Chinese modular high temperature nuclear reactors reach full power and 42% thermal efficiency. [View all]

[NNadir]

After many years of thinking big reactors were the best path forward, I changed my mind and became an aficionado of small modular reactors, running at high temperatures with heat exchange networks.

These Chinese reactors are not exactly what I had in mind, although they do feature something I like very much, nuclear islands working in tandem to drive non-nuclear devices.

Currently, most nuclear reactors (with some exceptions) run on the steam (Rankine) cycle, at fairly low thermal efficiency, around 33%. This means that quite of bit of energy is wasted as heat rejected to the environment, this at an environmental cost. It would be better to extract more exergy (work) from the system and thus reject less heat.

The Chinese are on the path to do this; they're reviving some very creative ideas from the past.

Here's the article describing the achievement:

China's demonstration HTR-PM reaches full power

Excerpts:

The demonstration High Temperature Gas-Cooled Reactor-Pebble-bed Module (HTR-PM) at the Shidaowan site in Shandong province of China has reached its initial full power with "stable operation under the mode of 'two reactors with one machine'".

The plant features two small reactors that drive a single 210 MWe turbine. It is owned by a consortium led by China Huaneng (47.5%), with China National Nuclear Corporation subsidiary China Nuclear Engineering Corporation (32.5%) and Tsinghua University's Institute of Nuclear and New Energy Technology (20%), which is the research and development leader.

They reported that it had reached "initial full power" on 9 December and "this operating state has verified that all systems of the demonstration project meet the design functions, laying the foundation for the project to be put into operation".

The Huaneng Shidaowan High Temperature Gas-Cooled Reactor Demonstration Project is the world's first pebble bed modular high-temperature gas-cooled reactor, and having achieved the initial full-power operation of the dual reactors and "tested the operation control capability" of it in "two reactors with one machine" mode, the operators describe it as "laying the foundation for future commercial operation".

The first reactor reached first criticality in September 2021 and the second one that November. The connection of the first of the unit's twin reactors took place in December 2021.

The HTR-PM features two small reactors (each of 250 MWt) that drive a single 210 MWe steam turbine. It uses helium as coolant and graphite moderator. Each reactor is loaded with more than 245,000 spherical fuel elements (‘pebbles’), each 60 mm in diameter and containing 7 g of fuel enriched to 8.5%. Each pebble has an outer layer of graphite and contains some 12,000 four-layer ceramic-coated fuel particles dispersed in a matrix of graphite powder. The fuel has high inherent safety characteristics, and has been shown to remain intact and to continue to contain radioactivity at temperatures up to 1620°C - far higher than the temperatures that would be encountered even in extreme accident situations, according to the China Nuclear Energy Association...

There are a number of features I don't like, including helium coolant, since the world supply of helium is at severe risk. I fully expect this element to become an exotic by product of the reprocessing of nuclear fuel where it will be formed by the alpha decay of short lived nuclei like Cm-242, Pu-238, and Cm-244.

Still the concept of "nuclear islands" distinct from non-nuclear conversion systems, in this case a turbine, is a good idea, allowing for swaps of nuclear components, and the ability to change reactor missions.

This system is operating at 42% thermal efficiency, better than Rankine systems, but we can and should go much, much, much further.

Have a nice evening.