Week 3: Core Design Limits Flashcards
What is the Zirconium-Water cladding temperature limit? Why is this important?
2200F; important to ensure that the Zirconium does not excessively react with water, oxidizing the cladding and releasing H2 into the environment.
What is the definition of the Heat Flux Hot Channel Factor?
The ratio of the maximum local fuel rod linear power density divided by the average fuel rod linear power density (Fq).
What is the basis of the Heat Flux Hot Channel Factor?
To prevent localized cladding failure and fuel melt. The Fq limit is more restrictive at higher powers and higher up in the core due to LOCA uncovery considerations.
What is the definition of the Nuclear Enthalpy Rise Hot Channel Factor?
The ratio of the integral of the linear power along the fuel rod with the highest integrated power to the average integrated fuel rod power.
What is the basis of the Nuclear Enthalpy Rise Hot Channel Factor?
To prevent DNB in the hottest coolant channel in the core.
What is the definition of the Departure from Nucleate Boiling Ratio?
The predicted critical heat flux over the actual local heat flux.
The predicted critical heat flux is the heat flux at which DNB is predicted to occur while at the corresponding temperature/pressure/flow conditions.
What are the Reactor Core Safety Limits?
The Safety Limit Lines in the COLR
A DNBR greater than 1.22
A fuel centerline temperature less than 5080F, reduced by 58F for every 10,000 MWD/MTU
What do the segments of the Safety Limit Lines protect against?
The left segment protects against Core Exit Boiling; this is important to ensure the dT = Power relationship is maintained (i.e. subcooling exists).
The right segment protects against DNB.
What functions protect the plant from exceeding these Safety Limit Lines?
OPDT, OTDT, and SG Safeties
What is the RCS Pressure Limit?
Less than 2735 psig
What is the function of the Pressure-Temperature Limits Report?
To define RCS pressure, temperature, and heatup and cooldown rates to be maintained in order to minimize the potential of brittle fracture of the RCS as well as provide COPS setpoints.
What is the function of the Cold Overpressure Protection System?
To protect against RCS overpressurization at temperatures less than 275F. Must be manually initiated by the operators. Alters the setpoints of the PZR PORVs to open at lower pressures.
