Raid on the Sun(7)

But it was fooled. Completely. Had the inspectors ventured to check the reactor core, they would have discovered huge stores of heavy water, a tip-off that the reactor was being used far above its stated capacity and generating great quantities of potential plutonium. To avoid that happenstance, Israel claimed that the reactor was in full operation—far too dangerous to allow inspectors into the core.

In truth, in view of Israel’s ultimate intentions, even the “real” reactor was something of a Trojan horse. Israel was not so much interested in the energy produced by the reactor, which was converted into heat and steam and, ultimately, electricity, but in the by-product of the energy’s production—the spent uranium fuel from which could be extracted plutonium, the essential ingredient of an atomic bomb.



The physics involved in a nuclear reactor is actually fairly basic. A reactor consists of a containment vessel, bundles of fuel rods filled with pellets of uranium 235, control rods (typically cadmium or boron, which absorb neutrons), heavy water (deuterium oxide produced from normal water by a process involving electrolysis), loops of pipe to carry superheated water, and a steam turbine outside the reactor vessel to produce electricity. The primary energy comes from the fissioning, or nuclear chain reaction, caused by the uranium 235 atoms, which, in concentrated and contained form, emit neutrons traveling at the speed of light. These neutrons collide with other highly charged U235 atoms, splitting the atoms’ centers, or nuclei, smashing them into fragments, and, at the same time, releasing heat and even more neutrons from the separated nuclei. The free neutrons collide with yet more atoms, creating a chain reaction that, if left unchecked, ultimately results in a nuclear explosion. But in a nuclear reactor, the fuel rods and pellets of uranium are immersed in heavy water, which absorbs neutrons and modulates the fissioning. In addition, control rods are inserted between the fuel rods to absorb even more neutrons, slowing down the rate of the splitting atoms or, when withdrawn, speeding the rate of fissioning. The heavy water and control rods allow nuclear techs to sustain what is essentially a controlled nuclear reaction. The immense heat produced by the continually fissioning uranium is transferred to the pipes of freshwater, which run through the reactor. Inside the pipes the water becomes steam, which is then used to drive the electric turbines outside the reactor.

What was important about a nuclear reactor in terms of building an atomic bomb was the by-product—the spent uranium fuel pellets inside the rods. While being bombarded with neutrons, the uranium becomes enriched with plutonium isotopes. This plutonium can be extracted from the spent uranium by a chemical process, then fabricated by a special machine into a metal form.

This was exactly what Israel was doing. Each weekly cycle in Dimona produced about nine “buttons” of pure plutonium, or 1.2 kilograms. It required roughly 11 kilograms of plutonium to produce one atomic bomb. Thus, approximately every ten weeks Israeli engineers had enough plutonium to create one more atomic bomb. For use in a bomb, the plutonium was shaped into a perfect sphere and surrounded by a high-explosive material. Triggered to explode inward in a precise sequence of nanoseconds, the blast would compress, or implode, the plutonium core into itself. The plutonium, like the U235 in the nuclear reactor, would begin discharging neutrons, but, unlike the controlled fissioning in the reactor, the neutrons in the bomb would discharge at an immensely faster rate—faster than they could escape from the core. Ultimately the pent-up energy would go “supercritical,” bursting outward and producing the immense explosion and familiar mushroom cloud of the classic atomic blast.

A process of “boosting,” that is, of inserting tritium extracted from heavy water into the warhead at the moment of fission, would flood the core with yet more neutrons and add an extra nuclear kick, dramatically increasing the bomb’s explosive “yield.” By the early fifties, physicists were already developing the so-called hydrogen bomb, a two-stage device that used the fission from an atomic bomb to compress and trigger the fusion of a second compartment of deuterium, a hydrogen isotope that burns as the primary fuel of the sun.

Israel’s atomic bomb–making facilities were far too expansive to hide on the ground at Dimona, even with the fake control rooms. So the Israelis went underground. Near the Dimona reactor was a nondescript, two-story, windowless administration building sheltering an employee canteen, a shower room, an air filtration system, and a storage area. On the second floor was a secret bank of elevators, bricked over and hidden from view of the inspectors. The elevator shaft sank eighty feet beneath the floor to a secret, six-story underground laboratory known to the Israeli workers as “the Tunnel.” A labyrinth of underground rooms and units, the Tunnel contained a chemical reprocessing plant and bomb factory where, beginning in 1965, the weapons-grade plutonium extracted from the Dimona reactor was fashioned into atomic warheads. Tritium extraction was done in Unit 92. Overlooking four floors where the plutonium was chemically extracted from the spent uranium rods, which cooled for weeks in water tanks, was a huge glass-enclosed control room, nicknamed Golda’s Balcony in honor of the famed Israeli prime minister who frequently visited Dimona after taking office in 1969.