Database of radiological incidents and related events--Johnston's Archive

Semipalatinsk nuclear test, 1974

compiled by Wm. Robert Johnston
last modified 29 January 2009

Date: 31 May 1974

Location: Semipalatinsk test site, Kazakhstan, USSR

Type of event: venting from underground nuclear test


On 31 May 1974 the USSR conducted an underground nuclear test at the Semipalatinsk test site. The device was detonated in a vertical shaft at a depth of 316 meters at 8:27 AM local time and yielded 150 kt. Two hours later venting occurred, producing a radioactive cloud which drifted downwind. At locations 9-10 km away, 162 people had been positioned as test subjects; 127 were directly in the cloud's path and 35 were 2.5 km off the path. The cloud reached these locations 9 minutes after venting, taking 10-20 minutes to pass. The cloud also passed over the nearby villages of Sarapan and Isa, 20 km and 30 km away, respectively; residents had not been warned of the test.

For the 127 test subjects, dosimeters measured external gamma doses of 22 rem, but external beta doses to exposed skin reached 200 rem. Of the subjects, 100 reported at feeling worse with at least one symptom, some within 30-40 minutes: 62 suffered headaches, 40 suffered nausea, 20 suffered vomiting, and 10 exhibited skin edema. Most symptoms reportedly diminished within 6 days. Symptoms exhibited were consistent with mild radiation sickness from cumulative doses between 100 and 200 rem for the main test group. Thyroid doses to individuals in the two villages was calculated at 3-6 rem.

Consequences: 100 injuries?


© 2009 by Wm. Robert Johnston.
Last modified 29 January 2009.
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