Richard R. Brey

Increasing PCB Radiolysis Rates in Transformer Oil

Abstract The kinetics of Aroclor 1242 radiolysis in transformer oil, using high-energy electrons, was found to be analogous to that previously measured for individual polychlorinated biphenyl (PCB) congeners irradiated with γ -rays. The plot of the pseudo-first-order rate constant for PCB decomposition versus initial PCB concentration is a power function, with high rate constants for low concentrations. The addition of alkaline isopropanol to transformer oil was found to increase the pseudo-first-order rate constant for PCB decomposition. The rate constant under these conditions is independent of concentration. This may be explained by the establishment of chain reaction dechlorination in the oil.

Potato sprout inhibition and tuber quality after treatment with high-energy ionizing radiation

The use of industrial-type linear accelerators may be an alternative treatment for controlling sprouts in potatoes during long-term storage. The technical aspect of treatment has been described and may include largescale treatment of bulk potatoes as they are moving along a system of conveyors either to or from storage. The objective of the study was to evaluate the use of a linear accelerator for long-term sprout control under commercial storage conditions and the effects on tuber quality. An 18-MeV linear accelerator was used to provide sprout-inhibiting irradiation to various lots of ‘Russet Burbank’ potatoes. Successful sprout suppression was achieved with doses of 40 to 50 Gy (0 g sprout weight after 9 months of storage at 7.2 C) while higher doses caused undesirable increases in reducing sugars in the tubers. Glucose concentrations of treated tubers (0.25% fresh tuber weight) were higher after treatment than the untreated controls (0.08%), but returned to control levels after 2 to 6 months in storage. Glucose concentrations in treated tubers were significantly reduced with storage management for reconditioning by increasing the storage temperature for one month (from 7.2 C to 14.4 C) resulting in glucose concentrations near control concentrations. By increasing the dose-rate from the accelerator, recovery of tuber glucose concentration due to radiation treatments was significantly faster than when the dose was given more slowly. Potato tubers irradiated with high rates (100 Gy) of high-energy electrons exhibited an increase in soft rot and dry rot incidence in storage. Disease development in potatoes treated with sprout inhibiting doses of radiation (50 Gy) increased in lots with a high rot potential. Treated lots with low rot potential were successfully stored for 8 months or more without an increase in rot potential or shrinkage. Selection of lots for irradiation treatment should include some preliminary evaluation for development of disease in long-term storage.ResumenEl uso de acelerador linear de irradiación de tipo industrial puede ser un tratamiento alternativo para controlar el brotamiento de los tubérculos de papa durante periodos largos de almacenaje. El aspecto técnico del tratamiento ya fue descrito anteriormente y puede incluir el tratamiento en gran escala de grandes volúmenes de papa a medida de que se transportan del o hacia el almacén. El objetivo de este estudio fue evaluar el uso de un acelerador lineal para controlar el brotamiento por largo tiempo, bajo condiciones comerciales de almacenamiento y su efecto sobre la calidad del tubérculo. Se utilizó un acelerador lineal 18-MeV para aplicar la irradiación de inhibición del brotamiento a varios lotes de papa ‘Russet Burbank’. Se consiguió una mejor supresión de brotes con dosis de 40 a 50Gy (0g de peso de brotes después de nueve meses de almacenaje a 7.2 C), mientras que dosis más altas causaron el aumento indeseable de azúcares reductores en los tubérculos. Las concentraciones de glucosa de los tubérculos) tratados (0.25% del peso fresco del tubérculo) fueron más altas después del tratamiento que en los testigos sin tratar (0.08%), pero volvieron a niveles del testigo después de dos a seis meses de almacenaje. Las concentraciones de glucosa en los tubérculos tratados se redujeron significativamente con un manejo de reacondicionamiento del almacén, incrementando la temperatura por un mes (de 7.2 C a 14.4 C), lo que dio como resultado que las concentraciones de glucosa estuvieran cercanas a las del testigo. Incrementando la velocidad de aplicación del acelerador, la recuperación de la concentración de glucosa de los tubérculos, debida a los tratamientos de radiación fue significativamente más rápida que cuando se aplicó más lentamente. Los tubérculos de papa irradiados con tasas altas (100 Gy) de electrones de alta energía mostraron en el almacén un incremento en pudrición blanda y pudrición seca. El desarrollo de enfermedades en papa tratada con cantidades de radiación inhibidoras de brotes (50 Gy) incrementó el potencial de pudrición. Los lotes tratados, con potencial bajo de pudrición fueron muy bien almacenados por ocho meses sin presentar un incremento de pudrición o arrugamiento. La selección de lotes para el tratamiento de irradiación debería incluir evaluación preliminar para el desarrollo de enfermedades en almacenamiento prolongado.

Comparison of ICRP 67 and Other Plutonium Systemic Model Predictions with the Biokinetic Data from Nonhuman Primates.

AbstractDespite the presence of a relatively large amount of human data available on the metabolism of plutonium, the experimental animal data is still important in constructing and parameterizing the biokinetic models. Recognizing this importance, the biokinetic data obtained from studies done by P.W. Durbin in nonhuman primates (NHP) were evaluated against the ICRP 67 systemic model and the two human models developed thereafter. The default transfer rates recommended for adult humans in these models predict the urinary excretion in NHP to a certain extent. However, they were unable to describe the fecal excretion rates several days post intake and the activities in skeleton and liver at the time of the death. These inconsistencies between the human reference models and the NHP biokinetic data are the result of metabolic and physiological differences between the species, as demonstrated by early biokinetic studies.

Investigation of irradiated soil byproducts

The high dose irradiation of windblown soil deposited onto the surface of spent nuclear fuel is of concern to long-term fuel storage stability. Such soils could be exposed to radiation fields as great as 1.08 x 10(-3) C/kg-s (15,000 R/hr) during the 40-year anticipated period of interim dry storage prior to placement at the proposed national repository. The total absorbed dose in these cases could be as high as 5 x 10(7) Gy (5 x 10(9) rads). This investigation evaluated the potential generation of explosive or combustible irradiation byproducts during this irradiation. It focuses on the production of radiolytic byproducts generated within the pore water of surrogate clays that are consistent with those found on the Idaho National Engineering and Environmental Laboratory. Synthesized surrogates of localized soils containing combinations of clay, water, and aluminum samples, enclosed within a stainless steel vessel were irradiated and the quantities of the byproducts generated measured. Two types of clays, varying primarily in the presence of iron oxide, were investigated. Two treatment levels of irradiation and a control were investigated. An 18-Mev linear accelerator was used to irradiate samples. The first irradiation level provided an absorbed dose of 3.9 x 10(5)+/-1.4 x 10(5)Gy (3.9 x 10(7)+/-1.4 x 10(7) rads) in a 3-h period. At the second irradiation level, 4.8 x 10(5)+/-2.0 x 10(5)Gy (4.8 x 10(7)+/-2.0 x 10(7) rads) were delivered in a 6-h period. When averaged over all treatment parameters, irradiated clay samples with and without iron (III) oxide (moisture content = 40%) had a production rate of hydrogen gas that was a strong function of radiation-dose. A g-value of 5.61 x 10(-9)+/-1.56 x 10(-9) mol/J (0.054+/-0.015 molecules/100-eV) per mass of pore water was observed in the clay samples without iron (III) oxide for hydrogen gas production. A g-value of 1.07 x 10(-8)+/-2.91 x 10(-9) mol/J (0.103+0.028 molecules/100-eV) per mass of pore water was observed in the iron (III) oxide containing clay samples for hydrogen gas production. This value was noticeably larger when the samples were spiked with both KCl and KNO3 salts. The ratio of oxygen to nitrogen gas was observed to increase as a function of absorbed dose particularly in the presence of both KCl and KNO3 salts. The creation of radiolytic byproducts produced an observable but small increase in headspace pressure. Temperature increases during irradiation were not observed. Additionally, KCl and KNO3 salts added to the clays enhanced nitrite production as a function of radiation-dose and the type of clay considered. The addition of aluminum to these samples had no statistically discernable impact at the alpha = 0.05 level. Generation of the irradiation products, hydrogen peroxide and hydrogen gas also depended upon the type of clay irradiated and the presence of both KCl and KNO3 salts and the total dose received.

Development of the Plutonium-DTPA biokinetic model

AbstractEstimating radionuclide intakes from bioassays following chelation treatment presents a challenge to the dosimetrist due to the observed excretion enhancement of the particular radionuclide of concern where no standard biokinetic model exists. This document provides a Pu-DTPA biokinetic model that may be used for making such determination for plutonium intakes. The Pu-DTPA biokinetic model is intended to supplement the standard recommended biokinetic models. The model was used to evaluate several chelation strategies that resulted in providing recommendations for effective treatment. These recommendations supported early treatment for soluble particle inhalations and an initial 3‐day series of DTPA treatments for wounds. Several late chelation strategies were also compared where reduced treatment frequencies proved to be as effective as multiple treatments. The Pu-DTPA biokinetic model can be used to assist in estimating initial intakes of transuranic radionuclides and for studying the effects of different treatment strategies.

Reevaluation of USTUR plutonium wound case 0262 using Bayesian methodology and new data.

Abstract Skin penetration by radionuclide contaminants serves as a route of entry into the body and may pose a serious health risk to humans depending on the magnitude of intake. The United States Transuranium and Uranium Registry whole body Case 0262 was involved in a wound intake of plutonium at the Hanford Site. The registrant died about 33 years later. Results were initially reported in 2007 regarding the deposition and retention of plutonium in various tissues, including the wound site. However in 2009, an additional (previously unrecorded) sample of the wound tissue was located in the National Human Radiobiological Tissue Repository. The new sample was analyzed using inductively coupled plasma-mass spectrometry (ICP-MS), and the results were used to calibrate the measurement of emitted 239Pu x-rays from the original wound tissue sample made in 2007. In the present study, the analysis of 239Pu absorption rates from the wound and axillary lymph node from the initial study is repeated using the additional wound activity data and ICP-MS calibration. This new analysis is carried out using the Weighted Likelihood Monte Carlo Sampling (WeLMoS) method and code, which applies Bayesian inference to calculate the posterior probability distribution of intake and wound absorption parameters directly from the observed data and the assumed biokinetic model structure. The resulting central estimates of empirical wound absorption parameters and their associated uncertainties are here compared with the empirical values recommended in NCRP Report No. 156 for plutonium and with the maximum likelihood point estimates derived in the initial study from the Case 0262 data available at the time.

Application of NCRP 156 Wound Model and ICRP 67 Systemic Plutonium Model for Analysis of Urine Data from Simulated Wounds in Nonhuman Primates.

AbstractThe predictions of the wound model described in NCRP Report No. 156, coupled with the systemic model described in ICRP 67, were compared with the actual urinary excretion data and wound retention data from nonhuman primates injected intramuscularly or subcutaneously with 238Pu(IV) citrate. The results indicated that the early behavior of 238Pu(IV) citrate in wounds can be adequately described by the default retention parameters for moderately retained radionuclides suggested by the report. The urinary excretion rates after 200 d post intake could not be described well by the parameters of any of the default wound models because of the differences in the systemic handling of plutonium by humans compared to nonhuman primates.

Proposed Modification to the Plutonium Systemic Model.

AbstractThe currently accepted biokinetic model for plutonium distribution within the human body was recommended by the International Commission on Radiological Protection in publication 67. This model was developed from human and animal studies and behavioral knowledge acquired from other known bone-seeking radionuclides. The biokinetic model provides a mathematical means of predicting the distribution, retention, and clearance of plutonium within the human body that may be used in deriving organ, tissue, and whole body dose. This work proposed a modification to the ICRP 67 systemic model for plutonium that incorporated the latest knowledge acquired from recent human injection studies with physiologically based improvements. In summary, the changes included a separation of the liver compartments, removed the intermediate soft tissue-to-bladder pathway, and added pathways from the blood compartment to both the cortical and trabecular bone volumes. The proposed model provided improved predictions for several bioassay indicators compared to the ICRP 67 model while also maintaining its basic structure. Additionally, the proposed model incorporated physiologically based improvements for the liver and skeleton and continued to ensure efficient coupling with intake biokinetic models.

Early blood plutonium retention in nonhuman primates compared to the NCRP 156 wound biokinetic model.

AbstractData from animal experiments are relied upon for understanding the biokinetics of contaminant retention and excretion where insufficient human data exist. Records involving nonhuman primate experiments performed from 1973 to 1987 were collected and compiled by researchers at the Lawrence Berkeley Laboratory. These records included early blood samples that were taken after soluble plutonium was administered via intramuscular, subcutaneous, or intravenous injection. Samples were collected as early as 5 min post injection with several samples collected during the first few weeks. The NCRP 156 biokinetic model was developed primarily from animal experiments due to insufficient human data not influenced by chelation therapy. This work compared the NCRP 156 biokinetic model default transfer rate constants to the early blood excretion data from nonhuman primate experiments for 238Pu. These results indicated that the blood content of nonhuman primates exhibited “moderate” retention properties for simulated wound conditions. Additionally, there was no evidence of long-term retention of plutonium in the whole blood samples, confirming that plutonium was not incorporated within blood cells. Particle solubility characteristics should be considered for wounds when using the NCRP 156 wound biokinetic model.

Measurements of activation products associated with Havar foils from a GE PETtrace medical cyclotron using high resolution gamma spectroscopy.

Havar foils are specially engineered for beam-line windows used in the General Electric (GE) PETtrace medical cyclotron that can withstand the high pressure differentials and also temperatures developed near the target with proton bombardment. These foils effectively separate components along the beam line of the cyclotron. Various activation products are produced in the foils from the primary proton beam and other secondary radiations. An accurate estimate of the activation products is necessary for the disposal of these foils. The foils were assayed using two High Purity Germanium (HPGe) detectors calibrated over a wide energy range. These were positioned at different distances (0.10 m, 0.24 m, and 1.74 m) away from the detector faces to accommodate their high activities. A summary of the anticipated relative abundance of each activation product and a scatter plot of the average exposure rate per unit charge incident on the foil vs. time post-activation are provided. A detailed spectral analysis of the foils in the energy ranges between 12 keV to 300 keV and 12 keV through 2,500 keV revealed the residual activation products 56Co, 57Co, 58Co, 54Mn, and 183Re at 264 d post-irradiation. Spectral examinations of the different foils removed between 2003 and 2005 show the same activation products regardless of the irradiation time or foil position in the target assembly. The information presented in this paper can be used along with the integrated charge incident on the foils in estimating the activity of Havar foils for the purpose of disposal.