[en] Full text: According to the law for nuclear phase out in Belgium, the third unit of the Doel NPP (referred to as “Doel 3”) was permanently shut down in September 2022 after 40 years of operation. Doel 3 entered in so-called Post Operational Phase, during which the licensee prepares notably its safe dismantling. Among these preparation activities, the licensee performed a chemical Full System Decontamination (FSD) of the Doel 3 primary circuit, including several auxiliary circuits (e.g., the chemical and volume control system). This activity mainly aimed at decreasing the radiation exposure of the workers during the future dismantling activities. The preparation and the realization of the FSD was a challenge for the licensee and Bel V, notably because it was the first FSD on a PWR unit in Belgium. The current paper will introduce the FSD performed by the licensee, present the approval process applied by the regulatory body, and the associated safety assessment performed by Bel V. This assessment consisted of several pillars, i.e., the justification of the FSD from the ALARA point of view, the safe and sustainable management of the generated radioactive waste (on the short and longer terms) and the management of radiation protection and hazards during the FSD. This assessment required interrelationships between several stakeholders, for instance with the waste management organization for the aspects related to the management of the generated radioactive waste. The main lessons learned for future FSD projects will be presented.

[en] The Belgian nuclear research centre SCK CEN is preparing to build MYRRHA, a heavy metal cooled fast reactor as part of an accelerator driven system (ADS). Due to the complexity of the facility and to build up sufficient knowledge and expertise for such an innovative design, the SCK CEN, FANC and Bel V launched a pre-licensing project as a preparatory phase for the licensing of the facility. The pre-licensing process allows for early interaction with the future operator to converge to a design that meets all expectations of the safety authorities. regarding safety, security and safeguards. The process also allows the development of specific regulation if needed, as well as to extend an independent knowledge base for all parties. For example, the use of lead-bismuth eutectic as a coolant leads to challenging radiation protection and safety issues (e.g. production of Po-210 and other elements of high radiotoxicity). The use of an opaque coolant medium introduces specific requirements with respect to corrosion which will add further safety, security and safeguards concerns for the regulatory body.

[en] The origin of the kinetic theory of granular flow was originally credited to Bagnold. By using a very primitive expression of the particle collision frequency, he derived an expression for the repulsive pressure of the particles in uniform shear flows. His repulsive pressure was proportional to the square of the velocity gradient and the particle diameter and directly proportional to the particle density. This theory was later extended by Savage and Gidaspow. Such theories provide insight on the dependence of the viscosity, and various moduli (elastic, non elastic, viscous...) in terms of the granular temperature and the associated shear-rates. Until recently, such parameters were difficult to measure because of the lack of specifically designed equipment. This challenge was successfully taken up and resolved by P. Marchal of ENSIC who designed a new rheometer for powders. This equipment can put in evidence the importance of the granular temperature on the elastic and viscous behaviors of the granular flows. Such rheological behavior is important in risk analysis for nanopowders, because as the nanopowder may be subjected to process shear rates and stresses, its structural and topological changes, in terms of the transformation of agglomerates into primary nanoparticles, have strong impacts on emission factors of nanosized particles that can be released in the environment or into a workplace from such dense-phase nanopowder processes. Such transformation can be analyzed by studying the nano-granular rheological signature of the system. Such risk assessment approach using these new fundamental rheological safety parameters is described in this paper.

[en] This work deals with the study of ignition and explosion characteristics of nanoparticles. It has been carried out on various powders: zinc, aluminum, carbon blacks... Specific behaviours have been highlighted during the first phase of this project (Nanosafe 2). For instance, it has been demonstrated that there mainly exists two combustion regimes that are either kinetically controlled, for small size particles, or diffusion controlled, for large size particles (generally with diameters greater than 1 or 2 μm). It has been found that as the particle size decreases, minimum ignition temperature and minimum ignition energy decrease (even lower than 1 mJ), indicating higher potential inflammation and explosion risks for metallic nanopowders. Moreover, the presence of agglomerates in the nanopowders could modify their reactivity. Thus, the explosion severity of Al powders tends to increase as the specific surface area decreases, before reaching a peak for 1 μm particle size. These results are essential for industries producing or handling nanopowders in order to propose/design new and proper prevention and protection means. Nevertheless, the validity of the classical characterization tools with regard to nanopowders should be discussed. For example, the experimental laminar flame velocity of Al dusts has been compared to a theoretical one, determined by Huang's model, which assumes that the propagation of the flame is run mainly by conduction. It has shown a good agreement. However, under certain conditions, the Al flame propagation is expected to be mainly conducted by radiation. Two hypotheses can then be made. On the one hand, it can be assumed that the 20 L sphere probably disturbs the flame propagation and thermal mechanisms by absorbing radiation (wall quenching effect). On the other hand, it has been observed, thanks to the use of a high speed camera that the preheating zone is smaller for some nanopowders than for micro-particles (figure below). It could notably be explained by the fact that the flame radiation is absorbed by the cloud of unburnt Al nanopowders. Several other factors may have an impact on the explosion severity. If these points are correctly addressed, it will be possible to get more reliable ignition and explosion characteristics.