Radioactive Cement Research Articles

Radiation safety assessments for radioactive concrete recycling workers and residents

Carried out was the assessment of the radiation safety for the recycling workers of the radioactive concrete generated from nuclear power plants and nearby residents. Decommissioning of a nuclear power plant with an electric output of 1000 MW generates approximately 500,000 tons of concrete waste. It is important to reduce the volume of concrete waste to reduce the costs of decommissioning projects. For this purpose, the low-level radioactive cement powder from bioshield concrete is recycled as a solidifying agent. The number of radioactive concrete waste drums to be disposed is reduced by extracting cement from the radioactive concrete and using it as a solidifying agent, rather than using cement from general industrial waste. Various exposure scenarios exist, and it is necessary to evaluate the radiation dose in each scenario. In this study, seven scenarios were selected and evaluated. The radioactive exposure to facility workers, nuclear power plant workers, and landfill management workers is within the annual dose limit, even if they work 2000 h per year. A loader can work close to the drum for 90–93 h per year, and a truck driver can drive 621 one-way trucks per year. Dose evaluations for road users and residents after landfill closure showed that both had values far below the dose limit for the public. Bioshield concrete recycling was confirmed to be radiologically safe in all scenarios if certain conditions were satisfied. Thus, this study showed that cement powder from bioshield concrete could be used safely without exceeding the radiation safety limits for workers and the public when recycling concrete.

Monte Carlo Dosimetric Study of Percutaneous Vertebroplasty and Brachytherapy for the Treatment of Spinal Metastases.

Percutaneous vertebroplasty employs bone cement for injecting into the fractured vertebral body (VB) caused by spinal metastases. Radioactive bone cement and also brachytherapy seeds have been utilized to suppress the tumor growth in the VB. This study aims to investigate the dose distributions of low-energy brachytherapy seeds, and to compare them to those of radioactive bone cement, by Monte Carlo simulation. In this simulation study, nine CT scan images were imported in Geant4. For the simulation of brachytherapy, I-125, Cs-131, or Pd-103 seeds were positioned in the VB, and for the simulation of vertebroplasty, the VB was filled by a radioactive cement loaded by P-32, Ho-166, Y-90, or Sm-153 radioisotopes. The dose-volume histograms of the VB, and the spinal cord (SC) were obtained after segmentation, considering that the reference dose is the minimum dose covered 95% of the VB. The SC sparing was improved by using beta-emitting cement because of their steep gradient dose distribution. I-125 seeds and Y-90 radioisotope showed better VB coverage for brachytherapy and vertebroplasty techniques, respectively. Pd-103 seeds and P-32 radioisotope showed better SC sparing for brachytherapy and vertebroplasty, respectively. The minimum mean doses that covered 100% of the VB were 62.0%, 56.5%, and 45.0% for I-125, Cs-131, and Pd-103 seeds, and 28.3%, 28.6%, 32.9%, and 17.7%, for P-32, Ho-166, Y-90, and Sm-153 sources, respectively. I-125 and Cs-131 seeds may be useful for large tumors filling the entire VB, and also for the extended tumors invading multiple vertebrae. Beta-emitting bone cement is recommended for tumors located near the SC.

Radioactive Waste Embedding in Cement Matrix and the Establishment of Cemented Waste Testing Laboratory at Paks Nuclear Power Plant

For the treatment of low and intermediate level radioactive wastes generated at the Nuclear Power Plant of Paks, a new compact waste package will be created with a new cementation technology currently under construction. During the operation, the solid waste will be placed in steel drums, which then will be put into a thin-walled steel container. The cavity volume of the containers will be filled with cemented slurry made using liquid radioactive waste. The compact waste packages must comply with the waste acceptance criteria described in the National Radioactive Waste Repository Safety Report. The task of the cemented waste testing laboratory, which is under construction, will be the in-service inspection of the finished cemented material and the determination of properties such as compressive strength and leachability (diffusion coefficient) of the specimens made thereof. During the installation of the laboratory and testing of the devices used in the cement / concrete industry, it turned out that in many cases special moulds are required due to the low viscosity and corrosive properties of the radioactive paste. In addition, the collection of debris generated during the measurement of compressive strength of radioactive cement stone and the minimization of dusting are important requirements.

Computational dosimetry evaluation in vertebral models using a radioactive bone cement with Sm-153, Ho-166 and Y-90

Background: Breast cancer is a disease that affects a large part of the Brazilian female population. Especially, those metastases developed in the spinal column can produce potential fractures with neurological compromise or reduction of the life’s quality of the patient due to chronic pain. Objective: The development of a computational dosimetry in vertebral models simulating bone metastasis applying a radioactive bone cement with Sm-153, Ho-166 and Y-90. Methods: 1. Based on radiological images of animal vertebrae was constructed in the code MCNPx. Absorbed doses were evaluated in the axial plane (XY) of the implant of the radioactive bone cement in the metastasis. The nearest organ of risk (OAR) was the spinal cord and the implant itself on the vertebras was the prescribed tumor volume (PTV). The Sm-153, Ho-166 and Y-90 radionuclides were considered. 2. The fluency of the electrons along the symmetrical axis of the vertebra x = 0 in the z = 0 planes was also studied. Results: The therapeutic absorbed dose obtained in the implant plane by radioactive bone cement reaches levels above 70 Gy for specific activities close to 3 GBq.mg-1 with suitable values for the Y-90 coupled to the cement. Exposure to Ho-166 produces a lower dose than in Y-90 but higher than in Sm-153. The doses obtained by radionuclide implants are better spatial distributed than IMRT, with a significant dose reduction in the spinal cord. Beta emitting from Y-90 found a greater range. Conclusions: The radioactive cement in an implant may potentially favor optimal tumor control and lower side effects in organs at risk.

Radioactive bone cement for the treatment of spinal metastases: a dosimetric analysis of simulated clinical scenarios

Vertebral metastases are a common manifestation of many cancers, potentially leading to vertebral collapse and neurological complications. Conventional treatment often involves percutaneous vertebroplasty/kyphoplasty followed by external beam radiation therapy. As a more convenient alternative, we have introduced radioactive bone cement, i.e. bone cement incorporating a radionuclide. In this study, we used a previously developed Monte Carlo radiation transport modeling method to evaluate dose distributions from phosphorus-32 radioactive cement in simulated clinical scenarios. Isodose curves were generally concentric about the surface of bone cement injected into cadaveric vertebrae, indicating that dose distributions are relatively predictable, thus facilitating treatment planning (cement formulation and dosimetry method are patent pending). Model results indicated that a therapeutic dose could be delivered to tumor/bone within ∼4 mm of the cement surface while maintaining a safe dose to radiosensitive tissue beyond this distance. This therapeutic range should be sufficient to treat target volumes within the vertebral body when tumor ablation or other techniques are used to create a cavity into which the radioactive cement can be injected. With further development, treating spinal metastases with radioactive bone cement may become a clinically useful and convenient alternative to the conventional two-step approach of percutaneous strength restoration followed by radiotherapy.

Evaluation of a radiation transport modeling method for radioactive bone cement

Spinal metastases are a common and serious manifestation of cancer, and are often treated with vertebroplasty/kyphoplasty followed by external beam radiation therapy (EBRT). As an alternative, we have introduced radioactive bone cement, i.e. bone cement incorporated with a radionuclide. In this study, we present a Monte Carlo radiation transport modeling method to calculate dose distributions within vertebrae containing radioactive cement. Model accuracy was evaluated by comparing model-predicted depth–dose curves to those measured experimentally in eight cadaveric vertebrae using radiochromic film. The high-gradient regions of the depth–dose curves differed by radial distances of 0.3–0.9 mm, an improvement over EBRT dosimetry accuracy. The low-gradient regions differed by 0.033–0.055 Gy/h/mCi, which may be important in situations involving prior spinal cord irradiation. Using a more rigorous evaluation of model accuracy, four models predicted the measured dose distribution within the experimental uncertainty, as represented by the 95% confidence interval of the measured log-linear depth–dose curve. The remaining four models required modification to account for marrow lost from the vertebrae during specimen preparation. However, the accuracy of the modified model results indicated that, when this source of uncertainty is accounted for, this modeling method can be used to predict dose distributions in vertebrae containing radioactive cement.

39-years Performance of Cemented Radioactive Waste in a Mound Type Repository

ABSTRACTLong-term field tests of cemented aqueous radioactive wastes in an experimental mound type surface repository were carried out at Moscow Scientific and Industrial Association “Radon” from 1965 to 2004. Aqueous radioactive wastes of different compositions containing short-lived radionuclides including 90Sr and 137Cs at concentrations from 0.34 to 1.8 MBq/L were immobilized using cementation technology. Water solution to cement ratio was 0.66, grout mixing time 10-15 minutes, and cement paste hardening time 7 days. 73 cement blocks with a volume of 0.027 m3 were disposed of for long-term tests in a simple mound type surface repository. The atmospheric precipitates, which contacted radioactive cement blocks, were collected and analyzed for the content of radionuclides. In August 2004 the experimental repository was opened, cemented blocks, underlying and covering materials were retrieved for analyses. XRD analyses showed that along with amorphous tobermorite gel the main crystal phases in cements are calcite and portlandite. Both visual inspection and radiometric analyses demonstrate that cemented blocks are in good condition and that the cement paste has retained radionuclides from the wastes. Thus after 39 years of storage in the mound type repository the cemented aqueous wastes are reliable immobilized.

Detection of Radioactive Cement in Cased Wells

In a previous article we have described a technique for measuring therelative intensities of gamma rays from the radioactive elements occurringnaturally in geological formations along the walls of a borehole. The apparatusconsisted of two Geiger-Muller tubes mounted inside a pressure tight chamber.Each counter tube was coupled separately to an amplifier and a frequency meterat the surface by means of a multi-conductor cable upon which the chamber wassuspended. The output currents of the two frequency meters were recorded on aphotographic paper as the chamber was moved in the hole. These traces showedremarkable correlation with the geologic formations, as evidenced by comparisonwith commercial electrical logs. Owing to the penetrating power of the gammarays, logs may be taken in both open and cased boreholes. The apparatus has recently been changed somewhat. One of the counter tubes hasbeen removed and a stage of amplification has been added inside the chamber.This arrangement seems to give a more favorable signal-to-noise ratio andsatisfactory logs can be now made in cased holes and also in open holes aspreviously. Briefly described, the chamber moving in the hole is made of 372-in. drill pipe and is about 10 ft. long. There is an additional extensionabout 2 ft. long at the top, inside which cable connections are made. TheGeiger-Muller tube is mounted inside the bottom end of the chamber. Above thisis the vacuum-tube amplifier with its batteries and transformer. In the toppart of the chamber, small 45-volt batteries are mounted, which in part supplythe high voltage for the counter tube. Additional voltage IS supplied from thesurface through the multi-conductor cable upon which the chamber is suspended.Also, the output of the transformer in the single-stage amplifier is coupled toanother single-stage amplifier at the surface through this cable. T.P. 1113