Civil Engineering Reference
In-Depth Information
The tritium produced in the core migrates along grain boundaries and cracks of
the fuel into gaps between fuel pellets and the cladding and is collected in the fission
product gas plenum of the fuel rod. The zircaloy tubes of LWR fuel rods bind some
60 % of the tritium inventory. Moreover, an oxide layer building up on the outer
wall of the zircaloy cladding tube acts as a diffusion barrier to the tritium. As a
consequence, more than 99.9 % of the tritium formed is retained in the LWR fuel
rod. Only if cladding tube failures occur, releases of tritium into the cooling water
will be increased. Some of the tritium is discharged with the gaseous effluents. In
water cooled reactors most of it remains in the coolant as tritiated water. Some of
the tritiated water is released at a controlled rate. Improved methods under study are
the concentration of tritiated water by evaporation and its prolonged storage in
decay tanks. With a half-life of tritium of about 12 years, some 90 % will have
decayed after 40 years.
Besides the radioactive noble gases and tritium, also such elements as rubidium,
strontium, technetium, ruthenium, silver, tellurium, antimony, iodine, cesium,
barium, rubidium, lanthanum and cerium are radiologically significant. Except for
iodine, cesium and rubidium, these elements have only low volatilities. They may
enter the primary coolant through defective fuel rod claddings. Non-volatile fission
products can enter the liquid effluent only through the primary coolant purification
system.
4.7.1 Radioactive Effluents from PWRs and BWRs
Radioactive effluents from PWRs and BWRs are given here for two countries:
Germany and the USA.
4.7.1.1 Radioactive Effluents from PWRs and BWRs in Germany
Table
4.7
shows emission data of typical German PWRs and BWRs (data are
normalized to 1 GW(e)
year). This set of data was reported in the annual report
for 2008 on radioactive releases and radiation exposure from German nuclear
installations [
12
,
13
]. The data collected for 2009 differ slightly [
13
]. The PWR
data are given for PWR plants at the site of Neckarwestheim (Germany). The BWR
data are valid for two BWR plants with a total power output of 2.7 GW(e) at the site
of Gundremmingen (Germany). For comparison also the half-lives of the different
emitted isotopes are given.
∙
