Term
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Definition
A. The reactor vessel contains the core where the nuclear chain reaction occurs to produce heat
B. Consists of components and assemblies which support the core, provide cooling flowpaths through the core, and allow
control of the nuclear process
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Term
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Definition
•The core, reactor control components, and ECCS mustensure:
ØFuel remains undamaged during Condition I and II events, although a very small number of rod failures may be taken care of by CVCS ØReactor can be brought to a safe state following a Condition III event with a small fraction of fuel damaged; extended outage likely prior to resuming operation
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Term
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Definition
ØReactor can be brought to a safe state and the core can be kept subcritical with coolable geometry following Condition IV events •Fuel assemblies are designed for easy handling during assembly, inspection, refueling & shipping •Fuel assemblies are designed to accept control rod insertions for required reactivity control •Fuel assemblies provide for the in-core instrumentation necessary for plant operation
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Term
| Design Basis Reactor Internals: |
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Definition
§ØSupport the core
ØMaintain fuel alignment
ØLimit fuel assembly movement
ØMaintain alignment between fuel assemblies and the Control Rod Drive Mechanisms (CRDM)
ØDirect coolant flow past fuel elements and through the pressure vessel head
ØProvide gamma and neutron shielding
ØProvide guides for the in-coreinstrumentation
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Term
| Design Basis Reactor Internals: |
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Definition
§Thermal shield to maintain ductility of the pressure vessel and limit neutron embrittlement
§Provisions for in-core instrumentation, and installation of test specimens for a pressure vessel irradiation surveillance program
§Withstand mechanical loading from operating
basis and design basis earthquakes and pipe
ruptures
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Term
| Design Basis Reactor Internals: |
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Definition
§Assure the core is intact with acceptable heat transfer geometry following abnormal operating conditions
§Limit deformation of critical reactor internals so that fuel cladding temperature is kept within specified limits following the design basis accident to allow reactor shutdown and core cooling
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Term
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Definition
§Fuel rod integrity is ensured by design to prevent excessive:
ØFuel temperatures
ØInternal rod gas pressures from fission gas release
ØCladding stresses and strain
§Fuel Pellet Temperatures
ØCenter of hottest pellet to be below the melting temperature of UO2 (5080oF unirradiated)reduced by 58ºF per 10,000 MWD/MTU
ØFuel centerline temperature ≤ 4700ºF is an overpower limit to prevent fuel melting
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Term
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Definition
§Internal Gas Pressure
ØMaximum value limited to prevent:
oPellet-to-clad gap outward increase due to clad creep during operation
oFuel Pin burst due to excessive internal pressure
§Clad Stress less than that which would cause general yield of the clad
oClad has some capability to accommodate plastic strain
oYield strength is set conservatively
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Term
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Definition
§Clad Tensile Strain
ØEstablished at less than 1%
ØBased upon tensile and burst test data from irradiated fuel due to irradiation effects on clad ductility
§Strain Fatigue
ØCumulative strain fatigue cycles designed less than the design fatigue life
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Term
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Definition
~6% of the flow through the
Rx Vessel bypasses the core
and is unavailable for heat
removal from the core
Nozzle Bypass 1%
The fit between the Hot Leg nozzle flange and the core barrel flange has a small gap allowing some flow to short circuit the core by passing directly from the cold leg to the hot leg
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Term
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Definition
~6% of the flow through the
Rx Vessel bypasses the core
and is unavailable for heat
removal from the core
Guide Tube Bypass &
Instrument Thimble Bypass
Flow 4%
Passes through the flow cutouts at the dashpot in the Fuel assembly guide tubes and up through the guide tubes
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Term
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Definition
~6% of the flow through the
Rx Vessel bypasses the core
and is unavailable for heat
removal from the core
Baffle Wall Bypass Flow 0.5%
A small amount of flow passes up through the baffles and around the outside of the fuel bundles
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Term
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Definition
6 % of the flow through the
Rx Vessel bypasses the core
and is unavailable for heat
removal from the core
Head Cooling Bypass Flow 0.5%
Some flow passes from the cold leg into the Rx Vessel head and then to the Hot Legs
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Term
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Definition
Total 193 Fuel Assemblies
@ fuel assembly 17 x17 array
264 fuel rods
24 Rod Cluster guide thimble
1 central in-core
Instrumentation thimble
A total of 289 possible
location (17 x 17)
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Term
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Definition
Each Fuel Rod contains
enriched Uranium
Dioxide (UO2 ) ceramic
pellets: Dished at both ends to allow for axial expansion
as fission product gases build-in.
Top and Bottom 6” have axial hole to accommodate He from IFBAs
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Term
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Definition
•24 tubes/assembly
•Welded in plug at bottom screwed into bottom nozzle
• Secured to top nozzle by crimped slip fit (top nozzle is removable)
•Bottom 12 " is tampered to slow RCCAs on trip (dashpot)
•4 holes above dashpot to let water out so RCCA fall in faster |
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