Very heavy lifting open top construction

In the past, the constraints on the installation of components within the reactor building and containment were a major challenge to the construction schedule. Historically, the reactor building and containment wall were constructed with temporary openings in the side of the buildings to allow entry of bulk commodities and large equipment. Recently, mainly due to advances in construction crane technology, significant improvements in schedule have been achieved through transportation of bulk commodities and installation of heavy equipment through the open top. Open top installation can provide cost savings and flexibility in delivery of heavy equipment that is not enclosed by ceiling slabs.

In the open top installation construction sequence, part of the reactor and containment wall is built. Major items of equipment such as the reactor vessel and steam generators are then placed into position through the temporary open top in the building, using a VHL crane. Once the equipment has been placed inside, work on connecting the equipment to the already built piping and electrical systems can proceed in parallel with the ongoing construction works.

There is a lot of heavy equipment in NPP buildings; e.g. reactor pressure vessel (RPV), containment vessel, steam generators, emergency diesel generators, heat exchangers, overhead cranes, condensers and feedwater heaters. This heavy equipment needs to be installed in the correct position. The open top method allows easier installation of the heavy equipment, as equipment can be installed directly into the final position, unlike the traditional methods that require complex rigging and manipulation. In addition, installation of these modules and equipment will affect the construction schedule of the NPP. The containment vessel will be the critical path to the schedule of the Nuclear Island, and the condenser will be the critical path to the Turbine Island. When larger and heavier assemblies are installed using this method rather than the stick-build approach, the construction schedule can be shortened.

Construction efficiency and quality can be enhanced by moving assembly and construction activities away from the excavation and away from the site in general, and performing the work in parallel in controlled and spacious environments. The drive to achieve this goal has resulted in larger and heavier assemblies being shipped, moved and placed on site.

Open top construction is a construction/erection technique that involves integrating the construction of the walls/slabs of a building with the installation of modules, equipment, and mechanical and electrical commodities.

The commodities are designed, procured and constructed, with equipment and materials being installed in and/or loaded in their final positions before those areas are fully enclosed by higher elevation slabs and the containment dome. In some cases, even surrounding walls are not erected until the equipment is set (especially true for large modules).

When properly used, this open top construction technique permits many of the advantages of modularization and pre-assembly to speed the construction process and reduce construction labour cost. Open top construction reduces temporary openings, which are used in the conventional method to carry in modules after the construction of the buildings. Open top construction also reduces material handling by using modules. The open top construction method should be used extensively for large equipment and bulk commodities such as piping and cable trays.

The following should be considered when the open top construction method is to be applied:

— The open top construction method requires the early procurement of equipment (four to six months in advance) compared to the conventional method which uses temporary openings, because the equipment needs to be installed before the ceiling is installed;

— The equipment to be installed using the open top construction method should be identified in the earliest stage of the project, and the engineering and procurement schedules should be adjusted to match the open top construction schedule;

— The open top construction method requires strict manufacturing and shipping management of the equipment.

Any delay in the equipment causes a delay in the construction of the building, which will affect the entire construction schedule;

— Equipment installed using the open top construction method should be properly protected against physical impact, the weather, humidity, and construction dust and fumes, because the upper slab is installed after the installation of the equipment;

— Open top modular construction requires VHL cranes:

— A large crane is used to lift the modules or equipment into the buildings. Large items of equipment such as the RPV, pre-assembled containment vessel, pre-assembled condensers and pre-assembled modules are lifted ‘over the top’ of the building to avoid interfering with the building construction. The VHL crane needs to have the capacity to lift the large equipment and modules into the building. Current industry practice typically uses VHL cranes with the capacity to lift and place modules with a mass of more than 900 t. In some instances, plant construction requires the VHL crane to pick up and travel with large modules. In current industry practice, the large block method was also introduced to the civil work by using the VHL cranes for lifting larger assembled rebar blocks, structural steel frames, metal deck blocks and assembled scaffold blocks;

— Construction crane technology has advanced significantly over the past 15 years. Significant improvements in lifting are being achieved every three to five years. Current lift limitations allow for modular prefabrication of major skids and entire rooms or even floors of combined process equipment, piping, electrical and controls components. Similarly, major vessels and other very large items of equipment that were previously shipped in sections and assembled on-site are now shipped whole, moved across the site and placed as a single piece. Marine access to a site has significant advantages in this regard;

— Movement of large assemblies, modules and equipment from port to port, port to site, and site to crane location is an additional area where efficiency has increased significantly. For example, heavy haul transporters can be used in conjunction with special barges for inland waterways such that no offloading is required at the barge port near the site. Ocean delivery vessels and ports can place the transported item directly on the transporters on the barge. When the barge reaches the site or site access port, the transporters drive directly off the barge and to the crane location for placement;

— Just-in-time delivery should be evaluated on a case-by-case basis, based on the economics. The concept of

‘single lift,’ which seeks to move material and equipment directly onto the site and into place without any interim lift or storage, should be utilized where possible;

— Very heavy lifting has been used for large scale capital projects. An important consideration in the application of a VHL crane is the area needed for strategic placement of the crane to conduct the numerous lifting activities. Planning for crane placement and movement is a crucial step in open top installation;

— Full exploitation of open top construction is expected to reduce total construction time, but attention must also be focused on the cost of heavy lift equipment and the facilities necessary for the prefabrication of modular components;

— The following items should also be considered when a VHL crane is applied to the construction:

— A VHL could be one of the long-lead items which may take two to three years, including design and manufacturing;

— A VHL crane requires a larger footprint close to the major buildings;

— A VHL crane plan should be in place to control crane movement around the site.

Examples of the use of the VHL open top construction technique are given in the following paragraphs.

9.1.2. Qinshan Units — China

During the construction of Qinshan III Units 1 and 2, approximately 70 items of equipment were set in place using the VHL crane, as shown in Fig. 119. This equipment included steam generators (shown in Fig. 120 — 220 t each), pressurizer (103 t), reactivity mechanisms deck (43 t), feeder frames (40 t each), fuelling machine bridges (16 t each) and major heat exchangers. The steam generator took one day to install, compared to the two weeks typically required using the traditional horizontal access method.

9.1.3. Olkiluoto — Finland

Figure 121 shows a VHL crane being used to lift the 200 t metallic containment liner double rings of Olkiluoto 3 into place in the reactor building, raising the inner containment from +12.50 m up to the 25 m level.

FIG. 119. Very heavy lift crane use in Qinshan, China.

FIG. 120. Steam generator installation in Qinshan, China.

9.1.4. Kudankulam — India

Figure 122 shows a VHL crane lifting the containment dome at Kudankulam.

FIG. 121. Lifting of containment liner double rings in Olkiluoto 3, Finland.

FIG. 122. Lifting of WWER-1000 containment dome into position at Kudankulam, India (credit: NPCIL).

9.1.5. Tarapur Units — India

Significant savings in time were also achieved by using open top installation at Tarapur Units 3 and 4. The VHL crane was used to set approximately 50 items of equipment in position, including the steam generators (shown in Fig. 123) moderator heat exchangers, pressurizer, calandria (shown in Fig. 124) primary circuit headers, fuelling machine, and several heat exchangers. The steam generator was lowered and positioned in less than a day, thus saving considerable construction time compared to that used for earlier heavy water reactors (HWRs) in India.

9.1.6. Tomari Unit 3 — Japan

In Japan, Mitsubishi used a VHL crane to install equipment at Tomari Unit 3 (shown in Fig. 125).