#FridayFlash: Burn the salted metals

She stubbed out her third cigarette of the evening and flicked the butt into the campfire. Four days of hiking, swimming, even a little drop-line fishing, and she still couldn't get the problem out of her mind. Between the haze of the summer evening and the light from the fire, she could see only the brightest stars overhead. Maybe later, when the deep purple of twilight gave way to full night, would there be more than a sprinkling of diamonds overhead.

Thorium, thorium, thorium! It was the solution to everything, but how to handle the initiation reaction? Without that, you might as well not go down that road at all.

There were only eight beers left in the cooler, and she didn't want to have to drive into town to get more before the end of the week. She cracked open the fifth of scotch instead. It was middling stuff; she never brought the good scotch on camping trips. The single malts were for conversation with friends, but for solitary concentration, she drank blends.

Since she was alone and didn't need to impress anyone, she drank right from the bottle. It didn't help her concentration, but it helped her mood. The answer was close, she could feel it. How much fresh air and exercise would it take to coax it out of hiding? She had things to do back in the lab and could ill afford so much time in isolation. This was the key to everything, though, and it was worth going off the grid for a while.

She jabbed at the fire with a stick. Where did ideas come from, anyway? They were nothing but random connections of preexisting facts and concepts, arranged into new insights and perspectives. A jar of varied pebbles, shaken for long enough, would randomly produce some pretty image. Was the shape inherent within the stones? Did the shaking create something new or merely draw out what was always there, the latent information content of the system?

Her head was filling with mystic nonsense. The scotch was having the intended effect, so she did what she always did when a thorny problem needed an oblique solution: she went back to the basics.

How many fissile isotopes were there? Thousands.

Of those thousands, how many were useful? Three: uranium 235, plutonium 239, and uranium 233.

Of those three, how many were clean burning and easy to handle, with no ugly and dangerous chemical reprocessing? One: uranium 233.

How do you get uranium 233? Hit thorium 232 with a neutron.

Where do you get the first neutron in the cycle? From uranium 233.

So which came first, the chicken or the egg? Well...

She threw the stick into the fire and took another pull on the bottle. The stars might come out later, but so might some clouds. It was hard to tell.

Natural thorium didn't need purification: it was all the same isotope, 232. Add a neutron to cheap, abundant thorium 232 and it turned into uranium 233. When the uranium 233 decays twenty-one minutes later, it gives off heat and another couple of neutrons. Just a bit of the uranium 233 mixed in with thorium fuel would initiate the reaction. After that, it was a simple matter to keep feeding in thorium for the next fifty years.

Cheap, easy, abundant power in a self-limiting reaction. The physics of thermal neutron capture in the thorium cycle made a runaway overload impossible. It didn't make any plutonium or other bomb-grade materials, nor did it make any long-lived radioactive waste. In fact, the molten-salt thorium reactor could burn up the waste from the old uranium 235 and plutonium 239 reactors.

But how to get the reaction started?

If you always needed an old solid-rod breeder reactor to make the uranium 233 initiators, then you couldn't wean society off the old style reactors 100%. That made the business model for switching to the thorium reactors untenable. Other fast neutron sources would poison the initial reaction and the thorium wouldn't convert properly. What she needed was a way to accelerate neutrons into the thorium capture zone. What she needed was a magic, non-nuclear way to make uranium 233.

What she needed was another drink.

She took it.

The fire was bright and hot. The night was cool and dark. Heat and light, cold and darkness, brought together. Sparks flew up, carrying with them the life of the fire until they disappeared, swallowed by the night and converted into darkness.

Converted into darkness? Or did the bits of light knock pieces of the darkness out of the way, taking their places as they were absorbed by the night?

And just like that, she had the answer.

Neutrons couldn't be accelerated, but electrons could. A sufficiently powerful electron gun, aimed at a neutron-rich target, would induce a temporary neutron scattering effect.

She stared at the open bottle in her hand. How powerful did it have to be? Ten million electron volts? Thirty? A hundred? And did that matter?

What kind of target? Something like tungsten, or spent uranium? How wide would the scatter cone be? What thermal spectrum would the induced neutrons have?

The cap went back on the bottle and she stepped uneasily to the picnic table where her notebook and pen were waiting. She began to scribble equations, notes, diagrams, facts to be looked up and unanswered questions.

Much work was ahead once she got back to the institute, but the hard part of changing the world was done.

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