The Hanbit nuclear power station in South Korea. Photo courtesy Korea Yonggwang NPP / Wikipedia. 27 May (NucNet): South Korea’s nuclear regulator is expanding its special investigation into the manual shutdown of the Hanbit-1 power reactor earlier this month because of concerns it may have been the result of a violation of safety protocol.

The Nuclear Safety and Security Commission said in a statement that during an inspection into the manual shutdown of the 995-MW pressurised water rector unit on 10 May it had found “some proof” that Korea Hydro and Nuclear Power Company (KHNP) “did not apply an adequate level of safety measures and violated the Nuclear Safety Act”.

The commission said it had ordered the suspension of operations at the plant and sent a team of special judiciary police officers to carry out a special inspection.

On 10 May, KHNP carried out a diagnostic test on the effectiveness of control rods, during which the reactor's power output surged 18% exceeding the 5% upper limit range.

Instead of shutting down the reactor immediately, it was almost 12 hours before the unit was taken offline, the commission said. Initial investigations showed that a member of staff who was not licensed to handle the control rods had been directly involved in the process.

The commission said this is the first time that special judicial police officers have investigated nuclear reactors in Korea since commercial operation of nuclear power began in South Korea at the Kori-1 reactor in 1978.

Hanbit-1, one of three reactors at the site, is being kept safe and there was no leak of radioactivity either inside or outside the facility, the commission said. For two months, until 20 July, the commission plans to monitor the reactor’s equipment and the company’s safety culture.

“Since the thermal output rose so suddenly, we’ll also have to check the integrity of the nuclear fuel. After thoroughly ensuring that the nuclear rods and nuclear fuel are both safe, we’ll take action related to nuclear power legislation,” the commission’s statement said.

Hanbit-1, in the south of the country, had recently been approved to restart operations after undergoing maintenance checks that started last year.

According to the International Atomic Energy Agency, South Korea has 25 reactors in commercial operation, generating about 24% of its electricity but has adopted a phase-out plan that aims to replace nuclear power with renewable energy sources.