Thermodynamic Processes

Question 1

Condensate depression is the process of…

Answer 1

cooling turbine exhaust steam below its saturation temperature.

Question 2

Excessive heat removal from the low pressure turbine exhaust steam in the main condenser will result
in…

Answer 2

condensate depression.

Question 3

Main condenser pressure is 1.0 psia. During the cooling process in the condenser, the temperature of
the low pressure turbine exhaust decreases to 100°F, at which time it is a…

Answer 3

subcooled liquid.

Question 4

Which one of the following explains why condensate subcooling is necessary in a nuclear power plant
steam cycle?

Answer 4

To provide net positive suction head for the condensate pumps.

Question 5

Which one of the following is the approximate condensate subcooling in a steam condenser operating
at 26 inches Hg vacuum with a condensate temperature of 100°F?

Answer 5

25°F

Question 6

Which one of the following is a positive effect of having condensate depression in the main
condenser?

Answer 6

Increased net positive suction head available to the condensate pumps.

Question 7

A nuclear power plant is operating at 80 percent power with 5°F of condensate depression in the main
condenser. If the condensate depression increases to 10°F, the steam cycle thermal efficiency will
__________; and the condensate pumps will operate __________ cavitation.

Answer 7

decrease; farther from

Question 8

What is the approximate value of condensate depression in a steam condenser operating at 2.0 psia
with a condensate temperature of 115°F?

Answer 8

11°F

Question 9

What is the approximate condensate depression in a condenser operating at 28 inches Hg vacuum with
a condensate temperature of 100°F?

Answer 9

Less than 2°F

Question 10

Condensate is collecting in a main condenser hotwell at 90°F with a condenser pressure of 28 inches
Hg vacuum. Which one of the following will improve steam cycle efficiency?

Answer 10

Main condenser cooling water flow rate decreases by 5 percent with no change in condenser
vacuum

Question 11

The steam cycle thermal efficiency of a nuclear power plant can be increased by…

Answer 11

decreasing the amount of condensate depression (subcooling).

Question 12

A nuclear power plant is operating at 90 percent of rated power. Main condenser pressure is 1.69 psia
and hotwell condensate temperature is 120°F.
Which one of the following describes the effect of a 5 percent decrease in cooling water flow rate
through the main condenser on steam cycle thermal efficiency?

Answer 12

Efficiency will decrease because the work output of the main turbine will decrease.

Question 13

A nuclear power plant is operating at 80 percent power with 5°F of condensate depression in the main
condenser. If the condensate depression decreases to 2°F, the steam cycle thermal efficiency will
__________; and the condensate pumps will operate __________ cavitation.

Answer 13

increase; closer to

Question 14

What is the approximate value of condensate depression in a condenser operating at 27 inches Hg
vacuum with a condensate temperature of 100°F?

Answer 14

16°F

Question 15

A main condenser is operating at 28 inches Hg vacuum with a condensate outlet temperature of 92°F.
Which one of the following is the approximate amount of condensate depression?

Answer 15

9°F

Question 16

Main turbine exhaust enters a main condenser and condenses at 126°F. The condensate is cooled to
100°F before entering the main condenser hotwell. Assuming main condenser vacuum does not
change, which one of the following would improve the thermal efficiency of the steam cycle?

Answer 16

Decrease condenser cooling water flow rate by 5 percent.

Question 17

A nuclear power plant is maintained at 2,000 psia with a pressurizer temperature of 636°F. A
pressurizer relief safety valve is leaking to a collection tank which is being held at 10 psig. With dry
saturated steam in the pressurizer vapor space, which one of the following is the approximate
temperature of the fluid just downstream of the relief valve?

Answer 17

240°F

Question 18

A pressurizer relief valve is leaking by with the leakage being collected in a pressurizer relief tank.
The pressurizer pressure is 2,200 psia and the relief tank pressure is 5 psig.
With dry saturated steam in the pressurizer vapor space, which one of the following is the condition of
the fluid just downstream of the relief valve?

Answer 18

Wet vapor

Question 19

A reactor coolant system is being maintained at 1,000 psia. A leaky pressurizer safety/relief valve is
slowly discharging to a collection tank, which is maintained at 5 psig.
With dry saturated steam in the pressurizer vapor space, what is the approximate enthalpy of the fluid
entering the collection tank? (Assume no heat is lost from the discharge line.)

Answer 19

1,193 Btu/lbm

Question 20

What is the approximate temperature and phase of the fluid just downstream of the pressurizer relief
valve if it sticks partially open with 2,200 psia in the pressurizer and a 50 psia backpressure?
(Assume the pressurizer vapor space contains dry saturated steam.)

Answer 20

281°F, saturated

Question 21

A routine nuclear power plant shutdown is in progress with a steam bubble (dry saturated steam) in the
pressurizer. Pressurizer pressure is 415 psig and pressurizer pressure and level are slowly decreasing.
The operator suspects a pressurizer power-operated relief valve (PORV) is partially open but the
position indicating lights are not working.
Which one of the following will be the approximate PORV tailpipe temperature if the PORV is
partially open? (Assume downstream pressure is 15 psia and no heat is lost from the tailpipe.)

Answer 21

330°F

Question 22

A nuclear power plant is operating at 100 percent power. As main steam escapes to atmosphere via a
main steam flange leak, which one of the following steam parameters will increase?

Answer 22

Specific volume

Question 23

A heatup and pressurization of the reactor coolant system (RCS) is in progress following a
maintenance shutdown. RCS pressure is 800 psia with a steam bubble (97.5 percent quality saturated
steam) in the pressurizer. Pressurizer power-operated relief valve (PORV) tailpipe temperature has
been steadily rising. PORV downstream pressure is 30 psia.
Which one of the following will be the approximate PORV tailpipe temperature if a PORV is leaking
by? (Assume no heat is lost from the tailpipe.)

Answer 23

284°F

Question 24

A nuclear power plant is operating at 100 percent power with steam generator pressure at 900 psia. A
steam generator safety valve is leaking dry saturated steam to atmosphere.
Which one of the following is the approximate temperature of the escaping steam once it reaches
standard atmospheric pressure?

Answer 24

308°F

Question 25

A heatup and pressurization of the reactor coolant system (RCS) is in progress following a maintenance shutdown. RCS pressure is 800 psia with a steam bubble (96.0 percent quality saturated steam) in the pressurizer. Pressurizer power-operated relief valve (PORV) tailpipe temperature has been steadily rising. PORV downstream pressure is 20 psia. Which one of the following will be the approximate PORV tailpipe temperature if a PORV is leaking by?

Answer 25

258°F

Question 26

A nuclear power plant is being maintained at 2,220 psig. A pressurizer relief valve is leaking dry saturated steam to a collection tank, which is being held at 20 psig. Which one of the following is the approximate temperature of the fluid downstream of the relief valve?

Answer 26

259°F

Question 27

Which one of the following is essentially a constant enthalpy process?

Answer 27

Throttling of main steam through a main turbine steam inlet valve.

Question 28

A nuclear power plant is operating with the following main steam parameters at the main turbine steam inlet valves: Pressure = 900 psia Quality = 98 percent The main turbine steam chest pressure is 400 psia. Assuming an ideal throttling process, what is the quality of the steam in the steam chest?

Answer 28

97 percent

Question 29

A heatup and pressurization of the reactor coolant system (RCS) is in progress following a maintenance shutdown. RCS pressure is 800 psia with a steam bubble (96.0 percent quality saturated steam) in the pressurizer. Pressurizer power-operated relief valve (PORV) tailpipe temperature has been steadily rising. PORV downstream pressure is 20 psia. Which one of the following will be the approximate PORV tailpipe temperature and phase of the escaping fluid if a PORV is leaking by?

Answer 29

258°F, superheated

Question 30

Refer to the drawing of two 1,000 ft3 pressure vessels with installed relief valves (see figure below). Both vessels are in saturated conditions at 281°F and approximately 35 psig. Vessel X is completely filled with saturated water. Vessel Y contains one-half saturated steam (100 percent quality) and one-half saturated water (0 percent quality) by volume. Both vessels are protected by identical relief valves. If both relief valves begin to leak at a rate of 0.1 percent of design flow, the higher temperature fluid will initially be leaving the relief valve of vessel _____. And, if 100 lbm of fluid is released through both relief valves, the larger pressure decrease will occur in vessel _____.

Answer 30

Y; Y

Question 31

A nuclear power plant is operating at 100 percent power. Steam is escaping to atmosphere through a flange leak in a steam supply line to the low pressure section of the main turbine. Given: C Steam line pressure is 300 psia. C Steam line steam temperature is 440°F. What is the approximate temperature of the steam as it reaches standard atmospheric pressure?

Answer 31

358°F

Question 32

A nuclear power plant is operating at 100 percent power. Steam is escaping to atmosphere through a flange leak in a steam line that supplies the low pressure unit of the main turbine. Given: C Steam line pressure is 280 psia. C Steam line steam temperature is 450°F. What is the approximate temperature of the steam as it reaches standard atmospheric pressure?

Answer 32

378°F

Question 33

A pressurizer safety valve is leaking by, allowing the dry saturated steam in the pressurizer to flow to the pressurizer relief tank (PRT). The reactor has been shut down, and a plant cooldown and depressurization are in progress. PRT pressure is being maintained constant at 35 psia. Which one of the following describes how the safety valve tailpipe temperature will be affected as pressurizer pressure slowly decreases from 1,500 psia to 500 psia? (Assume there is no ambient heat loss from the tailpipe.)

Answer 33

Increases, because the enthalpy of the pressurizer steam will be increasing.

Question 34

Dry saturated steam at 1,000 psia is being supplied to the inlet of a partially-open steam throttle valve on a main turbine. Pressure in the steam chest downstream of the throttle valve is 150 psia. Assume a typical throttling process with no heat gain or loss to/from the steam. When compared to the conditions at the inlet to the throttle valve, which one of the following describes the conditions in the steam chest for specific enthalpy and specific entropy?

Answer 34

About the same Significantly higher

Question 35

A nuclear power plant is shut down and steam is escaping to atmosphere through a leak in a main steam line. The main steam line contains dry saturated steam at 300 psia. What is the approximate temperature of the steam as it reaches standard atmospheric pressure?

Answer 35

322°F

Question 36

A heatup and pressurization of a reactor coolant system (RCS) is in progress following a maintenance shutdown. RCS pressure is 1,000 psia with a steam bubble (dry saturated steam) in the pressurizer. Pressurizer power-operated relief valve (PORV) tailpipe temperature has been steadily rising. PORV downstream pressure is 40 psia. Which one of the following will be the approximate PORV tailpipe temperature and phase of the escaping fluid if a PORV is leaking by?

Answer 36

312°F, superheated

Question 37

A nuclear power plant is operating with the following main steam parameters at the main turbine steam inlet valves: Pressure = 900 psia Quality = 99 percent The main turbine steam chest pressure is 300 psia. Assuming an ideal throttling process, what is the quality of the steam in the steam chest?

Answer 37

98 percent

Question 38

A pressurizer safety valve is leaking by, allowing dry saturated steam from the pressurizer to enter the discharge pipe, which remains at a constant pressure of 30 psig. Initial safety valve discharge pipe temperature is elevated but stable. Assume no heat loss from the safety valve discharge pipe. Upon discovery of the leak, the reactor is shut down and a plant cooldown and depressurization are commenced. Throughout the cooldown and depressurization, dry saturated steam continues to leak through the pressurizer safety valve. As pressurizer pressure decreases from 2,000 psig to 1,800 psig, the safety valve discharge pipe temperature will...

Answer 38

remain the same, because the safety valve discharge fluid will remain a saturated steam-water mixture at 30 psig in this pressure range.

Question 39

A nuclear power plant is operating at power. Steam is escaping to atmosphere through a flange leak in a steam line supplying the low pressure section of the main turbine. Given: C Steam line pressure is 200 psia. C Steam line temperature is 400°F. Assuming no heat transfer to/from the steam, what is the approximate temperature of the steam as it reaches atmospheric pressure?

Answer 39

339°F

Question 40

A nuclear power plant is operating with the following main steam parameters at the main turbine steam inlet valves: Pressure = 1,050 psia Quality = 100 percent The main turbine steam chest pressure is 400 psia. Assuming an ideal throttling process, which one of the following describes the steam in the steam chest?

Answer 40

Saturated, 98 percent quality

Question 41

A pressurizer safety valve is leaking by, allowing the dry saturated steam from the pressurizer to enter the discharge pipe, which remains at a constant pressure of 40 psia. Initial safety valve discharge pipe temperature is elevated but stable. Assume no heat loss occurs from the safety valve discharge pipe. Upon discovery of the leak, the reactor is shut down, and a plant cooldown and depressurization are commenced. Throughout the cooldown and depressurization, dry saturated steam continues to leak through the pressurizer safety valve. As pressurizer pressure decreases from 1,000 psia to 700 psia, the safety valve discharge pipe temperature will...

Answer 41

increase, because the safety valve discharge fluid will become more superheated as the pressurizer pressure decreases in this pressure range.

Question 42

A nuclear power plant is operating with the following main steam parameters at a partially open main turbine steam inlet valve: Pressure = 1,000 psia Quality = 100 percent The main turbine steam chest pressure is 50 psia. Which one of the following describes the steam in the steam chest?

Answer 42

Superheated

Question 43

A nuclear power plant was shut down to fix a steam leak from an inlet flange on a steam generator safety valve. A reactor coolant system cooldown is in progress. Given the following current steam conditions at the safety valve inlet: C Steam pressure is 500 psia. C Steam quality is 99 percent. Assuming no heat transfer to/from the steam, what is the approximate temperature of the leaking steam as it reaches atmospheric pressure?

Answer 43

308°F