Rx Vessel & Internals

Question 1

How is weight of fuel assembly in core transferred to ground?

Answer 1

• fuel assembly rests on lower core plate
• low core plate connected to core barrel bottom (core support forging) via a support column
• core barrel rests on ledge on inside of vessel flange
• all of Rx vessel rests on four nozzles (2 hot, 2 cold)
• nozzles rest on Rx cavity wall (cooled by CCW)

Question 2

What is held in place by Rx vessel head?

Answer 2

• Rx vessel head holds down upper internals
• upper internals rest on hold down spring
• hold down spring rests on core barrel

-upper internals also rest on all leaf springs of F.A.

Question 3

Describe flange leakoff system

Answer 3

• 2 self energizing o-rings with downstream flow going to isolation valves (8069A-outer, 8069B-inner)
• inner normally open to remote isolation valve 8032 and temp indication (TE-401)

Question 4

How many fuel assemblies in core?

Break down math of spaces in fuel assembly

Answer 4

193 fuel assemblies

17 x 17 = 289 slots

25 guide tubes ( 24-rods, 1-MIDS)

289 - 25 = 264 fuel rods

Question 5

Penetrations in core

Top

Bottom

Answer 5

Top- core exit thermocouples
Head vent (vent non-condensibles during casualty)

Bottom- 58 for mids

Question 6

Purpose of secondary support plate

Answer 6

• limit momentum of core falling to bottom of Rx vessel if core barrel flange fails
• limit length of travel fuel assemblies fall to less than 1.25” so fuel assemblies don’t become unaligned with upper internals and ultimately the control rods

Question 7

Describe core bypass flows

Difference between units flow

Answer 7

0.5% - cold leg inlet to head

1% - cold leg, gap between core barrel and hot leg nozzle

.5% - bottom core between baffle plates and core barrel

5% - through guide tubes

0.5% - bottom core between baffle wall and outer fuel assemblies

U-1 = 7.5%
U-2 = 9%

Question 8

Unit differences on core vessel

Answer 8

U-1
Full thermal shield
Lower support forging+diffuser
Top hat upper internals
Higher power rating b/c cut into margin

U-2
Thermal pads
No diffuser
No ribs on upper internals hat
Higher flow => higher power rating

Question 9

Features on fuel assembly for debris mitigation?

Answer 9

Bottom nozzles have debris filters

P-grid bottom of f.a.

Bottom 7” have oxide coating on fuel rods

Question 10

Describe fuel rods

Answer 10

Zirconium alloy cladding

End plugs

Plenum spring

UO2 pellets

He filled fuel clad gap

Question 11

IFBA description

Answer 11

Certain UO2 pellets coated with Zr(BO3)2 zirconium di-borate (middle 11 ft)

Top and bott 6” are not coated and are hollow to allow for He gas buildup from B-10 reaction.

Question 12

How is impact minimized for rods falling on Rx Trip?

How many control rods in core/ rodlets in Control Rod?

Answer 12

Dashpot effect at bottom of thimble tubes

Spring built into spider hub when contact top nozzle of f.a.

53 control rods / 24 rodlets

Question 13

What are control rods made up of?

Answer 13

Silver (80%), indium (15%), cadmium (5%)

Question 14

Purpose of neutron source inserts?

Material make up?

Answer 14

Provide positive indication of neutron level

Antimony-Berilium

Question 15

Describe Rx vessel head vent system

Answer 15

Two redundant parallel trains vent Rx vessel to CNMT atm (during casualty to vent non-cond gas)

8078B & 8078A

8078C & 8078D

Open down stream vlv first so pressure spike doesnt cause inadvertent opening of downstream valve