Final Report (Revision 2): Guideline for the clearance of materials during the decommissioning of a nuclear facility

Transcription

1 TÜVNORD SysTec GmbH & Co. KG Energie- und Systemtechnik TÜV Final Report (Revision 2): Guideline for the clearance of materials during the decommissioning of a nuclear facility Report Contract IKC carried out on behalf of the Ministry of Economic affairs, Agriculture and Innovation Hamburg, 30 June 2012 KIN2010/0066

2 Page 2 of 19, dated 30 June 2012 Table of content 1 Goal Scope Definitions Responsibilities Description of the process Decommissioning plan Determination of the radiological inventory Clearance criteria Preparation for clearance During decommissioning Clearance Management Preservation of radiological information Final Report Description of release Conclusion Literature... 19

3 Page 3 of 19, dated 30 June Goal The goal of this guideline is to support the licensee in fulfilling Dutch legislation on decommissioning. The legislation referred to relates to the determination of the radiological inventory before decommissioning and to the release of material from nuclear supervision for unrestricted use (clearance), which takes place during the decommissioning of a nuclear facility. Currently, Dutch legislation only establishes clearance levels. Regulatory requirements on clearance measurements and clearance procedures for the release of material are not available. In practice, this means that licensees often have to negotiate on a case-by-case basis with the authorities about the measurements and procedures that are necessary to demonstrate compliance with the clearance levels. This guideline supports the licensee by specifying what details have to be included in the decommissioning plan concerning the radiological inventory and the release of materials, how the release (including the measurement) can be implemented practically, what documentation must be compiled and retained, and what details of the completed decommissioning concerning clearance must be included in the final report. The licensee is not by law required to follow this guideline. He is also free to fulfill a different set of boundary conditions and requirements and to follow a different route of releasing materials. This is subject to approval by the licensing authority. 2 Scope This guideline is applicable to the release of materials within a nuclear facility (licensed under article 15b, Kernenergiewet (1)) from nuclear for unrestricted use. Concerning the radiological inventory, this guide applies exclusively to the contamination or activation of components or to the dose rates caused thereof. It does not apply to the contamination of buildings or sites or to the dose rates caused by these. With respect to clearance, this guideline applies exclusively to the release of radioactive material from nuclear supervision for unrestricted use that is incurred during the decommissioning of a nuclear facility. It applies to material which is not subject to a case-by-case decision. Clearance of buildings and sites is explicitly excluded from the scope of this guideline. For the clearance of buildings (including building rubble) and sites, reference is made to the respective guides. This guideline does not apply to radioactive material of natural origin.

4 Page 4 of 19, dated 30 June 2012 The definition of the scaling factors and the generation of nuclide vectors is not subject of this guidance. The guide is without prejudice to existing legal requirements, such as the minimization of generation of radioactive waste and dose (ALARA). 3 Definitions ALARA: A radiation protection principle whereby the dose is kept As Low As Reasonably Achievable (art. 19 Besluit kerninstallaties, splijtstoffen en ertsen (Bkse) (2) jo art. 5 Besluit stralingsbescherming (Bs) (3)). Armoring: Steel that is used to reinforce concrete. Calibration: The act of finding the relationship between a result of a measurement and the desired measure. The relation is the calibration factor. Within the context of clearance one usually calibrates a radiation detector so that one can infer the specific activity or surface related activity from the raw count rate. Clearance: The release from nuclear supervision for unrestricted use (art Bs (3)). Note: Release from nuclear supervision does not relieve the owner of the released material of the requirements based on general environmental legislation, such as requirements on the management of asbestos and chemicals, or on reuse. Clearance levels: Nuclide specific values of the specific activity (in Bq/g), surface related activity (Bq/cm²) or activity per year (in Bq/a), which are used as the basis for the clearance measurements (see section 5.1.2). The clearance levels (the specific activity and the total activity per calendar year) are numerically equivalent to the exemption levels. They are specified in table 1 of Bs (3). The surface related clearance levels are specified in the RP 89 (4). Clearance decision: The formal decision of the licensee to grant clearance, after having followed all steps in the release procedure, and having demonstrated that the clearance levels are complied with. Clearance measurement: Measurement that is used to demonstrate the compliance with the clearance levels. Component: A discrete element of a system. (5) Difficult to measure (DTM) nuclides. A radionuclide whose radioactivity is difficult to measure directly from the outside of the material by non-destructive assay means. Example: Alpha emitting nuclides, beta emitting nuclides and characteristic X-ray emitting nuclides. Refer to (6) adapted by (7).

5 Page 5 of 19, dated 30 June 2012 Decision threshold: Fixed value of the decision quantity by which, when exceeded by the result of an actual measurement of a measurand quantifying a physical effect, one decides that the physical effect is present (8). Detection limit: Smallest true value of the measurand which is detectable by the measuring method (8). Easy to measure (ETM) nuclides. Gamma emitting nuclide whose radioactivity can be readily measured directly by non-destructive assay means. Refer to (6) adapted by (7). Exhaustion rate: The nuclide specific ratio of (total / surface specific / mass specific) activity to the relevant clearance level of that nuclide. Hotspot: A location on a surface or within a volume of elevated activity with respect to the surroundings, where the elevation is so high that the surface or mass specific clearance levels would be exceeded if the averaging area of 10,000 cm² or averaging mass of 500 kg was applied, respectively. Key nuclide: A gamma emitting nuclide whose radioactivity is correlated with that of DTM nuclides and can be readily measured directly by non-destructive assay means. Note: Also called easy to measure nuclide or marker nuclide. Example: Co-60, Cs Refer to (6) adapted by (7). Material 1 : (9) armoring used within building structures 2, components of the facility, articles, equipment, items and devices, scrap metal and steel, non-ferrous metallic scrap, other solid items or articles, such as glass, plastics, mineral wool, asbestos. The above items may also originate from outside the controlled area, such as from the site. Measurement scheme: Series of steps and acts that have to be followed in order to perform a reproducible clearance measurement. Nuclide (isotopic) vector: A vector specifying the relative nuclide composition in the material. Each of the elements in the vector specifies the relative activity of the nuclide to the total activity. (On application of the 10% cutoff criterion (see section 5.1.2), the vector has to be renormalized to 100 %.) 1 Rubble is not included in the definition of materials. The clearance of rubble is described in the Guideline for the clearance of buildings during the decommissioning of a nuclear facility, Final report dated The clearance of armour is partially described in the Guideline for the clearance of buildings during the decommissioning of a nuclear facility, Final report dated

6 Page 6 of 19, dated 30 June 2012 Operational clearance levels: The operational clearance level is the raw response of a radiation detector, in counts/s or counts, to material with a specific activity or surface related activity equal to the clearance level. The operational clearance level depends heavily on detector and the nuclide composition. Radioactive material: Material for which the exemption levels are exceeded, which are specified in table 1 of Bs (3). Radioactive waste: Radioactive material for which no further use is foreseen (art Bs (3)). Release: A process that is undergone with the goal of granting clearance. Release procedure: Series of steps and acts that have to be followed in order to comply with clearance regulations. Rubble: lose mineral structure incurred during removal of components or decontamination of the building or incurred during refurbishing and renovation work or incurred after demolition of a building, after it has been concluded that the clearance measurement cannot take place at the standing structure. Release storage: Location within the facility where the material for which clearance has been granted is transported to and where the material is stored until it is transported from the site in order to prevent cross- or recontamination. Scaling factor (SF). A factor or parameter derived from a mathematical relationship used in calculating the radioactivity of a DTM nuclide from that of an ETM key nuclide as determined from sampling and analysis data. Refer to (6) adapted by (7) System: A system comprises several components, assembled in such a way as to perform a specific (active) function (5). Verification measurement: A second clearance measurement that serves to demonstrate compliance with the clearance levels either by a second sequential measurement with the same measurement method by different personnel but not with same device, or by a second measurement by a different measurement method, but not necessarily by different personnel.

7 Page 7 of 19, dated 30 June Responsibilities The licensee may grant clearance to material only if it complies with the clearance levels (Besluit stralingsbescherming (Bs) (3) art. 37). The licensee is responsible for demonstrating that material to be granted clearance complies with the clearance levels. (Bs (3) art. 37). Within the organizational structure of the licensee, the Radiation Protection Officer is responsible for declaring that the material submitted for release has been assigned to the appropriate release procedure approved by the competent authority. It is also the Radiation Protection Officer s responsibility to declare that the approved procedure was adhered to, and, if applicable, that the material can be granted clearance. The clearance measurements (and preparative measurements, such as the measurements to verify the nuclide vector) shall be performed by competent staff, taking into account the relevant legislation on radiation protection and radiation competence. 5 Description of the process The process of release can be roughly divided into three steps (see fig. 1): Preparation of the decommissioning plan before decommissioning during the (post)operational phase, o the determination of the radiological inventory, o compilation of the release measurements/procedures, Measurements and preservation of information during the decommissioning phase, and Compilation of the final report at the end of the decommissioning phase. Prior to decommissioning, the licensee is required to develop a (final) decommissioning plan, which shall be submitted to the authorities for approval during the licensing procedure (Besluit kerninstallaties, splijtstoffen en ertsen (Bkse) (2) art. 10). In the decommissioning plan, he describes the radiological inventory of the controlled area. With respect to clearance, the licensee proposes procedures for the release of materials during decommissioning. The decommissioning plan has to fulfill the requirements set out in this guideline. During decommissioning, the licensee acts according to the decommissioning plan (Kernenergiewet art. 15b (1) and Bkse (2) art. 10). Specifically, he follows the approved release procedures for material that is to be released. At the end of decommissioning, the licensee presents a final report to the authorities, containing (inter alia) information about the clearance process (m.r. boni (10) art. 10). The formal relations between the licensee and the authorities are shown in Figure 1.

8 Page 8 of 19, dated 30 June 2012 Licensee Authorities Decommissioning plan (See 5.1) Safety report Etc. (Additional) release procedures (see 5.2) End-report (see 5.3) Licensing of decommissioning phase Separate approval release procedures Withdrawal decommissioning license (post)operational phase Decommissioning phase Figure 1: Formal interactions between licensee and authorities 5.1 Decommissioning plan In (10) art. 3.1 and 4.1, the licensee is required to specify in the decommissioning plan measurement strategies and -methods that will be applied to determine whether the decommissioning is completed. As partial fulfillment of this requirement the licensee shall specify in the decommissioning plan how he intends to release material from nuclear supervision.

9 Page 9 of 19, dated 30 June 2012 In order for the supervisory authority to assess and to verify the radiological impact of decommissioning (including the decommissioning techniques), the licensee shall describe the radiological inventory (room wise dose rates and contamination of components) of the nuclear facility. The sections below give guidance what information regarding the radiological inventory and clearance is required in the decommissioning plan Determination of the radiological inventory With respect to clearance and clearance measurements, the aim of the determination of the radiological inventory is to assess the potential radiological impact caused by components in order to reduce exposure to personnel, obtain information for the optimal preparation of the relevant components for clearance. Before decommissioning, the licensee shall describe the radiological inventory of the facility in the decommissioning plan. For all components in the controlled area, he shall specify per room the type of material (plastic, stainless steel, ), the mass of the component, the geometry (e.g. density, thickness, so that the surface area can be deduced from its mass), Large rooms (e.g. within the containment of a nuclear power plant) shall be divided into smaller units. The licensee shall draw on existing historical data, technical drawings, lists and pictures to acquire this information. Associated with each of the listed components, the licensee shall specify the local dose rates, the level of surface activity, and, if applicable, the level and spatial distribution of volume bound activity. Dose rate measurements are an important input for the preparation of the work onsite, the minimization of the collective dose exposure by selecting appropriate radiation protection measures and decommissioning techniques. The components local dose rates shall be measured at various places, depending on the dimensions of the component, on contact and at a distance of 0.5 m. The maximum dose rate and an average dose rate shall be determined. For rooms with a high background radiation level, measurements shall be carried out with respect to the background radiation by providing appropriate shielding. The background radiation shall be documented. For each room, the highest of local dose rates at 0.5 m is selected. All rooms are classified by this highest local dose rate according to Table 1.

10 Page 10 of 19, dated 30 June 2012 The dose rate map contains drawings with colored areas, the class of the room and the maximum dose rate of all the components in the room according to Table 1. class color maximum dose rate at 0.5 m /h) A blue x < 10 B green 10 x < 100 C yellow 100 x < 1000 D orange 1000 x < E red x Table 1: colors in the dose rate map. The non-fixed surface activity on the outer surfaces of components is used to determine the level and distribution of the contamination in the room. Non-fixed contamination shall be determined primarily via smear tests and at locations where high contamination is to be expected. Scratch samples to determine the fixed surface activity on the outer surfaces of components are used to determine the surface specific activity and/or mass specific activity. The samples may also be used to determine a nuclide vector. Fixed surface activity may occur if contamination has penetrated the surface or is fixed in the surface. The contamination measurements consist of smear tests and/or scratch tests. For activated components, other types of measurements might be necessary. The type of measurement shall be chosen with respect to the operational history considering for example penetration of activity into the surface or coating. The contamination map gives information on the non-fixed activity by coloring, information to fixed activity or activation as remarks. The non-fixed contamination levels of components are used as a basis for the contamination map. The highest non-fixed contamination defines the contamination class of the room according to Table 2.

11 Page 11 of 19, dated 30 June 2012 class color contamination values (Bq/cm²) 1 blue x < green 0.4 < x < 4 3 yellow 4 < x < 40 4 orange 40 < x < red 400 x Table 2: Colors in the contamination map, depending on contamination values for non-fixed surface activity Clearance criteria Material is said to comply with the clearance levels if the following requirements are met (art Bs (3)): The summation formula of the total activity per nuclide using table 1 of the Bs (3) yields a result below unity, where those nuclides which contribute less than 10% may be neglected, and the duration over which the total activity is summed may not exceed one calendar year, or the summation formula of the specific activity using table 1 of the Bs (3) yields a result below unity, where those nuclides which contribute less than 10% may be neglected, and the mass the activity refers to may not exceed 500 kg. In addition, if the material is metallic, the summation formula for the surface activity using table 3-2 of the RP 89 (4) yields a result below unity, where those nuclides which contribute less than 10% may be neglected and where the surface the activity refers to may not exceed 1 m². Following boundary conditions apply: Larger averaging surfaces and masses are permitted in principle. The homogeneity (i.e., absence of hotspots) for this larger averaging area or mass must be demonstrated and recorded before the actual clearance measurement (see section 5.1.3). The licensee may choose to demonstrate compliance with a subset of these requirements (e.g. neglecting the surface specific activity requirement). In that case, he shall demonstrate that the selected clearance levels cover (i.e., are more conservative than) the ones for which compliance is demonstrated. The licensee may grant clearance only if all the conditions below are fulfilled: An appropriate release procedure has been submitted and it has been approved by the competent authority, the treatment and measurement of the material has taken place in compliance with the appropriate release procedure (including the measurement scheme), and the material complies with the clearance levels.

12 Page 12 of 19, dated 30 June Preparation for clearance During decommissioning, all material that is destined for clearance has to be assigned to an approved release procedure. Therefore, the licensee shall submit each release procedure to the authorities for approval. In principle, these release procedures shall be defined in the decommissioning plan 3. The decommissioning plan shall contain information on: how the licensee will sample, radiologically analyze and generate scaling factors and nuclide vectors from the analysis, the measurement devices that will be employed to demonstrate that material complies with the clearance levels. Also, it shall demonstrate that these devices are suitable for clearance measurements on the basis of estimated nuclide vectors and device specifications, in combination with special boundary conditions to be kept during the measurement. For a total-gamma-clearance portal these can include: o duration of measurement, o sensitivity of detectors, o background count(rate), o signal to noise ratio. For contamination monitors these boundary conditions can include: o scan velocity, o sensitivity of detectors, o integration constant, o surface properties of material (e.g. roughness), o geometry. how he will prevent inadvertent exchange of released and unreleased material or cross-contamination (this includes the organization of the obligatory release storage), how he in principle will guarantee the traceability of the released material after clearance, and release procedures, as far as reasonably feasible. Release procedures (described in the decommissioning plan, or subject to separate approval during decommissioning) shall include the following details: 1. the origin of the material, 2. the physical and chemical properties of the material, including at least: a. mass, 3 Sometimes, however, due to lack of information on nuclide composition or physical and chemical composition of the material to be granted clearance, poor accessibility of locations where samples have to be taken, or due to measures that would sensitively alter the nuclide composition (e.g., system decontamination), it is also permissible to define the release procedures during the ongoing decommissioning. In such a case, separate approval from the authorities is necessary.

13 Page 13 of 19, dated 30 June 2012 b. contamination class (see section Determination of the radiological inventory ), and c. contamination or activation. 3. the key nuclides, how the difficult-to-measure nuclides are correlated to them, and the nuclide vector, 4. the treatment imparted to the material to prepare it for clearance (e.g. cutting, decontamination, cleaning ), 5. how the nuclide vector is verified after the treatment, 6. the measures that will be taken to guarantee that the permitted (higher) averaging masses and areas are kept and that (if applicable) these higher averaging quantities are justified by the demonstration of absence of hotspots (see section Clearance criteria ), 7. the measurement scheme: a. what specifications the measurement devices, the measurement itself and the material to be granted clearance have/has to comply with, b. the type(s) of measurement that will be applied to demonstrate compliance with the clearance levels, and devices associated c. how the raw data (count(rate)) is processed to yield the desired quantities, including error propagation, d. the operational clearance levels of the measurement devices for the given nuclide vector, and the demonstration that the detection limits as calculated by ISO (8) are below these operational clearance levels for the estimated activity and its distribution, e. how the verification measurement is performed, 8. the responsibilities of different workers involved, 9. the organization of the release storage, and 10.the destination of the released material. 5.2 During decommissioning Clearance For every clearance measurement, the material to be subjected to this measurement shall be assigned to the appropriate and approved release procedure and to an identification number. The licensee prepares the release in line with the submitted release procedure. The measurement is performed according to the measurement scheme, as established in the release procedure. The measurement comprises all following steps: 1. Checking whether the properties of the material to be granted clearance and of the measurement device are in accordance with the specifications described in the relevant release procedure, 2. recording relevant parameters, especially the date of measurement, level of background radiation, ID of measurement device and of material to be granted clearance,

14 Page 14 of 19, dated 30 June performing the actual measurement according to the specifications in the measurement scheme, 4. recording the raw data (in counts/s or total counts), 5. if applicable, subtraction of effect of natural nuclides, 6. correction for background radiation including the error propagation according to ISO (8) (this yields the corrected value ), and 7. analysis of the raw data (in counts/s or total counts) and calculation yielding the desired quantities (Bq/g, Bq/a and/or, Bq/cm², whatever is applicable), by using the appropriate calibration factor(s) and nuclide vector (other factors might influence the analysis, too, such as geometric factors and surface property factors in case of a measurement with a contamination monitor). The Radiation Protection Officer may grant clearance to the material only if the approved release procedure (including the measurement scheme) has been followed, and the material complies with the clearance levels. The compliance is determined by comparing the corrected value to the decision threshold, that is, by checking whether or not there is a contribution from the key nuclide(s) to the measured signal. Should the corrected value exceed the decision threshold then the upper limit of the confidence interval of the corrected value shall be compared to the operational clearance level. Should the upper confidence limit exceed the operational clearance level, the material may not be granted clearance. In all other cases, the exhaustion rates shall be calculated from the best estimate of the true value of the measurand. During decommissioning, the licensee shall assure that the (clearance) measurement instrumentation is calibrated and its performance is periodically verified. If clearance is granted, the material is transported to the release storage 4, from where it can eventually be removed from the site. Otherwise, the material is transported to a dedicated space for radioactive waste management. It is left to the licensee to decide how to proceed, taking into account relevant legislation. During decommissioning, the authorities will perform inspections on a random basis Management In this guide, management refers to the organization of the creation, amendment and dissemination of documentation by the licensee during (post)operation or decommissioning. This organization is usually specified in the organizational handbook of the licensee, and is often subject to separate approval. Furthermore, the management is subject to relevant legislation on radiation protection and nuclear safety. Therefore, the management is not further described in this guide. 4 Armouring is left within the building if the building was released for reuse or for demolition only. The "Guideline for the clearance of buildings during decommissioning of a nuclear facility", Final Report dated , containing guidance on the treatment of armouring.

15 Page 15 of 19, dated 30 June Preservation of radiological information In order to present the relevant data and information in the final report at the end of decommissioning, the following information shall be retained after every positive clearance decision: origin of the material, ID, physical and chemical data, date of measurement, nuclide vector, applied release procedure, including the measurement scheme, result of measurement (raw values, possible effects of natural nuclides, background levels, corrected values, calculated values of Bq/g, Bq or Bq/cm² (or combination, as applicable) for every nuclide in nuclide vector, exhaustion rates, result of summation formula. Information required by the ISO (8) is also to be included.), and destination. 5.3 Final Report In (1), the licensee is required to compile a final report at the end of decommissioning, which shall be submitted to the authorities for application for withdrawal of the license. According to (10) art. 10, the report contains at least a description of the way the licensee removed the waste from the site. As partial fulfillment of this legislation the licensee shall specify how material was granted clearance during decommissioning Description of release The final report shall enable the supervisory authority to convince itself of the validity of the clearance decisions (this includes the adherence to the approved release procedures) and assess the destination of the released material. Therefore, in the final report the licensee shall provide following information, for each release procedure (cf. section 5.2.3): The origins of all released material, ID, its physical and chemical data, dates of the measurements, the applied nuclide vector(s), the measurement scheme that was used to release the material,

16 Page 16 of 19, dated 30 June 2012 results of measurements (raw values, possible effects of natural nuclides, background levels, corrected values, calculated values of Bq/g, Bq/a or Bq/cm² (or combination, as applicable) for every nuclide in nuclide vector, exhaustion rates, result of summation formula. Information required by the ISO (8) is also to be included.), and the destination of the material.

17 Page 17 of 19, dated 30 June 2012 Licensee intends to decommission nuclear facility Decommissioning plan: Radiological inventory Sampling and nuclide vectors Measurement devices Can all release procedures be included in decommissioning plan? YES Licensee submits decommissioning plan (with release procedures, if applicable) NO Apply for approval that some release procedures can be submitted during decommissioning Before decommissioning Release procedures: Origin of material Physical and chemical properties Nuclide vector Treatment Measurement scheme Does approved release procedure exist for material that is destined for release? NO Submit release procedures for material and obtain approval YES Clearance documentation: Origin of material ID Physical and chemical data Nuclide vector Applied release procedure and measurement scheme Results of measurement, Preparation of materials to be granted clearance in accordance with release procedures Perform measurement(s). Compliance with clearance levels? YES Licensee grants clearance Preservation of clearance data Transport to release storage if applicable Final report NO Actions to be defined by licensee During decommissioning After decom. Figure 2: Flowchart of release of materials.

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19 Page 19 of 19, dated 30 June Literature 1. Kernenergiewet. Wet van 21 februari 1963, houdende regelen met betrekking tot de vrijmaking van kernenergie en de aanwending van radioactieve stoffen en ioniserende stralen uitzendende toestellen. 2. Besluit kerninstallaties, splijtstoffen en ertsen. Besluit van 4 september 1969, tot uitvoering van de artikelen 16, 17, 19, eerste lid, en 21 van de Kernenergiewet. 3. Besluit stralingsbescherming. Besluit van 16 juli 2001, houdende vaststelling van het Besluit stralingsbescherming. 4. European Commission. Radiation protection 89. Recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations International Atomic Energy Agency. IAEA Safety Glossary. Terminology used in nuclear safety and radiation protection. Vienna : sn, International Atomic Energy Agency. No. NW-T Determination and Use of Scaling Factors for Waste Characterization in Nuclear Power Plants. Vienna : sn, Vol. IAEA NUCLEAR ENERGY SERIES. 7. International Organization for Standardization. ISO 21238:2007. Nuclear Fuel Technology - Scaling Factor Method to Determine the Radioactivity of Lowand Intermendiate-level Radioactive Waste Packages Generated at Nuclear Power Plants. Geneva : sn, SS-ISO 11929:2010. Determination of the characteristic limits (decision threshold, detection limit and limits of the confidence interval) for measurements of ionizing radiation - Fundamentals and application. 22 March, Strahlenschutzkommission. Freigabe von Materialien, Gebäuden und Bodenflächen mit geringfügiger Radioaktivität aus anzeige- und genehmigungspflichtigem Umgang. Empfehlung der Strahlenschutzkommission. 12 February Ministeriële regeling buitengebruikstelling en ontmanteling nucleaire installaties. Regeling van de Minister van Economische Zaken en de Staatssecretaris van Sociale Zaken en Werkgelegenheid van 23 februari 2011, nr WJZ/ , houdende regels inzake de buitengebruikstelling en ontmanteling van nucleaire inrichtingen en inzake de aanvraag om goedkeuring voor de wijze waarop financiële zekerheid wordt gesteld voor de kosten van buitengebuikstelling en ontmanteling van nucleaire inrichtingen waarin kernenergie kan of kon worden vrijgemaakt.