

Nuclear Reactor Renaissance - sprout
http://spectrum.ieee.org/energy/nuclear/nuclear-reactor-renaissance/0

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pjscott
This paragraph is wrong:

> Some analysts have expressed doubts that the EPR is the world's safest
> reactor. Their main concern is the spent fuel: The reactor's higher burn-up
> rate makes the waste more radioactive, raising concerns about proliferation.

They got this exactly backwards. Higher burn-up rate makes the spent fuel
_even harder_ to use for nuclear weapons, by screwing up the isotopic mix. The
way you make weapons-grade plutonium is to construct special reactors designed
for _very low_ burn-up. And then I come to this gem:

> Despite its higher temperature, the reactor operates at one-fifth the power
> of a PWR. That reduced power density enhances overall safety. What's more,
> additional heat naturally increases the carbon's ability to absorb neutrons,
> so the carbon acts as a passive safety mechanism capable of shutting down
> the core.

First, the power of a reactor depends on its size and power density. Phrases
like "one-fifth the power of a PWR" are meaningless. It's confusing power with
power density.

Second, they say "additional heat" when they mean "additional temperature".
Heat and temperature are completely different things, and you'd think the IEEE
would know that.

Third, high temperatures make the non-fissile U-238 in the fuel more likely to
absorb neutrons, not the carbon. The carbon is there as a structural component
of the fuel, and to act as a moderator to slow down the neutrons.

Finally, it's not so much that it shuts down the core, as that it keeps the
core at a roughly constant temperature. If you stop coolant circulation, then
sure, the core is going to reduce its power output drastically; in some pebble
bed research reactors they do this to turn it off at night. But the true
beauty of this negative feedback loop is how it regulates the temperature, not
some hypothetical "What if there's a stupendous accident?" application.

~~~
uvdiv
Another one is

>"Because it's a fast reactor, the HPM doesn't consume vast amounts of water,
making it attractive for areas where water is scarce or unavailable."

There's no reason a fast reactor should be different from an ordinary LWR in
water use. A thermal power plant uses river or ocean water as a heat sink;
nothing about a fast reactor changes the thermodynamic need for a heat engine
to have a cold reservoir. Of course there's no longer water in the closed loop
that cools the reactor core (which is what confuses them?).

------
Bdennyw
Sadly no mention of thorium or LFTR.

~~~
Confusion
No mention of pebble bed reactors[1] either, which is a shame, because AFAIK
they are still the only ones that cannot melt down. They produce less energy
the hotter they get and one can design them to, for instance, never exceed
1800K. If the cooling system fails, the system simply reaches a steady state
at that temperature. There is thorium variety of this reactor.

[1] <http://en.wikipedia.org/wiki/Pebble_bed_reactor>

~~~
lispm
Funky, the english Wikipedia page. It says that the German pebble bed reactor
was abandoned due to 'political and economic' reasons.

The truth can be read in the German version of the article, it simply did not
work problem free. It is also mentioned further down in the English article.
The German article about this specific reactor, the THTR-300, goes into
detail.

The pebbles were breaking. The concrete got too hot. The reactor got too hot
in its center. Taking out pebbles could only be done when he reactor was
running with reduced power. It also had an accident where the reactor was
leaking radioactivity.

All in all the handling of the pebbles had many ugly surprises for pebble bed
reactor designers. They were breaking at a rate of 1000 higher than expected.

~~~
pjscott
The German pebble-bed was built in 1983 and shut down in 1989. Pebble bed
reactor designers have had 21 years to improve on that design, and they've not
been idle. All real nuclear reactors have problems before you've had time to
work out the bugs in the design. They're big, complicated machines, and they
have to meet some pretty stringent engineering specs.

The German THTR-300 was the first attempt to build a full-scale pebble bed
reactor, after they'd run just one smaller research reactor. Problems with the
design are to be expected. That's not an indictment of pebble bed reactor
designs; that's just how nuclear engineering works. I'm glad that the pebble
bed guys are finally picking themselves off the floor and continuing on with
the Chinese HTR-PM reactors, which were designed to avoid the problems which
plagued the THTR-300.

~~~
lispm
This German study (2008) from Jülich (!) was quite critical about the whole
concept:

[http://juwel.fz-
juelich.de:8080/dspace/bitstream/2128/3136/1...](http://juwel.fz-
juelich.de:8080/dspace/bitstream/2128/3136/1/Juel_4275_Moormann.pdf)

