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.
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, nothing bad happened" doesnt quite hit the mark.
It's one of the more truthy backronyms. There was an actual ax man with an ax whose job was to cut a rope to let loose the control rods, and they did use the (existing, apt) word scram for the emergency procedure: https://en.wikipedia.org/wiki/Scram
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.
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.
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.
> 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.
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
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?
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.
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.
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.
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.
That assumes people mistrust LLM output, which is a perspective inside the HN bubble.
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.)
"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."
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.
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, nothing bad happened" 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.
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.
Despite the appearance, is it uniquely prone to flooding or storm surges?
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.
This is potentially interesting as this reactor recently had its operating license extended earlier in the year.
Event 58408, 'manual reactor trip'.
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.
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.
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.
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.)
Florida should be added to title, it's not like the European shutdowns for overheating
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.
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."