Systems Exam 2 - RX Vessel & Internals Flashcards
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?
→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
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 rode 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
