The pros and cons of neutrons in fusion technology

Massimo Zucchetti

Politecnico di Torino

Thursday, May 27, 2021

10:00am

PSFC Seminars

Abstract: Modeling neutron fluxes in fusion reactors is a quite different game than doing it for fission. One-group thermal neutron diffusion equations were enough to design fission experiments and reactors in the good old days: and they worked. In the early eighties, as a young undergraduate student, I proudly learned how to follow the footsteps of Fermi and Wigner to analytically solve the diffusion equation and design a thermal fission reactor. When I started my PhD research, months after the Chernobyl accident in 1986, I thought that studying neutronics for fusion reactors could be a natural step forward for my research. Well, it wasn’t. It was a giant leap for a young nuclear engineer.

Fusion reactors will be the most intense and powerful sources of fast neutrons ever thought to be applied to electrical energy production ever.

Hundreds of trillions of 14 MeV neutrons will escape from each square centimeter of the plasma chamber every second a tokamak fusion power reactor will be working. Neutrons are committed to do many good things: first of all, slow down and release thermal power that, via a two-loop cooling circuit will eventually produce a gigawatt or so of electrical power. Secondly, neutrons will breed tritium, the fusion reactor fuel that does not exist in nature.

There is good and bad in everyone, neutrons included: while doing those two essential jobs, they’re going to heavily damage the tokamak chamber and close-to-plasma structures, up to an unprecedented  level: each and every atom in those materials will be knocked off its natural position in the lattice tens of times. One could expect those materials could not resist for long in such an extreme environment. They don’t, actually, but we are working on it.

Neutrons turn all the structures to be radioactive, by the way, due also to threshold reactions we never had in fission. 

Tritium is a quite short lived nuclide, but before fading away it is a very social one: permeating everywhere through structures, and trying all its best to be released into the environment, as tritiated water. Humans are mostly water. However human life does not stand tritiated water much.

Neutrons are irritating and delightful for fusion technology: this short lecture will review some latest results and future perspectives of my thirty-five yearlong research activity, dealing with the worst and best objects in fusion: neutrons.

 

Bio: Massimo Zucchetti (B.S., 1986, PhD, 1990) is a full Professor since 2000 at Politecnico di Torino, Italy (www.polito.it, massimo.zucchetti@polito.it). He is currently teaching Radiation Protection and Nuclear Technology. He has been research affiliate and visiting scientist at MIT from 2005 until now, and visiting professor at UCLA in 2012. His research interests deal with ionizing and non-ionizing radiation protection, nuclear fusion technology, nuclear safety, radioactive waste management, advanced-fuel fusion reactors. He is coordinator of the IEA Co-operative Program on the Environmental, Safety and Economic Aspects of Fusion Power, Radioactive Waste Study, and he has been a candidate for the 2015 Nobel Prize in Physics for his research in the field of advanced-fuel fusion reactors. He is married, with two children, nevertheless he is a motorbike gentleman driver.