Will Fusion Plants Have Worse Reliability Problems Than The Disastrous "Renewable" Energy Scheme?
Let me preface my remarks here by saying I support fusion research, in particular for the personal benefit this research has provided me in the form of lectures I've attended at the Princeton Plasma Physics Lab. (This may be self-serving, but nonetheless it's incumbent on me to state this honestly.)
This said, in any form, fusion energy plants will not arrive in time to arrest the current global disaster in climate change which I personally regard as having arrived because of fear and ignorance. Anyone who is aware of my writings will know that I contend there is an exact equivalence between the malignity of anti-vaxxers and anti-nukes, although anti-nukes have certainly led to the death of more people, given the death toll associated with the continued use of dangerous fossil fuels, a situation so called "renewable energy" has experimentally been shown to be useless to address.
Unreliable energy cannot, under any circumstances, be clean or sustainable, nor can it function in the absence of dangerous fossil fuels.
The time to "shit or get off the pot" as the colorful metaphor states has come for fusion energy; the ITER in France will fire up soon and it will establish the operational parameters of fusion systems, but will not generate any electricity, as it's a research tool.
It is thus, with interest, I came across this news item in Science: Breakdowns could plague fusion power plants
I'm not sure if it's behind a fire wall or not, so here are some excerpts:
Some of fusion’s fitfulness is innate to the design of doughnut-shaped tokamak reactors. The magnetic field that confines the ultrahot, energy-producing plasma is generated in part by the charged particles themselves, as they flow around the vessel. That plasma current in turn is induced by pulses of electrical current in a coil of wire in the doughnut’s hole, each lasting a few minutes at most. In between pulses the magnetic field ebbs, interrupting tokamak operations—and power delivery. The repetitive starts and stops of the reactor’s powerful magnetic fields also generate mechanical stresses that could eventually tear the machine apart.
In theory, the beams of particles and microwaves used to heat the plasma can also drive the plasma current. So can a quirk of plasma physics called the bootstrap effect. Near the edge of the plasma, a sharp pressure gradient causes the particles to spiral in such a way that they interfere with each other and push themselves—by their own bootstraps—around the ring.
Using a combination of beams and bootstrap, researchers at ITER think they can get hourlong runs. But the bootstrap effect works best at high pressures and can push the plasma out of control, potentially damaging the reactor, says Alberto Loarte, head of ITER’s science division...
...The flood of high-energy neutrons produced by fusion reactions pose another threat. The neutrons are a “double-edged sword,” says materials scientist Andy London of the UK Atomic Energy Authority. On the one hand, they dump heat in the reactor wall that ultimately generates electricity, and they can bombard lithium to breed tritium fuel. But they can also penetrate the reactor walls and lodge in surrounding steel structures, knocking atoms out of position and weakening the material. Nuclei in the structures sometimes absorb the neutrons, creating radioactive isotopes that do further damage. For example, neutron bombardment can turn the nickel in many steel alloys into a form that gives off helium, causing the steel to swell perceptibly. “The metal turns into a sponge,” London says...
...Fixing damaged or weakened reactor components will be slow. Because of the hostile radioactive environment, repairs will rely on robots or remote handling arms that can navigate the narrow access ports of a tokamak. Mohamed Abdou, a nuclear engineer at the University of California, Los Angeles, believes future reactors may operate less than 5% of the time.
Compare this, he says, with today’s fission reactors. They can keep running even when individual fuel rods fail. Cranes can swap out fuel rods in just a couple of days. Availability can be as high as 90%. Achieving something similar for fusion will be “very challenging,” Abdou says.
My son mentioned this helium problem to me in the context of his readings as he prepares to join a nuclear materials lab.
I'm unaware of the way that nickel is involved, but I note that fusion neutrons are an order of magnitude higher energy than fission neutrons, and I did take a look at some of the cross sections of the Ni-x[n,α]Fe-y reactions in these energetic regions at the BNL Nuclear Data website. (Generally I am more familiar with the capture cross sections of lower energy fission neutrons, and seldom consider [n,α] reaction cross sections in my general reading.
Nevertheless these cross sections seem to be appreciable, not large exactly but appreciable. I have always understood the neutron fluxes of fusion reactors to be relatively low, but this said, over long periods of time, it may perhaps be an issue. I don't know.
Some sample cross sections for some nickel isotopes for the [n,α] reaction are shown below. Fusion neutrons have an energy of 14.1 MeV on the right side of the graphics, but as they travel through matter, particularly lithium blankets intended to breed tritium, they will be moderated to some extent, and thus the regions at the center matter, particularly in the case of Ni-59. Ni-59 is radioactive and decays to cobalt's only stable isotope, Co-59, but has a long half life. It will be formed by [n,γ] reactions in Ni-58, the most common isotope in natural nickel.
[n,α] cross sections:
= new reply since forum marked as read
