The Nuclear and Industrial Safety Agency will require electric power companies to undertake 30 measures at their nuclear plants, including extensive work on piping and ventilation systems, according to an interim report.
The requirements, described in NISA’s interim report completed on Feb. 1, will be overseen by a new nuclear regulatory body that will be set up in April. NISA will be merged into the new body.
Local governments that host nuclear plants have been calling for a new set of safety standards since the accident started last March at the Fukushima No. 1 nuclear power plant. The 30 requirements will be reflected in subsequent regulatory measures.
Some of the requirements for existing nuclear reactors are expected to involve large-scale work over prolonged periods of time.
During the most critical stage of the Fukushima No. 1 nuclear plant accident, gas was vented from the No. 1 and No. 3 nuclear reactor vessels to lower pressure levels. But that move may have led to the hydrogen explosions that rocked the No. 1, No. 3 and No. 4 reactor buildings.
Hydrogen may have flowed back into the reactor buildings via ducts shared by the venting system and other equipment, nuclear experts have said.
One of NISA’s requirements is to make the ventilation pipes independent of other equipment.
During the Fukushima crisis, increased pressure inside the reactors made it difficult to pump in water from the outside. The nuclear watchdog will require the utilities to ensure that powerful water injection pumps are present and that equipment allow "safety relief valves," which are designed to lower pressure, to operate even if the power supply is lost.
NISA’s interim report also said power receiving facilities at nuclear plants, including emergency power generators and switchboards, should be dispersed, in locations of high and low elevations inside the buildings, near the coast and further inland.
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