RPV Internals Flashcards
What is the purpose of the RPV?
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
What are the design concerns for the RPV?
Neutron embrittlement
Pressure/Temp Transients
Corrosion
Designed for 40 year life at 1250psig
How is the vessel supported?
Vertically by support skirt, ring girder, sole plate, and concrete foundation
Laterally by bioshield stabilizers 4 to vessel and 8 to containment.
What is the purpose of the Baffle Plate?
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
How many jet pumps are there?
20 - with 10 Recirc risers
What happens to core RPV flow with Jet pump failure?
Actual flow goes down, and core thermal power goes down. Indicated flow may go up or down.
How do the Jet Pumps Function?
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.
How is Jet Pump Flow measured?
Jet Pumps 1, 6, 11 and 16 have instrument tapped into bottom of diffuser
What is the purpose of the core shroud?
Provides lateral support for core plate, top guide and fuel bundle.
Vertical support for top guide.
Where are the Core Spray SPargers and how many are there?
2 redundant spray networks mounted on inside upper part of the shroud to spray on top of core.
What is the Core Plate?
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.
What is the CRD Housing?
Houses the CRD, providing later and vertical support for the drives. Transmits weight to reator bottom.
What is the function of the Orificed Fuel Support?
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.
How is feedwater injected to RPV
4 - 70 degree spargers distribute FW to jet and recirc pump suction.
What does the Vessel Head Drain do when not plugged?
Removes CRUD to RWCU system, prevents statification in bottom head
What is the function of the core shroud head?
Forces steam and water through steam separator by closing off core outlet.
How do the Steam Separators Function?
Increase steam quality from 10% to 90% at exit of separators
How do we improve core natural circulation?
Raise water to +48 inches (level of second stage steam separator)
What is Steam Carryunder?
When steam is entrained int he liquid returning to the downcomer region, this decreases fluid density reaching RR pump and may cause cavitation
What causes steam carryunder?
RPV Level too low
What causes Moisture carryover?
RPV Level too high
What is the steam quality leaving the steam dryer?
99.9%
What is the temperature requirement for vessel below top flange before tensioning head?
Greater than 100F
What can cause Head O Ring Leakage?
Undertensioning vessel studs
What provides shielding from RPV to DW components?
Bioshield
Engineered safeguard feature of CRD Housing Support?
Prevents rapid ejection of control rod in event of CRD Housing failure at RPV Pressure.
Where does RWCU take suction from?
One RR loop per unit and bottom head drain
What is RWCU flow?
~650gpm
Where does SDC Take Suction and Return to?
Suction off RR Suction piping and return via LPCI injection piping
How is stratification prevented?
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
How is the core cooled during a DBA LOCA?
LPCI injection to flood fore to at least 2/3 height. The upper 1/3 height will be cooled via steam cooling.
What is Nil-Dultility Transition Temperature?
Temperature at which a material will be susceptible to a brittle failure.
What are three main ways to stress RPV and how are they avoided?
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
What are the TS LCO requirements for Jet Pump operability?
All jet pumps Operable in modes 1 and 2
What is the TS allowed leakage for the RX coolant system?
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
