Complex sentence: The-reaction is optimized at a much higher temperature, so the burnup at the optimum-temperature may be low, so it seems reasonable to assume the but not the gets burned up and adds its energy to the net reaction.
Split into simpler sentences: The-reaction is optimized at a much higher temperature, so the burnup at the optimum-temperature may be low. Therefore it seems reasonable to assume the but not the gets burned up and adds its energy to the net reaction.