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

[John Plant]

TL;DR

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.