Thermal Hydraulic
Fundamentals
Problem 3-2 Power profile in a homogeneous reactor (section IV)
Consider an ideal core with the following characteristics: The 235U enrichment is uniform throughout
the core, and the flux distribution is characteristic of an unreflected, uniformly fueled cylindrical reactor,
with extrapolation distances 5z and SR of 10 cm. How closely do these assumptions allow prediction of
the following characteristics of a PWR?
I . Ratio of peak to average power density and heat flux?
2
. Maximum heat flux?
3. Maximum linear heat generation rate of the fuel rod?
4. Peak-to-average enthalpy rise ratio, assuming equal coolant mass flow rates in every fuel assembly?
5 . Temperature of water leaving the central fuel assembly?
Calculate the heat flux on the basis of the area formed by the cladding outside diameter and the active
fuel length. Use as input only the following values.
Total power = 34 1 1 MWt (Table 1 -2)
Equivalent core diameter = 3 . 37 m (Table 2-3)
Active length = 3 . 66 m (Table 2-3)
Fraction of energy released in fuel = 0 .974
Total number of rods = 50,352 (Tables 2-2, 2-3)
Rod outside diameter = 9.5 mm (Table 1 -3)
Total flow rate = 17.4 x 103 kgls (Table 1 -2)
Inlet temperature = 286°C (Table 1 -2)
Core average pressure = 1 5 . 5 MPa (Table 1 -2)
Answers:
I . cfJJ¢ = 3 . 1 1
2 . qô€ ¾ax = 1 . 88 MW 1m2
3. qô€ ¿,ax = 56 . 1 kW 1m
4. (Llh)maxl Llh = 2 .08
5. (Toul)max = 344.9°C"