ATLAS − Analysis simulator for interactive plant simulation

Today, complex computer codes allow the simulation of many different processes in nuclear power plants, from normal operation up to severe accidents. The operation of these codes and the evaluation of the results is, however, difficult and requires a high level of expert know-how. The possibilities of present-day computer technology make it possible to simplify the use of simulation codes by way of modern user interfaces and graphic processing of results.

One important tool in this area is the ATLAS analysis simulator developed by GRS. It allows the representation and assessment of the computation results with the help of modern visualisation methods. It also provides the possibility of interactive control of the simulation, with intervention possibilities similar to those of a real power plant.

Main features of ATLAS

The underlying objective of the development of ATLAS was to provide an integrative simulation environment for different models where the resulting data can be graphically represented and the simulation sequence interactively controlled. Currently there are a number of dynamic simulation codes available in ATLAS, covering a wide spectrum of reactor safety analyses. They presently include

  • ATHLET/ ATHLET-CD (GRS, reactor coolant system and ancillary systems)
  • COCOSYS (GRS, reactor containment  and containment structure)
  • ASTEC (GRS and IRSN, overall plant)
  • MELCOR (SNL, overall plant)
  • S-RELAP (AREVA, reactor coolant system and ancillary systems)

These codes comprise models for the reactor coolant system with thermal hydraulics and heat transfer, for reactor systems and instrumentation & control, for neutron dynamics, for core destruction processes and for the pressure build-up and fission product behaviour in the containment.


ATLAS can be used on different computer systems. At its analysis centre at Garching near Munich, GRS provides a special infrastructure for the application of ATLAS which is similar to a power plant digital control room.

Application and use

ATLAS is currently used by research and regulatory organisations worldwide for a wide range of tasks. Particularly noteworthy are the detailed analysis simulators developed on behalf of the Federal Environment Ministry for the German nuclear power plants, the performance of so-called Human Factor analyses, the training of personnel in the area of severe accidents, and the application as a visualisation tool for various computer codes.

Schematics of a pressurized water reactor with ATLAS
© GRS
Systemschaltbild: Druckwasserreaktor im Analysesimulator