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Primary System Mechanical > Reactor Coolant > Flashcards

Reactor Coolant Flashcards

1
Q

Purpose of reactor coolant system.

A

a) transfer thermal energy from the core to the steam generator where steam is produced for use in a turbine generator
b) serves as secondary barrier against fission product release to the environment
c) provide sufficient core cooling during normal operations and transients to preclude significant fuel damage

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2
Q

Purpose of reactor vessel

A

a) contain and support core and vessel internals
b) contain and direct flow through the core
c) pressure boundary along with RCS to prevent fission product release from containment

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3
Q

Purpose of reactor vessel internals

A

a) core support barrel support and orient reactor core fuel assemblies and CEAs
b) absorb dynamic loads and transmit loads to reactor vessel
c) direct coolant to core
d) guide in-core instrumentation

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4
Q

Describe the flow path of coolant within the vessel.

A

Coolant enters 4 inlet nozzles of the vessel ==> flows down between vessel wall and core barrel ==> passes through flow skirt section where it’s evenly distributed ==> into lower plenum ==> up through core removing heat from fuel ==> enters core outlet region and flows outside CEA shroud tubes to the outlet nozzle.

small amount flows through core bypass path (no contact with fuel) and prevents stagnation in low flow areas and keeps temp below saturation temp in the vessel. also removes heat generated by gamma radiation.

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5
Q

Purpose of surveillance capsule assemblies.

A

a) located on vessel wall
b) hold test specimens that are there so that we can remove them and test them to see what affect radiation is having on core materials.
c) results used to modify heat up and cool down rates and minimum temperature for vessel pressurization

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6
Q

Purpose of the pressurizer.

A

a) keeps RCS subcooled
b) acts as a surge volume
c) prevents primary system over pressurization

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7
Q

How is the RCS protected from over pressurization?

A

4 spring loaded safety valves on the pressurizer keep pressure less than 2750psia.

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8
Q

Where to the pressurizer safety valves discharge to?

A

reactor drain tank under water.

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9
Q

What is the purpose of the vent system?

A

permit the operator to vent the reactor vessel head or pressurizer steam space from the control room.

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10
Q

What does the pressurizer surge line do?

A

a) provides a flow path between the pressurizer and the RCS for surging
b) provides a means to transmit pressure to the entire RCS.

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11
Q

Where does the pressurizer surge line connect to the RCS?

A

loop 1 hot leg

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12
Q

How is main spray valve bypass flow rate controlled?

A

manually to establish differential temperature of 70F between cold leg and spray nozzle piping on top of Pzr.

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13
Q

What is fixed in core instrumentation?

A

Instruments in the core that measure neutron flux in multiple areas in the core and measures coolant temperature at 61 locations as it exits the core.

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14
Q

What is fixed in core instrumentation used for?

A

monitoring core characteristics to assure we don’t exceed allowable limits during normal ops and transients.

IT DOES NOT CONTROL ANYTHING

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15
Q

What does the CVCS system collect from the RCS system?

A

a) coolant from loop drainage during maintenance
b) RCP seal bleed off
c) Discharge of primary safety valves
d) Identified leakage

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16
Q

What does the CVCS system provide to the RCS?

A

a) means of supplying aux spray to Pzr when normal spray path is unavailable
b) means of constant purification
c) RCP seal injection
d) charging and let down to maintain Pzr level
e) method of chemistry control
f) method of maintaining boron concentration and increasing boron

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17
Q

What does the NC system cool in the RCS system?

A

a) RCP motor air cooler
b) RCP motor lube oil cooler
c) RCP thrust bearing oil cooler
d) RCP seal coolers

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18
Q

What cools NC?

A

plant cooling water system

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19
Q

When is the shutdown cooling system used?

A

When the use of steam generators is not possible

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20
Q

What system supplies air to the Pzr spray valves?

A

Instrument air

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21
Q

Where can you take a primary sample from?

A

a) loop 1 hot leg
b) surge line
c) pressurizer steam space

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22
Q

How many o-rings are there sealing the reactor vessel to the closure head?

A

2

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23
Q

Describe the two o-rings sealing the reactor vessel to the closure head.

A

metal self-energizing, polished, silver plated.

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24
Q

Does the outer o-ring ever see primary pressure?

A

only if the inner o-ring leaks, then it will energize.

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25
Q

How is any liquid between the two o-rings drained?

A

via the Rx vessel head seal drain valve that comes off of a line between the two o-rings.

26
Q

How many regulating groups are there and how are they designated?

A
  1. designated 1,2,3,4, & 5
27
Q

How many part strength groups are there and how are they designated?

A

2 P1 & P2

28
Q

How many shutdown groups are there?

A

2 Group A & Group B

29
Q

How many CEAs are twelve finger full strength?

A

48 exclusively used in shutdown banks A&B for shutdown margin

30
Q

How many CEAs are four finger full strength and how many are four finger part strength?

A

28 full and 13 part strength. Regulating groups 4&5 use only 4 fingered CEAs, while groups 1-3 use both 12 and 4 finger CEAs.

31
Q

What material do the P1 and P2 part strength rods use?

A

low strength inconel pellets throughout their active life

32
Q

What components make up a fuel assembly?

A

fuel spacer grids, upper end fitting, hold down plate, lower end fitting, guide tubes, fuel rods

33
Q

What are the fuel rods pressurized with at assembly?

A

Helium to prevent clad collapse due to stresses from d/p and improve thermal conductivity.

34
Q

Describe a fuel rod.

A

UO2 pellets, a round wire SS compression spring with a spacer disc located at each end of the fuel column all encapsulated in a seal welded tube and pressurized with helium

35
Q

Why are the pellets dished on the ends?

A

accommodate thermal expansion and fuel swelling

36
Q

What components make up the steam generators?

A 
primary chamber
tube sheet & u-tubes
secondary side shell
feedwater ring
economizer
wrapper plate
moisture separators
steam dryers
37
Q

What is it called when there is a hole in a steam generator tube and you can’t maintain pressurizer level or pressure with the CVCS system?

A

tube rupture

38
Q

What if you can maintain primary pressure and pressurizer level with the CVCS system and a hole in the S/G tube?

A

primary leakage

39
Q

Which Palo Verde unit has experienced a tube rupture?

A

Unit 2 (note the signs in the turbine building and shiny new steam generators)

40
Q

What two things do the reactor coolant pumps provide?

A

a) head to maintain flow in the RCS during normal ops

b) heat for plant heat ups

41
Q

Are the reactor coolant pumps covered by tech specs?

A

No, they are non-class/not needed for safe shut down

42
Q

What supplies oil to the reactor coolant pump (RCP) thrust bearing pads prior to startup and after shutdown?

A

lift oil system

43
Q

How is oil supplied during normal operation of the RCP?

A

by an impeller that is keyed to the main drive shaft assy of the pump. AKA main oil.

44
Q

What is the purpose of the accumulator in the lift oil system?

A

to absorb any shocks to the system by acting as a surge volume

45
Q

Will the RCP start without the lift oil pump running?

A

no. there is an interlock. Usually the lift oil pump is started 7 minutes before the RCP.

46
Q

How long after the pump has been running with the lift oil pump shut off?

A

2 minutes

47
Q

Will the lift pump start in auto if the RCP trips?

A

no. The operator must start the pump. There is no Auto start, only the auto stop after 2 minutes of RCP running.

48
Q

What components make up the RCP shaft seal assembly?

A

3 tandem mechanical pressure reduction seals and an aux impeller

49
Q

What system supplies seal injection water to the mechanical seals?

A

CVCS (charging).

50
Q

What is the flowpath of seal water through the RCP shaft seal assy?

A

Seal water enters a jet pump and mixes with flow from the cavity below the journal bearing
flow goes into the high pressure cavity of the #1 seal.
from the #1 seal cavity flow goes both down to the via the aux impeller to the lower journal bearing cavity for lubrication and to help keep contaminants out of the seal area and the other portion of flow goes up to #2 seal chamber via a cooler (Controlled Bypass Flow).
flow from #2 seal chamber goes through a cooler then up to #3 seal chamber and then out to the VCT.
any leakage is directed via a small screw pump to the RDT.

51
Q

How much flow is there across the RCP mechanical seals?

A

there is no measurable flow across the seals. Flow is on the molecular level.

52
Q

Can the controlled bypass flow (AKA seal bleed off) valves be isolated with RCPs running?

A

No. The isolation valves won’t close with the pump running.

53
Q

Why do we want to increase the coast down time of RCPs via a motor fly wheel?

A

to help ensure adequate heat removal from the core on a 4 pump loss of flow trip.

54
Q

Can you start a RCP without nuclear cooling water flow?

A

NO.

55
Q

What conditions must be met to start a RCP?

A

no motor faults
oil lift flow sufficient
NC flow sufficient
RCP bleed off valve fully open

56
Q

What trips are associated with RCPs?

A

under voltage
coast down
over current
speed <600rpm after a few seconds of running

57
Q

What must you have in order to have main spray flow?

A

D/P across the rx vessel. normally provided by RCPs.

58
Q

What supplies spray flow if RCPs aren’t running?

A

aux spray from the charging system (CVCS)

59
Q

Why do you not want to isolate spray valve bypass flow?

A

a) thermal shock may occur to the spray nozzle, piping, and valves due to lack of flow and differential temperature
b) thermal stratification in horizontal piping runs that could cause torsional stress
c) chemistry concentration/dilution and temperature differences in the pressurizer

60
Q

Draw RCS.

A

check that you included:
Rx vessel, RCPs, Hot leg & Cold leg piping,
PZR, primary safety valves, spray line piping,
spray valves, spray bypass valves, surge line piping, 2 steam generators

Primary System Mechanical (7 decks)

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