Handling of parameter values for the derivation and conditions for the application of clearance values for the disposal of minor radioactive substances at landfills in the clearance procedure

With the closure of the last three nuclear power plants in Germany in April 2023, the nuclear phase-out in Germany has been completed. There are now around 30 decommissioned nuclear power plant units in Germany that need to be dismantled. This generates large quantities of waste that can be released. In particular, the storage of cleared waste in landfills is in the public’s focus and is critically questioned by parts of the population. Intensive efforts are being made by the competent Land authorities and landfill operators to provide specific evidence of the harmlessness of disposal in the respective landfills, in addition to compliance with clearance levels. While this can contribute to public acceptance, it also leads to delays that can affect the progress of dismantling a nuclear power plant. 

Against this background, the German Commission on Radiological Protection (SSK) decided in 2021 to prepare a guidance document to assist the competent authorities in assessing compliance with the dose criterion for clearance – the effective dose may only be in the range of 10 μSv per calendar year – in the implementation of clearance for disposal in landfills. The SSK thereby intends to improve clearance procedures, in particular for the dismantling of nuclear power plants. During the application and discussion of the version of the handout adopted at the beginning of 2024, it became apparent that certain aspects needed further technical clarification and specification. At the beginning of 2026, the SSK therefore adopted an extended version of the handout, which deals in more detail with the groundwater pathway (well scenario). A calculation tool is now available to assess the relevance of the well scenario for specific releases. The significance of the other scenarios can now be seen from additional tables for all radionuclides for which a clearance value for disposal is set by the Radiation Protection Ordinance. A new sensitivity analysis was carried out with a significantly increased number of calculation runs, which allowed the statistical results to be made more meaningful again.

The handout deals with clearance for disposal in landfills, but not with clearance for disposal in incinerators or other clearance options under the Radiation Protection Ordinance.

The application of the clearance values for disposal in a landfill always requires an examination of the landfill site intended for the deposition of the waste by the competent authority. The StrlSchV lays down requirements for the class of landfill and the average annual total amount of storage, so these conditions must be verified by the authorities. If one of the conditions of the StrlSchV for release is not met, proof of compliance with the dose criterion is required on a case-by-case basis. In addition to such proof of individual cases, further official checks may be necessary under the Radiation Protection Ordinance if the competent authority has any indications that the dose criterion for release at the site of the waste management facility is not met. The dose criterion for clearance must be complied with under German radiation protection law; mere compliance with the clearance values is not sufficient proof. In addition to the legally required reviews, further audits can increase transparency, which can help increase public acceptance.

Verification of compliance with the dose criterion in specific release procedures requires knowledge of the mathematical model structure, the model assumptions made and the parameters and their chosen values when deriving the clearance values. This derivation is complex and the consequences of deviations of single conditions or parameters from the generic modelling assumptions and parameters are not easy to assess on a case-by-case basis. Therefore, no conclusions as to compliance with the dose criterion can yet be drawn from an isolated consideration of individual assumptions or parametric values. In general, deviations do not necessarily have to affect compliance with the dose criterion, in particular if they do not concern an exposure pathway relevant to the clearance value or are compensated for by conservativeness elsewhere in the model.  The sensitivity analysis is therefore of particular importance here, as it looks at the individual assumptions and parametric values in their contexts in a nuclide-specific manner. It identifies, on a nuclide-specific basis, the actually most unfavourable constellations of parametric values and radionuclides which could have adverse effects on compliance with the dose criterion. The sensitivity analysis shows the robustness of the procedure when deriving the clearance values with regard to different individual parameters.

However, the results of the sensitivity analysis also show which parameters are decisive with regard to the dose criterion and should therefore be given priority in a review. These are, in particular, the annual working hours of a single person when installing approved waste on the landfill site, as well as driving times during transport to the landfill site if it is more than about 100 km away from the waste producer. Where the water level of the draining canal from a waste water treatment plant treating the leachate of a landfill is lower compared to the model assumptions, the possible use of the draining canal water should be considered, as the extent of use determines the possible dose. The modelling of the dose via the groundwater pathway shows a particularly high conservativeness, which is described in detail.

As these results depend on characteristic properties of the radionuclides, such as half-life, type of radiation, and migration and transfer in the environment, the sensitivity analysis has been carried out for a number of radionuclides covering the full spectrum of radionuclides relevant in practice. The analysis also covers radionuclides, which must be taken into account when releasing waste from medicine, technology and research. Overall, the results of the sensitivity analysis show that there must be significant deviations from the assumptions and parameters used to derive the clearance values before the dose criterion could be violated.

On the basis of the results of the sensitivity analysis and previous practical experience, a step-by-step approach is proposed whereby official investigations can be targeted on sensitive modelling assumptions in order to demonstrate compliance with the dose criterion. In addition to deviations from the sensitive model assumptions and parameters, actual mass flows and utilisation rates of clearance values as well as the respective nuclide vectors can also be taken into account.

Calculation tool

The calculation tool (MS-EXCEL file) allows a quick assessment of whether the groundwater path (well scenario) is relevant for a specific planned clearance for disposal at a landfill with regard to compliance with the dose criterion of the Radiation Protection Ordinance. In the calculation tool, the nuclide vector, the exhaustion of the sum formula averaged over the mass released in a year and the mass deposited in a landfill each year can be varied.

More detailed explanations of the application are provided in the calculation tool itself. In addition, two examples of calculation can be found in Section 4.4 of the SSK Handout 'Handling of parameter values for the derivation and conditions for the application of clearance values for the disposal of minor radioactive substances at landfills in the clearance procedure'.

[Link to excel-file with calculation tool [XLSX, 69 KB] ]

The authenticity of the calculation tool provided can only be guaranteed by downloading it from the SSK website. Any changes to the tool may lead to incorrect calculation results. The calculation tool provided was tested in detail by the SSK. The responsibility for checking the correct calculation remains with the user.