Lots of knock on effects -- sub critical, let heat in the primary loop, less steam and electricity generated in the secondary loop, etc -- but generally a non event that you practice for.

There's no reason this would lead to a radiological event or more significant casualty.

Why do you think that? When rods are used to control the reaction rate I thought it was by raising and lowering them small amounts usually.

Being able to have a single fully inserted rod stop things would certainly make it more likely dropping rods into the core would stop an even than if you needed (say) all 3 to be fully inserted.

3x the chance of successfully stopping a serious problem, 1/3rd the chance of a blockage prevent the emergency shutdown.

This reactor type has 73 assemblies of 5 rods each.

Nuclear safety regulations require that the control rod system must be powerful enough to bring the reactor completely subcritical with all Control Element Assemblies (CEAs) inserted minus one assembly stuck in the fully withdrawn position.

One assembly (or 3) inserted would not bring the reactor subcritical.

depends on what your priors are. Is a dropped rod a fukashima or chernoble international emergency? No.

However, depending on the design characteristics of the core, dropping rods lowers the heat distribution proximal to the dropped rod(s), but may result in higher peaks distal to the rods as physics characteristics attempt to maintain the average, which may exceed design limits.

Furthermore, rods aren't supposed to drop. How that came to pass is a matter that requires honest investigation - manufacturing/quality control, maintenance practices, personnel error? Much to learn to ensure safety.

Saying "we just had to rely on a critical reactor safety feature and scrammed, this is a nonevent" doesnt quite hit the mark.

This link (second one down, first event is missing control rods in Texas...) has almost the exact same wording as the article.

https://www.nrc.gov/reading-rm/doc-collections/event-status/...

I found the root cause of the older issue on LinkedIn of all places.

https://www.linkedin.com/posts/robert-meyer-8672ab4a_st-luci...

Root cause of 2024 was apparently a procedural issue combined with electrical failure of the control rod grippers.

[1] https://chatgpt.com/s/m_6a82114f63a481919380c5f1e2b432e8

Can someone check my understanding: Control rods are suspended above the reactor as a sort of a "deadman's switch" - if a loss of power occurs, they will drop into the reactor core to limit reactivity. As a result, sometimes control rods will drop into the reactor accidentally. In these cases, the automatic system may withdraw other rods in order to maintain power output. However, this may overshoot the target power output or create a localized, dangerous "hot spot" elsewhere in the reactor core. In order to avoid this, in this case, the operators chose to insert other control rods instead of trying to stabilize the reactor under load.

The control systems are designed to err on the side of dropping the rods -- a failure to insert a rod is a lot worse than inserting one accidentally. So now they figure out why this happened while the reactor is in standby.

So this suggests that the dead man's switch has an automated anti-dead-man's switch that may result in more danger?

It'd be an interesting design choice, but defendable, if the "accidental dropping" rate is too high.

Safety wise, it would seem more sensible to try to keep the automatic drops unchallenged and try to prevent the conditions that make it happen.

I appreciate the factual nature of this story but I think an important aspect of journalism is giving people relatable references that allow them to better understand the information presented. It would be helpful if a story like this gave that context because without it it is hard to understand if this is 'Wow! What a close one!' or 'I guess this is a little interesting?'.

> The name "St. Lucie" is originally derived from the name of a settlement near Jupiter Inlet, which was founded on St. Lucia's Day in 1566. Due to numerous errors, the name later came to be associated with the present-day town of St. Lucie Village, Florida, north of present-day Port St. Lucie. After La Florida and St. Augustine, it is the oldest still-in-use European place name in the United States.

[^1]: https://en.wikipedia.org/wiki/Saint_Lucia

[^2]: https://en.wikipedia.org/wiki/Port_St._Lucie,_Florida

It would be a dream to no longer have to rely on fossil fuels, but my native island is at the peak possible cross-section of hurricane, earthquakes, and volcano eruption risks, so I guess we're only missing tsunamis and dry forest fires to complete our bingo for "best place to build nuclear"

You may also find it interesting that South Africa had nuclear weapons:

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

Despite the appearance, is it uniquely prone to flooding or storm surges?

It’s possible nothing was wrong and some sort of “blip” triggered them when they weren’t needed. And if so that’s annoying for the operators, but nothing bad was happening. And it confirmed the failsafe works.

If anything was starting to happen and the rods dropped and immediately stopped it that’s a failsafe working perfectly.

Either way this is fine. I know nuclear + unexpected = scary for many (maybe not you), but I don’t think that’s necessary here.

I wish it have provided some reasons on this

The details divulged seems to have been driven by event reporting regulations, not any specific news gathering or investigation, right?

Control rods are designed as fail safe so lots of scenarios can cause them to drop, could be a mechanical failure but probably more likely it was triggered by an electrical fault or intentionally by a safety system due to some condition they haven't quite worked out yet. Since having control rods in puts the reactor out of it's approved operating envelope it will lead to a trip out of an excess of caution. The fact that the trip wasn't triggered automatically suggests to me that the rods probably weren't inserted by a safety system but due to some fault.

3 rods inserted into the core out of the many available would have disrupted the neutron flux profile away from what the reactor is intended to operate against in steady-state, so manual shutdown is the right answer until the cause of the control rod being dropped can be figured out, repaired, tested and then the reactor restarted.

But while not typical, this kind of event has happened many times before and will again. Pretty boring IMO, which is why I agree with the non-emergency declaration by NRC.

Rig N+2 control rods with an actively powered electromechanical retaining mechanism. In any kind of serious electrical issue occurs on the protected circuit, all 3 drop automatically.

So when I read "3 control rods hit the bottom" what I hear is "there was an unexpected group scram", but I don't know enough about this reactor design to know if that's actually what happened, or whether it was 3 unrelated control rods instead.

This is potentially interesting as this reactor recently had its operating license extended earlier in the year.

Event 58408, 'manual reactor trip'.

[0] https://www.youtube.com/watch?v=v0afQ6w3Bjw&t=4007s

Some rods dropped. Something went wrong with the rod control system. Maybe an errant trip, maybe something mechanically wore, etc.

When a few rods dropped "accidentally" into the reactor, humans pushed the button to shut it down.

Now they figure that out and then turn the reactor back on.

what precisely is your point of describing how quality production engineering for infrastructure works?

Really, the "big AI story" will be when the next Snowden defects from the NRO and tells us what SENTIENT is doing. Until then it's just going to be a bunch of pie-in-the-sky wishcasting about what we want the future to look like. It's getting a little tiring hearing people insist that abundance is around the corner while surveillance is here-and-now.

I doubt anyone who works on reactors is that stupid.

But some idiot somewhere is going to put some industrial stuff under AI control pretty soon and murder a few people at minimum.

Which: it seems like we're already getting to the point of capability vs. unexpected behavior that having the ability to "trip" a complex system may be an important design criterion.

I mean, there's plenty of harm these systems can do besides trying to turn us all into paperclips.

A) Let AI override safety mechanisms (increases uptime while endangering humans)

B) Let AI impose additional safeties (decreases uptime with questionable safety uplift)

If you intend to go with option B) then there's basically zero benefit to investing in that kind of automation. AGI will be fallible, and even with all the safeties and safeguards it's hard to see what tangible benefit AGI would add to the system. It'll be a hard sell for critical infrastructure of any kind.

I understand that it's hard to get a man to understand something when his AGI Society executive credentials depend on it, but it feels glaringly obvious why AI isn't masterminding these sorts of systems. Even accounting for unprecedented advancement in AI, it's hard to see what AI could contribute to managing these things.

Remember, critical infrastructure attached SCADA systems to the internet and has had trouble removing them all despite 30 years of warnings and audits.

There's definite advantages to having a LLM in the loop. The best we can hope for is that it's architected in a way that it fails safe and damages are limited, so we get some of the advantages but less of the downside.

Outside, almost everyone I know - including highly educated people - takes even Google's search LLM output as fact, without a second thought, and even regarding serious issues (e.g., medical problems). Nobody raises a doubt or an eyebrow. A recent article says members of US Congress use it extensively for serious work. Lawyers use it to file cases. Doctors use it to summarize essential medical information. I even hear that software developers use it to create high-risk, high-value code.

In the public people think computers are superior to humans - more authoritative, objective, perfectly logical and error-proof. SV pushes that narrative, for example saying computer-driven cars are safer because computers don't have human flaws (that old sales technique - compare only the competition's unique flaws and don't mention your own; computers have their own flaws that humans lack). And of course, that one is popular on HN.

(IMHO the way to educate the public is to spread the narrative that every computer is created (designed, programmed) by normal, flawed, biased, etc. humans, and controlled by other flawed humans for their own agenda. And that computers have their own flaws.)

The general public distrusts them cuz they know that they're coming for their jobs. But they will use them out of convenience