5 ms·

St Lucie Nuclear Reactor Unit 1 manually shutdown, 3 control rods drop into core

196 points by toomuchtodo 3mo ago

stmw 3mo ago
To rephrase it: nothing happened, and reactor is back online generating clean electricity. This is the equivalent of a Kubernetes pod restarting.
high_na_euv 3mo ago
Why they dropped?
- toomuchtodo 3mo ago
  I was unable to find the NRC filling, if someone finds the link to it, please drop a reply with it. This is potentially interesting as this reactor recently had its operating license extended earlier in the year.
  - OJFord 3mo ago
    https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2026/20260814en https://www.nrc.gov/reading-rm/doc-collections/event-status/... Event 58408, 'manual reactor trip'.
- mpyne 3mo ago
  Perhaps an interruption of power to the field windings of the affected control rods. Could be as simple as a control cabinet fried unexpectedly or some other electrical gremlin. 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.
  - bob1029 3mo ago
    This could be an intentional design feature regarding power loss to critical reactor control systems. 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.
    - mpyne 3mo ago
      Yeah, on one of the reactor designs I was familiar with, control rods were bundled into groups which were managed as a set and were intended to be operated in different sequences over core life. 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.
Abh1Works 3mo ago
this is really interesting
AndrewKemendo 3mo ago
It’s great that nuclear power safety events are so well managed that nearly 100% of events go completely unnoticed by the public. Unironically this is the kind of headline I’m expecting in 2040 about one or more major AGI systems running an electrical grid, factory or similar.
- stefantalpalaru 3mo ago
  [dead]
- bigyabai 3mo ago
  I doubt AGI will be used for life-or-death systems like that if it resembles anything like the LLMs of today. Systems at that scale are about risk management, and everything we know about AI suggests that it cannot mitigate risk at all. All AI is seemingly a net-positive risk factor. 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.
  - mlyle 3mo ago
    The way I read it was that he expects large industrial systems with AI to have safeguards to "fail closed." 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.
    - AndrewKemendo 3mo ago
      Correct interpretation
      - bigyabai 3mo ago
        So, which do we choose? 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.
ImOssir 3mo ago
I wonder why so much repetition in the article. Do they have word limit to hit? I wish it have provided some reasons on this
- verytrivial 3mo ago
  From the article: "This story was reported on-air by a journalist and has been converted to this platform with the assistance of AI. [...]"
ck2 3mo ago
for "reasons" that they carefully left out? Florida should be added to title, it's not like the European shutdowns for overheating
- mlyle 3mo ago
  No one knows the reasons yet. 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.
- preisschild 3mo ago
  could have been something as minor as some sensor malfunctioning.
- chpatrick 3mo ago
  Overheating isn't exactly right, they got shut down because they couldn't be cooled, but they didn't overheat.
- redsocksfan45 3mo ago
  [dead]
fwipsy 3mo ago
https://www.nuclear-power.com/nuclear-power/reactor-physics/nuclear-safety/level-2-abnormal-operation/control-rod-drop-pwr/ https://www.nuclear-power.com/nuclear-power/reactor-physics/... 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.
- mlyle 3mo ago
  Yup. Often one rod fully in is no big deal -- it has been analyzed and you keep operating. But no one has certified to run the reactor with a few rods fully in. 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.
- solarkraft 3mo ago
  > 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 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.
  - s1artibartfast 3mo ago
    You should write them an email suggesting they try to prevent unintended rod drops
    - 3mo ago
verytrivial 3mo ago
This "dropping" activity is not defined well in the context. Was it e.g. a controlled but uncommanded insertion? Or did something or some three things slip, snap, or something else? Can the rods be retrieved using BAU procedures, or is reactor in an annoying state now? The details divulged seems to have been driven by event reporting regulations, not any specific news gathering or investigation, right?
- jcrawfordor 3mo ago
  This article is just an over length summary of a very short preliminary notice published by NRC. Since it is non-emergency there will not necessarily be much follow up either, plants are just required to report any abnormality to NRC which publishes the reports online. Most of these reports are, like, procedural problems in employee drug testing. 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.
aeonik 3mo ago
This happened in 2024 too. 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/event/2024/20241115en 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-lucie-ler-multiple-control-rod-drop-share-7288007676314238976-I1TW/ 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.
- robocat 3mo ago
  Relevant 2024 excerpt from linkedin link: double hold was placed on Subgroup 4 resulting in the associated control rod lower grippers being engaged prior to removing the upper gripper drawer. After successful replacement of the UG coil CPMD the double hold was removed, per 2-NOP-99.07, and CEAs 43, 45, and 49 fell and fully inserted into the core. CEA means Control Element Assembly. A CEA is a group of control rods that can be inserted into or withdrawn from a reactor core
julienchastang 3mo ago
I actually thought they were talking about the island in the Caribbean since Florida is not mentioned in the article. Anyway, in case you did not know, the reactor in question is in Florida: https://en.wikipedia.org/wiki/St._Lucie_Nuclear_Power_Plant https://en.wikipedia.org/wiki/St._Lucie_Nuclear_Power_Plant
- ashleyn 3mo ago
  I can't be the only one to see that location and think "Holy climate change risk, Batman!" Despite the appearance, is it uniquely prone to flooding or storm surges?
- sebastiennight 3mo ago
  I came here looking for that information, as I was incredibly surprised to learn of nuclear energy existing in the Caribbean. 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"
  - rsync 3mo ago
    "... as I was incredibly surprised to learn of nuclear energy existing in the Caribbean ..." You may also find it interesting that South Africa had nuclear weapons: https://en.wikipedia.org/wiki/South_Africa_and_weapons_of_mass_destruction#Nuclear_weapons_production https://en.wikipedia.org/wiki/South_Africa_and_weapons_of_ma...
    - sebastiennight 3mo ago
      I knew about it, but your post is the first I've heard that SA no longer had those (I only clicked the link because you used the past tense!). I actually thought that no country had ever withdrawn their nuclear program. This might be the most amazing and hope-inspiring I've read online this week, so I'm grateful for you sharing that link!
CoryOndrejka 3mo ago
Dropped rods are an incident but one that occurs because of pressurized water reactors being very default safe. Controls rods are one way the criticality of a reactor is controlled and US reactors (in general) will go sub critical if even one rod is fully inserted into the core. You will likely have heard of a reactor scram (which goes back to the safety control rod ax man) where in an emergency, all the rods are dropped back into the core, greatly reducing its criticality. In some cases, an interruption of electrical power will cause a rod (or three) to drop accidentally. This is a "dropped rod" incident and will force a reactor shut down because it is now sub critical. 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.
- joebig 3mo ago
  I think you said it: it's a non-event. It's the reactor reactor-ing within the design basis. But, I think "single rod-drop" will not shut down a reactor. That's a crazy amount of rod-worth. My opinion is that reactor safe-shutdown margin entails "single rod-stuck" scram to be feasible.
  - MBCook 3mo ago
    > But, I think "single rod-drop" will not shut down a reactor 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.
    - s1artibartfast 3mo ago
      Why don't you just look it up instead of actively arguing an assumption? 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.
stevecoalbear 3mo ago
[flagged]
- slipperybeluga 3mo ago
  [dead]
- throwawaytemp29 3mo ago
  Um what?
asmodeuslucifer 3mo ago
At least they didn't make 300 square km uninhabitable. https://www.pref.fukushima.lg.jp/site/portal/kyoten-kuiki.html https://www.pref.fukushima.lg.jp/site/portal/kyoten-kuiki.ht... "Current Status: While "Difficult-to-Return Zones" still exist, decontamination and lifting of orders have reduced the designated area down to approximately 2.2% of the prefecture's total land area."
- deleted 3mo ago
  [deleted]
bcjdjsndon 3mo ago
3.6 rods? Not great but not terrible either
iambateman 3mo ago
If you've never seen the Smarter Every Day series on nuclear reactors[0], it's must-watch. It completely reshaped how I think about reactors. Tremendous respect for the people who work on those plants. [0] https://www.youtube.com/watch?v=v0afQ6w3Bjw&t=4007s https://www.youtube.com/watch?v=v0afQ6w3Bjw&t=4007s
- jezek2 3mo ago
  And here is a reaction by an actual nuclear engineer. He has many good reactions to other videos as well, not limited to just nuclear stuff. https://www.youtube.com/watch?v=Vncf70UBsr4 https://www.youtube.com/watch?v=Vncf70UBsr4
paulnpace 3mo ago
I liked it better in the olden days when the paper would print the location of the story at the beginning of the first paragraph.
- encomiast 3mo ago
  This is not a paper. This is local TV news: it says WPTV West Palm Beach in the top left. It also says it is converted from an on-air report. My hunch is their audience knows what they mean when they say St. Lucie. Still, it seams like it wouldn't hurt in cases like this where the story gains a wider audience.
  - kube-system 3mo ago
    These types of comments always come up when local TV news makes its way to a broader audience. Yes, the story was originally spoken out loud on a TV broadcast to an audience who knows what St. Lucie is. It is a global journalistic standard to explain where something happened in context to geography that the intended audience would understand. It would be really weird to watch local news if every story reiterated “this happened in West Palm Beach in the American state of Florida”. They don’t need to say that when everyone watching lives there. It’s only weird because we’re expecting everything on the internet to be written for a global audience. But really this is like going to a Chinese newspaper website and getting pissed off that it’s not in English. If you don’t understand, you’re not the intended audience.
LastTrain 3mo ago
Florida. RIP 5Ys.
jmward01 3mo ago
A challenge with news like this is there isn't an easy risk reference to put it into perspective. People only think of Chernobyl, Fukushima, 3-mile island, etc etc. We don't have something personal to relate it to to help us determine 'NBD, why is this a story?' or 'Wow! That was close!'. In everyday life I generally use driving to help me determine how risky something is. Driving is something most people do somewhat regularly and that we recognize as risky so we put controls on like training, regulations, special services, etc etc. Anything more risky than driving makes me really take notice. Anything less and I don't shrug it off, but I also don't get too worried. 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?'.
- deleted 3mo ago
  [deleted]
- Gud 3mo ago
  You only accept the risks of driving because its normalised in your community. In many communities, public transport is the norm and it would be considered foolish to hand over car keys to a majority of the population.
  - zamadatix 3mo ago
    Sure, but the news usually writes it in the relative terms of their viewership. It's alright it's not an absolute so as people can relate to where the news org would rank concerns relative to them.
- consensus1 3mo ago
  I'm pretty sure the context here would require college level courses plus industry training on operational procedures to actually understand in any meaningful sense. Not much different than any other time some safety feature triggers at any other highly complex and hazardous industrial facility. Except that in all those other cases the media ignores it and leaves it to the technical experts who do understand the context to sort it out, and everybody goes on with their lives never knowing about it. But since this particular highly complex and hazardous industrial facility is a nuclear power plant what we will get is journalists who know nothing about the subject screaming about it to millions of other people who know nothing about it who will assume it was a near miss on killing half the population of Florida.
codyswann 3mo ago
I live about four miles from the plant. I have not grown a second head... yet.
fuckyah 3mo ago
[dead]
ck2 3mo ago
better article * https://lakelandgazette.info/news/2026/08/16/st-lucie-nuclear-plant-unit-1-shut-down-after-rod-drop/ https://lakelandgazette.info/news/2026/08/16/st-lucie-nuclea... archive because the website is overwhelmed and down most of day: * What Happened: At 9:47 a.m. EDT, Unit 1 was operating at 100% power when three control rods (part of the Control Element Assemblies) fell into the core due to an equipment/control fault. * Operator Action: Under standard safety protocols, dropping multiple control rods alters the reactor’s core dynamics. Plant operators with Florida Power & Light (FPL) executed a manual reactor trip (scram) to safely halt the fission reaction. * Current Status: The trip was uncomplicated, and all safety systems responded normally. Operators stabilized the reactor in Mode 3 (Hot Standby), with decay heat safely being removed via steam discharge to the main condenser. Unit 2 was completely unaffected and continued running normally. The Nuclear Regulatory Commission (NRC) Resident Inspector was notified via standard 4-hour non-emergency reporting procedures. * Why Control Rods Matter Control rods absorb neutrons inside a reactor. Inserting them slows or stops the nuclear chain reaction. While a single dropped rod can often be managed by reducing turbine output, multiple dropped rods require an immediate shutdown to prevent uneven power distribution and localized overheating in the fuel assemblies. Gravity-assisted dropping is a fail-safe mechanism designed into commercial pressurized water reactors so that if power to the drive mechanisms is lost or faulted, the rods default to falling safely into the core.
imnotr0b0t 3mo ago
I have mixed feelings. It seems like nothing serious happened, no one was hurt, and all the systems worked, but on the other hand, this is still an emergency. Why did those rods fall in the first place?
- MBCook 3mo ago
  The rods prevent an emergency. They’re a fail-safe. 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.
- hnuser123456 3mo ago
  The rod holding mechanisms require active power to hold the rods out of the reactor. It sounds like once in a while, a rod accidentally drops, which is infinitely preferable to the alternative, of once in a while a rod failing to drop. But that unplanned adjustment to reactivity means, you don't want to simply use other means to boost the reactivity back up (like reducing boric acid in the water), because once you get the rod back out, it'll be too reactive. So they insert a couple more rods and call it a shutdown to take a few days or weeks to investigate and perform maintenance. Sounds like this is a highly planned for and fairly routine procedure, if not ideal. I'm sure they'll find a couple reasons why the rod unexpectedly dropped, and make changes to prevent an identical incident in the future.
- deleted 3mo ago
  [deleted]
- hrldcpr 3mo ago
  Sounds like the Nuclear Regulatory Commission explicitly categorized it as a "non-emergency"
- briandw 3mo ago
  This isn't even worthy of a news article. Nothing of consequence happened. It's only news because the media loves to scare people. Does a gas plant breaking or shutting down deserve a big media presence? No? Then this shouldn't either.
scythe 3mo ago
Apparently people surf at the beach near this reactor. I never went there when I lived in Florida, but my dad told me about it.
andybak 3mo ago
Is this another post title that was mangled into ambiguity because of trying to hit the arbitrary HN word count restriction?
rglover 3mo ago
This graphic [1] may help others to understand this was normal behavior and what exactly took place. An actual engineer would have to confirm but from other comments this appears mostly accurate. [1] https://chatgpt.com/s/m_6a82114f63a481919380c5f1e2b432e8 https://chatgpt.com/s/m_6a82114f63a481919380c5f1e2b432e8
deleted 3mo ago
[deleted]
beloch 3mo ago
What's probably more interesting than the incident itself is that it elicited well over a hundred comments on this site. Explosions happen at natural gas plants semi-frequently, few make the news, and fewer still are likely to get much attention here.
- Mawr 3mo ago
  It's standard human bias — a plane falling out of the sky with 200 people on it once a year is a major catastrophe we all know about within hours, but 40_000 people dying per year in road accidents is just a statistic. Besides, driving can't be all that unsafe — I do it every day and I'm fine! Similarly here: something irrelevant happened at a nuclear power plant? PANIC! But 100_000 people died last year from coal plants dumping their waste products into the air we all breathe? Meh, who cares, how boring.
  - butvacuum 3mo ago
    A more accurate one: Comanche Peak Unit 1 SCRAM'd because the 2021 snowpocolypse caused a feed water issue... Good luck finding that as more than a footnote. source: https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2021/20210215en https://www.nrc.gov/reading-rm/doc-collections/event-status/...
- deleted 2mo ago
  [deleted]
MaintenanceMode 3mo ago
I guess everyone in west palm beach is nuclear reactor specialist according to this tv station’s reporting.
throwaway2037 2mo ago
Did anyone else see the footer for the article? > This story was reported on-air by a journalist and has been converted to this platform with the assistance of AI. Very cool! It probably helps these local TV stations to better monetize their on-air content by making it available in text.

196 points by toomuchtodo 3mo ago

stmw 3mo ago

To rephrase it: nothing happened, and reactor is back online generating clean electricity. This is the equivalent of a Kubernetes pod restarting.

high_na_euv 3mo ago

Why they dropped?

toomuchtodo 3mo ago
I was unable to find the NRC filling, if someone finds the link to it, please drop a reply with it. This is potentially interesting as this reactor recently had its operating license extended earlier in the year.
- OJFord 3mo ago
  https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2026/20260814en https://www.nrc.gov/reading-rm/doc-collections/event-status/... Event 58408, 'manual reactor trip'.
mpyne 3mo ago
Perhaps an interruption of power to the field windings of the affected control rods. Could be as simple as a control cabinet fried unexpectedly or some other electrical gremlin. 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.
- bob1029 3mo ago
  This could be an intentional design feature regarding power loss to critical reactor control systems. 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.
  - mpyne 3mo ago
    Yeah, on one of the reactor designs I was familiar with, control rods were bundled into groups which were managed as a set and were intended to be operated in different sequences over core life. 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.

Abh1Works 3mo ago

this is really interesting

AndrewKemendo 3mo ago

It’s great that nuclear power safety events are so well managed that nearly 100% of events go completely unnoticed by the public. Unironically this is the kind of headline I’m expecting in 2040 about one or more major AGI systems running an electrical grid, factory or similar.

stefantalpalaru 3mo ago
[dead]
bigyabai 3mo ago
I doubt AGI will be used for life-or-death systems like that if it resembles anything like the LLMs of today. Systems at that scale are about risk management, and everything we know about AI suggests that it cannot mitigate risk at all. All AI is seemingly a net-positive risk factor. 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.
- mlyle 3mo ago
  The way I read it was that he expects large industrial systems with AI to have safeguards to "fail closed." 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.
  - AndrewKemendo 3mo ago
    Correct interpretation
    - bigyabai 3mo ago
      So, which do we choose? 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.

ImOssir 3mo ago

I wonder why so much repetition in the article. Do they have word limit to hit? I wish it have provided some reasons on this

verytrivial 3mo ago
From the article: "This story was reported on-air by a journalist and has been converted to this platform with the assistance of AI. [...]"

ck2 3mo ago

for "reasons" that they carefully left out? Florida should be added to title, it's not like the European shutdowns for overheating

mlyle 3mo ago
No one knows the reasons yet. 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.
preisschild 3mo ago
could have been something as minor as some sensor malfunctioning.
chpatrick 3mo ago
Overheating isn't exactly right, they got shut down because they couldn't be cooled, but they didn't overheat.
redsocksfan45 3mo ago
[dead]

fwipsy 3mo ago

https://www.nuclear-power.com/nuclear-power/reactor-physics/nuclear-safety/level-2-abnormal-operation/control-rod-drop-pwr/ https://www.nuclear-power.com/nuclear-power/reactor-physics/... 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.

mlyle 3mo ago
Yup. Often one rod fully in is no big deal -- it has been analyzed and you keep operating. But no one has certified to run the reactor with a few rods fully in. 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.
solarkraft 3mo ago
> 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 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.
- s1artibartfast 3mo ago
  You should write them an email suggesting they try to prevent unintended rod drops
  - 3mo ago

verytrivial 3mo ago

This "dropping" activity is not defined well in the context. Was it e.g. a controlled but uncommanded insertion? Or did something or some three things slip, snap, or something else? Can the rods be retrieved using BAU procedures, or is reactor in an annoying state now? The details divulged seems to have been driven by event reporting regulations, not any specific news gathering or investigation, right?

jcrawfordor 3mo ago
This article is just an over length summary of a very short preliminary notice published by NRC. Since it is non-emergency there will not necessarily be much follow up either, plants are just required to report any abnormality to NRC which publishes the reports online. Most of these reports are, like, procedural problems in employee drug testing. 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.

aeonik 3mo ago

This happened in 2024 too. 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/event/2024/20241115en 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-lucie-ler-multiple-control-rod-drop-share-7288007676314238976-I1TW/ 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.

robocat 3mo ago
Relevant 2024 excerpt from linkedin link: double hold was placed on Subgroup 4 resulting in the associated control rod lower grippers being engaged prior to removing the upper gripper drawer. After successful replacement of the UG coil CPMD the double hold was removed, per 2-NOP-99.07, and CEAs 43, 45, and 49 fell and fully inserted into the core. CEA means Control Element Assembly. A CEA is a group of control rods that can be inserted into or withdrawn from a reactor core

julienchastang 3mo ago

I actually thought they were talking about the island in the Caribbean since Florida is not mentioned in the article. Anyway, in case you did not know, the reactor in question is in Florida: https://en.wikipedia.org/wiki/St._Lucie_Nuclear_Power_Plant https://en.wikipedia.org/wiki/St._Lucie_Nuclear_Power_Plant

ashleyn 3mo ago
I can't be the only one to see that location and think "Holy climate change risk, Batman!" Despite the appearance, is it uniquely prone to flooding or storm surges?
sebastiennight 3mo ago
I came here looking for that information, as I was incredibly surprised to learn of nuclear energy existing in the Caribbean. 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"
- rsync 3mo ago
  "... as I was incredibly surprised to learn of nuclear energy existing in the Caribbean ..." You may also find it interesting that South Africa had nuclear weapons: https://en.wikipedia.org/wiki/South_Africa_and_weapons_of_mass_destruction#Nuclear_weapons_production https://en.wikipedia.org/wiki/South_Africa_and_weapons_of_ma...
  - sebastiennight 3mo ago
    I knew about it, but your post is the first I've heard that SA no longer had those (I only clicked the link because you used the past tense!). I actually thought that no country had ever withdrawn their nuclear program. This might be the most amazing and hope-inspiring I've read online this week, so I'm grateful for you sharing that link!

CoryOndrejka 3mo ago

Dropped rods are an incident but one that occurs because of pressurized water reactors being very default safe. Controls rods are one way the criticality of a reactor is controlled and US reactors (in general) will go sub critical if even one rod is fully inserted into the core. You will likely have heard of a reactor scram (which goes back to the safety control rod ax man) where in an emergency, all the rods are dropped back into the core, greatly reducing its criticality. In some cases, an interruption of electrical power will cause a rod (or three) to drop accidentally. This is a "dropped rod" incident and will force a reactor shut down because it is now sub critical. 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.

joebig 3mo ago
I think you said it: it's a non-event. It's the reactor reactor-ing within the design basis. But, I think "single rod-drop" will not shut down a reactor. That's a crazy amount of rod-worth. My opinion is that reactor safe-shutdown margin entails "single rod-stuck" scram to be feasible.
- MBCook 3mo ago
  > But, I think "single rod-drop" will not shut down a reactor 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.
  - s1artibartfast 3mo ago
    Why don't you just look it up instead of actively arguing an assumption? 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.

stevecoalbear 3mo ago

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slipperybeluga 3mo ago
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throwawaytemp29 3mo ago
Um what?

asmodeuslucifer 3mo ago

At least they didn't make 300 square km uninhabitable. https://www.pref.fukushima.lg.jp/site/portal/kyoten-kuiki.html https://www.pref.fukushima.lg.jp/site/portal/kyoten-kuiki.ht... "Current Status: While "Difficult-to-Return Zones" still exist, decontamination and lifting of orders have reduced the designated area down to approximately 2.2% of the prefecture's total land area."

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bcjdjsndon 3mo ago

3.6 rods? Not great but not terrible either

iambateman 3mo ago

If you've never seen the Smarter Every Day series on nuclear reactors[0], it's must-watch. It completely reshaped how I think about reactors. Tremendous respect for the people who work on those plants. [0] https://www.youtube.com/watch?v=v0afQ6w3Bjw&t=4007s https://www.youtube.com/watch?v=v0afQ6w3Bjw&t=4007s

jezek2 3mo ago
And here is a reaction by an actual nuclear engineer. He has many good reactions to other videos as well, not limited to just nuclear stuff. https://www.youtube.com/watch?v=Vncf70UBsr4 https://www.youtube.com/watch?v=Vncf70UBsr4

paulnpace 3mo ago

I liked it better in the olden days when the paper would print the location of the story at the beginning of the first paragraph.

encomiast 3mo ago
This is not a paper. This is local TV news: it says WPTV West Palm Beach in the top left. It also says it is converted from an on-air report. My hunch is their audience knows what they mean when they say St. Lucie. Still, it seams like it wouldn't hurt in cases like this where the story gains a wider audience.
- kube-system 3mo ago
  These types of comments always come up when local TV news makes its way to a broader audience. Yes, the story was originally spoken out loud on a TV broadcast to an audience who knows what St. Lucie is. It is a global journalistic standard to explain where something happened in context to geography that the intended audience would understand. It would be really weird to watch local news if every story reiterated “this happened in West Palm Beach in the American state of Florida”. They don’t need to say that when everyone watching lives there. It’s only weird because we’re expecting everything on the internet to be written for a global audience. But really this is like going to a Chinese newspaper website and getting pissed off that it’s not in English. If you don’t understand, you’re not the intended audience.

LastTrain 3mo ago

Florida. RIP 5Ys.

jmward01 3mo ago

A challenge with news like this is there isn't an easy risk reference to put it into perspective. People only think of Chernobyl, Fukushima, 3-mile island, etc etc. We don't have something personal to relate it to to help us determine 'NBD, why is this a story?' or 'Wow! That was close!'. In everyday life I generally use driving to help me determine how risky something is. Driving is something most people do somewhat regularly and that we recognize as risky so we put controls on like training, regulations, special services, etc etc. Anything more risky than driving makes me really take notice. Anything less and I don't shrug it off, but I also don't get too worried. 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?'.

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Gud 3mo ago
You only accept the risks of driving because its normalised in your community. In many communities, public transport is the norm and it would be considered foolish to hand over car keys to a majority of the population.
- zamadatix 3mo ago
  Sure, but the news usually writes it in the relative terms of their viewership. It's alright it's not an absolute so as people can relate to where the news org would rank concerns relative to them.
consensus1 3mo ago
I'm pretty sure the context here would require college level courses plus industry training on operational procedures to actually understand in any meaningful sense. Not much different than any other time some safety feature triggers at any other highly complex and hazardous industrial facility. Except that in all those other cases the media ignores it and leaves it to the technical experts who do understand the context to sort it out, and everybody goes on with their lives never knowing about it. But since this particular highly complex and hazardous industrial facility is a nuclear power plant what we will get is journalists who know nothing about the subject screaming about it to millions of other people who know nothing about it who will assume it was a near miss on killing half the population of Florida.

codyswann 3mo ago

I live about four miles from the plant. I have not grown a second head... yet.

fuckyah 3mo ago

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ck2 3mo ago

better article * https://lakelandgazette.info/news/2026/08/16/st-lucie-nuclear-plant-unit-1-shut-down-after-rod-drop/ https://lakelandgazette.info/news/2026/08/16/st-lucie-nuclea... archive because the website is overwhelmed and down most of day: * What Happened: At 9:47 a.m. EDT, Unit 1 was operating at 100% power when three control rods (part of the Control Element Assemblies) fell into the core due to an equipment/control fault. * Operator Action: Under standard safety protocols, dropping multiple control rods alters the reactor’s core dynamics. Plant operators with Florida Power & Light (FPL) executed a manual reactor trip (scram) to safely halt the fission reaction. * Current Status: The trip was uncomplicated, and all safety systems responded normally. Operators stabilized the reactor in Mode 3 (Hot Standby), with decay heat safely being removed via steam discharge to the main condenser. Unit 2 was completely unaffected and continued running normally. The Nuclear Regulatory Commission (NRC) Resident Inspector was notified via standard 4-hour non-emergency reporting procedures. * Why Control Rods Matter Control rods absorb neutrons inside a reactor. Inserting them slows or stops the nuclear chain reaction. While a single dropped rod can often be managed by reducing turbine output, multiple dropped rods require an immediate shutdown to prevent uneven power distribution and localized overheating in the fuel assemblies. Gravity-assisted dropping is a fail-safe mechanism designed into commercial pressurized water reactors so that if power to the drive mechanisms is lost or faulted, the rods default to falling safely into the core.

imnotr0b0t 3mo ago

I have mixed feelings. It seems like nothing serious happened, no one was hurt, and all the systems worked, but on the other hand, this is still an emergency. Why did those rods fall in the first place?

MBCook 3mo ago
The rods prevent an emergency. They’re a fail-safe. 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.
hnuser123456 3mo ago
The rod holding mechanisms require active power to hold the rods out of the reactor. It sounds like once in a while, a rod accidentally drops, which is infinitely preferable to the alternative, of once in a while a rod failing to drop. But that unplanned adjustment to reactivity means, you don't want to simply use other means to boost the reactivity back up (like reducing boric acid in the water), because once you get the rod back out, it'll be too reactive. So they insert a couple more rods and call it a shutdown to take a few days or weeks to investigate and perform maintenance. Sounds like this is a highly planned for and fairly routine procedure, if not ideal. I'm sure they'll find a couple reasons why the rod unexpectedly dropped, and make changes to prevent an identical incident in the future.
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hrldcpr 3mo ago
Sounds like the Nuclear Regulatory Commission explicitly categorized it as a "non-emergency"
briandw 3mo ago
This isn't even worthy of a news article. Nothing of consequence happened. It's only news because the media loves to scare people. Does a gas plant breaking or shutting down deserve a big media presence? No? Then this shouldn't either.

scythe 3mo ago

Apparently people surf at the beach near this reactor. I never went there when I lived in Florida, but my dad told me about it.

andybak 3mo ago

Is this another post title that was mangled into ambiguity because of trying to hit the arbitrary HN word count restriction?

rglover 3mo ago

This graphic [1] may help others to understand this was normal behavior and what exactly took place. An actual engineer would have to confirm but from other comments this appears mostly accurate. [1] https://chatgpt.com/s/m_6a82114f63a481919380c5f1e2b432e8 https://chatgpt.com/s/m_6a82114f63a481919380c5f1e2b432e8

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beloch 3mo ago

What's probably more interesting than the incident itself is that it elicited well over a hundred comments on this site. Explosions happen at natural gas plants semi-frequently, few make the news, and fewer still are likely to get much attention here.

Mawr 3mo ago
It's standard human bias — a plane falling out of the sky with 200 people on it once a year is a major catastrophe we all know about within hours, but 40_000 people dying per year in road accidents is just a statistic. Besides, driving can't be all that unsafe — I do it every day and I'm fine! Similarly here: something irrelevant happened at a nuclear power plant? PANIC! But 100_000 people died last year from coal plants dumping their waste products into the air we all breathe? Meh, who cares, how boring.
- butvacuum 3mo ago
  A more accurate one: Comanche Peak Unit 1 SCRAM'd because the 2021 snowpocolypse caused a feed water issue... Good luck finding that as more than a footnote. source: https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2021/20210215en https://www.nrc.gov/reading-rm/doc-collections/event-status/...
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MaintenanceMode 3mo ago

I guess everyone in west palm beach is nuclear reactor specialist according to this tv station’s reporting.

throwaway2037 2mo ago

Did anyone else see the footer for the article? > This story was reported on-air by a journalist and has been converted to this platform with the assistance of AI. Very cool! It probably helps these local TV stations to better monetize their on-air content by making it available in text.