Materials selection

Selection of materials for the High Temperature Reactor Intermediate Heat Exchanger.

The indirect-cycle Very High Temperature gas cooled Reactor (VHTR) is one of the leading contenders for the next generation of nuclear reactor. It allows a common heat source to be used for both electricity generation and hydrogen production while minimising the complexity and risk associated with the nuclear part of the cycle.

The VHTR produces heat at temperatures in the order of 1000°C. This heat can be used for power generation, via a Brayton or combined cycle, and hydrogen production, via a variety of high temperature processes. A key component of the VHTR is the Intermediate Heat Exchanger (IHX)

Regardless of the exchanger type used in this duty, selection of an appropriate material is fundamental. A number of issues need to be taken into account and the material used must:

• have a design life of up to 60 years
• be of high strength and be suitable for operation in corrosive environments
• there may also be design code issues, as at present there are no "nuclear approved" materials available

On this basis a number of materials are being qualified by Heatric for IHX manufacture and include: Alloy 617, Alloy 230, Alloy X and XR, Alloy 800 variants and Alloy 602CA. The main factors in the preliminary selection of these materials are:

• mechanical properties
  - tensile properties
  - creep and creep-fatigue properties
  
  
• physical properties
  - thermal conductivity
  - thermal expansion
  
  
• corrosion resistance
  - helium contamination
  - nitridation resistance
  
  
• fabrication and joining technology 
  
  
• experience

Preliminary materials selection
Max temp limit: ASME VIII I (2006)