[en] An experimental program has been undertaken to confirm fast neutron spectrum calculations. The verification of calculational methods consists of comparing the measurements in a highly heterogenous media to two dimensional calculations effectuated on approach geometries. The measurements have been carried out in two testing rigs located in the center of the core and near the reflector of the Melusine Pool-type reactor. Counting techniques used for the determination of the reaction rate by beta-gamma activity measurements and activation foils are described. The following reactions have been selected: ¹⁹⁷Au(n,γ)¹⁹⁸Au, ¹¹⁵In(n,n')/sup 115m/In, ⁴⁷Ti(n,p)⁴⁷Sc, ⁵⁸Ni(n,p)⁵⁸Co, ⁵⁴Fe(n,p)⁵⁴Mn, ⁴⁶Ti(n,x)⁴⁶Sc, ⁵⁶Fe(n,p)⁵⁶Mn, ⁶³Cu(n,α)⁶⁰Co, ²⁷Al(n,α)²⁴Na, ⁹²Nb(n,2n)/sup 92m/Nb, ⁵⁸Ni(n,2n)⁵⁷Ni. A spectrum form has been elaborated from such activities by using the unfolding code SAND-II. On the other part, spectrum determinations are performed with Transport codes ANISN and DOT-III. The spectrum obtained from Unfolding and Transport Codes has been compared. Good agreement between the measured (foil activation) and calculated (SAND-II) activities was found with all detectors. Reasonable (SAND-II) solutions are observed in the two test cases

[en] The use of a neutron beam for the non-destructive control of materials is continually providing new original applications. This paper describes here initially the control of industrial type at the MELUSINE reactor, then its principal applications by neutron radiography and neutron counting

[en] MELUSINE, a swimming pool type reactor, in Grenoble, for research and technological irradiations is well fitted to the neutronic evolution qualification of the LWR fuel. Thus, with an adjustment of the lattice pitch, representative neutron spectrum locations are available. The re-leading management and the regulation mode flexibility of MELUSINE lead to reproductible neutronic parameters configurations without restricting the reactor to this purpose only. Under these conditions, simple calculations can be carried out for interpretation, without taking into account the whole core. An instrumentation by Self Power Neutron Detectors (collectrons) gives on-line information on the fluxes at the periphery of the device. When required by the neutronicians, experimental pins can be unloaded during the irradiation process and scanned on a gammametry bench immersed in the reactor-pool itself, before their isotopic composition analysis. Thus, within the framework of neutronic evolution qualification, are studied fuel pins for advanced assemblies for the light water reactors or their derivatives, with large advantages over irradiations in power reactors

[en] After a hypothetical accident in a fast neutron reactor core, the nuclear fuel and construction materials melt partially. In several out-of-pile devices, the melting materials and the sodium coolant come to interact thermodynamically. In short, a few seconds after the accident a bed of debris immersed in sodium is formed on a plane of steel. The PAHR program has as principal objective to study the thermodynamic behaviour of this bed in the MELUSINE reactor, taking into account the most crucial parameters that rule the phenomena. More particularly, the aim is to draw attention to the bed behaviour beyond the fusion point of the steel up to the partial fusion of the fuel. The authors describe the CELIA capsule and its instrumentation; the operation conditions of the reactor and the coupling factor; the out-of-pile materials and their operation conditions. (Auth.)

[en] An apparatus for irradiation in a swimming-pool with a magnetic field of 5000 oersteds is described. An aluminium coil with a very high current density is water cooled. A relatively great Volume can be used in the coil center, and two furnaces can be introduced, or a liquid nitrogen cryostat. (author)

[en] The authors outline the role played by polyvalent materials-testing reactors in France - in the area of primary and applied research - in neutronic irradiation production and the acquisition and diffusion of nuclear know-how. They then go on to describe the fields of application of these reactors

[en] Many irradiation devices call for supplementary electrical heating which can provide a constant temperature. We describe a coupling whose high performance makes it possible for the sheathed electrical resistance to provide maximum power. Since this coupling is sealed and does not require special cooling, it may be placed in any position on the irradiation device. (authors)

[en] Investigations have been in hand for over five years, under a EURATOM contract, on the behaviour of terphenyls under irradiation. The investigations have been carried out by mixed teams from the Commissariat a l'Energie Atomique (CEA), the PROGIL Company and EURATOM. Most of the trials were carried out at Grenoble Nuclear Research Centre, using the BLO 2, 3 and 4 loops on the MELUSINE and SILOE pool reactors. A preliminary synthesis of the results was carried out during the last Geneva Conference. By comparing the results obtained with the BLO 2 and BLO 3 loops placed in radiation fluxes of different intensities but the same quality, the authors demonstrated that in the presence of radiation a radiopyrolysis phenomenon occurred at irradiation temperatures above 360 deg C. They calculated rate constants for this new phenomenon by analysing the curves, assuming that radiolysis and radiopyrolysis were first-order reactions. It was then necessary to check the hypothesis regarding the order of the reaction and, if possible, separate the neutron and photon effects. BLO 4 was constructed for this purpose and has been operated differently from the previous loops. The investigations are now being made at a constant terphenyl level, the radiolysed product being automatically removed at regular intervals and replaced with new terphenyl. By comparing the amounts of terphenyl required to maintain two or three given stages, it is possible to determine the order of the reaction. The first results obtained show that in pure radiolysis the order of the reaction lies between 1.5 and 2, whereas in radiopyrolysis it is closer to 1. It is also possible to place the loop in different irradiation positions so as to vary the neutron-dose/total-dose ratio. This can vary from 12.6 to 28%. Assuming that the neutron and photon effects are additive, the value found for pure radiolysis is G_n/G_γ ≅ 3. The entire set of data collected since the beginning of this programme will have to be reviewed in the light of these new findings. (author)

[en] In this paper the authors indicate the studies made in the CEA in view to valid the conception of an under moderated reactor

[en] The uses of the French Atomic Energy Commission (CEA) Grenoble research reactors are presented. The main features of the three swimming pool, open core, MTR type reactors, SILOE (35 MW), MELUSIN (8 MW) and SILOETTE (100 kW) are described. Their uses are described in historical order along with the important relevant reactor upgrading that permitted scientific and technological advance. Finally, the beneficial advantages of those research reactors common type are recalled, as demonstrated by their achievements. (author)