FEA Assists in Safety Evaluation
For accurate evaluation of nuclear plant SCC, Hienstorfer’s group employs Abaqus finite element analysis (FEA) software from SIMULIA, the Dassault Systèmes brand for realistic simulation. "Abaqus is a very useful and powerful tool for many aspects of our work," says Hienstorfer (who also used it for aircraft crash analysis as a young engineer at Germany’s equivalent of NASA). "The processes of sensitive industrial facilities are very complex, and FEA helps us evaluate the safety margins in a more sophisticated way."
TÜV uses Abaqus to analyze stress loads over a wide range of scenarios such as rapid temperature and/or pressure changes, airplane impact, earthquakes, and radiation embrittlement. The software analyzes everything from key mechanical components — including pumps, piping systems, vessels, supports, and tanks — to fuel assemblies, building structures, and lifting devices such as cranes.
Modern nuclear plants are extremely well built to protect the facility from exterior damage: Thick concrete shells can withstand aircraft impact, while plants in earthquake zones are strongly buffered against seismic activity. An ongoing interior focus of regulators today is the reactor pressure vessel (RPV), the steel heart of the power plant that houses the nuclear fuel rods.
Strict Standards for Nuclear Reactors
A nuclear power plant using fission to produce steam that drives electric generators is subject to temperature and pressure stresses similar to those at any other kind of steam facility. But the possibility of pressurized thermal shock (PTS) affecting a radiation-embrittled RPV is unique to the nuclear industry. This is because bombardment from neutrons can, over time, alter the molecular makeup of the metal from which an RPV is built. This makes the vessel more prone to structural damage under stress. In a classic loss-of-coolant (LOC) accident scenario, a broken pipe in the primary system deprives the reactor core of vital coolant, and the hot vessel (at 300C) is then subjected to extreme PTS as colder water (at 30C) is rapidly piped into the vessel to cool the core and shut the reactor down.
IAEA standards require that RPVs have a proven ability to withstand this kind of event in order to receive certification (and also recertification at regular intervals) for operation. "You have to document the damage tolerance of the systems, structures, and components of a plant to pass inspection," says Hienstorfer. "FEA is an integral part of that analysis."
FEA can be used for virtual testing to provide guidance for new designs in the early stages of product development as well as for performance assessment of existing components under simulated stress conditions.
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