Shulou(Shulou.com)11/24 Report--

Li Cundong

School of Physics, University of Chinese Academy of Sciences

Training unit: Institute of Physics, Chinese Academy of Sciences

At 1: 00 p.m. on August 24, 2023 (12:00 Japanese local time), in defiance of the strong opposition of the international community, the Japanese government discharged nuclear sewage from the Fukushima nuclear power plant into the sea. this blatantly puts self-interest above the long-term well-being of the people of the world, bringing huge potential health risks to people all over the world.

Today, it has been a week since the discharge of nuclear sewage from Japan, and we start with the health risks that the discharge of nuclear sewage from Japan brings to people all over the world.

Where does radioactivity come from? the radioactivity in the nuclear sewage discharged from Japan comes from its radioisotopes. Let's first review a piece of knowledge-isotopes: we call different nuclides with the same number of protons but different numbers of neutrons as isotopes. The origin of the name is that these nuclides should be placed in the same place in the periodic table, because the periodic table is classified according to the number of protons.

Radioactivity comes from the spontaneous decay of unstable isotopes.

The nucleus is made up of protons and neutrons. The important role of neutrons is to balance the electromagnetic interaction. In fact, neutrons are not necessary hadrons for nuclei. Hydrogen nuclei have only one proton and no neutrons. However, when the protons are positively charged, there will be a Coulomb repulsion between the protons, which can not form a stable bound state. Note that the intensity of the Coulomb interaction is inversely proportional to the distance, and the closer the distance is, the stronger the interaction is. Therefore, the strong interaction between protons cannot overcome the Coulomb interaction. Therefore, the neutrons which only participate in the strong interaction force but not the Coulomb interaction become the key to balance the interaction in the nucleus.

On the nuclear scale, the strong interaction is characterized by attraction, which can balance the Coulomb repulsion between protons. With the increase of protons in the nucleus, more neutrons are needed, and the number of neutrons in stable nuclides at the back of the periodic table is obviously more than the number of protons. When the nucleus increases to a certain extent, the nucleus will not be stable and will spontaneously decay into a lighter but more stable nucleus. With the increase of the nuclear volume, the force range of the strong interaction between hadrons will eventually exceed, so the number of protons in the nucleus is limited.

For the determined number of protons, too many or too few neutrons will affect the stability of the nucleus, so even the lighter nuclei will have isotopes that can decay spontaneously. You may have heard that the isotopes of hydrogen atoms, deuterium and tritium, correspond to one and two neutrons in the nucleus.

Hydrogen atom diagram, there is only one proton | there are three kinds of spontaneous decay of the nucleus of the network, namely, α decay, β decay and γ decay, which you must have learned in the popular science a few days ago. However, it should be noted that no matter which kind of decay, the nucleus produced after decay is often in the excited state, which will deexcite spontaneously to a stable state with lower energy. this process is accompanied by the release of energy, which is released in the form of photons.

The radiation energy produced by isotope decay is higher, which is ionizing radiation. Ionizing radiation may cause damage to biological tissues such as the human body.

How radioactive is the nuclear sewage? the radioactivity in the nuclear sewage produced by the Fukushima nuclear accident comes from the radioactive isotopes in it. there are more than 60 isotopes in the initial nuclear sewage:

The Japanese side has also taken corresponding measures to remove radioisotopes.

They used a multi-radionuclide removal device (Advanced Liquid Processing System,ALPS) to remove all the radioisotopes except tritium.

The main principle of multi-nuclide removal device is adsorption. After treating the wastewater with Cs-137 and salt, iron salt and carbonate are added for coprecipitation pretreatment to remove the components that may cause adsorption effect in the wastewater. In this step, α nuclides, Co-60, Mn-54 and other nuclides are removed, and Ca, Mg and other nuclides are removed by carbonate. Then the wastewater passes through activated carbon, titanate, ferricyanide, impregnated activated carbon, titanium oxide, chelating resin and resin in turn. The expected effect of the device is that the concentration of Cs-134 and Cs-137 is reduced from the original 10Bq / mL to below the detection limit of 0.27Bq / mL and 0.32Bq / mL, and the level of β radioactivity is reduced from 10 ^ 5Bq / mL to below the detection limit (except tritium).

The picture comes from the network where Bq is a unit of radioactivity, defined as the number of nuclei that decay per unit time of a radioactive source, and 1 Bq means 1 nuclear decay per second. Bq / mL is the radioactive concentration.

In fact, the multi-nuclide removal device cannot remove tritium from nuclear sewage, so even the treated nuclear sewage can not actually meet the discharge standards. the preliminary results after the initial thermal test show that there are still a variety of radioisotopes in nuclear sewage that do not reach the detection limit.

Before the discharge, Tokyo Electric Power Co., Ltd. announced the concentration of radionuclides in nuclear sewage, but so far only it has tested the nuclear sewage, and Tepco has rejected the requirements of South Korea and other countries for nuclear sewage testing. A few days ago, there was even news that the employees of Tepco self-exploded and 70% of the nuclear sewage was still unqualified. It can be said that the credibility of the concentration of radioisotopes in nuclear sewage published in Japan is questionable.

At present, in addition to tritium, there may also be Cmur14, Sr-90, Imur129, cesium and other radioisotopes in nuclear sewage. The picture below shows their half-life.

Does radioactivity have to be harmful now, we have to understand the effects of nuclear radiation on the human body.

First of all, it is clear that putting aside the dose and talking about the harm is unscientific, and the nuclear radiation within the safe dose is harmless, just like everyone doing CT, there is no need to worry too much. According to the relevant national standards: the basic standard of ionizing radiation protection and radiation source safety (GB 18871-2002).

The safe dose values of radiation are as follows, this standard is aimed at the protection of ionizing radiation and the safety of radiation sources in medical, industrial, teaching and other environments.

For the public, the annual effective dose should not exceed 1mSv. Under special circumstances, if the annual average dose received for 5 consecutive years does not exceed 1mSv, the effective dose received in a single year can be increased to 5mSv. The annual equivalent dose of eye lens is 15mSv, and that of skin is 50mSv.

For occupational exposure, the average annual dose for 5 consecutive years should not exceed 20mSv, the effective dose in any year should not exceed 50mSv, the annual equivalent dose of eye lens should be 150mSv, and the annual equivalent dose of limbs or skin should be 500mSv.

The above values can be used for reference. At present, the country has launched radiation monitoring of the surrounding sea areas, please take the monitoring results as standard, do not be alarmist, and do not mind your own business.

Explain the units above. Sv is a unit of radiation dose.

The common unit of radiation dose is the absorbed dose, which refers to the energy absorbed by the irradiated material per unit mass, in Gy,1Gy=1J / Kg, which is a very large unit.

Considering that different types of energy will produce different biological effects, the same absorbed dose can not reflect the biological effects, so there is a different weight factor for different types of radiation, which is the equivalent dose, and the unit of equivalent dose is J / kg, but we use another unit Sievert:Sv here. The commonly used unit is mSv.

The weight factor corresponding to different types of radiation | the figure is derived from references because different tissues have different sensitivity to radiation, and the probability of random effects caused by radiation is also different, so we usually assign a weight factor to different tissues. After considering this factor, we have the concept of effective dose, and the effective dose unit is also Sv.

Weight factors corresponding to different biological tissues | the figure is derived from references. The next question is what is the harm of radiation.

As mentioned above, low levels of radiation are harmless to the human body. In fact, we are exposed to background radiation from space all the time, but this radiation level is also very low, and the average effective dose to humans is only about 3 mSv / a. In modern medicine, we even use radioactivity to do some tests, such as CT. Because of this, the effect of radiation on human body is also a key research topic in radiobiology.

Let's also give a brief introduction here.

In 1986, the United Nations Scientific Committee on the effect of Atomic radiation stipulated that low LET (linear energy transfer density) radiation with a dose of less than 0.2 Gy or high LET radiation with a dose rate of less than 0.05 mGy / min was called low level radiation. At present, those whose dose meets the above conditions and the dose rate is higher than 0.05mGy / min is called low dose radiation. At present, there is still controversy about whether low-dose radiation is harmful to human body. According to the traditional theory, the effect of radiation on human body is linear and unthreshold, that is to say, the effect of radiation on human body increases linearly with the radiation dose, and there is no threshold, zero exposure is zero risk. However, recent studies have also questioned this theory, some studies believe that low-dose radiation may be beneficial to the human body, can induce immune function enhancement, promote normal cell proliferation and so on.

But there is no doubt that medium and high levels of ionizing radiation (above 0.5Gy) can cause harm to the human body. Therefore, we should still pay attention to the results of our radiation monitoring in the surrounding sea areas.

What happens if the radiation exceeds the standard, and then let's take a brief look at the possible impact of radioactive isotopes in nuclear sewage if they do bring high levels of radiation. I hope it doesn't exceed the standard.

The first is tritium.

The position of tritium in the periodic table tritium is the main radioisotope in nuclear sewage. With a half-life of about 12 years, its properties, like hydrogen atoms, can participate in various chemical reactions and can be ingested through food, drinking water, or skin. In fact, tritium is quite common in water, and very low concentrations of tritium have no effect. However, if a large amount of tritium is ingested, tritium can release low-energy β particles after entering the biological tissue, which can interfere with the development of embryo or fetus and cause DNA damage, chromosome mutation, cell death, cancer, genetic and reproductive effects and so on.

Cmure 14

The position of carbon in the periodic table Cmur14 can participate in the carbon cycle in the form of solids, liquids or gases, so it is easy to enter the human body through various ways. Because carbon is an essential element of the human body, Cmur14 can be integrated into the body's proteins, nucleic acids and other biomolecules and cellular components. Cmur14 can also release β-rays, which can cause DNA damage, and then cause cell damage or mutation.

Imura 129

The position of iodine in the periodic table Imur129 mainly accumulates in the thyroid gland after entering the body, which affects the thyroid function. It has a long half-life and can have a lasting impact on the environment and organisms. In acidic medium, Imur129 is easy to volatilize into the air, mainly through diet and inhalation into the body. Imur131 is also radioactive, but its half-life is only about 8 days. Now we also use it for therapeutic purposes. In accidents involving the release of radioactive iodine, people often take stable iodine under the guidance of professionals, and long-term low-dose iodine exposure may cause the risk of thyroid cancer.

Sr-90

The position of strontium in the periodic table Sr-90 is β-radioactive, but its migration is affected by the content of pH, organic carbon, the total amount of Ca and Mg in the soil, and may settle somewhere to form a higher concentration. Strontium and calcium belong to the second main group with similar chemical properties. After being absorbed by the human body, strontium is easy to settle in bones, teeth and so on. Its radioactivity may affect bone metabolism.

Cesium

The main radioisotopes of cesium in the periodic table are Cs-134 and Cs-137. These two radioisotopes are easily absorbed by the soil and are not easy to migrate in the soil. The pH value of the soil is an important factor affecting its absorption. When pH is 8, it has the maximum adsorption capacity, so the area with the highest concentration of radioactive cesium may be in the surrounding sea area. Cesium is more easily absorbed by the fetus, and high doses of radioactive cesium can cause chromosome breakage, increase the mutation rate, and can be passed on to the next generation.

The level of nuclear radiation should still be subject to national monitoring, and our government will never let it go.

For everyone, eat more vegetables and fruits to ensure the intake of vitamins, vitamins can repair cell damage caused by radiation, exercise more and maintain a positive attitude. The country does not regard people's health as a child's play as some governments do.

May the world be a better place!

References:

Wang Xudong. The thermal test of multi-nuclide removal device ALPS was carried out [J]. Radiation Protection Newsletter, 2013 Regent 33 (05): 44-45.

[2] basic standards for ionizing radiation protection and radiation source safety

[3] how to understand the quantity and unit of radiation dose

[4] to understand the common units of radiation

[5] what is low dose irradiation?

Wei Xinfeng, Wang Rui, Yi Junxuan, etc. Research progress on biological effects of low dose radiation [J]. China radiation Hygiene, 2022, 31 (01): 113-118, 128.

Chen Haiyan, Yang Chunyu, Xu Rui, etc. Environmental and health effects of nuclear sewage-- from Fukushima nuclear sewage discharge [J]. China radiation Hygiene, 2022 and 31 (01): 105-112.

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: Li Cundong

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