RPV Internals

Question 1

What is the purpose of the RPV?

Answer 1

Provide closed volume in which reactor core can be submerged for purposes of moderatio, cooling, and power production
Contain core, internals, and moderator
Serve as high integrity barrier against radioactive leakage to containment
Provide floodable volume for cooling in event of primary system breach

Question 2

What are the design concerns for the RPV?

Answer 2

Neutron embrittlement
Pressure/Temp Transients
Corrosion
Designed for 40 year life at 1250psig

Question 3

How is the vessel supported?

Answer 3

Vertically by support skirt, ring girder, sole plate, and concrete foundation
Laterally by bioshield stabilizers 4 to vessel and 8 to containment.

Question 4

What is the purpose of the Baffle Plate?

Answer 4

Provides a mounting surface for the jet pump diffuser AND separates recirc suction area from core inlet plenum

Supported by 6 colum members to support jet pump, shroud, shroud head/moisture separator, core spray sparger, core plate, top guide, peripheral bundles

Question 5

How many jet pumps are there?

Answer 5

20 - with 10 Recirc risers

Question 6

What happens to core RPV flow with Jet pump failure?

Answer 6

Actual flow goes down, and core thermal power goes down. Indicated flow may go up or down.

Question 7

How do the Jet Pumps Function?

Answer 7

RR Risers feed rams head and diverts to two jet pumps.
Nozzle injects high pressure 1/3 RR flow to throat area and drives in 2/3 flow. The Diffuser convers kinetic energy to pressure.

Question 8

How is Jet Pump Flow measured?

Answer 8

Jet Pumps 1, 6, 11 and 16 have instrument tapped into bottom of diffuser

Question 9

What is the purpose of the core shroud?

Answer 9

Provides lateral support for core plate, top guide and fuel bundle.
Vertical support for top guide.

Question 10

Where are the Core Spray SPargers and how many are there?

Answer 10

2 redundant spray networks mounted on inside upper part of the shroud to spray on top of core.

Question 11

What is the Core Plate?

Answer 11

Provides vertical and lateral support for 16 peripheral bundles.
Lateral support for control rod guide tubes, fuel support castings, bundles, and in core guide tubes.

Question 12

What is the CRD Housing?

Answer 12

Houses the CRD, providing later and vertical support for the drives. Transmits weight to reator bottom.

Question 13

What is the function of the Orificed Fuel Support?

Answer 13

Provides alignment for bottom of fuel assembly
Controls 90% flow through fuel and 10% flow bypass to Ctrl rod and NI’s
Transmits fuel weight to CRD guide tubes.
Smaller orifices in perimieter to direct more flow through center bundles.

Question 14

How is feedwater injected to RPV

Answer 14

4 - 70 degree spargers distribute FW to jet and recirc pump suction.

Question 15

What does the Vessel Head Drain do when not plugged?

Answer 15

Removes CRUD to RWCU system, prevents statification in bottom head

Question 16

What is the function of the core shroud head?

Answer 16

Forces steam and water through steam separator by closing off core outlet.

Question 17

How do the Steam Separators Function?

Answer 17

Increase steam quality from 10% to 90% at exit of separators

Question 18

How do we improve core natural circulation?

Answer 18

Raise water to +48 inches (level of second stage steam separator)

Question 19

What is Steam Carryunder?

Answer 19

When steam is entrained int he liquid returning to the downcomer region, this decreases fluid density reaching RR pump and may cause cavitation

Question 20

What causes steam carryunder?

Answer 20

RPV Level too low

Question 21

What causes Moisture carryover?

Answer 21

RPV Level too high

Question 22

What is the steam quality leaving the steam dryer?

Answer 22

99.9%

Question 23

What is the temperature requirement for vessel below top flange before tensioning head?

Answer 23

Greater than 100F

Question 24

What can cause Head O Ring Leakage?

Answer 24

Undertensioning vessel studs

Question 25

What provides shielding from RPV to DW components?

Answer 25

Bioshield

Question 26

Engineered safeguard feature of CRD Housing Support?

Answer 26

Prevents rapid ejection of control rod in event of CRD Housing failure at RPV Pressure.

Question 27

Where does RWCU take suction from?

Answer 27

One RR loop per unit and bottom head drain

Question 28

What is RWCU flow?

Answer 28

~650gpm

Question 29

Where does SDC Take Suction and Return to?

Answer 29

Suction off RR Suction piping and return via LPCI injection piping

Question 30

How is stratification prevented?

Answer 30

The use of natural circulation during low flow conditions by raising water level to 48 inches or higher. This prevents temperature gradients that result in thermal stresses and inaccuracies in RW temperature measurements

Question 31

How is the core cooled during a DBA LOCA?

Answer 31

LPCI injection to flood fore to at least 2/3 height. The upper 1/3 height will be cooled via steam cooling.

Question 32

What is Nil-Dultility Transition Temperature?

Answer 32

Temperature at which a material will be susceptible to a brittle failure.

Question 33

What are three main ways to stress RPV and how are they avoided?

Answer 33

Tensioning the Head - minimum bolt up temp. of 100F when
Pressurizing the vessel - Min temp of a given Rx Pressure
Thermal stress from heat up and cooldown - Minimum temp that the Rx can be made critical

Question 34

What are the TS LCO requirements for Jet Pump operability?

Answer 34

All jet pumps Operable in modes 1 and 2

Question 35

What is the TS allowed leakage for the RX coolant system?

Answer 35

a. No pressure boundary leakage
b. <=5gpm unidentified leakage
c. <= 25gpm total leakage averaged over 24 hour period; AND
d. <= 2gpm increase in unidentified leakage within previous 24 hour period in MODE 1.

Applicable to Modes 1 2 and 3