Chernobyl Compared To Other Radioactivity Releases - Chernobyl Compared With Tomsk-7

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) 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:

• 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

It is important to note that 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 tributyl phosphate/hydrocarbon organic phase used in the first 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.