The Risk Report
Volume 2 Number 4 (July-August 1996)
Israel makes plutonium for atomic bombs at Dimona, a secret nuclear complex in the Negev Desert. The French-supplied reactor there has produced plutonium free from international controls since 1963. The quality of the plutonium created by the Dimona reactor is ideal for making atomic bombs.
The size of the reactor at Dimona is listed by the International Atomic Energy Agency [IAEA] as 26 megawatts (thermal). However, experts believe it is much more powerful than that. Mordechai Vanunu, an Israeli technician who worked at Dimona for eight years, reported that the reactor had been scaled up twice before he arrived at the site in 1977. The first scale-up was from 26MWt to 70MWt; the second was to some higher level.
The first scale-up was planned when Dimona was built. Israel convinced France to make the reactor's critical components--including its cooling circuit--three times larger than needed for a facility of its nominal size, and three times larger than originally agreed upon. This modification permitted a scale-up to 70MWt without the addition of extra cooling circuits, which would have attracted outside attention. Further evidence of a scale-up came in late 1968, when Israel diverted 200 metric tons of Belgian uranium on the high seas--a quantity considerably greater than a 26-megawatt reactor would have required. Israel probably needed the additional uranium for the first scale-up, which appears to have occurred in 1970.
Vanunu also said that Dimona had been producing 40 kilograms of plutonium per year for some time before he arrived in 1977. If the reactor at Dimona was unusually efficient (i.e., producing more than 1 gram of plutonium per megawatt day) and ran for as many as 300 days per year, the 40 kilograms could have been produced with a peak power of sightly more than 100MWt. If the reactor were less efficient, and operated for fewer days per year, the peak power would have to approach 150MWt.
To be used in weapons, plutonium must be extracted chemically from irradiated nuclear reactor fuel. A French firm, St. Gobain Techniques, supplied Israel with a chemical extraction plant at Dimona. The plant's first trial runs were in late 1965. By 1968, Israel had extracted enough plutonium for an atomic bomb.
The Dimona reactor, if operated continuously, could have created as much as 870 kilograms of plutonium through 1994. This figure assumes that the reactor started operating at 26MWt in 1963, was scaled up to 70MWt in 1970, and was scaled up again in 1977 to a level at which it could produce about 40kg of plutonium per year. Vanunu reported that the extraction plant where he worked produced 1.17 kilograms of plutonium per week for 34 weeks per year, a total of 40 kilograms annually. At this rate, 320 kilograms of plutonium would have been produced during the eight years Vanunu worked at Dimona. If the reactor experienced shutdowns, or was operated at a lower power, this figure could be significantly smaller.
Future plutonium production at Dimona is uncertain, primarily because of the reactor's age. The United States has urged Israel to cap its nuclear program and cease plutonium production at Dimona, but Israel has not agreed to do so.
Size of Israel's arsenal
The above figures for plutonium production indicate that Israel could have up to 175 bombs' worth of plutonium in its nuclear arsenal today. This figure assumes roughly 5 kilograms of plutonium are needed per bomb, including processing losses. (Vanunu reported in 1986 that Israel was using about 4.4kg of plutonium per bomb, an amount slightly greater than the reflected fast critical mass of plutonium-239.)
It is impossible to estimate the exact size of Israel's arsenal without knowing Dimona's true operating history and the characteristics of Israeli nuclear weapon designs. For example, Israel has produced enriched uranium, which could be used to make additional weapons. Israel has also made a number of "boosted" weapons using tritium, also produced at Dimona. Tritium can be produced by irradiating lithium-6 targets in the Dimona reactor.
Type: Heavy water
Power: 26-megawatt (thermal) scaled up to 70MWt or more
Plutonium created through 1994: Up to 870 kilograms