8. MODULARIZATION

8.1.DEFINITIONS

There are two main categories of modules:

—Mechanical or electrical modules;

—Civil modules.

There are three levels of modularization, defined as follows:

—Prefabrication — joined materials to form a component part of a final installation;

—Pre-assembly — joined component parts to create a subunit;

—Module — assembly of subunits to create an installation unit or assembly.

Mechanical or electrical modules are defined as a factory or workshop fabricated assembly consisting of structural elements, equipment and other items such as piping, valves, tubing, conduit, cable trays, supports, ducting, access platforms, ladders and stairs. Modules may also be fabricated and assembled at a workshop on the site. Figures 98 and 99 show two examples of mechanical modules.

FIG. 98. Mechanical module — example 1 (credit: Hitachi).

FIG. 99. Mechanical module — example 2 (Credit AECL).

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A civil module is defined as:

—Assembled structural steels including superstructures for building roofs (Fig. 100);

—Prefabricated rebar mats;

—Assembled deck slabs (Fig. 101);

—Assembled staircases (Fig. 102);

FIG. 100. Assembled roof truss module (left), prefabricated rebar (right), Kashiwazaki-Kariwa 7 — Japan.

FIG 101. Assembled deck slab, Kashiwazaki-Kariwa 7 — Japan.

FIG. 102. Assembled staircase, Kashiwazaki-Kariwa 7 — Japan).

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—Prefabricated steel plate reinforced structures (Fig. 103) to be filled with concrete after being installed as units (refer to ‘advanced formwork’ under Paragraph 4.1.2.6).

Refer also to Figs 104–107.

FIG. 103. Steel plate reinforced concrete structures (refer to Paragraph 4.1.2.6 — steel-plate reinforced walls).

FIG. 104. Modular rebar manufacturing at site (Toshiba Japan) (also refer to Paragraph 4.1.2.7).

FIG. 105. Modular wall prefabrication sequence at site — horizontal phase (AP1000).

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FIG. 106. Modular wall prefabrication at site — vertical phase (AP1000).

FIG. 107. Civil and mechanical modules lifted as one assembly (CA20 weighing 872 t on the left, and CA01 weighing 750 t on the right) (AP1000 in China at Sanmen and Haiyang sites).

8.2. DESCRIPTION

A module is an assembly consisting of, for example, structural elements, equipment and other items such as piping, valves, tubing, conduit, cable trays, reinforcing bar supports, ducting, access platforms, ladders and stairs.

Structures, systems and components in modern nuclear plants are to be designed as modularized systems that are shop-fabricated and installed as skid-mounted packaged systems wherever possible, and where such a configuration suits the schedule and cost of the system.

If modules are to be used, they must be incorporated into the design from the very beginning of the design process. Otherwise, there is very little chance that the construction organizations can use modular construction techniques. This approach influences the design philosophy from the feasibility phase, where systems are possibly combined to form a module, and therefore has a domino effect on all the functions following the design process. The approach also then has a major impact on the procurement philosophy, and therefore on the construction strategy.

A modularization methodology plan should be established upfront to allow this approach to be followed throughout the project, from the conceptual and detailed designs, through engineering, procurement, fabrication, and erection or installation (construction).

The module designs should be planned with a series of considerations, such as:

—Definition of module envelope parameters;

—Integration of all relevant technical disciplines;

—Temporary bracing;

—Analysis for transportation and lift;

—Selection of installation and alignment tolerances;

—Shipping and storage requirement;

—Handling or lifting requirement;

—Protection requirement;

—Standardization of modular specifications.

The design planning should also consider the necessary features of plant configuration to fit modularization. An entirely new approach to plant and building layouts may be considered. The use of rectangular structures instead

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of round structures may reduce risks with the modular approach. Designs should ensure sufficient access and lay-down areas on site and within the plant. Design inputs should include those from construction personnel to ensure that the plant can be efficiently constructed.

The actual paralleling of activities in the schedule that can be achieved through modularization must be optimized and utilized to the benefit of the project wherever possible. The advantage is that a large volume of mechanical/electrical work that is traditionally done on site is moved out of structures for fabrication into modules. This work can be done in parallel with the early civil programme.

Issues that must be considered in developing the modular construction plan include:

—Module construction schedule driven by the project schedule;

—Sequencing on-site movement, installation and testing of modules;

—Parallel conventional installation work in nearby areas;

—Appropriate use of on-site workshop(s) to support module installation.

It must be ensured that such systems can be installed and removed via the normal access routes of the building.

8.3.RECENT CONSTRUCTION EXPERIENCE IN MODULARIZATION WITH PREFABRICATION AND PREASSEMBLY

Modularization with prefabrication and preassembly, in combination with open top construction, has been applied in some recent construction projects for evolutionary water cooled reactors; e.g. at Kashiwazaki-Kariwa Unit 7 (Japan), by using the so-called ‘large scale modularizing construction method’. The heaviest and most complicated module was the ‘upper dry well super large scale module’, shown in Fig. 108, which consisted of a γ shield wall, pipes, valves, cable trays, air ducts and their support structures, and weighed 650 t.

At Lingao (China), the containment dome was assembled on the ground at the site and installed as a single module (weight 143 t, diameter 37 m, height 11 m, as shown in Fig. 109). Previously, the dome was assembled by moving sections into position — a process that took approximately two months.

Another example of modularization is the fabrication and installation of the containment shell liner plates at the Shin-Wolsong 2 project in the Republic of Korea, where a three-stage based modularization of these components was adopted. Containment liner plates form an inner structure of the containment building of the Korean Optimized Power Reactor. The installation process would normally consist of 15 stages, each stage involving installation of one containment shell liner plate ring. Since containment buildings are connected to auxiliary buildings, the installation of the containment liner plate could be very complicated when installing pipes, ventilation, electric wiring and other equipment. Therefore, in the construction of the Shin-Wolsong 2 unit, a threestage based modularization (weight 197 t, diameter 44 m, height 9.14 m) of the containment shell liner plates was

FIG. 108. Installation of upper dry well super large scale module, Kashiwazaki-Kariwa, Japan.

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FIG. 109. Lifting of dome module, Lingao, China.

FIG. 110. Modularization of containment liner plate assembly, Shin-Wolsong 2, Republic of Korea.

introduced. With this method, except for the first two stages, the remaining rings are modularized into three-ring sections and installed with one lift, thereby reducing the number of lifts and shortening the overall plant construction time. This modularization resulted in completion of construction in nine months as compared to the 11.5 months taken earlier using conventional methods. This method also simplifies connections with auxiliary buildings, since connecting provisions have already been attached to the ring modules, such as penetration sleeves for piping and electrical wire. Figure 110 shows the Manitowoc M-1200 ringer crane (main boom 115.2 m, work radius 52 m, capacity 238.4 t) being used to lift the 197 t containment shell liner module of Shin-Wolsong 2 into place in the reactor building.

The containment dome liner plates at the Shin-Wolsong 1 and 2 projects were also modularized. The containment dome liner plate comprises eight stages, as illustrated in Fig. 111. The dome liner plates were modularized with two lifts: the lower dome liner plate (shown in Fig. 112, weight 205.7 t, diameter 44 m, height

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