Core Construction Flashcards
What does the core barrel do?
- Provides the primary support of the core
What does the thermal shield do?
- Protects vessel by supplying shielding from high gamma and neutron flux
- Provides some preheat of reactor coolant
What does the Diffuser Plate do?
- Provides uniform flow distribution to the lower core plate
What do the Core Baffles and Formers do?
- Provide transition between rectangle fuel assemblies and circular core
What does the Upper Core Plate do?
- Provides upper support for fuel assemblies
- Holes to accept control rod assemblies and upper support columns
What does the Vessel Support Ledge do?
- Contains orientation pins for the fuel assemblies
- Support reactor internals via core barrel
- Cooled by CCW isolated on Phase A
What do the Reactor Vessel Internals do?
- Support and orient fuel and control rod clusters
- Absorb control rod dynamic loads and transmit these loads to the reactor flange
- Direct reactor coolant thru core
- Support in-core instrumentation
What does the Lower Core Plate do?
- Provides support and orientation pins for fuel assemblies
- 4 holes direct flow thru each assembly
What does the Secondary Support Assembly do?
- Limits core movement if core barrel falls
- With the maximum 1-1/4” downward displacement of the core the control rods would remain aligned in the fuel assemblies
What do the Upper Support Columns do?
- Maintains spacing between upper support assembly and upper core plate
What do the Upper Control Rod Guide Tubes do?
- Guides each control rod and drive shaft
What is a primary source of neutron radiation?
- Californium 252
- Spontaneous fission
- Used for int. startup only
What is a secondary source of neutron radiation?
- Antimony-Beryllium
- 4 sources installed each made up of 4 rodlets
- Activated by neutron flux during power operations
- Gamma is used to activate the Beryllium
- Beryllium is the neutron source ***
What is the vessel leak detection system made of?
- Inner and Outer O-Ring
- DTA-100 alarms at 140°F
- DRV-100 fails open on loss of air and power
What are the core penetrations?
- 58 for in-core NIs
- 53 for CRDMs
- 1 vent connection
- 5 In-core Thermocouples
- 1 RVLIS/Vent connection
What does the Core Support casting do?
- Core support casting is the bottom of the core barrel.
- Prevents rotation and horizontal movement of barrel by fitting in keyways** on vessel wall.
What is the Reactor Core flow path?
- Enters vessel through 4 inlet nozzles
- 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
- Flow between thermal shield and barrel for cooling
- Flow turns up through support casting, diffuser plate and lower core plate - proper flow distribution includes higher flow in center region of core
- 0.5% flows between barrel and baffles
- 2.5% flows up control rod guide thimbles
- Coolant mixes in upper internals region and exits via outlet nozzles
What are the important flows to core?
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
What is the TS 2.1.1.1 limit for DNBR with WRB-1 DNB?
- ≥ 1.17
What is the TS 2.1.1.1 limit for WRB-3 correlation with a DNBR where WRB-1 correlation is not applicable?
- ≥ 1.30
What is the TS 2.1.1.2(RCS Core Safety Limits) limit for peak fuel centerline temp?
- < 5080°F and decreasing by 58°F/10,000 MWD/MTU
What does TS 2.1.2 (RCS Core Safety Limits) state?
- RCS pressure shall be maintained ≤ 2735# in Modes 1-5
What mode(s) is TS 2.1.2 (RCS Core Safety Limits)required to be maintained?
- Modes 1-5
If TS Safety Limit 2.2.1 is violated, what needs to be done?
- Required to be in Mode 3 w/in 1 hr
If TS Safety Limit 2.1.2 is violated in mode 2, what needs to be done?
- Restore RCS pressure to ≤ 2735# (compliance) and be in mode 3 w/in 1 hr
If TS Safety Limit 2.1.2 is violated in mode 4, what needs to be done?
- Restore RCS pressure to ≤ 2735# (compliance) within 5 minutes
What is the TS Safety Limit Bases?
- 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
What is the control rod Composition?
- Silver - 80%
- Indium - 15%
- Cadmium - 5%
What is the purpose of the NSO Orifice?
- Limits downstream break flow to within the capacity of 1 CCP
