[en] The main purposes of this thesis are: - to point out the spectral effects on the radiation embrittlement of the pressure-vessel steels (A 508-Class 3). - to discern among the damage models proposed, using as gauge of exposure, the one that gives the best approach of the spectral effects observed between different irradiation locations. A simulated vessel-wall environment (called ''special location'') was constructed in the ''Melusine'' reactor of ''Centre d'Etudes Nucleaires de Grenoble'' that provided for measurements of steel embrittlement increase on Charpy-V notch samples and neutron flux detector activations as well as two other additionnal standard locations. Neutron spectra for these locations were calculated using Discrete Ordinate Transport Codes (ANISN and DOT 3.5.). Six campaigns of measurements of neutron spectrum by multiple foils activations were performed. Good agreement with results obtained from the calculations and the measurements were observed. The measured increases in steel transition temperature from the experimental locations revealed an important spectrum effect between the standard and special locations. If the data are expressed in (phi.t) > 1 MeV, this effect is about 50%. None of the tested damage models (displacement zones, Lindhard model, ...) does represent the observed effects

[en] An experimental program has been undertaken to confirm divers fast neutron spectrum calculations. The verification of calculational methods consists to compare measurements in a highly heterogeneous media to two-dimensional calculations effectuated on approach geometries. The measurements have been carried out in two testing facilities located in the centre 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') ¹¹⁵Insub(m), ⁴⁷Ti(n,p) ⁴⁷Sc, ⁵⁸Ni(n,p) ⁵⁸Fe(n,p) ⁵⁴Mn, Ti(n,x) ⁴⁶Sc, ⁵⁶Fe(n,p) ⁵⁶Mn, ⁶³Cu(n,α) ⁶⁰Co, ²⁷Al(n,α)²⁴Na, ⁹²Nb(n,2n) ⁹²Nbsub(m), ⁵⁸Ni(n,2n) ⁵⁷Ni. A spectrum form has been elaborated from such activities by using the unfolding code SAND-II. On other part, spectrum determinations are performed with transport computer codes ANISN and DOT-III. The spectrum obtained from Unfolding and Transport Codes have been compared. Good agreement between the measured (foil activation) and calculated (SAND-II) activities were found with all detectors. Reasonable agreement between transport (DOT-III) and iterative (SAND-II) solutions are observed in the two test cases. This analysis permits to retain a spectrum determination procedure in the actual case of a composite testing facility

[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 spectral effects on the radiation embrittlement of the pressure vessel steels (A508 classe 3) are studied. A simulated vessel-wall environment was constructed in the 'Melusine' reactor. The measured increases in steel transition temperature revealed an important spectrum effect of about 50% in the different locations of samples for fast fluence irradiations (E>1 MeV)

[en] An experimental program has been undertaken to confirm divers fast neutron spectrum calculations. The verification of calculational methods consists to compare 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 centre 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')115mIn, 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)92mNb, 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 have been compared. Good agreement between the measured (foil activation) and calculated (SAND-II) activities were found with all detectors. Reasonable agreement between Transport (DOT-III) and Iterative (SAND-II) solutions are observed in the two test cases. This analysis permits to retain a spectrum determination procedure in the actual case of a composite testing rig. (author)