
High radiation readings at Fukushima’s No. 2 reactor complicate robot probe - sinalc0
http://www.japantimes.co.jp/news/2017/02/10/national/high-radiation-readings-at-fukushima-no-2-reactor
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static_noise
Somehow it seems strange that Japan, the motherland of robots, fails to build
a robot.

Money can't be the reason. There has been an investment surge into radioactive
cleanup technology starting with the damaged reactors six years ago.

Six years and billions of dollars later we get a robot that gets stuck and
fails after just two hours. From what I've gathered they didn't even include a
proper radiation sensor but used the camera noise in order to "guesstimate"
the dosage after the fact. Did they not expect high radiation in that
location?

~~~
Pica_soO
Electronics of the shelve get very unreliable in high dosage environments. The
radiation rewrites your loaded programs, by flipping bits and causing rising
edges where there shouldn't be some.

So the program running on your camera will dissolve above some radiation
levels, locking it in a watchdog detects and reboot cycle. There are
approaches to circumvent that in low to medium environment- one is to have
redundant systems and select the "majority" vote on computation results.

But at this level, the only solution is to not have computation near the
source and put up with long cable/fibre cable delay- which is tough with
complex sensors (aka computers) like cameras.

It is probably some snail-eye setup- the camera a remote mini-drone on cable,
retracted on black out.

~~~
cnvogel
In my day-job, I (help) design electronics that is subjected to (much less)
radiation, and we also irradiate our devices to check for long-term effects
(and this is done with a comparable doserate in a facility for this purpose).

Damage to your electronics in practice is almost exclusively caused by Photons
(convention is to call this γ-Radiation when caused by radioactive decay in
the nucleus, X-Rays when created in an accelerator). β-radiation (fast
electrons) is easily shielded by thin layers of metal, and α (He nuclei) can't
penetrate sheets of paper.

Individual photons can't really deposit much energy at a single location in
your semiconductor, so they aren't able to generate enough charge to "flip
bits" instantly. Flash still uses a lot of charge/bit, so it's relatively
stable, DRAM is constantly refreshed and SRAM would need a jolt of high
current to flip, so that does not really happen, either.

What radiation does, however, is to slowly damage the Silicon and change its
crystal structure (introducing defects) which increases leakage and moves the
analog threshold voltages of circuits around in a funny way. So, what we often
see is flash becoming un-programmable on a more global scale (rather than
individual stuck bits), and most importantly the analog aspects (voltage
references, brownout-protection circuits, voltage regulators) cease to
function.

This is all very variable, but we normally observe effects starting at "a few
100 Gy" when testing more complicated modules. We don't research individual
components, though.

One especially nasty type or radiation are neutrons, though. When being
"moderated" (slowly decelerated by successive interactions with material) they
tend to have a high likelihood of merging with some other nucleus (being
captured), and the energy resulting from this capture effect can be huge and
concentrated on a single spot. This can be enough to flip bits, and this
indeed may be an issue near the funny isotope mixture present in Fokushima at
various places. Having a strong neutron emitter is very uncommon, though.

Unfortunately these damages are not specific to digital electronics, and
especially optical components (parent refers to long fibre cables) tend to be
rather sensitive due to their large structures, so "keeping the computers out"
may not help much overall.

~~~
ethbro
So, simple question: why isn't everything electronic shielded inside big lead
blocks?

I get why this isn't the prevailing approach in aerospace applications:
weight. But for a ground based robot with an external power source, why not
heavy shielding cubes with minimal connections to the necessary exposed bits?

And why not just load it down with 5x CotS sacrificial cameras, then expose
them as needed when the previous one dies?

~~~
cnvogel
For typical Gamma radiation of about 1MeV photon energy or higher, you need
about 1cm thickness of lead to reduce the radiation to about a third (by a
factor of 1/ℯ). One order of magnitude of radiation hardness (reduce radiation
to 1/10th) needs two centimeters of lead. That's getting heavy pretty fast.

Radiation intensity inside your box depends on the thickness t: I(t) =
I₀·exp(-tρμ)

t: thickness, say 1 cm ρ: density of the material, for Lead 11 g/cm³ μ:
absorption coeffcient 0.1 cm²/g [see ref 1] I₀: intensity outside of the box

    
    
        ...import numpy as np...
        In [5]: np.exp(-0.1 * 11.34)
        Out[5]: 0.32174370422037013
    

I(1cm) = 32,2%, I(2cm) = 10,4%

[1] [http://www.eichrom.com/PDF/gamma-ray-attenuation-white-
paper...](http://www.eichrom.com/PDF/gamma-ray-attenuation-white-paper-
by-d.m.-rev-4.pdf)

------
codecamper
Could a future earthquake jolt the reactor back into danger mode?

~~~
u_wot_m8
It's still in danger mode, still leaking massive amounts of radiation into the
pacific ocean. Based on what I've read of dying ocean life it's probably one
of the worst environmental disasters in history

~~~
tptacek
Reprising:

There are 187000000000000 million gallons of water in the Pacific Ocean,
meaning that "radioactive waste" is 2.1 x 10^-10% of the body of water itself.
The waste takes the form of HTO, tritiated water, which has extremely low
bioavailability and has already been introduced in abundance to the ocean by
other events. There are things to be alarmed about, but this isn't one of
them.

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mikemike5000
So, what's the long game with Fukushima? This has been going on for so long
and it's concerning that seemingly very little progress has been made.

Edit: added "seemingly"... as I can say for certain the degree of progress
that has been made.

~~~
Animats
Decommissioning a damaged reactor is insanely expensive and, in too many
cases, not possible. Chernobyl is at best contained, not cleaned up. 30 years
after the fire and meltdown, the giant curved roof built to cover it was moved
into position last year. That will hold things for a few more decades. The
next generation will have to work out the next steps.

The jammed AVR pebble bed reactor in Germany is contained, but there's no way
to dismantle and dispose of it. Current plans are to wait 60 years and then
try to figure out something.

Fukushima’s mess will also take decades. The site generated huge amounts of
contaminated water, and there's now a processing plant to take most
radioactive contaminants out of the water. The water still has tritium after
processing. The half-life of tritium is 12 years, so that will cool off in a
few decades. Meanwhile, huge farms of water tanks store the stuff. Lots of
radioactive dirt has been dug up and buried deeper somewhere else. There's a
refrigerated "ice wall" to try to stop leakage into the ocean. Not much has
been done with the reactor vessels themselves. As today's story reports, they
can't even get a robot close to the reactor vessel.

This makes one very discouraged about nuclear power.

~~~
codecamper
Solar panels folks. Solar panels. Wind. Batteries. We can do it, no problem.
Electricity costs a little more, but your car ends up costing less. Less
maintenance on fewer parts - just swap out the battery which declines in cost
each year.

Keep fossil fuels and wood for the things solar & wind will have trouble
covering: airplanes, ocean shipping, winter heating.

~~~
tptacek
We cannot do it:

[https://www.youtube.com/watch?v=9yNj1zEh-
nM](https://www.youtube.com/watch?v=9yNj1zEh-nM)

You only need the first 15 minutes of this talk to see why current renewables
won't scale. The world needs something like 15 terawatts. When this talk was
recorded, solar electricity produced something like .001 TW. We're now closing
in on .03 --- and there are huge parts of the world that still haven't
industrialized yet. We'd apparently need to be printing and distributing and
deploying solar cells the way we do newspapers to have any hope of using
photovoltaic to offset our total energy demand.

Nuclear doesn't scale either, but the notion that we're all just holding back
on renewables out of greed because all it takes is wind and solar... well,
it's easily refuted.

~~~
Animats
Our descendants have to do it. Coal, oil, and natural gas have maybe a century
left. Fracking made more hydrocarbons accessible, but the supply is still
quite finite.

~~~
tptacek
We can't do the thing suggested upthread, eliminating dependence on all
consumable energy sources by harnessing current wind and solar technology.
Ultimately I agree that we have to find a way to do it. But there's a virulent
belief that we can do it with technology that is being produced today, or
might be produced in the near future if demand changed. No.

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amelius
I'm wondering, can't they use the radiation as an alternative to light
(photons), in that environment? I'm guessing the radiation would scatter in a
way comparable to light, so you would be able to get a similar kind of
"imaging". Not sure how one would implement a radiation detector in silicon,
but at least you could shield it by some layer of metal to get out of the
range of overload and into the range of sensitivity.

~~~
the8472
High energy photons are quite different compared to visible light. They
scatter instead of being reflected. They have a low cross-section which means
you can't make tiny pixels. No reflection or diffraction means no optics.

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choonway
Are there any startup robotic companies that are doing robots that can deal
with hard radiation? It seems that they are trying to wash off some melted
gunk that is blocking their way into the area beneath the vessel where the
core is suspected to be.

Will building a robot capable of completing such a task under such an
environment attract any funding? Anywhere to apply?

~~~
dottedmag
One can arguably find the engineers who created robots used in Chernobyl,
which were oblivious to radiation by using pneumatic tubing for control.

