Safety auxiliary cooling system

The safety concept considers two nuclear shutdown systems, a set of six reflector rods for reactor scram and power control and a KLAK system of small absorber balls for cold and long-term shutdown. Decay heat removal is made via the heat exchanger, an auxiliary cooling system, and the panel cooling system inside the concrete cavern, or, in case of a failure of these systems, passively by heat transfer via the surface of the reactor vessel. 

To meet the passive safety requirements of the NGNP, the AHTR uses a reactor vessel auxiliary cooling system (RVACS) similar to that of S-PRISM. It may also use a direct reactor auxiliary cooling system (DRAGS) similar to what was used in the Experimental Breeder Reactor II to supplement the RVACS and reduce the reactor vessel temperature. 

Decay heat removal Primary reactor auxiliary cooling system (PRACS) Steam/water system Active Active N/C operation available Non-safety grade... 

Main and auxiliary cooling systems are driven by natural convection. The inherent safety features of the core are enhanced to avoid a core-disruption accident even in anticipated... 

Main and auxiliary cooling systems of the PBWFR are driven by natural convection. The inherent safety features of the core are enhanced to avoid a core disruption accident even in anticipated transients without scram (ATWSs). Specifically, void reactivity for the case when the core, the axial blanket, and the plenum are totally voided is limited by 3 (design modifications are foreseen to make this effect negative). The bum-up reactivity swing during 15 years of operation without refuelling is minimized down to 1.5% AK/K. 

Heat removal systems 1) Gas-turbine system is used for normal core heat removal and transient deeay heat removal. 2) Cavity cooling system is the only safety-related system it removes reactor heat through reactor pressure vessel passively, by naturally circulating atmospheric air. 3) Auxiliary cooling system is a non-safety grade system used to shorten eooling time imder normal and accident transient conditions. 

S has several safety systems active, passive, and inherent (IAEA, 2003) (see Fig. 20.22). Active shutdown systems are (1) inserting reflectors by using gravitational force and (2) inserting black control rods. The passive safety system of 4S uses natural circulation in RVACS and Intermediate Reactor Auxiliary Cooling System (IRACS). In addition, inherent safety system uses Doppler effect via metallic fuel and large inventory of coolant. 

Accompany with the RVCS, a shutdown cooling system(SCS) is proposed in the paper to provide a simple and reliable decay heat removal during normal shutdown period. The system is shown in Fig 3. It consists of an auxiliary blower, a cooler as well as a recuperator. Because the cooler and recuperator are also the parts of the RPV cooling system(RVCS), SCS is simple and its equipments have multi-function. The decay heat removal under the accidental conditions is depends on the passive reactor cavity cooling system. The SCS proposed in this paper therefore is not safety concerned. 

As in the case of the emergency cooling systems, the safety-related auxiliary electrical power supply equipment is divided into four independent and physically separated parts, or subdivisions, and the reactor protection system operates on a 2-out-of-4 logic for signal transmission and actuation. 

Electrical building - houses the two non-safety-related standby diesel generators and their associated auxiliary equipment, and the solid-state adjustable speed drive units powering the feedwater pump motors and others powering the Reactor Water Cleanup/Shutdown Cooling System pumps. 

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. 

After the Three Mile Island Unit 2 accident the NRC reviewed the auxiliary feedwater system for availability and reliability of components and decay heat removal capability. In particular, the EFW system was scrutinized with regard to the potential for failure under a variety of loss of main feedwater conditions. The safety concern was that a total loss of feedwater, i.e., loss of both main and emergency feedwater, could result in loss of core cooling. The NRC requested operating plants and plants under construction to review both the reliability and the capability of the EFW system to perform its intended safety function i.e., core decay heat removal. The evaluation by the plants was divided into three parts as discussed below. 

The decay heat and residual heat could be cooled for about 30 minutes through the natural circulation of primary coolant in the primary system, and through the operation of turbine operation auxiliary water supply pump and the main steam safety valve. Necessary power for the safety protection systems and the turbine-driven auxiliary feedwater systems is supplied from highly reliable batteries to secure the safety of reactor even during the total loss of power. 

There is a minor requirement for the auxiliary steam system after a turbine trip, when the main condenser is a desirable component of the defence in depth capability identified within the fault schedule for cooling down the steam generators and the reactor coolant system. Failure of the auxiliary steam system during such fault transients could result in the main condenser becoming unavailable if no gland sealing steam were available. A reliable auxiliary steam system is thus desirable but not essential, because defence in depth capability is not claimed by the safety case. 

Figure 1-2 shows the simplified schematic diagram of the SMART nuclear steam supply system (NSSS) and exhibits the safety systems and the primary system as well as auxiliary systems. The engineered safety systems designed to function passively on demand consist of a reactor shutdown system, passive residual heat removal system, emergency core cooling system, safeguard vessel and reactor overpressure protection system. 

This subsection should present relevant information on any other engineered safety features implemented in the plant design, as described in paras 3.65-3.70. Examples include, but are not limited to the auxiliary feedwater system, the steam dump to the atmosphere and backup cooling systems. The list of these systems will depend very much on the type of plant under consideration. 

This subsection should provide relevant information on the heating, ventilation, air conditioning and cooling systems in a format as described in paras 3.65-3.70. It should include the ventilation systems for the control room area, the spent fuel pool area, the auxiliary and radioactive waste area and the turbine building (in boiling water reactors) and the ventilation systems for engineered safety features. 

A. 1005. All water systems of the facility that have not been described previously shall be discussed in this section. These may include the primary purification system, the service water system, the cooling system for reactor auxiliaries and the primary coolant make-up system. In each case, the information provided should include the design bases, a system description, flow and instrumentation diagrams, a safety evaluation, if required, testing and inspection requirements, and instrumentation requirements. 

An integral primary system layout is employed (Fig. 12.4), ie, reactor core, variable frequency submersible coolant pumps, intermediate heat exchanges, safety system heat exchangers, and cold trap filters. The reactor vessel is enclosed in a guard vessel. There are no auxiliary sodium systems in the primary circuit. The reactor core consists of fuel assemblies, boron shield assemblies, and absorber rods. The central part of the core consists of wrap-spaced hexagonal fuel assemblies and cells with absorber rods. The spent fuel is stored in the reactor vessel for up to 2 years, which facilitates spent fuel cooling and eliminates the need for spent fuel storage casks. Assemblies with boron carbide are placed behind the spent fuel to protect the reactor vessel. 

Demonstrate that ESF systems have a low probability of abnormal leakage, rapidly propagating failure, and gross rupture. The fluid and material compatibility for the, ESF systems, and for the auxiliary systems that directly support the ESF systems, should be considered to reduce or eliminate the propensity of contaminant induced piping and component degradation. The ESF systems include the Supplemental Safety System (SSS), Moderator Recovery System (MRS), and the Emergency Cooling System (ECS). 

The safety system of the Super LWR has previously been schematically described in Figs. 1.3.38 and 3.2.1 [2]. The emergency core cooling system (ECCS) of the Super LWR consists of the auxiliary feedwater system (AFS), low pressure core... 

In BWRs, the auxiliary feedwater system is usually termed the reactor core isolation cooling system. This system is used to maintain the water level in the reactor vessel in the event of a loss of feedwater in hot shutdown conditions (in such an event residual heat is removed from the reactor core by means of the release of steam through safety relief valves to a suppression pool). Another function of this system is to supply the necessary inventory of reactor coolant in the event of a small loss of coolant during normal operation. 

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