08-16-2017, 09:52 PM
Advanced Construction Methods for New Nuclear Power Plants
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Introduction
Relative to coal fired and natural gas fired power plants, nuclear power plants are more expensive to
build but less expensive to run. This annex describes advanced construction methods to reduce nuclear
power s construction costs, mainly by shortening the time needed to build a plant.
Each of the methods described below has been used in one or more of the projects listed in Table IV-1.
None is unique to the nuclear industry, nor to any specific nuclear power plant design. Most are also
used for other large construction projects such as fossil fuel power plants, large civil construction
projects and shipbuilding.
Open Top Installation
Constraints on installing major components inside the reactor and containment building can have a
major impact on the construction schedule. In the past, the walls of the reactor and containment
building were constructed with temporary openings to allow the entry of large equipment. In open top
installation (Figures IV-1 and IV-2), the reactor and containment building is built with a temporary
roof with an opening through which major pieces of equipment, such as the reactor vessel and steam
generators, can be lowered into position using very heavy lift (VHL) cranes. Today s VHL cranes can
lift equipment weighing more than 1000 tonnes, with very long reach.
Modularization with Prefabrication and Pre-assembly
Prefabrication and pre-assembly of modules are construction techniques used in many industries,
including nuclear power plants. A module is an assembly consisting of multiple components such as
structural elements, piping, valves, tubing, conduits, cable trays, reinforcing bar mats, instrument
racks, electrical panels, supports, ducting, access platforms, ladders and stairs. Modules may be
fabricated at a factory or at a workshop at the plant site, and multiple modules can be fabricated while
the civil engineering work is progressing at the site in preparation for receiving the modules. This
reduces site congestion, improves accessibility for personnel and materials, and can shorten the
construction schedule. It can also significantly reduce on-site workforce requirements.
Modularization also facilitates mass production of modules in the event that several reactors are being
built at the same time. Mass production reduces production times and labour requirements.
Modularization makes it easier to assure a controlled production environment, with associated
improvements in quality and efficiency. It makes it possible to manufacture modules before the site
itself is available, and, in the case of concrete, it facilitates the use of accelerated curing techniques.
Advanced Welding Techniques
Nuclear power plant construction involves numerous welds to connect both components of structures
and components of pressurized systems. It also involves weld cladding, which refers to one metal
being deposited onto the surface of another to improve its performance characteristics. Quality
welding is both crucial and time consuming, and techniques to increase the rate at which weld metal
can be deposited while maintaining high quality can reduce construction times. Recent advanced
welding technologies that meet this objective include gas metal arc welding, gas tungsten arc welding
and submerged arc welding.
In addition, automatic welding equipment that makes it easier to weld in narrow spaces can further
decrease construction times. Automatic welding equipment has been used to weld titanium tubes to
condenser tube sheets at Tarapur-3 in India and to weld piping at Kashiwazaki Kariwa-7 in Japan
(Figure IV-10).