Pyongyang pledged to shut down the plant by the end of this week, as part of an agreement reached during talks in February.
Warming ties

"The North Koreans always consider protocol very important. They like to be considered a major power in the region"

Bill Richardson, US presidential candidate

Richardson's group is expected to oversee the transfer of remains from the North Korean army to UN personnel.
The visit is Richardson's sixth to North Korea.
"It could be the signal of an improved relationship," Richardson told The Associated Press on the journey to Pyongyang.
"The North Koreans always consider protocol very important. They like to be considered a major power in the region," he said.
Richardson also said he would stay clear of all matters related to the nuclear talks.
The delegation plans to drive from Pyongyang to South Korea bearing the US remains but Richardson said it was difficult to predict the North's actions.
In February a six-nation deal set April 14 as the deadline for the North to shut down its main nuclear facility and allow the return of UN nuclear inspectors in return for fuel aid.
But both China, North Korea's main ally, and Japan have expressed doubts over Pyongyang's ability to meet the deadline amid a row over $25m in North Korean funds frozen in a Macau bank account.
North Korea has refused to continue with negotiations until the money is released.
'Secret meeting'
In an effort to clear up the row over the North Korean funds, Christopher Hill, the US chief nuclear negotiator, is due to arrive in Tokyo on Monday for talks with his Japanese counterparts, officials said.
"It is important to resume the six-party talks as early as possible," said Yasuhisa Shiozaki, chief spokesman for the Japanese cabinet.
"We hope that substantive discussions will be carried out."
Last week the US State Department said officials from the US, China, the two Koreas and the Bank of China had agreed on a "pathway" for the money to be returned to Pyongyang.
On Saturday South Korea's Yonghap news agency reported that Hill had held a secret meeting with a North Korean diplomat in New York that produced a broad framework to speed up the release of the North Korean funds.