Research report summaries 2008–2009

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Contractors' reports are only available in the language in which they are submitted to the canadian Nuclear Safety Commission (CNSC).

RSP-0240 – Technical basis for G-144 trip parameter acceptance criteria for the safety analysis of CANDU nuclear power plants

G-144 is a CNSC regulatory guide and is for use in the safety analysis of a set of accident scenarios in nuclear power plants which are relatively more frequent. It in part specifies the values of the acceptance parameters to be used for determining the effectiveness of the trip parameters for reactor shutdown. The present work was done under contact from the CNSC for the purpose of surveying and compiling the available experimental data used in the development of G-144 and to evaluate if more recent data provides any further support for continuing to use or relax the acceptance criteria values given in G-144. In this report, the position of G-144 in the CNSC regulatory framework and the historical context in which this document has been developed has been presented. Technical considerations which lead to the choice of the acceptance parameters and their values have been discussed. The available experimental data has been surveyed with a view to assess the level of technical support this data provides to the acceptance parameter values. This forms the current status of the technical basis for G-144.

The conclusion from this survey is that more representative experiments need to be conducted to provide further support for the maximum sheath temperature criterion specified in G-144. Any relaxation of these criteria would certainly require a better understanding of the behaviour of the fuel elements and fuel bundles at temperatures above this value.

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RSP-0241 – Factors controlling the long-term performance of composite barrier systems

Ten factors controlling the performance and longevity of barrier systems incorporating composite liners are examined. The applications of interest include both bottom liners and covers for landfills. These issues include the effect of: (1) clogging of leachate collection systems; (2) clay-leachate compatibility; (3) the effect of freeze-thaw on geosynthetic clay liner (GCL) performance; (4) temperature; (5) holes in geomembranes (GMs); (6) protection of composite liners; (7) wrinkles in GMs; (8) leakage through composite liners; (9) diffusion through GCLs and GMs; and (10) service life of GMs. For the specific materials and conditions discussed:

  • Clogging of leachate collections systems is highly correlated with the presence of biodegradable waste and hence is likely to be greatest for municipal solid waste and least for inert industrial wastes at neutral (or slightly higher) pH.
  • GCLs may interact with municipal solid waste (MSW) leachate. The level of interaction is highly dependent upon the vertical effective stress at the time of permeation. At stress levels more typical of likely field conditions, the effect is far less significant with a hydraulic conductivity to MSW leachate still very low.
  • There is negligible flow of hydrocarbons through a saturated GCL until a critical breakthrough pressure is exceeded. This breakthrough pressure is greater than that likely to be experienced in many applications and hence a saturated GCL is likely to be an excellent barrier to hydrocarbons under these conditions.
  • Up to 150 freeze-thaw cycles had very little effect on the hydraulic conductivity of GCLs permeated with water under conditions where there was no chemical interaction with the bentonite prior to permeation.
  • More research is required to assess the potential combined effect of cation exchange and freeze-thaw cycles at relatively low stress on the long-term performance of GCLs used in covers and similar near surface applications. Hoverer, there has been at least one case reported in the literature with a very significant increase in the hydraulic conductivity of GCLs used in a landfill cover where there had been cation exchange with the porewater if the adjacent soil and it would appear that, where there is doubt, the use of a GCL with a geofilm is preferred.
  • Available evidence would suggest that temperatures of 30–40oC can be expected at the top of the primary liner for MSW landfills. Higher temperatures (40-60+oC) can occur in situations where there is sufficient moisture to accelerate biodegradation of organic waste (e.g., in bio-reactor landfills or when there is no operating leachate collection system) or due to hydration of incinerator ash.
  • Diffusive and advective transport are, respectively, 100 percent and 80 percent higher at 35oC than at a common groundwater temperature of 10oC.
  • The temperature of the GM in a secondary liner will be highly dependent on the nature of the primary liner. For a geocomposite primary liner composed of only a GM and GCL, the secondary GM temperature may be expected to be only a few degrees (at most) less than that of the primary GM. As the thickness of the primary liner increases (e.g., if there is a foundation layer below the GCL as part of the primary liner or if there is a CCL), the temperature of the secondary GM decreases. The temperature of the primary and secondary GM may have a profound impact on the service life of these GMs.
  • Both GCLs and CCLs may be susceptible to shrinkage and desiccation when used as part of a composite liner. This results from exposure to solar radiation prior to placement of adequate cover over the GM or after placement of waste (due to heat generated by the waste as discussed above). The potential for shrinkage and desiccation will depend on the temperature gradient, the characteristics of the GCL or CCL, the unsaturated soil characteristics and initial water content of the foundation layer beneath the clay liner, the overburden stress and the distance to the underlying watertable. The available information suggests that while there is potential for desiccation and shrinkage, this can be mitigated by appropriate design and construction. The most effective mitigation measure is to place the protection layer and overlying soil/drainage material on the composite liner as quickly as possible and before it is subjected to severe heating (eg., by solar radiation).
  • Typical construction practice will result in GMs developing a significant number of wrinkles (waves) by the time they are covered. New techniques have been developed for quantifying the size and distribution of wrinkles. It is important that drainage material be placed over the GM at times when the number of wrinkles is at a minimum (e.g., early in the day)
  • Under typical applied loads, wrinkles tend to remain in the GM.
  • While needle-punched, nonwoven geotextiles may provide reasonable protection against short-term holes in an underlying GM, recent research has shown that if gravel is used as the drainage layer then typical geotextile protection layers (up to 2000 g/m2) will not prevent large local strains in the GM and thinning of any underlying GCL.
  • A sand-protection layer between the gravel and the GM (perhaps combined with a traditional nonwoven geotextile) provides the best potential long-term performance.
  • Field evidence of significant increases in leakage into LDS due to damage to composite liners involving a GM and GCL due to landfill activities after liner construction highlight the need to place an adequate protection layer above the composite liner to minimize the risk of such accidental damage. It also highlights the need to closely monitor not only the construction of the liner but also any waste placement or other work that could potentially cause damage to the liner.
  • Field data indicates that the leakage through single GM liners is typically substantially higher than that through composite liners.
  • The observed leakage through a GM/CCL composite liner was typically one to two orders of magnitude higher than that observed for GM/GCL composite liners.
  • The calculated leakage obtained assuming direct contact (no major wrinkles) and typical size and number of holes in GMs using commonly used equations significantly underestimated the observed leakage for both GM/CCL and GM/GCL systems.
  • The typical observed leakage for composite liners with CCLs and GCLs can be readily explained by holes in wrinkles for the typical number of holes/ha and reasonable combinations of other parameters using the Rowe (1998) equation.
  • The design and construction of systems with a geonet LDS must ensure that the swelling and intrusion (under vertical stress) of any overlying GCL does not compromise the drainage function of the underlying geonet.
  • Available field data suggests that even with typical numbers of wrinkles and holes per hectare, for landfills with good CQC/CQA and where there is no damage to the liner during landfilling activities, the post-closure leakages are very small and contaminant transport is likely to be controlled by diffusion through the liner system for contaminants that can readily diffuse through a GM.
  • Volatile organic compounds (VOCs) can diffuse through both GMs and GCLs. Typical diffusion coefficients have been reported for both HDPE GMs as well as GCLs. Diffusion of hydrocarbons is much slower for fluorinated HDPE (f-HDPE) than conventional HDPE GMs. Control of the migration of these compounds will depend on the clay liner and any attenuation layer between the GM and any receptor aquifer.
  • Ionic contaminants exhibit negligible diffusion through intact HDPE GMs. The diffusion coefficient for ionic contaminates through GCLs is a function of the bulk void ratio of the GCL.
  • For landfills with double liner systems, the leakage through the primary liner will be mostly collected by the LDS. This will minimize the potential for advective movement through the secondary liner. However, volatile organic compounds will volatilize in the LDS and can then diffuse through the underlying secondary composite liner and hence diffusion needs to be considered for these cases. The time for VOCs to migrate through the primary liner at detectable levels can range from as little as a year to a decade, depending on the thickness of the primary liner and the concentration in the landfill leachate collection system.
  • The long-term performance of a GM will depend on the GM properties, the tensile strains in the GM (which can be induced by the overlying drainage material and wrinkles in the GM), the exposure to chemicals in the leachate, and temperature.
  • The service life of HDPE GMs meeting GRI GM-13 and used in MSW landfills are projected to be of the order of 600 years or more at a temperature less than 20oC. At a temperature of 35oC, the service life is projected to be of the order of 130–190 years. At temperatures of 50–60oC, service lives are very short (15–50 years).

It is suggested that GCLs and GMs can play a very beneficial role in providing environmental protection. However, like all engineering materials they must be used appropriately and consideration should be given to factors such as those addressed in this review. There is a need for site specific design, strict adherence to construction specifications, and appropriate protection of the geosynthetics after construction.

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RSP-0242 – Verification of the PROMETHEUS core analysis code and its advanced option

Various aspects of the PROMETHEUS core analysis code have been considered in order to verify whether the code can be used reliably for reactor core analysis.

The programming of the code has been converted to Fortran-90 and all programming constructions which do not comply with the Fortran-90 standard have been replaced. This makes the code fully portable to other computer platforms and Fortran-90 compilers.

Many corrections and improvements were made to the code programming to run the various input options correctly. The input description in the code manual was updated and considerably extended to include all findings.

It was deduced from the current programming that the code version of PROMETHEUS as provided by the CNSC is a stripped version from the original code as was developed at the Delft University of Technology, the Netherlands. Therefore, several options that can be selected in the input file cannot be actually run especially the option for time-dependent calculations and for burn-up calculations.

It was found that the boundary conditions in the x- and y-direction other than reflective boundaries, are not working correctly. The cause of this defect could not be found.

Criticality calculations with the PROMETHEUS code have been tested for a number of cases of different complexity. In all cases three-group cross sections were used. For the geometrically simpler problems the results for the effective multiplication factor and flux distributions are compared with analytical solution of the multi-group diffusion equations and excellent agreement was obtained. To compare the flux distribution with analytical results, a program was written to convert the binary flux output file to a directly readable ASCII file, which can also be imported in an Excel spreadsheet for plotting.

The results for a geometrically more complex three-dimensional system were compared with those of another multi-group diffusion code using an independent method for solving the diffusion equations. Here, also, good agreement was found.

It is concluded that the PROMETHEUS code is very well capable of solving the multi-group diffusion equations for reactor criticality problems.

The PROMETHEUS code has also been tested for its options with regard to thermal-hydraulic feedback. A few input cases were composed to run the simple and the detailed thermal-hydraulic model included in the PROMETHEUS code. Several corrections and improvements to the code had to be made to run these options. The input description has been improved and extended considerably.

The simple thermal-hydraulic model only applies to a time-dependent calculation, which could not be verified. A test with an initial fuel temperature different from the base temperature and its feedback to the cross sections could be verified in detail and gave correct results.

The detailed thermal-hydraulic model could be tested in particular for a static criticality calculation. Physically reliable results in terms of fuel and coolant temperature and coolant density were obtained, as well as in effective multiplication factor and axial flux profile.

It is concluded that the PROMETHEUS code is well capable of performing static criticality calculations with thermal-hydraulic feedback. Such calculations can give detailed information about the space-dependent behaviour of the fuel and coolant temperature and the coolant density.

For modelling control rods in PROMETHEUS, two different options are available: the black-absorber option and a detailed model representing different parts of a control rod. It was verified with various input cases that the black-absorber option works correctly. The detailed model shows some limitations and required an extensive update of the input descriptions for a correct interpretation of the necessary input and correct working of this option.

The option for a time-dependent calculation could only be tested as far as the necessary input items are concerned. To this end, the PROMETHEUS code had to be extended with a number of subroutines. The input description for this option could be corrected and extended. No actual time-dependent calculation could be performed as the PROMETHEUS code in its present form does not contain the module for time dependence.

The option in PROMETHEUS for performing burn-up calculations could not be actually tested, as the module for burn-up was not present in the current code version. Only the input reading for this option could be verified.

A number of recommendations is formulated to make the PROMETHEUS code a versatile tool for reactor core and accident analysis. The most urgent ones are to correct the effect of non-reflective boundary conditions in the x- and y-directions and to transform the PROMETHEUS code into a modular form running under Windows and to add the necessary modules for cross section processing, time dependence and burn-up.

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RSP-0243 – Review of AREVA surface gamma radiation survey of disturbed areas at Cluff Lake

AREVA Canada Resources Inc. (AREVA) is currently decommissioning the Cluff Lake uranium mine site and has completed remediation of nine sub-areas that were most disturbed by mining activities including the tailings management area and mining areas. A survey report, Submission for Gamma Radiation Clearance Cluff Lake Project, has been submitted to the CNSC describing the results of the AREVA surveys of these areas and indicates that the clean-up criteria have been met in the areas surveyed (other than D-Pit not meeting one of the ALARA guidelines).

A proposed procedure for gamma radiation clearance, CL-RP-62 Rev 0, was submitted to, and approved by, the CNSC. This procedure describes the dose basis for the criteria, a high density data collection procedure using radiation detectors linked to GPS systems, the data processing and the output to be included within the survey report. The data collection procedure may be used at several other mines during remediation and decommissioning.

The CNSC contracted SENES Consultants Limited (SENES) in January 2008 to conduct an independent review that included demonstrating: i) that the criterion of 1.0µSv/h averaged over 10,000 m2 areas was dose-based using site-specific considerations; ii) that AREVA used the approved procedures in CL-RP-62 Rev 0; and iii) that the results in the AREVA report met the criteria and guidelines for clearance. These three components have been completed and the assessment was that AREVA met these requirements. Although AREVA met the CNSC-approved procedure for this survey, some additional comments that would improve future surveys were provided. A summary of these reviews are included in this report.

A survey plan of an onsite verification survey was completed for the collection of gamma radiation dose rates from areas of particular concern to the CNSC and to compare these measurements against the results reported by AREVA for the same areas. The field survey was conducted in July 2008 using a data collection procedure similar to that used by AREVA. The gamma radiation levels reported by AREVA and verification surveys include negligible contributions from cosmic radiation; the detector is insensitive to the cosmic gamma radiation and the rate of electrons from cosmic radiation at the earth's surface is low compared to the terrestrial radiation.

The analysis of the data indicated that the majority of the surveyed areas agreed within 0.05µSv/h of the levels measured during the AREVA survey. There were, however, indications of a change in site condition between the surveys for some locations. Some locations had lower gamma radiation exposure levels during the survey compared to the previous surveys. Other areas showed an increase in gamma radiation levels since the AREVA survey.

A review of the leach vault area was conducted to reproduce the original assessment against criteria and guidelines that was used by AREVA. The boundary selected by AREVA was consistent with the edges of the open disturbed areas. Gamma radiation levels tended to be slightly higher on the leach vault area compared to the AREVA measurements of this area but the assessment against criteria and ALARA guidelines matched the original AREVA assessment.

A criterion used in the AREVA survey report was that the maximum individual measurement should be below 2.5µSv/h; however, there is no dose basis for this value. The detection of such locations and reproduction of previous surveys is difficult particularly for small locations and depends on many factors such as spacing between transects, speed of travel during surveying and averaging time for the detector. It is recommended that future gamma radiation surveys have a criterion for a smaller measurable and reproducible area rather than apply this to a single measurement. One small area, a radius of about 1 m diameter, was detected during the verification survey that had a maximum gamma radiation exposure of 5.7µSv/h.

The conclusions from the verification survey were that AREVA followed the approved procedure for conducting the gamma radiation survey and interpreting the results. A number of comments for improving future surveys and communicating results from these types of surveys have been provided. The onsite verification survey indicated that the majority of the areas surveyed had gamma radiation levels that closely matched the AREVA survey results. There was some change in gamma radiation levels, both increases and decreases relative to the AREVA results, which indicate that site conditions may have changed since the earlier survey. These changes are unlikely to affect the assessment against criteria.

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RSP-0244 – Loading of steam generator tubes during main steam line break – Phase 1

A main steam line break in a CANDU power plant will produce a rapid blow down of the steam generators. The resultant high velocity flow across the steam generator tubes will cause a transient loading which is difficult to predict. Since these tubes represent the boundary between the irradiated primary side fluids and the secondary side coolant, their structural integrity is extremely important. The overall purpose of this project is to develop a better understanding of the nature of this transient loading and its prediction through experimental studies.

This report summarizes the results of Phase 1 of this study which was to design and build an experimental rig to carry out the blow down simulations. The concept of the experimental rig for carrying out the experiments is outlined and detailed drawings of the rig and its component parts are provided.

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RSP-0245 – Development of an integrated approach for implementing the earned quality method

This final report is submitted in compliance with the scope of work described in contract 87055–1175 – R354.2 and amendment #1 to contract 87055-07-1175 – R354.2 – Development of an Integrated Approach for Implementing the earned quality method. It proposes an integrated approach for implementing the Earned Quality Method (EQM) to projects undertaken within the Operational Engineering and Assessment Division (OEAD) and provides an example on how the approach can be used for quality assurance in projects. The goal of this project was to develop a rigorous, useful and easy to use approach for quality management within OEAD projects.

It was decided to use the EQM as it allows not only to identify the quality criteria required to meet the stakeholders needs and expectations but also to assess their level of achievement throughout the project. However, the EQM is a complex method and its implementation requires a systematic and flexible approach. This report describes the approach developed to support the implementation of the EQM. The proposed approach contains the following eight steps:

  1. writing a need statement
  2. performing a stakeholders analysis
  3. developing a value proposition
  4. writing a project scope statement
  5. developing the Quality Breakdown Structures (QBS)
  6. developing a Logical Framework – Millennium (LF-M)
  7. developing a Work Breakdown Structure (WBS)
  8. measuring and controlling the Earned Quality (EQ).

The eight steps of the new approach ensure that all the information required to implement the EQM is available and in the appropriate format.

In the first step, writing a need statement, a problem or opportunity is identified by comparing an undesirable situation with a desirable situation as well the expected impact of the desirable situation on the mission of the organization or to its priorities is determined. Based on the need statement, a name is proposed for the project. In the second step, performing a stakeholders analysis, the project stakeholders, their needs and expectations with regard to the proposed project are identified. In the third step, developing a value proposition, options to deal with the problem or the opportunity are identified and compared to determine the best one. The options are compared with regard to their organizational value (the contributions to the mission of the organization), their benefits (the contributions to the desirable situation), their cost, the completion time of their deliverables, and their risk. Then in the fourth step, writing a project scope statement, the cost, the completion time and the quality attributes (customers' requirements) of each deliverable are specified for the preferred option. In the fifth step, developing the quality breakdown structures (QBS), a QBS is used to decompose the quality attributes (as identified in the previous step) of each deliverable into measurable quality criteria and an assessment function for each criterion is developed. In the sixth step, developing a logical framework – Millennium (LF-M), a LF-M gives a concise and complete vision of the project using the information obtained in the previous steps. In the seventh step, developing a work breakdown structure (WBS), a WBS is developed to identify all the tasks required to produce the deliverables according to their cost, time and quality objectives and a project schedule is proposed. In the last step, measuring and controlling the earned quality (EQ), the activities of the WBS are linked to the quality criteria of the QBS to ensure that all quality criteria are supported by at least one activity of the WBS and to allow measuring and controlling the earned quality throughout the project life cycle.

Developing the QBS and the WBS and linking them together can be quite time consuming as well updating them can be even more time consuming. Templates, using Excel™ spreadsheets, are proposed to guide project team members through the steps of the new approach. Links between the templates ensure consistency between the steps.

Using two ongoing CNSC projects, the templates were tested in late September 2009 for ease of use and accuracy. The analysis of the results of the test showed that the templates needed to be simplified further and better integrated. Consequently, the templates were modified significantly to ensure that there is no duplication of data or unnecessary data. More links between common fields were added to avoid inputting the same information twice. As well, the format of a few templates was simplified by using tables instead of graphs. The changes make the templates not only easier to use but also easier to modify. Gantt charting capability was added also. This capability makes the use of any other project scheduling software unnecessary. To our knowledge, no other Excel based template has similar capabilities.

This report provides examples from the Steam Generator Tubes Failure Model Development Project to show how the templates can be used to implement the EQM. The examples covered all the steps of the approach and should assist the project teams with their implementation.

A rigorous and flexible approach was developed to implement the EQM to projects undertaken within the OEAD. This approach should be part of the quality assurance effort undertaken by project teams for all projects. The integrated approach should increase the likelihood of project success by providing a systematic approach to manage the quality of R&D projects and by allowing to measure and to control periodically project performance.

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RSP-0246 – An evaluation of severe accident computer codes for CANDU nuclear power plants

This report describes work performed for the CNSC on:

  1. identifying the computer codes that have been used in the deterministic analysis supporting severe accident assessments for CANDU reactors, and provide general descriptions of these computer codes
  2. discussion of major features of SCDAP/RELAP5, and recommend potential improvements for it
  3. providing a comparison of the capabilities and limitations of the identified computer codes based on information available in open literature

The report highlights the major features and capabilities of MAAP-CANDU and ISAAC codes, and discusses open literature results obtained with the two codes. The report also points out the main limitation of these codes. The report presents extensively the mathematical models of RELAP and SCDAP, the validation of SCDAP/RELAP5 code and application of the code to the analyses of CANDU reactors until now. A number of SCDAP/RELAP5 code improvements have been proposed in order to improve the capability of CANDU severe accident analysis.

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RSP-0247 – Investigation of the environmental fate of tritium in the atmosphere

This report reviews the literature on environmental fate and behaviour of tritium in the atmosphere, including tritium transfer to and behaviour in the hydrological environment. It begins with a description of the various anthropogenic and natural sources of tritium in the atmosphere, the chemical forms of tritium in the atmosphere, and the physical and chemical behaviour of tritium in the atmosphere. The report also describes the dynamic behaviour of tritium in the hydrological cycle, including transfer of tritium from air to soil water and surface water, tritium transport from soil water to groundwater, and tritium behaviour in lake and river receiving environments.

Modelling approaches are described for representing atmospheric dispersion of tritium from point sources, and partitioning of tritium (HTO) from air to soil water, surface water and groundwater. Modelling was completed at a number of licensed facilities releasing tritium and model predictions were compared to measured environmental concentrations. Based on these comparisons, our ability to predict environmental concentrations based on current understanding of tritium behaviour is discussed and factors contributing to model uncertainty are identified.

The sector-averaged Gaussian dispersion model as described in the Canadian Standards Association (CSA) N288.1-08 standard was applied at a number of nuclear power stations and tritium light manufacturing facilities. In all cases, the model was conservative, tending to over-predict the tritium concentration in air. In three cases, predictions were slightly higher than annual average measured values (20–83 percent higher on average, generally within a factor of two). In two cases, tritium concentrations were over-predicted more substantially by two or three times on average. Measured air values are uncertain due to unresolved differences between active and passive air samplers.

Model-predicted tritium in soil water was compared to either measured soil water or measured rain water (since soil water derives from rain water and should be similar). In three cases, predictions were slightly higher than measured values (35–62 percent on average, generally within a factor of two). In one case, tritium in soil water was over-predicted more substantially by two times on average). It was noted that, when air concentrations are changing rapidly, soil water can lag behind.

Model-predicted tritium in groundwater was compared to measured groundwater at one facility and was 52 percent higher on average (generally within a factor of three). It was noted that groundwater wells may be influenced by nearby snow storage, or by horizontal groundwater flow, as well as vertical infiltration, and are subject to local variation in sub-surface conditions. Groundwater lags behind soil water based on well depth and vertical travel time.

Model-predicted tritium in pond water was compared to measured pond water at one facility and was 28 percent higher on average (generally within a factor of two). It was noted that ponds and marshes may be subject to up-gradient inflows of soil water or groundwater, and thus may not be at equilibrium with current local air concentrations. The greatest regulatory concerns related to tritium are in areas near a long-term atmospheric source (within 1 km) where people use well water and garden produce.

Recommendations include studies to resolve the discrepancies that are often seen between active and passive air sampler results, as well as near-field studies of air, soil water and groundwater designed to better understand the time lags in soil water and groundwater, and the importance of up-gradient effects.

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