[Occupational risk assessment levels before and after improvement on fueling devices in ammoniation facilities from 2 nuclear plants]

To evaluate and compare possible changes of individual health risk levels for ammonia exposed positions from ammoniation facilities in 2 nuclear power plants(X and Y) through occupational risk assessment models(OHRA) before and after devices improvement.

This study tried to understand the improvement of fueling devices in ammoniation facilities, to identify the ammonia exposed positions and their working content, to collect information on protective measures and personal protective equipment situation through on-sites survey and detailed records of work days. Next, detection on C_(STE) of ammonia at different worksites and C_(TWA) of 10 involved positions were conducted, fresh air requirement and ventilation air changing rates were calculated through wind speed detection or collected directly. Finally, a semi-quantitative comprehensive index model and a quantitative non-carcinogenic model from standard GBZ/T 298-2017 were utilized to assess risk levels before and after improvement.

After devices improvement, a series of innovations were observed, followed by:(1) ammonia steal tanks in stacking storage were replaced by metal pressure sealing tanks for reduction of exposure frequency and long time storage. (2) manual filling pattern was totally substituted by automatic filling devices with new installed ventilation systems and alarming apparatus. (3) increasing ventilation effect by doors opening when ammonia was filling. In this regard, conentration levels(C_(STE)) referred to positions of chemical analysis engineers, chemical sampling engineers, nuclear maintenance workers at 3# unit from X, and regular island operators at 1#unit, patrolling operators at 2# unit from Y were declined to qualified levels after improvement from unqualified levels before that, and significant difference of C_(STE )detected before and after improvement were found statistically(Z=10.856, P<0.001). C_(TWA )were all within the qualified ranges before and after improvement for relatively short cumulative exposure time. Moreover, the ventilation air changing rates from related indoor sectors were increased to 13.0 to 30.9 times/h after improvement which indicated a statistical difference as compared to quantitative ranges before started(Z=11.670, P<0.001). Further, a relative negative correlation was observed between C_(STE )and ventilation air changing rates(r=-0.39, P<0.05) while no correlation between them was spotted after improvement(r=-0.051, P>0.05). In addition, most positions like chemical analysis engineers and others changed their risk levels to a lower one from that they used to be after improvement with an observed significant difference(Z=1.345, P<0.05), by contrast, risk levels of positions like nuclear maintenance workers at 3#unit or patrolling operators at 4#unit increased a level or remained the same before and after improvement might be result ed from enhancement of cumulative exposure time. No significant difference among position risk levels under the quantitative non-carcinogenic model was observed(Z=0.447, P>0.05).

The measure of devices improvement indeed decreased the ambient ammonia concentrations at workplaces of ammoniation facilities in X and Y and changed individual risk levels for most involved positions. The semi-quantitative comprehensive index model was more appropriated for self-contrast risk assessment application than quantitative non-carcinogenic model did, especially when improvement occurred.