Monday, March 21, 2011

Japan Plant Had Troubled History

The Fukushima Daiichi power plant was already one of the most trouble-prone nuclear facilities in Japan, even before the devastating earthquake and tsunami that knocked out its cooling systems and precipitated the worst nuclear crisis in 25 years, a Wall Street Journal analysis of regulatory documents shows.

In addition, a standard practice at Japanese nuclear plants─to remove fresh fuel from a reactor and park it for weeks or months in a less-protected 'spent fuel' pool during maintenance─appears to have been a significant contributor to the crisis, engineers say.

On Sunday, disaster-response teams made progress toward taming the stricken nuclear reactor, restoring electrical power and preparing to restart crucial systems designed to cool the dangerously overheating nuclear material. But the latest analysis of safety and maintenance practices at the plant cast new light on how the situation threatened to spiral out of control.

When the 9.0 magnitude earthquake and tsunami struck little more than a week ago, all of the fresh fuel at the plant's Reactor No. 4 had been removed and stored in a pool that must remain filled with cooling water. That pool became one of the biggest problems for plant operator Tokyo Electric Power Co., or Tepco, after much of the protective water dissipated, threatening fire and widespread radiation release.

A Journal analysis of Japanese regulatory documents shows that the Daiichi plant was already one of Japan's most troubled nuclear facilities, even before it was severely damaged by this month's quake and tsunami. In the five-year period from 2005 to 2009, the latest data available, Daiichi had the highest accident rate of any big Japanese nuclear plant, according to data collected by the Japan Nuclear Energy Safety Organization, a mostly government-funded group that monitors safety and conducts inspections. Daiichi's workers were exposed to more radiation than their peers at most other plants, the data show.

Tepco says that overall it operated the Daiichi plants safely. It says the plant's age accounted for the higher rate of accidents, all of which were relatively minor until March 11.

On Sunday, Japan took major steps toward turning the tide in its battle to avoid large-scale nuclear disaster. Workers restored electrical power to parts of the plant and brought down radiation levels with a marathon water-spraying operation that, among other things, finally flooded Reactor 4's waste-fuel pool.

Key to that success: An elite disaster-response team from Tokyo, the Hyper Rescue Squad, and its massive water cannon known as the Super Pumper.

'No matter what protective gear you have on, if you touch or inhale radioactive material, that means death,' said Yukio Takayama, leader of a Hyper Rescue Squad unit, told The Wall Street Journal. 'That was on everybody's mind, and there was intense fear.'

Over the weekend, 'The most important thing we were able to do was to fill the spent-fuel pools at No. 3 and No. 4,' said Hidehiko Nishiyama, a top official at the Ministry of Economy Trade and Industry, which regulates Tepco.

At the time of the quake, Reactor 4 was offline and not generating power amid annual maintenance. As part of that, five months ago Tepco relocated all the fuel rods─the heavy tubes that contain radioactive fuel pellets─from inside the reactor to what's called a spent-fuel pool, a concrete holding tank that is less robustly protected than the reactor itself.

'We were carrying out checks on the inside of the reactor' and, thus, workers 'had to remove the nuclear fuel from the reactor,' said Takeshi Makigami, head of Tepco's nuclear-equipment-management section.

The active rods were in that pool when the March 11 quake struck. When the tsunami wiped out the plant's emergency generators, the water in the spent-fuel pool adjacent to the No. 4 reactor could no longer circulate, and fresh water could not be pumped in. Rods in the pools began to overheat, causing the water to evaporate as steam and exposing parts of the radioactive rods to the air─a critically dangerous situation. The heat spawned fires and the roof above the pool was partly destroyed, letting radiation out.

Over the weekend, emergency teams appear to have stabilized the situation. Still, officials cautioned they don't know if the pool has suffered cracks or other significant damage.

The events at Reactor 4 expose the risk of a commonplace practice in Japan, 'full core discharge,' in which all the fuel in a reactor is moved during maintenance shutdowns. 'The Japanese argue it's safer to move all the fuel to the pool, but the practice of full-core discharge caused a problem, in this case,' said Andy Kadak, a former professor of nuclear engineering at Massachusetts Institute of Technology, who has studied fuel handling for Tepco.

Tepco's Mr. Makigami defended the practice of removing still-usable fuel and stowing it in the spent-fuel pool, saying it can be done safely if ample water is available and sufficient space is maintained between the rods.

In the U.S., reactors shut down for refueling typically retain most of their fuel in the thick steel reactor pressure vessel that provides much more protection against a radioactive release. During refueling outages, when operators swap out depleted fuel for fresh fuel and do other maintenance, these rods are shuffled around in a process somewhat akin to rotating tires on a car to even out the wear.

In the U.S., only the most worn-out rods typically are removed and transferred to a spent-fuel pool for storage, where they can stay for decades. Thus, U.S., pools hold only the oldest spent fuel, which is also the coolest in terms of temperature and radiation.

By contrast, at Tepco and other utilities, it's common to temporarily remove all the fuel rods. The freshest are eventually moved back to the reactor pressure vessel and supplemented with new rods to replace the oldest ones, which are left in the storage pools.

Rods can be left in pools for many years for two reasons. First, they need to cool down. Second, no nation has yet solved the problem of what to do with large stockpiles of used nuclear fuel. As a result, much of it remains in utility holding pens.

In the first days after the quake, officials weren't focused on the situation at Reactor No. 4, since it was one of the three reactors at the plant, along with Nos. 5 and 6, that were offline for maintenance. The more critical situation appeared to be with Reactor Nos. 1, 2 and 3, which had been online at the time of the quake. When those reactors lost power, normal cooling systems for both the reactors and the storage pools were disabled.

But by March 15, four days after the quake, problems at Unit 4 became critical with the first outbreak of fire. Tepco officials said heat produced at the pool was much greater than heat produced in the spent-fuel pools at the three reactors that automatically shut down the day of the quake.

The Journal has reported that, in the early hours of the crisis, Tepco hesitated in its decision to use seawater to cool its reactors because it worried doing so could destroy a multi-billion-dollar plant at a time when it already was short of generating capacity. Eventually, officials were forced to resort to dumping seawater on the exposed rods using helicopters and fire trucks. Temperatures also rose in the pools at Nos. 5 and 6, though Tepco got those under control without explosions or fire.

Well before the one-two punch of this month's quake and tsunami, the Fukushima Daiichi ranked among Japan's most troubled nuclear plants, regulatory documents from the Japan Nuclear Energy Safety Organization indicate.

Tepco's Mr. Makigami said 'the main reason' some numbers for the Fukushima plant look poor in the report is that 'they're old reactors.' All of Daiichi's reactors first came online in the 1970s.

Mr. Makigami said Tepco does frequent repairs, and has 'replaced the various individual parts with the latest equipment, and in so doing we aimed to give old plants the same functionality as new plants. However, in reality it is quite difficult.'

The Daiichi plant has had 15 accidents since 2005, the most of any Japanese plant with more than three reactors, according to an analysis of the data by the Journal. Maintenance problems have been a leading cause of accidents at the plants, but it isn't clear whether age has been a major factor.

In February 2009, pressure levels spiked inside Reactor 1, forcing the release of steam through an emergency valve. Workers found a broken bolt and shut down the reactor. An investigation found that a nut hadn't been tightened properly and wasn't being inspected regularly.

Some accidents involved key safety equipment. In 2007 an emergency diesel generator began smoking during testing. An investigation found that part of the generator's circuit breaker had been put together backward.

The failure of diesel generators, which power water pumps that are critical to reactor cooling systems, was a leading cause of the current crisis. But there is no evidence they were malfunctioning before the tsunami struck.

In April 2009, a control rod─the shutdown device used to stop the nuclear reaction in a plant's core─malfunctioned in Reactor No. 3 due to a leaking valve. An investigation found that the device was assembled using two different kinds of bolts, leading to the leak.

None of the Daiichi accidents were considered major safety hazards, and none caused any injuries or led to the release of any radioactive material outside the plant, until this month's accident. As is true in most nations, nuclear operators are required to report more problems to authorities than operators of conventional, fossil-fuel plants, so there is more detail on even minor occurrences.

Mr. Nishiyama, whose Ministry of Economy, Trade and Industry regulates Tepco, pointed out that the company has had serious challenges, including major quakes spaced less than four years apart. He also said Tepco has 'made great progress in terms of disclosure' about their operations. He said the company is 'resilient,' but that 'once this emergency situation is over, we'll need to evaluate how Tepco is dealing with the situation.'

The Daiichi plant does expose its workers to more radiation than other plants, the regulatory documents show. Daiichi employees have received the highest average radiation doses of those at any Japanese plant every year over the past decade. Tepco's other plants also exposed their workers to higher doses of radiation than most other big Japanese operators.

Teruaki Kobayashi, head of Tepco's nuclear-plant-management section, said that since 'Fukushima Daiichi has older reactors, it requires more frequent repairs and checks than new nuclear plants.' Because the plant is of an old design, 'radiation tends to be higher.'

'When we carry out major improvements or checks, inevitably people are more likely to receive radiation,' Mr. Kobayashi said. 'That's because some tasks can only be done by human hands.'

For example, he said, when Tepco cleans the inside of the reactor, it uses specialized equipment and robots, but humans must manipulate them remotely and inevitably they get closer to radioactive material.