[en] Purpose: To prevent cooling water in a pressure vessel from leaking upon dismantling or assembling work of a water-submerged motor for driving a pump. Constitution: Refrigeration pipes are disposed to a flow passage to a pump section and a water-submerged motor passing through the bottom wall of a reactor container and refrigerant is introduced through the refrigeration pipes to refrigerate the cooling water in the flow passage to thereby obtain water sealing effects. That is, a refrigerator is operated upon maintenance work and the refrigerant is cyclically supplied to the refrigeration pipes by opening valves. Then, the cooling water present around the refrigeration pipes is refrigerated to block the flow passage. Then, inspection or like other operation can be carried out by opening the motor case. (Aizawa, K.)

[en] The subcooling in the downcomer of the reactor calculated by code TRAC-BF1 was not in agreement with the data measured in the reactor vessel at steady state conditions. The most important phenomenon, which influences the subcooling is steam-water separation by gravity above the chimney. The steady-state input model has been changed in several ways in order to investigate the effect on the subcooling. Some alterations have been definitively implemented in the model, not because they strongly influence the subcooling, but because they are physical more correct. The level tracking option was left off. The implementation in the input of a perfect steam separator model, located above the chimney, resulted in calculations with stable water height and subcooling data more consistent with the measured data. It is recommended to conduct additional test in the GKN reactor. The purpose will be comparing calculated results with measured data, such as downcomer subcooling and flow rate in order to improve the validity of the model. (author). 3 refs.; 3 figs.; 3 tabs

[en] In order to be realistic, an evaluation of the performance of helium-cooled direct-cycle reactors must be based on a preliminary study of the circuits and the architecture. This was the procedure adopted by the Department of Mechanical and Thermal Studies (Saclay Nuclear Research Centre) which recently developed a plant concept aimed at solving the various problems involved and also defined the sizes of the principal components. The circuits have been designed to obtain a good electrical generating efficiency but without prejudicing this it has also been attempted to obtain the best conditions for recovering heat from the coolants. Results are presented for the following cases: a two-compression-stage cycle with good electrical generating efficiency and non-preferential heat recovery; a two-compression-stage cycle with acceptable electrical generating efficiency and improved heat recovery; a single-compression-stage cycle for the production of electricity with recovery of heat in the form of hot water; a single-compression-stage cycle with large-scale production of heat in the form of steam and hot water. It appears that the characteristics of the hot water in the secondary recovery circuits are well suited to district heating. It should be noted that the overall performances of all the different variants are satisfactory for a helium temperature at the core outlet of 800⁰C, which is reasonable. (author)

[en] A description is given of a nuclear reactor fuel assembly comprising a cluster of fuel elements supported by transversal grids so that their axes are parallel to and at a distance from each other, in order to establish interstices for the axial flow of a coolant. At least one of the interstices is occupied by an axial duct reserved for an auxiliary cooling fluid and is fitted with side holes through which the auxiliary cooling fluid is sprayed into the cluster. Deflectors extend as from a transversal grid in a position opposite the holes to deflect the cooling fluid jet towards those parts of the fuel elements that are not accessible to the auxiliary coolant. This assembly is intended for reactors cooled by light or heavy water

[en] Quality assurance for ensuring the requisite quality of primary system components includes object-related and system-related measures. The object-related measures include assessment of the fabrication engineering preconditions, checking the documentation relating to design, ordering and fabrication, and supervision of the important fabrication steps and of testing. This work is carried out by independent experts and inspectors and by the KWU. The system-related quality assurance is aimed at creating the organisational preconditions for faultless fabrication, taking also into account the time schedules and costs. This work is carried out by the KWU. (orig.)

[en] A method developed for the prediction of critical flow of subcooled and saturated water is compared to the Marviken full scale experiments and some other relevant data. It is shown that this method gives better agreement with the data than other methods. Besides that, the method is relatively simple to use since its equations give the flow in an explicit form. (author)

[en] We present an efficient method for subrecoil cooling of neutral atoms by applying Raman cooling in two dimensions to a four-level tripod system. The atoms can be cooled simultaneously in two directions using only three laser beams. We describe the cooling process with a simple model showing that the momentum distribution can be rapidly narrowed to velocity spread down to 0.1v_rec, corresponding to effective temperature equal to 0.01T_rec. This method opens new possibilities for cooling of neutral atoms.

No abstract available

[en] Tests were carried out at Westinghouse Canada Inc., Hamilton, Ontario, to measure impact forces and axial depressurization of initially subcooled water jets discharging into the atmosphere. The purpose of the tests was to provide data for model studies investigating the consequences of a hypothetical nuclear reactor primary coolant circuit rupture. Break openings of 25 mm, 76 mm and 102 mm were tested using simple convergent nozzles. Two targets were used: A 1 m diameter flat circular plate and a section of 57 mm diameter pipe with axis on the jet centreline and perpendicular to it. Further tests were conducted with a slender instrumented probe supported on the jet centreline to measure the depressurization of the 'free' jet. Test conditions included initial reservoir pressures up to 7 MPa and liquid subcooling to 60 K. The impingement plate test results with the 25 mm nozzle indicate that a thrust coefficient of from 1.3 to 1.4 is appropriate, except where surrounding structures restrict free expansion. For the latter case, thrust coefficients up to 4 were measured. Also there are indications that a subcooled core exists within the jet extending to an L/D of at least 1. (orig.)

[en] This invention concerns improvements to secondary coolant-systems for sodium cooled nuclear reactors. It further concerns a protective device for a free level mechanical pump which prevents any gas bubbles due to leaks of the working gas of the pump from entering the secondary system of the nuclear reactor