FACTBOX: North Korea's Yongbyon nuclear complex

(Reuters) - North Korea is expected to hand China a long-delayed account of its nuclear activities on Thursday in a key step to implementing an initial atomic disarmament pact.

Pyongyang is expected to follow up the declaration with the demolition of the cooling tower at its key Yongbyon nuclear complex, a symbolic event highlighting its commitment to disable the nuclear reactor that had been the source of its bomb-grade plutonium.

Following are some facts about the Yongbyon nuclear complex.

LOCATION

- Yongbyon is about 100 km (60 miles) north of Pyongyang built in a clearing in the rugged mountain ranges of the North Pyongan province.

THE FACILITIES

- The complex consists of a five-megawatt reactor, a fuel fabrication facility and a plutonium reprocessing plant, where weapons-grade material would be extracted from spent fuel rods.

- The site also contains a 50-megawatt reactor whose construction was suspended under a 1994 nuclear deal with the United States. The reactor is nowhere near completion.

THE COOLING TOWER

- The cooling tower slated for demolition is connected to the five-megawatt reactor and the steam coming off it seen in spy satellite images has been the most visible sign of the plant's operation.

THE TALLY

- U.S. officials said the North has produced about 50 kg (110 lb) of plutonium, which proliferation experts said conservatively would be enough for about eight nuclear weapons.

ESCALATION OF TENSION

- In February 2005, North Korea declared for the first time it had nuclear weapons. It conducted its first nuclear test with a plutonium-based device in October 2006.

Sources: Reuters, Center for Nonproliferation Studies, intelligence reports, Congressional Research Service, South Korean Foreign Ministry, Korea Institute of Defense Analyses

(Reporting by Jon Herskovitz and Jack Kim; Editing by Jerry Norton)