Automatic depressurization system

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 AP600 passive safety system includes subsystems for safety injection, residual heat removal, containment cooling, and control room habitability under emergency conditions. Several of these aspects are in existing nuclear plants such as accumulators, isolation condensers as natural-circulation closed loop heat removal systems (in early BWRs), automatic depressurization systems (ADS - in BWRs) and spargers (in BWRs). 

Fig. 37. Schematic representation of the in-containment passive safety injection system (PS1S). 1RWST = in-containment refueling water storage tank. PRHR-HX = passive residual heat removal heat exchanger. ADS = automatic depressurization system (four stages). (Westinghouse)...

Core make-up keep core flooding High pressure coolant injection system (2) Low pressure coolant injection system (2) Accumulator tank (2) High pressure coolant injection system (2) Low pressure coolant injection system (2) Rehieling tank (1) Core makeup water tank (2) Automatic depressurization system (2) Accumulator tank (2j Containment vessel water (Water-filled containment vessel) (1)... 

The AP600 automatic depressurization system comprises 16 valves divided into four depressurization stages. These valves are installed in the reactor coolant system at three different locations. The valves... 

At the Vapore facility located at ENEA Casacda Research Centre, testing of the Automatic Depressurization System (ADS) of AP-600 reactor coolant system is in progress. 

Automatic Depressurization System (ADS) Passive Reduces pressure for passive safety injection... 

Automatic Depressurization System a Actuation mode (manual/automatic) - Automatic b Side location (primary/secondary circuit)- Primary... 

The Automatic Depressurization System Test is a full sized simulation of one of the two AP600 depressurization system flowpaths from the pressurizer which will duplicate or conservatively bound the operating conditions of the AP600 ADS valves, sparger, and quench tank. The ADS test is being performed at ENEA s VAPORE Test Facility in Casaccia, Italy, and will be conducted in two parts. Phase A and Phase B. 

Implemented system (Name) Automatic Depressurization System... 

Compared with current commercial LWR designs a number of safety-grade systems have been eliminated the control rods and the safety injection boron system are replaced by the density locks, the automatic depressurization system is not required, the auxiliary feedwater supply system for RHR is replaced by the reactor pool, the containment heat removal and containment spray systems are replaced by the passive cooling of the reactor pool. The safety-grade closed cooling water stem, HVAC sterns, and a.c. power supply systems have been replaced by non-safety-grade systems, allowing major simplification of the plant. 

Automatic depressurization system (ADS) X - five valves - total flow area of 0.057 m ... 

Accident mitigation can be achieved by using the passive safety systems such as Passive Reactor Shutdown System (PRSS), Pressure Balanced Injection System (PBIS) and Containment Water Cooling System (CWCS), and active Automatic Depressurization System (ADS). 

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. 

Automatic depressurization systems enable quick depressurization of the injection pressure of gravity force-driven systems. 

Automatic depressurization system (ADS). The ADS provides a controlled depressurization of the plant. It is actuated passively by the pressure difference between the reactor vessel and an accumulator filled with water and nitrogen ... 

Automatic depressurization system (ADS). Passive systems for emergency core cooling. OSU 1/3-scale test loop tests have been conducted. RELAP5 assessments have been performed. Additional tests being considered. 

Under accident conditions, the Automatic Depressurization System (ADS) depressurizes the reactor vessel, and equalizes the reactor vessel and containment vessel pressure. Feedwater flow to the steam generator is secured and a new heat transport path is established. The coolant in the core reaches sub-cooled boiling conditions and produces a steam filled region in the upper portion of the reactor vessel. The steam is vented to the containment via the upper ADS vent lines. Once in the containment, the steam condenses on the walls of the containment vessel and pools at the bottom of the containment. This pooled fluid enters the reactor vessel either by sump recirculation lines or the submerged ADS lines, completing the flow path. A simple schematic of the accident condition heat transport system is shown in Fig. I-15(b). 

Common cause failures of the automatic depressurization system Stage-4 squib valves contribute approximately 18 percent to the total shutdown core damage frequency. This indicates that maintaining the reliability of the automatic depressurization system is important. 

ADS Automatic Depressurization System ATWS Anticipated Transient without Scram CRDM Control Rod Drive Mechanism CV Containment Vessel DID Defence in Depth DOE Department of Energy DVI Direct Vessel Injection EBT Emergency Boration Tank EHRS Emergency Heat Removal System ESP Early Site Permit... 

ADS - Automatic Depressurization System RHR - Residual Heat Removal (System) DAV - Dry well ARI - Alternate Rod Insertion... 

Coolant inventory (low pressure) Accumulator LPFL Automatic depressurization system. 

Figure 14.11 The mixed spectrum supercritical water-cooled reactor safety system. ICS, isolation cooling system GDCS, gravity-driven cooling system ACC, accumulators ADS, automatic depressurization system PCCS, passive cote cooling system SLCS, standby liquid control system. 

Figure 20.13 Containment of W-SMR (Carelli et al., 2004 NRC, 2014a). ADS, automatic depressurization system CMT, core makeup tank RX, reactor.

Figure 20.20 MS ECCS system (CareUi et al., 2003b, 2003c). PORV, power-operated relief valve SG, steam generator RCP, reactor circulation pump EHRS, emergency heat removal system ADS, automatic depressurization system RV, reactor vessel FO, fail open valve DVI, direct vessel injection.

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