How can you reduce the power of technical expert in large projects

If the Roles, Responsibilities and Expectations and/or Risk Appetite, Tolerance, and Thresholds were not properly set/addressed in the charter then this is the outcome. If I was to make an educated guess, I would say that his “risk aversion” is based on his belief that management has given NO room for failure. I have a couple of quotes for you: 1) “Promoting tolerance of failure increases the opportunities for success” and 2) “The fear of failure introduces an unbalanced inclination to avoid risk”. As you can see, these are basically saying the same thing, so it may be advisable to address the question of Risk with your technical expert and give him and his teams “the room for failure”. Believe me, they will still see that failure is NOT an option, but their mindsets, responses and collaboration levels will all change for positive. Obviously, there is a lot more to be considered, but some aspect of this might be in-play in your situation.