{"id":18665,"date":"2025-09-27T15:30:04","date_gmt":"2025-09-27T08:30:04","guid":{"rendered":"https:\/\/www.cc1.vn\/?p=18665"},"modified":"2025-09-27T18:47:05","modified_gmt":"2025-09-27T11:47:05","slug":"nhung-ngay-khoi-phuc-va-mo-rong-lo-phan-ung-hat-nhan-da-lat","status":"publish","type":"post","link":"https:\/\/www.cc1.vn\/en\/2025\/09\/27\/nhung-ngay-khoi-phuc-va-mo-rong-lo-phan-ung-hat-nhan-da-lat.html","title":{"rendered":"THE DAYS OF RESTORATION AND EXPANSION OF THE DA LAT NUCLEAR REACTOR"},"content":{"rendered":"
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The latter half of the 20th century left a profound mark on Vietnam's nuclear industry with the construction and operation of the Da Lat nuclear reactor, which had a remarkably unusual fate. In the beautiful and picturesque tourist city of Da Lat, a research nuclear reactor was built and put into operation twice, using two different types of fuel, thanks to the assistance of two of the world's nuclear powers.<\/span><\/p>

I was fortunate enough to be involved in a part of that 60-year event. Specifically, I participated in the second of the two construction phases of this reactor. That historic event took place in the 1980s.<\/span><\/p>

On the occasion of the 40th anniversary of the inauguration of the Da Lat nuclear reactor (1984-2024), recalling memories of a bygone era, through this autobiography, I want to share with my colleagues then and now the beautiful memories of those days of shared hardship and unforgettable experiences in the misty city of Da Lat.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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1. The Da Lat nuclear reactor, built in two phases.<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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The first construction in 1961 involved a TRIGA Mark II reactor funded by the United States. In the 1950s, American nuclear scientists developed a new research nuclear reactor, the TRIGA, based on the design of theoretical physicist Edward Teller and his colleagues. The TRIGA reactor had three functions: training, research, and isotope production, and was manufactured by General Atomic (GA) in San Diego, California, USA. This reactor was designed with very high intrinsic safety due to the use of a homogeneous fuel consisting of uranium mixed with a zirconium hydride moderator to form U-ZrH crystals with an enrichment of 19.75% uranium-235. This is a relatively safe and easy-to-use small-capacity research reactor, so 35 reactors have been installed in research institutes in the United States and another 35 in 24 countries around the world, including Vietnam. Immediately after the first TRIGA Mark I reactor was commissioned on May 3, 1958, in the United States, TRIGA reactors were installed in several countries in the early 1960s, including Zaire (Mark I, 50 kW, 1959), Brazil (Mark I, 100 kW, 1960), Italy (Mark II, 1,000 kW, 1960; Mark II, 250 kW, 1965), Japan (Mark II, 100 kW, 1961; Mark II, 100 kW, 1963), Austria (Mark II, 250 kW, 1962), Finland (Mark II, 250 kW, 1962), South Korea (Mark II, 250 kW, 1962), Vietnam (Mark II, 250 kW, 1963), and Germany (Mark II, 250 kW, 1962). 100 kW, 1965; Mark I, 150 kW, 1966), Slovenia (Mark II, 250 kW, 1966). Other TRIGA reactors were supplied in subsequent decades, and by 2005, Thailand received the TRIGA Mark MPR-10 reactor with a capacity of 10,000 kW.<\/span><\/p>

The TRIGA Mark II reactor, with a power output of 250 kW, was built in Da Lat from April 1961 and completed in December 1962. The reactor structure and the concrete radiation shielding system surrounding the reactor vessel were similar to other TRIGA Mark II reactors worldwide. However, the reactor containment building and the facilities housing the auxiliary technological systems were modified by the Vietnamese side compared to the US design. Architect Ngo Viet Thu did not use a box-shaped model but switched to an atomic model, in which the reactor containment building was a cylindrical shape, 17 m high and 20 m in diameter, located at the center of a concentric annular building containing the auxiliary technological systems. Vietnamese engineers and workers were responsible for building this Nuclear Center according to the design of architect Ngo Viet Thu. On February 26, 1963, the TRIGA Mark II reactor reached criticality for the first time. By March 3, 1963, the reactor had reached its rated power of 250 kW; and was inaugurated on October 28, 1963.<\/span><\/p>

The TRIGA Mark II reactor, commissioned in Da Lat in 1963, was the first nuclear reactor in Southeast Asia. Ironically, however, it was built during a period of increasingly fierce warfare in South Vietnam. Therefore, in reality, it only operated for five years, until 1968. Finally, on March 31, 1975, three days before the liberation of Da Lat, the US military removed all the fuel rods from the reactor and transported them back to the United States, rendering the reactor inoperable.<\/span><\/p>

After the reunification of the country, the Soviet government helped Vietnam restore and expand the Da Lat nuclear reactor, increasing its capacity to 500 kW with Soviet-made VVR-M2 fuel, which is enriched with 36% uranium-235. Unlike the TRIGA Mark II reactor, a homogeneous reactor using U-ZrH fuel with high intrinsic safety, the new reactor, assisted by the Soviet Union with VVR-M2 fuel, has a heterogeneous structure where water slows and heatsinks run between the fuel rods, resulting in lower intrinsic safety. Therefore, the Soviet Union had to equip it with other, more complex auxiliary technical systems than the TRIGA Mark II reactor to ensure nuclear and radiation safety. The construction and expansion of the Da Lat reactor was almost a complete new construction project with many new technological systems.<\/span><\/p>

Thus, the second phase of construction of the Da Lat reactor began on March 15, 1982, at the same location as the 1961 construction site, and retained the same atomic model design by architect Ngo Viet Thu. A new annular structure surrounded and was concentric with the old annular structure, with the cylindrical reactor building at its center. During this phase, the active zone, graphite reflector ring, reactor vessel, concrete walls protecting the reactor, and reactor building remained unchanged. Major changes included the reactor control system and auxiliary technological systems such as electricity, water, ventilation, radioactive gas exhaust, radioactive liquid and solid waste disposal, radiation measurement and warning systems, etc.\u00a0<\/span><\/p>

The second phase of construction lasted for over a year and a half, completed at the end of October 1983. The new reactor was started up and brought to limit on November 1, 1983, and was inaugurated on March 20, 1984, with a nominal capacity of 500 kW.<\/span><\/p>

This reactor used Soviet-made VVR-M2 fuel with an enrichment of 36% uranium-235, known as High Enriched Uranium (HEU). The Da Lat reactor, operating safely with HEU fuel for over 20 years, was replaced with Low Enriched Uranium (LEU) fuel with an enrichment of 19,75% uranium-235. This fuel replacement was carried out in two phases. The first phase involved a mixed HEU and LEU reactor configuration from 2007 to 2011. The second phase involved a reactor configuration using only LEU fuel from 2011 to the present.<\/span><\/p>

I had the honor of participating in the second phase of reactor construction and the commissioning of the reactor to criticality with Soviet HEU fuel in the early 1980s. I would like to recount the main events in the process, beginning with the preparation of the personnel.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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2. Personnel preparation<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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In 1977, while I was teaching at the Department of Physics, Hanoi University, Professor Nguyen Dinh Tu proposed that I transfer to the Nuclear Research Institute to participate in the restoration and commissioning of the Da Lat nuclear reactor.<\/span><\/p>

On March 24, 1978, I officially transferred from the Ministry of Higher Education and Vocational Training to the State Committee for Science and Technology, the superior agency of the Nuclear Research Institute. After becoming an employee of the Nuclear Research Institute, Professor Nguyen Dinh Tu and Professor Pham Duy Hien suggested that I take charge of reactor physics and technology. I began to study reactor physics, as I had not had the opportunity to research reactors before, mainly focusing on nuclear reactions in proton accelerators.<\/span><\/p>

On October 9, 1979, the Soviet and Vietnamese governments signed an agreement to restore and expand the Dalat nuclear reactor. Subsequently, the Soviet Union sent the technical design for the Dalat reactor, known as reactor IVV-9, to Vietnam for evaluation. The Institute of Nuclear Research established an evaluation team led by Professor Pham Duy Hien, of which I was a member. I was responsible for evaluating the reactor's control and measurement systems, primarily using semiconductor and microelectronic components. This part of the work suited my abilities because in previous years I had researched and taught Nuclear Electronics at Hanoi University. Participating in the evaluation team allowed me to first access the technological systems of the Dalat nuclear reactor.<\/span><\/p>

To facilitate my research on reactor physics, the Board of Directors of the Institute of Nuclear Science and Technology sent me to work as a collaborator at the Joint Institute for Nuclear Research in Dubna, Soviet Union, for one year from mid-1980 to mid-1981. In Dubna, I worked in the IBR-2 Fast Neutron Reactor Laboratory of Dr. EP Shabalin, belonging to the Neutron Physics Laboratory. Although this was a fast neutron pulse reactor, different from the thermal neutron reactor in Da Lat, this year of research provided me with much useful knowledge about nuclear reactors to prepare for my upcoming work in Da Lat.<\/span><\/p>

In mid-1981, upon returning from Dubna, I was assigned by the Board of Directors of the Nuclear Research Institute to lead a delegation of the Institute's staff to the Soviet Union for a training course on operating a reactor. The delegation consisted of ten people; besides myself, who was approximately 40 years old, the other nine members were young staff members who had graduated from university a few years earlier, not yet 30 years old. These were Tran Khac An, Nguyen Thanh Binh, Nguyen Van De, Nguyen Nhi Dien, Ngo Phu Khang, Tu Van Nghia, Hoang Van Nguyen, Truong Cam Ranh, and Nguyen Truong Sinh (see Figure 1). For a year, the delegation trained at two thermal neutron reactors of the pool reactor type in the two Soviet republics of Georgia and Ukraine.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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\u00a0Photo taken in Tbilisi, Georgia, December 1981. From left to right: Tu Van Nghia (1), Truong Cam Ranh (2), Ngo Phu Khang (3), Tran Khac An (4), Nguyen Thanh Binh (5), Hoang Van Nguyen (6), Ngo Quang Huy (7), Nguyen Truong Sinh (9) (missing two brothers Nguyen Nhi Dien and Nguyen Van De)<\/i><\/b><\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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The delegation departed for Tbilisi, Georgia, in mid-October 1981 and spent four months practicing at the reactor of the Institute of Physics of the Georgian Academy of Sciences. There, each member of the delegation was assigned to specialize in a particular area, such as chief engineer (Mr. Huy), reactor physics (Mr. Khang), reactor technology (Mr. De), control and measurement systems (Mr. Dien, Mr. An, Mr. Sinh), radiation safety systems (Mr. Nguyen, Mr. Cam Ranh, Mr. Binh), reactor water treatment systems (Mr. Nghia), etc. Because it was their first time working with a reactor, the members received thorough theoretical instruction alongside practical reactor operation sessions, and each completed a thesis at the end of the internship. Each member presented their thesis to a panel established by the Institute of Physics, chaired by Dr. G. Karumidze, Vice-Director and Chief Reactor Engineer.<\/span><\/p>

In March 1982, the delegation left Tbilisi for Kyiv, the capital of the Republic of Ukraine. They were assigned to a four-month training program in reactor operation at the Kyiv Nuclear Research Institute. Because the theoretical training had been primarily conducted in Tbilisi, the focus of the second training period in Kyiv was on practical reactor operation. The training in Kyiv concluded in early July 1982, and the delegation returned home. However, Nguyen Van De was assigned to stay in Kyiv for an additional five months to train as Chief Reactor Engineer. In mid-September 1982, the Nuclear Research Institute also sent Do Van Hiep and Le Minh Tuan to Kyiv for further mechanical training at the Kyiv Nuclear Research Institute's reactor, alongside Nguyen Van De.<\/span><\/p>

On July 6, 1982, the Directorate of the Kyiv Nuclear Research Institute awarded certificates of completion for the reactor operation training course in the Soviet Union, held from October 18, 1981 to July 6, 1982, to all members of the delegation. On July 9, 1982, the delegation left Kyiv and flew to Moscow, and on July 16, 1982, they flew from Moscow to Hanoi, arriving on July 17, 1982. The delegation arrived in Da Lat in August 1982 to participate in the restoration and expansion of the Da Lat reactor.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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3. Construction site<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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On August 22, 1982, after a month in Hanoi preparing for work in Da Lat, I flew to Ho Chi Minh City and then took a vehicle from the Institute to Da Lat. This was my second visit to Da Lat; the first was in early 1980, after participating in the assessment group for the IVV-9 reactor in Hanoi and before going to Dubna to study reactor physics. The car traveled along the winding asphalt road, gradually ascending through the forests of the Prenn Pass. Upon reaching the summit, a bright city with a European architectural style unfolded before my eyes. The car entered the city, passing through streets filled with vibrant flowers. My heart swelled with excitement as I stepped into a new life and a new job awaiting me in this beautiful and famous city.<\/span><\/p>

In late 1981, while I was in the Soviet Union, the restoration and expansion of the Da Lat nuclear reactor began with the establishment of a Project Management Board headed by Professor Pham Duy Hien, Director of the Da Lat Nuclear Research Institute and concurrently Director of the Project Management Board. After a period of preparation, the restoration and expansion of the reactor commenced on March 15, 1982, six months before I started working in Da Lat. I was appointed by the Board of Directors of the Nuclear Research Institute as Head of the Reactor Physics Department and Deputy Director of the Project Management Board, in charge of the technology aspect.<\/span><\/p>

My first experience working on a construction site was a stark contrast to my years spent in the laboratory. The site was a chaotic mess; building number 2 was being dug and construction was beginning. Soviet-made equipment lay scattered across the site amidst the gloomy, drizzling weather of Da Lat. Yet, a spirit of enthusiastic and energetic work permeated the entire construction area. Officials from the Project Management Board and the Da Lat Nuclear Research Institute worked closely with the engineers and construction workers of Company 14 under Construction Corporation No. 1 and the Soviet expert team.<\/span><\/p>

The restoration of the Da Lat nuclear reactor essentially involved re-equipping most of its technological systems. The remaining components of the TRIGA Mark II reactor included the graphite reflector ring, the aluminum reactor vessel, the four horizontal experimental channels, the heat column, and the concrete walls for biological radiation shielding. New Soviet-era technological systems were installed to meet the increased reactor power from 250 kW to 500 kW and to enhance radiation safety. These systems included the active zone, heat transfer system, control and protection system, radiation safety monitoring system, radioactive gas exhaust system, liquid radioactive waste treatment system, radioactive waste disposal system, priority industrial and emergency power supply system, etc.<\/span><\/p>

The upgrade of technological systems requires an expansion of construction scale, including, in addition to the existing reactor containment building and control room (building 1), the construction of a second arc-shaped building (building 2); a transformer station equipped with diesel generators to ensure continuous power supply in case of city power outages (building 3); a radioactive waste disposal facility (building 5); a water tank providing backup water for cooling the reactor in case of core meltdown (building 6); a rainwater cooling tower for the second heat transfer water system (building 7); a 40-meter-high radioactive gas exhaust pipe (building 20); a telephone exchange station (building 13); and outdoor structures such as the second heat transfer water system, electrical system, water supply and drainage system, etc.<\/span><\/p>

Buildings No. 1 and No. 2 are two key construction projects. Building No. 2 is a new structure, serving as a technical support building comprising: a second-loop heat transfer water system; a radioactive water treatment system; a ventilation control station; laboratories for testing boiler water quality; a laboratory for testing environmental radiation; offices for the electrical and water control teams; offices for the boiler operating crews; bathrooms and a hot water heating station, laundry rooms, etc.<\/span><\/p>

The main workforce working daily on the construction site consists of hundreds of workers from Construction Company No. 14 under Construction Corporation No. 1, including two main enterprises: the Construction Enterprise and the Machinery Installation Enterprise. The company's leadership includes Mr. Nguyen Thiem, Deputy General Director of Construction Company No. 1; Mr. Nguyen Huu Quang, Director of Construction Company No. 14; Mr. Nguyen Quang Thuy, Director of Construction Enterprise No. 1; and Mr. Truong Van Bong, Director of the Machinery Installation Enterprise.<\/span><\/p>

On the part of the Nuclear Research Institute, the Project Management Board is the managing unit (Party A) headed by Professor Pham Duy Hien as Director, with three Deputy Directors: Dr. Pham Khac Chi, Professor Nguyen Van Dat, and myself, Ngo Quang Huy. The staff of the Project Management Board includes Trinh Hong Linh, Le Thanh Liem, Bui Van Quyen, Ha Dang Tien, Phan Thanh Cong, Le Chanh Phe, Pham Van Nhiem, Nguyen Thi Thanh A, Nguyen Thi Thanh B, Trieu Thi Tam, etc. Several staff members monitoring the construction work were seconded from the Ho Chi Minh City Nuclear Center, including Nguyen Mong Hung, Vu Huy Thuc, Nguyen Quoc Binh, Hoang Van Hung, Nguyen Le Son, Nguyen Thi Thu, Le Thi Phung, Nguyen Tuan Hoang, etc. (see Figure 2).<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Some members of the Construction Management Board during a vacation in Nha Trang city in 1983. From left to right: Nguyen Thi Thanh A (2), Ngo Quang Huy (3), Trinh Hong Linh (5), Truong Thi Hanh (6), Le Chanh Phe (10), Pham Van Nhiem (11), Le Thanh Liem (12)<\/i><\/b><\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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To monitor the assembly process of the technological systems, the Da Lat Nuclear Research Institute sent a team of technical staff to the construction site, including Nguyen Mong Sinh, Pham Quoc Trinh, Tran Lam, Ha Van Thong, Vo Quoc Lap, Nguyen Viet Long, Nguyen Van Quy, Hoang Xuan Vu, Phan Van Hieu, Nguyen The Ky, Phan Cong Thuyet, Vu Trung Hieu, Le Van So, Phan Truc, Tran Tich Canh, Hoang Van Nguyen, Nguyen Van Hung, Nguyen Ba Hung, Nguyen Van Long, Vu Xuan Biet, Tran Van Nguyen, Doan Ai Thu, etc. Playing a crucial role in this force were members of the 1981-1982 Soviet Union training group, including Tran Khac An, Nguyen Thanh Binh, Nguyen Van De, Nguyen Nhi Dien, Ngo Phu Khang, Tu Van Nghia, Hoang Van Nguyen, Truong Cam Ranh, Nguyen Truong Sinh, Do Van Hiep, and Le Minh Tuan. Figure 4 captures the meeting between Prime Minister Pham Van Dong and Mr. Tam Canh, Chairman of the Lam Dong Provincial People's Committee, with staff from the Da Lat Nuclear Research Institute.<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Photo taken at the entrance to the reactor building, early 1984. From left to right: Ngo Quang Huy (1), Mai Van Hung (2), Ulitin Valeri Fedorovich (3), Hoang Xuan Vu (4), Ozimai Nikolai Stepanovich (5), Nguyen Thi Nang (6), Tran Khanh Mai (7) and Nguyen Mong Sinh (8)<\/i><\/b><\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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To monitor the assembly process of the technological systems, the Da Lat Nuclear Research Institute sent a team of technical staff to the construction site, including Nguyen Mong Sinh, Pham Quoc Trinh, Tran Lam, Ha Van Thong, Vo Quoc Lap, Nguyen Viet Long, Nguyen Van Quy, Hoang Xuan Vu, Phan Van Hieu, Nguyen The Ky, Phan Cong Thuyet, Vu Trung Hieu, Le Van So, Phan Truc, Tran Tich Canh, Hoang Van Nguyen, Nguyen Van Hung, Nguyen Ba Hung, Nguyen Van Long, Vu Xuan Biet, Tran Van Nguyen, Doan Ai Thu, etc. Playing a crucial role in this force were members of the 1981-1982 Soviet Union training group, including Tran Khac An, Nguyen Thanh Binh, Nguyen Van De, Nguyen Nhi Dien, Ngo Phu Khang, Tu Van Nghia, Hoang Van Nguyen, Truong Cam Ranh, Nguyen Truong Sinh, Do Van Hiep, and Le Minh Tuan. Figure 4 captures the meeting between Prime Minister Pham Van Dong and Mr. Tam Canh, Chairman of the Lam Dong Provincial People's Committee, with staff from the Da Lat Nuclear Research Institute.<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Prime Minister Pham Van Dong (the gray-haired man in the middle, front row) and Mr. Tam Canh, Chairman of the Lam Dong Provincial People's Committee (standing to the Prime Minister's right), visit staff of the Da Lat Institute of Nuclear Science and Technology. To the Prime Minister's left is Mr. Pham Duy Hien, and to Mr. Tam Canh's right is Mr. Pham Khac Chi.<\/i><\/b><\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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In March 1983, I moved my family permanently to Da Lat, residing in the Institute's staff quarters at the Papal Academy. This allowed me to frequently work at the construction site, representing the Board of Directors of the Construction Management Board in handling tasks alongside Mr. Ulitin VF and the construction crew. We usually held weekly meetings to review the work of the previous week and plan for the following week.<\/span><\/p>

During the first year, from February 1982 to March 1983, the main work was the construction of structures No. 2, No. 3, No. 5, No. 6, No. 7, No. 13 and the installation of electrical, water supply and drainage, ventilation systems, etc. By May 1983, the assembly of technological systems such as the two heat exchanger systems (ring 1 and ring 2); the radioactive ventilation system in the reactor building; the radioactive wastewater treatment system; the radiation safety system; the electrical and diesel transformer systems; etc. It can be said that from May 1983 onwards, the construction site became bustling with activity, aiming for the Da Lat nuclear reactor to be started up on November 1, 1983, to celebrate the Soviet Union's National Day on November 7, 1983.<\/span><\/p>

However, an incident that hampered the project's progress was the loss of a large quantity of stainless steel components for the first and second heating systems at Saigon Port. In June 1983, when Technoimport Import-Export Company arrived at Saigon Port to receive goods for shipment to Da Lat, they discovered that a large quantity of stainless steel components had been stolen. On July 9, 1983, Ngo Quang Huy and Nguyen Mong Hung, along with Mr. Ultin VF, went to Saigon Port to conduct an on-site inspection and found a very small number of remaining components. The Nuclear Research Institute in Hanoi, together with Technoimport and Mr. Jukov, a representative of the Soviet Union's trade agency, discussed establishing a new contract with the Soviet Union to reproduce all the stainless steel components. On July 10, 1983, Technoimport and the Soviet Union's trade agency signed a contract to supply all the stainless steel parts for the Da Lat reactor once again. Immediately afterwards, Zhukov flew back to Moscow and went to the factories to place orders for production based on the existing blueprints, as these were non-standard components that could not be purchased on the Soviet market.<\/span><\/p>

On August 4, 1983, the Project Management Board met with Tecnoimport's leadership to discuss preparations for receiving the neutron flux measurement system, stainless steel, and reactor fuel at the airport. Fortunately, these shipments were transported by plane from Moscow to Hanoi, and then from Hanoi to Da Lat under strict supervision by the management departments of the Nuclear Research Institute in Hanoi, Ho Chi Minh City, and Da Lat, with the support of the Ministry of Public Security. Thanks to this, the assembly of the technological systems proceeded according to plan with the urgency of all parties involved.<\/span><\/p>

On September 15, 1983, the Project Acceptance Council was established, chaired by Professor Pham Duy Hien, with Nguyen Van Dat and Ngo Quang Huy as vice-chairmen. Representatives from the Design and Manufacturing Agency, the State Committee for Basic Construction, the Lam Dong Provincial Committee for Basic Construction, and the investment managing agency, the Nuclear Research Institute, represented by Mr. Tran Kim, participated in the council. The acceptance process was carried out in three phases. The first phase, preliminary acceptance, took place from September 26-29, 1983. The second phase from October 6-10, 1983. The final phase was conducted from October 20-30, 1983. Thus, the restoration and expansion of the reactor was completed on October 30, 1983, and October 30, 1983 was also the date the reactor was started up to reach criticality on November 1, 1983, as planned.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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4. Start up the reactor.<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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In August 1983, the construction and assembly of basic technical systems such as electricity, water supply, wastewater, and ventilation were completed. At this time, the assembly of technological systems for reactor commissioning began. By the end of October 1983, basic assembly items such as the reactor vessel, reactor door, first and second water supply systems, ventilation system, power supply system for building 1, first water filtration system, telephone system, radioactive wastewater discharge system, SUZ system, KIP system, priority high-voltage power connection, and chemical and physical laboratories were completed. On Saturday, October 15, 1983, all staff and workers of the Da Lat Nuclear Research Institute and all Soviet experts participated in a communist labor day, mainly cleaning and tidying building number 1 and the reactor chamber.<\/span><\/p>

On October 26, 1983, the Board of Directors of the Sub-Institute met with the reactor start-up team, assigning Vietnamese and Soviet experts to 11 positions. On the Vietnamese side were Pham Duy Hien, Ngo Quang Huy, Vu Hai Long, Tran Khanh Mai, Nguyen Dang Nhuan, Tran Khac An, Nguyen Nhi Dien, Nguyen Ngoc Lam, Do Van Hiep, Pham Xuan Phuong, Nguyen Truong Sinh, Pham Van Lam, Duong Quang Tan, Truong Cam Ranh, Nguyen Tac Anh, Luong Ngoc Chau, Le Vinh Vinh, Huynh Dong Phuong, Nguyen Thi Nang, and Tu Van Nghia. On the Soviet side were Arhanghenski NV, Terekhov AV, Kuznexov EM, Trophimov IV, Levrenov NP, Kharlamov NB, Sokolov IV, Bakharev VS, Truskin VS, Khandamirov Yu.E., and Semenov SM<\/span><\/p>

On October 30, 1983, the reactor began to start up. Members of the operating team and personnel in charge of the electrical, water, and ventilation systems, etc., took their positions. In the morning, a Cf-252 neutron pilot source was introduced into the central cell of the active zone. In the early afternoon, a final check of all technological systems was performed. At 3:30 PM, 18 fuel rods were taken from the fuel storage located in room 125, building 1. Present to inspect the fuel taking were Mr. Pham Khac Chi, Mr. Ngo Quang Huy, Mr. Do Van Hiep, Mr. Luan (police officer), and Soviet experts Arhanghenski NV, Khandamirov Yu. E., and Terekhov AS.<\/span><\/p>

The first fuel rod was installed in the reactor at 3:57 PM, and the loading of the 18th rod was completed at 6:25 PM, filling the two innermost rings of the reactor core. The 18 fuel rods were loaded in three groups of six rods each. After loading each group of six rods, physicists measured neutron counts to determine the extrapolated critical mass value.<\/span><\/p>

On October 31, 1983, refueling resumed at 10:15 AM. At 2:11 PM, the second batch of 18 fuel rods, consisting of 3 groups of 6 rods each, was loaded, filling the third ring of the active zone. From 2:51 PM to 6:17 PM, the next batch of 18 fuel rods, consisting of 4 groups (5, 5, 4, and 4 rods), was loaded, filling the fourth ring of the active zone. Thus, after two days of commissioning, 54 fuel rods, comprising 10 groups, had been loaded into the active zone. After loading the 10th group, the extrapolated critical mass obtained was between 60 and 70 fuel rods, not 77 rods as calculated in the design. Therefore, subsequent refueling had to be carried out with fewer fuel rod groups.<\/span><\/p>

On November 1, 1983, the 11th and 12th groups of fuel, comprising 7 fuel rods, were loaded in the morning, bringing the total number of rods in the active area to 61. The extrapolated critical mass was determined to be approximately 60 to 70 fuel rods. A problem occurred on the morning of November 1, 1983: operation was impossible at cell 12-4, located between the AZ-2 fault rod and the compressed air sample channel 13-2, because the space in this cell was only 32 mm wide, just enough for the fuel rods, while the operating pole had a diameter of 40 mm. Therefore, cell 12-4 had to be left unloaded during this fuel loading operation.<\/span><\/p>

On the afternoon of November 1, 1983, the 13th group of three reactors was loaded. There were also operational issues with cells 11-2 and 11-8, which are located between the KS-3 and KS-4 compensation bars and the beryllium bars. However, these two cells were also loaded by removing the beryllium bars, loading the fuel, and then reinserting them. By 4:20 PM, the three bars of group 13 were loaded, bringing the total number of reactors to 64. The subcriticality coefficient was calculated to be approximately 0.988, and the auto-recorder showed the reactor power beginning to increase rapidly. At 4:35 PM, the two reactors of group 14 were loaded and loaded slowly in small increments to monitor the power increase on the auto-recorder. At 5:05 PM, the two reactors of group 15 were loaded, bringing the total number of reactors to 68. Remove the KS-1, KS-2, KS-3, and KS-4 compensation bars from the active zone; the reactor has not yet reached its limit. Continue loading the 69th TNL, following the same step-by-step loading procedure.<\/span><\/p>

Removing the compensation rods KS-1, KS-2, KS-3, and KS-4 from the active zone revealed that the reactor was nearing criticality. At this point, the power increase cycle dropped below 100 seconds. However, the reactor had not yet reached criticality because power could not be sustained when the Cf-252 neutron source was removed from the active zone. Adding another beryllium rod to the active zone was then done. The three compensation rods KS-1, KS-2, and KS-3 were removed from the active zone, and the KS-4 rod was slowly pulled up. When the KS-4 rod was almost completely removed, the power increase cycle dropped below 100 seconds. Then, the Cf-252 neutron source was removed from the active zone, and the KS-4 rod was pulled up. When the KS-4 rod was still submerged in the active zone by about 6 cm, the reactor power remained unchanged, indicating that the reactor had reached criticality.<\/span><\/p>

The reactor reached its limit at 7:50 p.m. on November 1, 1983.<\/i><\/b><\/span><\/p>

The Da Lat nuclear reactor has reached criticality. All members of the reactor start-up team and many remaining staff members of the Institute were present in the reactor control room. Cheers and shouts of "hurray!" filled the room. Champagne popped and glasses overflowed as people passed around in celebration.<\/span><\/p>

It was incredibly joyful and moving, and everyone present in the control room at that time signed the paper cut from the automatic power recording machine and the fuel rod loading map in the active zone. The evidence is still preserved to this day and is shown in Figures 5 and 6.<\/span><\/p>

On the reactor power curve, the horizontal axis represents time, while the vertical axis represents power in relative units. We see that the power fluctuates around an average value and then stops at a constant value over time. This is the critical state of the reactor. The signatures are located within that constant region of the curve when the reactor is in the critical state. On the fuel loading map, the signatures are located around the active region of the reactor, which is a circle containing 69 loaded fuel rods.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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The graph shows the fluctuation of furnace power, with the horizontal axis representing time and the vertical axis representing power in relative units. We see that the power oscillates around an average value and then stops at a constant value over time. This is the critical state of the furnace.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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Fuel loading map of the active zone reaching criticality with 69 fuel rods loaded on November 1, 1983.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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5. Bring the reactor into operation.<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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The Da Lat nuclear reactor reached criticality at 7:50 PM on November 1, 1983, with a core configuration without neutron traps. The neutron trap was a beryllium block the size of seven fuel rods surrounding a water column with a diameter of 65 cm. The neutron trap was placed at the center of the core, its purpose being to increase the thermal neutron flux density in the water column. After the successful start-up, the reactor start-up team continued fuel injections to reach criticality for core configurations with neutron traps. This was the physical start-up phase with the neutron trap configuration, carried out from December 15, 1983, to January 27, 1984. There were two reasons for waiting a month and a half before starting the physical start-up.<\/span><\/p>

The first reason is the need to complete the preparatory work for bringing technological systems into stable operation, such as the first and second-loop heat transfer systems; the SUZ and AKNP control systems; the KIP testing systems; the diesel generator emergency power system; the radioactive wastewater discharge system; the auxiliary neutron counter systems; etc.<\/span><\/p>

The second reason is the appearance of graying on the fuel rod cladding. Each reactor consists of three fuel rings, each 2.5 mm thick, with a 0.7 mm thick fuel layer in the middle and two 0.9 mm thick aluminum claddings on either side. The aluminum cladding acts as both a heat conductor and a protective layer to prevent leakage of fission products. Therefore, protecting the integrity of the aluminum cladding is extremely important, and the first measure is to ensure the correct water quality in the reactor vessel to prevent metal corrosion. Monitoring of the reactors' condition began immediately after reaching the first critical state on November 1, 1983. Specifically, on November 2, 1983, several reactors and aluminum inserts were removed from the active zone and placed in temporary containment cups. On November 5, 1983, these reactors were inspected and their surfaces were found to be gray. Some of the fuel removed from the active zone for inspection was normal and not gray. However, the reactor start-up team decided to remove all the fuel from the active zone and store it in a warehouse, then conduct a water quality check. On November 12, 1983, the start-up team drained all the water from the reactor vessel, cleaned the vessel, and refilled it with fresh water whose physicochemical parameters were within acceptable limits.<\/span><\/p>

After more than a month of investigation without determining the cause of the graying of the fuel rod casings, fuel was refueled on December 15, 1983, to continue the reactor's physical startup program. On December 18, 1983, some fuel rods were removed for inspection and found to be severely grayed. From December 19, 1983, startup work was halted to investigate the cause, primarily focusing on three factors: the chlorine concentration in the water potentially exceeding the regulated limit, causing aluminum corrosion; the possibility of air bubbles in the water oxidizing the aluminum; and electrolysis. Additional measurements and experiments showed that these three factors were not the cause of the graying of the aluminum casings. To obtain objective verification data, on December 21, 1983, the Nuclear Research Institute sent two grayed aluminum support rods and a bottle of water taken from the reactor pool to Moscow for analysis. On January 12, 1984, analysis results received from Moscow showed that the water parameters were the same as those analyzed in Da Lat and within acceptable limits. In addition, a council of 10 experts was established in Moscow to examine the grayed aluminum bars and concluded that the furnace could still be put into operation despite this graying. Based on this conclusion, on January 14, 1983, more fuel was added to the active zone to continue the furnace startup process.<\/span><\/p>

During the physical startup period from December 15, 1983 to January 27, 1984, the startup team added fuel to obtain four critical neutron trap configurations with 74 TNL, 83 TNL, 86 TNL, and 88 TNL. Several reactor physical parameters were determined for these active zone configurations, such as the integral characteristics and efficiency of the control rods, the efficiency of some TNLs and beryllium rods, the relative distribution of thermal neutron flux density at several cells along the radius and height of the active zone, etc.<\/span><\/p>

After completing the physical start-up, between February 6, 1984 and February 11, 1984, the start-up team performed the energy start-up, that is, bringing the reactor to operation at its nominal power of 500 kW. The start-up team carried out reactor power calibration, measured neutron flux density, measured the temperature coefficient of reactivity, measured xenon contamination, measured the temperature of the reactor vessel water and heat transfer loops, measured gamma and neutron dose levels, measured the parameters of the first-loop heat transfer system, etc. The reactor's active zone was a neutron trap configuration consisting of 88 BNLs with a mass of 3537.0 g 235U. The temperature coefficient of reactivity related to the heat transfer fluid and moderator (H2O) was \u2013 1.10-2 \u03b2eff \/ 0C. The thermal neutron flux density at the neutron trap reaches 2.1 x 10\u00b9\u00b3 n\/cm\u00b2s, which is quite high for a 500 kW reactor. At the nominal power of 500 kW, the temperatures at locations within the active zone are around the calculated values.<\/span><\/p>

On February 11, 1984, at 7:06 PM, the reactor was put into operation at 500 kW and operated continuously for 72 hours, until 7:06 PM on February 14, 1984. The thermal power was calculated based on the measured values of the thermal parameters of the first and second water cycles. During this 72-hour operation, the reactor power was calibrated so that the power displayed on the control panel, the power set by the AR control bar, and the thermal power coincided.<\/span><\/p>

Thus, the physical and energy start-up demonstrated that the Da Lat nuclear reactor could be safely put into operation. Therefore, the reactor was officially inaugurated on March 20, 1984. From 1984 to the present, the Da Lat nuclear reactor has operated safely for 40 years, and the scientists of the Da Lat Nuclear Research Institute have achieved many results in their research on that reactor.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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6. Conclusion<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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The Da Lat nuclear reactor is a small-capacity research reactor; however, its construction, assembly of technological systems, commissioning, and operation over the past 40 years have provided us with valuable lessons.<\/span><\/p>

The most important lesson is the staff. During the 1960s and 1970s, the Vietnamese government sent many officials abroad for training, including in nuclear science. By the early 1980s, the Da Lat Nuclear Research Institute in particular, and the Vietnam Atomic Energy Institute in general, had inherited a highly qualified team of personnel from other countries. These scientists worked alongside hundreds of young scientists to successfully complete the construction work during the restoration and expansion of the reactor, as well as during the commissioning and operation of the reactor. Through the operation and research of the reactor over the past 40 years, a large number of young scientists have matured and mastered reactor technology, leading other scientific research and application directions.\u00a0<\/span><\/p>

The second lesson is that safety issues, including both nuclear and radiation safety, have received due attention. During the reactor startup process, safety issues were thoroughly discussed before starting and were always given priority throughout the startup process. The safe operation and exploitation of the reactor over the past 40 years is a testament to the due attention given by the scientific and technical staff of the Da Lat Nuclear Research Institute.<\/span><\/p>

The successful construction and safe operation of the reactor is a testament to the efforts of the staff and workers of the Da Lat Nuclear Research Institute under the leadership of Professor Pham Duy Hien. This success is also due to the management and leadership of the Vietnam Atomic Energy Institute, headed by Professor Nguyen Dinh Tu as Director, with Deputy Directors Nguyen Quy and Nguyen Dinh Dien, and other staff members in various departments such as Phan Vinh, Doan The Phi\u1ec7t, Bui Tien Chien, Tran Kim, Nguyen Thi Ty, etc.<\/span><\/p>

To successfully complete the construction of the reactor in Da Lat city, we remember the support and assistance of the Lam Dong Provincial People's Committee, which created favorable conditions for the Institute's activities. And the decisive factor in the successful restoration and commissioning of the reactor on schedule was the direct and close guidance of the highest leaders of the Party and Government, especially Prime Minister Pham Van Dong and General Vo Nguyen Giap.<\/span><\/p>

To achieve the current state of the Da Lat Nuclear Research Institute, we must not forget the contributions of hundreds of engineers and workers from Construction Company No. 14, under Construction Corporation No. 1, led by Engineer Nguyen Thiem. We sincerely thank the contributions of Technoimport Import-Export Company, headed by Mr. Nguyen Hao.<\/span><\/p>

We are also extremely grateful to the Soviet team of experts led by Mr. Pecherski Vladimir Makarovich as the project's chief engineer, Mr. Ulitin Valeri Fedorovich in charge of the reactor construction, Mr. Arhanghenski Nikolai Vasiliavich in charge of the reactor startup process, and Mr. Ozimai Nikolai Stepanovich in charge of the reactor operation team during the one-year warranty period after the reactor's inauguration.<\/span><\/p>

Forty years have passed since the inauguration of the Da Lat Nuclear Reactor. It's a short period in history, but quite long in a person's lifetime, because several generations have contributed their strength and dedication to the Institute's common cause. Some of us have passed away, leaving behind the imprint of a vibrant and proud youth. Some have grown and continued to develop their careers both within and outside the nuclear industry. A large number of young people are following in the footsteps of previous generations, continuing to be the core force in building a strong Institute. The Da Lat Nuclear Reactor deserves to be considered a highlight of Vietnam's nuclear industry, both in the past 40 years and for many years to come.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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According to the source<\/i><\/b><\/span>Nuclear Research Institute<\/i><\/b><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"

The latter half of the 20th century left a profound mark on Vietnam's nuclear industry with the construction and operation of the Da Lat nuclear reactor, which had a remarkably unusual fate. In the beautiful and picturesque tourist city of Da Lat, a research nuclear reactor was built and put into operation twice, using two different types of fuel, thanks to the assistance of two of the world's nuclear powers.<\/p>","protected":false},"author":2,"featured_media":18666,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[63],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/posts\/18665"}],"collection":[{"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/comments?post=18665"}],"version-history":[{"count":13,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/posts\/18665\/revisions"}],"predecessor-version":[{"id":18685,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/posts\/18665\/revisions\/18685"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/media\/18666"}],"wp:attachment":[{"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/media?parent=18665"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/categories?post=18665"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cc1.vn\/en\/wp-json\/wp\/v2\/tags?post=18665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}