Automatic depressurization function

The operation of the automatic depressurization function, the HPCS system, and two LPCl loops of the RHR system (failure of division 1)... 

The operation of the automatic depressurization function, one LPCl loop of the... 

The engineered safety features include the ECCS (HPCS system, LPCS system, LPCl function of the RHR system, and the automatic depressurization function of the nuclear boiler system) and the RCIC systems. 

Low water level in the reactor vessel A low water level in the reactor vessel trips the reactor, causes nuclear system isolahon, activates the automatic depressurization function, initiates the HPCS and LPCS systems, and initiates the RCIC system. 

High pressure in the reactor vessel High pressure in the reactor vessel will trip the reactor and initiate automatic depressurization function. 

In some BWR transient scenarios, the high pressure injection systems are postulated to fail. To make use of the low pressure injection system, it is necessary to depressurize the reactor coolant system, a function performed by the automatic depressurization system (ADS). In the scenario considered, ADS actuation is manual because the signals for automatic initiation of the system are not present. 

The primary functions of the Nuclear Boiler System (NBS) are (1) to deliver steam from the RPV to Ae turbine main steam systan (TMSS), (2) to deliver feedwater from the condensate and feedwater system (C FS) to the RPV, (3) to provide overpressure protection of the RCPB, (4) to provide automatic depressurization of the RPV in the event of a LOCA where the RPV does not depressurize rapidly, and (5) with the exception of monitoring the neutron flux, to provide the instrumentation necessary for monitoring conditions in the RPV such as RPV pressure, metal temperature, and water level instrumentation. 

Selected safety/relief valves are associated with the automatic depressurization of the primary system under assumed LOCA conditions. These valves have two independent logic channels powered from different power sources, either of which can initiate depressurization. Valves open automatically and remain open imtil the pressiue falls to a preset closure pressure. These valves open automatically upon signals of high drywell pressure and low reactor water level and confirmation of one LPCI function of the RHR system or LPCS system running. Initiation signals need not be simultaneous. The valves remain open until the primary system pressure is reduced to a point where the LPCI function of the RHR system and/or the LPCS system can adequately cool the core. The initiation of automatic depressurization is delayed from 90 to 120 s to allow the operator to terminate the initiation should the HPCS system initiation and acceptable reactor vessel level have been confirmed. 

In the unlikely event that the RHR shutdown suction line is unavailable during reactor shutdown to cool reactor water and during the period when the LPCI function of the RHR system and/or the LPCS system pumps are injecting water into the reactor vessel, safety/relief valves used for automatic depressurization can be used to pass water from the reactor vessel to the suppression pool via valve discharge lines. For this to occur, the reactor vessel floods to a level above the vessel main steam line nozzles, selected safety/relief valves are opened from the control room to pass reactor water to the suppression pool. 

The ECCS comprises the LPCl function of the RHR system, HPCS and LPCS systems, and automatic depressurization of the primary system. The ECCS is designed to perform the following functions ... 

The LPCl function in conjunction with the LPCS system, the HPCS system, and/or automatic depressurization of the nuclear boiler system (depending upon operability of the HPCS system or level of depletion of reactor vessel water) will restore and maintain the desired water level in the reactor vessel required for cooling after a LOCA. 

All safety systems are passive and function principally via density gradient-driven flow and/or compressed gas-driven accumulators. To ensure the functioning of densify gradient-driven flow provided by gravity-drain tanks, automatic depressurization systems are also included to depressurize the reactor to operational pressure levels for these systems. 

The core make-up water tanks are used in the design of AC600/1000 so as to eliminate the high-pressure safety injection pumps and increase reliability of the safety system. The function characteristics and coolant flow transient of core make-up water tank, accumulator and automatic depressurization system can be tested using NPIC core make-up water tank experiment facility to simulate a small LOCA. The facility parameters are as the following ... 

---