and, fuel with grid, zircaloy cladding and spectral shift

[en] The theory of spectral lines in a plasma with quasistatic ions is reconsidered. The ion microfield distribution, generalized to include field gradients and higher-order derivatives, is introduced without decoupling the ion and electron subsystems. It is shown that in a self-consistent treatment of ion-electron correlations the calculations of line shifts requires a more complete theory than has been used in the past. It is shown that level shifts due to a time average of the radiator-plasma interaction are closely related to shifts due to ion field inhomogeneities at the radiator. These two shifting mechanisms are not independent and the analysis indicates how to avoid overcounting. As a result, the time average of the radiator-plasma interaction, usually associated with the so-called plasma polarization shift, is formally different from the equivalent expression given by theories which treat electron-ion correlations in an ad hoc fashion. 14 references

[en] The aim of the present invention is to propose a flexible pressurized water reactor to be controlled, its core comprising assemblies of same geometry and interchangeable to allow its operation at different conversion ratios

[en] In a reactor core of a BWR type reactor, the area of a flow channel in a lower portion of a downcoming pipe for downwardly releasing steams present at the top portion in a water rod is increased. Further, a third coolant flow channel (an inner water rod) is disposed in an uprising having an exit opened near the inlet of the water rod and an inlet opened at the outside near the top portion of the water and having an increase flow channel area in the upper portion. The downcoming pipe in the water rod is filled with steams, and the void ratio is increased by so much as the flow channel area of the downcoming pipe is increased. Since the pressure difference between the inlet and the exit of the inner water rod is greater than the pressure difference between the inlet and the exit of the water rod, most of water flown into the inner water rod is discharged out of the exit in the form of water as it is. Since the area of the flow channel is increased in the portion of the inner water rod, void efficiency in the upper portion of the reactor core is decreased by so much. Since the void ratio is thus increased in the lower portion and the void efficiency is decreased in the upper portion of the reactor core, axial void distribution can be flattened. (N.H.)