Risks assessment for the retrieval of radioactive waste from the old Russian cemetery Al -Tuwaitha site

In this work the radioactive wastes in the Old RussianCemetery Al -Tuwaitha site were classified according to risks forworkers who are involved in the retrieval process. The exposureassessment results expressed as estimates of radionuclide intakes byinhalation and ingestion, exposure rates and duration for externalexposure pathways, and committed effective dose equivalents toindividuals from all relevant radionuclides and pathways. Resultsshowed the presence of natural radionuclides Ra-226, Th-234 and K-40, as well as the produced radionuclide Cs-137 and Eu-152 in thecemetery wells. The absorbed doses from the waste were classified totwo categories; exempt waste and low level waste according toabsorbed dose value. This studied site does not pose a radiologicalhazard for the workers.


Introduction
A health risk is generally thought of as something that may endanger health. Scientists consider health risk to be the statistical or mathematical probability that lead to radiation injury. Instead, most of us consider the health risk of a particular action in terms of whether we believe that particular action will, or will not, which caused us some harm. The intent of this appendix is to provide estimates of, and explain the bases of radiation risk for occupational radiation exposure. Risk can be easily quantified in terms of the probability of a health effect per unit of dose received. When ionizing radiation interacts with living materials, they may deposit enough energy to cause biological damage in the cells. The interaction is depending upon the type of radiation and its energy. Radiation can cause several different types of events such as tiny changing of molecular structure, removal of electrons from atoms and molecules. When deposited energy of radiation in living tissue is high enough, biological damage could occur as a result of breakage of chemical bonds leading to damaged or death of the living cells. These effects can result in observable clinical analysis. The radioactive waste is generated in enormous quantities throughout the wide usage and applications of radioactive materials in the modern life.RW should be managed properly throughout the whole series of activities and processes of handling, transporting, treatment, conditioning and eventually proper disposal of the waste that's ensure high measures of protection and safety for radiation workers, environment, any number of the public and eventually our future generations [1]. The RW is mostly classified as low, intermediate or highlevel waste and as short-lived or longlived waste, depending upon the radiation activity, half-life of radionuclides, type of emitted, radiation and heat if any, generated during the radioactive decay process.The absorbed dose refers to how much energy is deposited in material by the radiation [2,3]. The dose equivalent is the product of the absorbed dose and the quality factor of the radiation. In the case of presence several radiation types, and total dose equivalent is the sum of its determined individual amounts. Not all radiation has the same biological effect, even for the same amount of absorbed dose, as some forms of radiation are more efficient than others in transferring their energy to living cells. A risk assessment consists of four distinct steps: data collection and evaluation, exposure assessment, toxicity assessment, and risk characterization. The outcome of a risk assessment is either a set of chemicals, pathways, media, and/or scenarios of concern for which an appropriate action must be undertaken or a determination that no action is required. All individuals exposed to hazardous waste are potentially at risk, including those within health-care establishments that generate hazardous waste, and radiation workers at nuclear facilities such as radioactive waste management workers who are in direct touch with these waste [4].
The photon attenuation coefficient µ is an important parameter characterizes the penetration and diffusion of gamma rays in composite materials such as waste; RW may contain different radionuclides in different concentrations or activities. The effects of different parameters on the attenuation coefficients of waste were discussed in several studies. An extensive data on mass attenuation coefficients µ/ρ of gamma rays in compound and mixtures of dosimetric interest have been studied by Hubbel1 [5] in the energy range of 10keV to 100 GeV, an updated version of attenuation coefficients for elements having atomic number from 1-92 [5].

Experimental work
The RC in Al-Twiatha site is a very big above ground concrete block of 16 ×50 × 5 m. It contains around 91 concrete wells of 4 m depth, which means the cemetery was built on top of  The calculation of radiation dose equivalent by using the following Eq.(3): ( where D eq -is the equivalent dose rate in μSv/h Ґ -is the gamma factor (dose rate constant) in μSvm 2 /(MBqh). A-is the activity of the source in MBq.
d-is the distance in meters from the source [7]. The measured activities of the sample dose note represent the actual activity value due to the loss of some photons in the passage of the photons through the steel material of the barrel. Accordingly the measured activity value have to be corrected for the linear attenuation coefficient of the steel [5] to extract the µ value for each radionuclide in the sample as shown in Fig.4.

Fig.4 : The relation between energy and linear attenuation coefficient.
The attenuation of gamma rays, that dependent through a drum wall, is calculated as shown in Table 1. Classification of radioactive waste depending on the dose of radiation using the report of the International Atomic Energy Agency [8].

Results and discussion
The activity concentrations of radionuclides in waste samples from the RC in Al-Tuwaitha were determined by gamma spectrometry. Results showed the presence of natural radionuclides Ra-226, Th-234 and K-40, as well as the produced radionuclide Cs-137 and Eu-152 (from the nuclear fission and made man). As shown in Table1, the results of the activity concentrations in the waste samples collected from the studied location are presented and expressed in Becquerel. Analysis of waste streams, Table 1 and compare with Table 2 [8].
shows that more of the waste will be low activity waste (Category I). Waste that is above exemption levels, but with limited amounts of long lived radionuclides, such waste requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near surface facilities.

Conclusions
This work presented the measured results of radioactivity levels for the extracting radioactive waste from RC located in the Al-Tuwaitha region. It can be concluded from overall results that the activity concentrations of waste, province does not pose a radiological hazard for the workmen. The risk assessor should compile the supporting documentation to ensure that it is sufficient to support the analysis and to allow an independent duplication of the results.