H.P. Berg, P. Brennecke, R. Görtz
Federal Office
for Radiation Protection
Salzgitter, Germany
ABSTRACT
An overview is provided completed and ongoing on decommissioning projects in the Federal Republic of Germany discussed from a regulatory point of view. In total, a number of 18 nuclear power plants including prototype facilities as well as 6 research reactors and 3 fuel cycle facilities have been finally shut down and are at different stages of decommissioning. Only recently the final "green field" stage of the Niederaichbach Nuclear Power Plant total dismantlement project has been achieved. For all decommissioning projects the existence of appropriate criteria for waste management as well as for recycling and reuse are essential. To achieve an optimized solution of the overall material management problem, the options of radioactive waste management, the options for recycling and reuse and, last but not least, the options for disposal of the material as non-radioactive waste should be considered. Recent developments in this field are described. In addition, aspects of final disposal of radioactive waste relevant to decommissioning of nuclear installations are addressed in more detail.
INTRODUCTION
In the Federal Republic of Germany, decommissioning of nuclear installations has started in the last decade and will be growing importance beyond the year 2000. Hence, a substantial amount of experience is available with planning, licensing and realization of decommissioning projects.
After final shut-down of a nuclear facility, several basic decommissioning options are available. These options are usually classified according to the effort to dismantle the plant. This effort can be very low in periods of safe storage without any dismantling operations or very high in cases where the plant is being dismantled in a short time period. A variety of patterns for decommissioning is experienced in practice as these fundamental modes of decommissioning can be combined in different sequences in different parts of the plant. In Germany a lot of experience has been gained in planning, licensing and realization of decommissioning projects.
Except from safe storage periods, due to decommissioning operations like decontamination and dismantlement, substantial amounts of concrete metals and other solid material arises that can either be recycled or disposed of as conventional or radioactive waste. The availability of these options and the corresponding criteria are of paramount importance to decommissioning projects.
In the following, an overview is provided on decommissioning experiences and concepts available in Germany and on applied options both for waste management and recycling.
NUCLEAR POWER PLANTS IN GERMANY
Overview
The situation concerning the use of nuclear power in the Federal Republic of Germany (early 1996) is as follows (1):
Nuclear Installations Finally Shut-Down in Germany
The following overview of nuclear installations which are finally shut down is an updated version of the one given in (2).
The decommissioning of the first nuclear power plant of the Federal Republic of Germany, Versuchsatomkraftwerk Kahl (VAK Experimental Reactor) was decided in 1985. The decommissioning concept provides the total dismantling of the plant. The first two decommissioning licences for decommissioning allow the dismantling of internal and external systems of the controlled area, the handling with contaminated tools and equipment and with low activity secondary radioactive waste. Furthermore, procedures and equipment for the dismantling, disassembling, and packaging of contaminated and activated parts of the facility were tested. On 25th September 1993, the third licence for decommissioning according to section 7 of the Atomic Energy Act (Atomgesetz, AtG) was issued. Action against this third licence was dismissed by the Higher Administrative Court of the State of Bavaria on 17th August 1994, which means that the disassembling of the reactor pressure vessel and the biological shield as well as the clearance for reuse or disposal, of non-hazardous substances which have been authorized as non-radioactive waste has been approved. It is planned to finish decommissioning, including site restoration, by the year 2000.
For the Mehrzweckforschungsreaktor (Multi-Purpose Research Reactor), which was finally shut down in 1984, it was decided in 1989, after comparison of various decommissioning options, to perform the immediate and complete dismantling of the installation. The dismantling of the MZFR takes place stepwise, each step requiring a licence according to the Atomic Energy Act. On the basis of the five issued decommissioning licences for MZFR, the decontamination of the heat removal system and the moderator system, the dismantling of equipment, such as equipment of the turbine building, electric installations, reactor auxiliary and supporting systems, water treatment system as well as the dismantling of the cooling tower was performed or initiated. The dismantling including restoration of the site should be finished by the year 2001 after altogether 6 partial steps. On 15th April 1994, the fourth, on 30th May 1994, the fifth partial licence for the decommissioning of the MZFR were issued, approving further dismantling works.
Rheinsberg Nuclear Power Plant (KKR) with a gross capacity of 70 MWe (WWER reactor) was finally shut down in 1990. Application for decommissing of the plant was made on 30th March 1992. The first licence for decommissioning was granted on 28th April 1995. Demolition work has been started.
Total dismantling is planned for Gundremmingen Nuclear Power Plant Unit A (KRB- A) which was shut down in 1977. Dismantling is taking place in several project phases which are based on the corresponding atomic energy law licences. Phase I, in which lowly contaminated components and the steam- and feedwater circuits in the turbine building were dismounted, was finished in 1989. In phase II, the disassembling of higher contaminated reactor coolant contacted components and systems from the reactor building was performed. In phase III, the last dismantling step, the disassembling of the reactor pressure vessel and its equipment including the reactor shield, will be provided. Based on the licence for phase III issued on 12th August 1992, the disassembly of the reactor equipment was partly achieved in 1994 (e. g. 2 steam dryer units). Valuable information has been obtained on disposal and recycling of contaminated components (3). Only 7% of the total mass was disposed of as radioactive waste. Roughly 1/3 was recycled under controlled conditions, the rest could be cleared for recycling as conventional scrap. Furthermore, in the project advanced dismantling techniques (e.g. ice-saw) and decontamination techniques have been developed and applied (4).
The Jülich Experimental Plant (AVR-Reactor, an experimental high temperature gas-cooled pebble bed reactor), shut down in 1988, shall be transferred to safe enclosure after disassembly of equipment parts such as turbine, generator, condenser and condensate treatment system. The competent regulatory authority has approved the decommissioning concept and the safe enclosure in 1991. In the period from April to June 1992, the available 5,704 unused fresh fuel spheres were removed from the AVR-facility. The licence for decommissioning, unloading of the reactor core, dismantling and disassembling of equipment and safe enclosure of the AVR was issued on 9th March 1994. The unloading of the spherical fuel elements out of the reactor into the central interim storage facility in the Jülich Research Centre was started.
The Lingen Nuclear Power Plant (KWL) was decommissioned in 1977 after 9 years of operation. Based on the licence of 21st November 1985, the facility was transferred to safe enclosure, which began in 1988. The safe enclosure involves the reactor building and the auxiliary building including the connecting building. All controlled areas situated outside this area were decontaminated, canceled, and partly dismounted. The safe enclosure is monitored from the adjacent Emsland Nuclear Power Plant. After about 25 years of safe enclosure operation, it is planned to start the complete dismantling of the plant.
The Heißdampfreaktor Großwelzheim (HDR, a nuclear superheated BWR) finally shut down in 1971, was used after shut down for non-nuclear investigations and R&D on behavior of nuclear installations in the case of severe accidents. Decommissioning of the reactor was approved on 16th February 1983. The above-mentioned test program was finished in 1991. Complete dismantling of the facility is planned until 1998. A second licence for decommissioning was granted on 29th December 1994 which also covers the disassembling of the reactor pressure vessel and parts of the primary circuit.
The Niederaichbach Nuclear Power Plant (KKN, a heavy water moderated, gas cooled pressure tube reactor), which was decommissioned in 1974, is the first NPP in the Federal Republic of Germany being completely dismantled. The NPP was permanently shut down and transferred into safe enclosure in 1983, dismantling began in 1987. The dismantling of inactive and contaminated parts of the facility, except from activated areas near the core, was finished in 1990. The dismantling of the activated parts was finished at the end of 1993. Evidence taking measurements performed in the facility for clearance of the buildings were completed. The Ministry of State for Regional Development and Environmental Aspects of the State of Bavaria dismissed the KKN plant from the application of the Atomic Energy Act on 17th August 1994 and reported that the plant is released for conventional dismantling according to building law. Thus, the complete dismantling of a nuclear power plant was performed for the first time in Europe. The site restoration was celebrated on the 17th August 1995. The radioactive waste amounted to about 2% of the overall amount of decommissioning wastes.
The units 1 to 4 of the Greifswald Nuclear Power Plant (KGR, WWER type, W-230 reactor), were shut down in 1990. The dismantling of all five units will be achieved without preceding safe enclosure. An application for decommissioning and dismantling of plant units was submitted on 17th June 1994. The first licence for decommissioning was granted by 30th June 1995. Demolition of the facility has started.
In the line with the decision taken in 1990 to shut down and decommission the Greifswald and Rheinsberg Nuclear Power Stations, the waste management concept of the Energiewerke Nord is based on direct and complete decommissioning of the six shut down reactor units within the next fifteen years. One key element of this concept is the construction and use of the Zwischenlager Nord (Nord Interim Store, ZLN) for holding the existing nuclear fuels and for interim and decay storage of the radioactive materials arising in decommissioning and demolition. the owner and operator of the store is Energiewerke Nord GmbH. The interim store has the functions of a processing and treatment station and a buffer store for the flows of residues arising. A radioactive waste management station, it accommodates nuclear fuels, radioactive waste or residues which are not treated any further. It is used as a buffer store to allow the materials accumulating in disassembly to be stored temporarily before or after treatment in order to ensure continuous loading of the treatment plants. When operated as a processing station, the ZLN is able to handle nearly all types of radioactive waste and residues arising, except for nuclear fuels. These installations allow the treatment of radioactive residues to be separated from the demolition work both physically and in time. The possibilities of interim storage and buffer storage of untreated waste and waste packages make for high flexibility in logistics and waste management strategy. (5).
The Kompakte Natriumgekühlte Kernreaktoranlage (KNK II, a sodium cooled Fast Breeder Research Reactor) was finally shut down in 1991, after finishing its test program. The shut-down was started with the removal of the fuel elements. The decommissioning concept provides for a stepwise disassembly up to the full dismantling of the plant. The first licence for decommissioning of the facility was granted on 26th August 1993, the second one on 30th May 1994. Since 26th May 1994, the nuclear fuel is completely removed . The third licence for decommissioning was granted on 21st February 1995 approving, among other points, the taking out of operation of the secondary coolant circuit as well as construction, operation and dismantling of a drumming station for the disposal of the secondary natrium. An application for granting the fourth licence for decommissioning has already been submitted.
The Thorium Hochtemperaturreaktor (THTR-300, a gas cooled high temperature reactor) was shut down for being decommissioned in 1989. For the facility a period of safe enclosure is planned. On 17th March 1992, the Federal Office for Radiation Protection granted the licence for the storage of irradiated fuel elements from THTR-300 in the Ahaus Fuel Element Interim Storage Facility (BZA). The first licence for decommissioning, unloading of the reactor core and dismantling of equipment components was issued on 22nd October 1993. Since then, the spherical fuel elements have continuously been removed from the core. The core content had fully been removed by the end of 1994. All 305 Castor containers with fuel elements have been stored in the Ahaus Interim Storage Facility until April 1995.
In 1995, it was decided to finally shut down the Würgassen NPP, a BWR with an electrical power of 670 MW, which had been in operation from 1971 to 1994, an application for shut down has been submitted on 29 September 1995. Planning for decommissioning is underway. Dismantling of the cooling towers has began.
Obviously, there is a substantial amount of decommissioning experience in Germany. It covers all stages of decommissioning like immediate dismantlement, safe enclosure and dismantlement after safe enclosure and combinations of these basic patterns (Table I).
TABLE I Decommissioning Experiences in Germany
(Overview)
RADIOACTIVE WASTES
Wastes from Decommissioning
With the decommissioning and dismantling of nuclear facilities like
mainly solid plant items arise like pipes, instruments, containers, components, support structures, cables, insulation, concrete and building rubble as well as liquids from decontamination (6).
Compared to that, wastes from retrofitting/backfitting and decommissioning of other nuclear facilities (e. g. hot cells in research institutions or universities) arise with lower volumes and activities. Such wastes should approximately be covered by the respective operational wastes. Therefore, these wastes are not taken into account in the following.
Disposal of Wastes Originating from Decommissioning
According to the radioactive waste disposal concept pursued in the Federal Republic of Germany, wastes from decommissioning can be emplaced in the planned repositories Konrad and Gorleben. Both facilities are designed such that sufficient capacity for the disposal of radioactive wastes - including wastes from decommissioning - is available (7). It is planned to take the Konrad repository into operation by the turn of the century. The operational time will be at least 40 years. Taking the Gorleben repository into operation in particular requires that the suitability of the site is finally confirmed after the subsurface investigation has been terminated and a licensing procedure still due has been terminated with a positive decision.
Additionally, the Morsleben repository is available for the disposal of short lived low and intermediate level radioactive wastes with low concentrations of alpha-emitters. This facility resumed its operation in mid January, 1994. Since then, radioactive wastes are emplaced (8). According to the present state, the Morsleben repository will be operated until mid - 2000. At that time the existing operational licence will expire. A legal basis for the further operation of the Morsleben repository beyond June 30, 2000, does not exist at present. The initiation of a licensing procedure according to the Atomic Energy Act has been applied for the continuation of the repository´s operation and ist decommissioning. Because of contractual obligations wastes from decommissioning approximately amounting to 7,000 m3 shall be emplaced until the middle of the year 2000, mainly arising from the dismantling of the Greifswald and Rheinsberg nuclear power plants.
Waste Arisings from Decommissioning
A realistic data base is required for plans with regard to the necessity of interim storage facilities and repositories as well as for the safety-related examination of radioactive wastes from decommissioning and dismantling to be disposed of. This data base should comprise waste forms, radionuclide inventories and waste amounts to be expected including their temporal incurrence.
In accordance with the fundamental approach pursued by BfS as competent authority for disposal the waste generators have to specify the waste packages to be delivered to a repository. Thus BfS has currently based its repository planning works on the following data on wastes from decommissioning:
According to scenario 1 the operational phase is followed by 30 years of safe enclosure and 10 years of dismantling and nuclear waste management. As an average, the waste package volumes to be expected are estimated to be 4,300 m3 per 1,300-MW plant. The total amount of wastes to be expected can thus be estimated to be 90,300 m3. Taking this into account the above-mentioned amounts of wastes will arise within the period of time from 2034 to 2064. An averaged amount of about 2,900 m3/a will arise.
According to scenario 2 the operational phase is not followed by a safe enclosure but directly by 10 years of dismantling and nuclear waste management. In this case the waste package volumes to be expected are estimated to be 5,300 m3 per 1,300-MW plant on average. This results in a total amount of wastes of 111,300 m3 to be disposed of which is distributed over the period of time from 2003 to 2033 with an average amount of 3,600 m3/a.
These scenarios respectively data, however, have to be controlled with regard to the future development in the field of peaceful use of nuclear energy in the Federal Republic of Germany (e. g. after the conclusion of the consensus discussions which are planned to be taken up and continued) and to be brought into line with the changed conditions resulting.
REQUIREMENTS ON RADIOACTIVE WASTES
Safety Assessment
The disposability of radioactive wastes - including radioactive wastes originating from the decommissioning and dismantling of nuclear power plants - was safety-analytically investigated within the planning works for the Konrad repository project and the Morsleben repository.
The site-specific safety assessment for the operational and the post-closure phase of the planned Konrad repository was performed using basis data on type and amount of waste packages to be disposed of including the repository-relevant waste characteristics as well as on the technical design of the disposal mine with the planned mode of operation. Additionally, details relating to this were used in the continued safety-analytical investigations for the Morsleben repository. On the basis of the gained results corresponding requirements on the waste packages to be disposed of were then derived (9), (13) representing the safety-related framework those wastes have to fulfill.
Derivation of Waste Acceptance Requirements
The goal of deriving requirements on radioactive wastes to be emplaced into a repository was to elaborate a variable system of requirements. This requirement system was to be adapted to the currently arising radioactive wastes on the one hand and, on the other hand, it should be as flexible as possible with regard to future developments of radioactive wastes and their conditioning. The Morsleben waste acceptance requirements (9) take into account the determinations of the permanent operational licence dated April 22, 1986, they are therefore a little more "complicated" than the Konrad waste acceptance requirements (10).
So the waste generators may chose between different combinations of requirements, all of them guaranteeing the same safety level for the respective repository. Each waste generator, however, is given the opportunity to apply the specific requirements valid for his radioactive wastes to be disposed of and to fulfill them provably.
Waste Acceptance Requirements
The requirements on the waste packages to be disposed of resulting from the safety-analytical investigations can be subdivided in general basic requirements as well as in requirements on waste form, waste container and radionuclide inventory. The main results and requirements are as follows (in this case for the Konrad project):
On top of that, waste packages to be disposed of must meet additional general requirements.
In analogy to the requirements derived for the Konrad repository project, corresponding requirements on
have been compiled in the Morsleben waste acceptance requirements.
CLEARANCE
Material with sufficiently low values of specific activity and surface contamination need not to be disposed as radioactive waste but can be cleared for recycling or reuse or for disposal or incineration as non-radioactive waste. Distinction is made between conditional and unconditional clearance as described in IAEA-TECDOC-855 (12).
An overview over options available in German and the corresponding criteria are provided in (13) and (14):
The most important of these options are the following:
In 1987, the German Commission on Radiation Protection (SSK) has issued a recommendation on the clearance of steel and iron from nuclear power plants (15) with the following main features:
| - Clearance for general melting of scrap: | Specific activity below 1 Bq/g, surface contamination below limits prescribed in ORP (Table III) |
| - Unconditional clearance | Specific activity below 0.1 Bq/g, surface contamination below limits prescribed in ORP (Table III) |
| - Clearance of special products | Specific activity c of items fabricated under controlled conditions 0.1 Bq/g < c < 1 Bq/g |
The recommendation is based on a study of recycling of ferrous steel (16). The different values of specific activity in the clearance criteria is reflecting the fact, that during fabrication of metal from scrap in scrap processing and in preparing the charges for melting in the steel plant the scrap with residual radioactivity is mixed with scrap from other sources without radioactivity. The resulting steel products thus have in practically all cases a specific activity will below the clearance level. In the case of reuse of items such a reduction does not occur and consequently the clearance levels must be more restrictive.
In 1993, SSK has extended ist recommendation to non-ferrous metals using the same principles and criteria (17). Non-ferrous metal recycling was investigated in the study (18) which was taken into account by the commission.
BfS has developed a model for the derivation of clearance levels for disposal or incineration as conventional waste (19). Again based on an individual dose of 10 µSv/a, the criteria given in Table II for a number of relevant radionuclides are recommended in (19).
TABLE II Clearance Levels for Disposal and
Incineration as Non-Radioactive Waste According to Ref. 19
Criteria for the clearance of buildings have been issued by the SSK in December 1995 (20):
TABLE III Clearance Levels for Surface Contamination
(see appendix IX column 4 of the Ordinance on Radiation Protection (ORP) in the
version from 1989)
WASTE MANAGEMENT STRATEGIES
As explained above, different waste management options exist which can be applied taking into account safety-related aspects and cost-benefit considerations. Concerning the safety assessment of proposed decommissioning activities, first proposals exist to use probabilistic arguments in addition to deterministic considerations (21).
PROSPECTS
Within the scope of the manifold experiences with the decommissioning and dismantling of nuclear power plants gained up to now it has been shown that the by far greatest part of the masses arising can be utilized without harmful effects or can be disposed of conventionally. The part to be disposed of as radioactive waste lies within the range of percentages of the total mass. Due to the very advanced stage of the licensing procedure for the planned Konrad repository and due to restarting the emplacement of radioactive wastes in the Morsleben repository the well-ordered and safe removal of these wastes is guaranteed.
REFERENCES