There is a nuclear power plant in Changjiang Li Autonomous County in Hainan. In addition to continuously providing electricity, this nuclear power plant also has a by-product - pearls. Why do nuclear power plants produce pearls? Will pearls produced by nuclear power plants contain radiation? Today, let’s talk about pearls produced in nuclear power plants.
Nuclear power white butterfly oyster pearl finished product, photo: Liu Xuan
Pinctada maxima - Producer of "Australian White" pearls
To be precise, of course it is not the nuclear power plant that produces pearls, but the pearl oyster - Pinctada maxima, also known as the white butterfly oyster - that is cultured in the sea around the nuclear power plant.
Pinctada maxima, image source: Wikipedia
You may not have heard of the name of this oyster, but the pearls it produces are one of the treasures in the pearl world - Australian White. The reason why it is called "Australian White" is because the main producing area of this kind of pearls was Australia.
Of course, such pearls can also be produced in the Philippines, Indonesia and other places, so they are also called "South Sea pearls". Pinctada maxima is also distributed in our country, and they are mainly concentrated in relatively warm waters, such as the Leizhou Peninsula, Hainan, Taiwan and other places in the southernmost part of Guangdong.
"South Sea Pearl" produced in Indonesia, picture source: Wikipedia
Beginning in the 1960s, they were heavily fished for the Pinctada maxima oyster. At present, they have become national second-level protected animals.
These shellfish have very high requirements on water quality and environment. It is very difficult to cultivate them on a large scale and make them produce high-quality pearls. That is why "Australian white pearls" are so precious.
But we all know the truth, why can Pinctada maxima be cultivated around nuclear power plants? This is actually the "mutual achievement" of nuclear power and Pinctada maxima. To understand this, we must first start with the cooling water and warm drainage water of nuclear power plants.
Cooling water and warm drainage
The current mainstream power generation principle of nuclear power plants is to use the heat generated by the nuclear reactor core to boil water. The water vapor generated by the boiling water will push the turbine blades to convert kinetic energy into electrical energy.
After the water vapor completes its task of driving the turbine, it is not discharged directly. Instead, it needs to be cooled back into liquid water, and then the cycle is repeated. The process of cooling water vapor back into liquid water requires a large amount of cooling water.
For coastal nuclear power plants, cooling water is of course pumped from the surrounding sea. After the cooling water completes the task of cooling and cooling, it also needs to be discharged back to the sea. The temperature of the water discharged back to the sea is often higher than that of the surrounding seawater, so it is also called "warm drainage".
These warm water discharges entering the environment may have a certain impact on the ecosystem of the surrounding sea areas, so special assessments are required before the construction of nuclear power plants.
When the Changjiang Nuclear Power Plant was established, it certainly went through such an assessment to ensure that the warm water discharge would not cause damage to the surrounding ecology. However, Changjiang Nuclear Power Plant has gone a step further. They have also reused the heat from the warm water, which is a true "use of waste heat".
Schematic diagram of pearls produced by shellfish organisms. Source: Shanghai Museum of Natural History
Nuclear power plants and Pearl oyster "mutually achieve each other"
As we mentioned earlier, shellfish such as Pinctada maxima prefer warm waters, and the warm drainage water from the nuclear power plant can just keep the water temperature in a small area around the nuclear power plant at a warm level.
This provides conditions for large-scale cultivation of Pinctada maxima.
At the same time, when selecting sites for nuclear power plants, they will also choose sparsely populated areas with relatively stable hydrological conditions. The seawater quality here is generally very good, which is another necessary condition for the growth of Pinctada maxima.
In addition, there is another important factor that makes nuclear power plants and Pearl oyster "mutually successful".
Because the increase in water temperature caused by warm drainage may cause phytoplankton to multiply in the sea area around the nuclear power plant, if the phytoplankton reproduces too vigorously, it may cause marine disasters such as red tides (which can be simply understood as algae flooding).
Some algae blooms may block the cooling water inlets of nuclear power plants, thereby endangering the safety of nuclear power plants. Engineers at nuclear power plants originally wanted to find ways to reduce the occurrence of such disasters.
For filter-feeding shellfish like Pinctada maxima, one of their important food sources is phytoplankton. Therefore, cultivating Pinctada maxima around nuclear power plants can alleviate the problem of massive growth of phytoplankton to a certain extent.
If the mother-of-pearl oyster fills its stomach, it can grow healthily and produce pearls. Humans have eliminated the potential red tide crisis in the sea areas around nuclear power plants, so it is said that the Pinctada maxima and nuclear power plants are "mutual achievements."
Are pearls produced by Pinctada maxima radioactive?
The next question is, will pearls cultivated in the sea around nuclear power plants be contaminated by radiation? In fact, the warm water from nuclear power plants does not cause radiation pollution.
On the one hand, the warm water from a nuclear power plant does not directly contact the core of the reactor, and it does not even count as a secondary contact.
The reactor type of Changjiang Nuclear Power Plant is a pressurized water reactor. There is no direct contact between its core and the heated water, and the cooling water is used to cool the heated water vapor.
During cooling, the cooling water and water vapor are not in direct contact, so they are very far away from the "radiation source". This kind of water is completely different from the nuclear wastewater that caused controversy before.
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The cooling water is only in the area marked by the red box and does not directly contact the core. Image source: Wikipedia
On the other hand, in order to ensure nothing goes wrong, the cooling water must also undergo radioactivity testing before being discharged into the sea, and it can only be discharged if it meets the standards. Therefore, we do not have to worry about the radioactivity of pearls produced by Pinctada maxima.
Besides, the Pearl oyster itself is a very "delicate" shell. The fact that such delicate shells can grow here and produce high-quality pearls is the best testament to the quality of this water area.
Changjiang Nuclear Power Station and the cultivation of giant pearl oysters can be said to be models of industrial cooperation. Warm water, which once caused a headache for nuclear power plants, can now use "waste heat" to allow giant pearl oysters to grow better.
In return, the giant pearl oyster eats a large number of reproduced phytoplankton, eliminating potential red tide hazards, and at the same time breeds precious pearls. It can be said to be "killing three birds with one stone."
References
[1] Hainan Changjiang Nuclear Power Plant Units 3 and 4 Environmental Impact Report (Operation Phase) https://www.mee.gov.cn/ywdt/gsgg/gongshi/wqgs_1/202411/W020241125352282968236.pdf
[2] Guangzhou Ocean University, "Pincada maxima" https://bwg.gdou.edu.cn/info/1021/1024.htm
[3] Southern Weekend, "South of the Sea, Nuclear Tide: What does a nuclear power plant that can produce pearls look like?" 》https://www.infzm.com/contents/280201?source=131
Planning and production
This article is a work supported by the Science Popularization China·Creation Cultivation Program
Produced by Science Popularization Department of China Association for Science and Technology
Producer丨China Science and Technology Press Co., Ltd., Beijing Zhongke Galaxy Culture Media Co., Ltd.
Author丨Scientific scraps, popular science creator
Audit丨Dai Li, China Nuclear Industry Corporation, senior engineer of cold source safety
Planning丨Zhang Linlin
Editor丨Zhang Yinuo