[en] An assessment of the results given by a study carried out for the development of qualitative and quantitative analysis, by γ spectrometry, of plutonium in solid waste drums is presented. After having reminded the standards and their incidence on the quantities of plutonium to be measured (application at industrial Pu: 20% of Pu²⁴⁰) the equipment used is described. Measurement station provided with a mechanical system consisting of: a rail and a pulley block to bring the drums; a pit and a hydraulic jack with a rotating platform. The detection instrumentation consisting of: a high volume coaxial Ge(Li) detector with a γ ray resolution of 2 keV; an associated electronic; a processing of data by a 'Plurimat 20' minicomputer. Principles of the identification and measurements are specified and supported by experimental results. They are the following: determination of the quality of Pu by measuring the ratio between the γ ray intensities of the ²³⁹Pu 129 keV and of the ²⁴¹Pu 148 keV; measurement of the ²³⁹Pu mass by estimating the γ ray counting rate of the 375 keV from the calibrating curves given by plutonium samples varying from 32 mg to 80 g; correction of the results versus the source position into the drum and versus the filling in plastic materials into this drum. The experimental results obtained over 40 solid waste drums are presented along with the error estimates

[en] Up to now, criticality safety experts used density laws fitted on experimental data and applied them in and outside the measurement range. Depending on the case, such an approach could be wrong for nitrate solutions. Seven components are concerned: UO₂(NO₃)₂, U(NO₃)₄, Pu(NO₃)₄, Pu(NO₃)₃, Th(NO₃)₄, Am(NO₃)₃ and HNO₃. To get rid of this problem, a new methodology based on the thermodynamic concept of binary electrolytes solutions mixtures at constant water activity, so called 'isopiestic' solutions, has been developed by IRSN to calculate the nitrate solutions density. This article shortly presents the theoretical aspects of the method, its qualification using benchmarks and its implementation in IRSN graphical user interface. (author)

[en] After shortly recalling one among the many pertinent recent features of the French criticality CRISTAL package i.e. the perturbation algorithm (so called MORET 4 'Perturbation' or MP), this paper presents original MP validations. Numerical and experimental validations are made using close fission products (FP) experiments. As results, it is shown that, all being equal, MP can detect FP's absorption cross-section variations in the range 0.3-1.2%. (author)

[en] This paper provides for various cases of ²³⁵U enrichment or Pu isotopic vectors, and different reflectors, new minimum critical values of uranyl nitrate and plutonium nitrate solutions (H⁺=0) obtained by the standard IRSN calculation route and the new isopiestic density laws. Comparisons are also made with other more accurate routes showing that the standard one's results are most often conservative and usable for criticality safety assessments. (author)

[en] This paper presents recent actinides (reflected or not, moderated or not) critical masses calculations performed by the French standard route (APOLLO2 Sn 8 P3, 20 energy groups cross-section collapsed from 172 energy groups CEA 93 library). Comparisons are also presented against more accurate routes of the French criticality package CRISTAL, showing the fair conservatism of the standard values. Checks of the Paxton Woodcock rule for transportation exemption limit were also made. (author)

[en] Cofunded by Cogema, two complementary experimental programmes on burn up credit (BUC) related to fission products (FPs) are performed by CEA and IRSN at Cadarache and Valduc. After shortly recalling the main characteristics of each experiment, a first comparison of some results is presented, especially the energy range in which most part of cross section absorption are qualified. Both experiments exhibit great quality and accurate results, giving a high degree of confidence to the whole experimental French process of qualification devoted to BUC. (author)

[en] Up to now, criticality safety experts used density laws fitted on experimental data and applied them outside the measurement range. Depending on the case, such an approach could be wrong for nitrate solutions. Seven components are concerned: UO₂(NO₃)₂, U(NO₃)₄, Pu(NO₃)₄, Pu(NO₃)₃, Th(NO₃)₄, Am(NO₃)₃, and HNO₃. To obviate this problem, a new methodology based on the thermodynamic concept of mixtures of binary electrolytes solutions (one electrolyte + water) at constant water activity, a so-called 'isopiestic' solution, has been developed by the Institute de Radioprotection et de Surete Nucleaire (IRSN) to calculate the nitrate solutions density. This paper presents its qualification by using criticality experiments. The theory and the implementation are also given.Qualification results of the uranyl and plutonium nitrate solutions show that the new density law (also called the isopiestic law) is in good agreement with the benchmarks. Thus, no bias is put into evidence for the uranium solutions, and a small negative bias equal to 0.2% is found for the plutonium solutions.Moreover, the isopiestic law corrects the observed 1% overestimation of k_eff due to the empirical IRSN Leroy and Jouan density law for uranium solutions and the observed 3.4% underestimation of k_eff due to the ARH-600 density law for plutonium solutions.The isopiestic density law has been implemented in CIGALES V2.0, the graphical user interface of the French criticality safety package CRISTAL that calculates the atom densities of nuclides (and writes the input file for CRISTAL computations)