#CHERNOBYL ACCIDENT SIMULATION SOFTWARE#

The thermal-hydraulics within the containment using a 0D volumes approach, classically called 'lumped-parameter code' Special attention is particularly paid to the behavior of the many iodized species in its various forms (molecular iodine, gaseous organic iodides, iodine oxides aerosolsРІР‚В¦). The transport of FPs and aerosols as well as their physical and chemical behavior in the primary and secondary cooling systems, then in the containment ( see Figures 3 and 4). release from both standing pellets or relocated fuel compounds (either particulate debris or corium).

The release of fission products (FP), particularly iodine, from any fuel material in the core, i.e. This behavior is modeled until the vessel bottom barrier is either breached or the corium layers achieve to be stabilized on the inside if the vessel can be cooled from the outside (see IVMR below). The behavior of corium, once located in the vessel bottom after its slumping from the core, is modeled accounting dynamically for the possible stratification of materials to form several metal and oxide layers. Another possibility is the formation of solid debris from the premature fragmentation of fuel pellets combined with the embrittlement of fuel rod claddings. This may go as far as the materials melting, leading to the formation of a mixture of melted materials known as 'corium'. The degradation of materials within the vessel, when the temperatures reached under the effect of the core's residual power exceed a threshold leading to significant oxidization of the fuel rod claddings due to water vapor as well as various chemical interactions between the materials that make up either the fuel rods or the control rods. The two-phase thermal-hydraulics of coolant flows in the reactor coolant primary and secondary systems including a 2D description of the vessel

(see Figure 1) simplifies qualification of the physical models implemented in ASTEC by comparing the simulated results with those obtained experimentally.Р”В®ach module (described in details in and ) handles phenomena that occur in a part of the reactor or phase of the accident, and in particular:

#CHERNOBYL ACCIDENT SIMULATION SOFTWARE#

MC3D software) and the mechanical integrity of the containment (for which the IRSN uses the CEA CAST3M software package). It is also used by several organisations outside EuropeР’В (Canada, Russian Federation, India, Singapore, Ukraine, etc.).Р”Р„STEC covers the entire phenomenology of severe accidents except steam explosion (for which the IRSN uses the SARNET (Severe accident research network) network of excellence. Furthermore, ASTEC is also occasionally used for preparing certain crisis exercises (nuclear or radiological accident simulation exercises for training various players and the organization itself) at the IRSN Crisis Technical Centre.Р”Р„STEC is the European reference software within the European Commission It is also used to prepare and interpret the experimental programs with respect to either in-vessel or ex-vessel phenomena which could occur during meltdown accidents. ASTEC is widely used in IRSN level 2 probabilistic safety assessments (PSA2) for French reactors. the European Pressurised Reactor - EPR), source term evaluations in accident situations and the development of severe accident management guidelines. The main applications of the software package are safety analyses for nuclear reactors (e.g. ASTEC is currently maintained and developed by the IRSN. This particularly covers Western-designed pressurized water reactors (PWRs) such as those used for France's nuclear power supply, Russian-designed PWRs (VVERs), boiling water reactors (BWRs) and CANDU heavy water reactors. The ASTEC (Accident Source Term Evaluation Code) software system makes it possible to simulate all phenomena that take place during a water-cooled reactor meltdown accident, from the initiating event to the discharge of radioactive materials (called the 'source term') out from the containment.

Chernobyl accident simulation