Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 64

In the absence of a nuclear accident, chronic exposure to ionizing radiation can have health consequences. For this reason, worker cohorts in the nuclear industry are being followed up medically.

In Oak Ridge, the observed number of 1,017 deaths from all causes was 74% of what was expected. This finding, which has been repeated several times, is based in particular on the cohort’s relatively high socio-economic status, associated with good health [CHE 83].

Among workers at a spent fuel reprocessing plant (Tennessee Eastman Corporation, USA), the relative risk of lung cancer increased with increasing exposure even after controlling age and smoking, but only for those over 45 years of age at first exposure [COO 83]. Among the 999 workers exposed to atmospheric uranium from 1943 to 1947 at the Tennessee reprocessing plant, the doses received were as high as 74 rads or 740 rems if a quality factor of 10 is used [BEC 83].

Among female watchmakers who used radium-based light dials, a tripling of the risk of multiple myeloma occurred in the cohort working before 1930. However, analyses of body burdens and duration of use suggest that external radiation due to radium was more likely to be responsible than internal radium [STE 83].

The impact of working in a nuclear environment is understood in France thanks to the TRACY cohort. This cohort of French fuel cycle workers was the subject of a reconstruction of occupational exposures [SAM 12, SAM 16]. According to the IRSN [IRS 17a], during the follow-up period (1968–2008) and with an average follow-up period of 27 years, 2,130 deaths (17% of workers) occurred. The mortality analysis shows a strong effect of the statistically significant “healthy worker” with an under-mortality of 35% compared to the national general population. Significant under-mortality is also observed for deaths by cancer pathology, non-cancer pathology and external causes. A single location presented a significant excess compared to the French population: pleural cancer (17 cases) with a standardized mortality ratio (SMR) of 2.04 (95% CI 1.19–3.27).

UNSCEAR [UNS 00b] reported 136 nuclear accidents with clinical consequences causing serious injuries to 90 nuclear workers, at least 40 of whom died within a few days. In addition, the same organization recorded 13 other accidents with clinical consequences for 368 workers, 13 of whom died. The normalized annual effective doses per unit of energy production were significantly higher for miners operating uranium mines. These doses decreased steadily from 1975 to 1994 due to radiation protection measures taken over time (Figure 2.5). The number of nuclear workers monitored for radiation increased from 1975 to 1989 and then stabilized, while the annual effective doses to workers steadily decreased (Figure 2.6).

Figure 2.5. Standardized collective effective dose per unit of energy production for various stages of the nuclear fuel cycle (mining, conversion, enrichment and fuel production) and for various time periods (adapted from [UNS 00b]). For a color version of the figure, see www.iste.co.uk/amiard/industrial.zip

Figure 2.6. Changes in the number of workers (in thousands) under surveillance (A) and of effective doses received (in mSv) by nuclear fuel cycle workers (B) according to four periods (adapted from [UNS 00b])