Accidental Intake of Tritiated Water (THO), 1985

Accident scenario

At 11.30 a.m. on 11 July 1985 a factory worker, A, was filling glass capillary tubes with tritium gas stored in an uranium trap. This source and the tubes form a closed system located in a box which is ventilated to the exterior. By heating the uranium, the system is filled with tritium until a certain pressure, below atmospheric, is reached. This pressure is indicated on a precision instrument. In the next step valves connecting the source to three sets each of 10 capillaries are closed. The capillaries are then melted off with a gas flame. When A tried to melt off the first capillary it did not seal but burst open. She realised that this was unusual and asked a more experienced colleague, B, for assistance. B suspected that A had handled the sealing prcocedure awkwardly and so he melted off the broken capillary and then tried to seal off the first capillary of the second set. Again the melted glass ruptured and the hissing sound of escaping gas was heard. B then transferred the remaining gas in the system back to the uranium absorber. Meanwhile the room supervisor and B realised that a marked increase of tritium in the room air was indicated on area monitors. Although the sequence of events described here had never previously occurred, the release of tritium gas from a broken capillary had happened before and this had produced a transient rise on the monitors. Urine samples from A and B were collected in the afternoon of the next day, and measured in a liquid scintillation. Provisional results proved to be close 1.3 GBq/l for A and 28 MBq/l for B.       The leak produced by the flame probably released about 1.7 TBq from each of the two sets of capillaries which ruptured. The presence of the flame at the leak transformed the relatively harmless tritium gas into tritiated water. Unf'ortunately A left the plastic side of the box open in order to see better when she tried to melt off the first capillary. Her face was close to the leak and she must have inhaled about 35 GBq of tritiated water. This value was inferred from the urine data, assuming 54% of her weight was water. B was protected by the plastic side when he tried to melt off the capillary and consequently inhaled only about 1 GBq. Three other persons working in the same room inhaled between 120 and 140 MBq. According to ICRP 30(5) the annual limit of intake is 3 GBq for standard man and it would be 2.2 GBq for A, a female of 53.5 kg. Committed dose equivalents of about 0.8 Sv and 0.025 Sv were to be expected without any countermeasures for persons A and B respectively (1).

Chromosomal dosimetry

10 ml blood samples in lithium heparin tubes were sent by air to the cytogenetics laboratory. Person A was sampled on days 4, 18, 39, 50 and 178 after accident and person B on days 4, 18,50 and 178. A third person C who had not been involved in the incident was taken at the time of the 178 day samples. On the morning after the day of bklood sampling 48 hour lymphocyte cultures were set up.

References

1. Lloyd DC, Edwards AA, Prosser JS, Auf der Maur A, Etzweiler A, Weickhardt U, Gossi U, Geiger L, Noelpp U and Rosler H: Accidental intake of tritiated water: A report of two cases. Radiat. Prot. Dosimet., 15: 191-196, 1986. 2. Lucas JN, Poggensee M and Straume T: The persistence of chromosome translocations in a radiation worker accidentally exposed to tritium. Cytogenet. Cell Genet., 60: 255-256, 1992. 3. Lloyd DC, Moquet JE, Oram S, Edwards AA and Lucas JN: Accidental intake of tritiated water: a cytogenetic follow-up case on translocation stability and dose reconstruction. Int. J. Radiat. Biol., 73: 543-547, 1998.

Chromosome aberration analysis

.
	Subject	Days after accident	Dicentrics	Centric rings	Acentrics
	Aubject A	4	22	3	22
		18	29	1	31
		39	34	3	28
		50	30	1	27
		178	30	4	36
	Subject B	4	10	1	8
		18	10	0	19
		50	9	0	18
		178	9	1	16
	Subject C	178	3	0	11
						.