Microstructural Effects on Irradiation Creep of Reactor Core Materials

Area of Science:

• Materials Science
• Nuclear Engineering
• Physics

Background:

• Irradiation creep is crucial for nuclear reactor core materials.
• Experimental study of irradiation creep is challenging, leading to various theoretical models.
• Microstructure significantly influences irradiation creep mechanisms and mass transport.

Purpose of the Study:

• To describe and discuss microstructurally dependent irradiation creep mechanisms and models.
• To develop and validate a rate theory model for creep in Zr-2.5Nb pressure tubing.
• To determine dominant creep mechanisms and microstructural parameters for Zr-alloys and austenitic alloys.

Main Methods:

• Development of a rate theory model incorporating as-fabricated microstructure.
• Comparison of model predictions with experimental measurements for Zr-2.5Nb tubes.
• Analysis of microstructural dependencies for Zr-alloys and austenitic alloys.

Main Results:

• The developed rate theory model shows good agreement with experimental data for Zr-2.5Nb pressure tubing.
• Diffusional mass transport is identified as the dominant creep mechanism for Zr-alloys at temperatures < 300 °C and stresses < 150 MPa.
• Grain structure is the most critical microstructural parameter for irradiation creep in Zr-alloys under these conditions.

Conclusions:

• Diffusional mass transport is the primary mechanism for Zr-alloys under specific temperature and stress conditions.
• Grain structure is the most significant microstructural factor controlling irradiation creep in Zr-alloys.
• Austenitic alloys exhibit similar microstructural dependencies but extend to higher temperature and stress ranges, with dislocation slip dominating at low temperatures (< 100 °C).