Determination of Activity Concentrations and Internal Dose Assessments in Urine from Workers in Iraqi Nuclear Research Center, Iraq

: To detect tritium levels in the human body, tritium in the urine must be measured. The investigation of the level of tritium activity in the urine of workers of the Iraqi Nuclear Research Center (INRC) has been realized in order to assess vocational exposure levels. Three worker groups in INRCs were chosen, involved in the Central Laboratories Directorate (CLD), the Decommissioning Directorate (DD), and the Radioactive Waste Treatment and Radioactive Waste Store Directorate (WTWSD), among others in Al-Tuwiatha site, in addition to the control group, as the research targets. Tritium concentration was determined in urine samples from 52 workers (aged 32-61) and 13 control people (aged 30-58). 65 urine samples of 50 mL were collected and analyzed. The Eichrom's Tritium Column way was used to handle the samples of urine, and the distillate tritium activity concentration was then assessed using Liquid Scintillation Counter.


Introduction
Tritium ( 3 H) is radioactive hydrogen isotope, emitting a low-energy beta particle (electrons) with a highest energy of 18.6 keV, a mean energy of 5.7 keV, and a radiological half-life of 12.3 years.It is present in nature in very low level [1].It can be found in nature as a result of cosmic ray interaction in atmospheric gases or as a result of spontaneous fission of natural uranium in the Earth's crust, atmospheric nuclear and recent weapon testing.It is mostly made by human activities like reactors of heavy water and nuclear fusion technologies [2,3].The atmospheric amount of tritium elevated considerably due to nuclear weapons tests.Nuclear weapons experiments yielded levels of tritium in the atmosphere more than 1000 TU.Modern-day values have decrease to 50 -100 TU levels, with the decrease due to the eradication of atmospheric nuclear weapons testing and radioactive decay [4,5].Tritium due to being hydrogen isotope has properties similar to conventional hydrogen.Since tritium emitted low-energy beta particle, distance of most of them range in air only about 5 mm or in water or soft tissue 0.005 mm [4].Due to this low range it is non-dangerous in vitro.Tritium is considered to have a mild effect in vivo.Tritium enters the human body initially by inhalation of tritiated vapors in the air during work in a volatile atmosphere the second way through skin absorption.Inside the body tritium quickly and homogenously distributed in whole body.The minimum radiation level related to these tissues is basically homogenous and related to the tissues' hydrophobicity [4].Also uptaked of tritium from the human body through food and water ingestion [3].It is mostly known that tritium is a non-toxic isotope, but chronic exposure to a tritium source may lead to seriously harm human health.As a result, urine test of nuclear power plant workers should perform on a regular basis for radiation protection [6].With the active revolution production of nuclear power and the wide use of nuclear technique, more workers in nuclear power plants (NPPs) are exposed to radioactivity.Due to occupational risk factor, radioactivity can cause internal and external hazardous and subsequently cause immediate or late radiation insult [7,8].The tritium low decay energy limits its toxicity; thus, tritium has a harm effect from internal sources only.Despite its low energy, chronic exposure to tritium radiation has been found to have a greater biological efficacy than that of ɣ -rays and X-rays [9].Moreover, beta radiation from tritium has been shown to be more effective when combined within the molecule [10].The aim of the study to investigate the activity of tritium concentration in urine of the Iraqi Nuclear Research Center (INRC) workers, in order to evaluate the occupational exposure levels.Location was near Tigris River eastly about 1 km, to south of Baghdad about 20 km.This place belonged to the prior Iraqi Commission of Atomic Energy (IAEC); around it there was earthen berms that are approximately 4.6 km long and 30 m high and contain three gaps that allow for vehicle access.Prior to 1991, The Al Tuwaitha compound consisted of 90 infrastructures related to the radiochemistry lab, production of nuclear fuel, enrichment of uranium, handling and storage of radioactive waste, and biological research.In 1991 and during the Gulf War, most of the facilities in Al-Tuwaitha were extensively destroyed.Immediately following the Gulf War of 2003, there was a breakdown in security in Iraq, which adversely affected the security of access control to the Al-Tuwaitha site and other facilities throughout Iraq.As a result, there was huge looting of materials like equipment, some amount radioactive contamination occurred, and there was damage associated with many facilities.Information on distribution of radionuclide and radiation concentration in the environment is pivotal for detecting the terrestrial radiation exposure effects due to cosmogenic and human activities [11,12].In In addition, the control groups included 13 apparently healthy volunteers, randomly chosen from the population living in Baghdad, far away from the Al-Tuwaitha Nuclear Research Site.The age range of the unexposed control group was 30-58 years old.The samples were then transferred to separate 50-mL plastic bottles.Workers and control volunteers were asked to complete a questionnaire with information on their gender, age, working hours, and the types of ailments they suffer from, particularly disorders of the urinary system.They were also asked about the donor's drinking water source and if he or she is a smoker or alcoholic.

Pretreatment of Urine Samples
Urine samples were processed using Eichrom's Tritium Column Method.
Tritium columns ( 3 H columns) are used for the splitting and detection of free tritium are substitute for direct assessment or measurement after distillation [13].It has been developed to shorten the preparation time and decrease waste generation for a variety of sample matrices, and this method is used to substitute distillation for much of usual tritium analyses of aqueous samples.The practical procedure that was followed in the current work is to take approximately 25 ml of urine sample, add it to 4 gm of activated charcoal, introduce a suitable magnetic stirring bar in the container, shake well for approximately 15 minutes by Hotplate Stirrer Model L-81 (Labinco), Netherlands (to adsorb organic compounds in urine), and then filter to obtain a clear filtration that removes color and not all contaminate chemical material (these contaminates will act with the liquid of scintillation and cause luminescence).Then the filtered sample is collected in a 22-ml conical glass flask, and the sample is transferred to tritium separation columns to be separated by the vacuum system (coulombs, vacuum box, and vacuum pump) at a pressure of 10 mBar.The collected sample after separation is placed in a cold place before adding to the scintillation liquid Ultima Gold.luminescence, samples should be saved in scintillation vials for 1 day in a dark place or canister before measurement.
2.4 Preparation of Urine Samples 10 mL of the residue suppuration sample was added to 10 mL of Ultima Gold LLT cocktail (PerkinElmer) in a glass measuring vial (200 PCS standard size, 20 mL for the liquid scintillation counter), for a total volume of 20 mL.The vials were shacked for around one minute to make the solutions homogeneous.In added, the vials were cleaning by ethanol before being placed on the table to prevent contamination.The background sample was prepared using twice-distilled ground well water with a low level of tritium [14].Measurement of tritium concentration was made using counter of a small-level of scintillation liquid (Perkin Elmer Tricarb 3110 TR, USA).It is a computerized analyzer of liquid scintillation for exploring low level of alpha, beta, and gamma radiation.The samples are counted for 210 minutes (3 h 30 m).

Quality Control
The instrument was checked through performing a self-normalizing calibration (SNC) to ensure that the instrument accurately quantifies the energy for all beta particles emission, and the performance of instrument assessment (IPA) procedure using a non-quenched standard calibration of tritium, calibration standard of an unquenched carbon 14, and a basic standard supplied by PerkinElmer.The standard solution of tritium each with specific activity of 262900 DPM (0.2 µCi) were peaked into two samples handled for distillation of urine.

Measurement and Calculations 3.1 Counting Efficiency (IPA instrument performance evaluation)
The efficiency of the instrument used for counting of tritium E was measured by using the following equation: (1) Where, Nd is the measurement of tritium sample basic rate (counts per min); Nb is the rate of counting background sample (counts in min); D is the activity of tritium addition to the basal sample (decays in min).

Tritium Activity Concentration
The level of tritium activity concentration (A) in the sample of urine can be calculated as below [15]: (2) Where, Ns is the activity of the sample (counts/min), and V is the volume of the urine distillate sample (L).

Minimum Detectable Activity
The Minimum Detection Activity (MDA) was calculated according to the Currie formula [16]: (3) Where Rb is the count rate of the background (counts/min), ts is the counting time of the sample (min), tb is the counting time of the background (min).

Inner Dose Calculation
The internal active dose ( ) can be written in terms of tritium activity concentration and default half-life.The half-life is supposed to be 10 days when continuous deposition occurs in the absence of other evidence.The formula for this estimation can be written as follows [17]: (4) Where 5.3×10 -11 Sv per day per (Bq/L) is the dose coefficient of tritium.

Annual Effective Dose
The annual effective dose AED was formulated by the ICRP 78 as given by the following equation [18]: (5) Where the 0.73 is the coefficient of the fraction of water mass in the body, m is the body weight (kg), EDC is the effective dose coefficient (1.8 × 10 −11 Sv Bq −1 ).

Results and Discussion
The results in Table 1 showed the highest urine tritium level of three groups of workers in the INRCs, namely the Radioactive Waste Treatment and Radioactive Waste Store Directorate (WTWSD), the Decommissioning Directorate (DD), and the Central Laboratories Directorate (CLD), were 65.401, 3.351, and 39.323 Bq/L, respectively, while the highest concentration of tritium for the control group is 39.300 Bq/L.The highest internal effective dose due to tritium ingestion for the three worker groups was 497.048×10 -3 , 25.468×10 -3 , and 298.855×10 -3 nSv, respectively, while in the control group it was 298.680×10 -3 nSv.The annual effective dose of tritium was also assessed depend on the standard of measurement results and reference values recommended by the International Commission on Radiological Protection (ICRP) [19].The highest annual effective dose for the three worker groups was 5757.773×10-3 , 356.660×10 -3 , and 5167.042×10 - nSv, respectively, while the highest annual effective dose for the control group was 3356.613×10-3 nSv.These levels are lower than the allowed tritium dose inside the body, that is, 40000 nSv [19].Although all the results were less than the permissible value of tritium dose 40000 nSv recommended by ICRP, 1994 [19].However, it has been noted that there are abnormal results in each of the WT, WL, and C groups.This negatively affected the results of the standard deviation calculations, although all the results have been recalculated to ensure the validity of the results.So we disclosed Table2 to announce the effect of the presence or absence of the results of abnormal samples on the standard deviation.Where the reasons for the abnormality of these results were analyzed by examining and interrogating the practical history of the worker with the abnormal result from his peers in the same group, and they were as follows: The worker WT4 sample had activity 65.401 Bq/L , effective dose 497.048 nSv, and annual effective dose 5757.773nSv, respectively.The workers WT4 and WT9 deal directly with radiation through the removal of radioactive waste, but they do not abide by the conditions of occupational radiation safety because they believe that their long-term work in the field of radiation gives them protection.The Radiation and Nuclear Safety Directorate has been notified of the exposed workers, to apply its preventive measures with them to protect them from the dangers of radiation.The Worker WL8 sample had activity 39.323 Bq/L, effective dose 298.855 nSv, and annual effective dose 5167.042nSv, respectively.The Worker C6 sample had activity 39.300 Bq/L, effective dose 298.68 nSv, and annual effective dose 3356.613nSv, respectively.The workers of the WL and C groups were fully committed to all safety conditions.However, there appeared in each group a high concentration of the sample of worker WL8 and worker C6 from their peers.It is believed that this increase in tritium concentration is due to environmental conditions, especially that through dialogue with worker WL8; it became clear that he is the brother of worker C6, and this confirms that the cause of exposure is environmental, not occupational.As for group WD, its results do not contain outliers.
It is noted from Table 1 that when comparing the results of exposure of the worker group to tritium with the control group, the results were very close, and if we compared the concentrations of tritium in the urine of workers in the radiation field at INRC, they was very close to the concentration of tritium in the control group and less than the global results attached in Table 3. Figure 1 shows the variation between the highest, lowest, and average values of the annual effective doses for each group of workers within the work period.This is evident depending on each of them on the period of work.All results are within internationally permissible limits.

2. Materials and Method 2.1 Al-Tuwaitha Nuclear Site Description
Al-Tuwaitha Center of Nuclear Research (ATNRC) was started in about 1960.It was located 18 kilometers southeast of Baghdad, the capital of Iraq, at 33° 12.57' north and 44° 31.822'east.Its coverage area of about 1.3 km2.

Table 1 :
Tritium activity in urine and annual effective doses for the exposed workers groups in INRC and the control group.