3 Reactor Kinetics
59
For the kinetics calculations, time tallies were taken at the equivalent detector
position, without the actual inclusion of the detector in the calculation geometry.
The following is an alternative for the preceding highlighted part: Point detectors
with a sphere of exclusion 1 mm in diameter, as well as a flux tally in a 5 cm long
and 1 mm in diameter cylindrical volume, were centered at the detector position for
estimating the validity of the use of the point detector tally and the optimization of
calculation time.
3.1.3 Results and Discussion
3.1.3.1 Subcriticality
Positions of the control and safety rods in Cores 1–9 are shown in Table 3.1. The
results of measured and calculated subcriticalities are presented in Table 3.2. A
comparison of the experiments and the calculations demonstrates the ability of
MCNP calculations to reproduce subcriticality levels within 10% C/E. The simultaneous changes in the irradiation samples, the fuel mass, and the core geometry
limit precise conclusions on possible influences on the precision of calculations.
The apparent better C/E values for ENDF/B-VI.2 are not conclusive when a 5%
relative experimental error is taken into account. Namely, in Cases 1 and 3, there
was found to be a discrepancy of about 10% error between two libraries, due to
no irradiation sample in (15, K; Fig. 3.1c) and a large size window in front of fuel
Table 3.1 Control and safety rod positions in Cores 1–9 (dimension in mm) (Ref. [2])
Core
Case
C1
C2
C3
S4
S5
S6
1
1
0.00
0.00
0.00
1200.00
1200.00
1200.00
2
2
0.00
0.00
0.00
1200.00
1200.00
1200.00
3
3
0.00
0.00
0.00
1200.00
1200.00
1200.00
4
4
0.00
0.00
0.00
1200.00
1200.00
1200.00
5
5
0.00
0.00
0.00
1200.00
1200.00
1200.00
6
10
0.00
0.00
0.00
1200.00
1200.00
1200.00
11
0.00
0.00
0.00
0.00
0.00
0.00
7
12
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
13
0.00
0.00
0.00
1200.00
1200.00
1200.00
14
0.00
0.00
0.00
0.00
0.00
0.00
8
15
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
16
0.00
0.00
0.00
1200.00
1200.00
1200.00
17
0.00
0.00
0.00
0.00
0.00
0.00
9
18
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
0.00: Lower limit (Full insertion), 1200.00: Upper limit (Full withdrawal)
59
For the kinetics calculations, time tallies were taken at the equivalent detector
position, without the actual inclusion of the detector in the calculation geometry.
The following is an alternative for the preceding highlighted part: Point detectors
with a sphere of exclusion 1 mm in diameter, as well as a flux tally in a 5 cm long
and 1 mm in diameter cylindrical volume, were centered at the detector position for
estimating the validity of the use of the point detector tally and the optimization of
calculation time.
3.1.3 Results and Discussion
3.1.3.1 Subcriticality
Positions of the control and safety rods in Cores 1–9 are shown in Table 3.1. The
results of measured and calculated subcriticalities are presented in Table 3.2. A
comparison of the experiments and the calculations demonstrates the ability of
MCNP calculations to reproduce subcriticality levels within 10% C/E. The simultaneous changes in the irradiation samples, the fuel mass, and the core geometry
limit precise conclusions on possible influences on the precision of calculations.
The apparent better C/E values for ENDF/B-VI.2 are not conclusive when a 5%
relative experimental error is taken into account. Namely, in Cases 1 and 3, there
was found to be a discrepancy of about 10% error between two libraries, due to
no irradiation sample in (15, K; Fig. 3.1c) and a large size window in front of fuel
Table 3.1 Control and safety rod positions in Cores 1–9 (dimension in mm) (Ref. [2])
Core
Case
C1
C2
C3
S4
S5
S6
1
1
0.00
0.00
0.00
1200.00
1200.00
1200.00
2
2
0.00
0.00
0.00
1200.00
1200.00
1200.00
3
3
0.00
0.00
0.00
1200.00
1200.00
1200.00
4
4
0.00
0.00
0.00
1200.00
1200.00
1200.00
5
5
0.00
0.00
0.00
1200.00
1200.00
1200.00
6
10
0.00
0.00
0.00
1200.00
1200.00
1200.00
11
0.00
0.00
0.00
0.00
0.00
0.00
7
12
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
13
0.00
0.00
0.00
1200.00
1200.00
1200.00
14
0.00
0.00
0.00
0.00
0.00
0.00
8
15
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
16
0.00
0.00
0.00
1200.00
1200.00
1200.00
17
0.00
0.00
0.00
0.00
0.00
0.00
9
18
1200.00
1200.00
1200.00
1200.00
1200.00
1200.00
0.00: Lower limit (Full insertion), 1200.00: Upper limit (Full withdrawal)