With coal-fired power plants, the conveyor belts which carry the coal normally end at a great height in what is known as the intermediate structure of the turbine building, which for this reason must be considerably higher than the remainder of the turbine building area.

Nuclear power plant turbine buildings do not need such a high intermediate structure, so a continuous turbine floor level and hence a level turbine building roof can be made.

In structural engineering terms, this means that the turbine building roof must span more than 40 m, as the machinery crane must be able to cover the full width of the turbine building.

Most turbine buildings for nuclear power plants therefore use pre-stressed concrete precast girders (Figure 4.6), which are usually installed using the turbine building crane which is already in place.

The roof structure in earlier turbine buildings at nuclear power plants was generally made of hollow pre-stressed concrete slabs laid directly on pre-stressed concrete girders; however, as designing for earthquakes became increasingly necessary, this solution proved to have many problems because there was no enclosed roof segment to make the structure rigid.

More recent turbine buildings therefore seek to use semi-precast component solutions, with the cast in site concrete topping being added as continuous shear slab.

There is another particular feature with designing the turbine building with boiling water reactors such as Gundremmingen. With this reactor type, the slightly radioactive primary steam is fed directly to the turbine. To protect against radiation, a thicker and therefore also heavier roof construction is required, which in turn imposes particular requirements on the design of the pre-stressed concrete ties and designing to withstand earthquakes.

The global bracing systems in the lateral and axial directions of turbine buildings vary considerably, depending on the plant context as a whole.

While only relatively soft framework systems are available laterally, the building is rigidified mainly by a shear wall in the longitudinal direction. This bracing design, which is different in the two directions of the building, means 3D modelling is often required when it comes to dynamic earthquake analysis of turbine buildings.

This is where the highly rigid spring-mounted turbine table comes in, which absorbs the high levels of static and dynamic loads from the turbine and generator and transmits it to the framework structure. The spring bodies are still sufficiently rigid in horizontal terms that in dynamic studies of how the building as a whole would behave in the event of an earthquake, the relatively soft lateral framework is ‘connected elastically’ via the turbine base.

Like an airplane crash, an explosion pressure wave is rated as an extremely rare event (safety level 4), and thus qualifies as beyond design system status. An explosion pressure wave is a chemical explosion in the form of a deflagration (pressure rising relatively quickly, building up reflected pressure). It may be caused by using explosives or if a high-energy container bursts, so that an explosion pressure wave must be accepted as a design basis when carrying hazardous cargos by rail, water or road and when storing containers with high energy content.

A chemical explosion causes pressures on the building concerned and induced vibrations in that building. The external explosive loads due to air pressure waves give an explosion pressure which can be expressed in time and place terms

as follows:

P = Ps + c • q where

ps is the compression pressure, including reflected increase q is the velocity pressure (dynamic pressure) c is a coefficient of form

With box-shaped buildings (non-slender structures), the c • q component may be ignored; with slender structural sections, the explosion pressure can be treated as a static wind load c • q as defined in DIN 1055-4 [49]. For more details of using this function for explosion pressure see DIN 25 449 [15].

As a general rule, if no more precise local studies are available, possible explosion pressure waves can be established using the pressure wave in the BMI guidelines [50]. This function, as shown in Figure 5.8, is specified in the RSK guidelines for PWRs, and represents a conservative assessment of potential explosion pressure waves. This approach assumes that the pressure wave can come from any given direction and that there is a level pressure front.

The specifications of DIN 18195-6 [93] ‘Waterproofing buildings, proofing against outside pressing water and accumulating seepage water, design and execution’ largely represents the current state of the art. Continuing intensive technological developments have led to both new waterproofing materials and new waterproofing methods.

Design and Construction of Nuclear Power Plants. First Edition.

Rudiger Meiswinkel, Julian Meyer, Jurgen Schnell.

© 2013 Ernst & Sohn GmbH & Co. KG. Published 2013 by Ernst & Sohn GmbH & Co. KG.

Building waterproofs with different kinds of waterproofing strips and adhesives made in suitable combinations may be described as part of the state of the art. The individual components from which building waterproofs are made are defined in the materials tables in DIN 18195-2 [94] ‘Structural waterproofing’. The state of the art in science and technology is defined in KTA 2501 [92] ‘Structural waterproofing in nuclear power plants’. Waterproofing structures of various kinds are defined in Table 8.1.

Note: In the case of other types of waterproofing structures and the use of other waterproofing materials, cf. Section 4.1.7.

High soil pressures from permanent loads cause the bitumen in bituminous waterproofs to ‘extrude’ laterally. This effect can be counteracted by inserting copper ripple plates in the bitumen strips.

Which waterproofing structure can be used depends primarily on what stresses act on a building waterproof. As well as the verifications required, installation and design issues and particular aspects of execution must also be taken into account.

As the world’s population grows, the demand for primary energy, and hence electrical energy, is growing massively with it. At the same time, the demand for individual electrical power is increasing, especially as the so-called emerging nations are seeing their energy demand soar as they strive to become industrialised. The International Energy Agency (IEA) estimates that businesses and private households will need around 60% more energy by 2030 than they do today. With their massive populations, China and India will account for two-thirds of the increasing demand forecast.

The result, ‘More and more people needing more and more energy’, is shown in Figure 1.1. Between 2000 and 2020, world population is set to increase from six to eight billion (33%), but the demand for energy is forecast to rise at nearly twice the rate, by around 62%. This increase will mean major challenges in terms of a sustainable energy supply, based on the three-pillar concept of balancing economics, ecology and society, as set at the world summit in Rio de Janeiro in 1992.

Organising who is responsible for what and how things should run is of decisive importance when creating a major project. Clients, authorities, inspectors, contractors and designers must be involved in the project in such a way as to ensure that work proceeds perfectly and in an orderly fashion and that quality goals are achieved. Any project organisation is based on contractual foundations, which lay down the rights and obligations of those involved.

The overall project organisation chart of the general contractor in charge of building the OL3 power plant as a whole, the consortium of AREVA NP and Siemens PG, is shown in Figure 4.15.

By way of example, some of the governing tasks in these areas are listed below: Quality and environment

— Checking subcontractors’ quality documents

— Auditing subcontractors’ staff and own staff

— Monitoring the work of the other departments, to check that they comply with the quality assurance plan

— Managing and leading the quality assurance teams for the individual trades

— Training site staff in quality assurance

— Assisting the construction and engineering teams in coordinating specifically with the client and the authorities

Project control

— Bookkeeping

— Contract management for subcontractors’ contracts.

— Assisting subcontractors commercially

— Monitoring the subcontractors budget

— Invoicing (to client)

Logistics

— Organising delivery of plant components to site Communications

— Marketing/public relations

— Organising site inspections

— Producing presentation documents

— Producing and approving site photos

Human resources

— Dealing with staff employed on site Commissioning

— Managing and coordinating system commissionings Construction

— Coordinating construction and installation

— Organising and coordinating building construction sections, installing components

Engineering

— Coordinating schedules

— Producing working documents

— Checking subcontractors’ working, concreting and installation drawings

— Producing amendments to drawings

Health and safety

— Producing safety at work instructions for use on site

— Checking safety at work on site

— Reporting involved

Contract management

— Drawing up subcontractors’ contracts

— Negotiating subcontractors’ contracts

— Administrating client’s contract

Time scheduling

— Verifying that subcontractors’ timetables match project timetables

— Assisting construction department with producing specific coordination timetables

The tasks and communications paths between building management, client and subcontractors are shown in Figure 4.16.

Fig. 4.16 Tasks and communications paths in project management

With reinforced concrete containments with steel liners, the reinforced concrete structure ensures the structural integrity, and the steel liner the gas-tightness. A reinforced concrete containment is about as strong as a pre-stressed concrete one if the stressing steel is replaced with the concrete steel in proportion to their respective yield stresses. With the massive concrete cross-sections usually found in building nuclear power plants, this can be done without further ado.

The steel liner is anchored to the concrete structure via headed studs and/or steel sections so that a steel composite construction exists once it is completed with this concept; but the expansion of the steel liner and stresses on the laminate are less critical, as there is no pre-stressing. The reinforced concrete structure also enables a thicker steel liner to be used. Increasing the inherent rigidity of the steel liner makes it easier to install, and improves its strength and hence its integrity. As with a pre-stressed concrete containment, the design can be based on DIN 25459 [16]. The steel laminate effect must be considered in particular here, especially if using relatively thick steel liners, as with the non-pre-stressed containment of the KERENA BWR reactor model (steel liner t = 10mm).

We will now look in outline at the waterproofing concept selected at the OL3 nuclear power plant in Finland.

Buildings always conduct their loads via base slabs into the underlying rock. The difference in heights between the rock excavated and the underside of the building floor slab, which may be considerable in some cases, is made up for by using concrete with light constructive reinforcement.

The nuclear island structures below the 0.00 m level are made partly as white tanks, restricting crack widths accordingly (<0.2mm in part). A largely stress-free support for the main buildings was achieved, and waterproofing was also provided against seepage and stratum water which can get to the structure via cracks and spaces in the rock in the shape of an external black waterproofing on all vertical wall surfaces from below the top of ground height up to +0.60 m, and all horizontal upper structural surfaces, such as upper duct connections below ground height.

The waterproof is built up as follows:

Waterproofing on walls below ground surface level

— plastic-modified bitumen undercoat 0.2-0.3 l/m2 (cold)

— one layer of plastic-modified bitumen strip.

Additional thermal insulation

— Polystyrol XPS foam, compressive strength >180kN/m2

— thickness depending on where applied, between 100 and 160 mm.

Waterproofing upper structural surfaces below ground surface level

— sloping concrete at least 2%, at least 100 mm thick, with constructive reinforcement (steel mat c/c100, d = 6 mm),

— plastic-modified bitumen undercoat 0.2-0.3 l/m2 (cold)

— one layer plastic-modified bitumen coating.

Additional thermal insulation

— Polystyrol XPS foam, compression strength >250kN/m2

— thickness 140 mm.

The equalising concrete has drains fitted to drain the joint between it and the rock. This drainage was tailored to suit the local rock structure (depths/interfaces): it leads any water which occurs into the drains surrounding the building, which in turn lead it to the pump shafts from which the water is then pumped out.

The drains around the building consist of perforated PP pipes DN 2 x 110 or 200 in drainage gravel 6/16, enclosed in geotextile wool. In areas concreted against vertical rock surfaces, drainage mats are used to ensure that the rock surface is drained.

As part of the approval process to give the go-ahead to construct and operate a nuclear plant, it must be shown that the necessary safety precautions have been taken, in accordance with the current state of the art of science and technology. The evidence required must be considered deterministically, in the light of a reasonable safety strategy, as laid down by the banded safety strategy in Table 2.2, for example.

While plants are operating, the competent atomic supervisory authority monitors the state of their systems and how they are being operated, to verify that these comply with the conditions of the approval order. In addition to these checks, in the operating phase, regular safety status presentations must be made considering whether new safety findings from operating experience, safety studies and research and development should be incorporated.

In Germany, safety status is monitored by periodical safety reviews, or PSUs in German. These must be held every ten years, and cover:

— Deterministic safety status analysis (DSA) in the shape of a safety target oriented review of a plant’s safety status including how it is managed operationally and analysing its operating experience

— Probabilistic safety analysis (PSA) [8]

— Plant safety strategy review.

5.1.1 Leaks and ruptures of pipes

The impact of leaking/broken pipes must be taken into account in accordance with the underlying safety strategy for a plant. German RSK guidelines [5], for example, require a leak of 0.1 A (where A is the open cross-sectional area of the pipe in question) to be assumed in relevant pipes, such as main coolant pipes, for example, leading to jet loads and differential pressures in combination with increasing temperatures.

Jet loads are caused by the impact of the oncoming medium, and act as concentrated loads on the structural member involved. They are expressed as load-time functions or as static equivalent load, stating the impact area, load distribution and impact angle. Figure 5.1 shows the idealised function of jet load over time.

Leaks or ruptures in pressurised pipes induce pressures in the spaces affected which act as loads per unit area over time on the structural members and pressure differentials. What has to be taken into account here is how the differential pressures behave over time, as Figure 5.1 shows in idealised form.

Design and Construction of Nuclear Power Plants. First Edition.

Rudiger Meiswinkel, Julian Meyer, Jurgen Schnell.

© 2013 Ernst & Sohn GmbH & Co. KG. Published 2013 by Ernst & Sohn GmbH & Co. KG.

Combined with the jet loads and pressure forces involved, leaking or broken pipes can increase room temperature and hence structural member temperature. The tempera­tures in the structural components affected increase subject to a time delay, so that the temperature curves in those structural members must be recorded to obtain a realistic overlap of the jet loads or differential pressures with their associated temperature effects over time.

7.1.4 History

Anchors come in many shapes and sizes, from domestic rawlplugs to heavy load anchors carrying several tons.

The first industrially made anchors were invented by John Joseph Rawlings in 1910. The UPAT company first made similar anchor of hemp string with metal sleeves in 1926. Fritz Axthelm of NIEDAX applied for the first patent for a metal spreading anchor two years later (DRP 555 384).

In building nuclear power plants, metallic anchors were also an essential structural element right from the start for attaching light to moderately heavy system parts and components. Path-controlled spread anchors of the Spit-Gold, TiFiX and Hilti-HKD types were installed in large numbers in accordance with the manufacturers’ guidelines. The Liebig company supplied the Liebig safety anchor the first force-controlled force — spread heavy-load anchor used in German nuclear power plants. The first precursor of a General Technical Approval was issued by what was then the IFBt, today’s DIBt, in 1972. This was the first anchor ever to have a General Technical Approval, issued in 1975. The Liebig safety anchor was first used in nuclear power plants in 1973, due to the particular requirements involved for attaching safety-related anchorings, based on approvals on a case-by-case basis. Liebig then released the Ultraplus, the first displacement-controlled anchor on the market. Together with the FZA anchor devel­oped by the Fischer company, these two path-controlled anchor types were a major step forward in attachment systems in nuclear power plants.

Static verification for the anchoring with anchors was made until then as per approvals or consents on a case-by-case basis, but the so-called Kappa-method from 1988 and the introduction of the DIBt Guideline ‘Design methods for anchors for anchoring in concrete’ [87] based on the so-called CC method in 1993 revolutionised the verification of attachments in concrete.

In 1998, with the aim of creating a uniform evaluation basis for awarding consents in all German Federal States, the DIBt published the guidelines on ‘Using anchors in nuclear power plants and nuclear installations’ [63]. These guidelines recommended that only form lock anchors should be allowed for attaching safety-related components and system parts. Based on these guidelines, the first General Technical Approvals were issued, for Fischer’s Zykon-Bolzenanker FZA-K [88] in 1999 and for Hilti’s HDA undercut anchors [89] in 2000. These two approvals, and their current versions, provide a uniform design basis for the respective anchor models for all German nuclear power plants.

In June 2010, the DIBt published new guidelines entitled ‘Guidelines for anchor attachments in nuclear power plants and other nuclear installations’. This supersedes the 1998 version, and provides more differentiated details of the tests to be conducted, methods of verification and handling for anchors and anchoring to be approved for safety-related attachments subject to particularly high requirements in the event of accidental actions. It does not limit itself to undercut anchors so that other types of anchors may be approved for use in nuclear installations.

A KTA status report on allowing for the particularities of nuclear installations is expected in the near future.