Hose rip interrupts cooling of reactor 5

Seawater restored in 3 1/2 hours in latest mishap

Kyodo http://search.japantimes.co.jp/cgi-bin/nn20110704a1.html

The crisis-hit Fukushima No. 1 power plant briefly stopped cooling reactor 5 on Sunday to replace a damaged seawater hose, Tokyo Electric Power Co. said.

The cooling system was turned off at 10:15 a.m. after a worker on patrol found seawater leaking from the plastic hose in its Residual Heat Removal System earlier in the morning, Tepco said.

The makeshift hose, which has a diameter of about 20 cm, was found to have a tear about 30 cm long and 7 cm wide along a U-shaped section.

The reactor's temperature was 43.1 degrees as of 8 a.m. Sunday and rose another 5 degrees during the 3 1/2 hours it took to repair the hose, Tepco said.

If it hadn't been fixed, the reactor would have reached boiling point about 22 hours later, the utility said. That would cause all its water to evaporate, exposing the rods and causing another core meltdown.

After the March 11 megaquake and tsunami ravaged the six-reactor plant in Fukushima Prefecture, units 5 and 6, which are based on a safer design, were able to achieve cold shutdown because their Residual Heat Removal Systems survived the waves and were able to be restarted.

A reactor must stay below 100 degrees to be considered in cold shutdown.

On May 29, unit 5 nearly started boiling after a seawater pump broke overnight and its replacement was delayed until daylight.