Procedures for Control Rod
Calibrations Spring 2025
PURPOSE
Calibration of a control rod in a nuclear reactor will be performed in this experiment. Reactivity
changes are measured by observing positive asymptotic periods of the reactor. These asymptotic
periods are related to reactivity by the reactor kinetics equations and the Inhour equation. Several
examples of kinetic behavior in response to changes in reactivity are qualitatively observed so
that operating skill and appropriate attitudes pertaining to safe reactor operation may be
developed.
PROCEDURE
In this lab, we will measure the differential reactivity worth of Shim Safety #1 (SS1) and #2
(SS2) versus position in the NSCR core.
Part 1: Rod Calibration by Difference Method
1 Withdraw the Transient rod to its upper limit of travel and the regulating rod to mid-range
(40-60%). During this time the Log Power Channel and period meter should be closely
observed. A small multiplication should be observed during this time.
2 We will raise the shim safeties other than the one to be calibrated to a critical condition
with the rod to calibrated left at position 0.
3 We will then raise the rod to calibrated while closely observing the Log Power Channel
and period meter to produce a period of 20 seconds or longer.
4 We will then allow the reactor to rise from 300 watts to 1000 watts. We will record the
power and time which we can use to determine the reactivity.
5 Once we reach 1000 watts, we will insert the remaining three rods to bring the reactor
subcritical reducing power to around 300 watts.
6 Once we are at 300 watts, we will adjust the remaining rods to bring the reactor critical.
7 We will record the difference in the remaining rod heights. This is will be used to check
our reactivity calculated above.
8 Repeat earlier steps until the rod of interest is at 100%.
This procedure is for the calibration of SS1 and SS2 and assumes that we know the worth of the
other shim safety rods.
Reporting Requirements
Report your results along with the results from next weeks lab via a long report (long report 8+
pages). The report should include the following:
1 Introduction
Purpose and the importance of rod calibrations
Differences between the two procedures utilized
2 Experimental Set-up and procedure
a Diagram of the reactor with rods that are used
b Detail the procedures used for both laboratory exercises.
1
3
Results & Discussion
3.a Positive Period. Calculations for reactivity worth including the uncertainty . For
two of the data points, you must calculate the slope of the curve from the rod
calibration data (note the appropriate form). I would like for you to plot the data
(watts) versus time (you will have three points and will have to compare these to
determine the error bars). You will then fit a curve to the data. The form used for
fitting the points may help you here. You can then calculate the reactivity.
3.b Include a plot(s) of the measured differential rod worths from your data.
3.c Include a plot(s) of the integral rod worths from your data.
3.d Include a discussion of the differential and integral rod worth curves. Plot the
actual worth (from the data provided) on the same plots.
3.e Does the data fit well to the predicted curves (from perturbation theory), why or
why not?
3.f Describe any source of error and any assumptions made.
3.g Rod Drop. Calculate the reactivity worth including the uncertainty. Please attach
the plot handed out in class as an attachement.
3.h Include a plot(s) of the measured differential rod worths from your data.
3.i Include a plot(s) of the integral rod worths from your data.
4
5
3.j Describe the advantages and disadvantages of using these two methods for rod
calibrations.
Conclusions
References (at least three)
2