
"Nothing like this will be built again": a tour of a working nuclear reactor - gjm11
http://www.antipope.org/charlie/blog-static/rants/nothing-like-this-will-be-buil.html
======
arethuza
When I worked in academia I did one project with Scottish Nuclear and one of
their team had worked on the project to build Torness. He had a story about
one of the failure modes they had to consider during the design.

AGRs can be refueled while they are operational by a huge machine that moves
across the top of the reactor and allows the fuel rods to be extracted from
the extremely high pressure environment of the reactor core. The refueling
machine is basically a long thing container that fuel rods can be raised into
or lowered from.

They had to consider the case of what would happen if the refueling machine
wasn't properly pressurized before the connection to the reactor core was
opened (which can't really happen for a variety of reasons). However, if it
did happen they realized that the refueling machine would basically act like a
very large gun shooting hot fuel rods through the roof of the reactor building
powered by the high pressure CO2 from the reactor core.

Every time I pass Torness on the train I can't help looking to see if there
are any fuel rods flying into the air. So far, so good....

------
ScotterC
"Energy to cheap to meter". It pains me. I'm so glad to see a good writer give
some strength to how massive and impressive these reactors are. But it pains
me as he describes system after thoroughly redundant system adding to the
costs of these reactors.

I'm much more familiar with PWRs (Pressurized Water Reactors) which yes, are a
bit smaller and less efficient, but the plans and schematics are like a first
time run through of a problem. Nothing re-factored, nothing elegant, just
plain and simple brute force design to make it work.

There's no reason for four diesel generators when two would do. There's no
reason for multiple chemical volume and control systems. There's no reason for
6 foot thick, steel re-barred concrete containment in a negative void
coefficient reactor!

My take-away from working in the industry is regulation severely impedes
innovation. I fear that our greatest discovery since fire is languishing.
Nuclear energy will be used to great extent in the future, but I can't stand
the current delays. Energy is conceivably too cheap to meter in it's current
form. You could conceivably pay, not by your kilowatt-hour, but a fixed
monthly subscription to unlimited energy. Just think about what you could do
with that!

Edit: -- Misread the article. PWR's are less efficient than AGRs

~~~
uvdiv
> _There's no reason for 6 foot thick, steel re-barred concrete containment in
> a negative void coefficient reactor!_

To contain the steam explosion in the event of a coolant leak. That is,
pressurized liquid water at 300 °C flashing into steam as it's depressurized.

~~~
ScotterC
Coolant leak and steam explosion are in conflict with one a other. What you're
referring to is Chernobyl, which had a graphite moderator which allowed for a
dramatic increase in power and pressure with no release. Light water plants
use water as a moderator and a coolant leak would relieve pressure making a
steam explosion unlikely. For example Three mile Island was never in danger of
a steam explosion.

~~~
uvdiv
> _Light water plants use water as a moderator and a coolant leak would
> relieve pressure making a steam explosion unlikely._

I mean, the pressure in the containment building. Isn't that the purpose of
the containment walls, to withstand steam pressure from a coolant leak? Or am
I misunderstanding things.

> _Coolant leak and steam explosion are in conflict with one a other._

My mistake.

~~~
ScotterC
My argument is that there is no purpose for the containment walls. They are
theoretically yet another barrier to leak of radiation on top of the fuel rods
and the piping itself but I would argue this as unnecessary. Chernobyl should
have had a containment vessel. This would have averted that disaster. Three
Mile Island had a catastrophic systems failure with a partial meltdown yet
only 1 inch of the 7 inch thick reactor vessel was affected. Some xenon gas
and other radioactive elements were released to the atmosphere but of minimal
quantities.

------
Maro
When I was getting my degree is Physics we had a lab in the "student reactor",
which was still in a large building of its own. As part of the lab we got to
sit down to the control console of the reactor and control it, on our own. I
remember I was turning one knob increasing the power output when suddenly
there was a loud noise, everything shook, and the power output went to zero.
Turned out it was the failsafe (I think cadmium rods dropped into the core) as
I was too agressive with the controls --- it was a normal occurence for
students. (All modern reactors are designed in a way that you can't overdrive
them, they'll automatically shut down.) It was great fun and a story I'll be
telling for the rest of my life.

------
jedsmith
> For starters, some embedded controllers in racks in the auxilliary deisel
> generator control rooms have EPROMs which have been known to be erased by
> camera flashes in the past

Not being in EE, I didn't know that this was possible; and, with the knowledge
that a bright flash erases EPROMs, that they'd be left in a position where
this could occur. More interestingly, the NRO has a notice about it:
[http://www.nrc.gov/reading-rm/doc-collections/gen-
comm/info-...](http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-
notices/1997/in97082.html)

The government verbiage for the hack here (tape over the window) is amusing in
itself:

> They also confirmed that the light from the Canon flash and the Polaroid
> flashbulb could be effectively blocked by "black bagging" the flash, or by
> blocking the EPROM window with "tin foil" held in place by clear cellulose
> tape, or by blocking the EPROM window with "standard electrical tape."

~~~
HeyLaughingBoy
_Not being in EE, I didn't know that this was possible_

Not only is it possible, it has led to many interesting failure modes in the
past since visible light doesn't usually erase an EPROM, but sometimes just
flips a few bits. The n00b complaint, "it works fine until I turn on my desk
lamp" used to be a pretty common one in EE labs and online help forums :-)

~~~
CamperBob
I don't buy it for a minute. You can leave an uncovered EPROM in direct
sunlight for a week, and the data will probably survive.

I'd suspect a localized "EMP" transient from the camera flash before I'd
suspect an erased EPROM. It takes a _lot_ of energy, in the E=hv sense, to
erase an EPROM.

~~~
HeyLaughingBoy
Believe it: windowed EPROMS have been used as cameras. Their light sensitivity
is legend.

[edit] actually I was wrong about that. The memory devices used as cameras
were delidded RAMs, not EPROM. EPROMs are light sensitive, but too slow for
that.

------
gjm11
This has been posted here before, about two years ago --
<http://news.ycombinator.com/item?id=569564> \-- but (1) it's very good and
(2) the old URL no longer works.

It's by Charlie Stross, a science fiction author and former hacker. It
describes a lengthy tour of the nuclear reactor complex at Torness in
Scotland.

~~~
ScotterC
Not to mention that it's an AGR (Advanced Gas cooled Reactor) something that
doesn't exist in the U.S. or most of the world. Very cool.

~~~
lkiujhygjk
Very clever design, much more efficent, much safer - negative temp coeff and
no chance of a steam explosion.

But they never reached the critical mass (sorry) to make them standard and so
cheap to build and operate.

------
uvdiv
Here's a large (35 inches) cutaway drawing of a Magnox reactor, which gives
some visual scale to the monster that is a gas-cooled reactor:

(PDF) [http://econtent.unm.edu/cgi-
bin/showfile.exe?CISOROOT=/nucen...](http://econtent.unm.edu/cgi-
bin/showfile.exe?CISOROOT=/nuceng&CISOPTR=47&filename=42.pdf)

(Note this isn't the AGR that Stross depicts, but its predecessor the Magnox).
For size reference, the six boilers are 118 feet tall by 18 feet diameter (36m
* 5.5m); the building is 170 feet high (52 m).

