Thorium core from steelyard smelt with composed bearing (8)
I believe the answer is:
sedately
'thorium core from steelyard smelt' is the definition.
I can't judge whether this definition defines the answer.
'composed bearing' is the wordplay.
'composed' becomes 'sedate' (I've seen this before).
'bearing' becomes 'ly' (I am not sure about this - if you are sure you should believe this answer much more).
'sedate'+'ly'='SEDATELY'
'with' is the link.
Can you help me to learn more?
(Other definitions for sedately that I've seen before include "Primly" , "Staidly or with dignity" , "Calmly, unhurriedly" , "without getting ruffled" , "With composure" .)