**5. Acknowledgment**

194 Nuclear Reactors

Fig. 7. The large oscillation for: Set Point: 100, v: 7, H: 100, delay time: 10 ms

inordinate increasing can cause unstable states.

aspect, according to its control rod velocity is derived.

**4. Conclusion** 

The Figs.4, 5, 6 and 7 show if the velocity of control rod for upward and downward movements is increased then the Keff will be pendulous surrounds of defined Set Point (reference Keff) and also the oscillation amplitude will be more than lower velocity situations. For low velocities the oscillation amplitude is slight and acceptable. Another effective factor is inherent delay (such as derived delay of control rod mechanism) and its

By this simulation the best response and operation which a reactor can have from stability

According to Figs.4-8 the best status in the Fig.4 is observed in which there is no vibration in response. In this simulation the stability of reactor depends on either velocity or delay time values directly because delay time plays a key role. Therefore in this simulation the admissible ranges of velocity and delay time which can be caused to stable the reactor are respectively: low velocity of control rod around 1-3 units per second and short delay time (10ms). However in this case reach critical state (Keff=1) for nuclear reactor will be taken more than modes Figs.5-8. As in all the figures is observed, so can deduce the velocity of control rod plays the more important role than delay time of mechanism in stability of nuclear reactor. Whereas for minor and major changes of reactivity and shut down of reactor in emergency states, there are some kinds of control rods at nuclear reactors cores such as regulating rods, safety rods and shim rods, therefore this simulation can be applied for each control rod in either LWR nuclear reactor or research reactor cores which have vertical control rods. Also this simulation can be applied for each batch control rods which This book chapter is related to a research project entitled: "The Simulation of a Model by SIMULINK of MATLAB for Determining the Best Ranges for Velocity and Delay Time of Control Rod Movement in LWR Reactors" that by financial supporting the Islamic Azad University-South Tehran Branch has been carried out.
