A worker fell into a nuclear reactor pool

https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2025/20251022en?brid=vscAjql9kZL1FfGE7TYHVw#en57996:~:text=TRANSPORT%20OF%20CONTAMINATED%20PERSON%20OFFSITE

by nvahalik • 9 months ago

689 491 9 months ago

nrc.gov

piinbinary• 9 months ago

Does anyone have a sense for how significant of a dose of radiation this person got?

kibwen• 9 months ago

If it was just swimming in it that would be one thing. Ingesting the water could be very bad, depending on what's in it.

PaulHoule2• 9 months ago

They keep the water in an LWR pretty clean to avoid corrosion problems. Thing is the slightest almost of tritium in the water will light up a portal detector like a pinball machine on tilt.

tofof• 9 months ago

Radiation units are fiendishly tricky to convert between. Here, the only indication is that after decontamination their hair was still reading 300 counts per minute. CPM are instrument-specific and doesn't mean that's the correct number of disintegrations per second, nor easily converted to absorbed dose units, and this is after decontamination, and disregarding the amount of water they ingested.

All that disclaimer aside: a banana produces about 15 Bq (which is s^-1), i.e. 900 cpm.

ls612• 9 months ago

Water is a pretty good radiation shield so probably not too much. Certainly not good for your health but probably not seriously threatening.

specialp• 9 months ago

Not at all. My scintillating counter will do 300 cpm as background. The most concerning thing here will be the ingestion of the water. Even low level emitters can be very bad when the are inside the body

jcrawfordor• 9 months ago

I'm not an expert in this topic but I've been working on a book in a related area and had to learn a lot. Here's what I can figure.

Unfortunately radiation medicine is pretty complicated and the report gives us very little info, presumably mostly because they don't have very much info. It will take some time and effort to establish more.

What we do know is that they measured 300 CPM at the person's hair, which was probably where they expected the highest count due to absorbed water (likely clothing was already stripped at this point). CPM is a tricky unit because it is something like the "raw" value from the instrument, the literal number of counts from the tube, and determining more absolute metrics like activity and dose requires knowing the calibration of the meter. The annoying thing here is that radiation protection professionals will still sometimes just write CPM because for a lot of applications there's only one or a handful of instruments approved and they tend to figure the reader knows which instrument they have. Frustrating. Still, for the common LND7311 tube and Cs137, 300CPM is a little below 1 uSv/hr. That wouldn't equate to any meaningful risk (a common rule of thumb is that a couple mSv is typical annual background exposure). However, for a less sensitive detector, the dose could be much higher (LND7311 is often used in pancake probes for frisking because it is very sensitive and just background is often hundreds of CPM). Someone who knows NRC practices better might know what detector would be used here.

That said the field dose here is really not the concern, committed dose from ingesting the water is. Ingesting radioactive material is extremely dangerous because, depending on the specific isotopes involved, it can persist in the body for a very long time and accumulate in specific organs. Unfortunately it is also difficult to assess. This person will likely go to a hospital with a specialty center equipped with a full body counter, and counts will also be taken on blood samples. These are ways of estimating the amount of radioactive isotopes in the body. In some cases tissue samples of specific organs may be taken.

I believe that the cavity pool water would be "clean" other than induced radioactivity (activation products from being bombarded by radiation). Because water shields so well the pool should not be that "hot" from this process. Most of those products have short half-lives which, on the one hand, means that they deliver a higher dose over a shorter period of time---but also means they will not longer forever and are less likely to be a chronic problem if they are not an acute one.

I suspect this will get some press coverage and we will perhaps learn more about the patient's state.

Another way we can get at this question is by the bureaucracy of the notification. An 8-hour notification as done here is required in relatively minor cases. Usually for a "big deal emergency" a one-hour notification is required. The definition of such an emergency depends on the site emergency plan but I think acute radiation exposure to a worker would generally qualify.

numpad0• 9 months ago

"count" is that classical Geiger click, so 300 per minute is constant 5/sec gggggggg going on, which sounds bad but we don't know. They're boolean and also equipment dependent.

As others had said, more alarming part is that they ingested the water, which could go like defected Russian spy Alexander Litvinenko. But it could also be like man eating few bananas seasoned with expired Himalayan salt. The report just doesn't say how much of what was ingested.

Hobadee• 9 months ago

I have SOOO many questions, and this report answers SOOO few of them.

hshdhdhehd4• 9 months ago

Like what is a reactor cavity? HN title makes it sound like they fell into the reactor but maybe this is some sort of moat or something? what did they fall into and why?

PaulHoule2• 9 months ago

Almost certainly a refueling outage, this video will give you a good image of it

https://www.youtube.com/watch?v=IoCfapqYy00

JasonSage• 9 months ago

My question is what happened between when they went in the water and when they got off-site medical treatment. 7 hours seems like a long time. Is there on-site medical that would be doing something during that time?

_qua3• 9 months ago

Realistically, there is little to do besides decontamination which I'm sure they're equipped to do on site.

analog31• 9 months ago

Anecdote: My house mate in grad school was working in a national lab when an experiment caught fire and the fire consumed a certain amount of radioactive material. (Tiny little buttons used for calibrating detectors). He was on shift and was the person who discovered the fire and pulled the alarm.

Among other things, he had to sit inside an enclosure made of scintillator material for a period of time, to make sure he wasn't contaminated. Then he also got blood tests for heavy metals etc. They pretty much went by the book for all of these tests.

Also, the facility is the only place that's equipped for this kind of situation.

slicktux2• 9 months ago

It’s a process to come into a high radiation area, as well as, a process to come out; I’m sure the worker was not injured so they processed he/she out and decontaminated the individual and did a whole body count. Then release him to medical for evaluation…which in itself is a process.

christina97• 9 months ago

Relevant xkcd content: https://what-if.xkcd.com/29/

parker-3461• 9 months ago

So if I understand this correctly (solely from reading the xkcd), then the person might actually be okay?

LeifCarrotson• 9 months ago

They're totally fine.

I find it highly informative that the required PPE for working in that location is a life jacket so you float in case you fall in, rather than a tether and fall arrest harness so that it's not possible to fall in.

300 CPM is nothing, background levels might be 150.

kevincox4• 9 months ago

Plant officials today confirmed the worker sustained minor injuries from the fall and has already returned to work. - https://www.mlive.com/news/2025/10/michigan-nuclear-plant-wo...

He went back to work the next day. They don't provide much detail about the minor injuries but it seems that the biggest issue is maybe a bruised shin from the fall.

arresin2• 9 months ago

You may actually receive a lower dose of radiation treading water in a spent fuel pool than walking around on the street.

Wow

sparky_z2• 9 months ago

Is it relevant? It's writing about a pool for storing spent fuel, which is not a part of the actual reactor system.

  This incident report says that the worker fell into a "reactor cavity" containing water and that there was a measurable amount of radiation detected in their hair after the initial clean-up. The two situations don't seem remotely compatible to me.

drysart3• 9 months ago

I guarantee you there's 'a measurable amount of radiation' in your hair right now. Unless you're bald, I suppose.

lisper2• 9 months ago

And a video: https://www.youtube.com/watch?v=EFRUL7vKdU8

nojs• 9 months ago

Apparently it’s fine according to this xkcd: https://youtu.be/EFRUL7vKdU8

Centigonal3• 9 months ago

It's the reactor cavity in this case, not a nuclear waste storage pool.

mlindner4• 9 months ago

How is that different from the accident point of view. They're both quite radioactive and both sit in deep pools of water.

tapland• 9 months ago

Doesn’t seem like the same pool if you measure 300 counts/min from their hair afterwards.

hshdhdhehd4• 9 months ago

That makes it sound like a feature! Might get some rods for my pool to keep her warm.

hshdhdhehd4• 9 months ago

Non Emergency

I guess in a nuclear reactor there is a lingual shift and the word emergency cant be used for just any old 911 call.

Like how Australians apparently call a jellyfish bite "uncomfortable"

anakaine• 9 months ago

Aussie surfer here, the stings typically are uncomfortable. Some of the deadlier ones can be close to painless and only result in itching and result in you dying from respiratory failure 24 hours later. Others are downright painful with even strong opiate based pain killers struggling to cut through the pain.

cal_dent• 9 months ago

Hahaha eeesh that 2nd sentence took a turn

viraptor3• 9 months ago

Also it's in a way normalised to happen in a few places with beaches. There are vinegar stations every 100m or so. Basically a "yes, it will happen to a few of you".

https://www.reddit.com/media?url=https%3A%2F%2Fexternal-prev...

noduerme• 9 months ago

Is the deadly itchy one of those tiny box jellyfish? More than sharks or crocs, this is why I was an absolute coward and decided not to get in the water in Queensland. There are lots of ways to die, but I'd prefer not to blame myself in my last moments.

foobar1962• 9 months ago

A bite requires teeth. Sharks bite. Snakes bite. Bees and wasps sting. Jellyfish and bluebottles sting.

Not sure about spiders. Are their fangs considered to be teeth? Platypus have venomous spurs, not sure what that’s called.

doubled112• 9 months ago

Spiders bite. I've never heard it called anything else.

KPGv2• 9 months ago

Spiders bite with their fangs, much like vampires bite with their fangs, they don't sting. I might call the tarantula "hair" that makes you itch a sting, but I would feel a bit silly calling it that.

dlcarrier5• 9 months ago

Mosquitos bite with their nose.

loeg3• 9 months ago

Nah this is literally just not an emergency. The water isn't very radioactive.

thayne2• 9 months ago

It isn't an emergency. It was an accident that required medical attention.

If you fell in a lake and accidentally ingested some wayer known to contain some pathagen dangerous to humans, you might seek medical care, but I don't think most people would consider that an emergency. This is similar.

throwawaymaths• 9 months ago

i mean it might be a medical emergency but not a reactor emergency?

dlcarrier5• 9 months ago

Or how Brits call a civil war "trouble"

louthy2• 9 months ago

We’re not that flippant, they’re ‘troubles’, indicating ’ongoing concern’.

kmacdough• 9 months ago

There's no significant immediate threat to life or well-being. It's simply not an emergency. We're all constantly exposed to some ionizing radiation. It's a question of how much.

In this case, not much. It's still an exposure event and absolutely worth giving medical attention to assess continued exposure levels from ingested contamination and generally be overly cautious. But that doesn't mean it's ultimately going to be a significant factor in this workers risk for radiation induced disease. It's certainly better than living in the vicinity of coal mining and processing plants.

jasonjmcghee• 9 months ago

Obligatory xkcd (ish)

https://what-if.xkcd.com/29/

tt_dev• 9 months ago

This is bad but cavity water radiation is usually very weak. Ingestion could be bad but its not like he swallowed a uranium isotope which would be catastrophic.

IlikeKitties• 9 months ago

The Uranium Isotopes would also not be that terrible. It's the fission products that get you.

mlindner4• 9 months ago

I wouldn't even call it bad. Reactor pools have basically zero radiation at the surface. The water is constantly filtered and kept very pure to remove contaminants that can be activated by neutrons.

Even drinking it I would think would be completely fine. The water itself doesn't get activated.

happyopossum• 9 months ago

Then where did their radioactive hair come from?

jojobas3• 9 months ago

Water itself is activated by neutrons, even if slightly.

golem14• 9 months ago

Obligatory what-if:

https://what-if.xkcd.com/29/

nashashmi• 9 months ago

Is it not Heavy Water?

robocat• 9 months ago

FYI:

  the primary hazard from acute, high-dose uranium ingestion is chemical toxicity leading to acute kidney failure (nephrotoxicity), not radiation.

anothernewdude• 9 months ago

Fuck me, is there anything fun that isn't nephrotoxic?

yread• 9 months ago

Sounds like it was a lot more serious for the water than for the worker

sigmar• 9 months ago

It doesn't say worker, just "person." I could understand falling in with some freak accident where you trip. But they ingested the water?!

pixl97• 9 months ago

I mean that's something that happens commonly when people fall into things like pools. When you jump into a pool you tend to take a breath before you do so, so you don't suck in water. When you fall into water it's much more common for people to aspirate or swallow water from the surprise.

viraptor3• 9 months ago

Depending on a velocity, it also doesn't matter if you took a breath or not. Fall in quickly enough and at just the right angle (you can even do that from a fast water slide) and the water will be forced through your nose into lungs/stomach. (Unless you hold it closed)

rtpg• 9 months ago

probably likely just a thing that happens when you suddenly fall into a pool of water?

andy993• 9 months ago

Knowing nothing about nuclear reactor design, why would there ever be a dangerous pool that people could walk by that wasn’t covered? Hard to believe it’s like some kind of Bond villain complex with open pools everywhere. This must have been in the course of some kind of servicing that required opening something that normally stays closed?

donatj• 9 months ago

Because it's generally speaking, not that dangerous. Water is very good at blocking radiation. That's part of the reason why the pool is filled with it to begin with.

forthac• 9 months ago

They typically have a railing around them. The circumstances of this incident are unknown beyond a small set of details. The report indicates that the person who fell was wearing a life vest, it is likely they were doing work around the pool beyond the normal safety barriers.

bmacho• 9 months ago

Huh why not. It's far less dangerous than, say, a train station or a viewpoint where everyone can just jump and die. Many reactors are open for kids and class trips where everyone can stare into a reactor

_qua3• 9 months ago

Not a good place to be a klutz!

hammock• 9 months ago

When I was a kid I was amazed at how many of the other kids would take pool water in their mouth and drool it out, simply as a normal part of their treading water. I thought they were weird for this but it was really about 1 out of every 3 or 4 kids I noticed that did this.

0xDEAFBEAD2• 9 months ago

Your periodic reminder that coal is deadlier than nuclear.

https://cns.utexas.edu/news/research/coal-power-killed-half-...

arresin2• 9 months ago

More radiation released also which is hard to get your head around.

Zak• 9 months ago

Not really hard: nuclear power generation uses radiation and radioactive material, but tries very hard not to release it. Coal power generation burns a substance that contains a small amount of radioactive material, and makes no effort not to release radiation.

mlindner4• 9 months ago

It's not that surprising. We're burning a rock we dug out of the ground and turning it into a vapor. Rocks found underground contain some amount of natural radioactive material, for example granite/marble tend to be higher in radiation. If you burn that into a powder and put it into the atmosphere it'll spread around and expose the nearby area to very slightly radioactive pollution.

_qua3• 9 months ago

Interesting page overall. Didn't realize reactors get scrammed that often.

fwlr• 9 months ago

Scrolling up and down the list, just how onerous is this reporting regulation? It seems almost cartoonishly excessive, even for critical safety applications.

aaomidi• 9 months ago

Having the infrastructure for reporting incidents is the expensive part.

Doing it often doesn’t really add to the cost. More reporting is helpful because it explicitly makes it clear even operational issues can have lessons to be learned from. It also keeps the reporting system running and operationally well maintained.

WebPKI does this as well.

ang_cire4• 9 months ago

Literally no amount of incident reporting is excessive when it comes to nuclear power. Not just because of the safety of the plant itself, but because so much is reliant on it.

It's important to identify even small defects or incidents so that patterns can be noticed before they turn into larger issues. You see the same breaker tripping at 3x the rate of other ones, and even though maybe nothing was damaged you now know there's something to investigate.

pembrook4• 9 months ago

Aaaand it’s this alarmist attitude which is why we don’t have abundant cheap nuclear energy.

Sea-drilling rigs (oil) have far more potential for environmental damage than modern nuclear plants

Yet they have no federal public register for when a worker falls overboard (an incident far more likely to result in death).

iamronaldo• 9 months ago

https://what-if.xkcd.com/29/

thret• 9 months ago

This may be the most relevant xkcd yet. It answered all questions I had about this, thank you.

lisper2• 9 months ago

And a video version:

https://www.youtube.com/watch?v=EFRUL7vKdU8&t=11s

BobbyTables2• 9 months ago

Obligatory XKCD: https://what-if.xkcd.com/29/

(Not exactly same but close)

Animats• 9 months ago

Palisades MI reactor. Currently shut down and de-fueled but a restart of this reactor is apparently underway, with new fuel assemblies being delivered.[1]

Worker was wearing a life vest.[2]

[1] https://en.wikipedia.org/wiki/Palisades_Nuclear_Generating_S...

[2] https://www.mlive.com/news/2025/10/michigan-nuclear-plant-wo...

croemer• 9 months ago

Archive of [2] (blocked me): https://archive.ph/0pzuY

wiz21c2• 9 months ago

dunno if the life vest bit comment of yours was sarcastic, but it is a funny remark for sure :-)

it sounds like "guy felt down in a volcano, but fortunately, he had a life vest"

tialaramex2• 9 months ago

Rather more like "Guy fell over looking into the volcano but fortunately there's a metal fence". The most immediate danger to you is that you'll drown because radioactive water is water and you can't breathe. So the life vest avoids this. In contrast volcanic lava absolutely can kill you before you drown, no problem.

Yes, radioactivity isn't good. You should not, for example, drink this water, or swim in it once a week for good luck. But, it isn't magic death fluid, the worker will have been decontaminated - destroying clothing, washing skin and so on, and the additional exposure means they might get more monitoring, but they're probably fine.

afiori2• 9 months ago

My understanding is that reactor and waste pools are some of the least radioactive environments as they are constantly monitored for leakage.

tarruda• 9 months ago

dunno if the life vest bit comment of yours was sarcastic, but it is a funny remark for sure :-)

It was a quote of the linked article:

"Holtec International, which owns the closed nuclear facility, reported the worker was a contractor who was wearing all required personal protective equipment, including a life vest while working near the pool without a barrier in place."

cedilla• 9 months ago

If you work near water you should be wearing a life vest. Especially if it's an area that may be hard to get to or where other dangers are around or if you're alone.

ikari_pl• 9 months ago

it's actually important - close to the surface, the radiation should be mostly all filtered out by the water already.

the deeper you get, the worse for you. I assume the first second was critical.

nkrisc• 9 months ago

Anyone working around a large pool of deep water should be wearing a personal floatation device.

He was not working in a volcano.

haskellshill8• 9 months ago

Wow, people are really clueless about how nuclear power plants really work. It's really not that dangerous to fall into the water.

zamalek• 9 months ago

Your radiation exposure next to a coal power plant (thorium in ash) is significantly higher than a nuclear power plant (background radiation). I imagine this is much the same.

benmathes• 9 months ago

XKCD has a good video about this. The top of the water is remarkably safe, and a life vest would keep you up there! https://www.youtube.com/watch?v=EFRUL7vKdU8

slicktux2• 9 months ago

I’ve heard of people falling into the spent fuel pool but never the reactor pool. Usually there are strict FME barriers in place and one cannot even look over into the pool without violating the FME. I wonder what led to the event? Definitely an OSHA recordable!

feminintendo• 9 months ago

This is not true at all. I have personally looked into a reactor pool. I remember thinking how easy it would be to literally just jump in. I mean, I'd trip about a thousand alarms and probably end up in prison, but....

hexfish• 9 months ago

I second this. We went to one on a school trip and the intrusive thoughts were very strong that day.

Iulioh• 9 months ago

Least harmful call of the void there is

Quarrelsome• 9 months ago

was this place one of those who suffered firings as a result of the government shutdown? I believe at least 1,000 employs at nuclear facilities have been fired.

pembrook4• 9 months ago

Man in Michigan potentially exposed to radiation levels equivalent to undergoing 4 x-rays at the doctors office.

Meanwhile, in Texas, 1.5 people die every day working in Oil and Gas extraction.

A few people die every year installing or falling off of wind turbines.

But by all means, let's make this a news story instead and keep making nuclear sound scary. I’m sure the person who posted this to HN with this clickbait title has zero political beliefs.

gnarlouse• 9 months ago

Really puts it into perspective

kevincox4• 9 months ago

This is enlightening chart. Only Solar beats nuclear in deaths/Wh of energy. Even wind power results in more deaths. Additionally this uses very pessimistic numbers for large nuclear incidents and doesn't count thinks like deaths and health complications due to pollution and emitted radiation from fossil-fuel power sources (which emit way more radiation than nuclear power).

https://ourworldindata.org/grapher/death-rates-from-energy-p...

BirAdam• 9 months ago

If my childhood taught me anything, it’s that there’s about to be an awesome superhero.

satisfice3• 9 months ago

A spider will bite this guy and get the powers of a human.

sim7c002• 9 months ago

his super power will be misunderstanding other spiders and prosecuting them for their otherness -_-

DonHopkins• 9 months ago

Where is Jimmy Carter when we need him? And Rodney Dangerfield to explain how big Jimmy Carter is.

https://www.reddit.com/r/LiveFromNewYork/comments/1bh2edu/th...

gfalcao• 9 months ago

same thought here

escapecharacter• 9 months ago

If one falls into a tank like this, what steps are required to guarantee likelihood of developing powers?

robviren3• 9 months ago

I greatly appreciate the nuclear industry. Nuclear field engineering was my first "real" job out of college and they really committ to safety. Transparency in this industry is inspiring because everyone involved knows that one screw up and that's the end of the US nuclear industry. Good luck getting oil and gas to be accountable and as transparent about incidents. I carry the culture into the rest of my work and appreciate being involved. Wish events like this didn't happen but it is not of significant danger and I find it great that they communicate even "smaller" issues.

smilespray2• 9 months ago

I've lived through three major nuclear incidents, and what they had in common, regardless of the political systems of the US, The Soviet Union or Japan, was not the transparency, it was the lying. It started immediately after each incident.

I'm essentially pro-nuclear, I just don't trust people who run it.

consp• 9 months ago

You describe incidents which become political. At some point the normal rules are being ignored by those on the top of the information food chain. That says nothing about the rules of the game, but does say a lot about the people involved.

robviren3• 9 months ago

Totally valid perspective. I only became part of the industry after Fukushima. I only knew an industry by its disasters. I will say, having gone through the training programs we studied the nuclear incidents and spent a year in training before going to the plants. I just don't see parallel experiences looking back like that. The people in nuclear (at least from what I saw) want the industry to be safe and successful.

0xDEAFBEAD2• 9 months ago

Can you recommend a book or two in order to learn about that culture? IMO we could use more of it in AI.

robviren3• 9 months ago

I found strong parallels between tech safety and nuclear safety.

https://www.nrc.gov/docs/ML0534/ML053410342.pdf

NRC is a good place to start. They have been at trying to prevent tech from hurting people for awhile.

amarant2• 9 months ago

Mandatory xkcd: https://what-if.xkcd.com/29/

PhoenixFlame101• 9 months ago

Video format if anyone prefers it: https://youtu.be/EFRUL7vKdU8

almosthere2• 9 months ago

Is he going to die no matter what or is this survivable?

jasongill• 9 months ago

Ultimately, yes; he will die no matter what.

almosthere2• 9 months ago

As you get older this pedantry gets really tiring.

hshdhdhehd4• 9 months ago

Unprovable.

thayne2• 9 months ago

I'm not an expert but it definitely doesn't sound like an immediate threat to his life.

hunterpayne8• 9 months ago

He will be fine. He might not still have his job in a few months but other that, he will be fine. 300 CPM isn't even close to dangerous. You get a higher dose every time you fly in an airplane, or go to La Paz, Bolivia.

cma• 9 months ago

They ingested some amount of cavity water

Isn't it much worse internally than hitting your outer skin?

kevincox4• 9 months ago

According to https://www.mlive.com/news/2025/10/michigan-nuclear-plant-wo... he returned to work the next day (presumably at the nuclear reactor) and only suffered minor injuries due to the fall.

satisfice3• 9 months ago

No more horseplay around the reactor!

IngvarLynn• 9 months ago

relevant xkcd not: https://en.wikipedia.org/wiki/Andreev_Bay_nuclear_accident#A...

arthurcolle10• 9 months ago

300 CPM in hair after decontamination is a massive red flag. If this is from systemic circulation, could be GBq-level total body activity.

The non-emergency classification is bureaucratic nonsense. This is an internal contamination event with unknown but potentially severe consequences.

ramchip2• 9 months ago

From: https://www.vice.com/en/article/a-nuclear-plant-worker-fell-...

According to federal reports, the contractor ingested some of the reactor water before being yanked out, scrubbed down, and checked for radiation. They walked away with only minor injuries and about 300 counts per minute of radiation detected in their hair.
That sounds like a lot, but apparently it isn't terribly serious. He underwent a decontamination scrubdown and was back on the job by Wednesday.

arthurcolle10• 9 months ago

Litvinenko had about 10 MBq in his body and died in 3 weeks.

This might be 500+ MBq (0.5 GBq). Yeah it's a different isotope, but clearly not a "non-emergency"

EDIT: (after 1 hr) - Litvinenko dose was 4GBq - I was wrong by 3 orders of magnitude. My bad

orwin4• 9 months ago

External contamination is not comparable to internal, at all. Bq is a terrible unit to understand radioactive danger. Doses are usually detected in Grey, then converted into Sievert because Grey didn't take into account the difference between Alpha radiation and the others. And even then, when someone is truly contaminated, we calculate effective dose per organ.

The poor guy who fell in the pool probably didn't take any Alpha ray, wasn't taking all the radiation on a specific place, and while in my country we would calculate the dose he took before sending him back to work, he would probably work again in the same nuclear sector (this isn't the case for anyone, I know someone who dive to get the radioactive/explosive/poisonous trash we put in the water in the 50s until the 90s, he now cannot work on any radioactive trash.)

malfist2• 9 months ago

Can you quantify why you're better qualified to assess risk from this brief report than the nuclear experts on site that know the full picture?

__MatrixMan__• 9 months ago

Quantify? What kind of number would satisfy your request?

arthurcolle10• 9 months ago

I learned a few things from my father along the way. I can share my notes if you'd like

https://en.wikipedia.org/wiki/Ronald_Coll%C3%A9?wprov=sfti1

tgtweak• 9 months ago

300CPM above background is considered very low - likely why they classified this as non-emergency - the only reason it was reported was per NRC cfr that states any time there is transportation of a radioactively contained person offsite, it must be notified.

For reference, in Canada, that is considered trace contamination and not dose. You would experience 300-800 CPM on a commercial airliner during the entirety of your flight, for comparison.

edit: adding to this that the site in question, Palisades, is shut-down and is under decommissioning and was not operating at the time - so while the water would have had some radioactivity due to exposure to the formerly active core, it was not like falling into an operating reactor or into moderating heavy water... also something that cannot happen with a pressurized reactor such as this one.

LeoPanthera2• 9 months ago

A CPM value means nothing without additional context. Counts vary based on detector type and size, radiation type, energy, distance and geometry, all sorts of things. They're not comparable except in identical contexts.

This is why the Sievert exists as a unit.

As a general rule, falling into a reactor pool is probably fine, as long as you don't reach the bottom. (But please don't try it.)

There's even an XKCD "What if" about it. https://what-if.xkcd.com/29/

arthurcolle10• 9 months ago

Thank you for the followup (familiar with the XKCD)

Dumb question from a true non-expert:

So CPM varies with all those factors you mention, but wouldn't the site HP team know exactly what detector they used, the geometry, distance, etc.? They could convert to dose if they wanted, right?

Why report the ambiguous "300 CPM" instead of an actual dose estimate in mSv/μSv? Seems like that would be more useful for any medical team, any set of potential regulators or regulatory bodies as well as just general public understanding (drawing on my father's work here as he always emphasized the tension between "public fears radiation unnecessarily" and "industry safety protocols are inconsistent")

Follow-up: Is there any legitimate reason to report CPM instead of dose after a contamination event? Or does staying with CPM keep things conveniently vague? Because from my limited understanding, if they did a proper survey, they have everything needed to calculate dose.

yard20102• 9 months ago

From the what if:

On August 31st, 2010, a diver was servicing the spent fuel pool at the Leibstadt nuclear reactor in Switzerland. He spotted an unidentified length of tubing on the bottom of the pool and radioed his supervisor to ask what to do. He was told to put it in his tool basket, which he did. Due to bubble noise in the pool, he didn’t hear his radiation alarm.

When the tool basket was lifted from the water, the room’s radiation alarms went off. The basket was dropped back in the water and the diver left the pool. The diver’s dosimeter badges showed that he’d received a higher-than-normal whole-body dose, and the dose in his right hand was extremely high.

The object turned out to be protective tubing from a radiation monitor in the reactor core, made highly radioactive by neutron flux. It had been accidentally sheared off while a capsule was being closed in 2006. It sank to a remote corner of the pool floor, where it sat unnoticed for four years.

The tubing was so radioactive that if he’d tucked it into a tool belt or shoulder bag, where it sat close to his body, he could’ve been killed. As it was, the water protected him, and only his hand—a body part more resistant to radiation than the delicate internal organs—received a heavy dose

I love this book. Randall is such a gifted artist

godelski4• 9 months ago

  > A CPM value means nothing without additional context

Here to confirm this. If you're googling "CPM" you'll find charts that say different things. That's why you need to read carefully. Better, just chill, it is okay that you don't know. It's nuclear physics. It's not a subject you're expected to know about.

For CPM, what matters is "CPM of <WHAT>"

CPM just tells you the number of particle detection. It does not tell you the particle type (e.g. alpha, beta, gamma) nor the energy level (i.e. eV). Without context, it is meaningless.

As an example, I can confidently say you are getting over 100bn CPM right now. The reason it doesn't matter is that this is neutrinos and they're not interacting with you[0]. 1CPM or 1e20CPM, who cares. Conversely, 1 CPM can be deadly. You definitely don't want to be hit by a single ReV (10^27) proton (good luck producing that though). Context matters.

  > This is why the Sievert exists as a unit.

Which still needs context.

Sievert is joule per kilogram. So energy divided per mass, much like pressure is force over area. But determining biological impact still takes interpretation. You have weight factors by particle types (e.g. alpha = 2x beta) and there is also weighting factor for internal/external dose and locations like soft tissue (e.g. higher weighting for dose at throat vs dose at hands).

This is why it is incredibly important to use caution when interpreting radiation values. If you don't have training in this it is incredibly easy to unknowingly make major errors. The little details can dramatically change the outcome. Context is critical.

I'm not here to tell you how to actually do the calculation (you'll need a lot more info), I'm here to tell you that it's not easy and you're likely doing it wrong. The experts are not dumb. You're just missing context and a first order approximation is nowhere near enough for an accurate conclusion. It's nuclear physics lol

It shouldn't need be said, but nuclear physics is, in fact, complicated.

[0] https://neutrinos.fnal.gov/faqs/

hunterpayne8• 9 months ago

CPM is a measure of rate, GBq is a total amount. And 300 CPM is basically nothing. People live their entire lives in places where the natural background radiation is higher than that with no increased chance of cancer.

kragen• 9 months ago

GBq is also a measure of rate; it's a billion decays per second.

Someone2• 9 months ago

The non-emergency classification is bureaucratic nonsense

FTA: “This is an eight-hour notification, non-emergency, for the transportation of a contaminated person offsite“

I read that as that the “non-emergency” classification isn’t for the victim or the “fell into a nuclear reactor pool”, but for the effects on those outside the facility of sending the victim off site.

raggi• 9 months ago

There is no circulation in hair, hair is dead, and it is produced slowly. Nothing about your commentary passes basic scrutiny.

beowulfey• 9 months ago

Unless I'm misinterpreting what you mean, I believe if it was reflected in the hair in the immediate aftermath, it wouldn't reflect internal circulation because hair does not grow that fast. It would have been from exposure to the pool rather than any amount ingested.

harrall• 9 months ago

300 CPM on its own is both meaningless and not high.

CPM is a raw stat from the sensor. There’s many different designs of dosimeters and they all read differently so you have to ask “what brand and model did you use?” You then apply a function to the data to normalize it into a real unit.

But CPM is the cool thing that makes the click-click-click sound. (The absolute rate of clicks also is not useful.)

dudidn• 9 months ago

“worker fell off roof installing solar panels” — just getting ahead of the ‘anti-nuclear’ folks on here. Energy installations all come with risks, albeit nuclear long tail accidents are mutli-generational and externalised to people not involved in managing the risk

dlcarrier5• 9 months ago

That happens all the time; it's only news when something unusual happens.

DoctorOetker2• 9 months ago

Why didn't they shave off the hair and measure again before sending off to medical? They have the opportunity to report lower numbers, and would enable identifying non-hair-adsorbed radiatioactive matter on the subject. It sounds so easy and actionable it boggles the mind that it's not part of the protocol.

seb1204• 9 months ago

I thought this as well but given some other comments the measures numbers are open to interpretation/ spread. Also it could be considered a violation of the person's body if done without his consent.

DoctorOetker2• 9 months ago

and one could argue that showering without consent is also a violation of the person's body... consider an accident where a person is actually super hot with radioactive contamination, does the person have the right to exit the facility without shower and spread the radioactive particulates at will?

the thing is that this type of "violation" can easily be prevented by including the obligatory showering or shaving as part of the contract, so either they consent or they didn't end up in a position where they can be exposed to radioactive matter.

So this can not explain why the hair wasn't shaved.

loeg3• 9 months ago

Dude might prefer to keep his hair? Given the low exposure amount.

qwertytyyuu• 9 months ago

I can't help but be reminded of relevant xkcd^{TM} https://what-if.xkcd.com/29/

JackAcid• 9 months ago

Toxic Avenger remake.

notepad0x90• 9 months ago

I thought you could safely swim in that water so long as you stay a few meters clear of the rods? water being a good absorber of radiation and all. Is this just a precautionary reaction?

chistev• 9 months ago

Dude about to have superpowers and go after the government

sebmellen3• 9 months ago

Relevant from Randall Munroe https://what-if.xkcd.com/29/

What if I took a swim in a typical spent nuclear fuel pool? Would I need to dive to actually experience a fatal amount of radiation? How long could I stay safely at the surface?
Assuming you’re a reasonably good swimmer, you could probably survive treading water anywhere from 10 to 40 hours. At that point, you would black out from fatigue and drown. This is also true for a pool without nuclear fuel in the bottom.

trenchpilgrim2• 9 months ago

That blog post is about the spent fuel pool. The link is about the reactor cavity.

sebmellen3• 9 months ago

Wouldn’t the same principles apply?

aakkaakk• 9 months ago

Not bad, not terrible.

tzot• 9 months ago

Did you mean “not great, not terrible” or was the change deliberate?

mobeigi• 9 months ago

Hopefully the worker is okay. I have to agree that the non-emergency classification seems odd. This should warrant a proper investigation and steps to avoid this in the future.

Someone2• 9 months ago

FTA: “This is an eight-hour notification, non-emergency, for the transportation of a contaminated person offsite“

⇒ the “non-emergency” classification isn’t about the “fell into a nuclear reactor pool”, but about sending the victim off site.

drysart3• 9 months ago

I can guarantee you there will be a proper investigation and steps taken to avoid this in the future. The non-emergency classification here applies solely to the notification that the contamination was transported off-site. Not to the fact that the incident occurred. Every accidental incident that occurs within the controlled area of a nuclear facility is investigated and evaluated for necessary policy changes.

And the reason the contamination transport off-site was classified as non-emergency was because even though the amount of radiation detected on the guy is less than he'd have gotten from flying in an airplane; nuclear safety standards are so unbelievably rigorous and strict that even that small of an incident needs to be reported; even if it presents absolutely no danger to anyone anywhere (not even the guy that was contaminated) and hence is classified as a non-emergency notification.

kevincox4• 9 months ago

Plant officials today confirmed the worker sustained minor injuries from the fall and has already returned to work. - https://www.mlive.com/news/2025/10/michigan-nuclear-plant-wo...

They returned to work the next day with minor injuries due to the fall. It doesn't sound like it was an emergency to me.

defraudbah• 9 months ago

and so hulk was born

ggm• 9 months ago

Does the operator go to court for OH&S breaches?

unglaublich• 9 months ago

The Chemical Safety and Hazard Investigation Board has a great YouTube channel where they carefully analyze similar accidents.

https://www.youtube.com/@USCSB/videos

Not necessarily nuclear (since chemical and industrial accidents are much, muhc more likely), but highly recommended if you're interested in such incidents and their causes.

dubbel• 9 months ago

I loce their videos, too, but as far as I know the current US administration will shut them down at the end of this year. [0] [1]

But just now I read that a (sharply reduced) budget had passed the house? [2] does anyone know what the current state is?

[0] https://www.csb.gov/assets/1/6/csb_cj_2026.pdf

[1] https://www.pbs.org/newshour/show/only-federal-agency-that-i...

[2] https://www.safetyandhealthmagazine.com/articles/27090-house...

lazyasciiart• 9 months ago

That’s from July, and it says a committee has approved a specific line item to be put into the budget that would eventually be voted on.

system2• 9 months ago

The rest of the event reports are also very active. Reactor sites are fun places to work.

rurban• 9 months ago

Palisades was closed down 2022, but just reopened recently at August 27, 2025.

Hair contaminated

lavela3• 9 months ago

These are quite a few reports for one day for a technology we purportedly have under full control, nothing to worry.

rvrs• 9 months ago

Did a coal miner write this comment?

rs_rs_rs_rs_rs• 9 months ago

Worse, an environmentalist.

lavela3• 9 months ago

Miner vs. straw man, who wins? :o)

drysart3• 9 months ago

Which do you consider as being under better control: a technology that we exhaustively create reports on even in the face of incidents like this where the only real chance of harm was that the guy couldn't swim and might have drowned; or a technology where we don't report on anything at all whatsoever and thus have no idea what's actually going on?

Reports don't mean danger, and they don't mean lack of control. Reports are information.

lavela3• 9 months ago

Of the eight reports I only see one that relates to a guy being able to swim or not (and I suspect the same is true for the estimated 1400 reports so far this year). Also having transparency is obviously good and I don't understand what you want to prove with arguing that a worse situation would be worse. It clearly would be worse.

I'm also not totally against nuclear, in case you are suspecting that. I do think though, that we as a society aren't at the point where we have the ability to completely control such technology, contrary to what proponents of much higher utilization of nuclear like to claim. Reports of fuses seemingly without failover or stolen equipment seem to support that argument.

Cheezmeister• 9 months ago

For comparison: https://www.nrc.gov/about-nrc/radiation/around-us/calculator

In other news, a kitten named millicurie did a really adorable thing.

The only remarkable fact here is that the regulatory structure is strong enough that we commoners are entitled to hear about it. That's a Very Good Thing, and one I wish we enjoyed apropos, say, the corporate veil (looking at you, Chevron, Exxon, Shell, Aramco, Sinopec, Amazon, Oracle, AIPAC, United, The Trump Organization, X Corp, Paramount, Skydance, eMed Population Health, Inc., et. al.).

But the story here is a guy fell into some water, and is following SOP (which is also a Very Good Thing).

Please don't feed the clickbait.

lijok3• 9 months ago

Guys slow down, you're gonna hug xkcd to death

ByteDrifter• 9 months ago

Incidents like this show that “nuclear safety” is as much cultural as technical. Even the best systems fail when people and organizations stop treating the environment with the respect it demands.

pembrook4• 9 months ago

This harmless incident shows us nothing aside from why nuclear is so expensive.

There is essentially zero risk to the operation of the plant (or this worker!) from such an event.

Imagine if oil and gas facilities were required for any worker fall to have federal government workers visit onsite, draft a report for review, have it examined by expensive niche lawyers with rounds of revisions, and then have it published it publicly.

This is just a silly example of the hysterical safety-ism involving anything nuclear-related in the US.

Yes, working in any job related to energy carries risks. Just ask a roughneck, lineman, or wind turbine installer.

throw-10-13• 9 months ago

swimming in a reactor pool isnt that bad, water is a great radiation shield.

jenadine2• 9 months ago

Why is this interesting? Workers gets injured all the time and sometimes even die on various accidents in all industries and nobody ever talk about it. Is this anti-nuclear propaganda?

yoavm• 9 months ago

I guess that U.S. Nuclear Regulatory Commission is required to report any unusual events in the plants in the US, which would be reasonable. A worker falling into a nuclear reactor pool is unusual. The report itself doesn't seem like it's anti-nuclear in any way, and it clearly states "no impact on the health and safety of the public or plant personnel".

If you're asking why it's interesting for HN, I think it's actually because people are fascinated with nuclear, in a positive way.

aatd862• 9 months ago

Because another mutant might be joining our ranks soon.

jenadine2• 9 months ago

Like in Teenage Ninja Turtles? Sounds cool! (But you know it's fictional, right?)

matjazk• 9 months ago

New superhero on their way.

gethly• 9 months ago

They ingested some amount of cavity water.

How dumb do you have to be to not only fall into it but to also swallow it...

JumpinJack_Cash• 9 months ago

The fear about nuclear is so big that this idiocy gets 500 points and 350 comments because nuclear is scary

SV_BubbleTime• 9 months ago

We’re 50 years behind fusion because of people that now rage against fossil fuels. It’s tough to see it keep happening despite the educational resources we have now vs the 70s and 80s.

antirez• 9 months ago

Basically often it could be better to have an incident in a nuclear plant than in some building construction site... But the attention delta is incredibly high. 300 CPM sounds low, I hope they will be fine.

outside1234• 9 months ago

At Purdue university we had a small research reactor and to this day can remember looking down through the pool to see the blue glow of the nuclear reaction. It is crazy how well the water (boronized?) stops radiation.

Ericson2314• 9 months ago

The XKCD has come to life!

Accidental swimming is no fun, I wish the guy a full recovery from dihydrogen monoxide poisoning.

grork• 9 months ago

3.6 roentgen, not great, not terrible

fsh2• 9 months ago

I once worked in a nuclear research reactor, and they had lifebuoys at their pool. Quite prescient, as it turns out.

dbg31415• 9 months ago

300 counts per minute

Roughly 10x background radiation.

So like two weeks of sunshine in a day.

Not a good day. Not fatal.

Galanwe• 9 months ago

I'm not literate at all on nuclear physics, but I remember in the "Chernobyl" TV show (which seemed trustworthy) some divers died after going in the cooling water to close the pumps. How was that water different ?

nvahalik• 9 months ago

I watched the show but if I remember correctly they actually didn’t die. They survived.

The reality is much more positive than the myth, with all three men escaping such a grisly fate. Indeed, Alexei Ananenko and Valeri Bespalov are believed to be both still alive as of 2024, while Boris Baranov lived until 2005 when he passed away from heart disease.

Source: https://www.history.co.uk/article/the-real-story-of-the-cher...

Movah• 9 months ago

I wonder if it had anything to do with the empty "alcoholic bottles" being found?

FITNESS FOR DUTY (FFD) EVENT

The following information was provided by the licensee via phone and email:

"On 10/25/25, at approximately 1230 EDT, 3 empty alcohol bottles were found in the protected area by a contract employee. Site security was notified and took possession of the empty bottles which were removed from the protected area. The individual who accidentally brought in the empty alcohol bottles with other non-alcoholic empty bottles was tested for FFD and was negative. This event is reportable in accordance with 10 CFR 26.719(b).

"The NRC Resident Inspector has been notified."

everdev• 9 months ago

I'm sure it has nothing to do with corporate malfeasance.

shravani_05_01• 9 months ago

I have instagram id hack please

A worker fell into a nuclear reactor pool

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