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Reactor Safety Analysis > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

Control Rods

A

Quick shutdown by gravity and as a backup injection of Poison in primary water

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2
Q

Steam Generator

A

Heat is used to produced high pressure steam

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3
Q

Turbine

A

Steam energy is transformed into mechanical rotation energy

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4
Q

Electric Generator

A

Produces electric energy to supply to the grid

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5
Q

Pressuriser

A

Expansion of volume and pressurization of components and suppressing the steam production in primary system

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6
Q

Reactor

A

Nuclear reaction takes place and heat produced

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7
Q

Emergency cooling of reactor - Function

A

Radioactive products accumulated in reactor continue to generate heat after shutdown. The emergency cooling system is both passive and active

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8
Q

Containment

A

Provides protection after release of radioactive products, made with concrete and steel

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9
Q

Reactor Control System of PWR involves the control of:

A
  • Reactivity
  • Coolant volume
  • Water level of the steam generators
  • Steam flow to the turbine
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10
Q

Reactivity Control

A

Fast Control: Full-length control rods
Slow Control: Boric Acid concentrate in coolant

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11
Q

Volume Control - Purpose

A
  1. offset changes to coolant volume due to changes in temperature
  2. Replace lost coolant due to minor leakage in the primary system
  3. Adjust the boron concentration in the primary coolant
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12
Q

Volume Control - Components

A

Volume control tank
3 parallel charging pumps
Storage tanks with boric acid and deionised water

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13
Q

Volume Control - System

A
  • Manually controlled in the control room
  • “Automatic Makeup” is the mode of operation: Boric acid and deionised water are blended to the same composition as that of the reactor coolant and fed to the suction side of the charging pump
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14
Q

Feedwater Control System - Purpose

A

Balance the feedwater flow to the steam generators and the steam flow to the turbine.
Achieved by regulating the water level on the secondary side of the steam generators.

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15
Q

Steam flow to the turbine

A
  • Generator power is adjusted the grid demand by the regulation of the steam to the turbine.
  • Turbine generator speed is kept constant.
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16
Q

If more steam is generated than required by the turbine-

A

Excess steam is led directly to the turbine condenser by the use of bypass valves

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17
Q

Central Control room

A

Where the primary process systems are monitored and controlled

18
Q

Special computer

A

Registers, processes and presents data for core monitoring.
The computer calculates and proposes adjustments of control rod positions.

19
Q

Alarm signals and annunciators

A

Used to attract the reactor operator’s attention in the event of malfunction or if bounding values for process variables are exceeded.

20
Q

Control of neutron flux

A

Monitored by a large number of measuring channels with neutron detectors inside the core.
In order to cover the entire range from start-up to full power, three overlapping systems are used.

21
Q

Three overlapping systems for neutron control

A

Source range monitoring (10e-6)
Intermediate range monitoring (20% of relative power)
Power range monitoring (instantaneous)

22
Q

Insertion of control rods

A

By actuating the electromechanical transmission of the drive mechanisms or by hydraulic insertion.

23
Q

Time taken for control rods insertion

A

It takes about 4 minutes to screw the control rods into the core from a fully withdrawn position.
During scram, the control rods are fully inserted within 4-6 seconds.

24
Q

Power Control

A

Utilises the coolant flow as means to control the power.
Coolant flow ↓, the void content of the core↑, reactivity and power ↓

25
Q

3 operating modes for a power control system

A
  1. Pump speed regulation
  2. Power control
  3. Power and frequency control
26
Q

Pump speed regulation

A

When all main recirculation pumps are controlled by the operator.

27
Q

Power control

A

When the electrical power generated by the unit is maintained at a preset value.

28
Q

Power and frequency control

A

When the electric power generated is automatically adjusted to the frequency of the grid

29
Q

Plant components

A
  • Reactor pressure vessel
  • Piping
30
Q

Major components of the reactor pressure vessel

A
  • Reactor vessel
  • Core barrel
  • Reactor core
  • Upper internals package
31
Q

Reactor vessel anatomy

A

Cylindrical vessel with a hemispherical bottom head and a removable hemispherical top head

32
Q

Top head removable - Why?

A

Allow for refueling of the reactor

33
Q

Irradiation specimen holders

A

Samples of the material used to manufacture the vessel will be placed there.
At periodic time intervals, some of these samples will be removed and tested to see how the radiation from the fuel has affected the strength of the material.

34
Q

Upper internals package

A
  • Contains the guide columns to guide the control rods when they are pulled from the fuel.
  • Prevents the core from trying to move up during operation due to the force from the coolant flowing through the assemblies.
35
Q

Describe the flow path for the reactor coolant.

A
  1. The coolant enters the reactor vessel at the inlet nozzle and hits against the core barrel.
  2. The core barrel forces the water to flow downward in the space between the reactor vessel wall and the core barrel.
  3. After reaching the bottom of the reactor vessel, the flow is turned upward to pass through the fuel assemblies.
  4. The coolant flows all around and through the fuel assemblies, removing the heat produced by the fission process.
  5. The now hotter water enters the upper internals region, where it is routed out the outlet nozzle and goes on to the steam generator.
36
Q

What are the consequences of “the break”?

A
  • Pipe whip
  • Fuel jet
37
Q

Fuel jets

A

Due to decompression waves propagating inside the broken system.
Causes the generation of loads on the internal components.

38
Q

Cracks in the primary system

A

Small pipes have the probability of 0.01 breaks per reactor year

39
Q

Thermal fatigue

A

Caused by the defective closure of isolation valves and by consequent seepage of a fluid at different temperatures within the pipes.

40
Q

Where does mechanical vibration fatigue occur?

A

small pipes and in ‘socket welds’

41
Q

What is the cause of ‘socket welds’?

A

Stress concentration points are caused due to
unwanted but real notches, that are prone to initiate and propagate fatigue cracks.
The presence of pressure pulses due to pumps or due to ‘cavitation’ phenomena with rapid evaporation tends to enhance this tendency

Reactor Safety Analysis (2 decks)

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