Fukushima repair robots question

So apparently the Robots trying to clean up Fukshima are getting their IC’s fried by radiation.

One of the problems is that they are using tethered robots trailing power / control cables behind them that keep getting snagged in debris so it takes a long time to navigate to get to where the fuel rods are located. Another article I read mentions the robots had to be able to open doors to navigate through the building.

Question, why wouldn’t you just first use robots with water cutters or thermal lances to cut right through walls to make a straight line path to areas of interest? Then use debris clearing robots to pick up fragments and make a clean clear path? If they’re worried about releasing radioactive debris from cutting through walls they could erect an outer containment shell first. And surely they know which parts are load bearing and which aren’t and could pick a safe straight path through the building.

Side question, they mention millions of gallons of radioactive water being stored on site. This is generated from pumping the water through the melted down reactor to cool it. What sort of half life would the radioactive water have after that? How long until its safe to release back into the sea?

EDIT: yes yes, user name, post combo :wink:

Why are the robots being fried by radiation? Do they mean the heat generated by the active fuel rods?

All you wanted to know - and more.

Fantastic! Thanks!

Ionizing radiation can cause spurious signals in digital circuits. It can also create defects in the crystalline structure of semiconductors, degrading or disabling their function. These are the most common ways by which radiation affects electronics.

For these reasons, electronics used in spacecraft, nuclear reactors, etc are radiation-hardened. But even rad-hard electronics (which I’m sure these robots have) are not completely immune to radiation.

Cutting tools require a LOT of power. Also, cutting through a building (especially one that’s already damaged or collapsed) is a good way to get yourself trapped, or causing further damage, making it even harder to extract the core. In addition, cutting radioactive material will create radioactive vapor and/or dust.

“We thought it would be easier to cut thru to the center.”

I addressed these points in my OP. The robots are tethered, they can run 3 phase power behind them, and they can build a containment shell to contain any radioactive dust. AFAIK the damage to the building was a hydrogen explosion which only did superficial damage. Nuclear plants are built solidly, there should be ways to cut / clear safe paths without compromising the integrity of the building and they have all the architecural design plans to work off.

Have you ever seen an industrial water jet cutter or used a thermal lance? Water jet cutters require pumps that can generate tens of thousands of psi of pressure with high flow rates and the associated power requirements; they are not portable. Thermal lances are compact but difficult and dangerous to handle, especially if there are combustable items or gases around, and they generate so much heat and smoke that they’re very challenging to use even by hand much less remotely.

While the ionizing radiation is a problem for electronics, much of the problem in getting to and retrieving fuel elements is the thermal radiation, e.g. the molten fuel elements are very hot. This causes things like sensors, actuators, and control cables to degrade and stop working quickly. The robots are protected against thermal and radiation conditions as best possible, but again, insulation and shielding requires more mass and bulk that impedes the robots from performing useful tasks.

Estimates I’ve seen of the tritium concentrations are that it would be on the order of sixty years before activated water would be back to acceptable levels. Given how dependent Japan is on the marine aquaculture and fishing industries, it is understandable that there is considerable opposition to allowing radioactive escape. There are also other isotopes that may be longer lived such as [SUP]137[/SUP]Ce and
[SUP]90[/SUP]Sr which form bioavailable salts that can be harmful if ingested in even tiny quantities and for which half-lives are measured in decades.

Fukushima should serve as a caution to those who are cavalier about how “easy” and “safe” nuclear fission for power production is. Yes, it was caused by an unforeseen natural disaster that was beyond the design basis accident criteria, and no, no deaths have been attributed to the meltdown to date, but the economic and social costs of the Fukushima disaster will likely exceed the fiscal value of the reactor over its operating lifetime, and the ultimate cleanup and retirement is projected to go on for three or more decades. The need for nuclear fission power as a low carbon footprint method of transitioning from coal and natural gas is inevitable, but it is neither trivial in effort to do it correctly nor without risk regardless of any reasonable safety precautions. And the issue of what to do with waste, either from normal operation or contaminated residue from retirement or accident has not been effectively addressed beyond the facile “put it in a hole in the ground in a region with little political influence” plan, despite numerous technical proposals on effectively segregating or burning up (neutron bombardment) hazardous radioactive material.


Ok fair enough, but is there really no safe way you can cut through the (presumably) concrete walls to make a clear path? Their budget for cleanup seems to be almost unlimited so I imagine they could also isolate areas then flood them with inert gas before cutting.

Good question. I remember watching this documentary about and wondering the same thing. https://youtu.be/ezohqY-vg4s. (Right around the 57 min mark)

Here’s the full Reuters article. From it:

If these are underwater robots, I don’t see how a water jet or thermal lance would be of any use.

The same thing happened in Chernobyl 30 years ago. The Russians tried using remote controlled vehicles but the radiation fried their electronics too. So in good Soviet fashion they instead just ‘asked’ for soldiers to volunteer for the hazardous duty. They did at least limit each man’s exposure time to only a couple minutes (and probably gave them an extra ration of hazardous-duty turnips!).

I think part of the problem is we really don’t know what we’ll find when we get there. Sounds okay to say we’ll just cut through this wall, but there’s a chance what’s on the other side needs to stay on the other side, cutting that hole was the worstest thing imaginable. I can imagine liquid fuel rods spilling out the side door into the ocean. We do want to try and avoid that.

We’re not talking about a little bit of radiation, we talking about one hell of a lot of radiation.

You seem to be asking the question, “Why aren’t the authorities responsible for the Fukushima cleanup efforts using {INSERT INTO post (mythical concrete cutting method)} and just cleaning instead of bumbling around with robots playing Doom through the annals of a partially collapsed nuclear reactor?” That is a loaded question with the underlying assumption that there is some other method that could be used and that the cleanup effort is not using it because of cost, effort, or lack of technical competence.

There are, of course, methods for cutting through concrete and other stone-like materials. We use these methods to bore through solid granite of mountains and excavate sedimentary rock to make tunnels. These largely consist of the use of a combination of blasting explosives and large tunnel boring machines, neither of which are useful in trying to cut through the reinforced and potentially unstable structures of Fukushima Reactors 1, 2, and 3, especially since we’d like to keep the structures as intact as possible to contain the lower level radioactive material while removing fuel elements that continue to provide heat and neutron radiation.

Now, if we had a device that projected a beam of unstoppable cutting power from a compact device that could be carried by a person or small robot then we could just cut right through intervening material, and also Star Wars enthusiasts everywhere would be accidentally severing off body parts from here to Comic-Con. But such a device is purely science fiction and doesn’t actually exist.

However, there is a substantial difference between the cleanup efforts and goals at Chernobyl #4 and Fukushima; Chernobyl, located in a remote area of Ukraine nearly Pripyat (which was purpose built for workers at the Chernobyl plant), was out of the public eye and residual radiation beyond that released into the atmosphere was not an immediate threat to water supplied or agriculture. The efforts at Chernobyl largely focused on removal of accessible radioactive material, and containment and eventual entombment of the reactor and fuel elements within it. At Fukushima, because of its location on the coast and relative proximity to other populated areas, the desire is to permanently deactivate the reactors by removing all fuel elements including the melted material that is now below the reactor structure, or at least assuring that it will not leak into the water table or ocean. This is a much more difficult task further compounded by having to permanently segregate contaminated water and deal with debris from three reactors.