Coolant Flow Scheme

All core design concepts described here are based on the coolant flow scheme in Fig. 2.43. This unique flow scheme achieves effective cooling of fuel rods and 

An example of the fuel assembly top structure is shown with the coolant and moderator flow directions indicated in Fig. 2.44 [9]. The cmitrol rod cluster guide tube is connected to the water rod stmctures at the top of the fuel assembly and the moderator is distributed into the water rods by downward flow. On the other hand, the coolant, having risen from the mixing plenum, flows through the gap space between the water rods at the top of the fuel assembly and flows to the core outlet. 

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The basic coolant flow scheme is explained in Sect. 2.4.3 (see also Fig. 2.43). In this design, 30% of the inlet coolant is led to the top dome. The coolant then flows down... 

Coolant Flow Scheme Outer Core Downward Flow Cooling... 

The core coolant flow scheme can be characterized by the downward flow in the water rods. This flow scheme is intended to ... 

The basic SPRAT was modified to deal with water rods cooled by downward flow [6]. It is called SPRAT-DOWN [7-9], The coolant flow scheme is shown in Fig. 4.3. The fuel channel and the water rod chaimel are modeled as single channels with 20 meshes. At normal operation, 30% of the feedwater is led to the water rod channel through the upper dome and the control rod guide tube. The lower plenum, including the downcomer, is divided into 20 meshes. The upper plenum, including the main steam line, is also divided into 20 nodes. The main feedwater line and the... 

In the Super LWR analyzed in Chap. 5, the coolant channels of all the fuel assemblies are cooled by upward flow, so that only one hot channel is treated in the thermal analysis and thermal hydraulic stability analysis. On the other hand, the coolant flow scheme in the reactor pressure vessel of the Super FR is the so-called two-pass scheme where part of the seed fuel assemblies and all the blanket fuel assemblies are cooled by downward flow as shown in Fig. 7.35. The fractions of the downward flow rate in the seed assemblies, blanket assemblies, and downcomer at the normal operating condition are determined in the core design as shown in Figs. 7.36 and 7.58 [26]. The flow distribution among those downward flow paths would change during the power raising phase so as to balance the pressure drops. 

During blowdown, the coolant flow in the reactor vessel of the Super FR is more complicated than that of the Super LWR due to the two-pass flow scheme. The coolant flow schemes are illustrated in Fig. 7.105 [37]. In order to analyze the blowdown of the two-pass core, the SPRAT-F is modified to the SPRAT-F-DP [37]. Flow redistribution among the downward flow seed channels, blanket channels, and downcomer are calculated in this code. The initial conditions for the LOCA analyses are the same as those for the safety analyses at supercritical pressure. 

In this section we consider a CSTR with a very simple control system formed by two PI controllers. The first controller manipulates the outlet flow rate as a function of the volume in the tank reactor. A second PI controller manipulates the flow rate of cooling water to the jacket as a function of error in reactor s temperature. The control scheme is shown in Figure 12 where the manipulated variables are the inlet coolant flow rate Fj and the outlet flow rate F respectively. 

When reactor capacity is limited by heat removal, an often-recommended control structure is to run with maximum coolant flow and manipulate feed flowrate to control reactor temperature (Tr F0 control). This control scheme has the potential to achieve the highest possible production rate. However, if the feed temperature is lower than the reactor temperature, the transfer function between temperature and feed flowrate contains a positive zero, which degrades dynamic performance, as we demonstrate quantitatively in this section. The choice of a control structure for this process presents an example of the often encountered conflict between steady-state economics and dynamic controllability. 

Cascade control is one solution to this problem (see Fig. 8-35). Here the jacket temperature is measured, and an error signal is sent from this point to the coolant control valve this reduces coolant flow, maintaining the heat transfer rate to the reactor at a constant level and rejecting the disturbance. The cascade control configuration will also adjust the setting of the coolant control valve when an error occurs in reactor temperature. The cascade control scheme shown in Fig. 8-35 contains two controllers. The primary controller is the reactor temperature coolant temperature controller. It measures the reactor temperature, compares it to the set point, and computes an output, which is the set point for the coolant flow rate controller. This secondary controller compares the set point to the coolant temperature measurement and adjusts the valve. The principal advantage of cascade control is that the secondary measurement (jacket temperature) is located closer to a potential disturbance in order to improve the closed-loop response. 

Figure 5.28. A typical stirred tank reactor control scheme, temperature cascade control of coolant flow, and flow control of reagents.

The method has been demonstrated on a continuous stirred tank reactor (CSTR) simulation to identify an abnormal inlet concentration disturbance [340]. The jacketed CSTR, in which an exothermic reaction takes place, is under level and temperature control. An important process variable is the coolant flow rate through the jacket, that is related to the amount of heat produced in the CSTR, and it indirectly characterizes the state of the process. This variable will be monitored in this classification scheme. 

Flooded condenser schemes shown in Fig. 17.5a to c and f can be used instead of coolant flow variations. In such cases, the inerts normally leave finm the top of the condenser instead of the reflux drum (Fig. 17.8e). If the reflux drum is not flooded, a pressure balance line must be included otherwise, a stable pressure will be impossible to keep in the reflux drum. An overflow line should also be included in this arrangement. 

The scheme of coolant moving within the MCC is as follows throu die windows of reactor outlet chamber the coolant heated in the core flows to the inlet of the SG twelve modules which have parallel connection. It flows from top to bottom in the intertube gap of the SG modules and is cooled there. Then the coolant penetrates into the intermediate chamber, from which it moves in the channels of in-vessel radiation protection system, cooling it, to the monoblock upper part and there it forms the free level of cold coolant (peripheral buffer chamber), further from Ae monoblock upper part the coolant flow moves to the MCP suction inlet. 

The adopted circulation scheme with free levels of LBC existing in the monoblock upper part and SG module channels, which contact the gas medium, ensures the reliable separation of steam-water mixture out of coolant flow when the accidental tightness loss of SG tube system occurs, and existing of gas medium ensures the possibility of coolant s temperature changes. 

Cause The control switches for coolant flow and solvent flow are located side by side and are identical in appearance. As with the gauge assessment above, the result of this design scheme would be an increased potential for operator error in system activation. 

Figure 4.22. Flow scheme of a sampling system for both high-temperature and ambient-temperature sampling of coolant (Roesmer, 1985)...

The possibility of water or steam penetration into the core, e g. caused by a large SG leak, and the consequent over-pressurization of the reactor mono-block vessel (designed to be resistant against the maximum possible pressure under these conditions) are eliminated by the selected circulation scheme of lead-bismuth coolant. This scheme ensures that steam bubbles are thrown out into the gas volume on the coolant free-level by the upward movement of the lead-bismuth coolant flow. Then the steam goes to the gas system condensers. In the event of postulated failure, the steam goes through the rupture membranes to the bubbler devices of the tank of the passive heat removal system (PHRS). 

Moving to the next subcategory of schemes, another approach is to manipulate coolant temperature. While not applicable to air-hns it does offer some advantage if condenser fouling is an issue, since it permits a high coolant flow to be maintained - no matter what condenser duty is required. As can be seen in Figure 12.37, it does require additional pumping and so is more costly to implement. 

The necessity to meet the highlighted requirements has resulted in the development of a circulation scheme, in which the core hydraulic resistance equals to 90% of the total hydraulic resistance of primary circuit, while the hydraulic resistance of the SGs, in which lead bismuth coolant flow rate is much smaller, equals only to 10% of the total value. With due account of the listed requirements, the specific mass of lead bismuth coolant in SVBR-75/100 reactor installation is 1100 t/GWe. 

Like the reactor-prototype BN-800 has a three-circuit flow scheme with sodium coolant in the primary and secondary systems and water-steam in the tertiary circuit (Fig. 9.25). The reactor plant comprises the fast nuclear reactor with three primary loops, three secondary loops and three steam generators of sectional-modular type. The reactor uses the... 

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