View of the RASPLAV-3 Facility.

The Material Scaling (MASCA) Project was a follow-up of the RASPLAV Project  and investigated in-vessel phenomena during a severe accident with core melt. Specifically, it addressed the influence of the chemical composition of molten prototypical corium on heat transfer to the pressure vessel environment. The project addressed this by investigating stratification phenomena of the molten pool and the partitioning of fission products (FP) within the different layers of the melt. The project was scheduled to be completed in July 2003, but continued until 2007 under the project's second phase (MASCA-2), given the experimental needs that still existed after the first phase and the quality of the experimental work done up to that point. The Project has produced an invaluable data base to support the assessment of in-vessel retention strategies for both operating and future Light Water Reactors (LWRs). 

MASCA phases

First phase (2000-2003)

The first phase of tests aimed to reduce remaining uncertainties about the heat load on the reactor vessel during a core melt accident and thus the possibility of retaining the melt in the vessel. These uncertainties are mainly associated with scaling effects and coupling between the thermal-hydraulic and chemical behaviour of the melt. Supporting experiments and analyses, in addition to helping understand key in-vessel phenomena, facilitated a consistent interpretation of the results. The experiments were carried out with corium compositions prototypical of power reactors which use iron and steel materials. The MASCA experimental goal was achieved through corium tests of different scale and was complemented by pre- and post-test analyses and development of computational models. Additional measurements of thermo-physical properties of the melts such as density, thermal conductivity and liquidus-solidus temperatures considerably expanded the material properties data obtained during the RASPLAV Project.

Separate effects were studied in a series of small- and mid-scale experiments. Corium tests were performed in the RASPLAV, TULPAN, TF, STF, KORPUS, and TIGEL facilities. Salt tests were performed in the RASPLAV-A-Salt-3 facility.

Second phase (2003-2007)

The second phase (MASCA-2) was an extension of the first one. It was based on experiments that were mainly carried out at the Kurchatov Institute and that made use of a variety of facilities in which the corium compositions prototypical of power reactors could be tested. The tests aimed to provide experimental information on the phase equilibrium for different corium mixture compositions that can occur in water reactors. In order to enhance the application of MASCA results for reactor cases, the influence of an oxidising atmosphere and the impact of non-uniform temperatures (presence of crusts or solid debris) was addressed. The programme also generated data on the relevant physical properties of mixtures and alloys that are important for the development of qualified mechanistic models.

A MASCA-2 conluding seminar was held on 11-12 October 2007 in Cadarache, France and participants were provided with an integration report providing the main results of the project. 

In the framework of MASCA Projects, the technology to conduct high temperature corium tests has been developed, including design, fabrication and assembly of a large-scale facility capable to heat up and retain molten corium and steel at relevant high temperatures under controlled conditions. The experimental facilities used in MASCA are well suited for the study of any metal-oxide mixture at high temperature because the interactions between the corium and the crucible are very low.

Significant enhancement of the knowledge have been achieved on the following issues:
-  Melt stratification mechanisms;
-  Stratification phenomenon in iron containing melts;
-  Fission product spatial and chemical distribution in the melt pool;
-  Molten metal migration into the debris bed;
 - Boron effect on the melt stratification.

The discovered and quantified phenomena of component partitioning between the oxidic and metallic phases during the interaction of suboxidised corium and steel can be used for the development and verification of corresponding models describing the in-vessel molten pool behaviour. Precise measurements of the material properties and the composition of metallic and oxidic phases provide important data for validation of thermodynamic databases, such as the TAF-ID. The MASCA Project results obtained with corium compositions prototypical of power reactors provide qualitative and quantitative data for assessments of the in-vessel melt pool retention strategy as well as for ex-vessel phenomena. Nevertheless, it was identified at the end of the project that new studies were needed to reduce a number of uncertainties including uncertainties on the phase equilibria for U-Zr-O-Fe mixtures, on the physical properties of mixtures and alloys (liquidus and solidus temperatures, densities, thermal conductivity, viscosities), and uncertainties about the transposition of MASCA results to models for reactor cases, including scaling effects, the influence of an oxidising atmosphere and the impact of non-uniform temperatures. Reserach efforts in the area have been pursued with the MCCI, TCOFF and ROSAU projects. 

Project data

The Project data package can be requested through the NEA Data Bank.