Core Construction

Question 1

What does the core barrel do?

Answer 1

• Provides the primary support of the core

Question 2

What does the thermal shield do?

Answer 2

• Protects vessel by supplying shielding from high gamma and neutron flux
• Provides some preheat of reactor coolant

Question 3

What does the Diffuser Plate do?

Answer 3

• Provides uniform flow distribution to the lower core plate

Question 4

What do the Core Baffles and Formers do?

Answer 4

• Provide transition between rectangle fuel assemblies and circular core

Question 5

What does the Upper Core Plate do?

Answer 5

• Contains orientations pins for the fuel assemblies

Question 6

What does the Lower Core Plate do?

Answer 6

• Provides support and orientation pins for fuel assemblies

- 4 holes direct flow thru each assembly

Question 7

What does the Secondary Support Assembly do?

Answer 7

• Limits core movement if core barrel falls

- With the maximum 1-1/4” downward displacement of the core the control rods would remain aligned in the fuel assemblies

Question 8

What are the core penetrations?

Answer 8

• 58 for in-core NIs
• 53 for CRDMs
• 1 vent connection
• 5 In-core Thermocouples
• 1 RVLIS/Vent connection

Question 9

What does the Core Support casting do?

Answer 9

• Core support casting is the bottom of the core barrel.

- Prevents rotation and horizontal movement of barrel by fitting in keyways** on vessel wall.

Question 10

What is the Reactor Core flow path?

Answer 10

1. Enters vessel through 4 inlet nozzles
2. 1% leaks by upper core barrel to outlet nozzles
3. 0.5% goes into upper head area for cooling
4. 98.5% flows down between core barrel and vessel wall
5. Flow between thermal shield and barrel for cooling
6. Flow turns up through support casting, diffuser plate and lower core plate - proper flow distribution includes higher flow in center region of core
7. 0.5% flows between barrel and baffles
8. 2.5% flows up control rod guide thimbles
9. Coolant mixes in upper internals region and exits via outlet nozzles

Question 11

What are the important flows to core?

Answer 11

Enter:

• 1% leaks by upper core barrel to outlet nozzles
• 0.5% goes into upper head area for cooling
• 98.5% flows down between core barrel and vessel wall

Exit:

• 0.5% flows between barrel and baffles
• 2.5% flows up control rod guide thimbles

Question 12

What is the purpose of the NSO Orifice?

Answer 12

• Limits downstream break flow to within the capacity of 1 CCP