Incumbent of parish welcoming a source of energy (7)

I believe the answer is:

reactor

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'source of energy' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for reactor that I've seen before include "Nuclear power generator" , "(Nuclear) powerplant" , "chemical substance!" , "Heart of a nuclear power station" , "Producer of nuclear energy" .)

I've seen this clue in The Times.

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