A Restructuring of the MELCOR code to Establish the MIDAS Computer Code

A severe accident analysis code, MIDAS 1.0, has been developed for an easy understanding and model improvement of the MELCOR code, which analyzes severe accidents in a reactor. As the foundation for the MIDAS code, the MELCOR 1.8.4 code was adopted. The source code was then converted into standard FORTAN90, and restructured using a modular data structure based on ‘derived type’ variables and a new ‘dynamic allocation’ scheme. It has become easy to understand the workings of the code, and it is also easy to improve the code. The verification was done by comparing the results of the modified code (MIDAS 1.0) with those of the existing code (MELCOR 1.8.4). It is expected that the code restructuring will accelerate the code’s domestication thanks to a direct understanding of each variable and an easy implementation of modified or newly developed models.