16 Jul nuclearEngg-niii
plz cite the sources from which you get help for answering any question so i can follow along
1. True / False (mark the correct answer;some explanation is required to support your answer)
(1 × 10 = 10)
a) Generally, a CANDU reactor has a large pressure vessel. True False
b) The ideal c/a of a HCP unit cell is 1.363. True False
c) Hafnium can serve as a good fuel cladding material. True False
d) Alpha-Zr has a face centered cubic crystal structure. True False
e) For a crystallographic plane (hkil) in a HCP crystal, the following relationship,h + k = i , is valid. True False
f) The normal direction to any plane (hkil) in a HCP crystal will always have a Miller-Bravais index of [hkil]. True False
g) The atomic packing factor of simple cubic crystal is about 0.32. True False
h) One of the reasons that aluminum is not used as a fuel cladding material in LWRsis because it has a low neutron capture cross-section. True False
i)The U238isotope of uranium is known as a ‘fertile’ fuel. True False
j) Divacancies are more prevalent than monovacancies under general conditions. True False
2. a) Calculate the density of UO2 in gm/cc (describe the steps clearly to earn full credit). (6)
| Ionic Radius | Atomic Radius | Atomic Number | Atomic Weight | |
| U4+ | 0.105 nm | 0.138 | 92 | 238 |
| O2- | 0.132 nm | 0.060 | 8 | 16 |
b) Comment if the material becomes non-stoichiometric (such as UO2+x and UO2-x), how this may affect the physical density you calculated above. Or will they change at all? (2)
3. a) Writeat least three functions of fuel cladding in LWRs. b) Name two well known nuclear grade zirconium alloys with compositions. (3 + 2)
4. (a) If the activation energy for vacancy formation in iron is 35 kCal/mol, what is the vacancy concentration at 400 oC? (b) If the binding energy is 5 kCal/mol, what would be the divacancy concentration at 400oC? (c) Draw an octahedral interstitial position in an FCC unit cell.
(4 + 4 + 2)
5. (a) Draw a simple cubic unit cell and denote the Miller indices of individual cube faces. Also show the Miller indices of a body diagonal and a face diagonal in the same unit cell. (b) Name the close packed planes and directions in FCC and HCP unit cells. (c) What is polymorphism? Give an example of polymorphism in a metal of importance for nuclear applications. Also, state the respective crystal structures. (4 + 2 + 2)
6. If boron diffuses into a thick slice of silicon with no previous boron in it at a temperature of 1100°C for 5 hours, what is the depth below the surface at which the concentration of boron is 1017 atoms/cm3 if the surface concentration is 1018 atoms/cm3? Given: D = 4 10-13 cm2/s for boron diffusing in silicon at 1100°C. (5)
7. (a) Fast reactor cladding is not made of zirconium, but generally made of stainless steel. Why? (b) A nuclide has the total neutron cross section of 5.5 b at a specified energy. At the same energy, only three neutron interaction events are feasible. The different neutron cross sections for two interactions are the following: 1 b for capture and 2 b for alpha-producing reaction. What is the neutron cross section for the third interaction?
(2 + 2)
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