Zero Day (John Puller, #1)(115)

“Even numbers.”

“Another perspective.”

“Give me some context.”

His brother sounded engaged now, instead of just curious.

“Pure science. Your area of expertise.”

Two ticks of the clock went by.

“Ninety-two is the atomic number for uranium. Ninety-four is the atomic number for plutonium.”

“That’s what I remembered too.”

“Why?”

“Hypothetical.”

“Okay.”

“What sort of uranium and plutonium would you need to build a nuke?”

“What?”

“Just answer the question.”

“What the hell are you involved in, John?”

His brother did not often call him John. To his older sibling Puller was either “bro” or sometimes “Junior”—although lately the latter term had not been used by him very much because it was a reminder of their father.

“Just give me your best answer.”

“You need lots of things. Most you can obtain. Others you can build. If you have time and some expertise it’s not that hard. What’s hard to get is the nuclear fuel for the process. There’re only two that exist.”

“Uranium and plutonium.”

“Right. And you need highly enriched uranium, U-235 or HEU, to make a nuclear bomb. To do that you need a manufacturing facility, big bucks, lots of scientists, and a number of years.”

“And plutonium?”

“Should we be talking about this? They’re monitoring the call.”

“Nobody’s listening, Bobby,” said Puller. “I made arrangements for this to be private.”

His brother didn’t say anything for a long moment.

“Then I’d say whatever you’re involved in is way beyond a hypothetical.”

“And plutonium?”

“You get plutonium-239 mostly from radiating uranium in a nuclear breeder reactor. What you’re really doing is scrubbing out plutonium-240, which is abundant in reactor-grade plutonium but which can cause a fizzle when using it as a nuclear weapon.”

“But again, tough to get.”

“Impossible to get for the man on the street. Who has a nuclear breeder reactor in their backyard?”

“But could you get it?”

“I suppose you could steal it or buy it on the black market.”

“How about in the U.S.? How do they make it?”

“The only U.S.-owned gaseous diffusion plant is in Paducah, Kentucky. But that’s used to enrich uranium for fuel in nuclear reactors, totally different process.”

“But could it be highly enriched by that process? To get it to be the fuel for a nuclear weapon?”

“Paducah is set up to enrich uranium for use in nuclear reactors, not build the fuel for bombs.”

“But could a plant like Paducah highly enrich uranium?” Puller persisted.

“Theoretically, yes.” He paused. “Where exactly is all this going?”

“How much U-235 would you need to build a bomb?”

“Depends on what type of bomb and what type of method you’re using.”

“Ballpark,” said Puller.

“With a simple bomb design and a Nagasaki yield you’d need anywhere from fifteen to fifty kilograms of HEU or six to nine kilograms of plutonium. If your weapons program is super-sophisticated and your bomb design is perfect you could get the same boom with roughly nine kilos of HEU or as little as two kilos of plutonium.”

“So Nagasaki?”

“Yield equivalent to over twenty-one thousand tons of dynamite plus the radiation fallout kicker. That’s forty-two million pounds of TNT. Mass destruction.”

“And a little more HEU or plutonium?”

“Your results go up exponentially. It’s all in your bomb design. You can use the gun method, which is not good at all, although the first A-bomb dropped on Japan used that design. That’s basically a long tube. Half your nuclear charge at one end backed by a conventional explosive and the other half of your nuke fuel at the other end. The conventional explosives are detonated, it pushes the fuel down the tube where it hits the other half of the fuel, and you have your chain reaction. It’s crude, highly inefficient, and your explosive yield is severely limited. You’d need a tube of infinite length to sustain the chain reaction. And you can only use uranium, not plutonium, because of impurity factors. That’s why the industry moved on to the implosion method.”

Puller said, “Give me the two-cent tour on the implosion method.”

“You can use either uranium or plutonium. You basically use conventional explosives, called explosive lenses, to squeeze the pit where your nuclear fuel is located into a supercritical mass. The shock wave compressing the uranium or plutonium must be perfectly spherical, or the pit material will escape through a hole and you’ll end up with what’s called a fizzle. You also need an initiator, tampers and pushers, and ideally a neutron reflector to push neutrons back in the pit. The trick is to keep the pit from blowing apart too quickly, before you reach optimal supercritical mass. The longer the fission material is allowed to react, the more atoms are split and the bigger the boom. You can triple your explosive yield without a gram more of nuclear fuel if your design is good.”