Cladding strain is maintained at less than 1.0%. Fuel rod internal pressure is maintained at less than 155 bar. To prevent a DNB condition in the core, the actual heat flux must be less than the critical heat flux by a certain margin everywhere in the core. The limits applied during Category III (Infrequent Faults) and Category IV (Limiting Faults) which assure integrity of the cladding are: Peak cladding temperature (PCT) during a LOCA will not exceed 1200°C. By limiting PCT the zirconium-steam reaction is limited and thus cladding oxidation. This reaction increases significantly above 1200°C. Cladding oxidation will not exceed 17% of the total cladding thickness to prevent excessive loss of local cladding strength and ductility. Hydrogen generation (due to zirconium-water reaction) will not exceed 1% of the hydrogen generated if all the zirconium surrounding the fuel were to react; this is to prevent accumulation of an explosive mixture of hydrogen in the containment. A hydrogen burn in the containment could exceed its design pressure. Coolable core geometry must be maintained to prevent cladding failure from blocking coolant channels. Long term cooling must be provided to assure that the decay heat can be removed, preventing additional core damage. During the LOCA condition the reactor should be tripped. heat is transferred from the fuel to the coolant and dictates the cladding temperature. To limit the PCT, decay heat has to be limited which can be managed by limiting the maximum heat flux during normal operation. Limiting (defined in Module 1) in the core during normal operation means limiting the maximal heat flux in the core, which dictates the limit of the PCT during a LOCA. Integrity of the reactor coolant system The integrity of the second barrier Reactor Coolant System is assured by a set of values for pressure in the RCS. For example a Westinghouse PWR has the following values: Normal operating pressure is 154.1 bar. Design pressure of the Reactor Coolant System is 171.3 bar, the lift setting of the pressurizer safety valves. The Pressure Safety Limit is 110% of the design pressure, which represents 188.6 bar. The Reactor Protection System generates a reactor trip signal if the pressurizer pressure exceeds the value of 163.8 bar. The trip prevents the pressure Safety Limit from being
Cladding strain is maintained at less than 1.0%. Fuel rod internal pressure is maintained at less than 155 bar. To prevent a DNB condition in the core, the actual heat flux must be less than the critical heat flux by a certain margin everywhere in the core. The limits applied during Category III (Infrequent Faults) and Category IV (Limiting Faults) which assure integrity of the cladding are: Peak cladding temperature (PCT) during a LOCA will not exceed 1200°C. By limiting PCT the zirconium-steam reaction is limited and thus cladding oxidation. This reaction increases significantly above 1200°C. Cladding oxidation will not exceed 17% of the total cladding thickness to prevent excessive loss of local cladding strength and ductility. Hydrogen generation (due to zirconium-water reaction) will not exceed 1% of the hydrogen generated if all the zirconium surrounding the fuel were to react; this is to prevent accumulation of an explosive mixture of hydrogen in the containment. A hydrogen burn in the containment could exceed its design pressure. Coolable core geometry must be maintained to prevent cladding failure from blocking coolant channels. Long term cooling must be provided to assure that the decay heat can be removed, preventing additional core damage. During the LOCA condition the reactor should be tripped. heat is transferred from the fuel to the coolant and dictates the cladding temperature. To limit the PCT, decay heat has to be limited which can be managed by limiting the maximum heat flux during normal operation. Limiting (defined in Module 1) in the core during normal operation means limiting the maximal heat flux in the core, which dictates the limit of the PCT during a LOCA. Integrity of the reactor coolant system The integrity of the second barrier Reactor Coolant System is assured by a set of values for pressure in the RCS. For example a Westinghouse PWR has the following values: Normal operating pressure is 154.1 bar. Design pressure of the Reactor Coolant System is 171.3 bar, the lift setting of the pressurizer safety valves. The Pressure Safety Limit is 110% of the design pressure, which represents 188.6 bar. The Reactor Protection System generates a reactor trip signal if the pressurizer pressure exceeds the value of 163.8 bar. The trip prevents the pressure Safety Limit from being
Module11%20Operational%20Limits%20and%20Conditions.docx