The Radiochemistry Laboratory used the "chop-leach" PUREX process used in many commercial and military reprocessing facilities in other countries. The facility was estimated to be capable of reprocessing 200-250 tons of Magnox spent fuel and extracting 100 kilograms of plutonium annually. One end of the building had provisions for receiving spent fuel.
Construction of a reprocessing facility at Yongbyon began in 1988-1989. Some sources stated that construction began in 1987, while other sources identify 1985 as the starting date. By late 1988, US satellite imagery detected what was suspected to be a nuclear reprocessing facility under construction near the 5MW reactor at Yongbyon. The reprocessing facility separated weapons-grade plutonium-239 from the reactor's spent fuel. This large facility was key because it would have enabled Pyongyang to extract weapons-grade plutonium from irradiated fuel from both the 5- and 50-megawatt (electric) reactors.
A probable nuclear waste storage facility (nicknamed 'Building-500') was built in 1976 in close proximity to the radiochemistry lab as a waste liquid storage tank, connected to the test lab with steel pipes on the ground. With the IAEA inspection just around the corner, North Korea covered the connecting steel pipes with dirt in October 1991, encased the waste liquid storage building with a concrete wall, transplanted trees in the areas to camouflage it, and then built a storage building above the storage tank. However, the whole process was photographed by US imagery intelligence satellites. Two underground pipe lines connected the Radiochemistry Laboratory to Building 500.
The main source of concern for the IAEA was the reprocessing plant's ability to reprocess and store plutonium. The reprocessing plant was where they extracted the plutonium and this was the stuff of nuclear weapons. Without IAEA measures in place the Agency was not in a position to monitor that facility and therefore could not know whether this material was used for peaceful purposes or for weapons. The IAEA said North Korea could start removing about 8,000 spent fuel rods stored in a special pond at the Yongbyon plant. North Korea's purpose might be to move the spent fuel rods to sites around the country where they could be weaponized, in order to convince the US that there could be no pre-emptive strike. The plutonium reprocessing plant at Yongbyon could be ready to begin producing fissile material for bombs within a few months, according to the director general of the IAEA. By taking possession of the 8,000 spent fuel rods in late December 2002, the North could conceivably begin producing plutonium-based bombs in as little as 6 months, that is to say by late June 2003.
On 10 January 2003, Son Mun San, in charge of Pyongyang's relations with the International Atomic Energy Agency, said that the reprocessing plant stood in a state of "readiness." He said the reactor at the site would be up and running in a matter of weeks, roughly in line with earlier forecasts by the IAEA.
During talks in Beijing in April 2003, US officials said North Korea claimed it had reprocessed 8,000 spent nuclear fuel rods. However, US and South Korean officials said they could not verify the claim. Signs had been detected in late April 2003, but no additional activities or unusual movement had been confirmed as of early May 2003. Satellite imagery showed smoke coming from the Radiation and Chemical Laboratory reprocessing facility. Other signs of nuclear activity, such as traces of chemicals used in reprocessing or heat signatures, had not been detected. National security adviser Condoleezza Rice ordered an intelligence review, which was delivered to the White House in mid-April 2003.
On 8 January 2004, an unofficial American delegation visited North Korea and the Yongbyon complex. The North Koreans allowed the delegation to tour the corridor next to the hot cells in which the reprocessing occured. The campaign was said to have been complete and the facility was not operating at that time. Everything had been cleaned up and there was no radiation hazard in the corridor. Based on the tour, the delegation was not able to confirm or deny that the facility operated during the first half of 2003.
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