HTR-PM: Making dreams come true26 February 2019
China has been developing high-temperature gas-cooled reactor technology since the 1970s, and a commercial demonstration unit is now being commissioned. Zuoyi Zhang, Yujie Dong, Weiwei Qi, and Jun Sun reflect on the design process.
CHINA HAS BEEN DEVELOPING HTGR technologies for more than 40 years, mainly at the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in Beijing. INET began research and development of HTGRs in the mid-1970s, with fundamental research into reactor design and fuel fabrication.
Starting in the late 1980s, the National High-tech R&D Programme designed, constructed, commissioned and operated a 10MW thermal power test reactor (HTR-10). HTR-10 reached its first criticality in December 2000 and was connected to the grid in January 2003. Between April 2003 and September 2006, the inherent safety features of the modular HTGR was proven in four experiments that imposed extreme scenarios on the HTR-10 without counter-measures, supervised by the Chinese National Nuclear Safety Administration (NNSA).
During this period significant objectives were achieved, including manufacture of the spherical coated-particle fuel element, technologies for fuel handling and transport, helium process technologies, domestic manufacture of key equipment for HTGRs and successful development of fully digital reactor-protection systems.
Based on the HTR-10 achievements, INET began development of a commercial nuclear power plant comprising modular HTGRs. A demonstration project, the high-temperature gas-cooled reactor pebble-bed module (HTR-PM), was launched in 2001. As well as demonstrating inherent safety, this plant was also a demonstration of economic competitiveness, confirmed and proven technologies, standardisation and modularisation.
In January 2006, the HTR-PM project (see main design parameters in Table 1) became one of 16 National Science and Technology ‘major projects’, given top priority and stronger support. After a construction licence was issued by the NNSA and all government approval procedures were completed, first concrete was poured for the HTR-PM on 9 December 2012 in Shidao Bay, Rongcheng, Shandong. Civil work on the nuclear island was finished by June 2015. Main component installation started with the first reactor pressure vessel on 20 March 2016, followed by the metallic internals, water cooling panels for the reactor cavity cooling systems, ceramic internals, graphite pebbles, etc. The upper head of the first RPV was installed on 27 December 2017, marking completion of the first reactor. Steam generators will be delivered soon and enough fuel pebbles have been fabricated for the initial core loading. HTR-PM is now in the commissioning phase and it is planned to connect to the electric grid in the late 2019.
In 2014, INET began commercial design for a modular HTGR with higher power levels, (HTR-PM600). To improve economic competitiveness six reactor modules with the same reactor module design and safety features will be connected to one steam turbine. Feasibility studies for the HTR-PM600 have been undertaken for several domestic sites and it has attracted international attention.
In accordance with the development roadmap, the modular HTGR in China is planned to be used for cogeneration of electricity and process heat. The aim is to replace coal-fired power plants, reduce carbon emissions and to be a high quality thermal source for large-scale hydrogen production.
The HTR-PM takes the HTR-10 as a prototype and scales up the power level and component sizes. In January 2008, the State Council of China approved an implementation plan for the HTR-PM project with a detailed R&D technology roadmap. In these innovative designs, new phenomena were identified, and some key equipment required full scale demonstration tests.
Since 2009, INET has built the advanced nuclear power engineering laboratory and carried out full scale verification experiments in hot states and the helium environment.
Verified equipment and systems included the main helium blower, steam generator, fuel handling system, control rod drives, small absorber sphere shutdown systems, helium purification system and the spent fuel storage system. In addition, the distributed control system, reactor protection system, and the design of the main control room were also verified in full-scale test facilities. All tests are complete and they provided strong support for the HTR-PM project.
The helium circulator is the main force driving helium coolant flow in the primary circuit and it is within the reactor primary circuit pressure boundary. In engineering tests the electric-magnetic bearings developed by INET were employed in the full-scale prototype of the helium circulator. In 2014 the prototype was operated at full-power, full-speed tests in a hot state and under a nitrogen environment for 100 hours and 500 hours. It performed well in 2015 and 2016, in helium environment tests identical to HTR-PM operating conditions, including 50 hours’ full power operation, 50 life cycles, and 500 transients in six extreme conditions. After successful tests, the helium circulators were manufactured and delivered.
The fuel handling system allows for on-load loading and unloading of the fuel pebbles. Fuel pebbles can be discharged one by one, with their burnup measured, and broken ones can be recognised and separated. Two full-scale test facilities have been established for air flow and helium flow conditions, respectively. The movement of fuel pebbles was tested in the air flow under standard conditions. A full-scale prototype of the full handling system was tested under 7.0MPa helium condition and successfully completed 500 hours automatic operations in October 2016. The fuel handling system is now being commissioned on site.
The steam generator is the key component to transport nuclear heat from the primary circuit to the secondary circuit. It contains 19 helical heat transfer tube assemblies, each with a heat transfer capability of 13MWt. A prototype assembly was tested and verified in the helium engineering test facility and the steam generator engineering test facility. Conditions up to 80% full power at full scale were tested in 2017, and the hot helium flow in the primary loop reached 7MPa/750°C and the steam flow in the secondary loop reached 13.25MPa/570°C. On 31 October 2018, the steam generator passed factory acceptance tests.
The full scope simulator
As a commercial-scale demonstration nuclear power plant, HTR-PM requires a full scope simulator to train and certify the operators.
An engineering simulator was built with most of the HTR-PM subsystems for key reactor models to analyse the operational characteristics of the HTR-PM. Tests compared well with the design data.
The functions of the engineering simulator were also extended to include validating control systems, simulating startup and shutdown processes, and simulating commissioning programs.
R&D experience in developing key models and the engineering simulator fully supported developing the full scope simulator of the HTR-PM, which was delivered in December 2015. From then on, the full scope simulator was used to train operators in full time operation.
In 2016 and 2017, the operators and senior operators for the HTR-PM passed all the training, practices, and examination aspects on the full scope simulator, and were awarded operator licences. In addition to training and certification, the full scope simulator is now being used to validate operational procedures and support the HTR-PM project in the commissioning phase.
Author information: Zuoyi, Director of the Institute of Nuclear and New Energy Technology at Tsinghua University; Yujie Dong, Deputy director & deputy chief engineer at the Institute of Nuclear and New Energy Technology; Weiwei Qi, Head of HTR Major Project Office at the Institute of Nuclear and New Energy Technology; Jun Sun, Associate Professor & Head of Reactor Physics, Thermal Hydraulics, and Simulation at INET