Anthropogenic 14C Variations

Abstract

Continuous 14C data of 1 or 2 weekly samples of atmospheric CO2 are presented, collected near two nuclear power plants (NPP-Biblis and NPP-Philippsburg) located in the rather densely populated upper Rhine valley. Tree-leaf and tree-ring samples from the area of a boiling water reactor in northern Germany (NPP-Würgassen) are also presented and discussed. Additional atmospheric 14CO2 samples from two continental ‘clean-air’ stations in Germany and Austria were used as reference for the polluted areas. For January 1982, these samples yield a ‘clean-air’ 14C concentration in central Europe of Delta-14C=255 +/- 5 per mil (7.7pCi/gC = 1.45pCi/m3 air). In the vicinity of boiling water reacctors we found a mean excess in Delta-14C activity of ca 53 per mil (0.05pCi/m3 air) above the local level during normal periods of reactor operation. During revision, however, the Delta-14C excess may reach up to 300 per mil above the local background. From this, we calculate source strengths of ca 20Ci/GWa on the average, with peak values of up to 2Ci/week during specific periods. Pressurized water reactors emit 14C mainly as hydrocarbons, and consequently, we found no additional 14CO2 near the Biblis reactor. Stations located in the Rhine valley show significant summer-winter 14CO2 variation due to intensive fossil-fuel combustion. The fossil-fuel admixture leads to a depression of the 14C level and reaches Delta-14Cdepr = 120 per mil in winter; summer values, however, are only slightly lower than the 'clean-air' level.