Showing papers in "Transactions of the American Nuclear Society in 1994"

Management and disposition of excess weapons plutonium

Abstract: The National Academy of Sciences report, {open_quotes}Management and Disposition of Excess Weapons Plutonium,{close_quotes} warned that the vast excess stocks of fissile materials from ongoing weapons dismantlement pose a {open_quotes}clear and present danger{close_quotes} to international security and made recommendations in four major areas. 1. The report recommended an urgent program to improve security and accounting for weapons-usable nuclear materials in Russia; recent reports of thefts of such materials heighten the importance of such a program. 2. The report recommended a broad transparency regime involving declarations of all stocks of nuclear weapons and fissile materials, cooperative measures to confirm and clarify those declarations, monitoring of nuclear weapons dismantlement, and monitoring of excess materials in storage. 3. It recommended that bilateral monitoring of excess materials in storage be rapidly supplemented with international safe- guards and that these materials be stored under agreed, stringent standards of accounting and physical security, approximating the standards applied to assembled nuclear weapons - which the study called the {open_quotes}stored weapons standard.{close_quotes} 4. The study made detailed analyses and recommendations with respect to long-term disposition of excess weapons plutonium, arguing that plutonium disposition options should: a. minimize the time during which the excess plutonium is stored in forms readilymore » usable for nuclear weapons; b. preserve safeguards and security during the disposition process (the stored weapons standard); c. result in a form from which the plutonium would be as difficult to recover for weapons use as the larger and growing quantity of plutonium in commercial spent fuel; and d. meet high standards of environment, safety, and health protection.« less

Practical and efficient iterative method for LWR fuel assembly homogenization

Abstract: Light water reactor (LWR) fuel assembly homogenization methods fall into three broad categories: those derived from isolated assembly lattice physics (multigroup pin-by-pin assembly transport) calculations, multiassembly (minicore) calculations, or iterations between nodal and lattice calculations. The iterative category, has failed to achieve widespread application because of the computational burden imposed by repetitive lattice calculations. Minicore-based methods are used by some vendors but they are sensitive to the choice of minicore geometries (particularly in multicycle applications). This paper introduces a single assembly-based homogenization method for modeling environmental dependencies without adding lattice physics calculations and without iterating between nodal and lattice calculations.

Decision support system for emergency response to major nuclear accidents

Abstract: A methodology for supporting decisions concerning the establishment of short-term emergency response in the event of a nuclear accident has been developed. The methodology facilitates the selection of protective actions in the presence of a multitude of conflicting objectives. Conflicting objectives arise when the minimization of the potentially adverse effects of an accident and the simultaneous minimization of the associated socioeconomic impacts is attempted. Additional conflicting objectives appear whenever an emergency plan tends to decrease a particular health effect (e.g., acute deaths) while at the same time it increases another (e.g., latent deaths).

Degradation analysis estimates of the time-to-failure distribution of irradiated fuel elements

Abstract: The reliability of components is generally evaluated by estimating its time-to-failure distributions. These distributions are estimated from systematic life tests under conditions that simulate the actual operating conditions or under accelerated conditions that induce failures. In some cases, failures occur only after long periods of testing, and it may not be possible to obtain a sizable number of failures to estimate the time-to-failure distribution during the developmental stage of a comonent. An example is the case of metallic integral fast reactor IFR fuel pins irradiated in the Experimental Breeder Reactor-II (EBR-II). No pin failures have occurred in the lead experiments under normal reactor operating conditions, yet design decisions need to be made that take into account quantitative estimates of the reliability of these pins. Similar situations exist in cases where the rapid changes in the technology of some components, such as semiconductor devices, do not allow prolonged periods of time for testing to ensure significant failure statistics. We have applied a staistical mixed-effects model to the lead HT-9 clad metallic fuel pins irradiated in EBR-II experiment X425.

Turbulence prediction in two-dimensional bundle flows using large-eddy simulation

Abstract: Turbulent flow is characterized by random fluctuations in the fluid velocity and by intense mixing of the fluid. A wide range of eddies exists in the flow field. Because these eddies carry mass, momentum, and energy, this enhanced mixing can sometimes lead to serious problems, such as tube vibrations in many engineering systems that include fluid-tube bundle combinations. Nuclear fuel bundles and pressurized water reactor (PWR) steam generators are existing examples of fluid-tube bundle combinations in nuclear power plants. One of the critical areas in PWR steam generators is the weld between the tubes and the tube plate. Fluid-induced vibration problems are often discovered during the operation of such systems because some of the fluid-tube interaction characteristics are not fully understood. Large-eddy simulation, incorporated in three-dimensional computer codes, became one of the promising techniques to estimate flow turbulence. An investigation of the complex flow turbulence in tube bundles was carried out. Simulation of flow across tube bundles with various pitch-to-diameter ratios was performed. Power spectral densities of drag and lift coefficients were used for comparison with experimental data. Estimation of flow-length scales and other important turbulence-related parameters were obtained. Finally, important characteristics of the turbulent flow field were presented with the aid of flow visualization, using both vector and vorticity plots and the flow paths of flow tracers embedded in the flow field.

Development of a core follow calculational system for research reactors

Abstract: Over the last few years a comprehensive FWR and MTR core analysis code system based on modern reactor physics methods has been under development by the Atomic Energy Corporation of South Africa. This system, known as OSCAR-3, will incorporate a customized graphical user interface and data management system to ensure user-friendliness and good quality control. The system has now reached the stage of development where it can be used for practical MTR core analyses. This paper describes the current capabilities of the components of the OSCAR-3 package, their integration within the package, and outlines future developments.

The SHEBA experiment

Abstract: A new version of the SHEBA assembly is described. Several experiments are proposed for the facility.

Three-dimensional transient analysis capability in SIMULATE-3

Abstract: Transient analysis capability has been added to the advanced nodal methodology of SIMULATE-3. The transient modules couple a transient version of the steady-state nodal method QPANDA with a one-dimensional, bundle-by-bundle thermal-hydraulic feedback module. The accuracy of the code has been assessed by using several benchmark problems, including the LMW benchmark and the Nuclear Energy Agency Committee on Reactor Physics (NEACRP) pressurized water reactor (PWR) rod ejection benchmarks.

Computational model for an open-cycle gas core nuclear rocket

Abstract: A computational model of an open-cycle gas core nuclear rocket (GCR) has been developed. The model evaluates the rocket performance of an open-cycle GCR as a function of design and operational parameters. A schematic of the model is displayed in Fig. 1. The solution is divided into two distinct areas - thermal hydraulics and neutronics. To obtain the thermal-hydraulic solution, a computer code has been written that solves the two-dimensional Navier-Stokes, energy, and species diffusion equations. For the majority of the plasma, the optical thickness is sufficiently high to employ the diffusion approximation of radiative heat transfer. Near the walls, where the optical thickness is low, a transport integral is evaluated to calculate wall heat flux. A spatially implicit solution of the conservation equations is obtained by a direct solver that was developed specifically for the code. The two-dimensional transport code TWODANT is used to obtain the neutronics solution. The important requirements of the neutronics model are the ability to handle neutron upscattering and a highly inhomogeneous mesh. Fifty group nuclear cross sections were obtained from EG&G Idaho for a wide range of materials and temperatures. The thermal-hydraulic and neutronic models are coupled, and the solution proceeds in an iterativemore » manner until a consistent power density profile is obtained.« less

Size-spectra of trace elements in urban aerosol particles by instrumental neutron activation analysis

Abstract: Knowledge of composition and size of atmospheric aerosol particles is needed to elucidate their sources, atmospheric transformation processes, contributions to visibility reduction, and respiratory and environmental deposition. In a previous communication, we described size spectra and hygroscopic growth of arsenic, selenium, antimony, and zinc in College Park, Maryland, an urban, nonindustrial area located near Washington, D.C., wherein, concentrations of these elements are influenced largely by sulfate-containing aerosol transported from the Ohio River valley region, more than 200 km west of the area, and local coal utility plants and incinerators located 20 to 50 km from the sampling site. At College Park, mass median aerodynamic diameters (mmad) versus relative humidity (RH) data for these elements fell along different curves for samples influenced by local and distant aerosols; i.e., the curve for distant sources lay below the curve for local sources, at larger mmads for the same RH. In this paper we discuss size spectra, distribution parameters, and hygroscopic growth of aerosol particles bearing trace elements in aerosol collected in Camden, New Jersey, a heavily industrial area in which major sources, including an antimony roaster and municipal incinerator, lie in close proximity (i.e., 5 to 15 km) to the site.

Concerns with low-level ionizing radiation.

Abstract: Objective To clarify the effects of ionizing radiation and to dispel fear associated with the use of radioactivity in medical diagnosis and therapy. Design Studies of populations in geographic areas of increased cosmic radiation and high natural background radiation, radiation-exposed workers, patients with medical exposure to radioactivity, and accidental exposure are reviewed. Results No reproducible evidence shows harmful effects associated with increases in background radiation of 3 to 10 times the usual levels. American military personnel who participated in nuclear testing had no increase in leukemia or other cancers. Among 22,000 patients with hyperthyroidism treated with 131 I (mean dose, 10 rem), no increased incidence of leukemia was found in comparison with 14,000 similar patients who received other treatment. A 20-year follow-up of 35,000 patients who underwent 131 I uptake tests for evaluation of thyroid function revealed that those studied for other than a suspected tumor had only 60% of the thyroid cancers expected in a control group. Although early studies showed that high exposures of miners to radon and its daughters resulted in a substantial increase in lung cancer, no evidence exists for an increase in lung cancer among nonsmokers exposed to increased radon levels in the home. Conclusion Perhaps the association of radiation with the atomic bomb has created a climate of fear about the possible dangers of radiation at any level; however, no evidence indicates that current radiation exposures associated with medical usage are harmful.

Matrix rank in variational nodal approximations

Abstract: Diffusion and transport variational nodal methods are being used increasingly for two and three-dimensinal fast reactor calculations in both Cartesian and hexagonal geometries. This report is concerned with matrix rank in variational nodal approximations.

Large-diameter, high-plutonium metallic fuel testing in EBR-II

Abstract: The integral fast reactor (IFR) concept makes use of U-Pu-Zr metallic fuel alloys because of favorable core behavior characteristics and compatibility with a pyrometallurgical reprocessing scheme. Advanced reactor designs use U-x Pu-10 Zr (where 20 {le} x {le} 28). Most of the IFR fuel performance database was obtained with fuel containing {le}20 wt% Pu having a 0.439-cm diameter irradiated in cladding tubes having a 0.584-cm o.d. However, commercial implementations of the IFR concept (e.g., the advanced liquid-metal reactor by General Electric) will likely use fuel of larger diameter and plutonium contents {ge}20 wt%. The HT9 advanced driver fuel test, irradiated in Experimental Breeder Reactor II (EBR-II), was initiated to obtain irradiation performance data from larger diameter fuel cast with a range of plutonium compositions and clad in the reference cladding alloy HT9.

On spatial approximations for liquid enthalpy and two-phase quality during density-wave oscillations

Abstract: In the analysis of two-phase flow stability, reasonablyrealistic models that explicitly retain the space and time dependence of the conservation equations, lead to sets of equations that are difficult, if not impossible, to analyze. A one-dimensional problem can be formulated mathematically by integrating the momentum equations along the axial direction in the single- and two-phase regions and imposing appropriate pressure boundary conditions. Although, for the case of homogeneous equilibrium models and drift flux models this formulation can be carried out exactly, the set of partial differential equations (PDEs) is reduced to a set of nonlinear integrodifferential equations. To reduce the set of PDEs to a set of nonlinear ordinary differential equations (ODEs), simplifying assumptions are necessary. Various assumptions have been suggested and used to simplify the set of governing equations. In one simplifying approach, the spatial component in the space- and time-dependent variables is explicitly specified. Clausse and Lahey developed a simple model for the boiling flow problem by assuming a time-dependent but piecewise linear single-phase enthalpy profile in the axial direction and a time-dependent, spatially linear mixture-enthalpy profile in the two-phase region. To assess the extent of error introduced in the stability boundaries by such approximations, we have studiedmore » the effects of various approximations in the spatial variation of single-phase enthalpy and two-phase quality. We report the effects of these approximations on stability boundary in an operating parameter plane and compare the results with the exact solution of the mathematical model.« less

Prediction of the long-term performance of crystalline nuclear waste form phases from studies of mineral analogues

Abstract: This investigation outlines the use of natural analogues as a means of assessing the long-term performance of actinide host phases in crystalline nuclear waste forms. We employed several analytical techniques to study the mineral zirconolite, an important actinide host phase in Synroc and tailored ceramics. The following conclusions were reached: 1) Natural zirconolite experiences a crystalline to aperiodic transformation at doses of approximately 10 to 10 alpha/mg (0.08-1.0 dpa), consistent with the results of accelerated damage testing on synthetic zirconolite. 2) Damage microstructures are consistent with the accumulation and overlap of alpha-recoil collision cascades, resulting in aperiodic domains which increase in volume as a function of dose. 3) There is evidence for long-term annealing of alpha-recoil damage in zirconolite at a rate 2-5 times slower than in the structurally related mineral pyrochlore. 4) Analysis of data from the only documented natural zirconolites to show hydrothermal alteration [resulting from F- and P-rich aqueous fluids at T = 500-600 degreesC and P = 2 kb, Giere and Williams (14)], suggests diat Th and U were released to the fluid phase. 5) The effects of low temperature alteration of radiation damaged zirconolite by a Si-rich ground water or fluid phase were identified in the oldest (2.5 x 10 yr) sample in our research collection. Alteration involved incorporation of Si along microfractures at the expense of Ca, Ti, and Fe, but Th and U remained immobile. In this same sample, there is evidence for migration of at least 50% of the radiogenic Pb from both unaltered and altered areas of zirconolite. Most of the Pb may have been retained within the sample as fine precipitates of galena (PbS).

A practical guide to using MCNP with PVM

Abstract: The introduction of large workstation clusters and massively parallel computing platforms has lead to an increased interest in the distributed-memory multiprocessing feature of MCNP{trademark}. Such systems offer the potential of hundredfold increases in speedup. This paper provides step-by-step instructions on the creation and use of MCNP on such systems.

The AFEN Method for Hexagonal Nodal Calculation and Reconstruction

Abstract: The modern nodal methods developed in the past few decades have been successful in predicting the neutron behavior in light water reactors of rectangular assembly geometries. The interest in applying these methods to hexagonal geometries of VVER, high-conversion reactors, and fast neutron reactors has been growing recently. The transverse integration procedure typically used in most modern nodal methods, however, causes some limitations for both rectangular and hexagonal geometries. In particular, the transverse integration in hexagonal nodal methods results in very complicated transverse leakage that contains nonphysical singular terms.

Estimation and interpretation of k{sub eff} confidence intervals in MCNP

Abstract: In criticality calculations, MCNP has three types of indeividual l{sub eff}. The three-combined k{sub eff} estimator has been derived and verified, both theoretically and empirically (for the cases studied), to be the best available estimator in MCNP. It has been shown to be superior to other estimators, such as the simple average and the individual estimator, with the smallest variance. The three-combined k{sub eff} estimator should be presented as a confidence interval, which has been shown to have the correct coverage rates for several realistic problems.

Fokker-Planck approximation of monoenergetic transport processes

Abstract: For transport problems with highly forward-peaked scattering, the transport equation is often approximated by the Fokker-Planck equation or, if large-angle scattering is deemed sufficiently important, by the Boltzmann-Fokker-Planck equation In this paper, we state a simple, necessary, and sufficient condition for the validity of the simpler Fokker-Planck approximation for monoenergetic particle transport We also show that for screened Rutherford scattering, the Fokker-Planck approximation is only marginally valid and is inaccurate unless the scattering is extremely forward peaked (The same is true for more sophisticated models of elastic scattering of charged particles In this paper, we restrict ourselves to screened Rutherford scattering for simplicity) More details on the results presented here will be given in forthcoming publications

A review of the OECD/NEA study on the economics of the nuclear fuel cycle

Abstract: The paper presents an overview of the recent study carried out by OECD's Nuclear Energy Agency on the economics of the nuclear fuel cycle. The study's reference fuel cycle options and costs are discussed and a comparison with earlier NEA work is provided.

Preliminary results of a Rossi-alpha experiment on the University of New Mexico`s AGN-201 reactor

Abstract: A series of Rossi-alpha measurements was performed on the University of New Mexico`s AGN-201 reactor to measure the effective delayed neutron fraction {beta} and the mean prompt-neutron generation time of the system A{sub m}. An example of one of the Rossi-alpha measurements is shown in Fig. 1. Because the reactor is reflected, multiple prompt-neutron decay modes were observed.

KIKO-3D - a three-dimensional kinetics code for VVER-440

Abstract: A three-dimensional kinetics diffusion code has been elaborated at KFKI-AEKI, Hungary, to describe the dynamic behavior of a VVER-440 reactor core. Control rod ejection is one of the most important problems in which KIKO-3D will be utilized. KIKO-3D has been validated by rectangular and hexagonal benchmarks.

KARATE - a code for VVER-440 core calculation

Abstract: A modular calculation system has been elaborated at the KFKI Atomic Energy Research Institute for VVER-440 cores. The purpose of KARATE is the calculation of neutron physical and thermal-hydraulic processes in the core at normal, startup, and slow transient conditions. KARATE is under validation and verification (V&V) against mathematical, experimental, and operational data.

NORM contamination and decommissioning recommendations of the E-4 committee of the Conference of Radiation Control Program Directors

Abstract: The Conference of Radiation Control Program Directors is a nonprofit body comprised of members of state radiological health staffs, representatives of federal agencies with responsibility for radiological health, and others with professional interests in radiological health. The conference works through committees that assess radiological problems, review documents, draft position papers and proposed regulations, and provide information on radiological issues to state legislatures and to Congress. Because of the emerging consensus among state and federal regulators that contamination by naturally occurring radioactive material (NORM) and, in particular, by NORM from oil and gas production facilities, is a significant radiological problem, the conference`s E-4 Committee on NORM contamination and decontamination/decommissioning was charged to {open_quotes}scop(e) the problem ... by preparing an updated report ... which identifies an inventory of types of NORM sources, including oil and gas production/processing operations, the physical and chemical processes involved, the volume and isotopic inventory of material involved, geographical distribution, . . .{close_quotes} and to provide guidance for radiation protection, contamination limits, and disposal criteria. The committee recently finished its work and presented a report that has been published by the conference.

Consumer attitudes toward irradiated food

Abstract: Throughout history, new methods of food preservation have been met with skepticism and fear. Such processes as pasteurization and canning were denounced as being dangerous, detrimental to nutrients, or an excuse for dirty products. Now comes irradiation, and activists argue against this new process for the same reasons. Publicly, the perception is that consumers, distrustful of nuclear power, will never buy or accept irradiated food.

Buried-waste integrated demonstration retrieval projects

Abstract: Prior to 1970, the US Department of Energy`s (DOE`s) primary method for the disposal of transuranic mixed waste was burial in pits and trenches. As an example, between 1952 and 1970, more than 2 million ft{sup 3} of waste was buried at the Idaho National Engineering Laboratory`s (INEL`s) Radioactive Waste Management Complex (RWMC). The contaminants at the RWMC include plutonium and americium oxides, chlorides, hydroxides, volatile organics (trichloroethylene, carbon tetrachloride, etc.), and cutting oils. The waste containers are assumed to be severely deteriorated, and the waste is expected to be commingled with {approx} 6 million ft{sup 3} of fill dirt. The buried waste integrated program was designed to remove the waste and remediate the contaminated area. Current activities associated with this program are described.

Random number generation with arbitrary strides

Abstract: In this paper, we present techniques for the generalized initialization of random number generators for parallel Monte Carlo calculations. In particular, we develop and prove an algorithm for a fast, direct method for skipping ahead in the random sequence by an arbitrarily large positive or negative {open_quotes}stride.{close_quotes} This algorithm is currently used in three different production-level Monte Carlo codes on a variety of parallel, vector, and distributed computer systems to generate the initial seeds for different particle histories. In the extreme cases, the algorithm can reduce several years of {open_quotes}brute-force{close_quotes} computation to a few hundred microseconds.

Prospects for nuclear development in the UK

Abstract: It is four years since the UK electricity supply industry was privatised and in the process the UK nuclear industry did not fare well Concerns about escalating back-end nuclear costs led to the removal of the nuclear stations from the privatisation process with a moratorium being placed on the construction of new nuclear stations pending a review of the prospects for nuclear power Nuclear Electric, the nuclear generating company formed to own and operate the nuclear stations in England and Wales, has made great progress since (hat time Output is up and the UK's first Pressurised Water Reactor (PWR), Sizewell B, is being built to time and cost and to safety standards the world wants to copy Against this backdrop the UK Nuclear Review is about to commence A wide variety of issues will be on the Review agenda - The economics of electricity generated by nuclear power - The competitive position of new nuclear power stations - including follow on PWR plant - Safety and licensing issues in relation to investment in future nuclear stations - The scope for completing the privatisation of the electricity supply industry with the transfer of Nuclear Electric into the private sector - The diversity, security of supply and environmental benefits of nuclear power The UK Nuclear Review offers the most up to date examination of the prospects for Nuclear Power anywhere in the world and its findings should be of interest to nuclear proponents worldwide Nuclear Electric is confident that it's robust economic case and the environmental benefits of nuclear power will secure a positive outcome, allowing new nuclear construction to meet the UK's energy needs of the 21st century

CANDU fuel cycle flexibility

Abstract: High neutron economy, on-power refuelling, and a simple bundle design provide a high degree of flexibility that enables CANDU (CANada Deuterium Uranium; registered trademark) reactors to be fuelled with a wide variety of fuel types. Near-term applications include the use of slightly enriched uranium (SEU), and recovered uranium (RU) from reprocessed spent Light Water Reactor (LWR) fuel. Plutonium and other actinides arising from various sources, including spent LWR fuel, can be accommodated, and weapons-origin plutonium could be destroyed by burning in CANDU. In the DUPIC fuel cycle, a dry processing method would convert spent Pressurized Water Reactor (PWR) fuel to CANDU fuel. The thorium cycle remains of strategic interest in CANDU to ensure long-term resource availability, and would be of specific interest to those countries possessing large thorium reserves, but limited uranium resources.

Characterization of a D&D site using long-range alpha detectors

Abstract: Decontamination and decommissioning (D&D) procedures consist of an assessment phase and a remediation phase The primary problem during assessment is the location and identification of the contaminants Identification is difficult in buildings because contaminants may be hiding in difficult-to-sample areas and systems Detectors based on long-range alpha detector (LRAD) technology are useful during the assessment phase on piping and ventilation systems Not only can these detectors identify alpha emitter contamination, they can also be used to identify uncontaminated systems/areas (Subsequent operations can then be organized to prevent contamination of these systems) The LRAD-based detectors are also useful during remediation to identify uncontaminated material, such as structural debris, foundations, and soil, that could not be checked earlier Also of importance during remediation, is waste characterization for transportation and disposal because the radionuclides of the waste and their associated activity must be known The LRAD-based detectors are well suited for bulk item characterization (ie, concrete, debris, soil) because assay of the items can be done quickly without analytical delays Some additional characterization may be required to identify radionuclides and their proportional distribution Using the LRAD technology, we are currently building two types of detectors exclusively for D&D purposes These are a concretemore » surface monitor and a pipe monitor« less