7 Neutronics of Lead and Bismuth
187
Table 7.3 Comparison between the results of measured and calculated excess reactivities in
reference core shown in Fig. 7.1 (Ref. [1])
Calculation [pcm]
Experiment [pcm]
C/E*
98 ± 6
92 ± 5
1.07 ± 0.09
C/E*: calculation/experiment
Table 7.4 Comparison between the results of measured and calculated control rod worth in
reference core shown in Fig. 7.1 (Ref. [1])
Rod
Calculation [pcm]
Experiment [pcm]
C/E
C1
1003 ± 6
980 ± 29
1.02 ± 0.03
C2
447 ± 6
442 ± 13
1.01 ± 0.03
C3
356 ± 6
364 ± 11
0.98 ± 0.03
(β eff = 798 [pcm] and = 3.394E-05 (s) by MCNP6.1 with JENDL-4.0)
in Table 7.3, the C/E (calculation/experiment) value revealed good agreement with
a relative difference of 7%.
Furthermore, in the reference core, the measured control rod worth was compared
with the calculated one, using the same method as for the excess reactivity. The
results are as shown in Table 7.4. The MCNP eigenvalue calculations reproduced
the experimental results of control rod worth accurately, with the C/E values within
2%, ranging between 350 and 1,000 pcm, regardless of the kind of control rod used
(Table 7.4).
7.2.2.2 Eigenvalue Bias
On the basis of Eq. (7.2), numerical analyses of sample reactivity were conducted by
the MCNP6.1 eigenvalue calculations with nuclear data libraries as in Sect. 7.2.2.1.
In numerical simulations, sample reactivity worth was obtained by the two eigenvalue calculations in both critical and super-critical states: the difference between the
inverse values of eigenvalue calculations in the two states. The calculated results of
the sample reactivity were obtained by varying the nuclear data libraries, as shown in
Table 7.5 (comparison between Eqs. (7.1) and (7.2)), and, through an estimation of
C/E values, were compared at a high accuracy with the experimental results in almost
all cases, regardless of the kind of nuclear data libraries used. From the calculated
results in Tables 7.3 through 7.5, the precision of MCNP6.1 with JENDL-4.0 was
considered fairly good in the eigenvalue calculations, and JENDL-4.0 was found
reliable as a reference nuclear data library, comparing it with JENDL-3.3.
Prior to the MCNP numerical analyses, in the experiment results, interesting
discussions were provided from two aspects. First, the positive reactivity effect was
found in the sample reactivity experiments substituting Al plates for Pb ones, and
was mainly attributable to the difference between the values of moderating ratio
187
Table 7.3 Comparison between the results of measured and calculated excess reactivities in
reference core shown in Fig. 7.1 (Ref. [1])
Calculation [pcm]
Experiment [pcm]
C/E*
98 ± 6
92 ± 5
1.07 ± 0.09
C/E*: calculation/experiment
Table 7.4 Comparison between the results of measured and calculated control rod worth in
reference core shown in Fig. 7.1 (Ref. [1])
Rod
Calculation [pcm]
Experiment [pcm]
C/E
C1
1003 ± 6
980 ± 29
1.02 ± 0.03
C2
447 ± 6
442 ± 13
1.01 ± 0.03
C3
356 ± 6
364 ± 11
0.98 ± 0.03
(β eff = 798 [pcm] and = 3.394E-05 (s) by MCNP6.1 with JENDL-4.0)
in Table 7.3, the C/E (calculation/experiment) value revealed good agreement with
a relative difference of 7%.
Furthermore, in the reference core, the measured control rod worth was compared
with the calculated one, using the same method as for the excess reactivity. The
results are as shown in Table 7.4. The MCNP eigenvalue calculations reproduced
the experimental results of control rod worth accurately, with the C/E values within
2%, ranging between 350 and 1,000 pcm, regardless of the kind of control rod used
(Table 7.4).
7.2.2.2 Eigenvalue Bias
On the basis of Eq. (7.2), numerical analyses of sample reactivity were conducted by
the MCNP6.1 eigenvalue calculations with nuclear data libraries as in Sect. 7.2.2.1.
In numerical simulations, sample reactivity worth was obtained by the two eigenvalue calculations in both critical and super-critical states: the difference between the
inverse values of eigenvalue calculations in the two states. The calculated results of
the sample reactivity were obtained by varying the nuclear data libraries, as shown in
Table 7.5 (comparison between Eqs. (7.1) and (7.2)), and, through an estimation of
C/E values, were compared at a high accuracy with the experimental results in almost
all cases, regardless of the kind of nuclear data libraries used. From the calculated
results in Tables 7.3 through 7.5, the precision of MCNP6.1 with JENDL-4.0 was
considered fairly good in the eigenvalue calculations, and JENDL-4.0 was found
reliable as a reference nuclear data library, comparing it with JENDL-3.3.
Prior to the MCNP numerical analyses, in the experiment results, interesting
discussions were provided from two aspects. First, the positive reactivity effect was
found in the sample reactivity experiments substituting Al plates for Pb ones, and
was mainly attributable to the difference between the values of moderating ratio