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 from neutron embrittlement
• 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

Maintains the rectangular fuel assemblies in a circular pattern

Question 5

What does the Upper Core Plate do?

Answer 5

Contains orientation pins for the fuel assemblies

Question 6

What does the Lower Core Plate do?

Answer 6

• Contains 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 a ½ ” drop of the Core Barrel, control rod tips remain in fuel assembly guide tubes (still aligned)

Question 8

What is a primary source of neutron radiation?

Answer 8

Californium 252
- Spontaneous fission
- Used for initial startup only

Question 9

What is a secondary source of neutron radiation?

Answer 9

Beryllium

Question 10

What does the Core Support casting do?

Answer 10

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

Question 11

What is the Reactor Core flow path?

Answer 11

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 12

What are the important flows to core?

Answer 12

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 13

What is the TS 2.1.1.1 limit for DNBR with WRB-1 DNB?

Answer 13

≥ 1.17

Question 14

What is the TS 2.1.1.1 limit for WRB-3 correlation with a DNBR where WRB-1 correlation is not applicable?

Answer 14

≥ 1.30

Question 15

What is the TS 2.1.1.2(RCS Core Safety Limits) limit for peak fuel centerline temp?

Answer 15

< 5080°F and decreasing by 58°F/10,000 MWD/MTU

Question 16

What does TS 2.1.2 (RCS Core Safety Limits) state?

Answer 16

RCS pressure shall be maintained ≤ 2735 psig in Modes 1-5

Question 17

What mode(s) is TS 2.1.2 (RCS Core Safety Limits) required to be maintained?

Answer 17

Modes 1-5

Question 18

If TS Safety Limit 2.1.2 is violated in mode 2, what needs to be done?

Answer 18

Restore RCS pressure to ≤ 2735# (compliance) and be in mode 3 w/in 1 hr

Question 19

If TS Safety Limit 2.1.2 is violated in mode 4, what needs to be done?

Answer 19

Restore RCS pressure to ≤ 2735# (compliance) within 5 minutes

Question 20

What is the TS Safety Limit Bases?

Answer 20

Bases on not violating following fuel criteria
- 95% probability with 95% confidence level that the hottest fuel rod in the core does not experience DNB
- 95% probability with 95% confidence level that the hottest fuel pellet in the core will not experience centerline fuel melting

Question 21

What is the control rod Composition?

Answer 21

• Silver - 80%
• Indium - 15%
• Cadmium - 5%

Question 22

What is the purpose of the NSO Orifice?

Answer 22

Limits downstream break flow to within the capacity of 1 CCP