Scram system

Jnavailabilities ranged from 1.8E-5 for the scram system to >0.1 for several systems iring... 

The HFBR core uses fully-enriched (93%) uranium oxide-aluminum cermet curved plates dad m aluminum. The core height is 0.58 m and the diameter is 0.48 m or a volume of 103.7 Itr. The U-235 weighs 9.83 kg supported by a grid plate on the vessel bottom. The coolant flow u downward. Iience. How reversal is necessary for natural circulation. It operating temperature and pressure are 60 ( and 195 psi. There are 8 main and 8 auxiliary control rod blades made of europium oxide (Lii A)o and dysprosium oxide (DyjO,), clad in stainless steel that operate in the reflector region. The scram system is the winch-clutch release type to drop the blades into the reflector region. Actuation of scram causes a setback for the auxiliary control rods which are driven upward by drive motors,... 

The installation of a Safety Scram System (Complementary Shutdown System). 

The reactor is shut down either by driving the control rods into the core using the control rod drives, by rapidly inserting all of the control rods using a hydraulic system or by rapidly injecting boron into the reactor water. The accumulators of this system, which are filled with a boron solution, perform two functions on the one hand, they serve as a redundant backup to the water tanks of the scram system for rapid insertion of the control rods and, on the other hand, they provide a diverse means for stopping the chain reaction in the core by injecting the boron solution into the reactor water. 

Scram system Y 205 control rods, rapidly inserting hydraulic system... 

SAFETY CONCERNS ASSOCIATED WITH BREAKS IN THE BWR SCRAM SYSTEM... 

To meet section (c)(2) ( the prevention requirement ) of 10 CFR 50.62, the plant must have a scram system which is diverse and independent from the existing RTS. 

The following issues should govern the decision about whether to have an automatic scram system or operator action supported by seismic monitoring in the event of an earthquake ... 

Post-earthquake actions should be planned for a nuclear power plant, even if an automatic scram system is installed. 

The pressure relief system was not provided primarily to meet code requirements but rather Is an Integral part of the over-all protection system which includes the reactor power setback and scram systems Strict adherence to the code is impractical because the maximum thermal energy output of the reactor cannot be defined. Further at the hifpier conceivable powers fuel melting would probably occur in any event. Prevention of a fuel melting accident with consequent release of fission products depends primarily on the nuclear control and cool ant supply system and only Incidentally on the pressure relief systems. 3 Shutoff valves are not provided at the end of each instrument take-off connection, and the minimum size of instrument take-off connections is not necessarily l/2 or 3/if Inch as required by the ASA Code. 

Passive safety design options were preliminarily analyzed and the analyses have shown the STAR-LM concept to be robust with respect to them. Although scram systems are provided to insert rods to shut down the reactor neutronically, success of scram is not required to prevent the evolution of adverse power or temperature conditions. 

The reactor is designed for a near-zero reactivity bum-up swing such that the safety rod system is vested with minimal positive reactivity at Beginning of Life (BOL) full power. A safety rod scram system provides a first line of defence for reactivity initiators. Moreover, passive reactivity feedbacks and passive self adjustment of natural circulation flow could maintain reactor power to flow ratio in a safe operating range even with failure to scram this safe passive response applies for all out-of-reactor vessel initiated events, i.e., for any and all events communicated to the reactor through the flibe intermediate loop. Periodic in situ measurements would be made to confirm the operability of these passive feedbacks. 

The transient overpower (TOP) due to a control rod withdrawal, the loss of primary flow (LOT) and the loss of heat sink (LOHS) due to a loss of the heat removal capability of the secondary system are commonly postulated as accident scenarios for power reactors. Even though the loss of external power is commonly superposed on these events, this does not lead to any serious problem if the reactor is safely tripped. Severe accidents, where the failure of a scram system is superposed on the abovementioned accidents, are surveyed below, for the LSPR. The analytical methods employed are described in [XXV-7]. 

The active safety systems include control rods and a scram system, but they are provided mostly for convenience of changing the reactor power and for performing reactor start-up and shutdown operations. 

High speed shutdown system (scram system) Control rods Active system / small number of rods is sufficient for MSR... 

For severe accident analysis, a reactivity insertion of 0.3 %5K/K was assumed, coupled with the failure of the B4C based control rod scram system. As shown in Fig. XXX-6, the maximum fuel temperature is 1100°C, which is also below I500°C temperature limit for fuel... 

SS 18 Potential failure of the scram system due to loss of discharge volume (BWR)... 

Safety concerns associated with pipe breaks in the BWR scram system, Office for Analysis and Evaluation of Operational Data, USNRC. 

International practice considers the analysis of ATWS for a variety of initiating events such as loss of feedwater, loss of load, turbine trip, loss of condenser vacuum, loss of off-site power, closure of main steamline isolation valves, uncontrolled boron dilution, inadvertent control rod withdrawal, etc. ATWS analyses are performed in general by using best-estimate tools to determine the preventive (e.g. a diverse scram system) or mitigative measures (e.g. initiation of turbine trip and emergency feedwater supply) which need to be implemented for strengthening plants defence in depth. 

Figures G-21 and G-22 illustrate the consequences of a nuclear excursion with failure of both automatic scram systems. The...

Two parallel pumps are provided for each scram system. The smaller pump has a capacity of 3.25 gal/min and is operated continuously to make up leakage and maintain pressure in the individual rod scram accumulators The larger pumps have a capacity of 7 gal/min and Is used with the smaller pusip to recharge the accumulator rapidly after a scram. 

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