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Lester Haines writes in Sellafield's nuclear waste measured in El Reg units:

Most intermediate level waste is barely radioactive at all. If you put a completely legal luminous watch in a barrel containing half a tonne of dirt, that dirt would technically be intermediate-level nuclear waste according to the regulations.

Is that an accurate description of what gets classifed as intermediate level waste according to UK regulations?

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  • Does that article talk about the different types of radiation? Intermediate level radioactive waste is defined by the type of radiation rather than the level of radiation as different types have different impacts based on how you are exposed and some can be deadly at very low levels. – Joe W Nov 18 '20 at 15:49
  • @Federico : It seems to me that any critical reading should be able to expect "intermediate level" to refer to some standard that's defined somewhere in this sentence. I however added a reference to UK regulations as they are what the question is about. – Christian Nov 18 '20 at 15:55
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    It should be noted that modern luminous watches are not radioactive at all. While old luminous gauges were dangerously radioactive. – Daniel R Hicks Nov 18 '20 at 19:24
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    Classification definitions: Intermediate level = higher activity than low level. Low level = "Wastes having a radioactive content not exceeding 4 GBq/tonne of alpha activity or 12 GBq/tonne of beta/gamma activity." From ukinventory.nda.gov.uk/wp-content/uploads/2014/01/… which looks authoritative if a little old (march 2017). So using Fizz's figure of 1GBq/watch plus 1/12 tonne of dirt would seem to be ILW. But still much less than the core graphite (because ILW is a very broad classification). – Jack B Nov 18 '20 at 20:06
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    I've heard of one of those old watches tripping radiation alarms at a nuclear plant. They're hot. – Loren Pechtel Nov 18 '20 at 20:15
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[intermediate level nuclear waste] is not radiologically dangerous in any realistic way

This is false to the point of being irresponsible.

If you put a completely legal luminous watch in a barrel containing half a tonne of dirt, that dirt would technically be intermediate-level nuclear waste according to the regulations.

If the watch used tritium at the legal limit you'd need seven, not one. But the point remains that seems absurd.

But wait, if the watch used promethium-147 you'd need 3,000 watches! And if it used radium-226 you'd need 67,000 watches!

What's going on?

The problem stems from the measurement used, the becquerel.

The Regulations

According to the linked regulations from "Introduction to Intermediate Level Waste (ILW) issues"...

ILW is radioactive waste with radioactivity levels exceeding the upper boundaries for Low Level Waste (LLW):

  • Alpha emitters greater than 4 GBq/tonne.
  • Beta/gamma emitters greater than 12 GBq/tonne.
  • Waste that does not need radiological self-heating to be taken into account in the design of storage or disposal facilities.

Half tonne of dirt needs 2 gigabecquerels of alpha emissions or 6 gigabecquerels of beta or gamma emissions.

Note that this is an Introduction to Intermediate Level Nuclear Waste. I suspect the full regulation is much more detailed.

What's a becquerel?

A becquerel is the decay of one atomic nucleus per second. Its equivalent units are the curie (3.7e10 Bq) and the rutherford (1 MBq). GBq is a gigabecquerel, 1 billion becquerels.

A becquerel is a distinct measurement from a sievert (effective dose) or roentgen (exposure). See US Environmental Protection Agency - Radiation Terms and Units.

This is critically important. A becquerel only measures how many nuclei decay per second. It does not measure the type nor energy, nor does it measure the danger to humans. That's what sieverts and roentgens are for.

To use an analogy, becquerels measure how many times you've been shot, but it doesn't say if it was by a spitball or an artillery shell.

How many becquerels in a luminous watch?

According to the The Radioactive Substances (Clocks and Watches) (England and Wales) Regulations 2001...

(i) Clocks or watches having their dials marked at the time of manufacture with “T 25” (Tritium), “Pm 0.5” (Promethium 147) or “Ra 1.5” (Radium 226)

  • Tritium 9.3e8 bq
  • Promethium 147 1.9e7 bq
  • Radium 226 5.6e4 bq

(ii)Clocks bearing radioluminescent deposits and not falling within category (i)

  • Tritium 3.7e8 bq
  • Promethium 147 7.4e6 bq
  • Radium 226 7.4e3 bq

(iii)Watches bearing radioluminescent deposits and not falling within category (i)

  • Tritium 2.8e8 bq
  • Promethium 147 5.5e6 bq
  • Radium 226 5.6e3 bq

(iv)Watches containing small sealed glass tubes internally coated with a phosphor and filled with tritium gas

  • Tritium 7.4e9 bq

The claim approaches plausibility with the regulation of 930 MBq of tritium per T25 marked watch. Tritium is a beta emitter meaning 12GBq per tonne or 6GBq for a half tonne of dirt. We'd need 7 tritium watches.

But there's a problem. Why is one allowed 400 times more becquerels from tritium than promethium-147? And 20,000 more from tritium than radium-226?

Promethium-147 is also a beta emitter, but the beta particles is emits are much more energetic. When a tritium nucleus decays, one becquerel of tritium, it emits 19 keV. When Promethium-147 decays it emits 224 keV. They're both beta particle emitters, but Promethium-147 decays with 10 times the energy.

Becquerels only measure the number of nuclei decaying per second it does not account for the type nor energy. As such safety regulations must consider both becquerels and the material being measured.

Conclusion

If you put a completely legal luminous watch in a barrel containing half a tonne of dirt, that dirt would technically be intermediate-level nuclear waste according to the regulations.

This claim is incorrect, but not too far off the mark. It could have been used to make a point about how the regulation is written. They could have used the difference between 7 harmless tritium watches vs 140,000 radium watches to illustrate how the regulation could be rewritten, or just to educate. Instead they fail to explain their point and moan generically about regulations.

However, they reference an Introduction to Intermediate Level Nuclear Waste. The full regulation may contain additional measurements. They may use becquerels because they are easier to measure.

[intermediate level nuclear waste] is not radiologically dangerous in any realistic way

For the same reason the claim about watches is true(ish), this claim is false to the point of being irresponsible. Becquerels do not measure dosage nor exposure. They do not measure the danger to humans. That would be sieverts.

4 GBq of radium 226 is very dangerous. Radium 226 emits alpha particles which, if ingested, are very hazardous. It accumulates in the bones. It decays into radon gas which is very harmful.

Ever wonder why nuclear power never became too cheap to meter? This sort of thing is why. -Ed

Ever wonder why we put experts in charge of regulations? This sort of thing is why.

See also

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    Indeed the "usual" ILW discussed in a UK context is irradiated graphite (from reactor cores)... with which the main worry is that Carbon-14 (which accounts for about half of irradiated graphite GBq) can accumulate in living tissues. After about 30 years from core decommissioning, C-14 actually dominates the GBq of irradiated graphite due to its much longer half-life www-pub.iaea.org/mtcd/publications/pdf/te_1647_cd/PDF/… – Fizz Nov 23 '20 at 2:45
  • The radon is the big risk from radium: as long as it stays outside of you, the outer layer of your skin provides reasonable radiation shielding. But your lungs don't have any such protection from the radon that radium-226 decays into. – Mark Nov 23 '20 at 7:41
  • Good write. Small addition regarding Half-life (a). Higher the activity (smaller a) larger the Bq rate is. Matter releases energy (radiation) faster, is more dangerous but becomes harmless faster. Other way, you release radiation more slowly over longer time. Could be besides the point, but ppl tend to mix these things. – pinegulf Nov 23 '20 at 8:16

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