Fuel assemblies for reactor systems

A fuel cell assembly comprising:

• a first fuel assembly including
• a first fuel compact which defines a passage running from a flow inlet provided at a first end of the first fuel compact to a flow outlet provided at a second end of the first fuel compact, the passage defining an internal surface of the first fuel compact, and
• a first displacer element provided in the passage and mounted such that a clearance is maintained between the internal surface of the first fuel compact and the first displacer element to define an annular coolant flow passage;
• and
• a second fuel assembly including
• a second fuel compact which defines a passage running from a flow inlet provided at a first end of the second fuel compact to a flow outlet provided at a second end of the second fuel compact, the passage defining an internal surface of the second fuel compact, and
• a second displacer element provided in the passage and mounted such that a clearance is maintained between the internal surface of the first fuel compact and the first displacer element to define an annular coolant flow passage;
• wherein first heat transfer features are provided on the first displacer element, and second heat transfer features are provided on the second displacer element, the first heat transfer features configured to transfer heat at a different rate to the second heat transfer features.

A fuel cell assembly comprising:

• a first fuel assembly including
• a first fuel compact which defines a passage running from a flow inlet provided at a first end of the first fuel compact to a flow outlet provided at a second end of the first fuel compact, the passage defining an internal surface of the first fuel compact, and
• a first displacer element provided in the passage and mounted such that a clearance is maintained between the internal surface of the first fuel compact and the first displacer element to define an annular coolant flow passage;
• and
• a second fuel assembly including
• a second fuel compact which defines a passage running from a flow inlet provided at a first end of the second fuel compact to a flow outlet provided at a second end of the second fuel compact, the passage defining an internal surface of the second fuel compact, and
• a second displacer element provided in the passage and mounted such that a clearance is maintained between the internal surface of the first fuel compact and the first displacer element to define an annular coolant flow passage;
• wherein the first displacer element comprises a first material and the second displacer element comprises a second material that is different to the first material.