Reactor Startup and Operation

The operational sequence for the startup of the plant from a cold standby condition is as 

The flow control valves are set at the minimum position, which corresponds to approximately 25% of rated flow. 

The reactor water recirculation pumps are started. Because the low-frequency motor generator sets cannot start the recirculation pump motors, the pump motors are started from auxiliary power and transferred to the low frequency motor generator sets when the pump motor nears full speed and after the starting current has dropped. 

Control rods are manually withdrawn according to a predetermined schedule to achieve criticality of the reactor. They are further withdrawn to approximately 32% of rated power with the reactor water flow control valves fully open and the recirculation pumps operating at low speed (25%). The rate at which power level is raised is usually limited by conditions of thermal expansion of the reactor vessel. 

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Specific tests (as pump seizure for example) and periodic inspections (by means of a MIR telemetry able to measure relative displacements at connections for example, as provided in the EFR project) during reactor startup and operating life. 

Of what importance is the artificial neutron source to reactor startup and operation ... 

The design of the reactor internals has not been addressed yet, but they likely will be made of graphite or carbon composites to accommodate the high-core outlet temperature required by the NGNP (1000°C). It is possible that carbon-insulated metallic alloy will be used for the core support structure, although this has not been evaluated yet. Control rods will be required to provide for reactor startup, normal operation, and shutdown. The munber and placement of control rods has not been evaluated yet, but the rods will be constructed from carbon composites for the drive shafts and absorber casing and boron carbide or other high-temperature absorber for the neutron absorber. The control rod drive mechanisms will be located above the reactor enclosure head. 

The startup transient curves Indicate the the maximum excess reactivity during startup and operation is the cold, clean reactivity. Turnaround reactivity level is below startup level. This differs from the present Hanford reactors where the turnaround level for an infinite-outage startup is higher than the initial cold clean reactivity level. 

The Infinite. outage startup transient curves Indicate that the maxi mum excess reactivity during the startup and operation Is the cold, xenon-free reactivity This differs from the present Hanford reactors where the "turnaround" level for an Infinite-outage startup Is hlipa r than the initial cold, clean reac-tlvlty level ... 

Neutron sources are of two types (1) a primary source, which is active for initial reactor startup and startup early in the life of the first core and (2) a secondary source, used for later startup of the reactor and activated during the operation of the reactor. 

Kuan-Yeow Show (accelerated startup and operation of anaerobic reactors microbial granulation in wastewater treatment ultrasound applications in sludge and wastewater treatment conversion of sludge and wastes into engineering materials). Department of Environmental Science and Engineering, Fudan University (FDU), Shanghai... 

The reactor vessel surrounds the core and a combination of fixed and movable reflectors surround the vessel. The movable reflector is segmented and used to maintain reactivity at the desired operating temperature over life. Instrumentation to monitor power and temperature is used to determine when to move reflector segments during reactor startup and to compensate for uranium burn-up during operation. The reactor uses at least one safety shutdown rod. Safety rods are only used during transport and launch and would be withdrawn from the core prior to initial criticality. 

Two of the primary reasons for the extended shutdown of the Savannah River Site (SRS) production reactors were (1) a P-Reactor event in which an unfactored buildup of "poison" during a planned shutdown caused ah unpredicted level of reactivity in the core upon reactor startup, and (2) the way in which the operating contractor handled this event. 

The Phase 1 and Phase 2 Technical Specifications were submitted to DOE for approval as WSRC-TS-10003 Revision 0 on December 18, 1990 (Reference 5). At DOE request, WSRC included a new Technical Specification for the Ultimate Heat Sink. In the submittal, WSRC noted that the review verified the Limiting Conditions for Operation, and the associated Surveillance Requirements applicable to chargeback and shutdown. DOE approved Revision 0 on January 25, 1991,(Reference 6). Until WSRC-TS-10003, Rev. 0, is fully implemented, WSRC will comply with the existing OPST-TS-105 after implementation of WSRC-TS-10003, DPST-TS-105 will be withdrawn for the K-Reactor. Additionally, there are a number of open items remaining that relate to startup and operations, including ... 

The Heat Rejection Segment provides the heat sink necessary for (deration of the Brayton unit cycle. Full deployment of the radiator panels is required prior to reactor startup and the raising of the power system s temperature. Spacecraft operational planning assumes that trace heaters and a minimum ( survival flow will be utilized to prevent HRS fluids from freezing from launch until operation of the power system. 

Unsteady material and energy balances are formulated with the conservation law, Eq. (7-68). The sink term of a material balance is and the accumulation term is the time derivative of the content of reactant in the vessel, or 3(V C )/3t, where both and depend on the time. An unsteady condition in the sense used in this section always has an accumulation term. This sense of unsteadiness excludes the batch reactor where conditions do change with time but are taken account of in the sink term. Startup and shutdown periods of batch reactors, however, are classified as unsteady their equations are developed in the Batch Reactors subsection. For a semibatch operation in which some of the reactants are preloaded and the others are fed in gradually, equations are developed in Example 11, following. 

The operating conditions of the unit, particularly during startups and feed interruptions, will have a large influence on the formation of coke. Coke normally grows wherever there is a cold spot in the reactor system. When the temperature of the metal surfaces in the reactor... 

Startup and Shutdown Strategies. In addition to safe operation, the usual goal of a reactor startup is to minimize production of off-specification material. This can sometimes be accomplished perfectly. 

The next two steps after the development of a mathematical process model and before its implementation to "real life" applications, are to handle the numerical solution of the model s ode s and to estimate some unknown parameters. The computer program which handles the numerical solution of the present model has been written in a very general way. After inputing concentrations, flowrate data and reaction operating conditions, the user has the options to select from a variety of different modes of reactor operation (batch, semi-batch, single continuous, continuous train, CSTR-tube) or reactor startup conditions (seeded, unseeded, full or half-full of water or emulsion recipe and empty). Then, IMSL subroutine DCEAR handles the numerical integration of the ode s. Parameter estimation of the only two unknown parameters e and Dw has been described and is further discussed in (32). 

As in the case of a batch reactor for commercial operation, a CSTR is normally used for a liquid-phase reaction. In the laboratory, it may also be used for a gas-phase reaction for experimental measurements, particularly for a solid-catalyzed reaction, as in Figure 1.2. The operation is normally one of steady-state, except for startup, shutdown, and operational disturbances or upsets, in which cases unsteady-state operation has to be taken into account. 

In this chapter, we develop the basis for design and performance analysis for a plug flow reactor (PFR). Like a CSTR. a PFR is usually operated continuously at steady-state, apart from startup and shutdown periods. Unlike a CSTR, which is used primarily for liquid-phase reactions, a PFR may be used for either gas-phase or liquid-phase reactions. 

We have thus far considered only steady-state operation of the CSTR and the PFTR. Thi, s is the situation some time after the process was started when all transients have died out, and no parameters vary with time. However, all continuous reactors must be started, an d parameters such as feed composition, flow rate, and temperature may vary because feed composition and conditions change with time. We therefore need to consider transier it operation of the CSTR and the PFTR. Transients are a major cause of problems in reactoir operation because they can cause poor performance. Even more important, problems during startup and shutdown are a major cause of accidents and explosions. 

The reactor is characterized by no addition of reactant or removal of product during the reaction. Any reaction being carried out with this constraint, regardless of any other reactor characteristic, is considered batch. The assumptions for batch operation are (1) the contents of the tank are well mixed, (2) reaction does not occur to any appreciable degree until filling and startup procedures are complete, and (3) the reaction stops when quenched or emptied. The reactor can be operated with either a homogeneous or heterogeneous reaction mixture for almost any type of reaction. 

Operators use the heater to heat each reactor to startup conditions, one at a time. The reaction is exothermic, and once the reactor is up to full production the heater is shutdown and the operator isolates the reactor from that heater circulation loop. When another reactor is scheduled for startup, the operator aligns the valving, starts the circulation pump, ignites the heater burner, and brings the reactor up to temperature. 

The coke profiles in the reactor bed can be predicted excellently by the model as shown by the solid lines in Figure 1. Figure 2 shows good consistency is also obtained for the average coke content over the reactor bed versus time on stream. Note that within the time period of reactor startup plus one hour of operation, the average coke content of the reactor bed is already at about 5 wt%. The model cannot be applied to this startup and initial period with the rapid transients of temperature, activity "spike" and concentration. However, compensation for this interval can be made by a time translation of the model a model time of 36 hours is fixed at an experimental time of zero. A temperature difference of more than 20C between the center of the bed and outer wall of the reactor in the startup stage has been observed in our laboratory for some experiments. About three-fourths of this difference is across the catalyst bed itself. Startup of the reactor at reasonably lower temperatures in order to control the coke formation and to better maintain the catalyst activity is important, if not critical. 

This chapter is concerned with the mathematical modeling of coupled chemical reaction and heat and mass transfer processes occurring in porous catalysts. It focuses primarily on steady state catalyst operation which is the preferred industrial practice. Stationary operation may be important for the startup and shutdown of an industrial reactor, or with respect to dynamic process control. However, these effects are not discussed here in great detail because of the limited space available. Instead, the interested reader is referred to the various related monographs and articles available in the literature [6, 31, 46-49]. 

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