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Can Reverse Osmosis Membranes Remove Radioactive Substances from Water —— A Look at Tritium and Other Nuclides
Release Date:
2026-06-10
Source:
In the fields of industrial wastewater treatment and nuclear energy utilization, the removal of radioactive substances has always been a technical challenge. Among them, tritium (Tritium) is often asked can reverse osmosis (RO) membranes filter it out Today, let's take an objective look at the ability of RO membranes to remove different radioactive nuclides from a water treatment technology perspective.
1. What is an RO membrane and what are its filtration limits
Reverse osmosis (RO) membrane is one of the most widely used precision filtration technologies in industry. Its pore size is extremely small, approximately only 0.1 nanometers (nm). For comparison, the diameter of a human hair is about 80,000 nm, a bacterium is about 1,000 nm, and a virus is tens to hundreds of nanometers.
Under pressure, RO membranes allow very small water molecules to pass through while blocking dissolved inorganic salts, heavy metals, organic matter, bacteria, and viruses. Their salt rejection rate typically exceeds 99%.
So, are RO membranes effective against radioactive substances in nuclear wastewater The answer depends on the target.
2. Why can't RO membranes remove tritium
The direct conclusion is RO membranes cannot effectively remove tritium from nuclear wastewater.
This is not because RO technology is insufficiently advanced, but because tritium is a master of disguise.
Tritium (chemical symbol ³H or T) is a radioactive isotope of hydrogen. In nature and nuclear wastewater, tritium rarely exists as a free gas; instead, it replaces ordinary hydrogen atoms and combines with oxygen to form tritiated water (HTO).
- Ordinary water molecule H₂O
- Tritiated water molecule HTO
Titiated water is water itself!
Its chemical and physical properties (such as molecular size, charge distribution, etc.) are almost identical to those of ordinary water. Since RO membranes are designed to let water molecules pass while blocking non-water substances, tritiated water (HTO) — being water — cannot be distinguished from ordinary water (H₂O) by the membrane.
In the eyes of the membrane, they are all water molecules, so tritiated water passes through the RO membrane without obstruction. The industry consensus is that the removal rate of tritium by reverse osmosis is nearly zero.
3. For other radioactive heavy metals, RO membrane is the absolute workhorse
Although ineffective against tritium, do not be disappointed. When dealing with other radioactive heavy metal ions in nuclear wastewater, RO membranes exhibit near-dominant filtration capabilities.
Nuclear wastewater contains not only tritium but also other highly hazardous radionuclides such as cesium-137 (137Cs), strontium-90 (90Sr), and cobalt-60 (60Co).
These elements are not part of water molecules but exist as ions (e.g., Cs⁺, Sr²⁺). In water, these ions combine with water molecules to form hydrated ions, whose size (typically 0.4–0.9 nm) is much larger than the 0.1 nm pore size of RO membranes. In addition, the surface of RO membranes usually carries an electric charge, further preventing these multivalent metal ions from passing through via charge repulsion.
Thus, RO membranes can efficiently (removal rate 99%) retain these radioactive heavy metal ions, concentrating them for safe disposal. This is why in existing nuclear power plant wastewater treatment processes (such as the Advanced Liquid Processing System, ALPS), reverse osmosis technology remains an indispensable key step.
Summary
Simply put, the RO membrane is a sieve, not a magic wand.
- For tritium because tritium has disguised itself as part of the water molecule, the RO membrane cannot filter water out of water, so it cannot be removed.
- For other radionuclides (e.g., cesium, strontium) as they are larger heavy metal ions, the RO membrane can easily and efficiently remove them.
Removing tritium from nuclear wastewater is a global challenge facing the water treatment industry. Viable directions include dilution, low-temperature distillation, or chemical exchange methods, but these technologies are extremely costly and not yet suitable for large-scale industrial application. This reminds us that every water treatment technology has its boundaries — scientific understanding is more important than blind faith.
This article is purely a technical science popularization and does not involve any nuclear safety stance. If you have technical questions, please feel free to leave a message.
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