Complex sentence: The research reactor was a Argonaut class reactor with an initial output of 10 kW thermal, later increased to 100 kW in 1967, using Uranium-235 as fuel and cooled by water.
Split into simpler sentences: The research reactor was an Argonaut class reactor with an initial output of 10 kW thermal, later increased to 100 kW in 1967. It used Uranium-235 as fuel and cooled by water.