Prosecutors are poised to expand their probe of irregularities involving a parts supplier to nuclear plants to Korea Hydro and Nuclear Power Co., the state-run operator.

The scandal broke in May when it was revealed that Saehan TEP certified JS Cable’s products as being fit for use despite failing to meet quality standards. The revelation led to four nuclear reactors being shut down.

Investigators from Busan District Prosecutors’ Office on Wednesday raided KEPCO Engineering and Construction Co., which had given the final approval on the doctored quality reports on nuclear power station components compiled by Saehan TEP.

The subsidiary of Korea Electric Power Corp. became the first state-run firm to come under scrutiny in the unfolding scandal.

The Ministry of Trade, Industry and Energy announced Thursday that it would request President Park Geun-hye to remove Korea Hydro and Nuclear Power Co.’s CEO Kim Kyun-seop from office.

Kim, who told the National Assembly on Wednesday that he had submitted his resignation last week, will be replaced by the company’s vice president Chun Yong-gap until a new CEO is appointed.

Along with Kim, KEPCO Engineering and Construction CEO An Seung-kyoo will also be removed.

Saehan TEP’s chief executive and the head of the department responsible for testing products have since been arrested.

The Saehan TEP CEO, a 50-year old identified by the surname Oh, is suspected of ordering the forgery of the quality certificates. In addition to officials from the certification company, a former employer of JS Cable has also been taken into custody.

Also on Wednesday, the authorities arrested a company executive surnamed Lee, and raided the home of an executive of JS Cable. The latter is currently undergoing treatment at a hospital after he attempted to commit suicide during the raid.

Saehan TEP has been operating under a 300 million won ($269,000) contract with JS Cable for some years, and the former’s dependence on the cable maker is thought to have led to the forgeries.

In addition, the probe revealed that the company’s vice president is a former technology director of KEPCO Engineering & Construction, fueling suspicions that Saehan TEP may have lobbied the state-run company to turn a blind eye to the fake certificates.

The convoluted chain of corruption connecting parts suppliers, power companies and quality certifiers has incited public outrage and prompted a stern response from the highest level of government.

“Measures for improving the system must be drawn up so that the chain of corruption that has taken hold in the nuclear power sector can be severed under the new administration,” President Park Geun-hye said on Monday, saying that forging quality certificates for nuclear power components was “an unforgivable act.”

By Choi He-suk  (cheesuk@heraldcorp.com)