SSG-27 (Rev. 1) Criticality Safety in the Handling of Fissile Material

Ensuring and demonstrating subcriticality under operational states and under conditions referred to as ‘credible abnormal conditions’ or ‘conditions included in the design basis’;

Estimating the credible consequences of a potential criticality accident;

Minimizing the consequences if a criticality accident were to occur.

The scope and level of detail of the criticality safety assessment;

The methods and enveloping criticality events used in the criticality safety assessment;

The design of criticality detection and alarm systems;

The level of training and qualification of personnel involved in criticality safety;

Emergency preparedness and response for criticality accidents;

Administrative measures for criticality control.

The subcritical value of k_eff for the system under analysis.

A set of one or more macroscopic control parameters whose values, individually or in combination, for the system under analysis correspond to a k_eff of less than 1. Examples of such control parameters are mass, concentration, moderation, geometry, nuclide composition, chemical form, temperature, density, and neutron reflection, interaction or absorption.

Management responsibility, which includes the support and commitment of management necessary to achieve the objectives of the operating organization.

Resource management, which includes the measures necessary to ensure that the resources essential to the implementation of strategy and the achievement of the objectives of the operating organization are identified and made available.

Process implementation, which includes the activities and tasks necessary to achieve the goals of the organization.

Measurement, assessment, evaluation and improvement, which provide an indication of the effectiveness of management processes and work performance compared with objectives or benchmarks. It is through measurement and assessment that opportunities for improvement are identified.

A description of the organizational structure;

Functional responsibilities;

Levels of authority.

Developing and documenting all aspects of criticality safety assessment.

Monitoring the performance of activities and processes.

Ensuring that personnel are adequately trained.

Operating a system for keeping records that ensures control of performance and verification of activities important to criticality safety. The record keeping system should provide for the identification, approval, review, filing, retrieval and disposal of records.

Determining the necessary competence of criticality safety staff and providing training, as necessary;

Preparing and issuing specifications and procedures on criticality safety;

Supporting and performing criticality safety assessments;

Having frequent personal contact with personnel, including observing work in progress.

The design and arrangement of engineered safety measures;

The need for instrumentation to ensure that the operational limits and conditions are adequately monitored and controlled;

The need for additional administrative measures to ensure that the operational limits and conditions are adequately controlled.

Inherent safety of the process, which is independent of any safety measures.

Passive engineered safety measures⁷ that do not rely on control systems, active engineered safety measures or human intervention.

Automatically initiated active engineered safety measures (e.g. an automatically initiated shutdown or process control system).

Administrative safety measures:

(i) Active engineered safety measures initiated manually by operating personnel (e.g. operating personnel initiating a shutdown system in response to an indicator or alarm);

(ii) Safety measures provided by operating personnel (e.g. a mass limit that is implemented by an operator weighing a container and verifying that the mass limit will not be exceeded prior to introducing the container into a glovebox).

Mass and enrichment of fissile material present in a process;

Geometry (limitation of the dimensions or shape) of processing equipment;

Concentration of fissile material in solutions;

Degree of moderation;

Control of reflectors;

Presence of appropriate neutron absorbers.”

Restrictions on the dimensions or shape of the system to ensure a favourable geometry.

A limit on the mass of fissile material within a system to a subcritical mass. For example, the subcritical mass limit may be specified to be less than the minimum critical mass (incorporating a suitable safety factor) so that inadvertent ‘over‑batching’ of fissile material does not lead to criticality. Consideration may also need to be given to the potential for multiple over‑batching of fissile material as a credible abnormal condition (see para. 9.85(a) of SSR‑4 [2]).

A limit on the concentration of fissile nuclides, for example within a homogeneous hydrogenated mixture or within a solid.

Limits on the type and quantity of neutron moderating material.

Limits on the isotopic composition of the elements in the fissile material present in the system.

A limit on the density of the fissile material.

Limits on the amount, geometrical distribution and form of neutron reflecting material surrounding the fissile material.

The presence, geometrical distribution and integrity of neutron absorbers in the system or between separate systems that are individually subcritical.

Limits on the minimum separation distance between separate systems that are individually subcritical.

The limits on the nuclide composition of the elements in the fissile material are complied with.

The chemical and physical form of the compound to be used cannot change to make the compound more reactive.

A mixture of different compounds resulting in a higher k_eff cannot occur. The events described in (b) and (c) could occur in specific situations (e.g. the precipitation of a uranium or plutonium nitrate solution, modification of the diameter of pellets); both such events should be taken into account in the criticality safety assessment, and it should be proved that subcriticality would be maintained.

Specification and control of the nuclide composition of the fissile material; the fissile nuclide content; the mass, density, concentration, chemical composition and degree of moderation of the fissile material; and the spacing between systems of fissile material.

Determination and demarcation of criticality controlled areas (i.e. areas authorized to contain significant quantities of fissile material) and specification of the control parameters associated with such areas. Specification (and, where applicable, labelling) of materials (e.g. fissile material; neutron moderating, absorbing or reflecting materials). Specification (and, where applicable, labelling) of control parameters and their associated limits on which subcriticality depends. A criticality controlled area should be defined by both the characteristics of the fissile material within it and the control parameters used.

Control of access to criticality controlled areas.

Separation between criticality controlled areas, and separation of materials within criticality controlled areas.

Movement and control of materials within and between criticality controlled areas (including those areas containing different fissile materials and/or with different control parameters), and spacing between moved and stored materials (see also para. 6.147 of SSR‑4 [2]).

Procedural controls for record keeping systems (e.g. accounting for fissile material).

Movement and control of materials from areas without criticality safety control (e.g. wastewater processing areas) to criticality controlled areas or vice versa (e.g. flow of effluent waste streams from controlled to uncontrolled processes) (see also Requirement 28 of SSR‑4 [2]).

Use of neutron absorbers, and control of their continued presence, distribution and effectiveness.

Procedures for use and control of ancillary systems and equipment (e.g. vacuum cleaners in criticality controlled areas; control of filter systems in waste air and off‑gas systems).

Quality management, periodic inspection (e.g. control of continued favourable geometries), maintenance, and the collection and analysis of operating experience.

Procedures for use in the event of credible abnormal conditions (e.g. deviations from operating procedures, credible alterations in process or system conditions).

Procedures for preventing, detecting, stopping and containing leaks and for removing leaked materials.

Procedures for firefighting (e.g. the use of hydrogen‑free or very low hydrogen content fire extinguishing materials).

Procedures for the control and analysis of design modifications and of changes in operating procedures.

Procedures for criticality safety assessment and analysis.

Procedures for the appointment of suitably qualified and experienced criticality safety staff.

Procedures for training operating personnel and criticality safety staff.

Means of ensuring that the procedures are understood by operating personnel and contractors working at the facility.

Control of the facility configuration.

The safety functions and safety classification of structures, systems and components important to safety (e.g. in relation to the design, procurement and administrative oversight of operations, and to maintenance, inspection, testing and examination).

To facilitate the safe and efficient conduct of operations;

To include those controls, limits and measures that are important for ensuring subcriticality;

To include mandatory operations, advice and guidance for credible abnormal conditions and accident conditions;

To include appropriate links between procedures in order to avoid omissions and duplications and, where necessary, to clearly specify the conditions of entry to and exit from other procedures;

To be simple and readily understandable to operating personnel.

Criticality safety staff who are independent of operating personnel and who report (along with other safety experts) to a manager with responsibility for safety at the highest level of the organization;

The organizational means for ensuring that the criticality safety staff provide managers, supervisors and operating personnel with periodic training on criticality safety to improve their safety awareness and behaviour (see para. 9.83 of SSR‑4 [2]);

The organizational means for ensuring that criticality safety staff are provided with periodic training on criticality safety that is suited to their roles, responsibilities and operations;

The organizational means for ensuring that periodic reviews of criticality safety assessments (see Section 4) are undertaken;

The organizational means for ensuring that the criticality safety programme and its effectiveness are continually reviewed and improved.

Performing and documenting criticality safety assessments for systems of, or areas with, fissile material;

Ensuring the accuracy of the criticality safety assessment by, whenever possible, directly observing the activity, processes or equipment, as appropriate, and encouraging operating personnel to provide feedback on operating experience;

Providing documented guidance on criticality safety for the design of systems of fissile material, for processes and for the development of operating procedures;

Specifying the operational limits and conditions for ensuring criticality safety;

Specifying the necessary criticality safety measures and supporting their implementation;

Determining the location and extent of criticality controlled areas;

Assisting in determining the location of criticality detection and alarm systems, developing the associated emergency arrangements and conducting periodic reviews of these arrangements;

Assisting and consulting operating personnel, supervisors and management, and maintaining contact with them to ensure familiarity with all activities involving fissile material;

Conducting regular walkdowns of the facility and inspections of the activities;

Assisting in the establishment, modification and review of operating procedures;

Verifying and documenting criticality safety in relation to modifications or changes in the design of systems or in processes;

Ensuring that training in criticality safety is provided periodically for operating personnel, supervisors and management.

Maintaining an awareness of the control parameters and associated limits for criticality safety relevant to systems for which they are responsible;

Monitoring and documenting compliance with the limits of the control parameters;

Ensuring that inspection, testing and maintenance programmes for engineered safety systems are implemented;

If there is the potential for unsafe conditions to occur owing to a deviation from normal operations, stopping the work in a safe way and reporting the event, as necessary;

Promoting a questioning attitude from personnel and demonstrating a strong safety culture, including giving priority to safety over the needs of production.

To cooperate and comply with management instructions and procedures;

To adopt and contribute to a questioning attitude and strong safety culture;

If there is the potential for unsafe conditions to occur owing to a deviation from normal operations, to stop work and report the event, as necessary.

The complexity of implementing the safety measure;

The potential for common cause failure of safety measures;

The reliability claimed in the criticality safety assessment for the set of safety measures;

The ability of operating personnel to recognize the abnormality or failure of the safety measure;

The ability of operating personnel to manage abnormal situations;

The ageing management aspects;

Feedback from operating experience.

Defining the reference fissile medium and its constituents, chemical and physical forms, and nuclear and chemical properties.

Defining the processes and operations involving the fissile material.

Defining the methodology for conducting the criticality safety assessment.

Demonstrating the subcriticality of the design and procedures for operational states and credible abnormal conditions, including applying the double contingency principle and defence in depth, as appropriate. Identifying which criticality parameters are being controlled and their associated limits.

Verifying and validating the calculation methods (including the computer codes) and nuclear data, as well as the procedures for using these methods, codes and data.

Performing the criticality safety analyses, and documenting a description of the calculation method and the nuclear data used.

An independent review should be performed to confirm the adequacy of the criticality safety assessment. The reviewer should be competent in criticality safety assessment and knowledgeable about the facility or activity concerned. The review should include, at a minimum, the validation of the calculation method, the methodology for performing the criticality safety assessment, and a demonstration of the subcriticality of the design and procedures during operational states and during credible abnormal conditions. The reviewer should also confirm that all credible abnormal conditions have been identified.

The supervisor should verify that the scenarios described in the criticality safety assessment are appropriate and that the criticality safety assessment adequately identifies all associated operational states and credible abnormal conditions.

A structured and auditable approach should be used to identify credible initiating events. This approach should also include a review of lessons from previous incidents and take into account the results of any physical testing. Techniques that can be used to help identify credible scenarios include the following:

— ‘What‑if’ or cause–consequence methods;

— Qualitative event trees or fault trees;

— Hazard and operability analysis;

— Bayesian networks;

— Failure modes and effects analysis.

Input into the criticality safety assessment should also be obtained from the safety analysis report for the facility or activity, and from operating personnel and process specialists who are thoroughly familiar with the operations and initiating events that could credibly arise.

Reference to national and international standards;

Reference to accepted handbooks on criticality safety;

Reference to experiments, with appropriate adjustments of limits to ensure subcriticality when the uncertainties associated with the parameters reported in the experiment documentation are considered;

Use of validated calculation models and techniques.

Benchmarks should be reviewed to ensure that information is complete and fully addresses stated biases and uncertainties before their use as benchmarks. Benchmarks should have known and relatively small uncertainties compared with any arbitrary or administratively imposed safety margin.

Benchmarks should be selected from multiple independent sets to reduce the effect of shared benchmark uncertainties (e.g. correlations leading to systematic effect uncertainties).

Benchmarks should be reviewed to ensure that their neutronic, geometric, physical and chemical characteristics encompass the characteristics of the system of fissile material to be evaluated. Neutronic, geometric, physical and chemical characteristics are determined on the basis of system specifications that include the following:

Calculation methods should be reviewed periodically to determine whether relevant new benchmark data have become available for further validation.

Calculation methods should be reverified following changes to the computer code system, and periodically thereafter.

Chemical compounds, mixtures, alloys and their compositions or formulas.

Isotopic compositions.

Material densities.

Relative proportions or concentrations of materials, such as the moderator to fissile nuclide ratio. Effective moderators are typically materials of low atomic mass. Common materials that can be effective moderators include water (i.e. hydrogen, deuterium and oxygen), beryllium, beryllium oxide and graphite (i.e. carbon). In the absence of well absorbing nuclides, another element (e.g. oxygen in magnesium) can be an effective moderator.

The degree of homogeneity or heterogeneity, including gradients, of fissile and non‑fissile materials (e.g. the settling of waste fissile materials in irradiated fuel rods).

Geometric arrangements and compositions of fissile material relative to non‑fissile material such as neutron reflectors and materials contributing to the absorption of neutrons (cadmium, boron, hafnium and gadolinium are commonly used, but other materials such as iron also act as slow neutron absorbers).

Temperature of the system.

Relevant neutron reflectors.

Neutron energy spectrum.

Correlations between effective neutron multiplication factors due to nuclear data uncertainties.

There is no potential for criticality in facilities for mining of natural uranium and thorium ores and their processing, transport and conversion.

The potential for criticality exists in enrichment facilities, uranium and mixed oxide fuel fabrication facilities, fresh fuel storage facilities, irradiated fuel storage facilities, reprocessing facilities, waste processing facilities and disposal facilities, and in the transport of fissile material.

Buildings containing fissile material should be protected from inundations of water from internal sources (e.g. from firefighting systems, leaks or failure of pipework) or ingress of water from external sources (e.g. rainfall, flooding).

To prevent water leakage into fissile material, or fissile material leakage into water, and unexpected changes in conditions of criticality safety control, water should be avoided as the heating and cooling medium in facilities for fissile material storage or processing. If this is not practicable, measures to limit the amount of water that can leak should be considered.

For firefighting, procedures should be provided to ensure the safe use of fire extinguishing media (e.g. control of materials and densities of materials to be used, such as water, foam, dry powders and sand). Combustible materials should be minimized in moderator controlled areas to reduce the likelihood of introducing moderating materials as a result of firefighting. Moderator control requirements should be specified in firefighting procedures. See also para. 6.146(c) of SSR‑4 [2].

The storage of fissile material should be designed to prevent its inadvertent rearrangement in events such as firefighting with high pressure water jets.

Powders might absorb moisture. The maximum powder moisture content that could be reached from contact with humid air should be taken into account in the criticality safety analysis. If necessary, inert and dry glovebox atmospheres should be maintained to ensure the criticality safety of packaged powders. Furthermore, hydrogenated materials (e.g. additives in the manufacture of pellets) should be applied, with safety factors consistent with the double contingency principle. Criticality safety analyses for these types of material can be difficult to perform because of the limited number of experimental benchmarks that can be used in validating computer codes. Consequently, care should be taken in the extrapolation of available benchmark data for these types of material (see also para. 4.27).

The introduction and removal of moderating material under operational states and credible abnormal conditions (e.g. equipment or cleaning material within moderator controlled areas, such as in gloveboxes, packaging areas or criticality controlled areas) should be monitored (e.g. by weighing moderating material) and controlled to avoid unsafe accumulations of moderated fissile material.

The properties of all existing materials that could impact moderator content (e.g. hydric, hygroscopic, adsorptive, absorptive and radiolytic properties) should be assessed.

The spatial distribution of moderators within fissile material units should be considered, along with the potential for non‑uniform distribution due to chemical, thermal or mechanical (e.g. mixing) processes.

The tolerance to changes in the physical and chemical properties of moderators should be assessed.

The integrity of containers used to store and transfer moderating materials in moderator controlled areas should be assessed.

Moderating material that might be encountered during maintenance, decontamination, construction and other activities should be taken into consideration.

The overall nuclide composition (including the isotopic composition of specific elements) and the physical and chemical forms of the fissile material will have changed during irradiation in the reactor and subsequent radioactive decay. The effects of these changes on criticality safety (e.g. in terms of potential consequences, subcriticality margins, and emergency preparedness and response) should be considered.

The preferred method of ensuring subcriticality during spent fuel operations should be by means of geometrically favourable configuration of the fuel. Additional means, such as neutron absorbers and/or the use of a burnup credit, could be applied where subcriticality cannot be sufficiently or reliably maintained by means of favourable geometrical configurations alone. The effects of irradiation do not alter the preference for geometrically safe fuel storage.

Spent fuel is highly radioactive and will need to be handled remotely in shielded facilities or shielded packages. This affects the potential consequences of a criticality accident by reducing the direct radiation exposure, although the energy release might increase the amount of contamination.

Spent fuel will need cooling (e.g. in spent fuel pools) for several years following its removal from the reactor. The rate of change in fuel composition can be significant during this cooling period, and the subcriticality margin is affected by such composition change.

The fuel assemblies will have undergone physical changes during irradiation.

The most reactive composition and geometry of irradiated fuel inside the reactor core is often not the most reactive composition and geometry of fuel in operations outside the reactor core. The radioactive decay after irradiation could lead to a significant increase of k_eff compared with the k_eff derived from the nuclide composition at the end of the irradiation.

The buildup of new fissile nuclides from fertile nuclides is more significant than the depletion of the initial fissile nuclides.

The effect of the depletion of integral burnable absorber nuclides (usually gadolinium isotopes) within the fuel composition is stronger than the effect of the depletion of fissile nuclides, leading to a net increase in k_eff. Taking account of the burnable absorber is referred to as ‘burnable absorber credit’ (or ‘gadolinium credit’ when that absorber is involved).

The fuel can be demonstrated as not being irradiated.

It can be sufficiently demonstrated that the fuel has reached a minimum irradiation level (burnup) and that the effects of this burnup can be safely accounted for, taking credit for reductions in k_eff as a result of changes in the spent fuel composition due to irradiation. This more realistic approach is commonly known as ‘burnup credit’ (see paras 5.45–5.48).

Increased flexibility of operations (e.g. acceptance of a wider range of spent fuel types);

Verified properties of the sufficiently irradiated fuel, possibly resulting in an inherently subcritical material;

Increased loading densities in spent fuel storage areas;

Larger capacity transport packages.

Validation of the calculation methods used to predict the spent fuel composition (see paras 4.22–4.29).

Validation of the calculation methods used to predict k_eff for the spent fuel configurations (see paras 4.22–4.29). Calculations for burnup credit in spent fuel include many more nuclides than are present for fresh fuel calculations; consequently, additional uncertainties in nuclear data and the conservatism applied should be justified.

Specification and demonstration of a suitably conservative representation of the irradiation conditions, for example the amount of burnup, the presence of soluble absorbers, the presence of burnable absorbers, coolant temperature and density, fuel temperature, power history, and cooling time.

Justification for any modelling assumptions, for example the representation of smoothly varying changes in composition (i.e. as a result of radial and axial variations in burnup) as discrete zones of materials in the calculation model.

Justification for the inclusion or exclusion of specific nuclides such as fission products, of the in‑growth of fissile nuclides and of the loss of neutron absorbers.

The wide range of forms of fissile material involved in reprocessing, potentially making the use of multiple control parameters necessary.

Variations in neutron fluxes and spectra caused by actinides other than uranium and plutonium.

The mobility of solutions containing fissile nuclides and the potential for their misdirection.

The need for chemistry control to prevent the following:

The possibility of holdup and accumulations of fissile material owing to incomplete dissolution of materials, accumulation of fissile material in process equipment (e.g. conditioning and vacuum vessels) or ventilation systems, or chronic leaks (including leaks of highly active liquors onto hot surfaces).

The need for moderator control during furnace operations causing condensation in powders.

Difficulties in monitoring the continuous processes in operations with high radiation levels.

Precipitation, colloid formation and increases of concentration in solution;

Unplanned separation and extraction of fissile nuclides.

Fuel assemblies;

Fuel rods;

Sheared fuel;

Fines or swarf;

Solutions of uranium and/or plutonium;

Oxides of uranium or plutonium, or mixed oxides of uranium and plutonium;

Plutonium oxalate or mixed uranium oxalate and plutonium oxalate;

Uranium or plutonium metals;

Other compositions (e.g. materials containing minor actinides).

Increased concentration of fissile nuclides (e.g. by precipitation, colloid formation or extraction);

Unplanned separation of plutonium and uranium;

Carryover of uranium and plutonium into the raffinate stream¹¹;

Incomplete dissolution of fissile material.

Monitoring of the concentration of fissile nuclides (e.g. in‑line neutron monitoring, chemical sampling);

Monitoring of flow rates and temperatures;

Testing of acidity and quality control of additives.

Pre‑dissolution control of the conditioning of acids;

Monitoring of temperature and dissolution time;

Post‑dissolution monitoring for gamma radiation (e.g. to detect residual undissolved fuel in hulls);

Controls on material balance;

Density measurements.

The nuclear, radiological, physical and chemical properties of the waste;

Variation and uncertainty in the form and composition of the waste (see para. 5.76);

The need to address the degradation of engineered barriers and the evolution of waste packages after emplacement over long timescales (see para. 5.77);

Criticality safety requirements and other requirements to facilitate future transport of the waste (see paras 5.81–5.86).

Maintain subcriticality during routine, normal and accident conditions of transport; in particular, the following contingencies shall be considered:

Leakage of water into or out of packages;

Loss of efficiency of built‑in neutron absorbers or moderators;

Rearrangement of the contents either within the package or as a result of loss from the package;

Reduction of spaces within or between packages;

Packages becoming immersed in water or buried in snow;

Temperature changes.”¹³

Measures to ensure that packages of fissile material remain reliably fixed to vehicles;

Vehicle speeds and road conditions;

The potential for on‑site movement accidents (e.g. collisions with other vehicles);

The potential for and consequences of a release of fissile material out of the package (e.g. into storm drains);

Interactions with other fissile material during on‑site movement.

To promptly recognize and classify an emergency caused by a criticality accident. The operational criteria for classification are required to include emergency action levels and other observable conditions and indicators (see para. 5.16 of GSR Part 7 [9]).

To promptly declare the emergency class and to initiate a coordinated and preplanned on‑site response.

To notify the appropriate notification point and to provide sufficient information for the initiation of an effective, coordinated and preplanned off‑site response, if needed.

The location of the criticality accident;

The power history of the criticality accident (i.e. the number of fissions that have occurred as a function of time);

The effect of any shielding (including the source of the criticality itself) between the location of the criticality system and those likely to be affected (i.e. operating personnel);

The individuals likely to be affected (i.e. operating personnel), and the orientation of their bodies in relation to the criticality accident;

The neutron energy spectrum to which affected personnel were exposed;

The equivalent doses to individual organs to determine appropriate medical interventions.

Details of the items of equipment involved;

The radiological, physical and chemical properties of the fissile material, including quantities;

The reactivity insertion mechanism that caused the system to achieve criticality;

The feedback and quenching mechanisms¹⁵ present (such as venting);

An estimation of any radioactive release (see Ref. [41]).

The mass of the fissile region (particularly for systems with fissile nuclides in solution).

The reactivity insertion mechanism and reactivity insertion rate.

Parameters relating to reactivity feedback mechanisms, for example:

— Doppler feedback¹⁶;

— Duration time and time constant of reaction;

— Degree of confinement of the fissile material;

— Neutron spectral shifts;

— Degree of voiding;

— Change of temperature;

— Density changes.

Where a documented assessment concludes that no foreseeable set of circumstances could initiate a criticality accident (see para. 6.173 of SSR‑4 [2]), or where the provision of a criticality detection and alarm system would offer no reduction in the risk from a criticality accident or would result in an increase in the overall risk to operating personnel from all hazards, including industrial hazards.

Shielded facilities in which the potential for a criticality accident is foreseeable but the resulting radiation dose at the outer surface of the unit where the accident occurred would be acceptable (see para. 6.173 of SSR‑4 [2]). Examples of such facilities might include hot cells and closed underground repositories.

Packages for fissile material awaiting transport, during transport or awaiting unpacking.

It should be unique (i.e. it should be immediately recognizable to personnel as a criticality alarm).

It should actuate as soon as the criticality accident is detected and continue until manually reset, even if the radiation level falls below the alarm point.

Systems (with restricted access) to manually reset the alarm signal should be provided outside areas that need to be evacuated.

The alarm signal should be audible in all areas to be evacuated, and the alarm should continue for a time sufficient to allow a complete evacuation.

The alarm should be supplemented with visual signals in areas with high background noise.

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INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, Nuclear Criticality Safety — Evaluation of Systems Containing PWR UOX Fuels — Bounding Burnup Credit Approach, ISO 27468:2011, ISO, Geneva (2011).

HEALTH AND SAFETY EXECUTIVE, Leakage into the B205 Plutonium Evaporator Cell at Sellafield: HSE Investigation into the Leakage of Plutonium Nitrate into the Plutonium Evaporator Cell of the B205 Chemical Separation Plant, Sellafield, on 8 September 1992, HSE Books, Sudbury, Suffolk (1994).

INTERNATIONAL ATOMIC ENERGY AGENCY, Safety of Nuclear Fuel Reprocessing Facilities, IAEA Safety Standards Series No. SSG‑42, IAEA, Vienna (2017).

INTERNATIONAL ATOMIC ENERGY AGENCY, Storage of Radioactive Waste, IAEA Safety Standards Series No. WS‑G‑6.1, IAEA, Vienna (2006).

INTERNATIONAL ATOMIC ENERGY AGENCY, Decommissioning of Nuclear Power Plants, Research Reactors and Other Nuclear Fuel Cycle Facilities, IAEA Safety Standards Series No. SSG‑47, IAEA, Vienna (2018).

INTERNATIONAL ATOMIC ENERGY AGENCY, Compliance Assurance for the Safe Transport of Radioactive Material, IAEA Safety Standards Series No. TS‑G‑1.5, IAEA, Vienna (2009). (A revision of this publication is in preparation.)

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AMERICAN NUCLEAR SOCIETY, Nuclear Criticality Safety Control of Selected Actinide Nuclides, ANSI/ANS‑8.15‑2014 (R2019), ANS, La Grange Park, IL (2014).

INTERNATIONAL ATOMIC ENERGY AGENCY, Safety of Research Reactors, IAEA Safety Standards Series No. SSR‑3, IAEA, Vienna (2016).

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR OFFICE, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency, IAEA Safety Standards Series No. GSG‑2, IAEA, Vienna (2011).

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR OFFICE, PAN AMERICAN HEALTH ORGANIZATION, UNITED NATIONS OFFICE FOR THE COORDINATION OF HUMANITARIAN AFFAIRS, WORLD HEALTH ORGANIZATION, Arrangements for Preparedness for a Nuclear or Radiological Emergency, IAEA Safety Standards Series No. GS‑G‑2.1, IAEA, Vienna (2007). (A revision of this publication is in preparation.)

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Vol. 1 (1968), https://ncsp.llnl.gov/docs/ARH600_Vol_I.pdf

Vol. 2 (1969), https://ncsp.llnl.gov/docs/ARH600_Vol_II.pdf

Vol. 3 (1971), https://ncsp.llnl.gov/docs/ARH600_Vol_III.pdf

Module 1: Introductory Nuclear Criticality Physics

Module 2: Neutron Interactions

Module 3: The Fission Chain Reaction

Module 4: Neutron Scattering and Moderation

Module 5: Criticality Safety Limits

Module 6: Introduction to Diffusion Theory

Module 7: Introduction to the Monte Carlo Method

Module 8: Hand Calculation Methods — Part I

Module 9: Hand Calculation Methods — Part 2

Module 10: Criticality Safety in Material Processing Operations — Part 1

Module 11: Criticality Safety in Material Processing Operations — Part 2

Module 12: Preparation of Nuclear Criticality Safety Evaluations

Module 13: Measurement and Development of Cross Section Sets

Module 14: A Review of Criticality Accidents by Thomas McLaughlin

Module 15: Fundamentals of Criticality Safety for Non‑material Handlers

Module 16: Burnup Credit for Criticality Safety Analysis of Commercial Spent Nuclear Fuel

Chapter 1: Early History of Criticality Experiments

Chapter 2: Purposes of Early Critical Experiment Campaigns

Chapter 3: Early ORCEF Line Organizations and Facilities

Chapter 4: Facility Description

Chapter 5: Characteristic Experimental Programs

Chapter 6: Polonium‑Beryllium Neutron Source Experience

Chapter 7: Operational Safety Experiments and Analysis

Chapter 8: Additional ORCEF Experimentalists

Chapter 9: Solution Sphere Experiment

Chapter 10: Sponsor and Credit