hankyoreh

By Noh Hyun-woong, staff reporter

The Nuclear Safety & Security Commission (NSSC) is drawing fire for an administrative notice that critics say is aimed at "saving" the troubled Kori No. 1 Nuclear Power Plant.


At an August 23 party lawmakers' general meeting, the Democratic United Party unanimously voted through a resolution to urge reexamination of the reactor's safety. The controversy over the extension of its lifespan is growing at a time when many other first-generation power plants are nearing the end of their own 30-year design lives.

The country's first nuclear power plant, Kori No. 1 was completed in 1977. The NSSC, headed by chairman Kang Chang-sun, announced that it would be adjusting its pressurized thermal shock (PTS) temperature standard from the current 149°C to 155.6°C. Critics in the DUP and elsewhere said this was all a ploy to extend Kori No. 1's lifespan.

The pressure vessel, an external wall of steel, is the primary line of defense against a shock from an explosion within the reactor. The reason is the ductility of steel, or its ability to deform under stress. 
Steel is both solid and flexible, but it becomes brittle like glass because of neutron activity inside the reactor. The ductile-brittle transition temperature (DBTT), as its name suggests, refers to the temperature at which steel goes from ductile to brittle.

This means that the steel pressure vessel can become as fragile as glass even under the temperature differential from cooling water that erupts in the event of an emergency. This is the PTS temperature. A 2005 test of the Kori No. 1 reactor measured its PTS standard at 152.1°C, a level beyond the current standard.

There are two types of waterways within a reactor. One, the primary system, absorbs heat from the reactor. The water flowing in it does not flow out of the reactor, but instead transmits heat to the secondary system through nuclear fission. The water in the secondary system turns to steam, which drives the turbine. After sufficiently cooling the first system, it is discharged into the ocean as condenser effluent. This requires a high level of thermal conductivity, so the reactor includes a huge number of waterways. A 1,000-megawatt pressurized water reactor is packed with around 16,000 thin pipes.

The problem comes when cooling water is applied under high temperature and pressure conditions. Having absorbed heat from the reactor, this water travels around within the plant at a pressure of 150 atm and a temperature of 320°C. The question surrounds whether the pipes, which measure just 2.5 cm across, are capable of withstanding these levels over long periods of time.

Kori No. 1 had its steam generator replaced in 1994, just 17 years after the reactor went on line, after hundreds of defects were discovered.

Another problem is that the pipes are out of date. Korean Federation For Environmental Movement post-nuclear energy bureau chief Yang-Lee Won-yeong explained, "If there is a rupture in the pipes the coolant travels through, huge amounts of coolant could escape due to the high pressure."

"This kind of danger is higher for Kori No. 1 than for other reactors because it's such an old plant," Yang-Lee added.

The international environmental group Greenpeace has long expressed concerns about Kori's location. At present, around 3.41 million people live within a 30 km radius, the area that would be directly impacted by radiation in the event of an accident.

According to Greenpeace, only South Korea and Taiwan have nuclear power plants set up in such heavily populated areas. The group warned that an accident in either would be far more dangerous than the Fukushima Dai-ichi Nuclear Power Plant disaster in Japan last year. Its argument is that there is no reason to leave such a potential risk nearby a heavily populated city like Busan.

Democratic United Party lawmaker Park Hong-keun pointed to the discovery of fault zones in South Gyeongsang province as evidence that the area was not safe from earthquakes.

"A single nuclear power plant has 1,170 km of pipes and 1,700 km of electrical lines," he said. "The idea that such intricate devices can be safe from earthquakes and other external shocks is a myth."

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