2 Subcriticality
41
The above expression is a familiar formula for the integral count technique.
The technique is also applied to the present beam trip experiment. Prior to beam
trip operation, the average count rate used as N(0) is measured using a conventional
counting scaler. Then, the integral counts after the operation, which can be used as
an integral appearing in the denominator of Eq. (2.56), are also measured using the
scaler.
2.3.3 Results and Discussion
2.3.3.1 Time-Sequence Data
Figure 2.22 shows the time-sequence N(t) and Q(t) data obtained from counter
B4 in a beam trip experiment, where the control rod pattern is A and the beam is
turned off at zero time. The time-sequence N(t) data in this figure are indicated as
instantaneous count rate at every 0.1 s. After the beam trip, N(t) and Q(t) promptly
decrease and then asymptotically tend to zero. The statistical fluctuation of Q(t)
defined using Eq. (2.54) is slight, compared with that of N(t). This is because the
delayed-neutron emission rate Q(t) is an integral quantity of N(t) over a passing
time. The least-squares approximation fits a model function with minimum error on
the y-axis assuming no error on the x-axis. Therefore, the time-sequence Q(t) and
N(t) data should be assigned to x- and y-axis variables, respectively, for successful
least-squares fitting on the x-y coordinate.
Figure 2.23 shows the time-sequence N(t) and Q(t) data obtained from counter
B4 in a beam restart experiment, where the control rod pattern is A and the beam is
turned on at zero time. After the beam restart, N(t) and Q(t) promptly increase and
then asymptotically tend to their individual constants.
2.3.3.2 Least-Squares Fitting
In Fig. 2.24, the above Q(t) and N(t) data are plotted on the x-y coordinate, where
the fitted lines are drawn by a straight line. Equations (2.55) and (2.53) were fitted to
the data sets of Fig. 2.24a, b, respectively. The fitting is successful and the subcritical
reactivity can be determined from the slope of the fitted line.
Table 2.3 summarizes the reactivities obtained from the beam trip and restart
experiments. As the errors of these results of the LSIKM, the statistical uncertainties that originated from the least-squares fit were employed, while the uncertainty
of delayed-neutron yield β was not taken into account. The errors of the integral
count technique were estimated from counting statistics. For comparison, the results
obtained by a pulsed neutron experiment [11] are also shown in Table 2.4, where the
subcriticality obtained by a conventional analysis technique has a significant counterposition dependence. This dependence is originated from a higher mode excited by
41
The above expression is a familiar formula for the integral count technique.
The technique is also applied to the present beam trip experiment. Prior to beam
trip operation, the average count rate used as N(0) is measured using a conventional
counting scaler. Then, the integral counts after the operation, which can be used as
an integral appearing in the denominator of Eq. (2.56), are also measured using the
scaler.
2.3.3 Results and Discussion
2.3.3.1 Time-Sequence Data
Figure 2.22 shows the time-sequence N(t) and Q(t) data obtained from counter
B4 in a beam trip experiment, where the control rod pattern is A and the beam is
turned off at zero time. The time-sequence N(t) data in this figure are indicated as
instantaneous count rate at every 0.1 s. After the beam trip, N(t) and Q(t) promptly
decrease and then asymptotically tend to zero. The statistical fluctuation of Q(t)
defined using Eq. (2.54) is slight, compared with that of N(t). This is because the
delayed-neutron emission rate Q(t) is an integral quantity of N(t) over a passing
time. The least-squares approximation fits a model function with minimum error on
the y-axis assuming no error on the x-axis. Therefore, the time-sequence Q(t) and
N(t) data should be assigned to x- and y-axis variables, respectively, for successful
least-squares fitting on the x-y coordinate.
Figure 2.23 shows the time-sequence N(t) and Q(t) data obtained from counter
B4 in a beam restart experiment, where the control rod pattern is A and the beam is
turned on at zero time. After the beam restart, N(t) and Q(t) promptly increase and
then asymptotically tend to their individual constants.
2.3.3.2 Least-Squares Fitting
In Fig. 2.24, the above Q(t) and N(t) data are plotted on the x-y coordinate, where
the fitted lines are drawn by a straight line. Equations (2.55) and (2.53) were fitted to
the data sets of Fig. 2.24a, b, respectively. The fitting is successful and the subcritical
reactivity can be determined from the slope of the fitted line.
Table 2.3 summarizes the reactivities obtained from the beam trip and restart
experiments. As the errors of these results of the LSIKM, the statistical uncertainties that originated from the least-squares fit were employed, while the uncertainty
of delayed-neutron yield β was not taken into account. The errors of the integral
count technique were estimated from counting statistics. For comparison, the results
obtained by a pulsed neutron experiment [11] are also shown in Table 2.4, where the
subcriticality obtained by a conventional analysis technique has a significant counterposition dependence. This dependence is originated from a higher mode excited by