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Thermo > Brittle Fracture and Vessel Thermal Stress > Flashcards

Brittle Fracture and Vessel Thermal Stress Flashcards

1
Q

The pressure stress on a reactor vessel wall is…

A

tensile across the entire wall.

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2
Q

Brittle fracture is the fragmentation of metal resulting from the application of __________ stress at
relatively __________ temperatures.

A

tensile; low

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3
Q

The conditions for brittle fracture of the reactor vessel are most closely approached at…

A

120°F, 400 psig

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4
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

A high material strength in the reactor vessel rather than a high material ductility.

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5
Q

Which one of the following reduces the probability of brittle fracture of the reactor vessel?

A

Small heatup and cooldown rates.

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6
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

A tensile stress rather than a compressive stress.

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7
Q

Which one of the following statements describes the relationship between brittle fracture and the
nil-ductility transition temperature?

A

Operation below the nil-ductility transition temperature will increase the probability of brittle
fracture.

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8
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

Performing a 100°F/hr cooldown of the reactor rather than a 100°F/hr heatup.

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9
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

Performing a 50°F/hr cooldown at 1,600 psia rather than a 50°F/hr cooldown at 1,200 psia.

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10
Q

Brittle fracture of the reactor vessel wall is least likely to occur at…

A

400°F; 400 psig.

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11
Q

Brittle fracture of the reactor vessel (RV) is most likely to occur during a reactor __________ when
RV temperature is __________ the nil-ductility transition temperature.

A

cooldown; below

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12
Q

Which one of the following will normally prevent brittle fracture failure of a reactor vessel?

A

Operating above the nil-ductility transition temperature.

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13
Q

Brittle fracture of the reactor vessel (RV) is least likely to occur during a __________ of the RV when
RV temperature is __________ the nil-ductility transition temperature.

A

heatup; above

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14
Q

Brittle fracture of a low-carbon steel is more likely to occur when the temperature of the steel is
__________ the nil-ductility transition temperature; and will normally occur when the applied stress is
__________ the steel=s yield strength (or yield stress) at room temperature

A

less than; less than

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15
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

A 50°F/hr cooldown rather than a 100°F/hr heatup.

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16
Q

Which one of the following comparisons results in a lower probability for brittle fracture of a reactor
vessel?

A

A high gamma flux in the reactor rather than a high neutron flux.

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17
Q

The nil-ductility transition temperature for a reactor vessel is the temperature…

A

below which the probability of brittle fracture significantly increases

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18
Q

The nil-ductility transition temperature of the reactor vessel (RV) is the temperature…

A

below which the RV metal loses its ability to elastically deform as RV pressure increases.

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19
Q

The nil-ductility transition temperature is the temperature above which…

A

a metal exhibits more ductile tendencies.

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20
Q

The nil-ductility transition temperature is that temperature…

A

below which the probability of brittle fracture significantly increases.

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21
Q

The likelihood of brittle fracture failure of the reactor vessel is reduced by…

A

reducing vessel pressure.

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22
Q

Which one of the following reactor coolant system (RCS) conditions is least effective in preventing
brittle fracture of the reactor vessel?

A

Operating with a ramped RCS temperature as reactor power level increases.

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23
Q

Why are reactor coolant system cooldown rate limitations established?

A

Prevent brittle fracture of the reactor vessel.

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24
Q

The thermal stress experienced by the reactor vessel during a reactor coolant system heatup is…

A

compressive at the inner wall and tensile at the outer wall of the vessel.

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25
Q

The total stress on the reactor vessel inner wall is greater during cooldown than heatup because…

A

both pressure stress and thermal stress are tensile at the inner wall during cooldown.

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26
Q

The likelihood of brittle fracture failure of the reactor vessel is reduced by…

A

reducing reactor vessel pressure.

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27
Q

Which one of the following will increase the compressive stress on the outside surface of the reactor vessel wall?

A

Reactor coolant system cooldown

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28
Q

Which one of the following applies a compressive stress to the inner wall of the reactor vessel during a
reactor coolant system heatup?

A

Thermal stress

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29
Q

Which one of the following is the most limiting component for establishing reactor coolant system
heatup/cooldown rate limits?

A

Reactor vessel

30
Q

Which one of the following stresses is compressive on the outer wall of the reactor vessel during a
reactor coolant system cooldown?

A

Thermal stress

31
Q

Which one of the following will apply a compressive stress to the outside wall of the reactor vessel?

A

Performing a reactor coolant system cooldown.

32
Q

Reactor coolant system pressure-temperature limit curves are derived by using a conservative value
for the reactor vessel nil-ductility transition temperature (NDTT).
The conservative value used for the reactor vessel NDTT is __________ than the actual NDTT; the
actual NDTT is verified periodically by __________.

A

higher; removing and testing irradiated specimens of reactor vessel material

33
Q

Which one of the following operating limitations is designed to prevent brittle fracture of the reactor
vessel and/or the reactor coolant system (RCS)?

A

Maximum RCS pressure versus RCS temperature for a given RCS heatup rate

34
Q

A reactor is shutdown with the shutdown cooling system maintaining reactor coolant temperature at
240°F immediately following an uncontrolled rapid cooldown from 500°F. If reactor coolant
temperature is held constant at 240°F, which one of the following describes the change in tensile stress
on the inner wall of the reactor vessel (RV) over the next few hours?

A

Decreases, because the temperature gradient across the RV wall will decrease.

35
Q

Fast neutron irradiation of the reactor vessel results in __________ stresses within the vessel metal,
thereby __________ the nil-ductility transition temperature.

A

increased; increasing

36
Q

Fast neutron irradiation adversely affects the reactor vessel primarily by causing…

A

metal embrittlement.

37
Q

Prolonged exposure of a reactor vessel to a fast neutron flux will cause the nil-ductility transition
temperature to…

A

increase, due to changes in the material properties of the vessel wall

38
Q

The likelihood of reactor vessel brittle fracture is decreased by minimizing…

A

The amount of copper contained in the metal used for the reactor vessel.

39
Q

Which one of the following types of radiation most significantly reduces the ductility of a reactor
vessel?

A

Fast neutrons

40
Q

After several years of operation, the maximum allowable stress to the reactor vessel is more limited by the inner wall than the outer wall because…

A

the inner wall experiences more neutron-induced embrittlement than the outer wall.

41
Q

Prolonged exposure to __________ will cause the nil-ductility transition temperature of the reactor
vessel to __________.

A

neutron radiation; increase

42
Q

Two identical reactors have been in operation for the last 10 years. Reactor A has experienced 40
heatup/cooldown cycles with an average capacity factor of 50 percent. Reactor B has experienced 30
heatup/cooldown cycles with an average capacity factor of 60 percent.
Which reactor will have the lower reactor vessel nil-ductility transition temperature, and why?

A

Reactor A, due to the lower average capacity factor.

43
Q

The two factors that have the greatest effect on the nil-ductility transition temperature of the reactor
vessel over its life are…

A

fast neutron flux and vessel copper content.

44
Q

Two identical reactors have been in operation for the last 10 years. Reactor A has experienced 30
heatup/cooldown cycles with an average capacity factor of 60 percent. Reactor B has experienced 40
heatup/cooldown cycles with an average capacity factor of 50 percent.
Which reactor will have the lower reactor vessel nil-ductility transition temperature, and why?

A

Reactor B, due to the lower average capacity factor.

45
Q

Which one of the following is the major contributor to embrittlement of a reactor vessel?

A

High-energy neutron radiation

46
Q

Which one of the following describes the effect of fast neutron irradiation on a reactor vessel?

A

Increased nil-ductility transition temperature

47
Q

Two identical reactors have been in operation for the last 10 years. Reactor A has experienced 30
heatup/cooldown cycles and has an average capacity factor of 60 percent. Reactor B has experienced
40 heatup/cooldown cycles and has an average capacity factor of 50 percent.
Which reactor will have the higher reactor vessel nil-ductility transition temperature, and why?

A

Reactor A, due to the higher average capacity factor.

48
Q

Two identical reactors have been in operation for the last 10 years. Reactor A has experienced 40
heatup/cooldown cycles and has an average capacity factor of 50 percent. Reactor B has experienced
30 heatup/cooldown cycles and has an average capacity factor of 60 percent.
Which reactor will have the higher reactor vessel nil-ductility transition temperature?

A

Reactor B, due to the higher average capacity factor.

49
Q

Two identical reactors are currently shut down for refueling. Reactor A has an average lifetime
capacity factor of 60 percent and has been operating for 15 years. Reactor B has an average lifetime
capacity factor of 75 percent and has been operating for 12 years.
Which reactor, if any, will have the lower reactor vessel nil-ductility transition temperature, and why?

A

Both reactors will have approximately the same nil-ductility transition temperature because each
reactor has produced approximately the same number of fissions.

50
Q

Two identical reactors are currently shut down for refueling. Reactor A has achieved an average
lifetime capacity factor of 60 percent while operating for 15 years. Reactor B has achieved an
average lifetime capacity factor of 60 percent while operating for 12 years.
Which reactor, if any, will have the lower reactor vessel nil-ductility transition temperature, and why?

A

Reactor B, because it has produced less total fissions.

51
Q

Two identical reactors have been in operation for the last 10 years. Reactor A has experienced 30
heatup/cooldown cycles and has an average capacity factor of 60 percent. Reactor B has experienced
20 heatup/cooldown cycles and has an average capacity factor of 80 percent.
Which reactor will have the higher reactor vessel nil-ductility transition temperature, and why?

A

Reactor B, due to the higher average capacity factor.

52
Q

A reactor is shut down for refueling following 18 months of operation at an average power level of 85
percent. During the shutdown, a reactor vessel metal specimen was removed from the reactor vessel
for testing. The testing determined that the nil-ductility transition (NDT) temperature of the
specimen decreased from 44°F to 42°F since the previous refueling shutdown.
Which one of the following conclusions is warranted?

A

The test results are questionable because the specimen NDT temperature would not decrease
during the described 18-month period of operation

53
Q

A reactor is shut down for refueling following 18 months of operation at an average power level of 85
percent. During the shutdown, a reactor vessel metal specimen was removed from the reactor vessel
for testing. The testing determined that the nil-ductility transition (NDT) temperature of the
specimen increased from 42°F to 44°F since the previous refueling shutdown.
Which one of the following conclusions is warranted?

A

The test results are credible and the reactor vessel is more susceptible to brittle fracture now than
after the previous refueling shutdown.

54
Q

A reactor is shut down for refueling following 18 months of operation at an average power level of 85
percent. During the shutdown, a reactor vessel metal specimen is removed from the reactor vessel for
testing. The testing indicates that the nil-ductility transition (NDT) temperature of the specimen has
decreased from 44°F to 32°F since the previous refueling shutdown.
Which one of the following conclusions is warranted?

A

The test results are questionable because the actual specimen NDT temperature would not
decrease during the described 18-month period of operation

55
Q

Two identical reactors are currently shut down for refueling. Reactor A has an average lifetime
capacity factor of 90 percent and has been operating for 10 years. Reactor B has an average lifetime
capacity factor of 80 percent and has been operating for 15 years.
Which reactor will have the higher reactor vessel nil-ductility transition temperature, and why?

A

Reactor B, because it has produced significantly more fissions.

56
Q

A reactor is shut down for refueling following 18 months of operation at an average power level of 85
percent. During the shutdown, a reactor vessel metal specimen was removed from the reactor vessel
for testing. The tests determined that the nil-ductility transition (NDT) temperature of the specimen
increased from 42°F to 72°F since the previous refueling shutdown.
Which one of the following conclusions is warranted?

A

The test results are questionable because the specimen NDT temperature would increase by less
than indicated during the described 18-month period of operation.

57
Q

A reactor is shut down for refueling. During the shutdown, a reactor vessel metal specimen was
removed from the reactor vessel for testing. The specimen was last tested six years ago and then
returned to its original location in the reactor vessel. During the subsequent six years, the reactor has
completed several 18 month fuel cycles with an average power level of 85 percent.
The tests determined that the nil-ductility transition (NDT) temperature of the specimen has remained
unchanged at 44°F since it was last tested. Which one of the following conclusions is warranted?

A

The test results are questionable because the specimen NDT temperature should have increased
since it was last tested

58
Q

Two identical reactors are currently shut down for refueling. Reactor A has achieved an average
lifetime capacity factor of 60 percent while operating for 12 years. Reactor B has achieved an
average lifetime capacity factor of 60 percent while operating for 15 years.
Which reactor, if any, will have the lower reactor vessel nil-ductility transition temperature?

A

Reactor A, because it has produced less total fissions.

59
Q

Two identical reactors are currently shut down for refueling. Reactor A has an average lifetime
capacity factor of 90 percent and has been operating for 24 years. Reactor B has an average lifetime
capacity factor of 72 percent and has been operating for 30 years.
Which reactor, if any, will have the lower reactor vessel nil-ductility transition temperature?

A

Both reactors will have approximately the same nil-ductility transition temperature because each
reactor has produced approximately the same number of fissions.

60
Q

Which one of the following comparisons results in a higher probability for brittle fracture of a reactor
vessel?

A

A high fast neutron flux in the reactor rather than a high gamma flux.

61
Q

Two identical reactors are currently shut down for refueling. Reactor A has an average lifetime
capacity factor of 90 percent and has been operating for 16 years. Reactor B has an average lifetime
capacity factor of 80 percent and has been operating for 18 years.
Which reactor, if any, will have the lower reactor vessel nil-ductility transition temperature, and why?

A

Both reactors will have approximately the same nil-ductility transition temperature because each
reactor has produced approximately the same number of fissions.

62
Q

Which one of the following comparisons results in a lower probability for brittle fracture of a reactor
vessel?

A

A high gamma flux in the reactor rather than a high fast neutron flux.

63
Q

A nuclear power plant is shut down with the reactor coolant system at 1,200 psia and 350°F. Which
one of the following would be most likely to cause a pressurized thermal shock to the reactor vessel?

A

A rapid cooldown followed by a rapid pressurization.

64
Q

Pressurized thermal shock is a condition that can occur following a rapid __________ of the reactor
coolant system if system pressure is rapidly __________.

A

cooldown; increased

65
Q

Which one of the following reactor coolant system (RCS) events would be most likely to cause a
pressurized thermal shock to the reactor vessel?

A

Continuous emergency coolant injection to the RCS during and after a complete and unisolable
rupture of a steam generator steam outlet nozzle.

66
Q

During a severe reactor coolant system overcooling transient, a major concern is…

A

brittle fracture of the reactor vessel

67
Q

An uncontrolled cooldown is a brittle fracture concern because it creates a large __________ stress at
the __________ wall of the reactor vessel.

A

tensile; inner

68
Q

During an uncontrolled cooldown of a reactor coolant system, the component most susceptible to
brittle fracture is the…

A

reactor vessel.

69
Q

Which one of the following describes the thermal stress placed on the reactor vessel wall during a
cooldown of the reactor coolant system?

A

Tensile at the inner wall, compressive at the outer wall.

70
Q

A nuclear power plant heatup is in progress using reactor coolant pumps. The thermal stress applied
to the reactor vessel is…

A

compressive at the inner wall and tensile at the outer wall.

Thermo (10 decks)

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