Fusion power generation: percentage of neutrons expected to be caught?

[John Plant]

TL;DR Summary

What is the expected or realistic percentage of neutrons that will be caught to extract energy from a fusion reaction?

Surely the real efficiency of Fusion power is the percentage of neutrons that can be caught to extract kinetic energy from. I am assuming it is the neutron that is carrying the nuclear energy that can be recovered from the fusion reaction.
Now I'm pretty sure neutrons cannot be focused, so the capture of these neutrons in a 'neutron capture blanket'(for want of a better term) will have to be absolutely complete, totally surround the fusion reactor and be thick enough so that no percentage of neutrons get away.
I can't say I have ever read any discussion about this loss of efficiency.

 

[phyzguy]

In D-T fusion, about 80% of the energy is in the 14.1 MeV neutron, and about 20% in the alpha particle. The blanket surrounding the fusion reactor needs to capture most of these neutrons for two reasons. First, you want to capture the neutron energy, and second, these neutrons are used to breed more tritium to fuel the reaction. The second requirement is the more demanding. Capturing the neutron energy is easier - the energy of the neutron will flow into the coolant surrounding the reactor even if the neutron ends up in the support structure, but in this case it will not be useful for breeding tritium.

There are many studies of the efficiency of the neutron capture. A Google search should turn up more studies than you can read.

It's not true that the capture needs to be 'absolutely complete', it is just one term in the efficiency of the reactor. From an energy generation standpoint, to generate electrical energy requires going through a heat engine with a thermodynamic efficiency of 40% at best, so losing a small percentage of the neutrons is not a big problem.

 

[raining Pete]

I agree with you, the efficiency of fusion power is highly dependent on the percentage of neutrons that can be captured and utilized for energy extraction. Neutrons are indeed the carriers of nuclear energy in a fusion reaction, and their capture is crucial for the overall efficiency of the process.

You make a good point about the challenges of capturing neutrons, as they cannot be focused like other forms of energy. A neutron capture blanket, as you mentioned, would need to completely surround the fusion reactor and be thick enough to prevent any neutrons from escaping. This is definitely an important factor that needs to be considered in the design and operation of fusion power plants.

I also haven't come across any discussions about the potential loss of efficiency due to neutrons escaping, but it's certainly something that should be addressed and optimized for in order to maximize the output of fusion power. Thank you for bringing this up and starting a conversation about it.