Safety Assessment Analysis for Legacy Radioactive Waste

The storage facility is located at AL-Tuwaitha nuclear research site; it is intended for temporary storage of the radioactive waste (RW) with low half-life and low or medium radioactivity. The annual doses are calculated for the workers and public of the storage facility from a hypothetical accident involving drums falls to the ground by different climatic conditions. The results show the safety and exposure of the workers normal operational and public in accident scenario during periods to legacy RW drums in storage facility. In this study the results by SAFRAN calculations (SAFRAN is a computer program used to assess the safety of workers in the radiation fields and the main objective of using the program is to know the activities and activities that include high radiation dose affecting the workers and the public and the development of treatments for the purpose Reduced radiation dose) in Table (4) for normal operation showed that the highest radiation dose of the two most active radiation measurements and the sorting of drums was up to 430 μSv, which is acceptable for radiation field workers where (2.5%) of the annual value set by International Commission on Radiological Protection (ICPR) for radiation workers, which amounts to 20 mSv per year. The results of the scenario of the possible accidents occurred. The highest possible dose to be received by the workers in Table (5) is 5.68 μSv in the treatment of the extreme rain incident, which may enter the storage facility due to a fault in the discharge of water. Within the limits of the dose of accidents assumed by the SAFRAN program as an accident dose is the same as the one allowed by the ICPR which is 1 mSv per year, where 5.68 μSv is equivalent to 0.5% of the permissible dose.


Introduction
Safety assessment, an integral and important part of the safety case, is driven by a systematic assessment of radiation hazards. The latter involves quantification of radiation dose and radiation risks that may arise from the facility or activity for comparison with dose and risk criteria, and provides an understanding of the behavior of the facility or activity under normal conditions and anticipated operational occurrences and in the event of accidents [1,2,[3][4].
Waste management facilities and activities are varied in nature, size and complexity, and have different hazards associated with them, both from normal operation and from accidents. The magnitude and content of the radioactive inventory is also varied. Furthermore, a waste management facility or activity could be one of several facilities or activities on a site and may be independent of the other facilities, may be connected to other facilities or may be an integral part of a larger facility. Commensurately, the extent and complexity of the safety case and supporting safety assessment will differ according to the facility or activity, and will evolve through its lifetime (e.g. construction, commissioning, and operation). In view of these considerations, a graded approach is required to be applied to the development and review of the safety case and supporting safety assessment [4,5,[6][7].
The RW in Iraq comes from two major origins, the first one is the legacy waste which in turns comes from unidentified treated RW from contaminated wreckages and debris resulted from the second Gulf War in 1991, the second is the waste expected from the decommissioning of the destroyed nuclear buildings and facilities. Additionally, there are moderate quantities radioactive waste that comes from other activities in the universities, researches, agriculture and medical applications [2,5,[8][9]].

Objective
The objective of this assessment is to evaluate the consequences of radiological hazards in the waste management activities during normal storage operations period and during the occurrence of accidents for the workers and the public (for the nearest residential area from the store).

Storage Facility
The storage facility (as a part of radioactive waste management and treatment directorate (RWTMD) tasks) is located in Al-Tuwaitha nuclear research site, Baghdad. The storage facility established for temporary storage purposes of the radioactive waste containers and drums (shown in figure  1) [8-9]. There are 430 drums of radioactive legacy waste stored in the storage facility for low half-life radioactive waste.
The storage facility was designed with (70 m length, 20 m width and 9 m height) and a floor of concrete, also has two gates with a width of (4.5 m), the storage facility is designed according to the following specifications: a. Storage capacity (2000 drums), including concrete containers. b. The temperature inside the storage facility should not exceed (60°C). c. The height is (9 m) to ensure get air flow rate is about (14000 m 3 /h). d. Convection currents are used to dispose of gases which produced as a result of decay of stored elements. e. The gate allows passage of a vehicle to transport the drums and containers. f. The thickness of the sandwich panel walls is 0.05 m. g. The storage facility has two cranes at height of 8 m and a load of (10 tons).

Hand Held High Purity Germanium (HX)
Germanium portable device for the determination of isotopes and spectroscopy for Gama spectra, and its specification: Internal HPGe (is already acknowledged as the "perfect" detector for a radioisotope identifier) detector P-type highpurity germanium. Coaxial construction, crystal nominal dimensions 50 mm diameter x 30 mm length.
Gamma dose rate detector two detectors determine the gamma dose rate over a wide range from <0.05 µSv/h to >10000 µSv/h.

LUDLUM Model 2241-2
The model 2241-2 is a portable microprocessor-based digital scaler/ratemeter designed for use with scintillation, Geiger-Mueller (G-M), and proportional type detectors to measure ionizing radiation. Programmable display units are represented in either R/hr, Sv/h, cpm or cps with multipliers of micro (µ) or milli (m) for R/hr and Sv/h and kilo (k) for cpm or cps. The temperature range: -20°C to -50°C [11].

Experimental Method
The drum is isolated and then the radiation dose of the drum is measured contact with it and the radiation dose of the drum is measured at a distance of 1 m also to obtain the radiation dose received by the workers during the performance of various radiological activities, After that the radiation doses of all drums (430 drum) were documented and tabulated in the form of specific classes within multiple levels to obtain a higher average radiation dose that Reached 20 µSv/h as a contact dose with the drum.
Hand held high purity Germanium HX was used to obtain radionuclide concentrations inside the drums and the activity of the radioactive radionuclides was determined also.
After determining the radiation dose the time required for each activity, all data is entered into the SAFRAN program, also introducing special scenarios for the expected occurrence incidents during the implementation of activities. The calculations are calculated by SAFRAN and get the received dose for workers during the implementation of activity and the dose received for workers and the public during radiological accidents also (The public in this activity is facility protection service (FPS) and other on-site staff).

Results
Safety assessment accomplished using SAFRAN program during normal operation of the storage facility and during incident or probably events as input data tables and output results. Table 1, is the inventory for 430 drums of RW, Tables  (2, 3) represent a process in the store with their description and exposure time for each activity; and SAFRAN inputs for 430 legacy radioactive waste drums. Table (4) represent safety assessment SAFRAN output of RW legacy waste at normal operation and tables (5, 6, 7, 8) safety assessment SAFRAN output risk for accident situation and hazard factors for worker, driver and public per each activity [12].   In Table (4) for normal operation showed that the highest radiation dose of the two most active radiation measurements and the sorting of drums was up to 430 µSv, which is acceptable for radiation field workers where (2.5%) of the annual value set by International Commission on Radiological Protection (ICPR) for radiation workers, which amounts to 20 mSv per year.  The results of the scenario of the possible accidents occurred. The highest possible dose to be received by the workers in Table (5) is 5.68 µSv in the treatment of the extreme rain incident, which may enter the storage facility due to a fault in the discharge of water. Within the limits of the dose of accidents assumed by the SAFRAN program as an accident dose is the same as the one allowed by the ICPR which is 1 mSv per year, where 5.68 µSv is equivalent to 0.5% of the permissible dose. The approved annual dose for workers during accidents is the same as the dose limits for the public (1mSv/y).

Conclusion
The assessment of the radiological consequences of normal and incidents that may occur in the storage are summarized in table (4,5,6,7,8), shows acceptable exposure rate per activity to the storage workers. It is unanticipated that management of radioactive waste arising from normal operation will present significant nuclear or radiological emergency scenarios. In case of the most conservative normal operation, the potential dose of a worker due to sorting drums or radiation measurement will be 430 µSv which considerably less than the occupational dose limit of 20 mSv/y, assuming the unlikely case that the foreseen personal protective equipment will provide no safety function [5,[6][7][8][9][10][11][12][13], The dose consequence of an uncontrolled release is expected to be low in view of the limited radiological inventory associated with Al-Tuwitha nuclear research site [13,[14][15].
The results show compliance with the safety requirements in the radioactive waste storage site.