Systems Exam 2 - RX Vessel & Internals Flashcards
(21 cards)
What percentage of core flow is available to the core itself?
94%. The remaining 6% is core bypass flow.
Rx Vessel O-ring leakage is routed to the…
RCDT (identified leakage)
Which Rx Vessel O-ring seal is normally in service, i.e. open?
the inside ring
→Isolation valve for inside, uRC-8069B, O-ring normally open
→Isolation valve for outside, uRC-8069A, O-ring normally closed
→Valve u8032 provided downstream of manual isolations; normally open
(u8032 powered from uD2-3, fails open on loss of power)
At what temperature does leakage from the Rx Vessel O-rings alarm in the Control Room?
alarms at 140°F
(uTE-0401 with indication on MCB)
What do the secondary core supports do?
Limits the distance the core barrel will drop in a postulated failure of the core barrel flange and is designed to absorb the energy of the drop and limit the fall to ensure that the control rods may be inserted, coolant flow will not be blocked, and all fuel assemblies will remain within the core baffles.
What do neutron panels do?
provide neutron shielding for parts of the Rx vessel closest to the core in order to reduce neutron embrittlement
(could be different words used for neutron panels, e.g. thermal shield or similar)
Rx Vessel closure head vent penetration
1” diameter, vents non-condensable gases which may occur during natural circ or post-accident
2 vents in series
At what approximate temperature does ceramic fuel melt?
5080° F
What is the safety limit to the calculated fuel centerline temperature?
U1: 4700° F
U2: 5080° F at BOL, decreasing 9° F per 10,000 MWD/MTU Burnup
(U1 to change to be in line with U2 after 1RF24)
(based on remaining well under fuel melting temp)
Head Vent Valves
→Where are they powered from?
→How do they fail?
→Where do they vent to?
Two key operated valves
→powered from uED1-1
→fail closed on loss of power
→vent to containment atmosphere
(piped in series → if one fails, there is still isolation from the vessel)
How to the Reactor Vessel O-Rings work?
→two self-energizing o-rings
→part of the RCS pressure boundary
→small holes allow pressurized water to expand the o-rings and seal them
How many fuel assemblies in the Rx Vessel?
How many control rods?
→193 fuel assemblies
→53 control rods
Tech Spec 2.1.1 Core Operating Safety Limits
→Modes 1 and 2, The departure from nucleate boiling ratio (DNBR) shall be maintained > the 95/95 DNB (95% probability at a confidence level of 95% that the hottest fuel rod is not in DNB)
→Modes 1 and 2, Peak fuel centerline temp. shall be maintained <4700°F (U1) or less than 5080° F at BOL, decreasing 9° F per 10,000 MWD/MTU Burnup. DNB assumptions for 1.30 DNBR
→If violated, restore compliance and be in Mode 3 in 1 hour.
Staying within the temp/press curve in COLR ensures acceptable DNBR is maintained
(If safety limit is violated restart must be authorized by NRC. Shutdown driven by TS → report to NRC within 4 hours.)
Tech Spec 2.1.2 RCS Pressure Safety Limits
→Modes 1,2,3, 4 and 5, ≤2,735 psig, based upon Turbine trip w/o Rx Trip
→If violated in mode 1 or 2 restore and be in mode 3 in 1 hour.
→If violated in mode 3, 4, or 5, restore compliance within 5 minutes.
PZR Safeties, SG Safeties and Hi Press Trip ensure safety limit not exceeded.
(If safety limit is violated restart must be authorized by NRC. Shutdown driven by TS → report to NRC within 4 hours.)
IPO-003A
During initial startup of each fuel cycle, before exceeding 20% Thermal Rated Power, after extended low-power operation (>27 days)…
→no single step increase in power shall exceed 3% full reactor power
→the rate of reactor power increase between 40% and 100% of full power should be ≤3% per hour
Control rod guide thimbles have a ______________ inner diameter at the top and ____________ at the bottom. This is for…
larger; smaller
…rapid control rod insertion which allows water to escape as rods are inserted; also creates a dashpot effect at the bottom of travel to slow the rods
Fuel design clad temperature is limited to _____________.
This is because…
2200° F
…zirc water reaction becomes auto-catalytic at 2600° F, and the exothermic reaction exceeds ECCS capability
What are the different parts and percentages of Core Bypass Flow?
→2% control rod and instrument thimble bypass flow
(flows through CR and instrument thimble tubes in fuel assemblies without removing any heat generated by core)
→2% baffle cooling flow
(enters baffle and former plate region above lower core plate, exits baffle and former plate region below upper core plate)
→1% nozzle bypass flow
(directly from inlet nozzles to outlet nozzles)
→0.5% baffle wall bypass flow
(passes between inside of baffle wall surrounding fuel assemblies and the fuel assemblies themselves without rmeoving any heat generated by core)
→0.5% head cooling bypass flow
(passes through holes drilled in upper support structure flange and core barrel flange to maintain reactor head area at cold leg temp)
(percentages are approximate)
Tech Spec 3.4.3 RCS Pressure and Temperature (P/T) Limits
RCS pressure, RCS temperature, and RCS heatup and cooldown rates shall be maintained within the limits specified in the PTLR at all times.
Requirements not met in Mode 1-4:
→Restore parameter(s) to within limits within 30 minutes AND
→Determine RCS is acceptable for continued operation within 72 hrs
Requirements not met NOT in Mode 1-4:
→Initiate action to restore parameter(s) to within limits immediately AND
→Determine RCS is acceptable for continued operation prior to Mode 4
Tech Spec 3.4.12 Low Temperature Overpressure Protection (LTOP) System
An LTOP system shall be OPERABLE with a maximum of zero Safety Injection pumps and two charging pumps capable of injecting into the RCS and the accumulators isolated and ONE of the following pressure relief capabilities:
→two PORVs with lift settings within limits specified in the PTLR
→two RHR suction relief valves with setpoints ≥436.5 psig and 463.5 psig
Tech Spec 3.4.13 RCS Operational LEAKAGE
RCS operational LEAKAGE shall be limited to:
→no pressure boundary leakage
→1 gpm unidentified leakage
→10 gpm identified leakage
→150 gallons per day primary to secondary leakage through any one steam generator
