David M. Slaughter

Development of an improved dosimetry system for the workers at the Mayak Production Association

Databases are being created that contain verified and updated dosimetry and worker history information for workers at the Mayak Production Association. Many workers had significant external and internal exposures, particularly during the early years (1948-1952) of operation. These dosimetric and worker history data are to be used in companion epidemiology studies of stochastic and deterministic effects. The database contains both external and internal dose information and is being constructed from other databases that include radiochemical analyses of tissues, bioassay data, air sampling data, whole body counting data, and occupational and worker histories. The procedures, models, methods, and operational uncertainties will be documented and included in the database, technical reports, and publications. The cohort of the stochastic epidemiological study is expected to include about 19,000 persons while the cohort for the deterministic epidemiological study is expected to include about 600 persons. For external dosimetry, workplace gamma, beta, and neutron doses are being reconstructed. The models used for this incorporate issues such as known isotopes, composition, shielding, further analysis of film badge sensitivities, and records of direct measurements. Organ doses from external exposures are also being calculated. Methods for calculating dose uncertainties are being developed. For internal dosimetry, the organ doses have been calculated using the established FIB-1 biokinetic model. A new biokinetic model is being developed that includes more information of the solubility and biokinetics of the different chemical forms and particulate sizes of plutonium that were in the workplace. In addition, updated worker histories will be used to estimate doses to some workers where direct measurements were not made. A rigorous quality control procedure is being implemented to ensure that the correct dosimetry data is entering the various databases being used by the epidemiologists.

Uncertainties analysis for the plutonium dosimetry model, doses-2005, using Mayak bioassay data.

The Doses-2005 model is a combination of the International Commission on Radiological Protection (ICRP) models modified using data from the Mayak Production Association cohort. Surrogate doses from inhaled plutonium can be assigned to approximately 29% of the Mayak workers using their urine bioassay measurements and other history records. The purpose of this study was to quantify and qualify the uncertainties in the estimates for radiation doses calculated with the Doses-2005 model by using Monte Carlo methods and perturbation theory. The average uncertainty in the yearly dose estimates for most organs was approximately 100% regardless of the transportability classification. The relative source of the uncertainties comes from three main sources: 45% from the urine bioassay measurements, 29% from the Doses-2005 model parameters, and 26% from the reference masses for the organs. The most significant reduction in the overall dose uncertainties would result from improved methods in bioassay measurement with additional improvements generated through further model refinement. Additional uncertainties were determined for dose estimates resulting from changes in the transportability classification and the smoking toggle. A comparison was performed to determine the effect of using the model with data from either urine bioassay or autopsy data; no direct correlation could be established. Analysis of the model using autopsy data and incorporation of results from other research efforts that have utilized plutonium ICRP models could improve the Doses-2005 model and reduce the overall uncertainty in the dose estimates.

The historical and current application of the FIB-1 model to assess organ dose from plutonium intakes in Mayak workers.

One of the objectives of the Joint Coordinating Committee for Radiation Effects Research Project 2.4 is to document the methodology used to determine the radiation doses in workers from the Mayak Production Association who were exposed to plutonium. The doses have been employed in numerous dose response studies measuring both stochastic and deterministic effects. This article documents both the historical (pre-1999) and current (“Doses 1999”) methods used by the FIB-1 scientists to determine the doses. Both methods are based on a three-chamber lung model developed by the FIB-1 scientists. This method was developed in partial isolation from the West and has unique characteristics from the more familiar ICRP biokinetic models. Some of these characteristics are the use of empirically based transportability classifications and the parameter modification for chelation-therapy-enhanced excretion data. An example dose calculation is provided and compared to the dose that would be obtained if the ICRP models were used. The comparison demonstrates that the models are not interchangeable and produce different results.

Uncertainties analysis of doses resulting from chronic inhalation of plutonium at the Mayak production association.

A method is presented to determine the uncertainties in the reported dose due to incorporated plutonium for the Mayak Worker Cohort. The methodology includes errors generated by both detection methods and modeling methods. To accomplish the task, the method includes classical statistics, Monte Carlo, perturbation, and reliability groupings. Uncertainties are reported in percent of reported dose as a function of total body burden. The cohort was initially sorted into six reliability groups, with “A” being the data set that the investigators are most confident is correct and “G” being the data set with the most ambiguous data. Categories were adjusted based on preliminary calculation of uncertainties using the sorting criteria. Specifically, the impact of transportability (the parameter used to describe the transport of plutonium from the lung to systemic organs) was underestimated, and the structure of the sort was reorganized to reflect the impact of transportability. The finalized categories are designated with Roman numerals I through V, with “I” being the most reliable. Excluding Category V (neither bioassay nor autopsy), the highest uncertainty in lung doses is for individuals from Category IV—which ranged from 90–375% for total body burdens greater than 10 Bq, along with work histories that indicated exposure to more than one transportability class. The smallest estimated uncertainties for lung doses were determined by autopsy. Category I has a 32–38% uncertainty in the lung dose for total body burdens greater than 1 Bq. First, these results provide a further definition and characterization of the cohort and, second, they provide uncertainty estimates for these plutonium exposure categories.

Predictability of acute radiation injury severity.

Results of dose-response analyses for different clinical symptoms of acute radiation syndrome (ARS) are reported here. The analyses were performed on dosimetric and clinical data from a group of ARS patients (59 cases) exposed to gamma and neutron or gamma radiation alone due to nuclear accidents at Mayak Production Association (Mayak PA). Findings suggested the possibility of prediction of injury severity within the first hours or days after acute exposure based on clinical symptoms and signs such as the onset of vomiting, neutrophil count abnormalities in the peripheral blood within the first 2–3 hours after acute exposure, and lymphocyte count abnormalities in the peripheral blood within the first 24–48 h after acute exposure.

Inert pyrolysis of stoker-coal fines

This study provided information on the relative stability of nitrogen-, sulphur-, carbon- and hydrogen-containing species retained in the char during pyrolysis of the stoker fines. The presence of these principal constituents was determined by elemental analyses on the remaining char; this allowed a simple (but effective) means of correlating the loss of sulphur and nitrogen species against a variety of pyrolysis conditions. Inert pyrolysis experiments were performed in a CF-IR Lindberg tube furnace. Furnace temperatures studied ranged from 700 °C to 1300 °C while the residence time ranged from 1 to 40 minutes. The coal fines from typical stoker-sized coal included three size ranges (i.e. d < 0.16, 0.16 < d < 0.28 and 0.28 < d < 0.40 cm). The experimental results indicated the relative stability of the carbon species. Carbon evolution was least affected by an increase in temperature and relatively insensitive to changes in coal rank, although the highest-rank coal evolved the least carbon and the lignite coal evolved the most. Hydrogen evolution was also relatively insensitive to coal rank; however, the extent of evolution was large under all conditions tested and increased significantly with increasing temperature. Carbon evolution clearly approached a fixed, asymptotic value with increasing time and temperature, but hydrogen evolution was almost complete at 1100 °C. Nitrogen and sulphur both exhibited behaviour generally intermediate to that observed for carbon and hydrogen. Sulphur evolution consistently exceeded that of carbon but the dependence on temperature was essentially identical for both species. In contrast, nitrogen evolution at 700 °C was almost identical to that of carbon and relatively insensitive to coal rank. However, nitrogen evolution exhibited a stronger temperature dependence and at 1100 °C it far exceeded the evolution of the carbon species. Particle size was shown to have little influence on the evolution of the various species over the range tested in this study; therefore, the conclusions are relevant to stoker-coal fines in general.

A route-specific system for risk assessment of radioactive materials transportation accidents

A low-cost, powerful geographic information system (GIS) that operates on a personal computer was integrated into a software system to provide route specific assessment of the risks associated with the atmospheric release of radioactive and hazardous materials in transportation accidents. The highway transportation risk assessment (HITRA) software system described here combines a commercially available GIS (TransCAD) with appropriate models and data files for route- and accident-specific factors, such as meteorology, dispersion, demography, and health effects to permit detailed analysis of transportation risk assessment. The HITRA system allows a user to interactively select a highway or railroad route from a GIS database of major US transportation routes. A route-specific risk assessment is then performed to estimate downwind release concentrations and the resulting potential health effects imposed on the exposed population under local environmental and temporal conditions. The integration of GIS technology with current risk assessment methodology permits detailed analysis coupled with enhanced user interaction. Furthermore, HITRA provides flexibility and documentation for route planning, updating and improving the databases required for evaluating specific transportation routes, changing meteorological and environmental conditions, and local demographics.

Calculated organ doses for Mayak production association central hall using ICRP and MCNP.

Abstract— As part of an ongoing dose reconstruction project, equivalent organ dose rates from photons and neutrons were estimated using the energy spectra measured in the central hall above the graphite reactor core located in the Russian Mayak Production Association facility. Reconstruction of the work environment was necessary due to the lack of personal dosimeter data for neutrons in the time period prior to 1987. A typical worker scenario for the central hall was developed for the Monte Carlo Neutron Photon-4B (MCNP) code. The resultant equivalent dose rates for neutrons and photons were compared with the equivalent dose rates derived from calculations using the conversion coefficients in the International Commission on Radiological Protection Publications 51 and 74 in order to validate the model scenario for this Russian facility. The MCNP results were in good agreement with the results of the ICRP publications indicating the modeling scenario was consistent with actual work conditions given the spectra provided. The MCNP code will allow for additional orientations to accurately reflect source locations.

High‐temperature, radiation‐hard electronic technology

We report on two novel high temperature and potentially highly neutron and gamma radiation resistant electronc technologies that are suitable for nuclear and space applications. The operational effects on these technologies from gamma radiation doses up to 10 megarads and 1‐MeV equivalent neutron fluences up to 1014 neutrons/cm2 are examined using a calibrated (to appropriate ASTM standards) irradiation chamber in the University of Utah TRIGA Nuclear Reactor. The first high temperature, harsh environment technology is based on microminiature vacuum (MTV) devices. The second high temperature technology is gallium arsenide (GaAs) metal semiconductor field effect transistor (MESFET)‐based devices and circuits that can operate at temperatures up to 350 °C. This MESFET‐based technology also allows a wide range of control with respect to the MESFET’s enhanced resistance to breakdown at elevated temperatures. The MESFET‐based technology has general applicability and works equally well with both enhancement and d...

High temperature sulfation studies in an isothermal reactor: A comparison of theory and experiment

High temperature, isothermal data on SO 2 capture were obtained as a function of temperature, SO 2 partial pressure, and Ca/S molar ratio for a pulverized dolomite (34 micron mean size) and a high purity calcite (11 micron mean size). The experimental results indicated that sulfur capture increases approximately iinearly with increasing Ca/S ratio and is relatively insensitive to SO 2 partial pressure at the conditions tested. Reaction zone temperature was found to critically influence the overall effectiveness of sulfur capture by sorbent injection; as the local temperature increases, the rates of heterogenous chemical reaction and diffusion increase but these are ultimately compensated by a decrease in initial sorbent surface area due to desurfacing during flash calcination. The results of the experimental studies were compared with theoretical predictions using a combined diffusion/heterogeneous chemical reaction model which was developed based on a grain formulation. Initial analysis of various fundamental kinetic studies suggested that the intrinsic chemistry was first order in calcium sites and near zero order in SO 2 partial pressure. Model predictions, based on measured gas temperatures and limestone surface areas without sulfur plus kinetic and diffusion rates derived from previously reported fundamental studies, showed good qualitative and quantitative agreement with experimental data. Analysis of temperature profiles from full-scale utility boilers suggests that effectiveness of dry sorbent injection will depend strongly on the quench rate within the surfation zone even if sorbent injection is optimized.