RRFM 2009 Transactions - European Nuclear Society

1.00E+06
1.00E+05
Volume activity (Bq/l)
1.00E+04
1.00E+03
1.00E+02
1.00E+01
15.5.1996 15.5.1998 14.5.2000 14.5.2002 13.5.2004 13.5.2006 12.5.2008
Date of sampling
Figure 2 Time dependence of volume activity of 239 Np
3. Neutron activation analysis of evaporated water samples
0.5 l primary circuit water was evaporated on Al foil, and similarly demineralised water
sample was prepared. Evaporated water samples were irradiated in the reactor core for 24 h.
Then the induced activities were measured.
Fission products activities for evaporated sample of primary circuit water were much higher
then for demineralised water. Then source of fission products does not origin from
demineralised water.
The resulted mass concentrations for December 2006 are 0.25 μg/l for 235 U and 1.00 μg/l for
235 U. Similar measurement was made in November 2008 and concentrations decreased (see
Table 1).
4. Data analysis
Radionuclides in the water are produced by activation of stable nuclides and by fission of
fissile nuclides, mainly 235 U [3]. Demineralized water used for primary circuit water includes
small concentration of natural uranium. Fuel assemblies include uranium with enrichment of
36 %. Also uranium from surface contamination of fuel cladding has that enrichment.
Increased activities of fission products in 1996 were due to a damaged fuel assembly in the
reactor core. That assembly was removed from the reactor core and since that time the
activities of fission products in primary circuit water decreased until November 2006.
In 2005 more detailed analysis of data was made [4]. From comparison of theoretical results
and measured values of volume activities of fission products and 239 Np the enrichment of the
irradiated uranium was estimated. The resulted 39 % enrichment has high uncertainty due
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