
Nuclear Plant Accidents: Sodium Reactor Experiment - tehabe
http://allthingsnuclear.org/dlochbaum/nuclear-plant-accidents-sodium-reactor-experiment
======
Animats
At least they didn't have a sodium fire. Monju (Japan) and Clinch River (US)
both had sodium fires.

The U.S. Navy tried sodium reactors in the early days. In addition to
Nautilus, the first nuclear submarine, they also built USS Seawolf, with a
sodium-cooled reactor. Seawolf worked, but was enough of a headache that its
reactor was replaced with a Nautilus-type pressurized water reactor. The US
Navy didn't try sodium-cooled reactors again. Rickover on sodium-cooled
reactors: "expensive to build, complex to operate, susceptible to prolonged
shutdown as a result of even minor malfunctions, and difficult and time-
consuming to repair."

The USSR tried sodium-cooled reactors, with moderate success.[1] They had
leaks and fires too. One big reactor had 39 leaks over the years, none
catastrophic. In the last 15 years of operation, none. Eventually they found
all the construction defects.

Basic truth: complexity in the radioactive parts of a nuclear reactor causes
trouble. Sodium reactors have fires. Pebble-bed reactors have pebble jams.
(There's one in Germany that can't be unjammed or decommissioned.) Helium-
cooled reactors leak helium. The nice thing about water-cooled reactors is
that the complexity is on the outside, where repairs are possible. This is why
new fancy reactor designs are viewed sceptically in the industry. You can't
have any problems inside the reactor vessel, because you can't fix them.

[1] [http://www-
pub.iaea.org/mtcd/meetings/PDFplus/2009/cn176/cn1...](http://www-
pub.iaea.org/mtcd/meetings/PDFplus/2009/cn176/cn176_Presentations/plenary_session_6/INV-08.Ashurko.pdf)

~~~
pcl
I hadn't heard about pebble jams as a problem in pebble-bed reactors. Here's a
link to (scant) details about that German event:
[https://en.wikipedia.org/wiki/Pebble-
bed_reactor#1986_accide...](https://en.wikipedia.org/wiki/Pebble-
bed_reactor#1986_accident)

~~~
Animats
More info: [1] Most of the pebbles were removed through the fueling system,
but broken pebbles and dust remain, all highly radioactive. Bits of broken
pebbles are jammed into crevices in broken graphite. "The reflector bottom of
the core cavity is funnel shaped, with an inclination of 30°, ending in the
0.5 m wide vertical fuel discharge tube. In that geometrical setting it could
simply be assumed that all pebbles must have rolled into the discharge tube
and that there was no need for an inspection. The reflector bottom, however,
contains many slits for coolant penetration, 3.4 cm wide and in radial
orientation. A piece of broken pebble could have stuck in such a slit, and,
standing out, one or more pebbles might lay behind it guided by the slit like
by a rail."

"An upper limit of 197 fuel pebbles, respectively fuel pebble equivalent in
form of broken pieces, has been evaluated to be residual in the reactor
vessels containing an upper limit amount of 98g of fissile material."

"AVR has most probably the strongest β-contamination, and in the worst form,
of all nuclear installations world wide".

This is why complexity in the radioactive portion of the system is strongly
undesirable. If anything goes wrong, dealing with it is extremely expensive,
difficult, and dangerous.

[1]
[http://www.wmsym.org/archives/2000/pdf/36/36-5.pdf](http://www.wmsym.org/archives/2000/pdf/36/36-5.pdf)

~~~
varjag
Thank you, very enlightening.

It is often exhausting arguing with overly enthusiastic people claiming
certain reactor designs aren't just safer but "inherently safe". All
operations with massive energy releases are inherently unsafe. That's just
thermodynamics at work, and the reason we still have fire brigades after
millennia of using fire. What makes a difference with nuclear is the energy
concentrations and the material hazard involved. The problem from your
citation is a subtle and arguably minor engineering oversight which wouldn't
be much of an issue to handle on say a coal plant. Nuclear however multiplies
the consequences of any design defect.

~~~
emp_zealoth
I believe thats why certain molten salt reactors do away with any complexity
in the reaction chambers - some designs are planned to operate with fuel
dissolved in the salt. Criticality comes from the shape of the reaction
chamber vessel. Worst kind of failure mode - fuel cell rupture/core meltdown
are not really possible - simply because those are the normal operating
procedure. Should anything go really wrong the molten salt/fuel mix should
melt emergency reliefs and drain into non-criticality vessel. I do not
remember the nitty-gritty details and can't find it now, sorry.

~~~
varjag
Yes, that's another popular contender.

Now imagine the emergency drain failure, due to a quake seismic shift, massive
explosion nearby or a construction worker forgetting his helmet in. What's the
plan B?

~~~
VLM
Rely on gravity and put the non-critical tank underneath the critical tank.
Make sure to make the critical tank a much lower melting point than the non-
critical tank. Burst diaphragms (well, low melting point plugs, like steam
boilers have used for a few centuries now).

Possibly you're confusing "inherently safe" with "it can't break or become
uneconomical". Also talking about inherently safe plants, usually they're
talking physics, an inattentive enough electrician could probably find a way
to put his hand across the output of an alternator, there's just nothing
"nuclear" about those kind of accidents other than the worksite happening to
be a plant.

Inherently safe just means you can't have a Chernobyl because water doesn't
burn as well as charcoal. Its inherently very difficult to set PWR moderator
on fire (water) compared to the Chernobyl experience (graphite, more or less
purified coal). Although its against the spirit of the linked article, the PWR
"near" my house inherently can't have a sodium leak because it doesn't use
sodium as a coolant.

------
mixmastamyk
I have a bit of a connection with this incident, I grew up in Simi Valley, not
far from Los Angeles; it is not an academic subject to me. In short, they
built a defective reactor in a warehouse a few miles away from several cities
and covered it up when it exploded.

A number of workers and their spouses (known by my parents) died early in
their 40s from cancer ostensibly due to contamination. There is a belief in
increased birth defects in the area, but I can't find anything to cite right
now.

The shame is that we used to be proud of having rocketdyne nearby, testing
rocket engines and such, which we could hear from our school yards. Little did
we know how reckless they were, and had had a meltdown a few years prior.

------
jballanc
I find various accounts of nuclear accidents fascinating because, as the intro
of the article alludes to, they often involve complex systems undergoing
complex failure scenarios.

Then there's SL-1
([https://en.wikipedia.org/wiki/SL-1](https://en.wikipedia.org/wiki/SL-1)).
That was a really stupidly simple failure, but of all the accidents I've read
about I find it the most poignant reminder of why nuclear reactors _are_ such
complex systems in the first place.

~~~
hga
But it was well documented that you shouldn't lift that one rod above point X.
Maybe the message didn't sink into the guy, maybe he screwed up, they even
wonder if he committed suicide. Its big message was to eliminate all possible
single points of failure, especially ones controlled by fallible humans, even
at the cost of increased complexity.

~~~
cladari
It should be noted that reactivity control in military and commercial PWRs is
fundamentally different. That said it's hard to understand how the SL1
operator managed to yank the rod so far out of the core. The procedure was to
withdraw each rod 4 inches and attach it to the crdm, which in itself is a
little mind blowing to me. The rod was withdrawn 26 inches and prompt
criticality was achieved at 23 inches or so. The rod weighed 86 pounds. Even
if it was stuck it's hard to imagine yanking something that heavy that far to
unstick it.

------
jdblair
Santa Susana is notorious for a dangerously cavalier attitude about chemical
safety. For years they burned toxic chemical waste in open pits. They filled
barrels and shot them with rifles until they exploded. One person was killed
in 1994. They disposed of sodium coated parts by letting them burn in the same
open-air pits.

[https://en.wikipedia.org/wiki/Santa_Susana_Field_Laboratory#...](https://en.wikipedia.org/wiki/Santa_Susana_Field_Laboratory#Sodium_burn_pits)
[http://www.latimes.com/business/hiltzik/la-fi-
hiltzik-201406...](http://www.latimes.com/business/hiltzik/la-fi-
hiltzik-20140613-column.html)

------
totally
If you're into this, you might also like:

Inviting Disaster: Lessons From the Edge of Technology:
[https://www.amazon.com/gp/product/0066620821](https://www.amazon.com/gp/product/0066620821)

~~~
pinewurst
Or Atomic Accidents by James Mahaffey - this is a great book

[https://www.amazon.com/Atomic-Accidents-Meltdowns-
Disasters-...](https://www.amazon.com/Atomic-Accidents-Meltdowns-Disasters-
Mountains/dp/1605986801/ref=sr_1_1?s=books&ie=UTF8&qid=1467769048&sr=1-1&keywords=atomic+accidents)

------
spditner
I'm always surprised that the CANDU[1] reactor isn't more popular, as you
don't require uranium enrichment, can use a mix of fuels, and has a number of
fail-safes that work without power -- such as gravity-dropped control rods
into the low pressure chamber, and requiring the moderator (deuterium in the
original models) to be present to maintain a reaction.

[1]
[https://en.m.wikipedia.org/wiki/CANDU_reactor](https://en.m.wikipedia.org/wiki/CANDU_reactor)

------
crististm
Happens all the time. They ignored multiple and repeated warnings that they
should stop and think things through.

On a lower scale it's like (repeatedly) rebooting the PC when it's
misbehaving.

------
lb1lf
Reminds me of an old one-liner I saw in an email signature years ago -
"There's one really terrifying word in nuclear physics.

Oops."

I'll lead myself out.

------
wildlogic
This is a great read that sums up many criticality accidents and their causes
over the years - "A Review of Criticality Accidents"
[https://www.orau.org/ptp/Library/accidents/la-13638.pdf](https://www.orau.org/ptp/Library/accidents/la-13638.pdf)

------
sbierwagen
Kind of weirdly disingenuous that the article says "the workers" did this and
"the workers" did that. What, was management completely absent for a period of
months, and a bunch of yokels were just randomly flipping switches?

If "a worker" was overriding a failsafe, it's because right behind him a
supervisor was telling him they had to get the plant back online, or else he'd
be fired.

~~~
mikekchar
I think you are being just as disingenuous. Without knowing the processes, we
have absolutely no idea what the decision chain looks like. I can think of
many emergency situations where I would want workers who are close to the
problem to make judgement calls. Even if they make the wrong call, at least
the chance of success was optimised.

I often notice a bias amongst some people that they think management is more
susceptible to caving in to pressure for "success" (success being measured by
getting a job done quickly/cheaply, etc). In reality, I think it's just a
human condition.

Imagine working in a shop where every move you make is scrutinised. If you get
something done fast, everyone assumes that you cheated somehow or that you did
an exceptionally poor job. People always doubt you and assume that you are on
the take somehow. This would be pretty dysfunctional.

Now imagine working in a situation where when you do work everyone assumes
that it is of high quality. They don't have to check it because they know you
are capable, hard working and reliable. If you get it done more quickly than
expected, it's because you are a genius and should be promoted.

People often try to build companies like the latter. The problem is that it's
very easy to let your standards slide. If you do poor work very quickly you
get congratulated and rewarded. If you do good work very slowly, nobody looks
at it, nobody understands the quality and everyone complains that you took a
long time.

If you are in management, it's even worse. If you check up on the quality of
work of your workers: 1. They are upset that you don't trust them. 2. If you
find problems, it only causes you headaches and makes you look bad because
nobody understands quality _at all_. They just think everything is wonderful
and if you bring up a problem, then it's because you are the worst manager on
the team! It's really easy to close your eyes and reward poor work.

What I find really interesting is that on teams where there is absolutely _no_
pressure to deliver, conversely programmers often imagine pressure from
management to deliver quickly. Again, it's because nobody sees the quality of
their work and the only thing they see being evaluated is the speed with which
they deliver.

In the end, management must take responsibility when workers make mistakes.
Maybe the wrong people were hired. Maybe there was a lack of training. Maybe
the social dynamics were poor. It doesn't matter.

However, it is also possible that workers made the wrong choice, but that the
system still allowed the choice with the highest chance of success to be made
(given the information that they had). You are never guaranteed to have
success. Even when workers and management do an excellent job, sometimes you
fail because of something you didn't realise at the time. In that vein, I
wouldn't assume that "the workers did X" is an indication that they were
incompetent. Nor would I assume that management pressured them into doing
something stupid.

------
cocoablazing
Nuclear electric power production carries risks, which are outweighed by the
expectations of lives saved by reducing air pollution and greenhouse gas
production.

~~~
tobltobs
How can you calculate the risk if the modus operandi for the nuclear waste
management for the next few thousand years is not known yet?

~~~
CamperBob2
Clearly it's better to spew the radioactive waste randomly into the air, like
our existing coal plants do. The solution to pollution is dilution, right?

~~~
bildung
_> Clearly it's better to spew the radioactive waste randomly into the air,
like our existing coal plants do._

While coal plants do emit more radioactivity _through the chimney_ than
nuclear plants, that radioactivity pales in comparison to that emitted by both
the nuclear waste and accidents of the latter. See
[http://skeptics.stackexchange.com/questions/1018/do-coal-
pla...](http://skeptics.stackexchange.com/questions/1018/do-coal-plants-
release-more-radiation-than-nuclear-power-plants) for sources.

Also, nobody said coal and nuclear are the only possible technologies for
creating electricity.

~~~
CamperBob2
What matters isn't how much pollution is released. What matters is the harm
and suffering it causes. Nuclear has a long, long way to go to catch up with
carbon-based fuels in that regard.

I disagree that nuclear waste is a problem. To the extent that it is a
problem, the solution is stupidly simple: store it in Antarctica where no
technologically-illiterate humans can possibly come into contact with it, and
where we can reclaim it later if/when we need it.

 _Also, nobody said coal and nuclear are the only possible technologies for
creating electricity._

They're what we have to work with. Renewable sources should be aggressively
explored and developed, but they are currently not sufficient by themselves.

