Tokyo (CNN) -- About 11,500 tons of radioactive water that's collected at crippled Japan's Fukishima Daiichi nuclear facility will be dumped into the Pacific Ocean, a cabinet minister said Monday, as workers prioritize dealing with a crack that has been a conduit for contamination.
These are the latest, but hardly the only challenges facing workers at the embattled power plant and its six reactors, which have been in constant crisis since last month's ruinous earthquake and tsunami.
Authorities have decided to release excess water that has pooled up in and around the Nos. 3 and 4 reactors directly into the sea -- a step that Chief Cabinet Secretary Yukio Edano called "unavoidable," even though this liquid was contaminated in the process of trying to cool nuclear fuel rods.
The build-up of water could cause problems around the nuclear facility, which is 240 kilometers (150 miles) north of Tokyo, Edano said Monday.
More than that, the decision was made because authorities have made a priority of dealing with water coming out of the No. 2 unit, including some that has been gushing directly into the sea through a crack in a concrete shaft. By getting rid of water from the Nos. 3 and 4 units, authorities hope to get more room in limited storage space to keep seemingly more dangerous fluid that is collecting around the No. 2 reactor.
"The radioactivity level is very high near the No. 2 reactor, and we know this. We have to stop the leak as early as possible to prevent this from going into the sea," said Edano. "The radioactivity level is much less in the water from the Nos. 3 and 4 units (than it is in the No. 2 unit)."
"For the safety of the (No. 2) reactor, we have no choice," he added.
Neither of the first two attempts to fill up the 20-centimeter (8-inch) crack outside the No. 2 reactor's turbine building -- on Saturday by pouring in concrete, and then Sunday by using a chemical compound mixed with sawdust and newspaper -- was successful.
As they mull other ways to cut off the leak at its source, workers will install a silt fence along a damaged sea wall surrounding the plant, Hidehiko Nishiyama of Japan's nuclear and industrial safety agency said Monday. The aim of this screening, which is usually used to halt erosion at construction sites, is to prohibit the spread of radioactive particles into the sea.
Workers also have injected a dye tracer into the water to allow them to track the dispersal of such particles, the spokesman added.
Addressing the issue quickly is critical because officials believe it is one source of alarmingly high levels of radiation spotted in seawater near the plant, as well as in nearby groundwater.
"This situation has continued for a long time," Edano said Monday. "We need to stop the release into the seawater as soon as possible ... The soil contamination also needs to be stopped."
In some cases, authorities don't even know how much radiation is getting out.
After some high-profile errors while offering regular radiation measurements on seawater, groundwater and the air, little such new information has been released since Thursday. One reason is that the dosimeters being used don't go above 1,000 millisieverts per hour, Junichi Matsumoto, an executive with the plant's owner Tokyo Electric Power Company, told reporters Sunday.
Authorities know the water in the cracked concrete shaft, then, is emitting at least that much radiation -- which equates, at a minimum, to more than 330 times the dose an average resident of an industrialized country naturally receives in a year.
In the Pacific Ocean itself, the last reported measurement (from Thursday) of seawater taken 330 meters (361 yards) offshore were said to have levels of iodine-131 at 4,385 times above the standard and cesium-137 at 527 times beyond normal. Experts say the latter radioactive isotope may be a greater concern because it persists longer, taking 30 years to lose half its radiation -- compared to an eight-day half-life for the iodine-131 isotope.
Plugging the external leak is job one, in order to prevent the outflow of radiation into the Pacific. But it may not be the most difficult, or important, task ahead.
Authorities still have to figure out how the tainted water got into the concrete shaft in the first place. The water had to come from somewhere, potentially traveling across melted-down nuclear fuel in the reactor's core before somehow reaching the outside.
Nishiyama, the nuclear safety official, said Sunday that the working theory is that water injected in recent weeks into the No. 2 reactor to help cool its nuclear fuel rods somehow got out.
"We were assuming and hoping (that water) would stay in the containment vessel as vapor after being cooled," he said. "However, it may have flowed into the building, and then the trench."
Finding out why and how that happened -- and, more so, what to do about it -- promises to be "exceptionally challenging," said physicist James Acton, with the Washington-based Carnegie Endowment think tank.
To do so, officials must inspect a complicated array of pipes inside the dangerous radioactive environment inside the containment buildings, according to Acton. He is familiar with Japanese nuclear plants, having examined one rocked by a 6.8-magnitude earthquake in 2007.
The amount of emitted radiation, be it into the water or air, is also unknown. Authorities do believe there had been at least a partial meltdown of nuclear fuel -- thanks to intense heat, at one point, topping 2,700 Celsius (4,800 Fahrenheit) in the No. 1 reactor and 1,800 Celsius (3,200 Fahrenheit) in the Nos. 2 and 3 reactors, according to an analysis from Areva, one of the world's top nuclear energy companies based in France.
Temperatures in these reactor cores and spent nuclear fuel pool have largely stabilized of late, due to a steady influx of freshwater coolant. And this effort took a step forward Sunday, when the electricity source powering all three of those units' cooling systems was switched from a temporary diesel generator to a more permanent, external power supply, according to the International Atomic Energy Agency's website.
This complex process is just one of many going on at the plant, from pumping out standing water in various reactors' turbine buildings and exposed maintenance tunnels, to rooting out any more leaks, to preventing any new radiation from getting out.
On Monday, a Tokyo Electric spokesman said the idea of wrapping some or all of the plant's six reactors containment buildings in massive amounts of sheeting, in order to curb the release of radiation had been discussed in recent talks with government officials. The utility company is considering the concept, according to the spokesman.
Ultimately the goal is to make sure that the nuclear fuel, and the potentially cancerous materials it can release, never poses a threat again.
"Finally, we (need to) establish a long-term policy to cool the reactors," said Nishiyama, while acknowledging that much work needs to be done in the meantime.
