Les remontées d'eau active dans la piscine du réacteur Osiris

Abstract

The Osiris swimming pool type reactor has been in operation at the Nuclear Research Centre at Saclay since 1966. With its rated output of 50 MW and equipment it is the most irnportant irradiation research facility in France and one of the best-equipped in Europe, especially by virtue of a number of original hydraulic design features. The authors briefly describe the general problems encountered in designing the circulation pattern for this type of reactor and draw particular attention to the special arrangements proviclecl for. The hydraulic research and tests which confirmed the validity of the proposed schemes are gone into in some detail. Due to the site background, the only reasonable way to achieve the clesirecl 501MW rated output was by designing for rising How in the core, which also meant taking steps to counter the following possible undesirable efi'ects :- (i) Excessive pool temperature rise due to large-scale heat exchange behveen the hot core outf1cnv and the colder water in the pool; (ii) Unacceptable activity on the pool surface, which would impair case of operation enabling convenient direct access to the core, which is one of the main advantages of this kind of reactor. The proposed design reduces the upflow of warm water from the core in the pool to a minimum with the least possible adverse effect on flexible peactor operation. The tests canied out on a 1:3 scale model at SOGREAH Grenoble comprised the two following phases:- (i) A constant-temperature geometrical study in which the Reynolds number varieel but remained high enongh to ensure that the modelwas representative of real conditions; (ii) A study of the effect of temperature gradients in c ausing density differences conducive to an upward flow of active water. These etrects were reproduced to Fronde scale, with non-uniform salt wat·er concentrations in the model. A number of tricky scale problems in phase (ii) made it necessary to coyer a fairly wide range of Reynolds and Froude numbers. The tests established that pool pollution rates remained at an acceptable level. It is interesting to compare these results with the data observed when the actual Osiris reactor was put into service, which showed fairly close agreement. This is important as it confirms the reliahility of the scale model approach to mixed convection problems provised certain scale requirements are closely complied with.