[Terr_]

> When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity.

I wonder if any reactor-design groups do "fuzz testing" on simulated models, checking that they can recover from very weird states even if it's not clear how the state could have been reached in the first place.

For example, having one section just arbitrarily xenon-poisoned, while another is arbitrarily too hot.

[cyberax]

Yes. Reactors now are designed to never have positive feedback loops that can result in uncontrollable power spikes. They do the worst case simulations to prove that.

Russian atomic regulator downright shut down the project to design a light water breeder reactor, saying that it's not going to be licensed. Light water breeder reactors are barely theoretically possible, but they require trade-offs to limit the amount of water within the reactor core. So the trade-offs result in a positive void coefficient. It's supposed to be offset by other safety features, but better be safe than sorry.

[_n_b_]

Yes, essentially this happens. PWRs and BWRs have operating limits on their power shape derived from doing those kinds of analyses.

They’re tend do be more physical than “arbitrarily xenon-poisoned” but represent a variety of extreme and nominal states to form an operating envelope, and then healthy margins are applied on top of that.

[ahartmetz]

I'm not sure if that expression is known outside of physics, so: "physical" here means "conforming to, possible under the laws of physics"

[timewizard]

Yes, it wasn't intentionally, but it was at Ingalina.

https://en.wikipedia.org/wiki/Ignalina_Nuclear_Power_Plant

[xk3]

The disaster was a result of fuzzy testing :-)

https://en.wikipedia.org/wiki/Chernobyl_disaster#Safety_test