Comment by cj | Hacker News Reader

Comment by cj | Hacker News Reader

My mother worked for a company that made small cooling fans used in fighter jets and space craft.

She would bring one of the fans home and say “Look! I just sold 10 of these for $1,000,000”

The fans themselves were cheap to manufacture. But they were SO incredibly important that they could NOT fail under any circumstance. (They were mostly fans meant to cool electronic systems, and if they failed, would cause the plane or space craft to explode, literally)

The fans were so expensive because they had to go through so many quality checks to ensure they would sustain every environment imaginable, compounded with the fact that there’s no scale in demand (no one other than Boeing, NASA, etc is going to buy a tiny $100k fan)

Tiny production volume + huge quality requirements/standards = very expensive product.

I assume a similar dynamic applies to many components in a nuclear power plant. Volume is very low and the quality/reliability requirements are very high.

Many years ago it was my job to design and procure control systems for natural gas power plants - this included mostly valves and instrumentation. Of course, once you're dealing with superheated steam (whether fired by natural gas, coal, angry isotopes, etc) it's all the same valves and thermocouples. So I got to know the product lines of the handful of suppliers very well. A few had nuclear product lines (USA only) which were identical in spec to everything else...with two major differences:

1) Everything had to be manufactured in the US with all the requisite paperwork

2) Every non-destructive test under the sun was required for every distinct part, including an encyclopedia's-worth of paperwork per test per part

In this case, it's not the parts, or even the design that breaks the bank. It's the validation.

> In this case, it's not the parts, or even the design that breaks the bank. It's the validation.

See also "certified" versus "experimental" general aviation aircraft.

not sure if you care but they track comments like this on https://news.ycombinator.com/highlights

There has to be a way to build a safe system from several not as safe parts. At least for a system which doesn't need to fly.

The problem is that any system that's built around cheap redundant parts will gradually degrade to it's minimum viable state because the humans who maintain it will eventually be lazy| greedy| stupid enough. So it also has to fail early by design before reaching that state.

That’s not a given

It’s the opposite really - even if you have really safe parts, the overall system will be more likely to fail than any particular part.

Say you have 10 independent critical components each with a 0.99 probability of not failing. Well the probability of nothing failing in the system is 0.99^10 ≈ 0.9. So your collection of parts each with a 1% chance of failure has a 10% chance of some critical component failing overall.

Of course it’s more complicated because in real life nothing is really independent, and failure of one component will be coupled to failure in another. This makes simple solutions like redundancy not necessarily helpful (and sometimes even detrimental).

There is in software, but in hardware it's a chain with links and the weakest part will be the one to cause the chain to fail. Hence the focus on individual parts reliability and quality.

I think the only way to do that is redundancy.

Redundancy also adds a lot of complexity, as fail-over mechanisms aren't simple either. That added complexity then turns into additional possible error sources.

A friend of mine builds a component for a satellite system and the FDIR mechanisms need to be chosen very carefully, as adding more fail-safes can actually make the system overall more error prone.

There's an interesting blog post on from AWS about that topic [0]. Turns out adding more fallbacks and fail-safes is actually discouraged there.

[0] https://aws.amazon.com/builders-library/avoiding-fallback-in...

You make me think about how nuclear weapons tests are currently done. they are detonated underground, the soil above the device collapses on top, containing the majority of the fallout. it's a reliable and simple system and poses the question, could a nuclear power station be built in that way, because it wouldn't require the development of new technology.

Burying a structure under tons of earth when it contains a number of human beings tends to be politically unviable.

It is like the RAD750 radiation hardened processor. It is a PowerPC 750 but costs about $100K because under those harsh conditions - it can not fail!

Could you use it to cool a Pentium 4 processor?

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