On the morning of September 12, 2021, reactor number 1 of the eagerly awaited HTR-PM project was taken critical for the first time. Initial criticality for any new reactor is a big deal for the people involved in the project; this one is a big deal for the future of nuclear energy. It might also become a big deal for humanity’s ability to effectively reduce CO2 emissions enough to slow climate change.
HTR-PM is a demonstration reactor that uses two identical gas-cooled high temperature modular reactors to produce the heat for a modern, subcritical, 200 MWe steam turbine. The steam system operates at the same temperature and pressure as many recently constructed coal heated steam plants that China has been mass producing for more than a decade as it rapidly industrialized and became one of the world’s leaders in manufacturing, metals production and chemicals.
The press release from China National Nuclear Corporation (CNNC) includes the following statement.
They [HTRs) have broad commercial application prospects in nuclear power generation, combined heat, power and cooling, and high-temperature process heat. They are my country’s optimization of energy structure and guarantee of energy supply. An important path to safety and to achieve the “dual carbon” goal.
China National Nuclear Corporation press release dated 09-13-21 (https://www.cnnc.com.cn/cnnc/xwzx65/ttyw01/1112318/index.html) Note: Original in Chinese simplified, translated by Google Translate
Though the announcement does not specifically include coal furnace replacement, producing steam at the same temperature and pressure as used by modern coal plants qualifies as “high-temperature process heat.”
HTR-PM criticality is the most recent step in a long process of commercializing high temperature gas cooled reactors. Though they have a long history, proponents (like me) believe they are an advanced type of commercial atomic fission power technology. (See the high temperature gas reactor history description below.)
China has been purposefully working on high temperature gas reactor technology development for the past 30 years. They have absorbed lessons from HTR experience in Japan, the United States, the UK, and South Africa while also building their own domestic intellectual property and manufacturing capability. According to the China Huangeng Group Co. LTD (CHGC) press release, the project’s direction includes a strong emphasis on building indigenous capacity to build HTR without outside assistance.
As the world’s first pebble-bed modular high-temperature gas-cooled reactor, the demonstration project used more than 2,000 sets of equipment for the first time, and more than 600 sets of innovative equipment, including the world’s first high-temperature gas-cooled reactor spiral-coil once-through steam generator. The first high-power, high-temperature thermal magnetic bearing structure main helium fan, the world’s largest and heaviest reactor pressure vessel, etc., are of great significance to promote my country to seize the world’s leading advantage in the fourth-generation advanced nuclear energy technology.
China Huangeng Group Co. LTD press release dated 09/12/21 (https://www.chng.com.cn/detail_jtyw/-/article/ccgb60va5Gwc/v/962479.html) Note: Original in Chinese simplified, translated by Google Translate
Aside: The above includes a statement that helps explain why HTRs have not been universally popular and why they still face headwinds, even from nuclear energy advocates. Each reactor module produces about 250 MWth, which compares to about 3300 MWth in a 1000 MWe PWR or BWR. Even with higher temperatures and higher efficiency, each core can produce 1/10th of the electricity of light water reactors, but the first HTR pressure vessel is described as “the world’s largest and heaviest pressure vessel.” Pressurized gas has a far lower capacity to move heat than pressurized water.
But there are more factors to be considered in atomic fission power plant economics than the size and weight of the pressure vessel. End Aside.
China is rightfully proud of its accomplishment in achieving HTR-PM initial criticality. There are many more steps in the journey, but this step is important. It marks one more milestone in the process of creating nuclear fission power stations that can take full advantage of the world’s vast coal fired power station infrastructure.
Brief high temperature reactor history
Arguably, the basic idea for HTRs was initially proposed during the earliest days of nuclear power development – immediately following WWII. Dr. Farrington Daniels proposed a high temperature gas reactor as the heat source for what was then a modern steam system. The Daniels Pile project was initially funded by the Manhattan Commission and gathered some momentum before being abruptly cancelled by the nascent Atomic Energy Commission in early 1947.
In the late 1950s Germany’s Rudolf Schulten followed through on the idea and led the project to build the world’f first high temperature pebble bed reactor, the AVR. That small (46 MWth, 15 MWe) prototype operated for about 20 years. Its construction began in 1960, it was connected to the grid in 1967 and it was shut down in 1988.
The US and the UK built their own version of high temperature reactor prototypes, the US at Peach Bottom and the UK’s Dragon reactor at Winfrith in Dorset.
General Atomics, the US company that designed and built the successful prototype at Peach Bottom built a scaled up, significantly different design at Ft. St. Vrain (330 MWe). That reactor had a dismal operating history due to several FOAK system design problems. By the time the defects were corrected, the designer had lost all of the follow on orders. The plant owners had lost patience, didn’t want to own and operate an orphan plant design and shut the system down.
Germany built a larger, 300 MWe pebble bed reactor (THTR) but that reactor had unfortunate timing. It began operating in 1985 with a 1000 day temporary operating license. Before THTR had operated long enough to complete testing and rise to full power operation, the Chernobyl reactor exploded. Reports claimed that the graphite moderator was a primary contributor to the accident and there was a widespread, durable misinterpretation that the graphite actually caught fire.
THTR was a graphite moderated reactor. Owners could not convince the public or the regulators that there are fundamental differences between graphite moderated, helium cooled reactors and graphite moderated, water cooled reactors. THTR was shut down in September 1989 when its initial license expired and that license was not extended.
In the 1990s, South Africa invested several billion dollars and a lot of engineering effort in developing the pebble bed modular reactor (PBMR). A primary reason that effort did not achieve success is that it started with the notion that it was reasonable to build a 200 MWe turbine generator with high pressure helium as the working fluid and then to mount that large machine vertically inside a pressure vessel. That concept works on paper, but executing it proved to be extremely difficult and expensive. Before the project ended, designers had decided to mount the helium turbomachine in a more conventional, horizontal alignment, but the South African government had lost patience by that time.
Chinese technologists, led by Prof. Zhang Zuoyi, learned from PBMR’s experience. They chose to step back to what had worked well for the AVR and to gradually make improvements. They built the HTR-10, a 10 MWe prototype system with a helium to water steam generator that helped them learn on an affordable scale while planning for the next iteration.
HTR-10 has operated well as a prototype. Its capacity factor has been modest, but it wasn’t conceived as a steady state, commercial electricity producer. It has been used to test fuels, test materials, test equipment, train operators and refine operating procedures. In other words, it has done what prototypes are supposed to do.
Construction on HTR-PM began in 2012. It has taken a bit longer than initially planned, but part of the delay rests with the fact that some of the necessary components – like the unique, spiral-coil once-through steam generator – were difficult to design and refine into something that could be efficiently replicated.
The Shidaowan site is planned to eventually host 16 more HTR-PMs. There are already plans underway to design and build an HTR-PM600. That system will use pebble bed reactor models – each the same as the reactor modules used for the HTR-PM) to provide the required heat for a 600 MWe steam turbine power station.
