Main Steam System

Valve Arrangement of Auxiliary Feedwater System and Main Steam System during Shutdown - the auxiliary feedwater system has six MO Vs in the flow path to the steam generators and the main steam nonreturn valves are normally closed during shutdown. These valves depend on offsite power and are difficult to manually open. 

Pneumatic actuators are normally used to control processes requiring quick and accurate response, as they do not require a large amount of motive force. However, when a large amount of force is required to operate a valve (for example, the main steam system valves), hydraulic actuators are normally used. Although hydraulic actuators come in many designs, piston types are most common. 

Main steam system common pipe header rapture 1.5 X 10 ... 

Overpressure protection for the secondary side of the steam generators is provided by spring-loaded ASME Code safety valves located in the main steam system upstream of the steam line isolation valves. 

The main steam safety valves are direct acting, spring loaded, carbon steel valves. The valves are mounted on each of the main steam lines upstream of the steam line isolation valves, and outside containment. A schematic drawing of the main steam safety valves is given in Figure 5.4.13-2. The valve parameters are given in Table 5.4.13-2. For a description of overpressure protection equipment and components for the main steam system refer to Section 10.3.2. 

Reliability of the main steam system reliefs is discussed in the interface Chapter 10. The primary safety valves are passive, spring actuated mechanisms, and cannot fail closed if setpoint pressure is exceeded. The operational reliability of the primary safety valves is assured by ... 

The recirculation water within the steam generators will contain volatile additives necessary for proper chemistry control. These and other chemistry considerations of the main steam system are discussed in Section 10.3.5. 

The Main Steam Line Isolation System (see Section 10.3.2 for more details) is composed of portions of the Main Steam System and the Engineered Safety Features Actuation System. Discussed here are those portions of these systems that respond to a Main Steam Isolation Signal, as defined in Section 7.3. A discussion of radiological considerations is provided in Section 12.3. 

The logic circuitry required to isolate the main steam lines is discussed in Section 7.3. The main steam system valves and... 

A. At the onset of the loss-of-load transient, the reactor coolant and main steam systems are at maximum rated output plus a two percent uncertainty. By choosing the highest possible power output, the heatup rate of the primary loop is maximized along with the rate of pressurization. 

In the event that a complete loss of load the protection provided by the second safety grade reactor trip, primary safety valves and secondary safety valves is sufficient to assure that the integrity of the RCS and main steam system is maintained and that the minimum DNB ratio is not less than 1.24. 

The main conventional system is composed of main steam system, turbine bypass system, main feedwater system, and other auxiliary systems. 

MAIN STEAM SYSTEM CSACIUS2 DBE The safety related portion of the system mcludes Ihe steam generator secondary side and the mam steam safety valves The system providn overpressure protection of the steam generators and provides decay heat removal fiom the heal transport system. 

Safety related main steam system class>2 Secondary aide of SO. main steam iaoiadon and safety valvea are the main components of dw sysiem. The ayatem b dcaigiied to provide ovetpreasnm pfWKtion of SOa end decay heal removal by tbermosyphoii. 

The main steam system of MRX consists of a main generator turbine for propulsion, two hotel service generator turbines, three feed water pump turbines, a low pressure steam generator, etc. The main generator turbine is a double compound articulated type and produces 30MWe. The output is used for the propulsion motors. The electric power for auxiliary machines and accommodations is supplied by two hotel service generator turbines. 

The main steam system of SPWR is similar to that of the existing LWRs, which consists of one high pressure turbine (HPT) and two low pressure turbines (LPTs). The steam re-heater is installed between the HPT and LPTs. 

The design of the System 80+ Main Steam system adequately addresses dynamic loads caused by condensation-induced water hammer and has piping arrangement and drainage provisions to protect against water entrainment. These are described in CESSAR-DC, Sections 10.3.2.2D, M, N, and P. 

The results of the analyses show that a turbine trip presents no challenge to the integrity of the reactor coolant system or the main steam system. Pressure-relieving devices incorporated in the two systems are adequate to limit the maximum pressures to within the design limits. The analyses... 

Initiation of normal residual heat removal system operation at four hours following reactor shutdown, after the first phase of cool down by the main steam system has reduced the reactor coolant system temperature to less than or equal to 176.7°C and 3.1 MPa gauge. 

The first phase of plant cool down is accomplished by transferring heat from the reactor coolant system via the steam generators to the main steam systems (see Section 6.6.6). The component cooling water system, in conjunction with the normal residual heat removal system (see Section... 

The main steam system is required during start-up and operation at power, to remove the heat intentionally produced by the reactor core and also in the initial phase of shutdown operation before the normal residual heat removal system can be connected, to remove the fission product heat from the reactor core. The heat sinks are provided either by venting steam to atmosphere or by the turbine bypass system dumping steam to the condenser. 

The following design requirements for the main steam system support safe operation of the plant under normal conditions ... 

The auxiliary steam boiler is an electric package boiler. It supplies the steam required during a cold start of the main steam system and the turbine-generator additionally, it provides the steam for hot water heating. Main steam supplements the auxiliary steam header during start-up, and it supplies the auxiliary steam during normal operation at power. The auxiliary boiler provides the steam during a plant shutdown. 

Under these conditions, heat removed by water- to-water heat transfer In the steam generators Is transferred to the tertiary loop In the dump condensers, also by water to water exchange. The condensate pumps downstream of the dump condensers provide normal flow through the condensate system up to spprozlmately 30,000 gpm. Pressure is controlled by adjustments to the steam adnlssion system to the surge tank. The main steam system under these conditions la controlled at or near normal pressure by steam from the stand by boiler system. 

The pressure tubes were divided into two distinct regions in the core (Fig. 5.1). Each half received its cooling water from a dedicated set of pumps and supply manifolds. Each side also supplied a separate steam drum that connected to the main steam system and turbine. The overall effect of all of this equipment was that it produced a complex myriad of pipes housed within the reactor building. 

In operational states, the steam and feedwater system should be capable of removing the heat from the reactor core and the RCS to the ultimate heat sink at such a rate that the design limits of the fuel are not exceeded and the capability of cooling the core is maintained. In particular the pressures in the RCS and the main steam system should be maintained below the design limits. 

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