Reactor Vessel and Internals Flashcards
What is the flow path through the reactor core?
Coolant enters the four inlet nozzles (cold legs) of the reactor vessel, flows downward between the reactor vessel wall and the core barrel, passes through the flow skirt section where the flow distribution is equalized and goes into the lower plenum. The coolant then flows upward through the core removing heat from the fuel rods. The heated coolant enters the core outlet region where the coolant flows outside of the control element assembly shroud tubes to the reactor vessel outlet nozzles.
What is the purpose of the Core bypass flow paths?
prevent stagnation of water in areas of very low flow and keep the temperature of all the primary coolant in the Reactor Vessel below saturation temperature, particularly the head and upper guide structure.
How many CEAs are there?
What kinds are there and how many of each?
89 CEA’s total
13 - 4 finger part strength
76 - full strength
-48 CEA’s - 12 finger full strength
-28 CEA’s - 4 finger full strength
What does a Control Element Assembly (CEA) consist of?
○ Spider
§ Transition between control rods and extension shaft assy
○ Control Rods
§ Provide the neutron absorbing material necessary for the CEA’s to accomplish their function
○ Extension shaft assembly
contains a section at the top (extension sleeve) which contains the magnets for reed switch position indication which are used to indicate the CEA vertical position.
What is the purpose of the Fixed Incore Instrumentation?
acquire data for COLSS and QSPDS
no operational plant controls
What is the Reactor Vessel Level Monitoring System (RVLMS)?
Coming in from the top of the Vessel are 2 strings of heated and unheated junction thermocouples
used for determining Reactor Vessel Level during post-accident conditions
What is the purpose of the Flow Baffle?
perforated cylinder that provides uniform flow distribution
What is the purpose of the Core Support Barrel?
carries the entire weight of the reactor internals
How is the Reactor Head vented?
Where does it vent to?
Solenoid Valves controlled from B04
RDT or Containment
How do the Rx Vessel Head O-rings work?
Self-energized refers to the inner surface of the O-rings is drilled. This allows the RCS pressure to pressurize the O-ring and improve the seal.
Inner and outer O-ring for redundancy
Each O-ring has 100% capacity. The outer O-ring remains passive unless a problem develops with the inner O-ring seal.
Why is it important to follow correct sequencing of opening the Reactor Head Vents?
prevent damage to the valve internals due to backpressure hammer
How are fuel pellets designed to accommodate for thermal expansion/swelling?
dished at the ends of each pellet
Why are the fuel rods filled with helium?
preclude cladding collapse during design life of the fuel
improve thermal conductivity of the pellet to clad gap within the fuel rod
What is the purpose of the surveillance capsule assemblies
determine the effects of irradition on reactor vessel materials
