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E.ON’s nuclear decommissioning programme – the journey so far

Author : Alan Franck, Editor, Hazardex

15 April 2015

In the autumn of 2010, the German federal government extended the operating lives of all of the country's nuclear power plants (NPPs). However, the Fukushima incident in March 2011 led Germany to reverse its energy policy. The amended Nuclear Energy Act, which took effect in July 2011, mandated the immediate shutdown of eight NPPs and significantly curtailed the operating lives of the remaining nine. All of the latter will now be shut by end-2022.

Germany’s experience with the decommissioning process is thus extensive and its efforts to ensure best practice in the sector may have useful lessons for other operators of nuclear plant and organisations involved in the sector.

This article, drawing on information provided by Germany’s largest utility E.ON, looks at the practical aspects of nuclear decommissioning in Germany, with specific focus on the group’s plans for the Isar 1 nuclear power plant in Bavaria, and at some of the longer term ramifications of the process.  

E.ON says it accepts the decision by Germany's political majority to accelerate the phaseout of nuclear power and the transformation of the country's energy supply system. But even under the new circumstances, nuclear power will remain in the country’s energy mix until 2022.

The four NPPs for which E.ON has operational responsibility must be withdrawn from service at the latest by December 31 of the year indicated:

•  Grafenrheinfeld (2015)

•  Brokdorf (2021)

•  Grohnde (2021)

•  Isar 2 (2022)

E.ON also operates, and has a majority stake in, three NPPs in Sweden: Oskarshamn 1, 2, and 3. The installed capacity of the NPPs in Germany and Sweden for which it has operational responsibility totals about 8 gigawatts (GW). Two of the NPPs in Germany (Würgassen and Stade) were withdrawn from service several years ago for commercial reasons and are currently being dismantled.

The group has minority stakes in other operational German NPPs that will be closed over the next seven years, as well as in Fennovoima, a project company that plans to build a next-generation NPP in Finland.

The timetable for the shutdown of the other five commercial reactors currently in operation in Germany is as follows:

•  Gundremmingen B (2017)

•  Philippsburg 2 (2019)

•  Gundremmingen C (2021)

•  Emsland (2022)

•  Neckarwestheim 2 (2022)

Twenty-seven German nuclear power plants - including experimental, prototype and demonstration facilities built in the 60s and 70s – have been decommissioned to date.

According to Euronuclear.org, in August 2014 Germany’s nine operational nuclear power plants had an electric gross output of 12.69 GW. In 2013 they generated 97.3 billion kWh of electricity. The unit and energy availability amounted to 90%.

Decommissioning of E.ON nuclear power plants

Under the amended Nuclear Energy Act which came into force in July 2011, eight of the German nuclear power plants were shut down immediately and the remaining lifetimes of the other nine plants were significantly shortened.

E.ON’s Isar 1 and Unterweser NPPs were disconnected from the grid in March 2011, since when they have been in shutdown operation. The group plans – subject to the outcome of the constitutional proceedings against the 13th Amendment to the Atomic Energy Act – to decommission and dismantle the two nuclear power plants. It applied for the appropriate permits for the two plants in May 2012.

Just as in the operation of its remaining nuclear power plants, the group says safety will be the top priority in decommissioning and dismantling.

Legal framework

In Germany, the construction, operation and decommissioning of nuclear power plants are governed by the Nuclear Energy Act.

As in the case of construction and operation, a permit is required for the decommissioning of a nuclear power plant. Decommissioning is subject to a strict official approval procedure with the participation of the public in order to protect the public and the environment against radiation. An environmental impact assessment is carried out as part of the approval procedure.

The German Nuclear Energy Act provides for two approaches to decommissioning.

1.  Demolition following safe enclosure

This variant provides for the demolition of the plant following the construction of a safe enclosure. With this decommissioning strategy, a nuclear facility is transferred to a condition with low maintenance requirements for a period of about 30 years, after which it is finally demolished.

2.  Direct demolition

With this variant, the plant is demolished immediately. The dismantling of all systems and equipment starts directly after the plant has been disconnected from the network. Normally, demolition is completed in several phases. The number of phases depends on the application submitted by the operator.

Demolition materials

Most of the materials are sorted during the demolition process so they can be recycled. For example, reinforced concrete components are often shredded on site. In this process, the steel reinforcement is separated from the concrete. The rubble can then be used for road building while the steel scrap is used in steel production.

Cleaner than clean

Most of the material produced by the dismantling of the control building is only subject to surface contamination (radioactive contamination).

In order to facilitate decontamination, a special non-porous coating was applied to the surfaces of various components during construction. These components can normally be decontaminated by thorough washing or scrubbing. Contamination that has penetrated the material through cracks and pores is removed mechanically or chemically using high-pressure water jets, ultrasonic cleaning and jets with steel granulate.

Waste reduction

As a result of thorough decontamination, only a very small proportion of the material produced by demolition needs to be disposed of as radioactive waste. In order to further minimise the storage volume needed for radioactive waste, volume reduction technologies such as high-pressure compaction are used.

About 98% of the total mass can be released and recycled. Only about 2% needs to be disposed of as radioactive waste. This is conditioned during dismantling and packed so that the containers can be handled and stored safely.

Demolition volumes

Taking the example of Würgassen nuclear power plant, out of a total demolition volume of 255,000 tonnes, 97% can be released, 1% can be reused and 2% is radioactive waste

The Isar 1 project

Direct demolition in two phases

E.ON intends to apply the direct demolition procedure to Isar 1. It is assumed that not all the fuel assemblies exposed to radiation will have been removed from the plant at the beginning of demolition work.

It is currently planned to complete demolition in two phases. Separate permit applications under the Atomic Energy Act have been made for each of the phases. When these permits have been issued, the work in the two phases may also be carried out in parallel, provided that the various operations do not have an adverse impact on each other and that the work is carried out in accordance with the protection objectives as well as radiation protection, health and safety, and fire protection requirements.

Basic principles

The top priority in the planning and implementation of the decommissioning and demolition project is the protection of employees, the public and the environment.

Any impact of the decommissioning and demolition work on fuel assemblies in the fuel pool will be prevented until the disposal of the fuel assemblies has been completed.

The quantity of radioactive waste produced (see Demolition materials above) will be minimised.

Procedure

When demolition work starts, the removal of fuel elements exposed to radiation and individual faulty fuel rods will not have been completed. At this stage in the project, demolition work will be limited to systems, components and areas not linked in any way with the safety of the systems used for the cooling and storage of fuel assemblies and the fuel pool (freedom from impact).

For the demolition of the Isar 1 nuclear power plant, infrastructure for the processing of residual materials and waste will be established within the existing controlled area of Isar 1. This infrastructure will be designated as a residual material processing centre and is also to be used for the later decommissioning of the Isar 2 plant. The main components of this infrastructure will be installed in the generator building.

Working areas will be equipped and established in accordance with the applicable health and safety, fire protection and radiation protection requirements.

Demolition phase 1

In this phase, demolition work will focus on

·  systems and plant components with no safety significance for this plant status,

·  reactor pressure vessel internals and

·  containment internals.

The systems to be dismantled inside the containment include piping systems, such as feedwater piping, fresh steam piping, shutdown cooling piping, safety and pressure relief valves with associated piping, etc.

In addition, work platforms and systems for the later demolition of the containment will be installed in the containment.

Demolition phase 2

The demolition work of phase 1 will be continued. At the same time, phase 2 work will start. This will include

·  the demolition of the reactor pressure vessel,

·  further clearance and demolition of the containment,

·  the demolition of the reactor shield, and

·  the radiation inspection of building structures and areas that are not to be used for the decommissioning of Isar 2.

Buildings and building areas that have been inspected and released (i.e., the controlled area consisting of the reactor building, turbine building and decontamination building) will be blocked off, sealed (if appropriate) and secured to prevent any risk of re-contamination.

Demolition of buildings

The conventional demolition of buildings which have been released in accordance with the Nuclear Energy Act is outside the scope of the atomic energy law permits for phase 1 and phase 2 of the Isar 1 decommissioning project.

Disposal

Most of the material produced during demolition work in the controlled area of Isar 1 will not be radioactive or radioactively contaminated. This material will mainly consist of metal scrap and rubble.

Cutaway of Isar 1
Cutaway of Isar 1

Residual radioactive materials from the dismantling of the power plant will consist solely of waste with negligible heat development (low-level to medium-level materials). These materials will be identified prior to dismantling and disposal objectives will be defined. These objectives include unrestricted release (i.e. the parts can be reused or recycled without any restrictions), release for recycling or disposal (transfer to landfills), supervised recycling in the atomic energy industry, direct reuse within the scope of another atomic energy permit and storage in a final storage facility for low-level and medium-level radioactive waste.

The various material groups will be collected separately. If dismantled plant components need to be disposed of as radioactive waste for radiological reasons, they will be conditioned in accordance with the approved acceptance conditions of the Konrad final storage facility. Waste containers will be stored at an intermediate storage site (e.g. the Mitterteich intermediate storage site) before they are transferred to the Schacht Konrad final storage site.

Material which is not radioactive or radioactively contaminated may be used or recycled immediately in other sectors. Most metal components will be returned to the material cycle as scrap. Concrete waste from the demolition of buildings may be used in the construction industry.

Estimates of demolition volumes for Isar1 are that about 98% of materials from controlled areas can be released.

Estimates of demolition volumes, Isar 1

The mass of materials to be disposed of was estimated on the basis of previous experience with the decommissioning of nuclear facilities.

The total mass of waste from the controlled area (reactor building, generator building plus internals, decontamination building) will be about 224,000 tonnes.

·  Of this total, 200,000 tonnes represent the mass of buildings which can be released. The demolition of buildings is not subject to the atomic energy permits for phases 1 and 2 and will be completed conventionally.

·  A further mass of 20,600 tonnes may be released in accordance with Section 29, Radiation Protection Ordinance or re-used in the atomic energy field.

·  There will be about 3,400 tonnes of radioactive waste. This waste will be prepared for final storage at the Schacht Konrad repository.

Radiation protection

The protection of the public, employees and the environment will be the top priority in the planning and implementation of decommissioning.

Approved discharges from the nuclear power plant will be continuously monitored and supervised by the competent authority. In addition, the surroundings of the nuclear power plant will be continuously monitored for radioactive materials.

The radiation exposure of individual person as a result of discharges from nuclear power plants is so low that it cannot be measured despite the use of the best measurement equipment available. It was therefore estimated on the basis of conservative assumptions.

For the remaining operation and decommissioning of the Isar 1 nuclear power plant, radiation exposure was calculated in accordance with the General Administrative Regulation issued under the Radiation Protection Ordinance.

Even if full use is made of all the discharge limits applied for during decommissioning and demolition, the radiation load in the surrounding area will still be significantly below the statutory limits.

Control rod mechanism at bottom of pressure vessel
Control rod mechanism at bottom of pressure vessel

As in power generation operation, the actual discharges will be considerably below the statutory limits and the effective radiation burden on the surroundings of the plant will only reach a few percent of the statutory limits.

Safety at all times

Protective measures will be taken during the demolition and remaining operation of the Isar 1 nuclear power plant to ensure that the maximum radiation exposure in the event of an incident laid down in the Radiation Protection Ordinance is not exceeded in the surroundings of the plant.

Extensive precautions have been taken to avoid any incidents and to limit the impact of any incidents. These precautions include regular inspections of all the equipment, protection systems and standby protection systems required, a barrier system for the retention of radioactive materials and shielding against radioactivity.

In addition, incidents which could theoretically occur as a result of internal or external impacts have been considered on the basis of conservative assumptions. The radiological consequences of such incidents in the surroundings of the plant have been assessed.

Even in the event of the possible incidents considered in connection with the remaining operation and decommissioning of Isar 1, expected radiation exposure in the vicinity of the plant will still be far below the statutory limits.

Unforeseen events during decommissioning

The high safety level at Isar 1has been based on the solid, proactive basic design of the plant, according to E.ON. For example, the fuel pool is protected against external impact by a strong reinforced concrete enclosure. The reactor building where the fuel pool is located is even designed for protection against a fast-flying military aircraft crashing into the building.

The fuel pool is designed for the storage of all fuel assemblies for an indefinite period and offers the highest possible safety levels for residual heat removal via the existing cooling systems. The heat generated by the fuel elements is also very low (about 650 kW). The design of the Isar 1 nuclear power plant is therefore in accordance with the current safety criteria.

In connection with decommissioning, various possible scenarios have been considered and an incident analysis has been drawn up. The appropriate analyses have been carried out on the basis of conservative assumptions. This ensures, E.ON says, that every conceivable event has been covered.

E.ON’s experience

In the paper Best Practice in E.ON Decommissioning Projects*, E.ON’s Andreas Ehlert estimates a cumulative value for nuclear decommissioning projects of between 20 and 30 billion euros in Europe (excluding Russia) by 2030, with E.ON contributing 6.6 billion euros towards that total.

This huge potential market will provide many opportunities for engineering and other companies well into the future.

Ehlert says many decommissioning technologies are already fit for purpose, but further developments are needed in a number of areas.

E.ON's Grohnde NPP in Lower Saxony will be shut in 2021
E.ON's Grohnde NPP in Lower Saxony will be shut in 2021

These include improving standardisation and automation for work on and in reactor pressure vessels, introducing more flexible and intelligent tools, developing better decontamination techniques and improving standardisation and recycling options.

E.ON has gained substantial experience in the process through the direct dismantling of its Stade Pressurised Water Reactor and Würgassen Boiling Water Reactor NPPs over the past 15 years, with both now decommissioned. These will be followed by the nuclear power stations shut in 2011, with others joining the programme as and when they close over the next seven years.

The group’s expertise relies on a number of technologies that it has developed and mastered, as well as on qualified staff and established processes and practices, including radiation protection, surveillance, material and surface decontamination, and project and team management.

According to the group, a key aspect of any decommissioning project is the planning phase, starting from the backend, in particular the disposal of the radioactive waste. Critical path analysis is required to avoid any bottlenecks (related to easy-to-use technology, interference between parallel work packages, licensing or staffing aspects) in the project, and ensure that all phases run smoothly.

In terms of managing radioactive waste, the availability of repositories for high level waste on one hand, and in particular low and medium level waste on the other, is crucial. If these are not available in the timeframe of the decommissioning planning, intermediate storage facilities need to be available, and licensed to receive the waste from the decommissioning activities, otherwise the decommissioning activity may be delayed. The purchase and delivery of containers and casks licensed for the storage and transport of waste has to be planned and controlled carefully too.

In addition to planning, challenges exist in managing financial and human resources: as funds are based on current decommissioning cost estimates, project management is crucial to ensure that the work is performed within the expected budget.

From a human resource point of view, the challenge is to motivate staff who have worked part of their professional lives to maintain the existing asset. However, as decommissioning is the final end in the lifetime of the plant, the company has to develop career paths to keep staff motivated so that they will participate in the decommissioning project and remain within the company once the plant has been dismantled.

Conclusion

In an interview at the International Youth Nuclear Congress in July, 2013, Dr. Ralf Güldner, CEO of E.ON Kernkraft GmbH, emphasised the importance of decommissioning in the group’s future.

“We have already accumulated experience in decommissioning. In Stade and Würgassen our teams have developed specific skills and a broad knowledge of decommissioning. We intend to use this successful experience to good effect with our forthcoming projects.

“Our Centre of Competence for Nuclear Decommissioning coordinates these activities from Hannover. For the units shut down in March 2011, we need first to unload the fuel. This should be done by 2015 for Unterweser and by 2016/17 for Isar 1. Then we need to know under which conditions the waste will be sent to the final disposal and we need certainty about the commissioning of the final disposal site.

“So far, these decisions have not yet been taken by our government. As this clearly impacts upon our decommissioning strategy, we need clear messages and action from the German government.

“Decommissioning will become a core activity for our company. We will focus on our projects first, but we might develop this business externally too if we have enough resources to do so – perhaps through the creation of partnerships as we don’t have all the required capabilities in-house and will not take full responsibility over assets from other owners.”

* www.iaea.org/OurWork/ST/NE/NEFW/WTS-Networks/IDN/idnfiles/WkpPlanLicencingDecomProjetc_Germany2012/WkpPlanLicencingDecomProjetc_Germany2012-Best_practice_EON_decom-Ehlert.pdf


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