Preliminary results of the autonomous radiation mapping in Malaysian Nuclear Agency

Autonomous radiation mapping refers to the use of autonomous robots to perform radiation mapping to measure and analyse the levels of radiation intensity of a target area. The primary purpose of the radiation mapping is to uncover the dose distribution across the target area and identify the presence of any hotspots. In this paper, the findings of the autonomous radiation mapping experiments at selected sites in Malaysian Nuclear Agency were presented. The experiments were conducted with a radiation mapping robot namely Autonomous Mobile Robot for Accurate Radiation Detection and Mapping (AMoRA) developed in the previous research. The results consisting of radiation maps of the target areas were presented and discussed.


Introduction
Radiation in the workplace originates from various sources and exposure to it can pose health risks to employees if not properly managed.Some common sources of workplace radiation are coming from nuclear reactor and nuclear research facilities, radioactive materials, X-ray machines and radiation therapy equipment.On top of that, there is a regulation that specifies that each licensee and employer engaged in activities associated with regular or potential occupational exposure is required to ensure the safety of their workers from occupational hazards [1].In order to protect the workers from the harmful effects of radiation, it is imperative to implement safety measures and practices.These measures and practices encompass conducting risk assessments, monitoring radiation levels in the workplace and regularly inspecting and maintaining radiation-emitting equipment to ensure safety [2].
Towards the realisation of this matter, the radiation dose measurement was conducted to measure a radiation dose in the workplace by [3].The primary objectives of this work include acquiring the radiation dose distribution, creating a dose database and producing a dose map within the facility.The work has been implemented in the waste storage facility using the Ludlum Model 2241-3 survey meter with 118 sampling points were recorded as shown in Figure 1.The process of manually measuring radiation doses for each grid was time consuming and posed a significant safety risk to the workers responsible for this task.

Figure 1.
The data grid for the manually recorded radiation readings at the waste storage facility (Harun et. al., 2018) Due to these circumstances, there is a study from Zakaria et al. ( 2017) that explores the development of a spatial radiation map by an autonomous mobile robot that is equipped with a Geiger Muller (GM) sensor.The study was intended to develop a gamma radiation mapping system that reads and process location data of a mobile robot with encoder as well as the radiation data transmitted by the GM sensor on the mobile robot [4].It was conducted with the zigzag waypoints sweeping pattern and the radiation source is placed at a certain point of the designated waypoint.As shown in Figure 2, the result of the experiment conclude that higher radiation activity is recorded when the robot moves near the sources and the radiation activity decreases when the robot .isfar from the sources which satisfy the inverse square law theorem.Following that, Autonomous Mobile Robot for Accurate Radiation Detection and Mapping (AMoRA) were developed to map the distribution of radiation in the area [5].AMoRA ensures measurement accuracy by indicating hotspots on the physical map [6].This autonomous radiation measurement capability offered by AMoRA can effectively decrease exposure time to radiation.In this study, AMoRA was employed to grid the radiation exposure levels at specific facilities.The facilities were chosen based on the operational activities and associated risk factors.
The primary goal of this paper is to observe AMoRA capabilities in producing the radiation mapping autonomously.As well as to assess radiation distribution, enabling the identification of areas with higher radiation levels to be avoided during work at these facilities.This approach ensures that work activities in the selected areas can be more efficiently coordinated in accordance with the ALARA (As Low As Reasonably Achievable) principle.

Radiation mapping
AMoRA consists of a Turtlebot2 as a mobile robot platform together with a GM detector LND7121 as the radiation detector [5].The GM electronic module is connected to the Turtlebot2 host computer via USB connection as shown in Figure 3. Initially, the sites survey was performed to assess the suitability and necessity for the autonomous radiation mapping for a number of potential sites.It was conducted by the team members including radiation safety personnel along with the site owner.Sites survey was done by taking into account a few criteria such as train and surface conditions.This is because of the limitations of the robot which can only move on flat and smooth surfaces.Based on the owner and radiation safety personnel, a necessity of performing the operation will be analysed and decided depending on the operating conditions the sources involve.
Next, a 2D map of each selected site was created with Simultaneous Localisation and Mapping (SLAM) by running the Robot Operating System (ROS) gmapping package.The procedure was manually operated by personnel and created a 2D map.Both processes are presented in Figure 4(a  The following step is shown in Figure 5, where AMoRA is deployed to perform autonomous radiation mapping by executing the ROS rad_mapper package developed in the previous work [3].The rad_mapper divides the 2D map into a grid and generates sampling points at the centroid of each unoccupied grid cell shown in Figure 6.The counting time for data collection can be configured manually.The mapping may be repeated at different conditions depending on the requirement of the site and will be discuss in the discussion section.Finally, the radiation map was generated and a corresponding report was produced.However, in the cases where the site is found to be unsuitable during the site visit, a report is generated to explain the reasons for its unsuitability.

BTP Development Laboratory
The radiation mapping at BTP Development Laboratory was executed twice.Initially during the rest state, where the radioactive material source remained in the generator with proper shielding.The result shown in Figure 7(a) demonstrate only background reading was detected at rest state.After that, AMoRA was deployed again during the workload state.The workload state is the process where the radioactive source (Ga-68/Tc-99m) which is eluted from the generator and transferred into a shielded fume hood for research work.During the ongoing work, there is a concern from the employer regarding the effectiveness of the shielding in preventing radiation exposure to personnel.The results obtained clearly demonstrate the presence of radiation distribution during the work as shown in Figure 7 (b).It proves that the radiation around the working area is slightly elevated.Finding of this is useful for facility personnel to evaluate and coordinate the activities to ensure that the radiation exposure is within permissible limits.Based on the findings provided, employer can strategize to enhance shielding measures and restructure their work procedures to minimise radiation exposure.

Interim Storage Facility
The Interim Storage Facility serves as a storage site for low-level radioactive material originating from reactor operations, medical, academic, industrial and other commercial uses of radioactive materials [7].The configuration of radioactive material within this facility is constantly changing.Radiation mapping is carried out to observe scattered radiation and detect areas with elevated levels of radiation.The results obtained clearly reveal hotspots in various areas within the facility.This contour map allows for the precise identification of hotspot regions because the mapping is conducted on the actual location map as can be seen in Figure 8.In contrast, manual mapping [3] only offers a general location estimate for the hotspot.Additionally, the exposure to radiation workers during the radiation mapping process is minimised by the autonomous operation.

Conclusions and future work
As a conclusion, the results presented in this paper have demonstrated AMoRA capabilities to perform autonomous radiation mapping and produce comprehensive radiation maps of the target areas.These radiation maps can be referred to effectively manage and minimise radiation exposure in the workplace, to ensure the safety compliance with local regulations and standards.Based on issues and challenges observed during AMORA deployment at the selected site, the design and algorithm will be improved in the future.

Figure 3 .
Figure 3. Complete set of AMoRA used in this study.

Figure 4 .
Figure 4. a) The AMoRA was manually deployed to create a 2D mapping operation, b) the generated 2D map of the area.

Figure 5 : 6 : 3 .
Figure 5: AMoRA in autonomous mode mapping the area Figure 6: Robot trajectory during the autonomous radiation mapping

Figure 7 .
Figure 7. Radiation mapping contour map at BTP Development Laboratory, a) at rest, b) at workload.

Figure 8 .
Figure 8. Hotspot areas are cleary visible in several location.

3. 3
Reactor TRIGA PUSPATI Research Reactor TRIGA PUSPATI equipped with the facilities such as Neutron Radiography (NUR), Small Angle Neutron Scattering Neutron (SANS), Diffraction and Thermal Column for Boron Neutron Capture Therapy (BNCT).Research activities are conducted at each of these facilities while the reactor is in operation.The radiation levels inside the reactor hall were monitored by area monitoring instruments in each corner of the building.However, despite all the facilities having shielding in place, scattering radiation remains a concern.To provide a detailed view of radiation distribution inside the reactor hall, autonomous radiation mapping was carried out.As anticipated, the highest radiation hotspots are observed around facilities like between Diffraction and Thermal Column for BNCT as shown in Figure9.This contour map precisely pinpoints the location of these hotspots.

Figure 9 .
Figure 9. Distribution of the radiation inside the reactor hall.