The BAEC TRIGA Research Reactor (BTRR) with a capacity of three megawatts (3 MW) (Safety Analysis Report (SAR), 2005) was purchased from the US General Atomics Company and installed at the Atomic Energy Research Institute in Savar, Bangladesh. It is the countrys only nuclear research reactor having 100 erbium-uranium-zirconium hydride fuel elements in a circular grid array, 6 boron carbide (B4C) control rods and 1 Am-Be neutron source of 3 Ci strength (General Atomics, 1984). On 14 September 1986, the reactor started operating after achieving criticality. The research reactor plays a key role in the production of radioisotopes, research activities (neutron activation analysis, neutron radiography, neutron scattering and other studies related to reactor safety) (Islam et al., 2004) and the development of human resources in nuclear science and engineering. The knowledge and experience gained through operating the research reactor has been directly and indirectly instrumental in the development of the nuclear power programme of the country. BTRR provides educational and training support to students of nuclear science and engineering departments of various universities. Also the specialized knowledge gained through operating the reactor is playing a significant role in nuclear safety, human resource development, environmental protection, emergency preparedness, physical security, waste management, fuel handling and conservation.

Fig. 1: Reactor Shield Structure (1a, left) and Reactor Digital I & C System (1b, right).

Modernization of the reactors primary and secondary cooling systems

The reactors primary and secondary cooling systems have two pumps each, driven by two electric motors of 37.5 kW and 30.0 kW, respectively. The reactors primary cooling system requires a water flow of 3,500 gallons per minute (Ajijul Hoq et al., 2017). To achieve this, previously, two pumps had to be operated with the valves in the pump discharge line closed by about 50%. This would have created additional vibration in the pump and discharge line and consumed additional power in the motors. To reduce vibration in the discharge line, some pipe supports were installed in 2001 to bring the vibration to a tolerable level. Four Variable Frequency Drives (VFDs) have been installed to drive and control the frequency of the motors to maintain a flow of 3,500 gallons of water per minute in the primary cooling system through control logic of the new Digital I&C System. As the two valves in the discharge line of the primary cooling system are fully open, the vibration of the discharge line has been further reduced and the two pumps are consuming about 50% less electricity. This has resulted in a reduction in overall reactor power consumption by about 20%. In addition, new Plate Type Heat Exchanger and Cooling Tower have been installed to increase the cooling performance of the reactors primary and secondary cooling systems. It is also worth noting that the field instruments of the reactors Primary and Secondary Cooling Systems, On-line Purification System, Emergency Core Cooling System have been replaced with digital instruments and connected to the reactors Digital I&C System. As a result, it is possible to monitor all parameters from the control room during reactor operation.

Fig. 2: Primary Cooling System Pumps (2a, left), VFD (2b, middle), and Heat Exchanger (2c, right).

Reactor Hall Ventilation System

The Reactor Hall Ventilation System is one of the most important systems of the reactor facility for ensuring radiation safety. With the system a 0.08 inch-of-water negative pressure [8] is maintained inside the reactor hall and airborne radioactive substances are monitored by the Stack Monitor, filtered if necessary, and released to acceptable levels through the Building Stack. Beforehand, the reactor hall ventilation control system was manually operated analogue system. Under the said project, negative pressure was maintained inside the reactor hall by installing a Programmable Logic Controller (PLC), the Air-tight Door Control. Moreover, Inflation System was renovated, a Biometric Access Control System was added, and the Stack Monitor and Continuous Air Monitor were replaced. 

Construction of 1250 KVA electrical sub-station

The former electrical sub-station and 250 kVA emergency diesel generators were located on the ground floor of the building adjacent to the reactor building. A new 1250 KVA sub-station has been constructed under the project to reduce extreme external hazards (fire accidents) as per IAEA guidelines. The 250 KVA diesel generators is placed side by side in the 650 KVA generator room.

Radiation Monitoring System

To enhance radiation monitoring and protection system of the reactor facility new Continuous Air Monitor (CAM) and Area Radiation Monitoring (ARM) Systems have been installed. The previous monitors reached the end of their lifetime and the efficiency of them begun to decline from the standard level. New area radiation monitoring system monitors the radiation level of specific points of the facility for 24 hours. New ARM is fully digitalized and consists of seven detectors (reactor top, four beam ports, heat exchanger room and primary pump room) with two local display units to monitor the radiation levels from the reactor hall and control room. The previous ARM system was analogue and had detectors on six locations which became faulty over the time [9]. Moreover, two new hand foot monitors have been installed in the facility to enhance personal radiation safety for the radiation workers and avoid contamination. 

Physical Protection System

To increase the physical security of BTRR, a 10 feet high security wall with 2 feet barbed wire placed on top has been constructed. Inner Security Fence has been installed around the reactor building which is protected by Perimeter Protected Camera. Biometric Access Control System has been installed inside the reactor building. 

Fig. 3: 1250 kVA Electrical Sub-station (3a, left), and Outside View of CRR (3b).

A new Vehicle and Personnel Portal has been set up to access the CRR. Archway Gate, X-ray Bag Scanner, Full-height turnstile/Flap Barrier, Hand held Metal Detector, Vehicle inspection mirror and Boom Barrier have been installed at both places. Besides, the entire facility has been brought under the cover of CC cameras.

In the light of the long practical experience of operating the BAEC TRIGA Research Reactor, it has been possible to eliminate the identified problems of reactor safety and other supporting systems through successful completion of repair, renovation and modernization work. It is expected that the BTRR will be able to run for another 15 to 20 years ensuring operational safety. If new TRIGA fuel can be acquired, it may be feasible to restart the production of radioisotopes alone with extensive research in several scientific and engineering disciplines and training of personnel to ensure its best use.

A.H.: Conceptualization, methodology, writing the manuscript. N.J.; M.O.R.; and M.A.M.S.: Contributed in investigation, visualization. M.R.H.; M.A.S.; and M.M.U.: Finally checked the manuscript and editing, and funding acquisition. All authors who are involved in this research read and approved the manuscript for publication.

The authors are very much thankful to honorable Director General, Atomic Energy Research Establishment for his constant inspiration to solve radiological issues of the reactor. The authors are also very thankful to the BTRR facility staff for their cooperation in the experimental works.

The authors sincerely admitted no conflicts of interest to declare.