Monitoring and Surveillance of Uranium Mining Residues. Peter Waggitt Waste Safety Section, IAEA Namibia October 2007

Transcription

1 Monitoring and Surveillance of Uranium Mining Residues Peter Waggitt Waste Safety Section, IAEA Namibia October 2007

2 Radioactive waste management: mining & minerals processing Safety Guide WS-G-1.2 Applies mainly to uranium mining and milling Currently being revised to apply more generally to NORM residues Recommends monitoring

3 Internal and external role of the monitoring program Monitoring is a critical component of successful management because it quantifies the emissions and discharges at the end of the pipe and measures and identifies possible impacts of the operation in the environment Data assist in developing solutions Monitoring provides the proof of compliance with regulatory requirements and proves operations are performing as expected Monitoring is often a condition for permitting the operation: No monitoring no license to operate Monitoring results demonstrate to stakeholders, including the general public that mining is an environmentally acceptable industry

4 Development of a Monitoring Program Before defining a monitoring programme you should become familiar with : The environment in which you operate Operation of mine and process plant it s emissions and discharges and their characteristics Identify and quantify residue streams Potential contamination pathways and possible effects on the surrounding environment Identify the most important potential impacts Identify the best means of monitoring these parameters Collect and interpret the data Report and document the results Periodically review and repeat the above process In development and review of a Monitoring Program the following items should be examined and optimized: Total number and location of sampling sites Frequency and timing of sampling Method of sampling Sample preservation protocol Critical groups and sensitive areas in the environment

5 Radiological and non-radiological parameters to be monitored Radiological Parameters Aquatic & groundwater U series radionuclides Th series radionuclides Maybe U235 series Chemical form Examine both liquid and particulate components Terrestrial U series radionuclides Th series radionuclides Radon & progeny External gamma Dust, soil, vegetation & fauna Form (Chemical & Physical) Non-radiological Parameters Meteorology Wind speed &direction Temperature & humidity Rainfall & evaporation Aquatic & groundwater ph, cations & anions Solids & conductivity Flowrate & current Terrestrial Dust concentration & deposition Cations & anions Particle sizing Biota ecologies The selection of parameters should be based on site specific requirements

6 Commonly Monitored Media and Parameters & Sampling Techniques Surface water and liquid discharges: Grab sampling (sometimes combined to make a composite sample); Proportional flow sampling; In flow analysers Rain water: Grab sample; Continuous sampling Ground water: Grab sample; Depth measurements; Purge and inflow of bore; In bore analysis Airborne emissions: Grab samples; Isokinetic sampling; Continuous sampling Airborne dust: Grab sampling; Low volume dust sampling; High volume dust sampling; Particle size dependant sampling Dust deposition: Dust deposition gauges (a funnel in a bottle on a pole); Sticky material (adhesive coated plastic); Biological accumulators (lichen or moss pads) Radon emanation: Charcoal cups; Track etch devices; Drum emanation; In-situ radon monitors Radon: Grab samples; Time delayed progeny counting; Integrating devices (charcoal cups, track etch devices, charge coupled devices); Direct radon monitors Radon progeny: Grab samples; Use radon and an equilibrium factor; Continuous monitors; Unattached vs attached radon progeny monitors Gamma: Environmental gamma meter (grab or continuous sampling); ThermoLuminescence dosimeters (TLD s); Airborne gamma survey Soil: Grab sampling; Composite sampling; Sampling at different depths Biota: Grab sampling; Composite foodstuff sampling

7 Relevant laboratory analytical instruments Gamma Spectroscopy : A common technique for identifying and measuring a range of radionuclides. Generally based on high purity Ge or GeLi systems. Systems relatively costly and need cooling (normally liquid N2). Partial identification and measurement is possible using far cheaper NaI detector systems but poor energy resolution. Gross alpha and beta analysis : A common and comparatively cheap method of monitoring. Often used as a screening level (check of water concentrations) or to determine higher concentrations (such as occupational dust exposure). Sensitivity can be increased by concentration of the medium being sampled (e.g. evaporation). Does not provide information on the relative contributions of different radionuclides. If the sample being counted is physically thick, the alpha result will be downgraded due to self adsorption Radiochemical separation: This method uses various chemical separations to extract and purify each individual radionuclide. The processed sample is normally deposited onto an analysis medium for subsequent alpha spectroscopy or beta counting. By using tracers, the chemical recovery can be measured and accounted for. Process can be complex, needs specialised training and has a limited sample throughput. Liquid Scintillation Counting: Used generally for liquid samples. LSC can give quick gross levels of alpha and beta but no generally provide no radionuclide specific information. More advanced systems can allow some separation of specific radionuclides but the use can often be problematic and dependant on scintillant and sample chemistry. Automated systems allow high throughput and relatively low cost and resource requirement. Choice of scintillant and preparation of non aqueous samples is often crucial to the accuracy of the result. Radon De-emanation: This method is used to determine Ra226 concentrations. The method is based on sealing the sample, allowing equilibrium and then extracting and measuring the radon. Somewhat complex technique but equipment is relatively low complexity. Applicable to liquid samples only.

8 Examples of Common Analysis Techniques (continued) Field Monitoring Common field equipment items include: A small pump for collection of airborne dust and radon decay products An alpha counter for field counting A contamination monitor for measuring surface contamination, Dose rate meter - a environmental gamma meter (either Geiger- Mueller or NaI based), Collection vessels for water, soil vegetation, etc. Documentation, field instructions, watch with second hand, camera, ruler, etc.

9 Distinction between impact and background contribution Baseline information: If pre-operational baseline levels available, select them as reference levels. Best use is for parameters with small variability such as soil and groundwater radionuclide concentrations concentration and external gamma levels. Use of a background site: Use values from comparable sites but not affected by the operation. Most suitable for parameters which do not have a naturally high spatial variability, such as airborne dust concentration. The site must be representative for the preoperational conditions and must not be affected by other impacts Look at upstream/downstream variations: Most commonly used for aquatic sampling. With more sophisticated analysis this approach can also be used for airborne sampling (by correlating short term wind direction with radon concentrations the operational contribution may be identified). Modeling: Estimation of expected impacts by modeling based on parameters such as source discharge rates and knowledge of the transport pathways. Can be used for airborne, groundwater or aquatic problems when the background component cannot be distinguished on the basis of conventional monitoring or when the potential impact is very small, so that it cannot be directly measured. Because of a conservative approach, modeling generally tends to overestimate the impact.

10 Example: Background estimation by using wind sectors Wind correlation method for calculation of operational radon progeny exposure to a critical group Background Only Sectors Operational +Background Sector Meteorological Tower and Radon Progeny Monitor Background Only Sectors Background Only Sectors

11 Example: Background estimation by using wind sectors Assign wind sectors to background only and operation plus background Average background radon progeny (maybe seasonal) is measured when wind is from the background sectors This result is subtracted from the operational sector to leave the background subtracted radon progeny contribution from the operation Public exposure is calculated using the fraction of time when the wind is coming from the operation multiplied by the operational concentration In some areas, a low wind speed cut-off may be required for times when there is no significant air movement Use of this method may be difficult where one receptor is influenced by multiple sources

12 Reporting: Monitoring results, Schedule and Programme Revisions Often a multi-phase approach to reporting has proved to be most beneficial A notification system in the event of an incident with environmental impact (24 hour response) A short term reporting of raw data (often monthly but can even be on-line for some measurements e.g. those that may be seasonally critical) A longer reporting period to allow incorporation of interpretation of results, determination of background contribution and calculation of dose (quarterly and\or annually) Revisions ensure that monitoring is in accordance with the program and approved schedule Initial monitoring usually changes as data become available and the knowledge base increases. Formal revisions can be at set intervals (every 1, 2 or 3 years) and changes of the Monitoring Program must be documented, justified and approved. Revision can be supported by more frequent audits A revision should also be triggered if there is a significant change in operations : A significant plant expansion or partial decommissioning New or changed transport pathways e.g. river diverted, new settlement built Revised regulations e.g. new dose limits or conversion factors Revision should incorporate input from major stakeholders e.g. regulatory authorities and potentially affected local residents

13 URANIUM TAILINGS HAZARDS Human & Animal Intrusion Radon & Gamma Radiation (Radium, Arsenic, ) Dust Blowing Tailings Dam GROUNDWATER Seepage Arsenic, Uranium, Radium M. Ben Belfadhel, CNSC

14 Surveys and Safety Assessments Surveys and safety assessments are required: Prior to remedial activities to assess potential occupational exposures During remedial activities to assess occupational doses During remedial activities to ensure the effectiveness of remedial activities After remedial activities are completed in order to ensure that clean up criteria have been meet.

15 Radiation Surveys Systematic surveys are carried out: To determine residual levels of contamination on surfaces and in materials and environmental media To determine potential occupational doses during remediation and rehabilitation activities Measurements commonly used include: Gamma radiation: doserates on contact and at 1 metre Radon gas and radon daughter concentrations Alpha and beta contamination on surfaces Radionuclides in materials e.g. soils, water, concrete, residues &l wastes, biota, foodstuff and similar materials

16 Safety Assessments based on monitoring and modeling An assessment of potential hazards arising from residual radioactive materials on the site is needed to make a realistic decision regarding the extent of remedial activities required This can be achieved by a combination of : Systematic monitoring of the site (surface and underground) and structures, and Simple modelling of exposure scenarios e.g. potential exposures to radioactive dusts during a variety of remedial activities

17 Waste Management Facility Failures Waste management facilities (e.g. tailings dams) may fail due to a number of factors: e.g. Poor siting Poor design Poor QA and controls during construction Human intrusion e.g. mining, removal of material Lack of cover: erosion Unexpected events e.g. earthquakes The probability of failure at a properly controlled and regulated facility built in accordance with good engineering practice should be very low Since there are significant cost implications this probability must be thoroughly assessed and considered in planning and design phases

18 Unstabilised Tailings Facility

19 Potential for Cost Savings Good operating practice - in particular for radioactive materials - can significantly reduce potential remediation costs during the closure phase Controls over: Inappropriate disposal of materials on the site Inappropriate use of waste materials Inappropriate diversion of materials Effluent discharges and releases Implementation of progressive clean up during operations (ensures ease of disposal)

20 Documentation/Reporting Regulatory requirements and review process Documentation to be submitted by the operator may include Monitoring methods Procedures Survey strategies Remediation methods Survey results Statistical analysis of results Reports QA etc Clearance from regulatory control & release from liability

21 Monitoring and Surveillance after closure

22 Monitoring and surveillance Even after closure of a facility, monitoring and surveillance should continue regulatory requirement & public assurance Post closure monitoring can be based on a scaled down version of operational monitoring Surveillance uses regular inspections to verify that the integrity of the rehabilitated facility is being maintained

23 Why do we need Monitoring and Surveillance? Waste contains materials with a very long half-life Rehabilitated structures change over time (e.g. seepage, settling, erosion) and these changes may result in a reduction in the integrity of the structure If no monitoring or surveillance is performed, major releases may occur which require remedial action Often, with a good monitoring and surveillance system, changes can be detected early and maintenance performed relatively cheaply and with little impact on the public or the environment A monitoring and surveillance (M&S) programme allows prompt identification of conditions that might lead to migration or release of radioactivity

24 Components of a Monitoring and Surveillance Programme The monitoring part of M&S program often builds upon the monitoring measurements performed during operation, however, the extent is reduced to a more appropriate level for a closed facility Monitoring should focus on the key aspects monitored during operation but use the experience gained during operations to reduce the frequency of observations to an appropriate level The surveillance part of the M&S program should focus on ensuring the structural integrity of the waste facility (walls, spillways, seepage collectors, cracks, slope deformations, deformation of cover, cracking of cover) Surveillance uses a process of regular, detailed and/or special purpose inspections to determine the early warning signs of potential failure of the structure Observation of additional factors of relevance: Erosion flooding, water course changes, rainfall, wind; Biota trees and shrubs, animal control, human intervention; Releases of material seepage, salt deposits, dust emission

25 Hole in tailings cover caused by decomposing wood

26 Measurement of erosion gullies Measureme nt of erosion gullies

27 Cracks and sliding in a waste pile cover

28 Shrubs growing through a rip-rap cover

29 Animal burrow in a cover layer

30 Tailings brought to the surface by burrowing animals

31 Differential settlement in a tailings pond cover

32 Contents of a Typical Long Term Surveillance Plan Introduction site history, licensing Final site conditions waste facility description Site drawings and photographs baseline information Permanent site surveillance features survey, signs, markers Site inspection frequency, qualifications, locations Environmental monitoring air, water, biological Inspection documentation checklist, map, photographs, report Unscheduled (special purpose) inspections- events, remediation Institutional control ownership, signs, fences, security Record keeping and reporting Emergency notification and response Quality Assurance (QA) Personnel health and safety inspections, incidents References

33 Basic Equipment for Surveillance Inspections General equipment - maps, compass,gps, keys to locks, field book, copy of M&S program, check list, pens, clipboard, erasable board, camera, marking paint, measuring tape, photo scale stick, basic tools (screwdrivers, wrenches, bolt cutters), binoculars, shovel, radios? Radiation equipment Personal monitoring (TLD), survey meter, contamination meter, spare batteries Specialised equipment (site and inspection specific) ground water sampler, dip stick, chain saw, air sampler, plant press, animal trap, rifle/shotgun?, ph and conductivity meter, public relations information

34 Surveillance Check List Full details in Safety Report # 27 Inspect off site- agriculture, roads, populations Inspect access- fence, intrusion, tampering, damage, signs Examine markers- survey points, overgrown Inspect crest- settling, cracks, breaches, erosion, biota Inspect slopes- movement, cracks, depressions or bulges, channeling, seepage, biota, cover Examine periphery- seepage, sediment, biota, drainage Examine diversion channels- erosion, blockage, disturbance, sedimentation Examine monitoring wells- disturbance, integrity, missing caps or locks, biota Conclusions- imminent threat?, frequency of inspections, follow up, maintenance or repair?, access controls effective?

35 Conclusions Monitoring during operations is an essential part of the management of mining and processing projects Programme development must be consultative It is important to consider all aspects of the operation and its potential impacts on the environment during the development of any monitoring programme Appropriate analysis and interpretation of results along with documentation and reporting are an integral part of the programme Monitoring programmes should not remain static but should be reviewed and altered to ensure they remain relevant Monitoring & Surveillance continue post-remediation