Reactor Vessel and Internals Flashcards
Discuss Reactor Vessel Construction.
- 14.3’ ft diameter.
- Welded Carbon Steel plates clad internally with 5/16” SS-304 (for corrosion resistance)
- Ledge in vessel supports weight of internals which is transferred to nozzles
Discuss Reactor Vessel Closure Head.
Low Alloy Steel.
* Bolted to, and supported by the Rx vessel by 54 – 7” diameter threaded studs, washers, and nuts
* Studs “stretch tensioned” to develop clamping force, nuts run against flange then tension is removed
* 2 alignment pins aid in precise alignment of head on flange
* 74 [102] penetrations total; 8 [10] for instrumentation; 1 for vent
Discuss Reactor Vessel Closure Support Structure.
Beams embedded in the concrete over 1 Hot Leg and Two Cold Legs
Discuss Reactor Vessel Flange/Head ‘O’ Rings.
- Consists of 2 “O” Rings (inner and outer) that fit in 2 concentric grooves in head flange
- Inconel tubing, coated with pure silver
- Holes in vessel flange between O-rings ported to pressure indicator (local) and switch
- Leakage past inner O-ring pressurizes the space and is detected by PI and switch
- Local gauge and Rx Head Seal High Pressure Alarm (~2000 psia [~1000 psig] -RTGB)
- If alarm clears it is indication that outer O-ring may have failed. Can be reversed
Discuss Reactor Vessel Insulation.
Limits RCB (CNMT) temperatures by limiting the heat loss from the RCS to CNMT
Discuss Reactor Flow Skirt.
Inconel
* Equalizes flow and pressure across the core support barrel
* Sits on very bottom of vessel
Discuss Reactor Vessel Weight Transfer.
- Vessel is supported by steel pads welded to the underside of nozzles (B1-Th, A1/A2-Tc)
- Pads sit on steel girder columns (support structures) which permits radial expansion (thermal growth), maintains centering, and restrains seismic induced motion
Discuss Reactor Core Barrel.
Suspended from a ledge on the inside surface of the Rx vessel flange and supports the entire weight of the Rx Vessel Internals
Discuss Reactor Core Stops.
Inconel
* 9 core stops limit the downward motion (fall) of the core support barrel should the support ledge fail
Discuss Reactor Core Support Plant (Assembly).
SS-304
* Aligns the fuel assemblies via locating pins and directs coolant flow into the fuel
* Transfers the weight of internals to the barrel
Discuss Reactor Core Shroud.
SS-304
* Surrounds core to limit bypass flow (square fuel, round hole)
* Flow holes in support plate allow bypass flow to minimize thermal stresses b/w barrel and shroud
Discuss Reactor Upper Guide Structure (UGS) & Support Plate.
- Supports the upper end of the fuel assemblies to prevent movement.
- Provides hold down force to prevent core uplift due to coolant flow forces
- Supported by the Rx vessel flange.
- Supports the ICI plate assembly, CEA shroud, and ICI guide tubes
- Fuel Alignment plate on bottom of UGS
Discuss Reactor CEA Shrouds.
Austentitic SS
* Guides CEA’s through fuel alignment plate
Discuss Reactor Instrument Plate (ICI Plate).
Provides a guide path for Incore detectors
Discuss the Reactor Core.
- 217 Fuel Assemblies
o Gadolinium is the burnable absorber used for fuel. (Homogeneously integrated into fuel pellets) - 73 [87] CEA’s.
o {Unit 1 has 73 CEAs but 12 SD CEDMs are duals (control 24 CEAs). Thus 61 CEDM extension shafts operate 73 CEA’s}
o B4C is the absorber used in CEAs. - 14X14 [16X16] fuel pins per assembly (Zircaloy tubes with low enrichment UO2)
- [16X16 matrix for Unit 2 fuel assemblies gives us more linear feet of fuel rods which Reduces the Peak Linear Heat Rates on Unit 2]
Discuss Reactor Core Bypass Flow.
- Total: ~4.2% [2.54%]
- Guide Tube - 1.61% [1.29%] 43-48% (**MAJOR CONTRIBUTOR **)
Discuss Reactor Vessel Sampling Package System.
- Test specimens used to determine the effects of irradiation on vessel materials
- 6 capsules are located in the Core Support Barrel. Analysis of these specimens is used to establish the permissible Nil-Ductility Transition Temperatures for the Rx
Discuss Reactor Refueling Sequence.
- Shutdown and Cooldown Unit to Mode 5 conditions
- Remove interference
- Permanent cavity seal ring - only need to close hatches
- De-tension head studs (Mode 6),
- Remove Head and set on 62’ elevation,
- Unlatch CEA’s
- Install UGS lift rig and remove UGS and from vessel and place in lower cavity,
- Perform core off-load or fuel shuffle,
- Re-assembly is reversal of sequence described.
Which ONE of the following components does NOT receive direct support from the Rx Vessel Flange?
a. Core Barrel
b. Shroud
c. RV Closure head
d. Upper Guide Structure
b. Shroud
Which ONE of the following best describes the Reactor Vessel Support Structure?
a. Supported by all 4 Cold legs
b. Supported by Both Hot Legs
c. Supported by 1 hot and 2 cold legs
d. Supported by a ledge in the RV Flange
c. Supported by 1 hot and 2 cold legs
Describe how the integrity of the reactor vessel and internals are protected by Tech Specs?
Safety Limits, Section 2.1.2 limits RCS pressure to less than 2750 psia. LCOs
Why aren’t CEDMs removed?
CEDM housings are part of pressure boundary. Only operating coils are outside. Latches and other moving parts are inside the housing which is seal-welded (Omega) to dome.
What are the Fission Product Barriers?
- Cladding
- RCS
- Containment
Unit 2 Lift setting of the Pzr Code Safeties is found to be 2498psig. Any T/S impact?
No T/S impact because all within 1% - Code safeties – TS 3.4.10
Given: Unit 2, Heatup is underway, Tc=250F, Pzr pressure 1300psia
Given: Unit 1, Heatup in progress, Tc =191ºF, Tcet=192ºF, Press=1406psia, HU Rate= 11ºF /15mins
Any T/S impact?
Not meeting T.S. 3.4.9 per Fig 3.4-2 for heatups Apply action to restore within 30min - P/T limits – TS 3.4.9.1[3.9.1] Heat up & CD limits max CD to mode 5 is 100F/hr (more restrictive admin limits will also apply)
Chemistry – TS 3.4.7 Given: Unit 1, 300psia, C/D in progress, Tc= 230F, Th= 231F, Cl .1ppm, Fluoride .16ppm, DO 1.19ppm. Any T/S impact?
No actions required
Given: Unit 2, 300psia, C/D in progress, Tc= 100F, Th= 101F, Both SG Press. 200psig. Any T/S impact?
No actions required. T.S. 3.4.7 LCO is met. (Not Steady State, O2 limit N/A if < 250F.
Why are the P/T curves different for each unit?
Variation due to Operating history and results of surveillance testing
