Hitachi Developing Reactor That Burns Nuclear Waste

Zothecula writes The problem with nuclear waste is that it needs to be stored for many thousands of years before it's safe, which is a tricky commitment for even the most stable civilization. To make this situation a bit more manageable, Hitachi, in partnership with MIT, the University of Michigan, and the University of California, Berkeley, is working on new reactor designs that use transuranic nuclear waste for fuel; leaving behind only short-lived radioactive elements.

Comments

Already commented on this elsewhere

[AutodidactLabrat]

Baring that the new tech involves Neutron saturation transmutation, the end result will be MORE transuranics, as well as higher liklihood of meltdown, witness Fukushima Dai-Ichi's IMOX in #3. Total melt. Nothing new here, move along.

Re:Already commented on this elsewhere

[Giant Electronic Bra]

Mmmmmm, no, you can definitely burn up transuranics and you pretty much HAVE to end up with less at the end of the day, but the question is whether or not you have LESS OF A PROBLEM at the end of the day because there are plenty of "short lived" radionuclides that you really would rather trade for some nice plutonium or americium. On top of that the entire structure, premesis, possibly nearby things, etc will become waste, and even low level waste is costly to deal with. This is the same sort of set of issues that have made it totally uneconomical to reprocess spent fuel. ANY handling is messy, dangerous, and produces a lot of expensive to dispose of waste.

Re:Already commented on this elsewhere

[perpenso]

Will these new elements have significantly shorter half-lives?

In general the waste from a 4th gen reactor design is cited as being hazardous for a few hundred years. Something manageable, unlike the current situation where we are looking at tens of thousands of years.

Re:Already commented on this elsewhere

[Tailhook]

Fukushima Daiichi's problems began forty years ago when they removed the natural 35 meter bluff that use to be there.

The plant is on a bluff which was originally 35 meters above sea level. During construction, however, TEPCO lowered the height of the bluff by 25 meters. One reason for lowering the bluff was to allow the base of the reactors to be constructed on solid bedrock in order to mitigate the threat posed by earthquakes. Another reason was the lowered height would keep the running costs of the seawater pumps low. TEPCO's analysis of the tsunami risk when planning the site's construction determined that the lower elevation was safe because the sea wall would provide adequate protection for the maximum tsunami assumed by the design basis. However, the lower site elevation did increase the vulnerability for a tsunami larger than anticipated in design.

Not considered in the above would be the simple yet modestly more costly possibility of obviating the need for a sea wall by preserving the bluff and setting the reactors back, using modestly sized canals to cycle the sea water to and fro. That, naturally, wasn't the cheapest conceivable option, so it didn't survive the bean counters. Instead, they removed 25 meters of foothill, a feature that was originally 2.5 times the height of the tsunami before they fucked it up. The whole `bedrock' smokescreen is easily dismissed for the lie that it is; they could have reached bedrock from a setback design with no more difficulty.

This was done for one reason; grading the beach provided cheaper access to the ultimate heat sink, sea water. Less construction cost, less pumping, less maintenance, etc. This isn't lost on the perpetrators either. They know they're at fault and they knew it at the time, whatever lies they tell today notwithstanding.

This isn't speculation, either. Fukushima Daini did not get submerged, did not melt down and did not contaminate the land and the sea. Why? Primarily because it was built at higher elevation, which is about the only significant difference between these sites.

TEPCO bean counters. End of story.

Re:Already commented on this elsewhere

[ShanghaiBill]

He blatantly made a biblical reference to Noah

The story of Noah did not originate in the Bible. Both the Sumerian Epic of Gilgamesh and the Akkadian Atra-Hasis Epic included the story centuries earlier.

Re:Already commented on this elsewhere

[Cyberax]

What is "neutron saturation transmutation"?

Nuking it until it glows. First you separate your waste into constituent elements (their oxides, whatever) then you irradiate it with neutrons until most of the medium-level waste transmutes into something with a short enough half-life. You can optimize it a bit by playing with neutron energy to maximize the capture by most problematic isotopes. The size of neutron capture cross-section is not an issue, since you don't need those neutrons to support a chain reaction.

The concept is pretty old, but requires a shitload of neutrons (since you typically need to capture multiple neutrons to transmute a single waste atom). The only practical way to get that much is to use a fast neutron reactor. And even then it's marginal. In future, when we get fusion reactors, fusion neutrons could be used much more economically for that.

Re:Already commented on this elsewhere

[careysub]

but it does seem like important stuff in a flood plain

Fukushima wasn't in a flood plain.

Yes it is. Take a look at this US Army topo map (the latitude is (37.427 degrees, its on the coast). It is on an extended flood plain stretching along the coast, created by several rivers (Takase, Maeda, Kuma. Tomioka, etc.) . The whole area is a sea-level marsh consisting of soil deposited by these rivers at flood.

The problem wasn't glaring except in hindsight.

Because, you know, no one had ever seen a tsunami in Japan before. Oh wait, tsunami is a Japanese word. That doesn't seem quite right, does it?

Japan had fifteen of them since 1900, before Tohoku (the slightly dated linked list misses the 2007 Niigata tsunami).

Duh

[Cyberax]

If you have a strong enough neutron flux then you can burn the waste (i.e irradiate it until it transmutes to something with a short-enough half-life). Unfortunately, only fast neutron reactors have neutron balance good enough to allow a significant fraction to be diverted for uses other than supporting the chain reaction.

Broken link?

[BringsApples]

Try here: new reactor design.

By far not the only design that does this.

[quax]

By I much prefer inherently safe reactor designs.

Re:No mention of thorium

[brambus]

I don't think they do so in the breeder cycle - their neutron loss margins are fairly thin, hence why most designs propose extracting at the Pu-238 step (unusable for weapons, but great for space batteries). The burner cycle might be better in this regard. Fast reactors are able to do it, they have plenty of neutrons to spare.

Re:No mention of thorium

[brambus]

They don't, but the ratio of absorption to fission in the thermal spectrum for them is pretty bad, so that can mess up your neutron budget. Depends on the exact composition, though - each reactor produces a slightly different mix and that makes the TRU content in spent fuel fairly heterogeneous, which complicates reactor design and makes fabrication of reliable fuel fairly expensive (hence why MOX fuel only contains the Pu content, not all the other TRUs and even so it's much more expensive than fresh Uranium fuel).

Water cooled, TRU burning reactor = BS

[macpacheco]

Humm, let's see.
U-238 absorbs a neutron becoming Np-239 then decays to Pu-239
Pu-239 has only a 2/3 probability of fission upon neutron absorption
Water also has the tendency to absorb neutrons
It's no wonder that no TRU burning reactor has been proposed that uses water or helium for cooling, it's always sodium, lead or molten salt as coolant.

Also weird, is Hitachi already has a TRU burning design, the S-PRISM (GE/Hitachi project). Fast sodium reactors are actually known to be workable for that job.

Re:How about protons instead of neutrons?

[russotto]

I'm pretty sure the energy required to add a proton to the nucleus of a large atom is prohibitive.