VGB POWERTECH 5 (2021) - International Journal for Generation and Storage of Electricity and Heat

VGB PowerTech 5 l 2021
Radioactivity calculation for retired nuclear power plant
Fig. 9. Specific activities considering operation
history compared with traditional
method for 4 th surveillance capsule R.
Fig. 10. Specific activities considering operation
history compared with traditional
method for 5 th surveillance capsule P.
Fig. 11. Specific activities considering
operation history for 6th surveillance
capsule N.
Activity
(Bq/g)
operation history
(diff. vs meas.)
traditional
(diff. vs meas.)
Capsule N
63 Cu(n,α) 60 Co 54 Fe(n,p) 54 Mn 58 Ni(n,p) 58 Co
1.510E+04
(2.3 %)
activity calculation results were higher in
all cases. In the (F i g u r e 7, 8 , and 9 ),
the decrease curves reflect the decay until
measurement after irradiation.
(Ta b l e 4 ) shows a comprehensive comparison
between calculated activities and
measured activities. There is good agreement
between the calculated activity results
considering operation history and
measured activity results. The relative error
between them is less than 17 %. The relative
error between traditional method and
the measured activity results reaches 64 %.
The 6 th surveillance capsule, N, which has
a complicated irradiation history, was excluded
from this comparison. Only the activity
calculation results obtained using
the proposed method are shown in (F i g -
u r e 11 ) because it is unreasonable to assume
a representative production rate or
flux in case of a complicated irradiation
history. However, it is observed in (Ta -
b l e 5 ) that the calculated activity results
considering detailed plant-specific history
and the measured activity results for capsule
N show good agreement.
4. Discussion
With the long and complicated operation
history of a retired nuclear power plant,
consideration of the operation history in
Tab. 5. Specific activities comparison for product nuclides between measurement and calculation
for dosimeters in surveillance capsule N.
3.541E+06
(-6.4 %)
5.528E+07
(2.0 %)
- - -
measurement 1.545E+05 3.328E+06 5.640E+07
calculations is important in generating an
accurate radioactivity distribution because
the production rates are variable. In addition,
various radionuclides must be identified
before disposal and daughter nuclides
with a short half-life are more sensitive to
operation history. In this study, for radioactivity
calculation, the detailed operation
history is considered by using the thermal
power ratio per month. The calculated
activity results considering the detailed
operation history show good agreements
with measured activity results compared
with traditional calculated activity
results.
In the 63 Cu(n,a) 60 Co reaction of capsules V
and T in (Ta b l e 4 ), the traditional calculated
activity results seem to fit better with
measured activity results because the effect
of measurement error may be larger
than the effect of considering the operation
history. Except for these two cases,
the method considering the operation history
has less error than the traditional
method.
The number of target nuclides represented
by N 0 in Eq. (2) is also an important parameter
in the radioactivity calculation to pre-
67