국내 원전 삼중수소의 거동특성 및 선량평가를 통한 인체 노출 영향분석 연구

Abstract

A tritium released at domestic nuclear power plants is an important nuclide in terms of emission quantity among all of gaseous and liquid radioactive wastes. Especially, a tritium is produced and discharged in heavy-water reactors much more than light-water reactors. In this paper, a discharge amount and environmental behavior characteristic of tritium was investigated, and exposure dose by it was analysed by using urine samples of Wolseong NPP surroundings. Also, based on above analysis results, improvement methods for reducing the exposure dose of residents were presented

By research result, in case of Gori NPP, although the tririum discharge amount of gaseous and liquid form is similar, that of liquid form increased as time passed. And, in case of Hanbit NPP, the tritium discharge amount of liquid form is about four times more than that of gaseous form, and an influence according to time didn't appear. Otherwise, gaseous tritium was discharged three times more than liquid tritium, and the discharge amount of gaseous tritium decreased as time passed. it is judged that these trend is due to the operation of tritium removal facility.

By an evaluation result on the tritium discharge amount of NPP, it can be seen that Wolseong NPP discharge a gaseous tritium above 53 times compared with Hanul NPP, and that release a liquid tritium above 4.5 times compared with Gori NPP. It can be seen that the discharge amount of gaseous tritium in light-water reactor is the lowest at Hanul NPP, and that the discharge amount of liquid tritium is the lowest in Gori NPP. Therefore, it is judged that measures for reducing the discharge amount of liquid tritium in Gori NPP, and the discharge amount of gaseous liquid tritium in Hanul NPP must be established.

By analysis result on behavior characteristic in environmental media, it can be seen that the correlation according to distance from Gori, Habbit, Wolseong NPP targeting rain samples turns up as relatively R2=0.950, R2=0.889, R2=0.990. That is, the more the distance from nuclear power plants is near, the more tritium concentrations included into rain samples is high.

Also, by a behavior characteristic evaluation result on environmental media-moisture in air(Gyeongju and Ulsan direction), rain(Gyeongju direction), surface water(Ulsan direction) etc.-of Wolseong NPP surroundings, the correlation of three points turns up as relatively R2=0.921, R2=0.967, R2=0.903, R2=0.988, and it can be seen that the effect by tritium appear distinctly as the distance from NPP increase

Merely, to confirm the effect by a distance difference from NPP targeting environment media which the picking sites of tritium is only 2, it is judged that picking sites above 3 for analyzing have to be selected, and that sample picking sites on main wind direction is needed additionally.

By an human exposure influence valuation result due to tritium targeting the resident of Wolseong NPP surroundings, the more the distance from Wolseong NPP is near, the correlation between detectability factor and degree of exposure a noticeable distinction by way of R2=0.9744. And chromosome abnormality frequency does not appear, because of a low level radioactivity

By an exposure dose evaluation on environmental media and urine samples, it can be confirmed that a contribution by inhalation is low, and that a contribution by ingestion is high. Especially, by an exposure dose evaluation result by ingestion targeting Wolseong NPP, environmental media which have the greatest effect on exposure dose were barley, cabbage, rice etc.

An exposure dose evaluation was carried out targeting one year of age and the barley of Wolseong NPP surroundings, and by an evaluation result, it turns out that an exposure dose calculated amounts to 4.5 % of annual dose limit(1 mSv/hr). Generally, because values measured are more accurate than those calculated theoretically, it is judged that the retention of measurement data by supplementing picking sites according to main wind direction is very important in this paper.

By an exposure dose evaluation on urine samples, even if Uljin country residents are exposed to radiation during 1 year by the high tritium concentration, an exposure dose calculated amounts to 0.253 % of dose limit(1 mSv/hr)

In this paper, because a tritium intake standard on a drinking water does not exist, an intake standard on drinking water based on foreign examples was established. By establishment and analysis result, it is judged that a tritium intake standard of 2,000 Bq/L-which amounts to 2 % of domestic radioactivity disaster prevention measures law-on a drinking water is the most resonable in this paper.

Because the energy tritium is low, the effect on environment is insignificant. However, the discharge amount of tritium is lots of, and because tritium is continuously released from NPP, it is judged that continuous monitoring is needed. Especially, it is judged that technical studies and applications on tritium removal facility of heavy-water reactor are needed, and that management solutions for continuous monitoring on the surrounding environment and residents of NPP are needed.

Also, in respect of an resident exposure dose evaluation, because values measured are correct compared to those calculated theoretically, it is judged that long-term plan on this is needed.