Vessel & Internals

Question 1

Explain the purpose of the Reactor Vessel and Internals

Answer 1

The reactor vessel is part of the PCS boundary and is a Fission Product Boundary.

Reactor Vessel Internals - Provide support for and orient the reactor core fuel bundles and control rods, absorb the control rod dynamic loads and transmit these and other loads to the reactor vessel flange, provide a passageway for the reactor coolant and support incore instrumentation.

Question 2

Given a sketch of the Reactor Vessel and Internals, trace the normal primary coolant flow path through the reactor vessel, without error.

Answer 2

Draw:

Normal Flow - Coolant enters through four (4) inlet nozzles (cold legs) and is directed downward in the annulus region between the Core Support Barrel (CSB) and the Reactor Vessel. At the bottom of the CSB coolant is directed toward the center of the reactor vessel by the flow skirt. The coolant then travels upward through the core and into the Upper Guide Structure (UGS). The coolant then exits the reactor vessel via two (2) outlet nozzles (hot legs). A significant amount of coolant flows upward through the Upper Guide Structure (UGS) and into the upper head region prior to exiting via the hot leg nozzles.

Question 3

Given a sketch of the Reactor Vessel and Internals, trace the bypass primary coolant flow path through the reactor vessel, without error.

Answer 3

Draw: Bypass Flow - Most is from coolant flowing upward through the region between the CSB shell and the core shroud. This flow minimizes thermal gradients, provides some head cooling and minimizes unacceptable chemistry conditions that might result from stagnant water.

Question 4

Describe the operational design of the Reactor Vessel Flange Inner and Outer Seals

Answer 4

• Function to seal the vessel head interface.
• Two silver-plated, self-energizing, inconel O-rings. A self-energizing O-ring is one that is hollow with flow passages that allow the pressurized fluid inside the O-ring to assist the sealing force.
• Inner seal pressurized. The outer seal would be pressurized only if there were a failure of the inner seal.

Question 5

What alarms are associated with the Reactor Vessel Flange Inner Seal?

Answer 5

EK-0767, “REACTOR VESSEL FLANGE INNER SEAL LEAKAGE”

• Setpoint: 1500 psig on PS-0101 . Can be verified by indication PI-0101
• Sensing line penetrates the reactor flange and terminates in the space between the two O-ring seals.
• Drain path is to the Primary Drain Tank that is normally isolated by CV-0101 being closed.

Question 6

What alarms are associated with the Reactor Vessel Flange Outer Seal?

Answer 6

EK-0768, “REACTOR VESSEL FLANGE OUTER SEAL LEAKAGE”

• Sensing line is located outside the outer O-ring groove and does not constitute part of the pressure boundary. Setpoint: 120” water column on LS-0160.
• Drain path is to the containment floor drain. Normally isolated by SV-0160 which opens on LS-0160 actuation.

Question 7

Describe the operational design of the Core Support Barrel

Answer 7

• Cylindrical with an inside diameter of 150 inches and a wall thickness of 1 inch
• Suspended by 4-inch thick flange from the reactor vessel core support ledge
• Carries the entire weight of the core and other internals
• A 1.5‑inch thick core support plate containing flow distribution holes and fuel assembly alignment pinholes is supported by a ledge inside the core support barrel and by 52 core support columns. The core shroud is attached to the core support plate and limits core bypass flow.
• Within the core support barrel are axial shroud plates and former plates that are attached to the core support barrel wall and the core support plate and form the enclosure periphery of the assembled core.

Question 8

Describe the operational design of the Core Support Assembly

Answer 8

• It is the major support member of the reactor internals.
• Consists of the core support barrel, the core support plate and support columns, the core shrouds, the core support barrel to pressure vessel snubbers and the core support barrel to upper guide structure guide pins.
• Supported at its upper flange from a machined ledge in the reactor vessel flange. The lower end is restrained in its lateral movement by six core support barrel to pressure vessel snubbers.

Question 9

Describe the operational design of the Core Shroud

Answer 9

• Follows the perimeter of the core and limits the amounts of coolant bypass flow.
• Consists of rectangular plates 5/8 inch thick, 145 inches long and of varying widths.
• The critical gap between the outside of the peripheral fuel bundles and the shroud plates is maintained by seven tiers of centering plates attached to the shroud plates.
• Holes in core support plate allow some bypass flow upward between core shroud and CSB - minimize thermal stress, eliminate stagnant pockets of coolant.

Question 10

Describe the operational design of the Upper Guide Structure

Answer 10

• Consists of a flanged grid structure, 45 control rod shrouds, a fuel bundle alignment plate and a ring shim.
• Aligns and supports the upper end of the fuel bundles, maintains the control rod channel spacing, prevents fuel bundles from being lifted out of position during a severe accident condition and protects the control rods from the effect of coolant cross flow in the upper plenum. It also supports the incore instrumentation guide tubing.
• The periphery of the flange contains four alignment keyways, equally spaced at 90-degree intervals, which engage the core barrel alignment keys. The reactor vessel closure head flange is slotted to engage the upper ends of the alignment keys in the core barrel.
• The fuel bundle alignment plate is designed to align the upper ends of the fuel bundles and to support and align the lower ends of the control rod shrouds.
• Since the weight of a fuel bundle under all normal operating conditions is greater than the flow lifting force, it is not necessary for the upper guide structure assembly to hold down the core. However, the assembly does capture the core and would limit upward movement in the event of an accident condition.

Question 11

Describe the operational design of the Core Stops

Answer 11

• Nine core support lugs (stops) are attached to the vessel lower wall.
• Designed to catch the core barrel in the event that the upper core supports failed. The Core Support Lugs contain a small yield pad that is intended to deform and absorb the energy of the falling core.

Question 12

Describe the operational design of the Core Support Barrel Snubbers

Answer 12

• Sometimes referenced as CSB Stabilizing Lugs.
• Prevent flow-induced vibration and seismically-caused movement of the CSB.
• Six core support barrel snubbers provide a close fit between the core support barrel and the lower vessel wall.

Question 13

Describe the operational design of the Flow Skirt

Answer 13

• Used to reduce inequalities in core inlet flow distributions and to prevent formation of large vortices in the lower plenum.
• It is a cylinder broken into 900 2.5-inch holes that break the large annular wall jet into approximately 900 2.5-inch diameter jets.
• Provides a nearly equalized pressure distribution across the bottom of the core support barrel.
• It is hung by welded attachments from the core stop lugs near the bottom of the pressure vessel and is not attached to the core support barrel.

Question 14

Describe the operational design of the Fuel Assembly

Answer 14

Typical reload fuel bundle that consists of a square (15 by 15) array of 225 positions: 216 fuel rods, 8 Zircaloy-4 guide bars, and 1 Zircaloy-4 instrument tube

Question 15

Describe the operational design of the Surveillance Capsules.

Answer 15

They measure the long term effects of temperature and radiation on reactor vessel materials

Question 16

Describe the operational design of the Control Rod Shrouds

Answer 16

They enclose the control rods in their fully withdrawn position above the core, thereby protecting them from adverse effects of flow forces

Question 17

Given a sketch of the Reactor Vessel and Internals, identify the following major components and penetrations:

• Reactor Vessel Flange Inner and Outer Seals
• Core Support Barrel
• Core Support Assembly
• Core Shroud
• Upper Guide Structure
• Core Stops
• Core Support Barrel Snubbers
• Flow Skirt
• Surveillance Capsules
• Control Rod Shrouds
• Inlet and Outlet Nozzles (6)
• CRDM Nozzles (45)
• Incore Instrument Nozzles (8)
• Reactor Vessel Head Vent (1)
• Flange Leakoff detector Taps (2)

Answer 17

Draw

Question 18

Given a sketch of a fuel assembly, identify the following components of a fuel assembly:

• Zircaloy Guide Bars
• Center Instrument Tube
• Tie Plate
• Fuel Rod
• Spacer Grid

without error.

Answer 18

Review

Question 19

What are the Control Room indications for Reactor Vessel and Internals?

Answer 19

LIA-0105/LIA-0106: Provides indication of water level in Reactor Vessel/Primary Coolant System above bottom of hot legs

LIA-0105: Level indication taps off Loop 1 Hot Leg

LIA-0106: Level indication taps off Loop 2 Hot Leg

The loop is powered from preferred AC Bus Y20. The instrument loop consists of a level transmitter, a power supply and an LIA located in the control room.

Question 20

Design feature for PCS to monitor Vessel Level

Answer 20

LIA-0105

Wide range = 628’ 6” - 617’

Narrow range = 620’ 9” - 617’

LIA-0106

Range = 619’ 6” - 617’

Question 21

What is Reactor Vessel Monitoring System (RVLMS) LE‑0101A & LE‑0101B

Answer 21

Sensors consist of differentially connected thermocouple pairs. One junction is electrically heated and one is not. In water, the heat transfer is high so the Delta-T is low. In steam, heat xfer is reduced, so Delta-T rises. High Delta-T is an indication that the sensor is not covered by water.
Green light is the highest water level detected (should assume water level is at that point)

Question 22

What makes an RVLMS operable?

Answer 22

A RVLMS channel consists of 8 sensors. A channel is considered operable if four or more sensors (2 or more upper, and 2 or more lower) are operable. Recorders must be on.

Question 23

What are the physical relations between the Reactor Vessel and Internals and the Control Rod Drive Mechanisms?

Answer 23

45 CRDM nozzles penetrate the reactor vessel head and are a potential source of PCS leakage.

Question 24

What are the physical relations between the Reactor Vessel and Internals and the Incore Nuclear Instrumentation System?

Answer 24

Eight (8) instrumentation nozzles penetrate the reactor vessel head, thus potential exists for a PCS leak path.

Forty-three (43) Incore nuclear instruments detectors are located within the reactor core (fuel). These are routed through the eight (8) instrumentation nozzles that penetrate the reactor vessel head.

Question 25

What are the physical relations between the Reactor Vessel and Internals and the RVLMS?

Answer 25

Function of RVLMS system is to provide reactor vessel level indication for detection of inadequate core cooling (ICC) situations. Instrumentation is routed via the 8 Incore Instrument Penetrations on the head.

Question 26

What is EK-0748, "REACTOR WATER LEVEL LOW"

Answer 26

Use LIA-0105/0106 to validate

Question 27

What is EK-0767, "REACTOR VESSEL FLANGE INNER SEAL LEAKAGE"

Answer 27

To validate: WHEN Plant conditions permit Containment entry, THEN verify alarm by observing PI‑0101, RV flange seal leak pressure. Drain line to Primary Drain Tank with CV‑0101 at C‑40. IMPORTANT: The total accumulation from 0 psig on PI‑0101 to receipt of this alarm is approximately 130 in³ = 0.56 Gallons.

Question 28

What is EK-0768, "REACTOR VESSEL FLANGE OUTER SEAL LEAKAGE"

Answer 28

Containment sump level will be rising to validate alarm -- SV-0160 opens to drain leak off line to floor drain. Containment sump level and PCS leakage can be used to determine leakage. IMPORTANT: The total accumulation between closure of SV‑0160 and receipt of this alarm is approximately 35 in³=0.15 Gallons.

Question 29

What is T.S. 3.3.7 Post Accident Monitoring (PAM) Instrumentation

Answer 29

In modes 1, 2 and 3 there will be: 4 channels of CET in each quadrant 2 channels of Reactor Vessel Water Level

Question 30

The primary purpose of the Post Accident Monitoring (PAM) instrumentation

Answer 30

To provide information to operators during accident situations so they can take the manual actions for which no automatic control is provided which may be required for safety systems to accomplish their safety Functions for Design Basis Events. Only the 4 qualified CETs per quadrant can be used to satisfy this LCO. Indication can be obtained from either the Chart Recorders on C-11A or the PPC. A channel of RVLMS is OPERABLE if four or more sensors, two or more of the upper four and two or more of the lower four, are OPERABLE. Only the LED lights on C-11A can be used to satisfy the LCO.