Core Cooling System Working at Two Fukushima Reactors

Special Report: Fukushima and the Future of Nuclear Power

Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency.

Six months after the Fukushima Dai-1 nuclear incident began, Tokyo Electric Power Co. (TEPCO) is still struggling to gain control of the crippled reactors by cooling them to safe temperature.

Yoshinori Moriyama, deputy director-general of the Nuclear and Industrial Safety Agency (NISA) and in charge of nuclear accident measures, told the foreign press on 7 September TEPCO has begun using another cooling system the “core spray line” of the No. 3 reactor to help bring the temperature down in that unit. The core spray line is a part of the Emergency Core Cooling System (ECCS), a collection of sub-systems that can be called on in emergencies to cool a reactor when normal cooling operations are lost. It’s being used is in addition to the feed water line system currently cooling all three reactors.

Until the core spray line was put into operation on 1 September, the reactor’s core was cooled by rising steam from the bottom of the pressure vessel supplied by the feed water line. With the addition of the core spray line, water is now being pumped into the core spray ring header situated above the core causing water droplets to fall onto the core and cool it directly. As it has increased the amount of water pumped through the core spray line, TEPCO has been reducing the amount of water used in the feed water line. Right now, the latter is maintaining a flow of 4 cubic meters and hour, while the core spray line is maintaining a flow of 3 cubic meters/h.

The core spray line could not be used until recently because TEPCO first had to survey the pertinent piping and valves of this subsystem, both inside and outside the reactor building, to see if they were still operable. Given the high radiation in the area, this was difficult, but workers completed the job in July. After the system’s feasibility was confirmed in August, workers attached a temporary hose connection to the core spray line using a make-up water line and began pumping.

 “As a result, the temperature at the bottom of reactor number 3 is now below 100 degrees Centigrade,” said Moriyama. “And we can see it is being cooled quite steadily.” Given the success of the operation, TEPCO reported today that it has begun employing the core spray line of reactor No. 2. The bottom of reactor No. 1 has been registering below 100 degrees since July even without that reactor’s core spray line.

Moriyama went on to say that the greatest challenge they faced in stabilizing the reactors was the disposal of the contaminated water. This stagnant water—the result of continuous efforts to cool the reactors using several methods—has been accumulating for months in the basements and trenches of the reactor and turbine buildings and now totals over 100 000 metric tons. Moriyama added that a water decontamination system has been in operation since June, but he says that from the 10 June to the 30 August, the system had been disrupted more than 30 times.

 “The system was introduced in an emergency situation to treat the accumulating (contaminated) water, so the actual construction time for the system and installation was very short,” said Moriyama. “After analyzing the situation, we consider the quality control of the water treatment system was not necessarily adequate because of these circumstances. For example, human errors accounted for approximately 40 percent of the of the troubles that occurred, and because work on (the system) has to be done in an environment with high levels of radioactivity, there are cases where we are not sure yet of the cause of some troubles.” He added that after investigating the situation, NISA is now in a better situation to direct TEPCO to deal with the problems.

Political fallout fells prime minister
Though the safety agency can claim progress is being made, the government’s overall handling of the nuclear crisis and the speed of facilitating the recovery from the earthquake and tsunami have come under widespread criticism. Prime Minister Naoto Kan finally bowed to this pressure and resigned as president of the Democratic Party of Japan on 26 August, which ended his tenure as Japan’s prime minister.

In an interview with the Yomiuri Shimbun following his resignation, Kan said the two nuclear watchdogs NISA and the Nuclear Safety Commission, had been “unable to foresee the possibility that all the power sources could be lost,” at the plant. Consequently, both agencies were unable to respond effectively to the events that followed. To make matters worse, the off-site emergency response center located near the site had to be vacated soon after the accident, when radiation levels rose to dangerous levels. Consequently “arrangements that had been assumed in accident simulations hardly worked at all,” he said.

Kan has now been succeeded as prime minister by Yoshihiko Noda, who visited the Fukushima nuclear plant on 8 September, just one week after assuming office. After inspecting the damage to the plant, he told a gathering of some 200 workers there that, “Everyone in the country and the world is hoping for an end to the crisis. You are the key to whether we can overcome this (crisis). I will work hard with you.”

The good first impression he made on his visit was blighted, however, when Yoshio Hachiro, Noda’s new head of the Ministry of Economy, Trade and Industry (METI), the ministry in charge of NISA, quit his post just eight days after his appointment because of controversial remarks made following his visit to the plant. After explaining how he intended to help rebuild the towns in the evacuated areas, he later told reporters that the towns and villages near the troubled plant “were like towns of death.” He also joked with reporters that his protective clothing was contaminated, comments and actions not appreciated by the thousands of evacuees wishing to return to their homes. He has now been replaced by Yukio Edano, the former Chief Cabinet Secretary during the Kan premiership.

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