WNISR, 24 December 2021
Grid connection for one of the two modules that make up Shidao Bay-1 nuclear plant took place on 20 December 2021. The plant consists of two High Temperature Gas-Cooled Reactor - Pebble-bed Modules (HTR-PM) located at the Shidaowan site, in the eastern China province of Shandong. Construction start was 9 December 2012 with grid connection originally planned for 2017. The 2 x 100 MW reactors are owned by the China Huaneng Group and operated by the Huaneng Shandong Shidao Bay Nuclear Power Company, Ltd. Upon completion of full power tests on the first unit, the second reactor unit, which went critical in November 2021, will be connected to the grid.
The HTR-PM is promoted as inherently safe, with graphite as a moderator, helium as a coolant and with uranium fuel in the form of tennis ball sized (6 cm) ’pebbles’. Future HTRs are planned for cogeneration, high-temperature heat utilization, and hydrogen production. The China Nuclear Energy Industry Association in welcoming the start of operations at Shidao Bay-1 promoted its safety stating that it is not possible to suffer a fuel meltdown and described it as the world’s first pebble bed modular high temperature reactor.
In fact, it is not the first of its kind. And significant safety issues with high temperature reactors emerged during the 1970s and 1980s. Germany invested considerable efforts in HTRs, including the AVR and THTR-300, both of which used pyrolytic graphite fuel. The AVR (Arbeitsgemeinschaft Versuchsreaktor, or Working Group Test Reactor operated from 1967-1988, and the THTR-300, operated sporadically between 1985-1988. Both were closed mainly due to safety concerns – including lack of sufficient protection against external impact leading to an air ingress with a core fire, and a potential positive void coefficient of reactivity in water ingress events; there also existed excessively high core temperatures.
Anticipating the start-up of the demonstration HTR-PM in China, in 2018, the science journal Joule published an analysis on lessons learned from Germany’s experience with HTR pebble bed fueled reactors which calls for caution with the new Chinese reactors. It concluded that construction of the HTR-PM in China were useful from a research perspective, but that significant safety issues existed with the HTR design, in particular: incomplete understanding of core behavior, dust physics and fuel materials which “means one needs to proceed cautiously”; and that “Important behaviors are not fully understood, the graphite reflectors may not last more than 30 years, and the safety systems may not be able to cope with a beyond-design-basis accident. Of particular note, HTR-PM is not surrounded by a robust, airtight containment to protect the public”. They concluded that HTR’s were in a situation similar to the early light water reactors of the 1960s, which experienced a range of unexpected behaviors and accidents.
With Shidao 1-1 connected to the grid, there are now 53 operating units in China, and 18 additional reactors remain under construction.