Whole report - STUK

STUK-YTO-TR 175
3 MEASUREMENTS
3.1 Fuel data
The total number of measured assemblies was 26.
Sixteen assemblies were measured during the first
campaign (no. 1–16 in Table I) and eleven during
the second campaign (no. 17–27 in Table I). The
assembly #12323 was measured in both campaigns.
All assemblies except for the assemblies
#7289 and #13285 have been irradiated in 3–5
sequential one-year cycles. The assemblies #7289
and #13285, which were measured during the second
campaign, have had an intermediate oneyear
off-reactor cycle.
3.2 The first measurement
campaign
On every measurement day the functioning of the
neutron measurement system was tested with
help of an Am–Be neutron source, which was
mounted in an assembly shaped box. The neutron
source was lowered into the pond, and the signals
of both the cadmium wrapped and the bare fission
chambers were taken. These neutron count rates
were found to be constant throughout the measurements.
The assemblies to be measured were brought
from the storage pond to the evacuation pond by
the fuel handling machine. The accurate positioning
of the fuel assembly between the prongs of the
fork was made with the fuel handling machine
and the detector head was kept in a fixed position.
Angular gamma spectroscopic scanning of assembly
#12350 was performed using only the CZT
detector with the fork prongs removed. The assembly
was rotated 95º clockwise and the scanning
was taken at 5º intervals (i.e. 20 points). To
check the sensitivity to repositioning of an assembly
some measurements were repeated at some
measurement positions. All other measurements
were performed with the fork prongs attached,
and the total neutron count, the gross gamma
current and the gamma spectrum were taken.
The assembly #12350 was moved horizontally
towards the measurement head and measured at
10 mm intervals in the central part of the assembly
(z = 5705 mm). The first measurement point (x
= 0 mm) corresponds to a situation, when the
farthest side of the assembly was in line with the
end of the fork prong (Figure 9). The nearest
position to the measurement head corresponds to
a situation, when x-coordinate was –40 mm (Distance
from the collimator end plate was about
10 mm.)
In the axial scanning measurements and in the
measurements taken at one vertical level the
horizontal coordinate x = 0 mm was used.
The total neutron, the gross gamma and the
gamma spectrum of assemblies no. 1–16 listed in
Table I were measured in the central part of the
assembly, at x = 0 mm and z = 5705 mm (Figure
9). The assemblies were measured at four sides
with 90 degrees rotation to even up possible
azimuthal asymmetry.
Figure 9. Measurement of an assembly in the position
(x,z) = (0 mm, 5705 mm). The farthest side of
the assembly is in line with the end of the fork prong.
There is a large water gap between the assembly and
the collimator end plate.
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