North Korea appeared to be speeding up its construction of a light-water reactor at its Yongbyon nuclear complex, raising eyebrows in Seoul as fears rise over radioactive materials from Japan’s tsunami-stricken nuclear power plant.

Satellite photos taken last month and broadcast by KBS-TV showed a new round structure being built in Yongbyon and foundation work underway next to it.

A high-ranking South Korean official said Friday the foundation work seems to be for subsidiary facilities such as a steam generator, adding that high-level waste from the North’s reactor could contaminate groundwater.

“We don’t know whether the North can properly handle nuclear waste, especially as it is not under international supervision,” he told reporters.

“High-level nuclear waste could be leaked and this could contaminate groundwater.”

Pyongyang last year vowed to complete an experimental light-water reactor by next year for development of nuclear energy for peaceful purposes. Some suspect that it may be using what it learned from an international consortium’s nuclear reactor construction in Sinpo which was stopped as the North broke an agreement with the U.S.

A 1994 deal between North Korea and the U.S. was intended to provide the destitute state with two 1,000-megawatt light-water reactors built by an international consortium, but the agreement fell apart in 2006 after the North was accused of pursuing a nuclear arms program.

Seoul officials say they are unable to tell from the photos whether the North is actually building a reactor, and that if it is building one, it is unlikely to meet international safety standards.

“North Korea claims it is building a light-water reactor, but the question is whether it is capable of building nuclear reactor, and not just a concrete dome,” a government official said.

“The North has built a five-megawatt experimental reactor in the past, so we should not underestimate their technology, but we don’t know if they can build one based on international safety standards. Clearly, there are safety concerns.”

Another official also said it was difficult to accurately make out what the round structure is from the satellite photo.

The South Korean government is closely monitoring the North’s moves as it has pledged to build a reactor, but it doesn’t know if the reclusive state has the necessary equipment and technology for it, another Seoul official said.

Former foreign minister Yu Myung-hwan in late February acknowledged the North’s reactor construction in Yongbyon.

“The ongoing reactor construction in Yongbyon is raising serious safety concerns in all neighboring countries,” he said during a seminar in Stanford University.

“Some say nuclear safety (regarding the Yongbyon reactor) is a more imminent problem than the North’s nuclear arms program.”

Siegfried Hecker, former chief of the Los Alomos National Laboratory, said he saw the beginning of the reactor construction during his visit to the North late last year.

Hecker had pointed out that the fact that North Korea was in fact an isolated country raises safety concerns as nuclear safety issues require cooperation with other nations with nuclear experience.

By Kim So-hyun (sophie@heraldcorp.com)