Decommissioning of Nuclear Facilities · • Decommissioning of facilities and site cleanup are prerequisites • Measures that may be carried out should reduce the radiation exposure

1 International Atomic Energy Agency

Decommissioning of Nuclear FacilitiesDecommissioning of Nuclear Facilities-- Release from Regulatory Control Release from Regulatory Control --

Ernst Warnecke; NSRWR²D²Project: Basics of Decommissioning of Research

Reactors / Manila; 16-20 October 2006


Lesson ObjectivesLesson Objectives

• Understand the rationale for establishing the criteria used for release of materials, buildings and sites from regulatory control (often termed “clearance”)

• Understand the specific criteria recommended by the Agency for “clearance”

• Understand the difference between releasing of materials and releasing of a site, including buildings

• Understand how the clearance process is actually implemented

• Provide Agency guidance on the above topics


Design,Construction &Start-up Phase

Prepare Initial Decommissioning Plan

OperatingPhase

Prepare ShutdownPlan

Shutdown

Update FinalDecommissioning

Plan

1. Source TermReduction2. De-fueling3. WasteConditioning

Safe EnclosurePreparation

Safe EnclosurePeriod

1. Site Preparation2. InitialDismantling

Surveillance & Maintenance

Final Phase

1. FinalDismantling2. Final Survey3. LicenseTermination

UpdateDecommissioning

Plan

Faci

lity

Stag

eD

e co m

mis

sio n

ing

A ct iv

ityM

onito

ring

Activ

ity

1. Routine Monitoring2. MaintenanceSupport

BackgroundMonitoring

Characterization& Surveillance

Post RemediationSurveillance

Support & ContinuedCharacterization Support &

Verification


Options for Radioactive Material ControlOptions for Radioactive Material Control

RadioactiveMaterial

RegulatoryControl

AuthorizedDisposal

AuthorizedDischarge

Exemption

Exclusion

Clearance


• Exclusion - any exposure whose magnitude or likelihood is essentially not amenable to regulatory control and is deemed to be excluded from the standards (legal framework)”

• Ingestion of naturally occurring radionuclides (e.g. K40, natural U/ Th)• Cosmic and terrestrial radiation• Fallout from atmospheric weapons testing

Concepts of Exclusion, Exemption, and Clearance (1)


Concepts of Exclusion, Exemption, and Clearance (2)

• Exemption - Practices and sources within a practice may be, a priori, exempted from the requirements of the standard (not from legal framework) if exposures or risks will be sufficiently small

• Quantitative criteria specified (for reference limited amounts of material)

• Practice must be justified (will introduce more overall benefit than detriment

• Clearance - Removal of radioactive materials or objects from within authorised practices without any further control by the regulatory authority

• Clearance levels shall not be higher than (reference) exemption levels

• clearance of bulk amounts of material require particular regulatory consideration


Control / Clearance of a siteControl / Clearance of a site

RadioactiveMaterial

RegulatoryControl Clearance

Once a site has been cleaned to (the very low) residual contamination levels accepted by the regulatory body, then

the termination of the site license can be requested


Release of materials and sites: General (1)Release of materials and sites: General (1)• Large amounts of materials are generated during decommissioning

• Some materials may be released from regulatory control (clearance), e.g. after decontamination (applicable to contamination, not activation)

• Clearance minimises the radioactive waste amounts to be disposed of drastically

• NPP example: total amount of material ~140 000tconditioned radioactive waste ~5000m³

• Guidance is needed on acceptable release levels and their derivation• A decision is to be made on the termination of a site license and its further

use• Guidance is needed on the release of sites from regulatory control

• Release levels define a boundary of what is regarded “radioactive” and what is regarded “non-radioactive” material

• Exclusion of natural radionuclides (unaffected by a “practice”)• Prohibit re-contamination of clean materials or cleaned surfaces etc.


Release of materials and sites: General (2)Release of materials and sites: General (2)• Natural radionuclides (if unaffected by a “practice”) are excluded• Exclusion concept for radionuclides of natural origin (GS-R-1.7):

• Based on upper end radionuclide distribution in soil worldwide• Activity concentration for

• K-40: 10 Bq/g• All other radionuclides of natural origin: 1 Bq/g

• U-238, U-235, Th-232: parent of decay chain; secular equilibrium• Ra-226: Decay product in the chain or head os a subset of the chain

• How to deal in clearance with natural radionuclides from practices?• Establish a baseline concentration of natural radionuclides in soil,

concrete or any respective other material• Attribute concentrations above natural contamination to a practice and

take them into account in the clearance process

10

International Atomic Energy Agency

Clearance of MaterialClearance of Material


Release of Materials: Basics (1)Release of Materials: Basics (1)• Motivation for clearance

• No repository for radioactive waste available• Storage of radioactive waste for many years before disposal• High disposal costs for radioactive waste• Saving of resources (re-use and recycling)

• Re-use and recycling options (examples)• Melting of metals and fabrication of waste containers for storage and

disposal of radioactive waste• reluctance of steel industry to accept cleared steel• Concrete recycling in road construction

• Option: Disposal as non-radioactive waste• Find a disposal facility to accept cleared waste• Geological disposal of chemo-toxic waste which is used as backfill


Release of Materials: Basics (2)Release of Materials: Basics (2)• Effective dose to a member of a critical group in the order of 10µSv/a (trivial

hazards)• 10µSv/a concept widely accepted• Measurable levels generated by safety assessment (multiple scenarios)

• Direct radiation from the use of recycled material• Ingestion of radionuclides from released material• Take accumulation of radionuclides into account

• Levels for unrestricted release are given in RS-GS-1.7 for individual radionuclides in bulk

• Higher levels may be accepted for defined destinations of materials• Clearance of material is an irreversibly release from regulatory control• Waste may be disposed of as non-radioactive waste• Materials may be re-used and can be traded as resources• Great care necessary: “No” unintentional release of contaminated materials• Strict regulatory control: licensing of equipment and supervision of

operation, i.e. no release of material without regulatory permission


Release of Materials: Application (1)Release of Materials: Application (1)• Clearance levels are very low• Consequence: Requirements for clearance measurements are very high• An intelligent approach is necessary• Elements of a “intelligent” approach

• Sophisticated characterisation, including full radionuclide inventory• Attempt to characterise materials in such a way as to be able to declare

concentrations of about 1% of clearance levels [“summation formula”]• Develop conservative correlation factors [scaling factors, fingerprints]

between easily measurable radionuclides and others (key radionuclides Cs-137 and Co-60) and get regulatory approval / agreement

• Correlation factors will differ within a plant• Decide on a reasonable number of different correlation factors • Check the key radionuclides in the release measurement and develop

the full radionuclide inventory through the radionuclide correlation

• A similar approach applies to radionuclide inventories in waste packages!


Release of Materials: Application (2)Release of Materials: Application (2)• Release measurement

• Develop / buy appropriate equipment to measure the key radionuclides• Demonstrate to the regulator that the equipment works as required• Find approval / agreement of the regulator• Develop a measurement procedure, including regulatory reviews,

agreements and measurements independent of the operator• Find approval / agreement of the regulator• Measure each batch of material

• low level measurements may need a long time• Develop the full radionuclide inventory through correlation techniques• Check whether the batch can be released • All measurement result have to be checked by the regulator• The regulator decides on the release and on independent measurements• Never release a batch before approval / agreement of the regulator


Clearance of materials: Release MeasurementClearance of materials: Release Measurement


Release of Materials: Application (3)Release of Materials: Application (3)• How to deal with natural radionuclides from practices?

• Establish a baseline concentration of natural radionuclides (soil, concrete)

• How to deal with inactive equipment and inactive buildings (e.g. offices) at a the site of a nuclear facility?• (see release of buildings)

• French approach:• “Zoning”: release of “inactive” parts• Very Low Level Waste (VLLW) disposal (large amounts)• Morvillier disposal facility for VLLW is in operation

• Clearance is a complicated approach often applied to large projects• Can it reasonably be applied to a small, singular facility?• Is sharing / passing on of clearance equipment to another project a

benefit?

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Clearance of BuildingsClearance of Buildings


Clearance of Buildings• How to deal with inactive buildings on a licensed nuclear complex?

• Release of all of the materials through the clearance procedure?• Such an argument / consideration may be raised on legal grounds• A reasonable approach may target at giving evidence of clean buildings

• Provide evidence that radionuclides were never used• Provide evidence that contaminations did never occur• Provide factual evidence by random / designated measurements

• Clearance of buildings where radionuclides were used• Decontaminate walls, ceilings, floors• Remove (deep) contamination along fissures, cracks, joints etc.• Prevent re-contamination after decontamination! (Protect surfaces)• Clearance measurements on the existing structure

• If the building will be re-used• Before demolition of the building

• Clearance of the rubble of a demolished building is conceivable, but not the typical approach


• Applicable to trivial radionuclide contamination in decommissioning materials, maybe after decontamination

• Motivation: Need for waste minimisation• Elaborate clearance process• Sophisticated release measurements: low radionuclide concentration levels• Application of radionuclide correlation technique (Characterisation!)• Irreversible process, i.e. no releases beyond acceptable levels• Give special attention to natural radionuclides• Application to large facilities / projects• Check benefits for small projects / pass equipment to next project• Apply an appropriate approach to inactive buildings with a nuclear license• Clearance measurements are typically carried out on the existing structure

Summary Summary –– Clearance of Materials / BuildingsClearance of Materials / Buildings

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Release of SitesRelease of Sites


Release of sites: Basics (1)Release of sites: Basics (1)• Increasing number of facilities are being decommissioned

• Release of sites is an authorised practice• It is aiming at the release of a site from regulatory control

• Decommissioning of facilities and site cleanup are prerequisites• Measures that may be carried out should reduce the radiation exposure

from existing contamination through actions applied to the contami-nation itself (the source) or to the exposure pathways to humans

• The earlier use of the site, its complexity, the hazard involved and the envisioned future use of the site is important

• The site includes land / buildings / structures

• Release from regulatory control• Unrestricted / Restricted • Radiological and non-radiological hazards must be taken into account


Release of Sites: Basics (2)Release of Sites: Basics (2)• Dose limit of 1 mSv/a for a member of the public is an upper bound for the

sum of all doses arising from practices• Optimisation of long term exposure of the public from residual site

contamination• Dose constraint for multiple pathways of exposure < 300 µSv/a above

background (in accordance with the figure next page)• perform a baseline survey before commissioning• If not: Use analogous, undisturbed, not contaminated areas with similar

conditions• Application of optimisation below 10 µSv/a (trivial dose) is not warrented• Hidden, buried, contaminated structures should be taken into account• Developing of generic levels (regulator) or site specific levels (operator)

• 300 µSv/a concept less common• Some countries implemented a 10 µSv/a concept for site release• A site cannot be moved; it is fixed at a given location

• Corrective actions at a later point in time are possible


Dose limit (1mSv in a year)

Dose constraint (300 μSv in a year)

Optimised site dose release criteria

10 μ Sv in a year

Region where dose reduction measures are unlikely to be warranted

Region of optimization for unrestricted site use

Region for release of a site for restricted use if restrictions fail

Region of optimization for site release for restricted use provided that restrictions are in place


Release of Sites: Basics (3)Release of Sites: Basics (3)• Natural radionuclides are excluded: not amenable to regulatory control

• Difficult situation; situations are even more difficult if natural radionuclides are involved, e.g. U / Th fuel fabrication

• Intervention, i.e. cleanup after a nuclear accident, is different from the normal site release• Intervention situations are not being addressed

• The endpoint of a site release determines the acceptable level of remaining contamination• Nuclear use (site remains under nuclear regulatory control)• Non-nuclear use

• “Green” field: Unrestricted release, normal public use of the site, e.g. presence of humans (children) for 24 h/d

• “Brown” field: Industrial use, limited use of the site, e.g. presence of humans for ~8 h/d (no children)


Cleanup ActivitiesCleanup Activities• Development of the cleanup activities

• Site characterisation (panning and execution)• Definition of release criteria / levels (no generic IAEA data)• Definition of endpoints (see before)• Development of a cleanup plan (as part of a decommissioning

plan)• Approval of the cleanup activities• Implementation of the cleanup activities• Management of radioactive waste and material resulting from the

cleanup activities• Surveillance and monitoring of the cleanup activities• Release of the site from regulatory control


Site CharacterisationSite Characterisation• General site conditions (e.g. chemical / physical / soil conditions)• Current use and history of the site• Identification of radiological contaminants and concentrations

• Three-dimensional radionuclide distribution / homogeneity• Contamination below buildings• Potential for re-suspension of contaminants

• Potential presence and contamination of underground structures (e.g. pipes, tanks)

• Groundwater and surface contamination (if any)• Non-radiological contamination requiring cleanup under other legislation• Conventional hazards

• Search for existing data / information• Retrieve information from (former) staff• Define data information needs and prepare characterisation plan


Characterisation / Monitoring for ComplianceCharacterisation / Monitoring for Compliance• Radionuclides of concern• Acceptable site release levels• Categorization of areas based on

information on spills / contamination• Determination of boundaries of survey

and survey units• Selection of background areas, if needed• Reference coordinate system• Direct measurements versus sampling• Determination of sampling locations

• Sampling equipment• Sampling / Sample size• Analysis / Measurement

• In case of contamination: increase density of grid / additional samples


Cleanup ActivitiesCleanup Activities• Excavation of contaminated soil

• Equipment / technology• Avoid any re-contamination!• Measurement to a predetermined

gamma level (exclusion of natural radionuclides)

• Clearance decision• Management of contaminated soil

as (non-)radioactive waste• Identify a destination for the waste

• Backfill of excavations with uncontami-nated soil (check!)

• Take, maintain and store records of cleanup activities

• Have cleanup levels been achieved?• Are release restrictions to be applied?


Decision on the Release of SitesDecision on the Release of Sites• Removal of regulatory control:

• Regulatory body is responsible for the release decision• Basis: Demonstration by the operator that release levels have been

met (final radiological survey)• Regulator may decide to make independent reviews, inspections,

analysis etc.• If compliance is not demonstrated: further proof, cleanup is required• Release of site:

• if compliance demonstration is acceptable; and• If an acceptable final decommissioning report has been prepared

• Important:• Store and maintain documentation;• Decide on the storage of the documents (Who?, Where?, How?); and• Enforce any restrictions on the release of the site


• Release of a site is the final step in the decommissioning process• It can be granted if facilities have been removed and the site been

cleaned in accordance with the cleanup levels• Compliance has to be demonstrated by the operator• The regulator may review, check or otherwise act on data of the

operator• A site can be released for unrestricted or restricted use• A final decommissioning report has to be prepared• The details of storage and maintenance of the decommissioning

report have to be specified• Any restrictions on the site have to be documented and enforced

Summary Summary –– Release of SiteRelease of Site


Release of Site for Unrestricted UseRelease of Site for Unrestricted UseC. StoiberC. Stoiber


ReferencesReferences• IAEA Safety Series No.115 BSS• IAEA Fundamental Safety Principles, DS298 – approved to be published,

2006

• Materials• IAEA RS-G-1.7 Application of the Concepts of Exclusion, Exemption

and Clearance• IAEA Safety Report No. 44 Derivation of activity concentration values• IAEA DSS 740 Monitoring for Compliance with Clearance Values

• Sites• IAEA DSS 332 Release of Sites from Regulatory Control• IAEA TRS No. 334• IAEA WS-G-5.1

Documents

Decommissioning of Nuclear Facilities · • Decommissioning of facilities and site cleanup are prerequisites • Measures that may be carried out should reduce the radiation exposure