A factor that could vastly complicate the problem is the presence of tritium, or heavy water, which is produced during fission. Tritium cannot be filtered out of water, instead requiring an extremely expensive treatment process.
"If the contaminated water has relatively high tritium or tritiated water concentration, then treatment could be more complicated," said Joonhong Ahn, a nuclear waste expert at UC Berkeley.
Nuclear power plants normally have systems in place to treat tritium on site. But the condition and capacity of the Fukushima system is not known.
Enokida and Morse contend that if the water can be concentrated, it can then be put into dry form or even turned into glass, as is planned at Hanford and other contaminated sites around the world. But this process, called vitrification, is expensive and requires a small-scale industrial facility.
The alternative -- processing the waste elsewhere in Japan -- is likely to be controversial.
"The fishermen will protest; this is inevitable," Enokida said.
Morse said that the plant faces at least six months of emergency stabilization, about two years of temporary remediation and anywhere from two years to 30 years of full-scale cleanup. Furthermore, the high levels of ground contamination at the site are raising concerns about the viability of people working at the site in coming decades.
It will take hundreds or even thousands of workers years or decades to handle the cleanup, experts said.
U.S. officials have not yet discussed the water management problems with their Japanese counterparts. But Nuclear Regulatory Commission spokesman Scott Burnell said the nuclear industry has a long experience with filtering radioactive contamination out of water, though never at a plant that has suffered such damage. At Three Mile Island it was decided to allow the tritium-contaminated water to evaporate, though that meant the tritium escaped as well.
At some point, however, Japan will have to add facilities to existing treatment plants in order to vitrify the radioactive material into glass logs or other dry forms that could be stored in alloy canisters. Those logs or canisters would have to be buried somewhere.
Where that burial ground is built is a question that the Japanese are only beginning to consider.