Workers have entered the buildings that house the damaged unit 1 reactor at Fukushima nuclear power plant. They probably haven’t stuck around for very long, robot scouts have shown dangerously high radiation levels inside the building.

Given the risk, it might seem more sensible to let the robots do the indoor work for now. But this incursion is an important first step in bringing the damaged reactors under control.

At the moment, the reactors are being cooled by water, which is injected directly into their cores. That water becomes contaminated and then leaks out into the surrounding environment, creating a big radioactive waste problem.

So far, the Tokyo Electric Power Company (TEPCO), which runs the plant, has had to either dump that water into the ocean or pump it into temporary storage tanks. But with around six months of constant of cooling to go, it’s going to be difficult to continue that strategy.

It would be better if they could recirculate the cooling water, as is done in normal nuclear reactors. The idea would be to pump the water into the core, then pump the hot steam to a heat exchanger that would allow it to be cooled and reinjected.

TEPCO has released some detailed plans of how they intend to do this for unit 1. It looks like it will involve using elements of the existing cooling system along with some improvised facilities.

But hooking up a cooling system is too complicated for robots alone. To get it all working, they’ve got to get people inside, and to do that they need to get radiation levels down. The workers will also be installing new instruments to monitor the reactor water level, and feed lines to inject nitrogen gas.

The workers who just entered the plant installed blowers that will filter out some of the radioactive isotopes from the air. That should, in theory at least, get radiation levels low enough for more prolonged trips inside the reactor building. The goal, according to TEPCO documents, is to reach dose rates below 1 millisievert per hour. That’s a pretty high dose rate, but workers are currently allowed to be exposed to 250 mSv, so it would be low enough to let them get in and do some work.

The blowers appear to be the first step in setting up an airlock between the unit 1 reactor building and its turbine hall. If it works, the system will ultimately allow brief forays into the reactor to set up a cooling system. The preliminary schedule suggests that they could enter the building as soon as this weekend, assuming things go according to plan.

For an overview of what lies ahead for the facility, check out our brief video:

For full coverage of the Fukushima disaster, go to Nature’s news special.

For a selection of our coverage in Japanese, see Nature Asia Pacific.

Image: TEPCO