This first 36 months of the IVMR project were dedicated to set-up the general organization, start and complete some of the work packages, consolidate the directions of research selected in the project proposal and initiate international contacts as well as communication about the IVMR project. Among the main results already achieved, we may mention:
WP2.1: work on the methodology has started by a state-of-the-art about the implementation of IVR in VVER-440 plants in Europe. A generalization of the methodology is now proposed for high power reactors in order to take into account the very thin remaining part of the vessel wall. It also allows to take into account the possible peaks of heat transfer which can lead to more ablation than the standard steady-state approach would predict.
WP2.2: work started with a synthesis of developments planned for each code. A PIRT for the phenomena related to in-vessel retention was built. New models were developed by some partners and implemented in some of the codes.
WP2.3: So far, activities have been devoted to validation and code development. Relevant experiments, all performed at the CEA Grenoble in the 90s, have been identified regarding thin layers, homogeneous pools and external vessel cooling. Satisfactory turbulence models for oxide pool were identified. The study of thin metal layer is going on in order to derive new correlations for integral codes.
WP2.4: A benchmark was defined, to predict vessel resistance or failure near the location where the vessel wall is significantly thinner because of high local heat flux. It is planned to make use of results to assess simpler models for SA codes.
WP2.5: All participants were able to calculate severe accident (SA) scenarios with External Reactor Vessel Cooling (ERVC), for the reactor and with the code of their choice. Very high values of heat flux are always associated with transient conditions leading to temporary presence of a thin metallic layer on top or inversion of stratification.
WP3.1: small scale experiments with prototypic corium have been made at NITI (Russia). The results confirm that inversion of stratification is likely to occur, driving metal to the top part of the pool, with possible high heat flux.
WP3.2: Measurements of oxide conductivity, metal density and metal surface tension were performed.
WP3.3: Larger scale experiments with simulants were designed for the study of heat transfers in various configurations of stratified pools. The two main facilities are SIMECO-2 (Under design) and LIVE 2D. New simulants have been selected allowing tests at higher temperature.
WP3.5: A heated wall simulates the molten pool boundary, surrounded by a debris bed. Preliminary tests have reached heat fluxes up to 600 kW/m2. CHF was reached for small (2mm) particles.
WP3.6: CVR has designed and installed two new induction furnaces dedicated to melt either metal or oxide (or both) in cold crucibles. Preliminary tests with stratified oxide/metal were performed.
WP4.1.1: Tests with vessel samples modified by surface treatment (“cold spray” coating) were performed. It was shown that this coating could enhance the local heat flux up to 30-50% locally.
WP4.1.2: Large scale facility THS-15 was built by UJV as a full-scale representation of a VVER-1000 geometry. Preliminary tests, with representative heat flux profiles were performed.
WP5: Review of innovation and technical engineering applicable to IVMR –
One way to avoid the IVMR failure is to increase the CHF by modifying the surface state of the vessel wall. A positive effect of the cold spray coating was noticed whatever the inclination of the wall. In the same framework, EDF studied the effect of the oxidation at the vessel wall. The porous super hydrophilic layer of 40µm obtained enhances the CHF of at least 30%. Possibilities of injecting water in the vessel after molten pool formation were also proposed.
