C. TECHNICAL AND ECONOMIC QUESTIONS ON THE DEVELOPMENT OF DEEP GEOLOGICAL REPOSITORY

1. Where, for how long and in what is the SNF stored before it can be disposed in the DGR? Is it safe?

The SNF is stored on the premises of nuclear power plants in SNF storage facilities, which are nuclear facilities. The SNF is placed in transport and storage packages, the types of which are approved by the SÚJB.

After the SNF is removed from the reactor, it is placed in the SNF storage pool next to the reactor, where it is placed for 5-10 years, when it is cooled down. The shielding against radioactivity is water. The SNF is then transferred to a type-approved transport and storage package (19 SFAs for NPP Temelín and 84 SFAs for NPP Dukovany in one cask) and moved to the on site SNF storage facility for about next 50 years. Thereafter, the SNF package should be moved to the surface area of the DGR to prepare SNF for disposal. SNF in disposal packaging (three SFAa from NPP Temelín or seven SFAs from NPP Dukovany in one cask) is then disposed in the underground part of the DGR.

SNF storage facilities are nuclear facilities and are subject to all provisions of the Atomic Act, including the issuance of the relevant SJB permits. At the same time, the transport and storage packages must be type approved by the SÚJB. These processes ensure that the storage of SNF is safe.

2. Why can't the SNF and HLW be disposed in existing disposal facilities?

The existing disposal facilities are of near-surface type, designed for the disposal of low- and intermediate-level waste. High-level waste and spent nuclear fuel, for which the storage and disposal must take into account the release of heat from the conversion of the radionuclides contained therein, must be stored in a deep geological repository located in a geologically stable environment, at depths of several hundred metres below the Earth's surface.

Disposal of this type of RAW in existing repositories would not be safe enough and would not guarantee the isolation of radionuclides for hundreds of thousands of years, when the radioactivity would drop to a level comparable to that of the rock environment. In practice, this means that this RAW does not meet the defined limits and conditions for acceptability in existing near-surface repositories established based on safety analyses.

For the time being, SF is stored in storage facilities on the premises of NPPs and RAW that cannot be disposed in existing disposal facilities is stored safely in NPPs, the RAW disposal facility Richard, etc. (answer prepared in cooperation with SÚRAO).

3. Is the possibility of retrieval of SF from the DGR being considered in the Czech Republic?

The DGR is intended for the permanent disposal of RAW. Therefore, the removal of SNF from the DGR is not considered for the time being, although technically it would be possible to remove it during the period of DGR operation.

4. How much does spent nuclear fuel "glow" after it is removed from the reactor? How much do containers ("Castors") of spent nuclear fuel stored in a nuclear power plant "glow"? How much will the spent nuclear fuel containers in a deep geological repository "glow"?

The activity of the nuclear fuel in the reactor core is significant, but within four days after the reactor is shut down and before the nuclear fuel balance begins, the reactor's thermal power drops by an order of magnitude to tens of kW per fuel assembly. The spent nuclear fuel is then moved to a storage pool where it is cooled for several years. No other handling is expected during this period due to the still high heat output and activity. The removal of residual heat as well as the necessary shielding function from the effects of ionising radiation is provided by water.

Dry storage technology was selected for long-term storage of spent nuclear fuel in Czech nuclear power plants. Packaging assemblies for spent nuclear fuel were designed taking into account the parameters of this fuel. Thus, after 5-7 years of cooling, it is normally possible to load fuel with residual power in the hundreds of W and activity in the order of 10 ¹⁶Bq per fuel assembly (maximum values can reach over 1 kW and up to almost 10¹⁷ Bq per fuel assembly). The quantity that then becomes important, in addition to the residual thermal power of the whole containment (which is given by the sum of the powers of the individual fuel assemblies), is the dose equivalent power at the surface of the containment and at a distance of 2 m from it. The normal required limits (from the Atomic Law) for transport and storage are ≤ 2 mSv/h on the surface and ≤ 0.1 mSv/h at 2 m from the surface of the package.

For spent nuclear fuel after e.g. 65 years of long-term storage, a residual power of hundreds of W (max. 500 W) per fuel assembly is assumed. The residual power further decreases and after 100 years of storage it drops to 300 W per fuel assembly (response from SÚRAO).

5. How much spent fuel in kg is in one storage package? How many kg of plutonium will be in one storage package? What will be the total capacity of the DGR in terms of storage packages?

There are approximately 10 t of HM (heavy metal, i.e. U and Pu) in one transport and storage package. The plutonium content of the SNF is approximately 1 %, so the mass of plutonium in one package will be around 0,1 t. This applies to the packages used in both NPPs.

The total capacity of the DGR has to cover the amount of SNF produced in both our NPPs over the whole period of their operation and the SNF from the planned new nuclear sources (completion of new units at NPP Dukovany and Temelín) over the whole period of their operation and is estimated at about 9 000 t HM.

6. How much "energy" remains in nuclear waste?

Spent nuclear fuel contains approximately 1 %  of ²³⁵U, 93 % of ²³⁸U and approximately 1 % of ²³⁹Pu. Thus, around 95 % of the fuel is still unused. However, for technical and economic reasons, spent nuclear fuel is not reprocessed or otherwise used in the Czech Republic or in most nuclear countries, i.e. countries operating nuclear power plants.

7. Why is the large amount of heat produced by spent fuel (waste) not used?

The amount of heat produced by one package together with the continuous decrease of its amount in time and the non-negligible radiation load from gamma radiation and neutrons of the package does not allow to effectively use the total heat output of all packages loaded with SNF e.g. for heating of households.

The maximum thermal output for which the transport and storage package are designed is in the range of 20 - 30 kW. However, the actual heat output of committed packages is significantly lower, being approximately one third to one half of the maximum heat output. The total storage capacity of the three SNF storage facilities on the nuclear power plant sites is 345 packages (more than half full as of 1 August 2020). Theoretically, their thermal capacity would thus be sufficient to heat 300 - 1000 flats of 100 m.² However, taking into account the losses in heat conversion and transfer, the usable heat output is considerably lower. This fact, together with the gradual reduction of the thermal output of the package, precludes the effective use of the waste heat of the loaded packages.

8. What is the longest half-life of radionuclides contained in disposed RAW?

Radioactive waste contains isotopes of elements from a wide range of disciplines from medical applications, from industry, research and nuclear power stations. Key radionuclides were selected from the entire inventory for long-term and operational safety assessment. Of these important radionuclides from fission products in spent nuclear fuel, the longest half-life is that of ¹²⁹I, at 15.7 million years (answer in collaboration with SÚRAO).

9. What element in the disposed spent fuel is the largest contributor to the heat production from the disposed waste?

The heat sources in spent nuclear fuel are different at different stages of spent nuclear fuel management. Heat production is linked to the activity of the isotopes in the fuel, as each transformation generates heat.

The storage stages can be divided into three time periods - fresh out of the reactor (on the order of days), short-term storage (on the order of years) and long-term storage (decades). The last stage of loading is then the permanent placement in the DGR, i.e. disposal.

Fresh out of the reactor, radionuclides with short half-lives (short-lived radionuclides) are the largest heat source, with the La isotope¹⁴⁰ being the most significant. In short-term storage, fission products with half-lives on the order of years, namely the isotopes ^137M Ba and ⁹⁰Y, are the largest contributors to heat generation. In the long-term storage phase, the largest contributors to heat generation are actinides with long half-lives, namely the isotope ²⁴¹Am. In the disposal phase of the SNF in the DGR, long-lived actinides, namely the isotope ²³⁹Pu, are the largest heat source.

In order to determine the isotope with the largest contribution to heat production in spent nuclear fuel, a specific time at which this question is investigated is needed (response from SÚRAO).

10. We are only able to use a few percent of nuclear fuel. What are the chances that we will be able to use more of it in the future? Is anyone doing such research, and if so, with what results?

Research in the field of SF utilisation is ongoing both in the Czech Republic and abroad, but no new technologies for more efficient SF utilisation have been developed so far. Therefore, it cannot be assumed that in the near and even distant future it will be possible to further use SF for power generation outside the framework of existing SF reprocessing technologies.

Research projects on alternative fuel cycle policys, such as the Global Nuclear Energy Partnership (GNEP), Direct Use of PWR Fuels in Candus (DUPIC), Accelerator Driven Systems (ADS) and Partitioning & Transmutation (P&T), have not yet led to any commercially viable technologies.  Moreover, if any of the international projects aimed at verifying the practicability of fusion of light deuterium and tritium nuclei for power generation (e.g. ITER) are successfully completed in the future, further use of SF cannot be envisaged.

11. How is the constancy of hydrogeological conditions guaranteed for ten times the longest half-life.

The long-term stability and development of hydrogeological conditions are studied in the process of research and development of the DGR mainly through palaeohydrogeological processes, or the influence of changes in the properties of the geosphere on the development of transport from the DGR area to the biosphere.

The DGR is a project whose safety must be demonstrated in the long term. The aim of this work is to investigate possible long-term geological, geomorphological and climatic changes and their influence on the evolution of radionuclide transport from the DGRarea to the biosphere. Not only the current geological and hydrogeological state of the site, but also the past geological, geomorphological and climatic changes are and will be studied throughout the DGR. And all this in order to provide the most relevant prediction - scenario - of the future development of these geospheres and their influence on hydrogeological (and transport) conditions.

Within the framework of the activities, integrated hydraulic and transport models will be applied to predict the evolution of migration of substances from the DGR area in the long term. The models will also vary predictions of geological and climatic changes. The basis is the preparation of predictive scenarios of geosphere evolution, geological scenarios and related input data for the models. These will be implemented through computer tools (SW), and the results will be compared with each other in order to validate the models while knowing the strengths and weaknesses of the SW used for applications in complex rock environments and over long time scales. In general, the rock environment of the sites is mainly composed of rocks of Variscan age with predominantly metamorphosed and deep igneous rocks (with a minimum age of about 350 million years), which are only to a small extent overlain by younger sediments. Tectonic processes have disturbed the rock environment over a long geological evolution, resulting in less disturbed rock blocks being spatially restricted and fault and fracture zones occurring in selected locations, which are hydraulically significant and therefore significantly affect the safety of RAW disposal. Another important factor affecting the safety of the disposal facility is the significant morphological gradient, which ranges from tens to the first hundred metres in height. This profile then determines the groundwater level, which in turn is a determining boundary condition for the hydraulic conditions at the site.

However, it is important to note that the essence of the safe disposal of any RAW is its long-term isolation from the environment until its radioactivity has fallen to a level comparable to that of the host environment. To achieve this, a multi-barrier principle is used, where the actual radioactive waste, e.g. former spent nuclear fuel, is placed in several barriers independent of each other. As a result, safety must be demonstrated - in this case in response to a possible change in hydrogeological conditions according to projected site development scenarios - for all three barriers, i.e. the disposal packaging, the fill and backfill material and the rock environment. Each of these barriers must have predetermined physical and chemical properties and must prevent the penetration of radioactivity into other components of the disposal system. It is therefore necessary that the geological environment in which the deep geological repository is located be as 'homogeneous' as possible, without significant geological disturbances (cracks, faults) and without the presence of current and future human activity that could compromise the containment properties of the disposal system. This is both today and for the next hundred thousand years (response from SÚRAO).

12. Why not pour the waste into concrete?

Concrete is an important component in DGR. It is used for immobilization of high and intermediate level waste, filling of the disposal facility voids and other structural elements of the disposal facility.  A major advantage of concrete for immobilising radioactive waste is its high pH, which reduces the mobility of a large number of different radionuclides. Concrete is also used in some policys, such as the Belgian policy, for the disposal of SNF as a material surrounding the steel containment assemblies because it significantly reduces the corrosion rate of the steel by allowing a passive layer to form on its surface. 

In the Czech reference policy, which was inspired by the Swedish and Finnish policys, classical concrete is used less because its high pH could accelerate the degradation of the bentonite surrounding the VPP containment. The very low permeability and swelling pressure of the latter prevents advective groundwater flow and ensures that the migration of radionuclides into the rock environment following damage to the containment packages is limited (response from SÚRAO).

13. Why doesn't the Czech disposal packaging consider the use of copper, like the Swedes and Finns?

Due to the geochemical conditions in the crystalline rocks in the Czech Republic, it was decided to develop steel-based disposal package in contrast to Finland or Sweden, where the groundwater composition is different from the Czech Republic.

The disposal packaging for SF is under development in the Czech Republic since 1994. Škoda JS, a. s., which has extensive experience in the production of packaging sets for the storage of SF, has participated in its development. Researchers from ÚJV Řež, a. s. and, in recent years, VŠCHT Praha have also been involved in the research since the beginning. 

Due to the different composition of groundwater in Sweden or Finland, where copper is expected to be used as an outer layer for disposal package, it was decided to develop steel-based disposal package due to the different geochemical conditions in crystalline rocks in the Czech Republic and Sweden or Finland.  This is mainly due to the order of magnitude lower chloride concentrations in groundwater, which can create an unfavourable environment initiating local corrosion of steels.  A two-layer disposal package consisting of an outer layer of carbon steel and an inner layer of stainless steel is now considered as a reference option. According to the experimental results obtained so far by the researchers of UJV Řež, a. s. and VŠCHT, the lifetime of this disposal package in the anaerobic environment of the DGR exceeds several hundred thousand to one million years, which is the time it takes for the radioactivity of SF to decrease to the activity of uranium ore.

However, there will still be long-term laboratory and in-situ experiments over the next decades that must demonstrate that the proposed disposal package will meet all requirements to ensure the safety of the disposal facility. It is also possible that, if the very promising results so far are not confirmed, a different disposal package design will be chosen (response from SÚRAO).

14. What should the barriers of the DGR consist of? Is each barrier alone capable of preventing the release of radioactive waste back into the biosphere?

The safety policy of a deep geological repository is based on the principle of protection to depth (described in more detail in Section 6 of Decree No. 329/2017 Coll.), which consists in the creation of a series of back-up physical safety barriers that are inserted between the radioactive substances and the surroundings of the disposal facility.

In the Czech safety policy, the main barriers are double-layered disposal packaging surrounded by compacted bentonite and intact crystalline rock at a depth of about 500 m below the surface.  It is a system of interconnected barriers that prevent radionuclides from entering the environment. The safety of the disposal facility is planned in such a way that even if one of the barriers fails for any reason, the safety of the disposal facility cannot be compromised, i.e. the other barriers prevent the rapid release of radionuclides into the environment.   Even in the hypothetical case of failure of all disposal packages in one year, which can be considered as a practical impossibility, although the dose optimisation limit (0.25 mSv in a calendar year for a representative person) could be exceeded, human safety cannot be compromised because of the very slow migration of radionuclides through compacted bentonite and the rock environment (response from SÚRAO).

15. How long is the planned lifetime of the deep geological repository and what will happen to the deep geological repository and the disposed nuclear waste at the end of its lifetime?

The DGR is intended for permanent disposal of SF and RAW and therefore its lifetime is not limited. From the point of view of the fulfilment of the safety functions, in particular the prevention of the release of radioactive substances into the environment, the duration of this safety function ('lifetime of the reactor') can be estimated to be in the order of hundreds of thousands of years.

The "lifetime of DGR" differs significantly from that of other, not only nuclear, facilities, which is usually in the range of several decades.  The safety functions of a deep geological repository must be ensured both during operation and after closure. In simple terms, the 'lifetime of the disposal facility must last for the entire 'hazardous' lifetime of the radioactive waste. However, even the policy of the 'hazard lifetime' of radioactive waste is not clearly defined, as it is based on the decreasing amount of radionuclides due to their conversion into inactive nuclides. As a rule, however, a period of several hundred thousand years is considered, when the activity of the SNF will have fallen to approximately the level of uranium ore (answer in cooperation with SÚRAO).

16. What types of nuclear waste will be disposed in the deep geological repository and what will be its capacity?

The radioactive waste that will be disposed in the DGR is divided into three groups based on how it will be managed: former spent nuclear fuel, RAW from decommissioning of nuclear facilities and other institutional RAW (industry, research, medical applications) not acceptable for near-surface disposal.

Assuming that the 3 new planned nuclear power reactors will be commissioned, the SNF will be disposed in 7,600 disposal packages with a total mass of approximately 9,000 t of uranium. Other radioactive waste weighing about 4 500 t will be disposed in 4 000 concrete containers (response from SÚRAO).

17. In what (what packages/containers...) will the nuclear waste be disposed in the deep geological repository? How will the condition (impermeability / hermeticity) of these containers be monitored? What will be the procedures in case of breach of these packages?

The deep geological repository is designed as a passive multi-barrier system. In addition to the natural barrier, which is a suitable rock environment (in the Czech Republic, crystalline rocks), safety will be ensured by engineered barriers, which include a disposal packaging, bentonite, or cementitious materials.

The policy of the Czech spent nuclear fuel disposal packaging is based on a two-layer disposal packaging, where the first inner layer is designed from stainless steel and the second, outer layer consists of carbon steel. The overall thickness of the containment is designed to be 13 cm to give a containment lifetime of 100 000 years. In addition, current research shows that the lifetime of the disposal packaging can be up to ten times higher. The hermeticity of the disposal packaging will be checked directly in the hot cell before the packaging is loaded onto the disposal horizon. If leaks are found, a correction action will be performed.

During operation, the DGR will be monitored radiologically and technical measures are proposed to deal with such situations (e.g. closing of the hot chamber, stopping air extraction into the chimney) (response from SÚRAO).

18. How much does it cost to build a DGR and who will pay for it? Is there enough money for it? And who sets the price of the DGR?

The price for the construction of the DGR depends on several basic factors, which are mainly:

• the chosen method of placement of the packaging files in the DGR, either vertically or horizontally,
• the relative position of the underground and surface areas and the associated extent of the interconnecting mine workings,
• the chosen mining technology (tunnelling machines or conventional mining),
• local conditions on the site, including the possibility of connection to transport and technical infrastructure,
• the process and location of disposal of the SNF from the time of declaration as RAW until its transfer to disposal package.

The costs of the construction of the DGR (around CZK 32 billion) will be covered from the nuclear account, which will gradually receive funds from mandatory levies of RAW originators (ČEZ, ÚJV), so that there will be sufficient funds for the construction of the reactor. The price of the DGR is determined in the context of the preparation of relevant projects and studies, the content of which is the design solution of the DGR in relation to the development of prices over time and the refinement of the design solution (response from SÚRAO).

19. Who will bear all the costs associated with the management of radioactive waste once it has been disposed of in a deep geological repository. What is a nuclear account and who is obliged to collect funds in it to cover these costs.

The costs associated with the management of RAW are always borne by the generator of the radioactive waste; the State manages these funds and has a dedicated nuclear account for them.

Details of the Nuclear Account, its administration, income to the Nuclear Account and contributions from the Nuclear Account are set out in Sections 115-135 of the Atomic Energy Act (answer in cooperation with SÚRAO).

20. How much annual contribution from the nuclear account a municipality, in whose cadastral territory an exploratory area for underground nuclear waste disposal will be established or the operation of a nuclear waste disposal facility is already permitted, can obtain?

After the establishment of the exploration area for special interventions in the Earth's crust, the contribution for each affected municipality on whose cadastre the exploration area is established is a flat rate of CZK 600,000 per year, and a contribution of CZK 0.40 per year for each square metre of the cadastral area of the municipality on which the exploration area is established (in the order of higher or lower units of millions of crowns for each affected municipality per year for the entire period of the establishment of the exploration area). The final site will be designated as a 'protected area', which involves 2 types of contribution - a one-off contribution and a regular contribution. Once the protected area is established, each municipality concerned will receive a one-off contribution of CZK 50 million. Every second and subsequent year after the designation of the protected area, each municipality concerned will receive a contribution of CZK 600 000 per year until the start of operation of the DGR  (for a total period of about 40 years) and a contribution of CZK 0.60 per year for each square metre of the cadastral area of the municipality on which the protected area is designated. Once the deep geological repository is operational, the contributions to the municipalities are based on the volumes of disposed spent nuclear fuel and high-level waste. The amount of contributions from the nuclear account for a municipality in whose cadastral territory the operation of a radioactive waste disposal facility is authorised is, according to the current legislation, CZK 4 000 000 per year. In addition, the municipality will receive a contribution of CZK 10 000 for each cubic metre of radioactive waste disposed of in a given calendar year, to be received in the first half of the following year (response from SÚRAO).