A multi-scale and multi-physics approach to main steam line break accidents using coupled MASTER/

One-dimensional system analysis codes such as RELAP5, TRACE, CATHARE-3, and SPACE are generally used to address nuclear safety issues with an umbrella of conservativeness. The three-dimensional (3-D) approach for 3-D components like reactor vessels, however, is always of concern in nuclear safety analysis.

A simplified 3-D approach by which the “cross-flow junctions” between 1-D modules represented some multi-dimensional flow features, was first developed in system codes like RELAP (The RELAP5-3-D Code Development Team, 2001) and ATHLET (Burell et al., 1989). This may be sufficient in some cases particularly for a porous body like a reactor core when only small cross flows exist due to high resistance to transverse velocity. Explicit 3-D modules exist as an option in the codes TRACE (Bajorek et al., 2015) and CATHARE-3 (Barre and Bernard, 1990) for the reactor pressure vessel. In this case, the main objective is the modelling of large scale 3-D effects in a pressure vessel during Large Break Loss of Coolant Accidents (LBLOCAs) such as ECCS water reflooding of the core with transverse power profile effects. The 3-D modules are straight forward extensions of the 1-D modules for cylindrical or Cartesian coordinates. A multiscale software platform, including a CFD module and CATHARE-3 as a system code, were developed to model reactor pressure vessels effectively. Development of a 3-D reactor core module using 1000 or fewer cells was also started using SPACE code (Ha et al., 2010).