Shika NPP « nuclear-news

Rainwater flood in Shika nuclear plant raises concerns at NRA

Shika NPP Ishikawa Prefecture.jpg

The Shika nuclear plant in Ishikawa Prefecture operated by Hokuriku Electric Power Co.

The Nuclear Regulation Authority has instructed Hokuriku Electric Power Co. to further investigate and prevent a recurrence of flooding that short-circuited the emergency lighting system at its Shika nuclear plant in Ishikawa Prefecture.

The 6.6 tons of rainwater that entered the No. 2 reactor building at the Shika plant in late September also came close to drenching power batteries prepared for emergency use.

“It was never imagined that such a volume of rain would flood the building,” NRA Chairman Shunichi Tanaka said Oct. 19. “There was the possibility of losing an important safety function.”

The Shika plant is currently offline, but the flooding incident could prompt the NRA to review the screening process required before the nuclear reactor is cleared to resume operations.

Hokuriku Electric President Yutaka Kanai apologized for the incident at a special meeting with the NRA on Oct. 19 and acknowledged that the downpour caught the company off-guard.

“Measures to stop flooding were an afterthought because the altitude of the plant site is comparatively high,” Kanai said. “There was a delay in dealing with the warning signals because of a weak sense of crisis among those on duty at the time.”

According to the utility’s report submitted to the NRA, a drainage ditch next to the reactor building was partially covered for road construction work. The rainfall on Sept. 28 flooded the road, and some of the water entered cable piping leading to the reactor building because a lid had been partially moved to allow for passage of a temporary cable.

The rainwater eventually reached the first floor of the reactor building, and power sources for emergency lighting short-circuited. Some of the rainwater leaked through cracks in the floor and fell as far as the second floor basement, according to the report.

The water reached the floor just above the room on the first floor basement where power batteries are kept. Those batteries are a crucial power source for the plant’s operations in the event electricity is cut off in an earthquake.

According to the Japan Meteorological Agency, as much as 26 millimeters of rain fell per hour on that day.

The 2011 disaster at the Fukushima No. 1 nuclear power plant was caused in part by the loss of emergency power sources in the tsunami that swamped the plant.

That accident led to the creation of stricter safety standards on measures to prevent flooding of reactor buildings, including erecting levees against tsunami and installing watertight doors.

However, not much attention was focused on the possibility of flooding through piping.

Anti-flooding measures were not high on the priority list at the Shika plant because there are no nearby rivers. Piping into the reactor building was also not required to be sealed off.

The NRA will ask Hokuriku Electric for new safety measures when it screens the No. 2 reactor at the Shika plant under the utility’s application to resume operations.

The NRA is also expected to wait until Hokuriku Electric presents a more detailed report before looking into whether the incident was unique to the Shika plant or whether there is a need to expand the safety measures to other nuclear plants when conducting screenings before operations can resume.

http://www.asahi.com/ajw/articles/AJ201610200027.html