Japan will attempt to staunch the massive amounts of contaminated groundwater flowing into the sea from the crippled Fukushima Daiichi nuclear complex with a giant wall of ice.

Japan’s Nuclear Regulatory Agency, the government oversight body created after the ongoing Fukushima crisis revealed previous official watchdogs to be ineffective, has signed off on construction of a network of pipes, pumps and compressors designed to freeze the ground and create a mile-long “ice wall” to block the path of water flowing between surrounding mountains and the Pacific Ocean.

The plan, adapted from procedures used to dig tunnels near waterways, has been discussed for over a year. No ground-freezing project of this size has ever been attempted, and there is no real sense of how well it would work.

The plan also comes with concerns: What if freezing causes the ground to sink? What if the ice and the ensuing expansion and contraction interrupts or further damages drainage in the reactor buildings? What if a heat wave or heat from the plant causes parts of the wall to melt? And, what if there is a prolonged loss of power to this cooling system?

And what happens if (or more like “when”) the water goes around the ice wall (because, as they say, water seeks its own level)?

The OK on the ice plan comes days after TEPCO, the nominal owners of Fukushima, started dumping water directly into the Pacific that they said had been diverted around the highly radioactive nuclear plant structures. That water is not completely free of radioactive contamination, but TEPCO has assured area fisherman, who had long opposed the dumping, that the amount of radioactivity in this water is low.

What constitutes “low,” both in terms of the amounts in each ton of water and what will accumulate and bio-concentrate in sea life, is a matter of much debate.

The latest plan also comes less than a week after another failure of the system designed to decontaminate radioactive water. The system, built over a year ago to deal with the tens of thousands of tons of water accumulating in aboveground tanks at the site, cannot remove all radioactivity and has never been fully functional.

All of these plans and mitigation scenarios easily go with descriptors like “stopgap” and “too little too late” — and that speaks to a broader point about nuclear power.

Fukushima supposedly had backup systems and was said to have protocols to handle all emergencies. Clearly, it did not even have the less-than-adequate fail-safes TEPCO claimed were there, but even if it did, what if that still didn’t prevent disaster? (And, indeed, in the case of at least two of the damaged reactors, it probably would not have.)

“Defense in depth” is catchphrase across the nuclear power industry, and it is meant to imply that backups on top of backups will head off the biggest kinds of disasters (station blackout, loss of coolant accidents, loss of containment, core melt-downs and melt-throughs). There is evidence on the grounds of a number of nuclear plants to contradict these confident predictions, but even beyond the evidence, the question that is not posed, the question that Fukushima indicates can still not be answered, is “OK, nothing can go wrong — but what if something does?”