Nuclear Regulatory Commission Regulations Research Articles

High dose rate (HDR) brachytherapy quality assurance: a practical guide

The widespread adoption of high dose rate brachytherapy with its inherent dangers necessitates adoption of appropriate quality assurance measures to minimize risks to both patients and medical staff. This paper is aimed at assisting someone who is establishing a new program or revising one already in place into adhere to the recently issued Nuclear Regulatory Commission (USA) regulations and the guidelines from the American Association of Physicists in Medicine.

Safety of ocean shipments of plutonium between Europe and Japan

Sandia National Laboratories (SNL) has conducted an extensive study of emergency response planning applicable to sea transport of plutonium for the Japan Nuclear Cycle Development Institute (JNC). This work covered four separate areas to better define the accident environment for long range sea transport of nuclear materials. A probabilistic safety analysis evaluated technical issues for the transport of plutonium between Europe and Japan. An engine room fire aboard a purpose built ship was used to analyse the vulnerability of plutonium packaging designed to International Atomic Energy Agency (IAEA) standards. A comprehensive corrosion study estimated the time required for sea water to breach a containment boundary in submerged generic plutonium packaging. A survey of worldwide commercial recovery capabilities provided a compilation of information on the capabilities of salvaging high value cargo from sunken ships. This paper addresses salvage modes from harbour depths to the deepest ocean trenches. Previous studies (J. L. Sprung et al., SNL reports SAND98-1171/1 and SAND98-1171/2, May 1998) included a probabilistic risk assessment of the overall safety, source term evaluations and finite element structural dynamics calculations to determine the effects of ship to ship collisions on nuclear material containers and the effects of ship fires on transport packaging as determined by actual fire experiments conducted on board a test ship. The previous studies, together with this work, form a comprehensive technical basis that encompasses the overall safety of sea transport of plutonium between Europe and Japan. Based on these technical analyses, transport of nuclear materials by sea in Type B packaging, approved in accordance with US Nuclear Regulatory Commission (NRC) and IAEA regulations, and carried in purpose built ships with adequate surveillance, has a very high degree of safety for the failure modes studied. Non-purpose built ships do not have the redundancy in safety features provided by the newer purpose built ships. However, SNL studies on non-purpose built ships have shown accident environments to be within NRC and IAEA regulatory assumptions for Type B packaging. These studies were carried out for both structural ship to ship collisions and engine room fires by analysis (for the collisions) and direct experimentation and analysis (for the fires). Thus, land transport mode regulations are applicable for sea transport accident conditions.

Regulatory Perspective on Implementation of a Dose Standard for a One-Million Year Compliance Period

AbstractThe disposal of high-level radioactive wastes in a potential geologic repository at Yucca Mountain, Nevada is governed by the U.S. Environmental Protection Agency (EPA) standards and U.S. Nuclear Regulatory Commission (NRC) regulations. The EPA has the responsibility for setting public health and safety and environmental standards for radioactive waste disposal at Yucca Mountain and it is the NRC's responsibility to implement those standards in its regulations to ensure public health and safety and the environment are protected. The U.S. Department of Energy (DOE), as the developer of the potential repository, must submit a license application to the NRC to seek approval to construct the repository. DOE must comply with NRC's regulations for NRC to authorize construction and license operation of a potential repository at Yucca Mountain. In 2005, EPA issued proposed revised standards and NRC issued proposed revised regulations for conducting performance assessment beyond 10,000 years up to 1 million years. The challenge for the EPA and NRC is to develop standards and regulations that provide an appropriate method for evaluating the safety of the potential repository given the unprecedented time period to be analyzed and the inherent uncertainties in estimating the future evolution of the Yucca Mountain site and the containment of the waste in the waste packages. A fundamental aspect of the proposed EPA standard is the specified approach for limiting undue speculation on future behavior of the site by constraining the features, events, and processes that need to be considered in the performance assessment. EPA proposed to limit the assessment of specific features, events, and processes in the period after 10,000 years to effects on the repository system that are most relevant (i.e., ignoring lesser or secondary effects that may add to speculation and uncertainties but would not be expected to have a significant effect on peak dose over a 1 million year period). For example, DOE's performance assessment may (1) limit the analysis of seismic activity to the effects caused by damage to the drifts and the waste package; (2) limit analysis of igneous activity to effects on the waste package that result in release of radionuclides to the atmosphere or ground water; (3) require DOE to include general corrosion in its analysis of engineered barrier performance, and (4) limit the effect of climate variation to those resulting from increased water flowing to the repository. NRC has been reviewing its performance assessment models and techniques to assure they are consistent with EPA's proposed requirements for the period after 10,000 years and adequate to assist the review of a potential license application from the DOE. Currently, only slight modifications to the models and approaches used in the performance assessment for the initial 10,000 years are expected to be needed to accommodate calculations for longer times (e.g., modifications to implement a steady-state value to represent the proposed climate change). NRC staff will be able to use the modified performance assessment to identify additional sensitivities associated with estimating doses over very long time periods and improve its understanding of the performance of a potential repository at Yucca Mountain.

WE-C-P-618-02: NRC Update: Part 35 Training and Experience and Who's ACMUI and Why Should a Medical Physicist Care?

The Nuclear Regulatory Commission (NRC) finalized the training and experience requirements for Authorized Medical Physicists, Authorized Users and Radiation Safety Officers in March 2005. A brief summary of the changes to the regulations will be presented. The Advisory Committee on the Medical Uses of Isotopes (ACMUI) was established in 1958 to advise NRC staff on policy and technical issues that arise in the regulation of the medical uses of radioactive material in diagnosis and therapy. The ACMUI membership includes health care professionals from various disciplines who comment on changes to NRC regulations and guidance; evaluate certain non-routine uses of radioactive material; provide technical assistance in licensing, inspection, and enforcement cases; and bring key issues to the attention of the Commission for appropriate action. A general description of the ACMUI composition and interactions with NRC will be given. A discussion of the recent activities of the ACMUI and the implication for medical physicists will be presented. Future issues where NRC may have significant impact on the medical physicist will be addressed. Educational Objective: 1. To understand the make-up and responsibilities of the ACMUI and the issues being discussed and their implications on medical physicists.

TU‐B‐I‐611‐01: Releasing Nuclear Medicine Patients to the Public: Dose Computations and Discharge Instructions

Thousands of patients are treated annually in the United States with iodine‐131 for various medical conditions. Prior to 1996, patients treated with more than 30 millicuries of iodine‐131 were required to be hospitalized in a private room until their iodine‐131 body burden decreased to less than 30 millicuries. In 1996, the United States Nuclear Regulatory Commission (NRC) introduced a revision to 10 CFR 35.75 that permitted release based upon the anticipated dose to members of the public, rather than upon patient body burden. Consequentially, many treatments that formerly required hospitalization may be performed as outpatient treatments, and required hospitalizations can be significantly shortened. These regulations have been adopted by the Agreement States, and “early release” of in‐patients and treatment as outpatients is becoming more widespread. Medical physicists who work in hospital settings can expect to participate in “early release” and outpatient radioiodine therapeutic procedures. Medical conditions that are treated with iodine‐131 include hyperthyroidism, thyroid cancer, neuroendocrine tumors and non‐Hodgkin lymphoma. Candidacy for outpatient treatment depends in part upon whether patients are continent of urine and capable of self‐care. The revised NRC regulations permit conservative public dose computations that account for tissue shielding, biological elimination, physical decay and occupancy factor, which is an index of the amount of time members of the public could spend in close proximity to the released patient. Computations must demonstrate that radiation dose to members of the public will not exceed 500 millirem (5.0 mSv) if the patient is to be released. If the patient is released based upon such computations, a record of the release must be created and retained by the licensee for three years. The record must document the anticipated dose to a member of the public and the method by which the anticipated dose was calculated. In addition, detailed written instructions regarding how the patient can maintain the radiation dose to family members other members of the public as low as reasonably achievable (ALARA). The implementation of “early release” has apparently been successful from an ALARA standpoint. Measurements of actual external radiation exposure to family members of released iodine‐131 patients demonstrate cumulative doses that are a small fraction of the anticipated dose computed using conservative assumptions. Educational Objectives: 1. Introduce participants to the medical conditions that are treated with radioiodine. 2. Review the regulatory considerations under 10 CFR 35.75 and 10 CFR 20 regarding both inpatient and outpatient radioiodine procedures. 3. Review ways in which the regulatory requirements may be satisfied, including dose‐rate measurement, “public” radiation dose computations, post‐discharge instructions, and addressing the concerns of patients and their families. Web‐based methods to facilitate documentation of outpatient treatment will be introduced.

Proposed nuclear waste repository at Yucca Mountain generates discussion

By December 2004, the U.S. Department of Energy (DOE) plans to submit a license application for a proposed high‐level radioactive waste repository at Yucca Mountain, Nevada. The U.S. Nuclear Regulatory Commission (NRC) would review DOE's application and decide whether to authorize repository construction. That application would include a performance confirmation plan for the proposed site. Performance confirmation (PC) refers to the tests, experiments,and analyses that will be done to evaluate the adequacy of information used to show compliance with performance objectives in NRC's regulation 10 CFR Part 63. The program must provide data that indicate, where practical, whether subsurface conditions encountered and changes in those conditions during construction and waste emplacement are within limits assumed in the licensing review; and whether natural and engineered systems and components required for repository operation that are designed or assumed to operate as barriers after permanent closure are functioning as intended and anticipated. The PC program must begin during site characterization and continue until permanent closure of a repository.

Adoption of TS-R-1 in the United States Nuclear Regulatory Commission Regulations for Type-B and Fissile Material

Abstract The US Nuclear Regulatory Commission (NRC) is currently conducting a major revision of its regulations on the transport of radioactive material which are found in Title 10 of the Code of Federal Regulations, Part 71 (10 CFR Part 71). The NRC and the U.S. Department of Transportation (DOT) jointly share responsibility for regulating the transport of radioactive material. Consequently, the NRC and the DOT are both revising their regulations to be compatible with the latest edition of the International Atomic Energy Agency's (IAEA's) standard TS-R-1 (1996) for the transport of radioactive material. Since the NRC and the DOT share responsibility for regulating in this area, challenges arise in determining which provisions of TS-R-1 should result in conforming changes to the NRC's and the DOT's respective regulations, while also ensuring that the NRC's and the DOT's regulations remain consistent.

Nuclear Regulatory Commission regulatory status of approved intravascular brachytherapy systems

Purpose: To review current and potential future regulatory status of intravascular brachytherapy (IVB) systems. Methods: There are three approved IVB systems; two commercial IVBs are hand-operated manual devices; the third is remotely operated. In three Guidances, the Nuclear Regulatory Commission (NRC) applied certain regulatory concepts applicable to remotely operated high dose rate (HDR) afterloaders to manually operated IVBs. This article reviews these Guidances, newly released NRC regulations on the medical use of by-product material, and potential regulatory issues related to IVB systems. Results: The Guidances are specific. However, newly released NRC regulations on the medical use of byproduct material, including HDR afterloaders, omit IVB systems as a category. NRC licensure of IVB systems is considered case-by-case. Conclusions: The current limited application of regulations applicable to HDR remote afterloaders to hand-held IVB systems could lead to other HDR-like regulations for hand-held IVB systems in future regulations.

Feasibility and Safety of Outpatient Bexxar® Therapy (Tositumomab and Iodine I 131 Tositumomab) for Non-Hodgkin's Lymphoma Based on Radiation Doses to Family Members

Radioimmunotherapy with anti-CD20 antibodies is a promising treatment approach for relapsed low-grade non-Hodgkin's lymphoma. Under revised Nuclear Regulatory Commission regulations (May 1997), patients may be released following treatment provided the maximum dose to any individual is not likely to exceed 500 mrem. Non-Hodgkin's lymphoma patients have been studied to evaluate radiation exposure to caregivers/family members after outpatient treatment with tositumomab and iodine I 131 tositumomab (Bexxar® therapy). Estimates of total radiation doses to individuals expected to be maximally exposed to patients posttreatment have revealed that the doses should be within revised guidelines. In a University of Nebraska Medical Center study, the predicted total radiation doses (based on patient dose rate at 1 meter) ranged from 95–423 mrem. Family members were provided radiation-monitoring devices to directly monitor radiation exposure. Measured doses ranged from 10–409 mrem. In this and other studies, estimated and measured dose equivalents to maximally exposed individuals were below 500 mrem. Measured doses were, in most instances, lower than those predicted by patientspecific calculations, thus confirming the validity of the calculated dose predictions. Therefore, radioimmunotherapy with tositumomab and iodine I 131 tositumomab can be safely conducted on an outpatient basis.

Radiation exposure from outpatient radioactive iodine (131I) therapy for thyroid carcinoma.

In May 1997, the US Nuclear Regulatory Commission (NRC) revised its patient release regulations, allowing for outpatient administration of larger activities of sodium iodide 131I than previously permitted. To measure the radiation exposure to household members from patients receiving outpatient 131I therapy for thyroid carcinoma in accordance with the new regulations. Consecutive case series from October 1998 to June 1999. Thirty patients who received outpatient 131I therapy following thyroidectomy for differentiated thyroid carcinoma were enrolled, along with their 65 household members and 17 household pets. Radiation exposure to household members and 4 rooms in each home, as monitored with dosimeters for 10 days following 131I administration. The patients received 131I doses ranging from 2.8 to 5.6 GBq (mean, 4.3 GBq). The radiation dose to 65 household members ranged from 0.01 mSv to 1.09 mSv (mean, 0.24 mSv). The dose to 17 household pets ranged from 0.02 mSv to 1.11 mSv (mean, 0.37 mSv). The mean dose to the 4 rooms ranged from 0.17 mSv (kitchen) to 0.58 mSv (bedroom). In our study, 131I doses to household members of patients receiving outpatient 131I therapy were well below the limit (5.0 mSv) mandated by current NRC regulations.

Radiation safety role in institutional disaster planning.

United States Nuclear Regulatory Commission (NRC) materials license applicants (non-nuclear power) must submit spill procedures with their application. While our counterparts in the nuclear power industry historically have concerned themselves with disaster drills and evacuation plans as a result of fire, explosion, or an act of terrorism, other licensees are looking only at minor spills of unsealed radioactive material and only at tile radiation hazard. Beyond NRC regulations, various oversight and accrediting organizations require, or at a minimum encourage, a written disaster plan outlining actions to be taken for events likely to occur in the region of the institution. Some of these organizations require drills to practice implementation of the written plan. On 5 May 1999, Mayo Clinic performed a wide-scale disaster drill involving Rochester City and Olmsted County response organizations, and several Mayo Clinic departments. Planning took several months; the drill took approximately three hours. Participants gathered at several meetings post-drill for "debriefing" sessions to discuss successes, areas for improvement, and lessons learned. There were three overriding lessons learned: critical responders need special identification to allow access to the disaster site; initial victim surveys are for gross contamination only; and access to the potentially contaminated disaster site might take weeks or months following a real event.

Radiation safety parameters following prostate brachytherapy

Purpose: To determine the degree and variability of radiation exposure to the general public from patients after I-125 or Pd-103 prostate brachytherapy.Methods and Materials: Radiation exposure measurements were made from 38 consecutive, unselected patients with stage T1 or T2 prostatic carcinoma who had transperineal I-125 or Pd-103 implants at the University of Washington in 1998.Results: The exposure rate at the anterior skin surface following a I-125 implant ranged from 2.2 to 8.9 mrem/hour (average: 5.0). The exposure rate at the anterior skin surface from a Pd-103 implant ranged from 0.5 to 4.9 mrem/hour (average: 1.7). Based on the current Nuclear Regulatory Commission (NRC) regulations the time required to reach the annual limit at the anterior skin surface would be 20 hours for I-125 and 59 hours for Pd-103. For exposure at the lateral skin surface, the times would exceed 500 hours for either isotope.Conclusions: This data suggest that patients need not be concerned about being a radiation risk to the general public following their procedure.

The regulation of radioactive materials and wastes by federal agencies

AbstractPerhaps no area of environmental law is less understood than the law that regulates radioactive materials and wastes. Radiation experts such as health physicists who talk in terms of “curies,” “Sierverts,” and “critical mass” have a language and methodology that seem alien to most environmental practitioners used to dealing with the intricacies of the Resource Conservation and Recovery Act, the Clean Air Act, or the Clean Water Act. When I think of how most environmental engineers and attorneys view the rules that regulate radioactive materials, I am reminded of a Churchill quote that Russia was “a riddle wrapped in a mystery inside an enigma.”Many people assume that virtually all rules pertaining to radioactive materials and waste are governed by the Nuclear Regulatory Commission (NRC) regulations. While the NRC obviously is a major “player,” it is not the only one. Depending on the quantity and type of substance involved, the activity involved, that is, possession, use, transportation, disposal, or cleanup of contamination, other agencies may be “players” as well. Those agencies include the Environmental Protection Agency (EPA), the Department of Energy (DOE), the Department of Transportation (DOT), the Occupational Safety and Health Administration (OSHA), other federal agencies such as the Department of Defense (DOD), and even state radiation protection agencies.

Whistleblowers and nuclear medicine.

Healthcare facilities that practice nuclear medicine are subject to federal "whistleblower" protection laws when an employee reports a potentially unsafe radiological condition. This article addresses enforcement of the applicable sections of the Atomic Energy Act and the Nuclear Regulatory Commission's regulations in order to help such facilities avoid running afoul of those laws, which can result in fines, generate civil lawsuits by the claimant, and significantly disrupt the operation of a healthcare facility.

Drug Testing as Part of the War on Drugs

Drug testing programs in the United States may broadly be classified as mandatory (such as under DOT or Nuclear Regulatory Commission regulation) or nonmandatory. In the first group, a regulated employer is required by federal regulations to test. In the second, the employer chooses to test for reasons other than the federal requirements. It always was intended that the federal program would be the model for testing by private employers, and that mandatory testing would be extended to private employers who are regulated by various agencies of the federal government. This has happened. In addition, private employers who are not required to test under federal authority have instituted employee drug testing programs closely modeled on the federal program. Whether mandated or not, a well-designed and implemented drug testing program is a valuable tool in the effort to fight drugs in the workplace.

Implications of the Rosa/AP600 High- and Intermediate-Pressure Test Results

Westinghouse has submitted the new AP600 reactor design for certification under the U.S. Nuclear Regulatory Commission (NRC) regulations for standard designs. The NRC has performed confirmatory testing in the Rig of Safety Assessment (ROSA) - V Large-Scale Test Facility run by the Japan Atomic Energy Research Institute (JAERI). The ROSA/AP600 test results as provided by JAERI are reviewed in terms of their implications for the original technical concerns that were to be addressed by the testing program. Implications for computer code capabilities are also discussed. Since gravity-driven natural circulation flow in a complicated piping network was a key concern, the review concentrates on this aspect of the ROSA/AP600 test results. In particular, it looks at the possible effect of system interactions at high pressure and during early depressurization. It identifies those ROSA/AP600 test occurrences that point to processes that could delay automatic depressurization system initiation or in-containment reactor water storage tank injection. Since most of the tests run were small-break loss-of-coolant accidents (SBLOCAs), the review focusses on this type of scenario. A comparison of several SBLOCA tests is presented.

A Comparison of Current Regulations and Regulatory Guide Governing Quality Control of Dose Calibrators

The U.S. Nuclear Regulatory Commission recently amended its regulation governing the calibration of dose calibrators. The changes include (1) the radioactivity of radiopharmaceutical dosages that contain photon-emitting radionuclides has to be measured by a dose calibrator prior to administration to patients and human research subjects; (2) the lower end of the radioactivity limits for linearity testing has been raised to 1.1 MBq (30 microCi) to be consistent with the Nuclear Regulatory Commission Quality Management Program Requirements; and (3) the requirement for signature of the Radiation Safety Officer on the records for accuracy, linearity, and geometry dependence tests has been removed. Although these are practical amendments, further clarification of the new Nuclear Regulatory Commission regulation is required for the following issues: (1) inconsistency in individual's identification requirement for the record keeping (i.e., initials of the individual who performed the constancy check and identity of the operator for the accuracy, linearity, and geometry dependence tests); (2) whether the use of 99mTc is adequate for linearity testing when other radionuclides are being measured in the dose calibrator; and (3) lack of provision for dose calibrator adjustment when conducting the accuracy test. In addition, Nuclear Regulatory Commission Regulatory Guide 10.8 should be revised to become consistent with the Nuclear Regulatory Commission's regulation in order to assist licensees with full compliance of the requirements or recommendations.

Panel to Feds: Hands Off Radioisotopes

The deregulation fever gripping Washington has spread to the radioisotopes used in medicine and biomedical research. The Nuclear Regulatory Commission (NRC) has monitored these isotopes for the past 40 years as part of its oversight of the nuclear reactors where they are produced, but a panel of experts convened by the Institute of Medicine has now recommended that it turn over its authority to the states. The panel deemed many of the NRC's regulations burdensome and unnecessary.

Optimal response to a shift in regulatory regime: The case of the US nuclear power industry

This paper studies the impact of the March 1979 Three Mile Island (TMI) accident on the regulation of nuclear power plants (NPPs) and its consequences for the operating behaviour and profitability of the US nuclear power industry. We treat the TMI accident as a ‘natural experiment’ that caused a sudden, unexpected, and permanent increase in the intensity of safety regulation by the US Nuclear Regulatory Commission (NRC) and a shift towards increased disallowances of operating costs by state and local public utility commissions (PUCs). We analyse the nuclear power industry's reaction to this shift in regulatory regime using detailed monthly data on NPP operations collected by the NRC. One of the industry's responses was to increase the planned durations between refuellings from 12 months in the pre-TMI period to 18 months in the post-TMI period. We estimate a simple dynamic programming (DP) model of NPP operations that shows how an operator optimally balances the potential increases in capacity utilization rates associated with longer operating cycles against the increased costs of unplanned and forced outages associated with longer cycles. Under the maintained hypothesis that NPP operators seek to maximize expected discounted profits, we use the NPP operating data to infer profit functions for NPPs in the pre- and post-TMI periods. The estimated profit functions reveal that utilities have been responsive to NRC regulation insofar as they impute a significantly higher cost to ‘imprudent’ operation of a reactor in the post-TMI period than in the pre-TMI period. The results show that utilities responded optimally to the change in regulatory regime since the DP model predicts that optimal planned operating cycles were approximately 12 months in the pre-TMI period and 18 months in the post-TMI period. We find that while NPPs appear safer in the post-TMI period (in terms of having a lower rate of forced outages), they are also substantially less profitable: over 90% of the expected discounted profits from continued operation of existing NPPs have been eliminated in the post-TMI period. However, since most of the investments in existing NPPs are already sunk and given the high costs of plant decommissioning, the DP model predicts that utilities will continue to operate NPPs rather than shut them down. Interestingly, we find that the hypothesis of expected discounted profit maximization provides a much better approximation to NPP operating behaviour in the post-TMI period than in the pre-TMI period.

Groundwater Flux, Travel Time, and Radionuclide Transport

AbstractInflow measurements at Stripa and in other underground openings in Sweden, as well as observations elsewhere in mines and tunnels, reveal that there is generally an extremely broad distribution of groundwater flux in fractured rock. Non-sorbing and sorbing tracer tests typically show similar variability in groundwater travel time (GWTT) and tracer transport.In the U.S. Nuclear Waste Program, Nuclear Regulatory Commission regulations require the GWTT from the disturbed zone to the accessible environment to exceed 1000 years. The regulations seem to envision a rather uniform and narrow distribution of travel time, with perhaps a few identifiable “fast pathways” contained within the rock mass surrounding a potential repository. The premise is that most of these features could be mapped during site characterization, and that regions of the potential repository host rock containing such features could be avoided during waste emplacement.However, both field experience and theoretical studies in recent years provide strong evidence that groundwater flux, GWTT, and aqueous transport of dissolved substances exhibit extremely heterogeneous behavior, even in intact porous media and in fractured rock regions between major features. These phenomena are all dominated by the spatial distribution of permeability within the rock mass of interest. The permeability distribution is often approximately log-normal, with a natural log standard deviation, σ. For unfractured porous rock, σ typically ranges from about 0.6 to about 1.2 for field-scale investigations, and for fractured permeable media, it frequently exceeds 2. Values of σ smaller than 0.6 may be observed in small field-scale projects when the macroscopic flow regime is essentially linear within very uniform sediments and in laboratory displacement experitments.With some additional assumptions, a log-normal permeability distribution implies that groundwater flux, GWTT, and the transport of radionuclides from a potential repository are also log-normal. To first order, the appropriate value of σ describing these distributions is the same as the value for the permeability distribution. This allows σ to be estimated from a large number of hydraulic or pneumatic packer tests within the fractured rock mass of interest.We define a groundwater transport function (GWTF) for the rate of radioactivity release to the accessible environment (AE) at time t resulting from the release of a pulse of unit activity at time 0. The GWTF depends on the mean groundwater travel time, tw, and σ, as well as the retardation factor and decay constant. As σ increases from 0 (a hypothetical completely homogeneous system), the radioactivity breakthrough at early time increases from 0 to 100%. This behavior is consistent with our intuitive notions of “fast transport pathways” in heterogeneous systems, and σ is thus seen to be a parameter for quantifying the effects of heterogeneity.Convolution of the GWTF with a time-dependent release function for the Engineered Barrier System (EBS) is easily performed numerically, resulting in the rate of release to the AE as a function of time, which can then be integrated numerically to calculate the cumulative release as a function of time. The convolution approach clearly separates the effects of uncertainty and heterogeneity on repository performance and is extremely useful for sensitivity analyses. An example calculation shows the combinations of σ and tw required for compliance with total system release standards.Since the effect of heterogeneity is captured by a single parameter in a deterministic calculation, uncertainty can be investigated separately by Monte Carlo sampling from distributions of such parameters as σ, tw and source term strength, allowing (in the future) specific and scientifically meaningful goals to be defined for both site characterization and design.Finally, we emphasize that this approach, in its present form, does not include thermal effects. These effects may dominate both the EBS failure rate and hydrogeochemical behavior, including radionuclide transport, for most of the compliance period and beyond. It cannot be used directly to support any particular thermal loading strategy.