Constant pressure startup

Startup schemes of the Super LWR are considered by referring to those of supercritical FPPs [43—45]. The constant pressure startup systems of the Super LWR and a supercritical FPP are shown in Fig. 1.16 [41]. The register tube and flash tank are installed on the bypass line. The supercritical steam is depressurized at the register tube and used for heating up the turbine during the startup (Table 1.6). 

Fig. 1.16 Constant pressure startup systems of the Super LWR and supercritical FPP. (a) Super LWR (b) Supercritical FPP...

There are two kinds of startup schemes currently used in FPPs [1]. One is the constant pressure startup scheme, in which the boiler operates at constant supercritical pressure after the coolant is pressurized to this point. The other is the sliding pressure startup scheme, in which the boiler operates with variable pressures and the pressure increases with the generation output. 

The constant pressure startup is proposed with reference to that of FPPs. Nuclear heating starts at supercritical pressure, and the pressure is kept constant during load change. Because the reactor operates at a constant supercritical pressure, the coolant in the fuel channels is single phase and steam-water separation is not necessary. The constant pressure startup system for the Super LWR is shown in Fig. 5.3 [2]. It is required to establish a sufficient flow rate to prevent the... 

The constant pressure startup system can be classified into five phases, which are briefly described below. 

The flash tank and pressure reducing valves are necessary initially during constant pressure startup of the Super LWR. The flash tank is designed such that the moisture content in the steam at turbine inlet is less than 0.1%. The dimensions of the flash tank required for startup are determined by using the correlations for the droplet entrainment and carryover from a boiling pool by a streaming gas, developed by Kataoka and Ishii [4]. 

Table 5.2 Calculated dimensions and weight of the flash tank requited for constant pressure startup of the Super LWR for various flash tank pressures (taken from ref. [3] and used with permission from Atomic Energy Society of Japan)...

Power Increase Phase in Constant Pressure Startup or Sliding Pressure Startup... 

There is no difference between the pressurization phases of the constant pressure startup and sliding pressure startup schemes because the pressurization phase appears after the line switching to the once-through mode. It is assumed that the core inlet and outlet temperatures are kept equal to their respective values in the normal operating condition. While the reactor core power is increased, the feed-water flow rate is also increased proportionally. MCSTs are calculated for various core powers from 30 to 100% at intervals of 10%, and the calculated results are shown in Fig. 5.11. It is found that MCST satisfies the criterion of 620°C throughout the power increase phase. 

Based on the thermal considerations above, the general startup curves for the constant pressure startup scheme of the Super LWR are designed as shown in Fig. 5.22 [3]. Those for the sliding pressure startup scheme are designed as shown in Fig. 5.23 [3]. 

The startup curve for the sliding pressure startup scheme that is designed based on only the thermal considerations (Fig. 5.23) is redrawn taking the stability considerations into account as well. The constant pressure startup is not discussed here because the partial power operating conditions in the constant pressure startup are covered by the temperature increase phase and power increase phase of the sliding pressure startup. 

In this chapter, the plant startup and stability were introduced. Both constant pressure and sliding pressure startup schemes are designed by referring to FPPs. The constant pressure startup system requires a startup bypass system consisting of a flash tank and pressure-reducing valves. The sliding pressure startup scheme... 

The CR withdrawal at startup is analyzed. The initial condition is the hot standby where kgff is 1.0, the reactor power is 1.0 x 10 of the rated power, and the main coolant flow rate is 20% of the rated flow. The analysis is made assuming adoption of the constant pressure startup scheme described in Chap. 5. The similar analysis for the sliding pressure startup scheme is described in Sect. 6.7.2. The reactivity worth of the withdrawn CR cluster is 2.8%dk/k. The same withdrawal speed as of PWRs is taken. The CR cluster is withdrawn until the reactor period decreases to the scram setpoint (10 s). The inserted reactivity is 0.39. 

For positive displacement pumps, a bypass-type control valve should be furnished to set the primary lube system pressure. The valve should be able to maintain system pressure during pump startup and pump transfers, which includes relieving the capacity of one pump, while both are running. The valve should provide stable, constant pressure during these transients. Flow turndown of 8 to 1 is not unusual. Multiple valves in parallel should be used if a single valve is not suitable. The valve should be sized to operate between 10 and 90% of the flow coefficient (Cv). Additional pressure control valves should be furnished as required to pro ide any of the intermediate pressure levels. 

It is of course important to control the total flow of brine and at the same time to control the flow to each electrolyzer. This is why brine header flow control often is in fact line pressure control (Section 11.2.2.4D). Maintaining a constant pressure in the line balances the flow into the header with the total flow to all the cells. It also allows individual electrolyzer feed rates to remain steady even dirough manually set valves. It is important that the cell room headers have very small pressure drops. This will cause the pressures at all control points to be essentially the same. In turn, the rates of flow to the individual electrolyzers will also be equal. Header pressure control also offers a simple way to make nearly instantaneous changes in flow to all the electrolyzers during startup, shutdown, or load changes. 

Schulenberg and Starflinger (2012) reported about a constant pressure start-up and shut-down system for the three-pass core design of the HPLWR, trying to keep the feed-water temperature constant to minimize thermal stresses of the reactor pressure vessel. This concept also includes a warm-up procedure for the deaerator during startup from cold conditions. A battery of cyclone separators is foreseen outside of the containment to produce some steam from depressurized hot coolant of the reactor. 

There are two types of supercritical FPPs. One is the constant pressure FPP that starts heating and operates at partial load at the supercritical pressure. The other is the sliding pressure FPP that starts heating at a subcritical pressure, and operates at subcritical pressure at partial load. A steam-water separator and a drain tank are needed for the startup of the sliding pressure FPP. The sliding pressure FPP operates with better thermal efficiency at subcritical pressure at partial load than the constant pressure FPP. In Japan, nuclear power plants are used for base load, and the FPPs are used for daily load following. Minimum partial load is 30% for the constant pressure FPP and 25% for the sliding pressure one [41,42]. 

The plant system of the constant pressure supercritical fossil-fired boiler is shown in Fig. 5.1. The startup bypass system includes a flash tank, pressure-reducing valves, and bypass valves. First, a minimum feedwater flow is established in the furnace prior to the firing of the boiler to prevent overheating of the tube walls. During the cold cleanup mode of operation, the flow is bypassed from the inlet of the primary superheater to the flash tank, until the water chemistry is brought to a predetermined level and the boiler firing starts. 

The system configuration of the constant pressure supercritical boiler is complicated and pressure ramp-up operation is required. The startup valves experience a... 

Semibatch Model "GASPP". The kinetics for a semibatch reactor are the simpler to model, in spite of the experimental challenges of operating a semibatch gas phase polymerization. Monomer is added continuously as needed to maintain a constant operating pressure, but nothing is removed from the reactor. All catalyst particles have the same age. Equations 3-11 are solved algebraically to supply the variables in equation 5, at the desired operating conditions. The polymerization flux, N, is summed over three-minute intervals from the startup to the desired residence time, t, in hours ... 

V=10 -.VAPOUR BOIL-UP RATE R=lel0 STARTUP AT TOTAL REFLUX Pbar=l TOTAL PRESSURE Accur=le-2 rACCURACY FOR SUBROUTINE CONSTANT CINT=0.2, NOCI=5, TFIN=300 1 SIM INTERACT RESET GOTO 1 INITIAL INITIAL CONCENTRATIONS... 

The second function of the bypass valve is to control reactor pressure during startup of the turbine. This allows the reactor power level to be held constant while the turbine steam flow is varied as the turbine is brought up to speed under the control of its speed governor. 

In the turbine-following-reactor control mode (i.e., turbine-follows-reactor), station loads are made to follow the reactor output. This is achieved by the steam generator pressure-control program, which adjusts the plant loads in order to maintain a constant steam generator pressure. This mode is used at low reactor power levels, during startup or shutdown, when the steam generator pressure is insensitive to reactor power. It is also used in some upset conditions when it may not be desirable to maneuver reactor power. 

Because of this factor, an alternate method of control is available during startup and shutdown transients. In this mode, the steam pressure is held constant and the reactor inlet coolant temperature will vary. The nuclear reactivity effects of this varying coolant temperature will be overridden by the movement of the control rods made to change the power level and at these times there will be no need... 

Outlet Volumetric Flow The nominal volumetric flow of 0.15 m /sec (corresponding to a mass flow of 3.08 kg/sec) for the four loop non-optimized Brayton system of Section 6 is assumed. The range 0.01-1 m /sec has been selected to cover a sufficiently wide range of operation to provide for plant startup at reduced flows, full power operation, and casualty performance. The accuracy of 0.0025 m /sec typifies the accuracy of 0.25% of point found in gas industry ultrasonic flow metering equipment The time constant of 1 second typifies high precision pressure sensor with digital instrumentation. 

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