Nuclear Power Plants--Design + Construction: Approval aspects

1. Atomic energy and construction law

Building, operating and making major changes to nuclear installations must be approved under atomic energy law. The government approval process used depends on the national law requirements involved in each case, so varies from one country to another.

Before they can be allowed to build and operate nuclear installations, there are a number of basic requirements that applicants and operators have to meet:

- Applicants and operating managers must be reliable and expert.

- Those working at the company must know how to run it safely, what the potential risks are and the safety precautions required.

- Know what precautions are required under the state of the art of science and technology to prevent erection and operating the plant causing damage.

- Know what protection is required against anomalies and other effects by third parties.

- Keep water, air and soil clean in the public interest.

In Germany, the legal framework for using nuclear energy for peaceful purposes is provided by the Atomic Energy Act and regulations issued pursuant to it. The safety goals and measures are laid down in Section 2.5 of the Atomic Energy Act. These are clarified specifically by Atomic Energy Act regulations and internal administrative rules and guidelines, such as the guidelines for PWRs or design basis accidents guidelines. These guidelines cover the design basis accidents to be considered and managed; they also specify the requirements of the radiological protection ordinance.

The building structures required to meet the safety targets, which are therefore classified as safety-related, have to meet not only the requirements of construction law but also those of the Atomic Energy Act. That means both planning permission and permission under the Atomic Energy Act are required in Germany. To be approved under Atomic Energy Act, constructors/operators must show that they have taken the necessary precautions against damage in accordance with the state of the art of science and technology. Safety-related building structures must therefore meet not just the conventional requirements of construction law but also additional safety requirements in line with the state of the art of science and technology.

2. Interface between plant and structural engineering

The inspection required to be approved under the Atomic Energy Act includes a holistic examination of the safety precautions of the building structures. This involves defining the interface between the building structures (structural engineering) and plant components (plant engineering) and hence the distinction between construction and atomic energy law. Generally speaking, plant components such as pipes and containers are part of the building, so that the fastenings in each case (anchor plate) constitute the interface. In exceptional cases, this interface will have to be defined in the official planning process.

Each interface must have an interface document which, amongst other things, specifies the loads calculated from the plant technology and the structural member or structure in each case. Such documents are generally called structural design requirements. They are first considered as part of the atomic energy law terms, covering systems engineering aspects, and then used as the basis for the construction assessment.

3. Periodical safety reviews

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 PSU ¨ sin 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 analyzing its operating experience

- Probabilistic safety analysis (PSA)

- Plant safety strategy review.

4. Planning and design requirements

4.1 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 organization 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.

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 Center (ISSC) was founded in Kashiwazaki, Japan, in 2007.

4.2 European catalog of requirements

Many new nuclear power plants are currently being built or are at the planning stage worldwide, especially in China, Japan and the USA; however, there are also numerous newbuild projects at the planning or construction stage in Europe, such as in England, France and Finland. For these European projects, the European nuclear power plant operators have drawn up a catalogue of requirements in the shape of the European Utility Requirements (EUR).

The EUR relates to nuclear power plants as a whole, and includes details of specific nuclear power plant actions to be taken into account when designing them, such as earthquake design spectra for minimum earthquake design requirements and specific load/time functions to protect against aircraft impact. The EUR also includes basic design criteria. In terms of construction design, these criteria assume basically that Eurocode standards will be observed.

The EUR is intended to ensure that the various nuclear power plant providers can rate and offer their products based on them. Corresponding qualifications have already been drafted for system strategies for Europe, such as EPR or AP1000.

4.3 Safety standards of nuclear safety commission

Nuclear installations must meet stringent safety requirements, and so require design strategies accordingly, but which are not covered by conventional plant and construction rules. In 1972, therefore, the Federal German Ministry of Education and Research (BMBW, now the BMU or Federal Ministry for the Environment, Nature Conservation and Nuclear Safety) set up the Nuclear Safety Standards Commission (KTA), on the model of the German steam boiler committee. The Nuclear Safety Standards Commission has assumed responsibility for drawing up safety rules in nuclear systems and promoting their use, through bringing about consistent opinions amongst specialists from those who build, install and operate nuclear power plants, inspectors and the authorities.

Safety Standards of the Nuclear Safety Commission (KTA safety standard) lay down safety requirements, compliance with which provides the precautions required when building and operating plants in accordance with the state of the art of science and technology. These precautions required under the Atomic Energy Act are necessary to achieve the safety targets as laid down in the Atomic Energy Act and radiological protection ordinance and in more detail in the safety criteria for nuclear power plants and design basis accidents guidelines.

The KTA safety standards cover more than 100 fields which include all the issues relevant to nuclear technology and relevant disciplines. They are reviewed regularly (every five years) to see if they need revising: that means more than 50 proposed rules are currently being considered.

KTA safety standards must be regarded as mandatory overall standards in Germany which must always be complied with. They can be varied, in theory, but that means those involved (nuclear regulators and inspectors) would have to reach a consensus viable in law. KTA safety standards are publicly available, and are not used in Germany alone: there are many countries, especially in Europe, that accept these codes or would even like them to be used for their nuclear installations, so that KTA safety standards are largely available in English also.

4.4 DIN Codes

The codes of DIN, the German standards institute, are generally accepted as codes of the art which are reflected in the KTA safety standards. These standards do not normally apply to nuclear facilities, or are even expressly excluded from applying to them; so the DIN has set up a nuclear technology standards committee, now standards committee materials testing (NMP) specialist area 7 - nuclear technology, which is responsible for producing and updating specifically nuclear standards.

As far as construction technology is concerned, there are two of these codes whose status means that they are also applied internationally: DIN 25449 and DIN 25459. DIN 25449 covers designing reinforced concrete and pre-stressed concrete components to allow for the rare effects from inside (EVI) and outside (EVA) as safety levels 3 and 4. DIN 25459 also lays down rules for designing safety containments using reinforced and pre-stressed concrete. Due to the integrity requirements involved, such containments also require additional claddings such as steel or plastic liners; this standard also deals with their design, including laminate effects with the reinforced or stressed concrete design. DIN 25459 only exists to date as a pre-standard, which is currently being revised and should be published as a fully fledged standard in the near future.

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