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Archived Web Page: Draft Regulatory Document RD-364Joint Canada - United States Guide for Approval of Type B(U) and Fissile Material Transportation Packages

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3.0 THERMAL EVALUATION

This section of the application should identify, describe, discuss, and analyze the principal thermal engineering design of the packaging, components, and systems that are important to safety and describe how the package complies with the performance requirements of 10 CFR 71.33(b)(5), 10 CFR 71.33(b)(7), 10 CFR 71.43(d), 10 CFR 71.43(g), 10 CFR 71.55(f)(1)(iv), 10 CFR 71.71(c)(1) and (2), and 10 CFR 71.73(c)(4) or Paragraphs 642, 651, 652, 653, 654, 655, 660, 661, 662 of TS-R-1, which are incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1, and Paragraphs 728, and 736 of TS-R-1 which are incorporated in Subsection 1(4) of the PTNS Regulations by reference to Paragraph 716 of TS-R-1.

This section should address the thermal performance of the package under normal and hypothetical accident conditions of transport in terms of the maximum allowable temperatures and subsequent effect on the containment, structural, shielding, and criticality safety design. Any operational, fabrication and maintenance requirements with respect to the thermal evaluation important for the package safety should be included in Section 7, Package Operations, and Section 8, Acceptance Tests and Maintenance Program, of the application.

3.1 Description of Thermal Design

This section should provide a description of the significant thermal design features and operating characteristics of the package and discuss the operation of all subsystems. The thermal criteria that will be directly applied to thermal results (e.g., maximum fuel temperature, shield temperature not to exceed melt) should be identified. Properties evaluated here but used to support other evaluations (e.g., pressure, temperature, distributions relative to thermal stress) should also be identified. The significant results of the thermal analysis or tests and the implication of these results on the overall thermal performance of the package should be summarized. The minimum and maximum decay heat loads assumed in the thermal evaluation should be specified. The maximum decay heat load assumed should include the energy from all source terms contained in the package, including those that might be neglected in the shielding and containment analyses.

3.1.1 Design Features

This section should describe the design features of the package that are important for thermal performance. The package design must not rely on mechanical cooling systems to meet containment requirements specified in Section 4, Containment, of this document.

Packaging design features important for the thermal evaluation include the following:

  1. Package geometry and materials of construction;
  2. Structural and mechanical features that may affect heat transfer, such as cooling fins, insulating materials, surface conditions of the package components, and gaps or physical contacts between internal components; and
  3. The identity and volume of any coolants if applicable.

3.1.2 Decay Heat of Contents

The maximum decay heat and the radioactivity of the contents should be specified in accordance with the requirement of 10 CFR 71.33(b)(7) or Paragraph 651 of TS-R-1 as incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1. This section should show that the derivation of the decay heat is consistent with the maximum quantity of radioactive contents. In the case of SNF packages, the computer codes discussed in Section 5, Shielding Evaluation, of this document for determination of neutron and gamma sources may be used for calculating content decay heat loads.

3.1.3 Summary Tables of Temperatures

This section should present summary tables of the maximum or minimum temperatures that affect structural integrity, containment, shielding, and criticality under both normal conditions of transport and hypothetical accident conditions. All information presented in this table should be consistent with the information used within other sections of the application. For the fire test condition, the tables should include the following information:

  1. Maximum temperatures of various package components and the time at which they occur after fire initiation (e.g., containment vessel, seals, shielding, fuel/cladding); and
  2. Temperatures of the steady-state condition.

3.1.4 Summary Tables of Maximum Pressures

The summary tables should include the maximum normal operating pressure and maximum pressure under hypothetical accident conditions. All information presented in this table should be consistent with the information used within other sections of the application.

3.2 Material Properties and Component Specifications

3.2.1 Material Properties

This section should specify the appropriate thermal properties for materials that affect heat transfer both within the package and from the package to the environment. Liquids or gases within the package and gases external to the package for hypothetical accident conditions should be included. For packages using anisotropic materials, the directional properties of these materials should be provided. The thermal absorptivities and emissivities should be appropriate for the package surface conditions and each thermal condition. When reporting a property as a single value, the evaluation should show that this value bounds the equivalent temperature-dependent property. In addition, this section should include references for the data provided.

These properties include the following:

  1. Thermal conductivity;
  2. Specific heat;
  3. Density;
  4. Thermal radiation emissivity of the package surfaces;
  5. Coefficient of thermal expansion; and
  6. Modulus of elasticity.

3.2.2 Component Specifications

This section should include the technical specifications of components that are important to the thermal performance of the package as illustrated by the following examples:

  1. In the case of valves or seals, the operating pressure range and temperature limits;
  2. The properties of fabricated insulation and coatings, including a summary of test data that support their performance specifications;
  3. The maximum allowable service temperatures or pressures for each package component, including pressure relief valves and fusible plugs; and
  4. The minimum allowable service temperature of all components, which should be less than or equal to -40°C (-40°F).

3.3 General Considerations

The thermal evaluation of the package can be performed by either analysis or test, or a combination of both.

3.3.1 Evaluation by Analysis

For computer analyses, the method used should be properly referenced or developed, and the computer program should be shown to be well benchmarked for thermal analyses, applicable to the evaluation, and sufficiently described to permit review and independent verification. The assumptions used in modeling the heat sources and heat transfer paths should be clearly stated and justified.

The thermal analysis should assume that the heat transfer medium is air, and the effects of air on the contents and packaging components (e.g., oxidation of depleted uranium shielding) should be considered. For packages using other fill gas (e.g., argon, helium), the analysis should assume air and may also include an analysis with the actual fill gas to show the impact on the thermal performance of the package.

The analysis should include the following:

  1. Thermal properties for the package materials;
  2. Calculations for conductive, convective, and radiative heat transfer among package components and from the surfaces of the package to the environment;
  3. A description of the changes in package geometry and material properties resulting from structural and thermal tests under normal conditions of transport and hypothetical conditions of transport;
  4. The heat produced by the combustion of package components if applicable;
  5. A description of the temperature and thermal boundary conditions for normal conditions of transport and hypothetical conditions of transport; and
  6. A demonstration that the time interval used for the evaluation of the temperature following the thermal test is adequate to ensure that the components reach their maximum temperature and that steady-state temperatures have been reached.

For the 30-minute fire test, the majority of the heat input to the package will be through radiation. For convective heat transfer, a convective heat transfer coefficient appropriate for the conditions that would exist if the package were exposed to the fire should be used. Flame velocities in an open pool fire may be used in determining the appropriate convective heat transfer coefficient. Any correlation used in the analysis should be properly explained and justified. For the cooldown, natural convection should be assumed.

Any assumptions for contact resistance at material interfaces, energy transport across gaps, enclosures, and other factors should be provided and justified.

For SNF packages, an analysis should be considered to evaluate the potential impact of the fission gas to the cask component temperature limits and the cask internal pressurization if any of the following conditions are met:

  1. The cask component temperatures are within 5% of their limiting values under hypothetical accident conditions;
  2. The maximum normal operation pressure is within 10% of its design-basis pressure; or
  3. Any other special conditions exist.

3.3.2 Evaluation by Test

The evaluation should include a detailed description of the design of the test package and test facility. This description should demonstrate that the test package was fabricated under a proper quality assurance program. In addition, the evaluation should include a description of how the test facility operates and provide details on how the results were evaluated.

The application should include the following:

  1. Demonstration that the test facility (pool fire or furnace facility) and the test procedure can meet the range of thermal conditions such as fire heat fluxes or temperature;
  2. A description of the performance of the test package, including the simulated content and any attached test instrumentation and mounting hardware;
  3. Demonstration that the temperature-sensing instrumentation has been located to measure the maximum temperature of the package components and can adequately characterize the heat transfer pathways; and
  4. Demonstration that the package instrumentation, such as temperature- or pressure-sensing devices, has been mounted in locations that minimize its effects on local test package temperatures.

Some conditions, such as ambient temperature, decay heat of the contents, or package emissivity or absorptivity, may not be exactly represented in a thermal test. The thermal evaluation should include appropriate corrections or evaluations to account for these differences. For example, the thermal evaluation should include a temperature correction if the ambient temperature at the onset of the fire test was lower than 38 °C.

3.4 Thermal Evaluation under Normal Conditions of Transport

This section should describe the thermal evaluation of system and subsystem operation under normal conditions of transport. The temperature ranges bounded by the minimum and maximum ambient temperatures and minimum and maximum decay heat loads should be considered. The results should be compared with allowable limits of temperature and pressure for the package components. The information should be presented in summary tables along with statements and appropriate comments. Information that is to be used in other sections of the review should be identified. The margins of safety for package temperatures, pressures, and thermal stresses, including the effects of uncertainties in thermal properties, test conditions and diagnostics, and analytical methods, should be addressed. The analysis or test results should be shown to be reliable and repeatable.

In addressing the sections below, the following general information should be considered and included as appropriate:

  1. Assumptions that are used in the analysis should be clearly described and justified.
  2. Models and modeling details should be clearly described.
  3. For thermal evaluation by test, the test method, procedures, equipment, and facilities that were used should be described in detail.
  4. If the specimen tested is not identical in all respects to the package described in the application, the differences should be described and justification given that these differences would not affect the test results.
  5. Temperature data should be reported at gaskets, valves, and other containment boundaries, particularly for temperature-sensitive materials, as well as for the overall package; and
  6. Both interior and exterior temperatures should be included.

The damage caused by the tests and the results of any measurements that were made should be reported in detail, including photographs of the testing and the test specimen.

3.4.1 Heat and Cold

This section should demonstrate that the tests for normal conditions of transport do not result in a significant reduction in packaging effectiveness. The following items should be considered and addressed:

  1. Degradation of the heat-transfer capability of the packaging, such as creation of new gaps between components;
  2. Changes in material conditions or properties (e.g., expansion, contraction, gas generation, and thermal stresses) that affect the structural performance;
  3. Changes in the packaging that affect containment, shielding, or criticality, such as thermal decomposition or melting of materials; and
  4. Ability of the packaging to withstand the tests under hypothetical accident conditions.

The component temperatures and pressures should be compared to their allowable values. This section should explicitly show that the maximum temperature of the accessible package surface is less than 50°C (122°F) for non-exclusive-use shipment or 85°C (185°F) for exclusive-use shipment in accordance with the requirements specified in 10 CFR 71.43(g) or Paragraphs 652 and 662 of TS-R-1 which are incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1.

3.4.2 Temperatures Resulting in Maximum Thermal Stresses

The evaluation of thermal stresses caused by constrained interfaces among package components resulting from temperature gradients and differential thermal expansions should be addressed in Sections 2.6.1.2 and 2.6.1.3 of the application.

3.4.3 Maximum Normal Operating Pressure

This section should report the maximum normal operating pressure consistent with the other sections of the safety analysis report and show how it was calculated, assuming the package has been subjected to the heat condition for one year as specified in 10 CFR 71.4 and 10 CFR 71.33(b)(5) or Paragraph 660 of TS-R-1 which is incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1. The calculation should consider possible sources of gases, including the following:

  1. Gases initially present in the package;
  2. Saturated vapour, including water vapour from the contents or packaging;
  3. Helium from the radioactive decay of the contents;
  4. Hydrogen or other gases resulting from thermal or radiation-induced decomposition of materials such as water or plastics; and
  5. Fuel rod failure.

For SNF packages, Table 4-1 provides guidance on release of fill gas and fission product gas for pressurized and boiling light-water reactor fuel.

This section should also address the requirement in 10 CFR 71.4 or Paragraph 661 of TS-R-1, which is incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1, with respect to Type B(U) packages (i.e., that the maximum normal operating pressure must not be greater than 700 kPa gauge pressure).

In addition, this section should demonstrate that hydrogen and other flammable gases comprise less than 5% by volume of the total gas inventory within any confined volume and will not result in a flammable mixture within any confined volume of the package as specified in 10 CFR 71.43(d) or Paragraph 642 of TS-R-1 which is incorporated in Subsection 1(1) of the PTNS Regulations by reference to Paragraph 650 of TS-R-1.

3.5 Thermal Evaluation under Hypothetical Accident Conditions

This section should describe the thermal evaluation of the package under hypothetical accident conditions. The hypothetical accident conditions defined in 10 CFR 71.73 or Paragraphs 726-729 of TS-R-1 which are incorporated in Subsection 1(4) of the PTNS Regulations by reference to Paragraph 716 of TS-R-1 should be applied sequentially to meet 10 CFR 71.73 or, in the most damaging sequence, to meet PTNS Regulations (see Section 2.7). For the accident condition thermal evaluation the general comments in Section 3.3 above should be considered and addressed as appropriate.

3.5.1 Initial Conditions

The thermal evaluation should consider the effects of the drop, crush (if applicable), and puncture tests on the package. This section should identify initial conditions, including the following, and justify that they are most unfavourable:

  1. An ambient temperature between -40°C (-40 °F) and +38°C (+100°F) with no insolation. This range is specified in the Canadian and the IAEA regulations. The U.S. regulations specify a minimum ambient temperature of -29 °C (-20°F) for the initial condition. Therefore, an ambient temperature range between -40°C (-40°F) and +38°C (+100°F) should be considered.
  2. An internal pressure of the package equal to the maximum normal operating pressure unless a lower internal pressure, consistent with the ambient temperature, is less favourable.
  3. Contents at its maximum decay heat unless a lower heat, consistent with the temperature and pressure, is less favourable.

3.5.2 Fire Test Conditions

This section should provide a detailed description of the analysis or tests used to evaluate the package under the fire test conditions. The evaluation should address the requirements in 10 CFR 71.73(c)(4) or Paragraph 728 of TS-R-1 which is incorporated in Subsection 1(4) of the PTNS Regulations by reference to Paragraph 716 of TS-R-1.

The package should be subjected to full insolation, and it should be ensured that the evaluation is continued until the post-fire, steady-state condition is achieved and that no artificial cooling is applied to the package. In addition, all combustion should be allowed to proceed until it terminates naturally.

When a thermal test is performed to evaluate the package performance, the description of the test should include the following:

  1. Fire dimensions;
  2. Package orientation and support methods;
  3. Test temperatures and duration;
  4. Heat source;
  5. Initial ambient temperature;
  6. Period following the thermal test; and
  7. Adequate availability of oxygen supply.

For a pool fire, the fire width should extend horizontally between 1 and 4 m beyond any external surface on the package. In addition, the package should be positioned 1 m above the surface of the fuel source.

The analysis should include the thermal performance of the test package, including simulated package contents and any attached test instrumentation and mounting hardware, and also including the location of temperature-sensing instrumentation used to measure the appropriate maximum package component temperatures and characterize the significant heat transfer pathways. These should be mounted at locations that minimize their effects on local test package temperatures. Ensure that any possible perturbations caused by the presence of these sensors are appropriately considered.

Any physical change in the package condition resulting from the fire test, such as change in material properties, combustion or melting of package components, and increase in internal temperature and pressure during the fire and post-fire period, should be adequately evaluated and justified.

3.5.3 Maximum Temperatures and Pressure

This section should report the peak temperatures of package components as a function of time both during and after the fire as well as the maximum temperatures from the post-fire, steady-state condition. This section should include those temperatures at locations in the package that are significant to the safety analysis and review. In particular, the temperatures for items such as contents, gaskets, valves, and shielding should be reported. These temperatures should not exceed their maximum allowable values; melting of lead shielding is not permitted. The calculations of temperatures should trace the temperature-time history up to and past the time at which maximum temperatures are achieved and begin to fall.

The evaluation of the maximum pressure in the package should be based on the maximum normal operating pressure and should consider fire-induced increases in package temperatures, thermal combustion or decomposition processes, fuel rod failure, phase changes, and other factors.

This section should provide a general description of package performance and should compare the results of the thermal test with allowable limits of temperature, pressure, and other characteristics for the package components. Damage to the package either from interpretation of the analysis or from test observation should be considered or described. The assessment should include possible structural damage, breach of containment, and loss of shielding.

3.5.4 Temperatures Resulting in Maximum Thermal Stresses

This section should present results of thermal analyses used in the structural evaluation for calculating the most severe thermal stress conditions that result during the fire test and subsequent cooldown. The temperatures corresponding to the maximum thermal stresses should be reported.

3.5.5 Fuel/Cladding Temperatures for Spent Nuclear Fuel

For spent nuclear fuel (SNF) packages, the maximum allowable fuel/cladding temperature should be identified and justified. The justification should consider the fuel and clad materials, irradiation conditions (e.g., the absorbed dose, neutron spectrum, and fuel burnup), and the shipping environment, including the fill gas. In general, the cladding temperature for commercial light-water-reactor spent fuel should be kept below 400°C under normal conditions of transport and below 570°C under hypothetical accident conditions. Other necessary considerations include the hydride reorientation effects on mechanical properties, the elapsed time from the removal of the SNF from the core to its placement into the transportation packaging, its duration in the packaging, and its post-transport disposition. Examples of temperature limits include the following:

  1. The temperature limit for metal fuel, which should be less than the lowest melting point eutectic of the fuel; and
  2. The temperature limit on the irradiated clad in an inert gas environment as appropriate.

3.5.6 Hypothetical Accident Conditions for Fissile Material Packages for Air Transport

If applicable, applicants should address the expanded fire test conditions specified in 10 CFR 71.55(f)(1)(iv) or Paragraph 736 of TS-R-1 which is incorporated in Subsection 1(4) of the PTNS Regulations by reference to Paragraph 716 of TS-R-1.

3.6 Appendix

The appendix should include a list of references, applicable pages from referenced documents, justification of assumptions or analytical procedures, test results, photographs, computer program descriptions and examples of input and output files, specifications of O-rings and other components, detailed materials test data, and other supplemental information.

If the package has been subjected to a thermal test, the appendix should include a description of the test facility with respect to the following:

  1. Type of facility (e.g., furnace, pool-fire);
  2. Method of heating the package (e.g., gas burners, electrical heaters);
  3. Volume and emissivity of the furnace interior;
  4. Method of simulating decay heat if applicable;
  5. Types, locations, and measurement uncertainties of all sensors used to measure the fire heat fluxes affecting critical components, such as seals, valves, pressure, and structural components, and fire temperatures;
  6. The post-fire environment for a period adequate to attain the post-fire, steady-state condition; and
  7. Methods for both maintaining and measuring an adequate supply and circulation of oxygen for initiating and naturally terminating the combustion of any burnable package component throughout the fire and post-fire periods.

The appendix should also include a complete description of the tests performed. This description should include the following:

  1. Test procedure;
  2. Test package description;
  3. Test initial and boundary conditions;
  4. Test chronologies (planned and actual);
  5. Photographs of the package components, including any structural or thermal damage, before and after the tests;
  6. Test measurements, including, at a minimum, documentation of test package physical changes and temperature and heat flux histories;
  7. Corrected tests results; and
  8. Method used to obtain the corrected results.

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