DETERMINATION OF IRRADIATED CONTROL ROD WORTH OF NIGERIAN RESEARCH REACTOR – 1 (NIRR – 1) USING THE OPERATIONAL DATA
CHAPTER ONE
INTRODUCTION
1.1 Introduction
Nuclear reactors are initially loaded with a significantly large amount of fuel than that required to achieve criticality, because the intrinsic multiplication factor of the core will change during operation due to fuel burn-up and fission products. Sufficient excess reactivity is also provided to compensate for negative reactivity feedback effects due to temperature and power defects reactivity (Dudersadt, 1976). Therefore the core loading or enrichment will be determined by the desire to build into the core enough excess reactivity to allow power operation for a predetermined period of time.
The basic purpose of the reactor control system is to provide a means for starting the reactor, that is, bringing the power output up to the desired level, for maintaining it at that level, and for shutting it down in the course of routine operations. As an adjunct to the control system, a power reactor has a protection system designed to shut the reactor down automatically in the event that potentially unsafe conditions should arise. Safety rods was also designed and proposed for MNSR facilities (Ibrahim et al, 2012). An essential requirement of the control system is that it must be capable of introducing enough negative reactivity to compensate for the built-in (positive) reactivity at initial startup of the reactor (Glasstone and Sesonke, 1967)
The power level of the reactor depends on the macroscopic fission cross-section and the neutron flux. Over a short time interval, the cross section remains essentially constant, although it may not have the same value at all locations in the core. Hence, the power level at any instant can be considered proportional to the neutron flux. Four general methods are possible for changing the neutron flux in a reactor: they involve temporary addition or removal of (1) fuel, moderator, (3) reflector, or (4) a neutron absorber (poison).
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DETERMINATION OF IRRADIATED CONTROL ROD WORTH OF NIGERIAN RESEARCH REACTOR – 1 (NIRR – 1) USING THE OPERATIONAL DATA
