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It's safe to leave your bunker: Blame that Chinese nuclear plant alarm on fuel rod faults

Meltdown over a non-meltdown

Analysis You may have seen in the news some panic about a Chinese nuclear reactor going wrong, and a warning of an "imminent radiological threat." Well, don't worry: it's a routine fuel rod problem.

CNN claimed an exclusive on Monday after seeing a June 8 memo indicating there was a build up of "noble gases in the primary circuit" of the coolant system in the Taishan-1 nuclear power plant.

The letter was written by nuclear engineering firm Framatome, which is mostly owned by French energy giant EDF and was contracted to design and help run the French-Chinese plant. The facility in the Guangdong province went online in December 2018, and serves the manufacturing hubs Guangzhou and Shenzhen.

Framatome wrote to the US government's Dept of Energy to request permission to access American technical data and resources to help tackle the issue. It was further claimed by the biz that Chinese regulators were increasing the limit on the amount of gas that could be released from the coolant circuit, exceeding French safety standards, to avoid shutting down the plant.

Word of this memo sparked fears of a nuclear disaster being covered up by Beijing. However, the truth is less terrifying.

EDF said the build up of inert gases – understood to be xenon and krypton – was due to a fault with one or more of the fuel rods and their seals. These gases were collected, treated, and released in "accordance with regulations," the power giant added.

As the uranium in the reactor's fuel rods is hit by neutrons and undergoes fission, it splits into smaller elements, including the radioactive isotopes of iodine, krypton, and xenon. Small amounts of these fission fragments are expected to leak, though if the fuel containers are pierced, ruptured, or have some other defects, more material will be released into the coolant loop. This is where the aforementioned gas buildup came from: radioactive fission byproducts escaping from the fuel into the primary coolant circuit. This gas had to be removed from the coolant, and the fuel responsible for the leaks will need to be addressed eventually.

Damage to fuel rods is not unheard of. A US government report from last year stated that, for pressurized water reactors, there are 1.6 leaking fuel rods per failed fuel assembly on average worldwide between 1994 and 2004. Each assembly, we note, typically contains between 170 and 230 rods, and up to 65 per cent of fuel failures in the US were caused by grid-to-rod fretting.

"For pressurized water reactors (PWRs), which are the most common reactor type in the US as well as the type of reactor at the Taishan Nuclear Power Plant, the biggest causes of fuel leaks are debris and grid-to-rod fretting, which occurs when a nuclear fuel rod rubs against the metal spacer grids that hold the rods in place," Katie Mummah, a nuclear engineering PhD student at the University of Wisconsin-Madison, told The Register.

"Less common but still causing occasional failures is corrosion, fabrication defects, and fuel handling errors. Most failures are also quite small, pinhole or hairline cracks. Less common are larger failures which result in fuel pellet wash-out, where a fuel pellet or a partial pellet is able to fall out of the fuel assembly."

Fuel failures ... are undesirable because leaking or damaged fuel assemblies require additional investigation and handling. However, they are not considered a major safety or security concern

She added that a fuel rod issue doesn't usually lead to the shutdown of a reactor. The containers are usually left until the reactor is refueled, and then fixed.

"Fuel failures are generally not considered events that require press releases," she said. "They often cause no change to reactor power level and usually do not cause a shutdown of the reactor.

"They are undesirable because leaking or damaged fuel assemblies require additional investigation and handling, and will eventually require different storage and transportation containers after discharge from a spent fuel pool. However, they are not considered a major safety or security concern."

But what about the detection of admittedly radioactive krypton and xenon? Well, as noble gases, they are chemically inert, so any damage to the actual plant should be minimal or non-existent.

Xenon-133 is one of the possible fission fragments. It has a habit of slipping through pipes and walls, it has a half life of just over five days, and it has been approved by the FDA for mapping lung function and blood flow. The gas decays by beta radiation, and also emits a small amount of gamma rays. Xenon-137, meanwhile, has a half-life of about four minutes, and Krypton-90 has a 32-second half-life, though other fission fragments can have half-lives that are much longer.

A slight elevation in gamma radiation was detected around the plant, which on the one hand suggests some amount of radioactive material escaped or was vented, and on the other, looks like normal background radiation. So, essentially, judging by the numbers from China's nuclear monitors, there is little to worry about.

According to CNN, US officials did not believe this episode was a crisis though said it should be monitored. The Chinese authorities also said the whole affair was a non-issue and that everyone should just calm down. Of course, they would say that, but it appears, in this case, they're probably right.

"Since it was put into commercial operation, the Taishan Nuclear Power Plant has strictly controlled the operation of the units in accordance with operating license documents and technical procedures," the Chinese government told CNN. "All operating indicators of the two units have met the requirements of nuclear safety regulations and power plant technical specifications."

Framatome, meanwhile, said in a public statement that "according to the data available, the plant is operating within the safety parameters." The UN's International Atomic Energy Agency added: "At this stage, the agency has no indication that a radiological incident occurred."

So there it is, a new reactor dealing with some early fuel rod wobbles. Far be it from us to accept the word of energy companies, but if we're gonna panic over a disaster, then it ought to be an actual disaster and not a blip that nuclear engineers are more than capable of handling. You can come out of your bunker now. ®

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