[en] We can consider the different safety issues within French fuel transport as follows: (a) the proof as regards the leaking fuel assembly transport with hydrogen generation coming from potential in leakage water inside fuel rods; ( b) the measures taken to enforce the new design as well as the new manufacturing which have been decided since January 1^st 2007 in the frame of the 96 IAEA Regulation as regards the full water penetration as compared to the 85 IAEA Regulation, the latter allowing partial water penetration on certain conditions; and (c) the obligation of implementing various risk controls on exploitation site in order to take into account the possible human failure which are intrinsically increasing the permissible doses rates for workers. Even quite recently the leaking fuel assembly transport has been considered with no specific measure as regards the radiolysis phenomenon or the quality of drying cask holds. All these measures were sufficiently in accordance to rule out this issue. Lately, the leaking fuel assembly transport needs the implementation of equipment controls involved in nuclear power plants as regards the hydrogen rate before loading departure in order to determine on the evolution law, the maximum duration authorized for the transportation to not exceed the lower limit of inflammable status. As regards the proof of the criticality-safety casks, the main justification to be held on the irradiated fuel assembly on drop accident conditions could find a key in the hypothesis of the important damage of the fuel but should be in this matter, compensated by a limit of containment penetration for safety reason. For this case, the application of the 96 IAEA Regulation involves the use of independent leak tightness barriers. TN International is introducing different examples in France linked to the selection of multiple barriers. When limited in leakage quantity of water inside the cask is considered for the criticality studies, the French Competent Authority requires various independent controls before loading transportation in order to eliminate human failure. All this process being ensured for supplemental guarantees on the casks closing quality and without leaking after drying. TN International is introducing some examples to be implemented to suit this requirement of independent and various controls. (author)

[en] International regulations require that a packaging for the transport of radioactive material has to withstand a 9-meter drop onto an unyielding target. It has to be shown that the containment of the radioactive contents is guaranteed. For some packagings the trunnions are not only used during handling and transport but serve also to absorb the energy of the shock during a 9-meter drop. An LS-DYNA3D model of an angular sector of a trunnion has been developed taking into account the rupture of the structure. The finite element analysis has been validated by successfully calibrating it with an actual drop test. The cask consists of a main cylindrical steel body equipped with thermal fins and additional neutron shielding encased in an external thin steel shell. During transport, two shock absorbers made of wood in a steel shell are attached to the top and the bottom of the main body. There are two pairs of trunnions to allow fixing and handling of the packaging. A comparative view of the actual and the simulated deformed structure shows that the residual deformation of the finite element analysis coincides almost perfectly with the one observed after the test. Comparing the acceleration, as a function of time, measured at the top and the bottom between the reduced scale model and the finite element model some differences are observed although the general shape of the signals is similar

[en] Orano TN has implemented Burnup Credit (BUC) approaches for the demonstration of the sub-criticality for transport and dual purpose casks loaded with PWR uranium oxide (UO₂) used fuel assemblies. Usually, the BUC methodology uses Enriched Natural Uranium (ENU) to determine the isotopic composition of the fuel after irradiation for criticality calculations. Nevertheless, Enriched Reprocessed Uranium (ERU) may be used for the manufacturing of the PWR UO₂ fuel assemblies. As far as criticality is concerned, the main difference between ENU and ERU, for the same U²³⁵ content, is the presence of U²³², U²³⁴ and U²³⁶ in the ERU initial composition. This paper presents sensitivity calculations to assess the impact on transport cask reactivity when ERU initial composition is used for BUC applications. The results show that ENU considered as initial composition before irradiation is a bounding assumption for advanced BUC method compared to the use of ERU. Despite the important decrease of U²³⁴ during irradiation, the presence of U²³⁴ and U²³⁶ for ERU fuel is sufficient for balancing the production of fissile isotopes during irradiation which is more important for the Enriched Reprocess Uranium than for the Enriched Natural Uranium. Nevertheless, the important reactivity discrepancies between ENU and ERU fuels is due to the penalizing initial isotopic concentrations retained for ERU (U²³⁴, U²³⁶); for actual ERU fuel, the reactivity is obviously closer to the one of ENU fuel.

[en] Criticality safety analyses related to the transportation of PWR uranium oxide (UO₂) used fuel assemblies are usually performed under the fresh fuel assumption. This leads to huge safety margins, as the negative reactivity worth due to the irradiation of the assemblies is not taken into account. Since 1987, AREVA TN has been using a limited burnup credit method based on the sole consideration of major actinides and the use of a uniform axial burnup profile corresponding to the mean burnup at the 50 least-irradiated centimetres of the assembly. This method is quite limited today for some applications, due mainly to the increase of the fuel enrichment in PWR UO₂ fuel assemblies. The strategy of AREVA TN to deal with high enriched PWR UO₂ fuel assemblies and also to limit the increase of the neutron poison content in the new baskets' designs is to take benefit from the reactivity reserve, which can be gained by considering main fission products and less penalizing axial burnup profiles instead of uniform axial burnup profiles. The Burnup Credit (BUC) calculation route for PWR UO₂ used fuel is based on the connection of the depletion code DARWIN (developed by the CEA) and the Criticality Safety Package CRISTAL V1 (developed by the CEA and the IRSN in partnership with AREVA and EDF). French BUC experimental programs have been also separately performed in Cadarache and in Valduc in order to validate respectively the APOLLO2-DARWIN2 depletion code and the CRISTAL V1 Criticality Safety package. This paper presents the BUC methodology including actinides and fission products but also the approach used for the criticality safety assessment of representative transport cask loaded with PWR UO₂ used fuel assemblies approved for the first time by the French Safety Competent Authority. (authors)

[en] Taking credit for the presence of gadolinium contained in some fuel rods of the BWR assembly in criticality safety analyses is commonly referred to as gadolinium credit. The implementation of this approach in criticality safety assessment of BWR UO₂ used fuel assemblies transportation requires, among many other aspects, the definition of a method that ensures the conservatism of the isotopic composition. In particular, the choice of the isotopic modeling approach can have a strong impact from criticality safety point of view. Indeed, BWR UO₂ fuel depletion calculations depend on the local core conditions, mainly the axial coolant void fraction and control blade insertion during operation. The impact of these core operating parameters on transport cask reactivity may significantly differ according to the methodology (actinides only plus gadolinium vs. actinides plus fission products plus gadolinium) implemented for criticality safety analyses. This paper presents the results of sensitivity calculations performed in order to study the influence of the main operating core parameters (i.e. axial coolant void fraction and control blade insertion) on the choice of isotopic modeling for the implementation of gadolinium credit in criticality analysis for BWR UO₂ used fuel transportation. (Author)