Note: This post has been supplemented by Revised: US assessing reported leak at Chinese nuclear power facility.
The Taishan reactors are a pressurized water design (PWR), with two water loops.
- At high temperature and pressure, the primary loop cools the reactor core.
- The primary loop transfers heat to the secondary loop.
- The secondary loop generates steam which powers turbines.
- The turbines turn electric generators.
The primary loop is subject to the intense radiation of the reactor core. Under normal operation this causes radiolysis; a small quantity of water is broken down into free hydrogen and oxygen. In a PWR design, this can be a stable arrangement; the dissolved hydrogen suppresses more radiolysis.
- Radiolysis is a normal source of gas.
If a bubble of free H and O forms somewhere in the piping, it could recombine explosively, so most designs bleed off the gas at the top of the loop. The expected rate of bleed-off is known to the designers. The Framatome report of excessive, progressively increasing gas release indicates gas is being generated by other mechanism(s).
- Metal-water interaction. Many metals, and some semiconductors, are weakly catalytic, accelerating radiolysis. Fuel rods are clad with zirconium, which tends to make gas: Zr + 2 H2O → ZrO2 + 2 H2 . This becomes critical with a core melt-down.
- Dissolved impurities, such as chlorine,and corrosion products, including zirconium, and whatever leaches out of a bad weld.
Why has Framatome approached the U.S. ? The U.S. is the heir to the Manhattan Project knowledge base. Contrary to popular impression, most of the project dollars were spent on chemistry and materials science, not design of the Bomb. Including post war, 307 research reactors were constructed. Since one cannot look easily inspect the inside a reactor core, methods of remote diagnosis were developed.
Samples of water from the high pressure loop have dissolved chemicals with radioactive signatures. Excess gas implies corrosion in the system, but from what? A radiation chemistry analysis of primary-loop water could narrow the scope to a bad weld, (not the worst) or a hot spot in the core (bad).
In the early phase of COVID-19, the Wuhan regional bureaucracy engaged in what could charitably be called self deception. When the Beijing government took charge, China’s response ranked with the best in the world. COVID has left China without visible scars.
A Taishan miscalculation could be much worse. If the containment vessels hold, a Three-Mile Island results, with almost no consequences. If containment fails, you have a Chernobyl or Fukushima.
Are you listening, China?