Tritium formation

The fact that tritium is formed in nuclear reactors has given rise to some concerns about its radioactivity and its potential effects on the environment and human health.

What is tritium?

There  are three types (or isotopes) of hydrogen. The most common kind has no neutrons in its nucleus. A second form, deuterium, has one neutron, and it accounts for about one in every 6,420 of hydrogen atoms. Concentrating water molecules (H2O) that have deuterium atoms is how “heavy water” is made. Tritium is the third form of hydrogen: it has two neutrons. It is much rarer than deuterium, because the tritium nucleus is unstable. When the nucleus decays, it emits radiation.

Hydrogen isotopes

All three forms of hydrogen occur naturally, but tritium is also produced in nuclear reactors, both when heavy water absorbs neutron radiation, and when uranium is used as reactor fuel. Nuclear power-generating stations do emit tritium into the air and water, but in amounts well below regulatory limits.

How tritium levels are managed

The Canadian Nuclear Safety Commission sets regulatory limits on releases from nuclear facilities into the environment, and tracks these releases to ensure the protection of the public and the environment. Systems, equipment, and processes exist at nuclear facilities to remove and reduce the amount of tritium emitted to air and water to ensure that regulatory standards are complied with, reducing risk to people and the environment.

Tritium is managed in three ways:

  • Tritium concentrations in heavy water used in CANDU reactors are reduced in a process called “detritiation.” This process requires dedicated facilities, two of which are for use with CANDU reactors: one at the Darlington nuclear site in Ontario, and one at the Wolsong reactors in South Korea.
  • Containment and confinement of tritium emissions are accomplished by plants designed with advanced seal technology to prevent leaks.
  • Segregation and recovery of tritium involves the extraction of escaped tritium from gaseous, liquid, and waste streams prior to release.

Radiation from tritium

The type of radiation that tritium emits (beta radiation) is too weak to penetrate human skin, so it is not harmful when tritium is outside the body. Tritium inside the body will contribute a minor radiation dose, but the body will eliminate it quickly, mostly through urination.

Radiation is a natural part of life. On average, residents of Canada receive an annual natural background radiation dose (from sources such as cosmic radiation, natural ores, and food) equivalent to approximately 3 millisieverts (mSv). At the current maximum acceptable concentration for tritium in drinking water (7000 Bq/L), tritium would contribute and extra dose of only 0.1 mSv, or 20-30 times less than the natural background level.

As pictured here, if a person’s annual natural background dose is represented by a 15-L water jug, the amount added by tritium (at 7000 Bq/L) is only a 500-mL personal bottle. Realistically, tritium concentrations tend to be less than one hundredth the limit, so the actual added dose (relative to a 15-L jug) is comparable to a teaspoon.

Radiation from tritium

So, although tritium exposure can pose health risks as a weak carcinogen, several governmental and scientific organizations, such as the United States Environmental Protection Agency (EPA), regard tritium as one of the least dangerous radioisotopes, far less dangerous than many commonly used chemicals. The Canadian public is not at risk from tritium intakes at current levels. Furthermore, biological experiments, observations of humans after accidental intakes of tritium, and routine surveillance of radiation workers have produced no evidence of adverse health effects at these levels.