The cooling water supply structures form part of the safety-related structures of nuclear power plants, as they still have to ablate residual heat even when a station is not in operation or experiencing any incidents.

The cooling water intake structures, usually right on the bank of a river or on the coastline, in particular, are subject to high requirements in terms of protecting property and being designed to withstand external actions. Being designed to cope with explosions internally, or external aircraft impact, leads to large buildings with extremely thick walls. Alternatively, if they are not so designed, there are discussions as to whether an adequate flow of water can still be guaranteed in the event of a partial collapse (after an aircraft impact, for example). In more recent plants, this has led such buildings to be arranged redundantly, spaced at minimum distances apart, so that they do not need to be designed to withstand an aircraft impact.

5.2 Underlying standards

When designing structural systems for nuclear power plants in Europe, the verifications of stability and serviceability for purpose must be conducted based on Eurocode standards with the semi-probabilistic partial safety concept. Eurocode standard prin­ciples are therefore followed in the specific rules for nuclear power plants, consisting of the KTA rules [14] and DIN standards. KTA status report KTA-GS-78 [51] and the corresponding new DIN 25449 [15] are of fundamental importance here.

KTA status report KTA-GS-78 provides recommendations to be used in the partial safety concept required for designing building structures in Europe. These recommen­dations, which focus particularly on categories of requirements specific to nuclear power plants relate to both reinforced and pre-stressed concrete and to steelwork. The new DIN 25449, which is guided by the recommendations of KTA status report KTA — GS-78, includes specific definitions of specific extraordinary actions involved in nuclear power plants and details of proofs and design concepts for concrete, reinforced and pre-stressed concrete structural members.

Apart from KTA status report KTA-GS-78 and DIN 25449 with their fundamental design requirements, KTA 2201.3 [42] and DIN 25459 [16] should also be mentioned. KTA 2201.3 gives details on designing nuclear power plant structures to withstand earthquake effects and DIN 25459 governs designing containments, covering possible containment variants — reinforced concrete and pre-stressed containments with liners.

Structural waterproofing must be designed to withstand the stresses acting immediately on it. These include, on the one hand, the permanent compression, composed of water pressure and ground pressure or soil pressure as the case may be, and on the other hand the cracking in the structures bearing on the structural waterproof. As the manner in which the reinforced concrete structures which carry the structural waterproof crack depends on their design: there is a connection between designing those reinforced concrete structures and the design of the structural waterproof.

When designing structural waterproofing, the behaviour must also be considered at pressures which are significantly greater than the limits stated in the rules. More extensive requirements of structural waterproofs in nuclear installations also result from the special load cases mentioned above. The stresses that these cause on structural waterproofs must be determined (cf. [92], Section 4.1.1 et seq.).

Design rules for structural waterproofs for bridging cracks are defined in [93]. They apply to stress cracks not more than 0.5 mm at their point of origin and opening gradually over long periods of time up to 5 mm. These design rules cannot be used for cracks several millimetres wide that open spontaneously or open and close rapidly due to the risk of the waterproof structure suffering fatigue cracks, even though tests on some waterproofing structures have proven that a structural waterproof is able to bridge such cracks to a limited extent (cf. [92] and Section 4.1.6).

A number of options are available to cover this energy demand: they can basically be divided into two groups, thermal power plants and power plants running on renewable energy sources. Thermal power plants break down into oil-fired, gas-fired, lignite-fired, hard-coal-fired and nuclear power plants. Apart from hydroelectric power, the main renewable energy sources are wind power, solar energy, biomass and geothermal energy.

Different electricity production options are rated differently in environmental and economic terms, but the difference in generating power (a 1000 MW coal-fired power

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.

Hydroelectric power Natural gas

Coal

Nuclear energy Other renewable energies

plant is equivalent to 200 offshore or 400 onshore wind farms, for example) makes it clear that, essentially, the only way that rising world energy demand will be met is by using powerful cogeneration plants.

As Figure 1.2 shows, even though renewable energies are set to expand enormously in the coming decades, the capacity they actually generate will only grow slightly, so that their percentage share of total electricity generated will actually fall. The forecasts by World Energy Council (WEC) and IEA also say that even after 2020, more than 70% of energy will be obtained from coal, oil and gas, and the share of nuclear power will increase considerably. As well as output, having a reliable electricity supply is also extremely important, which also shows that thermal power plants are essential. If we look at a typical day load curve as in Figure 1.3 — broken down into baseload, average load and peak load — it is clear that thermal power plants are needed for baseload particularly.

Work on nuclear power plant projects is subject to strict quality assurance requirements.

With the OL3 project, as well as the usual design documents, the designers also produced governing documents on quality assurance which were checked by the client and authorities:

— Work specifications, such as defining specific works, indicating training required

— Quality control plan — checklists defining what checks are to be conducted and how, and stating who is responsible in each case

Based on these documents, the contractors involved produce work plans, which essentially extrapolate the designers’ quality control plans with specific construction aspects (materials, work rates, etc.).

Work plans are produced based on the overall quality assurance system, referencing the underlying performance documents. In substantive terms, they include the working resources and procedures required to perform tasks, the project organisation stating who is in charge of performing work and what to do in the event of problems. They also include risk assessments on individual relevant issues.

7.1 Fastening types

In nuclear power plants and other nuclear installations, a basic distinction is made between safety-related and non-safety-related fastenings. Safety-related fastenings are those used to attach safety-related structural and system components. In nuclear power plants, safety-related structural and system components are those required to meet safety goals (controlling reactivity, cooling fuel elements and containing the radio­active materials) and to limit radiation exposure as part of incident management.

Important safety-related fastenings performed using anchors also include those to which structural and system components are attached which are not safety-related in themselves, but which could cause unacceptable effects on safety-related structural and system components in case of their failure.

Today, that means that the fastenings used in nuclear power plants and other nuclear installations are overwhelmingly safety-related ones. These fastenings can be divided into cast-in fastenings and subsequently mounted (or post-mounted) fastenings.

7.4 Overview

To ensure that nuclear power plants are safe and reliable, the system components and structural systems must be built to the quality required. Life cycle management is generally defined as a combination of ageing management and financial planning. Ageing management is thus part of life cycle management, and covers everything that the operators need to do to ensure that their nuclear power plants remain safe as they get older. The fundamental principles here are laid down by KTA 1403 [106] which gives rules for ageing management at nuclear power plants.

The main role of ageing management in structural installations is to map what may happen to building materials as they age and prevent their having harmful effects specifically and effectively. These ageing mechanisms are also known as physical ageing: so ageing management deals primarily with physical ageing, with measures to ensure permanence and in particular the structural safety of building structures in use.

The term life cycle management is used instead of ageing management if the focus is on financial aspects as well as structural safety. Life cycle management thus goes beyond ageing management: as well as physical ageing, it also includes conceptual ageing and technological ageing (see Figure 9.1).

Conceptual ageing covers changes to design standards due to introducing new rules such as standards and guidelines with altered requirements or changes to safety philosophy. These changes must be assessed to see how far they are relevant to the structural safety of buildings designed to the ‘old’ rules.

Technological ageing covers changing findings in terms of possible harmful operating mechanisms and material characteristics. It also covers innovations in verification methods (changes to calculation standards) and testing and calculation methods. It is relatively unimportant in structural engineering compared with plant engineering, as the characteristics of the principal materials, concrete, reinforced concrete and building steel, have remained fundamentally unchanged for the past 40 years.

Like life cycle management, ageing management involves maintaining buildings as knowledge-based preventive maintenance. This preventive maintenance covers the different measures involved in terms of maintenance, inspection, repairs and strength­ening as shown in Figure 9.2.

3.1.1 IAEA Rules

Given the potential threat of nuclear weapons, but particularly in expectations that atomic energy would be used peacefully, the International Atomic Energy Agency (IAEA) was set up at the initiative of the United Nations (UN) in 1957. The IAEA has its headquarters in Vienna, and is an independent international organisation with close links to the UN. It sees its task as making it possible to use nuclear energy, subject to the necessary safety requirements, and ensuring technology transfer.

The IAEA lays down safety requirements for building and operating nuclear installa­tions, assisted by international experts, and is constantly updating these requirements. Once agreed with the countries that operate nuclear installations, these are published as IAEA Safety Standards (see [9-12] for example). Individual countries can then use them as they stand or as the basis for further-reaching national rules, such as German nuclear safety standards (see Section 3.4.3).

One particular area that the rules of the IAEA focus on is earthquakes respectively seismic risks. It has published a number of standards, including methods for determin­ing seismic load assumptions, earthquake-proof design and the earthquake safety of existing nuclear installations. The IAEA also provides advice in cases where nuclear power plants are hit by earthquakes. Calling in experts as required, it assesses damage, considers whether plants can continue to operate and in some cases makes new findings on earthquake risks. To improve this work, the International Seismic Safety Centre (ISSC) was founded in Kashiwazaki, Japan, in 2007.

Potential problems and incidents when carrying fuel elements must be considered in the course of the fuel handling process. This mainly involves the consequences of dropping a load, which could happen while handling fuel elements in the fuel element storage pool, including loading fuel element containers or moving them around in the reactor building or interim fuel element storage. In an interim fuel element storage, for example, the possible effects of fuel element containers being dropped must be covered which could occur in the delivery area when lifting fuel element containers off carrier vehicles or in the storage area itself when moving fuel elements by crane.

Other internal installation events could include fires, explosions and flooding which could also occur. This calls for specific plant studies to show where such events could occur and what might be the impact of those events in terms of differential tempera­tures, pressures and flooding heights.

Anchor attachments may be divided, depending on how they work, into undercut, spread and composite anchors although there are also anchor system that combine two of these methods, such as composite spread anchors.

Undercut anchors can be divided into self-undercutting anchors and those in which the undercut is made in a preceding step. The preceding undercut is made using a special undercut tool or a special drill, swinging the drill out in a circular motion. The anchor is then placed using a setting tool (e. g. Fischer FZA-K, Figure 7.6). With self­undercutting anchors the undercut in the concrete is made by hard metal cutting at

the anchors sleeve (e. g. Hilti HDA Figure 7.7). Undercut anchors transmit tension loads, even if there are wide cracks, such as in the event of an earthquake, as they are anchored in a form lock way within the concrete: so the undercut must be inspected very carefully. With the products available on the market today, the undercut can be checked via coloured markings which must be visible if the anchor is installed correctly.

Spread anchors can also be divided into path-controlled and force-controlled (or even torque-controlled) anchors. Path-controlled spread anchors are installed by being hammered in or driven in by machine and then checked by measuring the set depth. Anchors can be marked to ensure they are installed to the set depth required. Force — controlled spread anchors are inserted using a torque wrench, which applies the tensile or spread force required for the anchor to grip as it should (Figure 7.8).

Spread anchors transmit tensile loads via the grip between the spread anchor and the surrounding concrete.

Composite anchors consist of a composite mortar containing an embedded metal component. The composite material may be made of synthetic mortar, cement mortar or a mixture of the two. In practice, cartridge and injection systems are used. With cartridge systems, glass or synthetic capsules are fitted into the borehole. When the anchor is inserted, the cartridge is destroyed and the chambers it contains are mixed with the two components of the mortar.

Injection systems consist of the metal component to be inserted and a two-chamber injection cartridge. The composite material is mixed when it is expelled from the cartridge and injected into the borehole. The metal component is then inserted by hand or mechanically, depending on the anchor system involved.

Composite anchors work via the grip between the metal part and the composite mortar and the grip between the composite mortar and the borehole wall. The grip with the

concrete means that great attention must be paid to cleaning the borehole particularly thoroughly in accordance with installation instructions.

Composite anchors can also include combinations with undercut or spread anchors (Figure 7.9).

The loads in a composite spread anchor are transmitted via a combination of bonding and spreading, in which the spreading is also achieved through its particular shape. This enables it to bridge even broad cracks up to 1.5 mm and shows a ductile load-bearing behaviour.

The load-deformation diagram for a composite spread anchor shows the wavelike course of the load very well. This is caused by the individual spread cones penetrating into the composite mortar. With smaller crack widths, all spread cones in a anchor can be assigned to the individual waves in the load-deformation diagram.

With undercut composite anchors, the load is transmitted by a combination of the bonding of mortar to the borehole walls and the mechanical form locking of the mortar in the undercut of the concrete.