**9. Acknowledgement**

The authors are thankful InTech publication for their scientific effort to develop the sciences. We also, thank Mrs. M. Mohammadi for her effort to preparing the manuscript.

#### **10. Conclusion**

Power monitoring channels play a major role in retaining a safe reliable operation of nuclear reactors and nuclear power plants. Accurate power monitoring using advanced developed channels could make nuclear reactors a more reliable energy source and change public mind about this major energy resource. Regarding harsh accidents such as Chernobyl, Three-Mile Island and the recent accidents in Fukushima nuclear power plants and their dangerous effects on the environment and human life, the importance of developing reactor safety system like power monitoring channels are more attended. New generations of nuclear power plants are much safer than their predecessors because of their new accurate safety systems and more reliable monitoring channels. They produce energy from nuclear fission and are the cleanest, safe and environment-friendly source of energy among many investigated power resources (Javidkia et al., 2011).

There is no doubt that nuclear power is the only feasible green and economic solution for today's increasing energy demand. Therefore, studying, researches and more investments on the power monitoring systems and channel in nuclear reactors will help to create an inexhaustible source of safe and clean energy.

#### **11. References**

IAEA, (2008). *On-line monitoring for improving performance of nuclear power plants part 2: process and component condition monitoring and diagnostics*, International atomic energy agency (IAEA), Vienna, ISSN 1995–7807; no. NP-T-1.2, STI/PUB/1323, ISBN 978– 92–0–101208–1.

the difference between the temperatures at loop the inlet and outlet (°C). Figure 21 shows the power evolution in the primary and secondary loops during one reactor operation.

Fig. 21. Thermal power evolution in the cooling system (Zacarias Mesquita and Cesar

We also, thank Mrs. M. Mohammadi for her effort to preparing the manuscript.

investigated power resources (Javidkia et al., 2011).

inexhaustible source of safe and clean energy.

92–0–101208–1.

The authors are thankful InTech publication for their scientific effort to develop the sciences.

Power monitoring channels play a major role in retaining a safe reliable operation of nuclear reactors and nuclear power plants. Accurate power monitoring using advanced developed channels could make nuclear reactors a more reliable energy source and change public mind about this major energy resource. Regarding harsh accidents such as Chernobyl, Three-Mile Island and the recent accidents in Fukushima nuclear power plants and their dangerous effects on the environment and human life, the importance of developing reactor safety system like power monitoring channels are more attended. New generations of nuclear power plants are much safer than their predecessors because of their new accurate safety systems and more reliable monitoring channels. They produce energy from nuclear fission and are the cleanest, safe and environment-friendly source of energy among many

There is no doubt that nuclear power is the only feasible green and economic solution for today's increasing energy demand. Therefore, studying, researches and more investments on the power monitoring systems and channel in nuclear reactors will help to create an

IAEA, (2008). *On-line monitoring for improving performance of nuclear power plants part 2: process* 

*and component condition monitoring and diagnostics*, International atomic energy agency (IAEA), Vienna, ISSN 1995–7807; no. NP-T-1.2, STI/PUB/1323, ISBN 978–

Rezende, 2007).

**10. Conclusion** 

**11. References** 

**9. Acknowledgement** 


**1. Introduction** 

rendering them unsuitable for the desired application.

supersaturated defect concentrations and radiation induced segregation.

**12** 

*USA* 

Chaitanya Deo

*Georgia Institute of Technology* 

**Multiscale Materials Modeling** 

**of Structural Materials for Next** 

In the process of energy production via fission – and fusion in the years to come - both fuel components and structural materials within nuclear reactors can sustain substantial radiation damage. Regardless of the type of reactor, this damage initially appears in the form of local intrinsic point defects within the material – vacancies and interstitials. The point defects agglomerate, interact with the underlying microstructure and produce effects such as void swelling and irradiation creep. Vacancies provide a pathway for solutes to segregate to grain boundaries and dislocation leading to chemical inhomogeneities that translate into phase transformations and/or property variations in these materials,

Many deleterious effects of irradiation on material properties—e.g. void swelling, irradiation creep, radiation-induced hardening and embrittlement—can be traced back to the formation of the aforementioned point defect clusters and gas bubbles. These effects include such phenomena as swelling, growth, phase change, segregation, etc. For example (Was 2007), a block of pure nickel, 1cm on a side, irradiated in a reactor (to a fluence of say, 1022 n/cm2) will measure 1.06cm on a side, representing a volume change of 20%. The volume change, or swelling, is isotropic and is due to the formation of voids in the solid. Other examples are irradiation growth which is distortion at constant volume, phase changes under irradiation where new phases form as a consequence of diffusion of

In addition, the transmutation of reactor elements produces extrinsic defects such as hydrogen, deuterium and helium. For example, Zircalloy high-pressure-tubes used in light water reactors are known to absorb deuterium which can cause delayed hydride cracking (Cirimello, G. et al. 2006). Similarly, in Pebble Bed Modular reactors and in other technologies based on inert gas cooling, formation of ionic gas bubbles within both fuel and structural materials is common(Was 2007). This is critical in structural materials as their behaviour depends on their microstructure, which is in turn affected by neutron radiation.

**Generation Nuclear Reactors** 

*Nuclear and Radiological Engineering Programs, George W. Woodruff School of Mechanical Engineering,* 

