Fire Risk At Older Japan Reactors Shows Potential Worldwide Problem

The NRA announced recently that reactors built before 1975 likely have sub standard fire protection designs. This includes having important cables coated in fire resistant insulation, isolating and protecting cables and creating barriers to prevent fires from spreading to other areas of critical equipment.

NRA announced that about 10 reactors in Japan likely have these outdated unsafe systems. The 1975 changes in Japan were only mandatory on new reactors being built, any retrofit of old units was voluntary by the reactor owners. Mainichi found that 13 nuclear plants in Japan have these unsafe cables. Some operators coated these vinyl or polyethylene cables with a resin to give them some fire resistance. NRA claims the resin doesn’t prevent the coating underneath from melting and the resin will degrade with age. Mainichi also spoke to experts on the issue that said this:

“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.”

In Japan the older cable systems are run together and not separated. This is something specifically cited as a fire problem as one cable fire can introduce multiple cable fires. There were also situations in Japan where critical systems like cooling pumps were housed next to each other without any barrier leaving the potential for a fire to spread to the redundant systems taking them all out.

The 1975 change in Japan may have been initiated after a 1975 fire at the Browns Ferry nuclear plant in the US. Workers were testing for air leaks with a candle and started a fire that caused considerable damage to the control cable system. Control systems for units 1 and 2 were damaged. The control cable failures cascaded into a series of problems inside the control room and began to cause the reactor systems to malfunction. A meltdown was averted but just barely as workers scrambled to find a working system on the reactors to keep water over the fuel. Adding to the problem was the fire causing breathing issues and limited functional breathing equipment.

Cable tray fire via Union of Concerned Scientists

The US initiated new rules by 1981 mandating US reactor owners upgrade systems in their reactors to replace unsafe cables and make other fire safety changes. These included cable coatings and isolating important cables so fires could not spread to multiple control cable systems.

“Plant layout, egress routes, facility arrangements, and structural design features which control separation or isolation of redundant safety systems and selection of the methods for fire detection, control and extinguishing; control of fire hazards; fire barriers and walls; use of noncombustible materials; floor drains, ventilation, emergency lighting and communication systems.”

DOE also instituted upgrades and changes to their reactor facilities which included facility modifications as a result of Browns Ferry fire. Private sector nuclear power reactors in the US are not all fully up to the newer rules. The NRC has issued a number of exemptions that watchdog groups have criticized as being unsafe. Browns Ferry still does not meet the NRC fire rules for cables. 47 of 52 reactors in the US still do not comply with the 1980 fire regulations.

The US DOE initiated a program in the 1990’s to assist Russia with similar fire safety failures at their reactors. Flammable cables were found and a variety of fire safety failures like wood fire doors were found during a visit to Russia’s nuclear facilities in 1992. Part of these upgrades included using resin to coat flammable cables, the upgrade the NRA has cited as not being sufficient. Reactors at Smolensk, Chernobyl and Zaporizhzhya used the resin coating rather than replacing flammable cables.

The costs of these full retrofits being suggested in Japan could be quite expensive. US watchdog group CCNR cited a cost of $7,680,000,000 and $12,343,000,000 to upgrade US reactors that needed fire upgrades. This was the dollar amount cited in 1976, obviously today it would be considerably more.

The new NRA standards would require the replacement of the up to 2000 kilometers of cables in each reactor and installation of a number of new fire safety measures. Experts Mainichi spoke with  said it would take more than a year to make these changes and these unrecoverable costs may be enough to cause these older reactors to be shut down permanently.

Many reactors around the world are documented as having these sub-standard fire safety upgrades. Fukushima Daiichi is likely to be one of them due to the age of the units and voluntary compliance with the changes. This photo below was taken by a scope in June 2012 inside the torus room of unit 1. The right side of the cable in the photo shows the insulation melted off the cable, taken in an area of the torus room that was peppered with dark marks that appeared to be fire or heat related.

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