Part of the work of GRS is to analyse the sequences of possible incidents and accidents in nuclear power plants (NPPs), using various methods and simulation programmes, so-called computer codes. In this context, our experts study the effects of the physical phenomena that occur and the structure-mechanical loads with regard to the effectiveness of the different barriers of an NPP that retain radioactive substances. The main barriers are the fuel cladding, the reactor coolant pressure boundary (i.e. the pressurised components containing the cooling water of the reactor), and the containment system.
Incident and accident behaviour in the containment system
The focus of the work and research related to the incident and accident behaviour in the containment system derives from the following questions:
• What physical phenomena and thermodynamic plant states have to be expected in the containment system of an NPP during possible incident and accident sequences?
• Do these result in a risk to the effectiveness of the relevant barriers?
To clarify such complex issues, GRS develops and verifies various different simulation codes (e.g. ATHLET, COCOSYS, ASTEC). They can be used to simulate the thermal and process-based behaviour of the reactor coolant system and the containment system.
The simulation codes are used e.g. to
• study the effectiveness of the barriers,
• assess accident management measures to enhance the safety of NPPs, and
• analyse accident sequences within the framework of probabilistic safety analyses (PSA) − especially those of Level 2.
The simulation codes can also be used to study the effectiveness of innovative passive systems in the containment systems of future NPP generations.