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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Unsafe cables may be too expensive to replace

January 1, 2013


Over 10 nuclear plants in Japan have flawed fire-prevention equipment: sources



More than 10 nuclear power plants in Japan are plagued by flaws in their fire-prevention equipment, nuclear regulatory sources have revealed, raising the possibility some reactors may be shut down.

Sources close to the secretariat of the Nuclear Regulation Authority (NRA) and the Ministry of Economy, Trade and Industry (METI), respectively, say that deficient equipment includes flammable electric cables in wiring. They say apparatuses important to safety are also installed close to each other, increasing the risk that fire could spread from one apparatus to the other.

The Agency for Natural Resources and Energy has already launched an investigation into the matter, while the NRA is poised to interview electric company officials in the near future.

METI anticipates that some nuclear reactors may be decommissioned due to the high cost of exchanging cables and repairing equipment. It also expects that reactivation of other plants could be delayed by several years.

Since December 1975, utilities obtaining approval for reactor construction have been required to use flame-resistant cables in important safety equipment and to appropriately space apparatuses to prevent fires from spreading. However, due to the absence of regulations for reactors built before then, the decision on whether to improve such equipment has been left up to each plant operator.

The total number of plants using flawed equipment has not been determined, but the Mainichi Shimbun interviewed power companies across the country and found that cables made of such flammable materials including vinyl and polyethylene are used at 13 out of 50 nuclear reactors. Because the surfaces of those cables are coated with fire-resistant agents using special types of resin, utility officials say they are on par with flame-resistant cables. However, the NRA secretariat and METI officials dismissed the utilities' claims.

"Even if the fire-resistant agents do not burn, the flammable cables inside would burn," one source told the Mainichi. "Those cables may also be aging and deteriorating. We can't recognize them as being equivalent (to non-flammable cables). Most of the cables are fraught with problems in terms of fire prevention and need to be renewed."

At some plants, it has also emerged that equipment controlling the so-called reactor "safety system," which includes control rods, the core cooling system, and instrument surveillance at the time of a nuclear accident are flawed in terms of fire-prevention measures. Although the principle of "system separation" that allows one failed electric system to be complemented by another one is prioritized in safety systems, at some plants electric cables for two separate systems are installed in close proximity. Cooling water pumps are also set up next to each other, raising the risk of such critical apparatuses catching fire simultaneously. Both the NRA secretariat and METI officials are expecting that such flaws will be found at more than 10 reactors.

The NRA is planning to include both the "system separation" rule and stipulations on the use of flame-resistant cables in new safety standards to be drawn up by July. However, as each reactor has roughly 1,000 to 2,000 kilometers of cables, including several hundred kilometers which are important to safety, it will take more than one year and cost a huge amount to renew the cables. Due to the prospect of unrecoverable costs, some reactors may be forced to be decommissioned, the sources said.


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