Proliferation concerns centered around the weapons-grade plutonium production capacity of the 5MW(e) reactor. Although North Korea has not been forthcoming about the details of the operating history of this reactor, several governmental and non-governmental analyses have estimated the amount of weapons-grade plutonium that North Korea may have separated from this reactor's spent fuel. In addition, further analysis has estimated the quantity of plutonium contained in the 8,000 spent fuel rods removed from the reactor in 1994, as discussed below.

Accurately assessing the amount of weapons-grade plutonium produced would require knowing the operating history of the reactors. Determining the amount of plutonium separated from the spent fuel requires knowing how many times the reactors were shut down to be refueled, and how many spent fuel rods were removed and reprocessed during each shutdown. These quantities are uncertain. Knowledge of the operating history is very uncertain, whereas the estimate of the number of shutdowns is on firmer ground. For the 5MW(e) reactor, there appears to have been at least three shutdowns prior to 1994 when North Korea removed all the fuel rods from the reactor. The three other shutdowns were in 1989 for about 70 days, in 1990 for one month, and in 1991 for about 50 days. The 70-day shutdown in 1989 would likely have been sufficient time to remove a significant fraction of the fuel rods or perhaps the entire reactor core, depending on whether the DPRK used one or two de-fueling machines and whether it de-fueled around the clock. According to the DPRK, its nuclear workers removed about 70 fuel rods in 1989 and extracted approximately 90g of plutonium.

Independent governmental and non-governmental assessments of the amount of plutonium that could have been extracted are considerably higher than the DPRK's stated amount. For the most plausible case, David Albright, has estimated 7 to 9.5kg of weapons-grade plutonium was separated from fuel rods as a result of the 1989 shutdown. If North Korea had removed all the fuel rods, he calculated that they could have extracted about 14kg of weapons-grade plutonium.[2] In late 1993, the CIA and the Defense Intelligence Agency reportedly estimated that North Korea may have extracted about 12kg of plutonium. Other governments such as Japan, South Korea, and Russia have estimated that the North Korea could have reprocessed even greater amounts of weapons-grade plutonium--up to 24kg.[3]

Based on the known number of shutdowns of the 5MW(e) reactor and the estimated operating history of this reactor, this evidence indicates that up to 10kg of weapons-grade plutonium was removed from the spent fuel prior to 1994.

The IRT-2000 reactor may have contributed to an additional 4kg of plutonium resident in spent fuel.[4] However, there is essentially no open source evidence that North Korea extracted this much plutonium from the IRT-2000 spent fuel. But North Korea did admit to having separated grams-worth of plutonium from the IRT-2000 spent fuel prior to the trilateral safeguards agreement signed in 1977. Presumably, this plutonium would be weapons-grade or close to weapons-grade quality. However, the exact composition of the plutonium depends on the operating history of the reactor, which is not known.

North Korea's future plutonium production capability could substantially expand its current stockpile. The stored spent fuel rods, the 5MW(e) reactor, and the unfinished 50MW(e) and 200MW(e) reactors could provide plutonium for nuclear weapons. Of immediate concern, additional weapons-grade plutonium resides in the 8,000 spent fuel rods that North Korea removed from the 5MW(e) reactor in 1994. These rods probably contain about 25 to 30kg of plutonium or roughly enough material for about 5 implosion-type nuclear bombs, as discussed below.[5]

The next greatest concern is that North Korea could restart the frozen 5MW(e) reactor within weeks to months. Once the 5MW(e) reactor is operational, it could produce about 5.5kg of plutonium per year, or enough for about one bomb annually. North Korea might complete construction of the 50MW(e) and the 200MW(e) reactors within two to five years. Assuming that these reactors are optimized for plutonium production and would operate at an 75% capacity factor, the 200MW(e) reactor could produce about 220kg of plutonium per year and the 50MW(e) reactor could produce about 55kg of plutonium annually. Assuming that about 5kg of plutonium would be required for a fission bomb, the 200MW(e) and 50MW(e) reactors could produce enough fissile material for roughly 40 and 10 bombs, respectively, per annum.