(super 14) C measurements at PWR-type nuclear power plants in three Middle European countries.

Abstract

Regular (super 14) C sampling of discharged air began in 1988 at Paks Nuclear Power Plant (NPP), Hungary, and in 1991 at NPPs in Krsko, Slovenia and Bohunice, Slovakia. Monitoring of (super 14) C discharges is carried out at all NPPs with similar differential samplers continuously collecting (super 14) C in the form of (super 14) CO (sub 2) and (super 14) C (sub n) H (sub m) . The main results of airborne discharge monitoring are as follows: (super 14) C activity concentration varied roughly within a factor of two around their mean values, 125 Bq m (super -3) and 90 Bq m (super -3) for Paks and for Krsko NPP, respectively. The pattern of discharge for Bohunice NPP is slightly different from that at the other two stations. At Bohunice, there has been a continuous increase in the discharge rate at power unit V1, starting with 70 Bq m (super -3) in 1991 and reaching a value of 190 Bq m (super -3) in 1995. The values for power unit V2 are 50 Bq m (super -3) and 82 Bq m (super -3) . The average normalized yearly discharge rates are 0.887 (TBqGW (sub e) (super -1) yr (super -1) ) for Paks, 0.815 (V1) and 0.500 (V2) for Bohunice, and 0.219 for Krsko. Most of the discharged (super 14) C is in hydrocarbon form, 95% for Paks and Bohunice V2, but the CO (sub 2) fraction may reach 25% or 43% at Bohunice V1 and Krsko, respectively. At Bohunice V1, not only the discharge rate increased but the (super 14) CO (sub 2) ratio to the total changed from 30% to 13%. The local radiological impact is estimated to be 1.5 mu Sv a (super -1) for Paks, 1.7 mu Sv a (super -1) for Bohunice, and 0.12 mu Sv a (super -1) for Krsko. The (super 14) C excess in the environment has been measured at Paks NPP since 1989. Based on the monitoring data, the long-term average (super 14) C excess from the Paks NPP was D (super 14) C = 50 per mil for hydrocarbons. Tree-ring analysis has shown a slight excess around Krsko NPP: D (super 14) C is equal to 199.9 per mil for a tree at 1 km from the NPP compared with a "reference" one for which D (super 14) C was equal to 111.6 per mil (in 1994).