Four-loop plant

The body of the vessel is of low-alloy steel. To minimize corrosion, the inside surfaces in contact with the coolant are cladded with a minimum of some 3-lOmm of austenitic stainless steel. The major characteristics of the RPVs used for four-loop plants are listed in Table 4.1 (IAEA, 2009). The PWR RPV design pressure is about 17 MPa and the operating pressure is about 15.5 MPa. The design temperature is 343 °C where the operating temperature is typically 280-325 °C (IAEA, 2009). 

High-pressure safety injection water is provided by separate high-head pumps while lower pressure injection water is supplied by the RHRS pirnips. Passive accumulator tanks are inside the containment to provide for fast injection of water after a LCXZA. Figure 2.19 shows the injection phase of the SIS and is the configuration for a four-loop plant. The configurations for two- and three-loop plants differ only in the size of the components and the number of branch injection lines to the RCS. 

Describe a supervisory control system for the plant of Example 23.4 (Figure 23.10) using as local controllers (a) analog devices controlling one loop each, and (b) microcomputers capable of handling four loops each. How would you select the loops to be controlled by each local microprocessor ... 

An example of a Generation II plant is shown in Table 24.3. It is a four-loop Westinghouse PWR, nominally rated at 1200 MW net electric output. Construction began in 1976, and the plant went commercial at the end of 1984. This was one of the last of the plants to be completed in the United States nominally on schedule, and which has had a reasonably successful operating history of nearly 30 years to date. The plant has an operating license extension to 2043. 

At present, two EOF reference systems are implemented in French plants (34 units with three loops and 24 units with four loops) ... 

The generalized state approach set of EOPs ( approche par etat in French), which is implemented on all four loop units (including a fully computerized version for the N4 plants, the most recent 4 loop units) and on some three loop units. 

Both EdF reference sets of EOPs have four separate procedures for the reactor operator, for the water and steam (turbine) operator, for the shift supervisor (containing a combination of reactor, water and steam operator procedures) and for the safety engineer. All procedures are in the colour flow chart format (paper based). The recent four loop N4 plants have fully computerized procedures (with computerized operating actions actuated from the operator video display units) as well as a complete backup paper based set of procedures for operating from the auxiliary panel if the computer system fails. 

Unit 1 of the Zion Nuclear Power Plant, a Westinghouse-designed four-loop reactor in a large, dry containment building, located near Chicago, Illinois. 

For systems with two or one Brayton units, the four heat rejection loops can interface through gas coolers arranged in series as shown in Figure 7. For a two loop plant, each loop would have a pair of cooler sections arranged in series. The upstream cooler section would be operational (with flowing coolant) while the... 

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. 

Inlet Temperature The nominal heat rejection system inlet tonperature of 505 K is based on the four loop non-optimized Brayton system of Section 6. The range 250-570 K assumes the plant maintains temperature not below 250 K, a 10 K control band for reactor operation at full power, the stated accuracy of 1% and a 10% uncertainty for transient performance due to casualty or maneuvering. The number is rounded. The accuracy of 3 K (1 % of range) and the resolution of 1.5 K (0.5% of range) and the 10 second response typify the diaracleristics of quality commercial temperature sensors and instrumentation. 

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