Nuclear Power Plants Pre-operational Radiological Monitoring Mapping for the Coastal Boarders and Islands of the United Arab Emirates (UAE)

In the light of the peaceful nuclear power plants (NPPs) project of the United Arab Emirates (UAE), the operation license has been issued and the first unit is being in commercial operation. This work deals mainly with radiological surveillance of the coastal boarder and some Islands of UAE as a baseline reference natural and artificial radioactivity mapping. Ultra-sensitive hyper pure Germanium (HpGe) detector was used to carry out the non-destructive gamma measurements. The area of study was divided into; Abu Dhabi region, northern emirates and islands. About 85 soils, shore sediment and water samples were collected based on the scientific sampling mechanism. The samples were analyzed for X-ray diffraction mineralogy (XRD). The radioactivity in Bq/kg of the natural 238U(226Ra), 232Th and 40K were calculated for all the collected samples. The artificial 137Cs was also observed in very low activity. The hazard indices were also calculated and found to be less than the recommended international and regional limits. The correlations between the measured radioisotopes were also depicted. The results were compared, presented and given in 3D histograms.


Introduction
The United Arab Emirates is the first state in the Middle East to operate nuclear power plants for electricity production. Preoperational monitoring mapping is a vital target to be carried out as pre-operational and postoperational safety measures. This natural background forms a baseline which the levels and impacts of other sources of radioactivity in the environment are subjected to evaluation. Naturally occurring radioactive materials (NORMs) from the 232 Th and 238 U series are present in the earth's crust (1). According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and other sources, about 87% of the radiation received by mankind is due to natural radiation sources (2). Natural radioactivity has been determined in working environment (3,4,5). Environmental analysis is one of the vital instruments to assess the impact of man-made activities on the environment, and the methods of determine radioactivity levels are well documented. The UAEs started to commercially operate the first nuclear power plant (NPPs); the operation license for the first reactor has been awarded in Fab. 2020., There are very limited studies on the evaluation and pre-operational monitoring of natural and man-made radioactivity levels in the country (UAE). Establishing a baseline reference radiological map before the full commercial operation of the UAE`s nuclear power plants is the main target and objective of this paper including the hazard indices calculations to evaluate any potential environmental threat.

Site description and characteristics
The United Arab Emirates (UAE) is located in the Middle East, in the south-eastern part of the Arabian Peninsula.

Sampling program and locations
This surveillance monitoring covers the coastal border of UAE as well as some marine islands. The systematic sampling method was used for sampling location selection. The samples numbers and the interval between them were selected based on the study area, analysis and measurement capacity, evidence of variation (like soil type change or human activity) and finally cost benefit analysis. A total number of 85 sampling stations were selected for the 79 collected samples. The detailed sampling sites, codes and samples types are presented in figure 1.

Sample preparation:
After sampling, the shore sediment and soil samples were prepared for gamma analysis according to the following procedure: i.The sample was separated from pebbles and plant roots, weighed and dried for 10 hrs. in an oven at a temperature of 110 0 C, re-weighed until constant weight achieved to determine the water content.
ii.The sample was crushed, homogenized and finally sieved through a 2 mm mesh sieve.
The sieved samples were weighed, packed in Marinelli-type beakers and carefully sealed and stored for 4 weeks to reach secular equilibrium between 226 Ra and its decay products [7,8]. The XRD analysis was then carried out for some samples. The major minerals of soil and shore sediments are quartz and calcite.
The Gulf-water samples were collected from the surface beyond the tidal area, filtered through 0.45µ membrane filter, acidified with 11M HCl at the rate of 10 ml per litre of sample immediately after filtration to avoid the adsorption of radionuclides on the walls of the container [7,8] transferred to polyethylene bottles and transferred to laboratory.

Gamma spectrometry efficiency and activity analysis:
The gamma ray spectrometers were equipped with hyper pure germanium detector, which consists of: A hyper pure germanium coaxial detector of a vertical configuration (Canberra, Model GC4020) with a relative photo peak efficiency of 40% at the 1332.5keV transition line of 60 Co. The detector is mounted on a 30 litres liquid nitrogen. The preamplifier is coupled to the detector and connected to the germanium crystal, and the components are kept at liquid nitrogen temperature (77 0 K) to reduce detector noises which are caused by the leakage current generated by the charge carriers at room. The energy calibration and efficiency calculation were then carried out. The generated efficiency curve is given in figure.2.

Quality assurance and control (QA/QC) program
Quality control program was precisely applied for confident radioactivity measurements, calculations and results. Replicate samples usually consist of two or more aliquots of homogeneous solid and liquid samples. Individual samples that are measured by non-destructive techniques, such as (γ-ray spectrometry, may be measured more than once to obtain replication of the data. The QAQC system applied in this work includes analysis of reference standard IAEA materials such as; RGU-1 and RTh-1. This is in addition to documentation from sampling to activity calculations. New correlation for nuclear fields was recently given for activity calculations (9) 2.6.

Hazard indices assessment
The major hazard indices were calculated using the following equations to evaluate the potential risk due to the measured radioactivity (Ra equivalent, absorbed dose rate, external hazard index, gamma index and alpha index respectively) (2,10).
Where: CRa, CTh and CK are the specific activities of 226 Ra, 232 Th and 40 K in Bq/kg, and this formula is based on the estimation that 1 Bq/kg of 226 Ra, 0.7 Bq/kg of 232 Th or 13.0 Bq/kg of 40 K produce the same gamma dose rate. The Raeq limit should be less than 370 Bq/kg (2,5 Where: ARa, ATh, and AK are the mean activities of 226 Ra, 232 Th, and 40 K in Bq/kg. The safe value of this index must be less than 1 (2).
Where ARa, ATh and AK are the specific activities of 226 Ra, 232 Th and 40 K, respectively, The value of Iγ ≤ 0.5 corresponds to a dose rate criterion of 0.3 mSv/y, whereas 0.5 ≤ Iγ corresponds to a criterion of 1 mSv/y . Materials with Iγ > 1.0 should be avoided in building construction. They will deliver an effective dose rate higher than 1 mSv/y to the occupants of such buildings.
Iα= ARa/200 Where, ARa is the specific activity of 226 Ra. The safe use of materials in building construction requires Iα (alpha index) to be less than 1. This limit corresponds to the design action level for the 222 Rn concentration of 200 Bq/m 3 on an annual average basis for future buildings.

3.
Results and discussion.
The studied three regions (Abu Dhabi, Dubai & Northern emirates and Islands) results of analyses and calculations were compared and given in the following tables and 3D figures. The comparison was carried out for the observed radionuclides in soil, shore sediments and water samples. The correlation and its coefficients were also given and depicted.

Average Activity of soil for the three studied regions
The comparison of measured average activity concentrations for 226 Ra, 232 Th, 40 K, 137 Cs (table 1 and figures [3][4][5] and the world average for soil samples (2). The variation in the measured specific activities may be related to the differences in major minerals of soil and shore sediments; quartz and calcite. The grain size fractionation shows that silt and sand are the main constituents of the analyzed samples. The results are also depicted and compared as given in the following figures  The correlation between 226 Ra and 232 Th in soil of the 3 regions was carried out and given in fig.7. It can be observed that a low correlation coefficient (R 2 = 0.3691) was found.

Average activity of shore sediment for the three studied regions
The comparison of measured average activity concentrations observed for 226 Ra, 232 Th, 40 K, and 137 Cs in shore sediment (table 2 and figures [8][9][10][11] and the world average in shore sediment samples (2). These values are fairly low compared to those in coastal marine sediments reported in literature. The slight variation of radionuclides activities may be attributed to the sediment components and textural properties. The results are also depicted and shown in the following figures. The correlation between 226 Ra and 232 Th in shore sediment of the 3 regions was carried out and given in figure.12. It can be observed that a medium correlation coefficient (R 2 = 0. 6182) was found. Figure 12: The correlation between 226 Ra and 232 Th activity of the three regions

Average activity of Gulf water for the three Regions
The comparison of measured average activity concentrations for 40 K (table 3 and figures 13) and the average value in the Gulf water samples of the three studied regions (2). The presented results can be shown in the following figure (Fig.13). Figure 13: The activity of 40 K in the three studied regions

The calculated Hazard indices values:
The calculated radium equivalent (Raeq) activities for soils and sediments were determined and their mean values were well below the defined limit of 370 Bq/kg as stated in UNSCEAR 2008 (2). The absorbed dose rate from external gamma radiation from soils and sediments was also estimated and the average values were far below the international recommended limit of 79.0 nGy/hr (2). The annual effective dose from the soil and sediment samples was determined and found to have an average value of 0.02 and 0.01 mSv/yr respectively, which are both far below the world average value of 0.09 mSv/yr. The mean values of the external and internal hazard indices were calculated; for soils and sediments, they are 0.07 and 0.06 respectively, which are far less than unity, and that keep the radiation hazard insignificant. The activity indices (gamma index -alpha index) were also calculated and their values were also found to be below the world limits (2) and other regional monitoring values (11,12,13).

Conclusion
The preoperational monitoring is a must for any nuclear power plants safe operation. The Surveillance and monitoring along the United Arab Emirates (UAE) coastal areas and some islands have been carried out to ensure that the radiation levels and doses received to the public are below the authorized national and international limits. The following major observations are concluded: • Based on this work, the pre-operational natural and artificial monitoring mapping. for the NPPs site of the UAEs were carried out and available.

•
The results obtained in this work cover a wide area along the United Arab Emirates (UAE) coastal line, and can be considered as a baseline radioactivity map for these regions that can be utilized as a preliminary pre-operational map before the full commercial operation of the first nuclear power plants (NPPs) and effluents control signals and monitor for post-operational mode.

•
The average specific activity of the natural 226 Ra, 232 Th, 40 K and the artificial 137 Cs due to the global fall-out, in the soil samples were 14.5, 3.7, 98.2 and 0.7 Bq/kg respectively. These values were found to be lower than those reported in soils from different countries and the international UNSCEAR levels (35, 30 and 400 Bq/kg for 226 Ra, 232 Th and 40 K respectively).

•
The average specific activity of 226 Ra, 232 Th, 40 K and 137 Cs in the sediment samples were 9.7, 3.2, 98.6 and 0.4 Bq/kg respectively. • It is observed that 137 Cs is the only man-made anthropogenic isotope to be detected in the regions. • Potassium-40 was the only natural radionuclide detected by gamma spectrometry in the sea (Gulf) water samples with a mean value of 10.6 Bq/L. This value was expected for the natural radioactivity in seawaters and oceans. This value does not impose any considered exposure for swimming and recreational activities along the coastal beaches of the UAE • The calculated radium equivalent (Raeq) , the absorbed dose rate from external gamma radiation ,the annual effective dose, the mean values of the external and internal hazard indices ,the activity indices (gamma index -alpha index) values due to soil and sediment were found to be below the world limits and they don't pose any radiological hazards.
Finally, it can be concluded that the results of this study is of great importance for emergency planning and the site monitoring before and after the plants (NPP) operation. The results can be considered as reference to control and evaluate the plant impact on the environment and public in the UAE.