Comparison of Chernobyl and other radioactivity releases

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This article compares the radioactivity release and decay from the Chernobyl disaster with various other events which involved a release of uncontrolled radioactivity.

Chernobyl compared to background radiation

fission products
like Cs-137 contribute nearly all of the gamma dose now after a number of decades have passed, see opposite.
The relative contributions of the major nuclides to the radioactive contamination of the air after the accident. Drawn using data from the OECD report [1] and the second edition of 'The radiochemical manual'.

Natural sources of radiation are very prevalent in the environment, and come from cosmic rays, food sources (bananas have a particular high source due to potassium-40 but all foods contain carbon and thereby carbon-14), radon gas, granite and other dense rocks, and others. The banana equivalent dose is sometimes used in science communication to visualize different levels of ionizing radiation. The collective radiation background dose for natural sources in Europe is about 500,000 man-Sieverts per year. The total dose from Chernobyl is estimated at 80,000 man-sieverts, or roughly 1/6 as much.[1] However, some individuals, particularly in areas adjacent the reactor, received significantly higher doses.

Chernobyl's radiation was detectable across Western Europe. Average doses received ranged from 0.02

mrem (Portugal) to 38 mrem (portions of Germany).[1]

Chernobyl compared with an atomic bomb

Far fewer people died as an immediate result of the Chernobyl event than the immediate deaths

fission products undergo exponential decay
at different rates. Hence the isotopic signature of an event where more than one radioisotope is involved will change with time.

"Compared with other nuclear events: The Chernobyl explosion put 400 times more radioactive material into the Earth's atmosphere than the atomic bomb dropped on Hiroshima; atomic weapons tests conducted in the 1950s and 1960s all together are estimated to have put some 100 to 1,000 times more radioactive material into the atmosphere than the Chernobyl accident."[4]

The radioactivity released at Chernobyl tended to be more long-lived than that released by a bomb detonation hence it is not possible to draw a simple comparison between the two events. Also, a dose of radiation spread over many years (as is the case with Chernobyl) is much less harmful than the same dose received over a short period.

The relative size of the Chernobyl release when compared with the release due to a hypothetical ground burst of a bomb similar to the Fat Man device dropped on Nagasaki.

Isotope Ratio between the release due to the bomb and the Chernobyl accident
90Sr 1:87
137Cs 1:890
131I 1:25
133Xe 1:31

A comparison of the gamma dose rates due to the Chernobyl accident and the hypothetical nuclear weapon.

Normalized to the same Cs-137 level. (logarithmic scale).
Normalized to the same dose rate for day one.
Normalized to the same Cs-137 level (dose rate on day 10000).

The graph of dose rate as a function of time for the bomb fallout was done using a method similar to that of T. Imanaka, S. Fukutani, M. Yamamoto, A. Sakaguchi and M. Hoshi, J. Radiation Research, 2006, 47, Suppl A121-A127. Our graph exhibits the same shape as that obtained in the paper. The bomb fallout graph is for a

radioactivity. The following gamma-emitting isotopes are modeled 131I, 133I, 132Te, 133I, 135I, 140Ba, 95Zr, 97Zr, 99Mo, 99mTc, 103Ru, 105Ru, 106Ru, 142La, 143Ce, 137Cs, 91Y, 91Sr, 92Sr, 128Sb, and 129Sb. The graph ignores the effects of beta emission and shielding. The data for the isotopes was obtained from the Korean table of the isotopes. The graphs for the Chernobyl accident were computed by an analogous method. Note that in the event of a low altitude or ground bursted nuclear detonation that fractionation of the volatile and non volatile radionuclides occurs, also during the Chernobyl accident the ratio between the different elements released by the accident did change as a function of time.[5]


A

fission product fraction of the total activity
resulting from the ground burst is shown.

Chernobyl compared with Tomsk-7

The release of radioactivity which occurred at

Tomsk-7 (an industrial nuclear complex located in Seversk rather than the city of Tomsk) in 1993 is another comparison with the Chernobyl release. During reprocessing activities, some of the feed for the second cycle (medium active part) of the PUREX process escaped in an accident involving red oil. According to the IAEA it was estimated that the following isotopes were released from the reaction vessel:[6]

  • 106Ru 7.9 TBq
  • 103Ru 340 GBq
  • 95Nb 11.2 TBq
  • 95Zr 5.1 TBq
  • 137Cs 505 GBq (estimated from the IAEA data)
  • 141Ce 370 GBq
  • 144Ce 240 GBq
  • 125Sb 100 GBq
  • 239Pu 5.2 GBq

The very short-lived isotopes such as 140Ba and 131I were absent from this mixture, and the long-lived 137Cs was only at a small concentration. This is because it is not able to enter the

liquid-liquid extraction cycle of the PUREX process. The second cycle is normally to clean up the uranium and plutonium product. In the PUREX process some zirconium, technetium, and other elements are extracted by the tributyl phosphate. Due to the radiation induced degradation of tributyl phosphate the first cycle organic phase is always contaminated with ruthenium
(later extracted by dibutyl hydrogen phosphate). Because the very short-lived radioisotopes and the relatively long-lived caesium isotopes are either absent or in low concentrations the shape of the dose rate vs. time graph is different from Chernobyl both for short times and long times after the accident.

The size of the radioactive release at Tomsk-7 was much smaller, and while it caused moderate environmental contamination it did not cause any early deaths.

Normalized to the same first day dose rate. (logarithmic scale).

Chernobyl compared to Fukushima Daiichi

Main article:
Comparison of Fukushima and Chernobyl nuclear accidents

Chernobyl compared with the Goiânia accident

While both events released 137Cs, the isotopic signature for the Goiânia accident was much simpler.[7] It was a single isotope which has a half-life of about 30 years. To show how the activity vs. time graph for a single isotope differs from the dose rate due to Chernobyl (in the open air) the following chart is shown with calculated data for a hypothetical release of 106Ru.

Normalized to the same first day dose rate. (logarithmic scale).

Chernobyl compared with the Three Mile Island accident

Main article: Three Mile Island accident

Three Mile Island-2 was an accident of a completely different type from Chernobyl. However, both accidents have vague similarities.

Chernobyl was a design flaw-caused power excursion causing a steam explosion resulting in a graphite fire, uncontained, which lofted radioactive smoke high into the atmosphere; TMI was a slow, undetected leak - caused by the technical malfunction of a pilot-operated relief valve - which lowered the water level around the nuclear fuel, resulting in over a third of it shattering when refilled rapidly with coolant.

Similar to Chernobyl, operator error played a role but did not directly cause the accident. Both accidents had grueling and costly cleanup efforts. Chernobyl and TMI's unaffected reactors were restarted and continued operation until 2000 and 2019, respectively.

Unlike Chernobyl, TMI-2's reactor vessel did not fail and contained almost all of the radioactive material. Containment at TMI was not breached. On the day of the accident, a small "hydrogen burn" occurred inside the reactor building, but it was not enough to affect normal operation of the reactor itself.

Following the accident, an estimated 44,000 curies of radioactive gases - particularly Krypton-85 - from the leak were vented into the atmosphere through specially designed filters under operator control. A government report concluded that the accident caused no increase in cancer rates for local residents.[8]

Chernobyl compared with criticality accidents

During the time between the start of the

Manhattan project and the present day, a series of accidents have occurred in which nuclear criticality has played a central role. The criticality accidents may be divided into two classes. For more details see nuclear and radiation accidents. A review of the topic was published in 2000, "A Review of Criticality Accidents" by Los Alamos National Laboratory (Report LA-13638), May 2000. Coverage includes United States, Russia, United Kingdom, and Japan. Also available at this page
, which also tries to track down documents referenced in the report.

Process accidents

In the first class (process accidents) during the processing of

fission products
remained in the vessel.

These accidents tend to lead to very high doses due to direct

inverse square law
the dose suffered by members of the general public tends to be very small. Also very little environmental contamination normally occurs as a result of these accidents.

Reactor accidents

In this type of accident a reactor or other critical assembly releases far more fission power than was expected, or it becomes critical at the wrong moment in time. The series of examples of such events include one in an experimental facility in

IAEA report (2001).[11] Even the SL-1
accident (RIA, power surge in an experimental nuclear reactor in Idaho, 1961) failed to release much radioactivity outside the building in which it occurred.

See also

References

  1. ^
    S2CID 189914132
    .
  2. ^ Health effects of the Chernobyl accident: an overview
  3. PMID 16628547
    .
  4. ^ This is written in page 8(9) of "Ten years after Chernobyl: What do we really know?" of the PDF official document: http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/28/058/28058918.pdf
  5. doi:10.1080/23312009.2015.1049111
    .
  6. ^ The Radiological Accident in the Reprocessing Plant at Tomsk - IAEA Publications
  7. ^ IAEA Publications – Details
  8. ^ "Three Mile Island". Washingtonpost.com. 1990-09-01. Retrieved 2014-02-04.
  9. ^ World Nuclear Association Archived 2006-09-23 at the Wayback Machine
  10. ^ NRC.gov
  11. ^ The criticality accident in Sarov
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