Heat Transfer and Heat Exchangers

Question 1

The transfer of heat from the reactor fuel pellets to the fuel cladding during normal plant operation is
primarily accomplished via __________ heat transfer.

Answer 1

conduction

Question 2

Refer to the drawing of a fuel rod and coolant flow channel at the beginning of a fuel cycle (see figure
below).
Which one of the following is the primary method of heat transfer through the gap between the fuel
pellets and the fuel cladding?

Answer 2

Conduction

Question 3

During a loss-of-coolant accident, which one of the following heat transfer methods provides the most
core cooling when fuel rods are not in contact with the coolant?

Answer 3

Radiation

Question 4

Reactor fuel rods are normally charged with __________ gas; which improves heat transfer by
__________.

Answer 4

helium; conduction

Question 5

A nuclear power plant is operating at 60 percent power. Which one of the following is the primary
method of heat transfer from the outer surface of the steam generator tubes to the bulk feedwater?

Answer 5

Convection

Question 6

Which one of the following describes a heat transfer process in which convection is the most
significant mode of heat transfer?

Answer 6

From the fuel rods to the steam generators 24 hours after a trip of all reactor coolant pumps.

Question 7

Which one of the following describes a heat transfer flow path in which conduction is the dominant
mode of heat transfer?

Answer 7

From a fuel pellet to the fuel cladding via the fuel rod fill gas during normal operation.

Question 8

If excessive amounts of air are entrained/dissolved in the cooling water passing through a heat
exchanger, the overall heat transfer coefficient of the heat exchanger will decrease because the…

Answer 8

thermal conductivity of the cooling fluid will decrease.

Question 9

Why is bulk boiling in the tubes of a single-phase heat exchanger undesirable?

Answer 9

The turbulence will restrict fluid flow through the heat exchanger tubes.

Question 10

Which one of the following pairs of fluids undergoing heat transfer in identical heat exchangers will
yield the greatest heat exchanger overall heat transfer coefficient?

Answer 10

Steam to water

Question 11

Which one of the following pairs of fluids undergoing heat transfer in identical heat exchangers will
yield the smallest heat exchanger overall heat transfer coefficient?

Answer 11

Air to water.

Question 12

A nuclear power plant is operating near 100 percent power. Main turbine extraction steam is being
supplied to a feedwater heater. Extraction steam parameters are as follows:
Steam pressure = 414 psia
Steam flow rate = 7.5 x 105 lbm/hr
Steam enthalpy = 1,150 Btu/lbm
The extraction steam condenses to saturated water at 414 psia, and then leaves the feedwater heater via
a drain line.
What is the heat transfer rate from the extraction steam to the feedwater in the feedwater heater?

Answer 12

5.4 x 108 Btu/hr

Question 13

A nuclear power plant is initially operating at a steady-state power level with the following main
condenser parameters:
Main condenser pressure = 1.2 psia
Cooling water inlet temperature = 60°F
Cooling water outlet temperature = 84°F
Due to increased condenser air inleakage, the overall heat transfer coefficient of the main condenser
decreases by 25 percent. Main condenser heat transfer rate and cooling water temperatures are
unchanged. Which one of the following is the steady-state main condenser pressure resulting from
the reduced heat transfer coefficient?

Answer 13

1.7 psia

Question 14

Which one of the following pairs of fluids undergoing heat transfer in identical heat exchangers will
yield the greatest heat exchanger overall heat transfer coefficient?

Answer 14

Steam to water.

Question 15

A nuclear power plant is operating near 100 percent power. Main turbine extraction steam is being
supplied to a feedwater heater. Extraction steam parameters are as follows:
Steam pressure = 500 psia
Steam flow rate = 7.0 x 105 lbm/hr
Steam enthalpy = 1,135 Btu/lbm
The extraction steam condenses to saturated water at 500 psia, and then leaves the feedwater heater via
a drain line.
What is the heat transfer rate from the extraction steam to the feedwater in the feedwater heater?

Answer 15

4.8 x 108 Btu/hr

Question 16

During steady-state power operation, core thermal power can be most accurately determined by
multiplying the total mass flow rate of the…

Answer 16

feedwater by the change in enthalpy in the steam generators.

Question 17

A reactor is currently producing 200 MW of core thermal power. Reactor coolant pumps are adding
an additional 10 MW of thermal power to the reactor coolant system. The core is rated at 1,330 MW.
Which one of the following is the current core thermal power output in percent?

Answer 17

15.0 percent

Question 18

The power range nuclear instruments have been adjusted to 100 percent based on a heat balance
calculation. Which one of the following would cause indicated reactor power to be greater than
actual reactor power?

Answer 18

The reactor coolant pump heat input term was omitted from the heat balance calculation

Question 19

Which one of the terms in the equation, Q̇ = UA(T1-T2), is affected the most, and therefore most
responsible for the initial increase in heat transfer rate from the reactor fuel during a minor (3 percent)
steamline break? (Assume no initial change in reactor power.)

Answer 19

T2

Question 20

The power range nuclear instruments were just adjusted to 100 percent power, as determined by a heat
balance calculation. Which one of the following would result in indicated reactor power being
greater than actual reactor power?

Answer 20

The reactor coolant pump heat input term was omitted from the heat balance calculation.

Question 21

A secondary heat balance calculation is being performed at 90 percent reactor power to calibrate
reactor power instrumentation. Which one of the following will result in a calculated reactor power
that is less than actual reactor power?

Answer 21

Steam generator pressure indication is 20 psi greater than actual steam generator pressure.

Question 22

The power range nuclear instruments have been adjusted to 100 percent based on a heat balance
calculation. Which one of the following will result in indicated reactor power being lower than actual
reactor power?

Answer 22

The feedwater temperature used in the heat balance calculation was 20°F higher than actual
feedwater temperature.

Question 23

The power range nuclear instruments have been adjusted to 100 percent based on a heat balance
calculation. Which one of the following will result in indicated reactor power being higher than
actual reactor power?

Answer 23

The reactor coolant pump heat input term was omitted from the heat balance calculation.

Question 24

The power range nuclear instruments have been adjusted to 100 percent based on a calculated heat
balance. Which one of the following will result in indicated reactor power being lower than actual
reactor power?

Answer 24

The feedwater temperature used in the heat balance calculation was 20°F higher than actual
feedwater temperature.

Question 25

The power range nuclear instruments have been adjusted to 100 percent based on a calculated heat balance. Which one of the following will result in indicated reactor power being lower than actual reactor power?

Answer 25

The ambient heat loss value used in the heat balance calculation was only one-half the actual ambient heat loss.

Question 26

The power range nuclear instruments have been adjusted to 100 percent based on a calculated heat balance. Which one of the following will result in indicated reactor power being lower than actual reactor power?

Answer 26

The feedwater flow rate used in the heat balance calculation was 10 percent lower than actual feedwater flow rate.

Question 27

Two of the parameters listed below are used for calculating core thermal power using the standard heat balance method. Which one of the following identifies the two parameters?

Answer 27

Reactor Coolant Feedwater Steam Generator Mass Flow Rate Temperature Pressure No Yes Yes Steam Generator Water Level No

Question 28

The power range nuclear instruments have been adjusted to 100 percent based on a heat balance calculation. Which one of the following will result in indicated reactor power being higher than actual reactor power?

Answer 28

The ambient heat loss value used in the heat balance calculation was twice the actual ambient heat loss.

Question 29

When performing a heat balance calculation to determine core thermal power, the measured thermal power is __________ by a value associated with the reactor coolant pumps (RCPs); the adjustment is needed because __________ of the flow energy added to the reactor coolant by the RCPs is converted to thermal energy of the reactor coolant.

Answer 29

decreased; nearly all

Question 30

Two of the parameters listed below are used for calculating core thermal power using the standard heat balance method. Which one of the following identifies the two parameters?

Answer 30

Feedwater Feedwater Steam Generator Pressure Mass Flow Rate Pressure No Yes Yes Steam Generator Mass Flow Rate No

Question 31

A PWR nuclear power plant has 2 steam generators (SG). Feedwater enters each SG at 3.3 x 106 lbm/hr with an enthalpy of 419 Btu/lbm. Steam exits each steam generator at 800 psia with 100 percent steam quality. Ignoring all other heat gains and losses, what is the reactor core thermal power?

Answer 31

1,510 MW

Question 32

Reactor coolant enters a reactor core at 545°F and leaves at 595°F. The reactor coolant flow rate is 6.6 x 107 lbm/hour and the specific heat capacity of the coolant is 1.3 Btu/lbm-°F. What is the reactor core thermal power?

Answer 32

1,258 MW

Question 33

A reactor is operating with the following parameters: Reactor power = 100 percent Core ΔT = 42°F Reactor coolant system flow rate = 100 percent Average reactor coolant temperature = 587°F A station blackout occurs and natural circulation is established with the following stable parameters: Decay heat rate = 2 percent Core ΔT = 28°F Average reactor coolant temperature = 572°F What is the core mass flow rate in percent?

Answer 33

3.0 percent

Question 34

A nuclear power plant is initially operating at 80 percent power with a core ΔT of 48°F when a station blackout occurs. Natural circulation is established and core ΔT stabilizes at 40°F. If reactor coolant mass flow rate is 3 percent, which one of the following is the current core decay heat level?

Answer 34

2 percent

Question 35

During a nuclear power plant outage, 5 percent of all steam generator (SG) tubes were plugged due to wall thinning. Full power reactor coolant system flow rate and average reactor coolant temperature (Tave) have not changed. Given the following 100 percent power conditions before the outage: Tave = 578°F TS/G = 538°F Which one of the following will be the approximate SG pressure after the outage when the plant is returned to 100 percent power? (Assume the overall heat transfer coefficients for the S/Gs did not change.)

Answer 35

930 psia

Question 36

A nuclear power plant is operating with the following parameters: Reactor power = 100 percent Core ΔT = 60°F Reactor coolant system flow rate = 100 percent Average coolant temperature = 587°F A station blackout occurs and natural circulation is established with the following stable parameters: Decay heat = 1 percent Core ΔT = 30°F Average coolant temperature = 572°F What is the core mass flow rate in percent?

Answer 36

2.0 percent

Question 37

During a nuclear power plant outage, 6 percent of all steam generator (SG) tubes were plugged. Full-power reactor coolant system flow rate and average reactor coolant temperature (Tave) have not changed. Given the following 100 percent power conditions before the outage: Tave = 584°F TS/G = 544°F Which one of the following will be the approximate SG pressure after the outage when the plant is returned to 100 percent power?

Answer 37

974 psia

Question 38

During a nuclear power plant outage, 5 percent of all steam generator (SG) tubes were plugged. Full-power reactor coolant system flow rate and average reactor coolant temperature (Tave) have not changed. Given the following 100 percent power conditions before the outage: Tave = 588°F TS/G = 542°F Which one of the following will be the approximate SG pressure after the outage when the plant is returned to 100 percent power?

Answer 38

961 psia

Question 39

A nuclear power plant is operating at power. Total feedwater flow rate to all steam generators is 7.0 x 106 lbm/hr at a temperature of 440°F. The steam exiting the steam generators is at 1,000 psia with 100 percent steam quality. Ignoring all other heat gain and loss mechanisms, what is the reactor core thermal power?

Answer 39

1,589 MW

Question 40

A nuclear power plant is operating with the following stable steam generator (SG) and feedwater (FW) parameters: SG pressure = 1,000 psia Total SG steam flow rate = 1.0 x 107 lbm/hr (dry, saturated steam) Feedwater inlet temperature = 470°F Based on the above information, what is the thermal power output of the reactor?

Answer 40

2,169 MW