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.
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.
"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.
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
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.
