1. Field of the Invention
The present invention relates to devices and methods for monitoring and measuring tritium levels. More particularly, the present invention relates to monitoring the concentration of tritium in aqueous samples.
2. Discussion of Background
Tritium is a radioactive isotope of hydrogen that is produced in nuclear reactors by bombarding lithium with neutrons. Tritium also occurs naturally in small concentrations, and may result from the bombardment of water molecules by a neutron flux or other high-energy radiation. Indiscriminate tritium release to the environment is forbidden by law. Therefore, the presence of tritium in nuclear power generating and production facilities dictates the need for effective tritium monitoring. Furthermore, the sensitivity (or detection limit) of tritium monitors must be appropriate for the particular monitoring application.
Devices and methods for detecting the presence of tritium in liquids and gases are known. Hascal et al, in U.S. Pat. No. 4,618,774, disclose an instrument for measuring tritium and tritium oxide levels in air. The instrument uses a scintillation detector and a pair of scintillators, one serving as a reference. The device compares the measured counting rate of airborne tritium and tritium oxide passing over one scintillator with that of the reference scintillator. The air is condensed onto and evaporated from the surface of the non-reference scintillator.
Osborne et al, U.S. Pat. No. 3,999,066, disclose a system comprising a method and apparatus for continuously monitoring air for the presence of tritiated water vapor. Tritiated water vapor contained in the sample air is transferred to a liquid which is contacted with the air sample. Radioactive noble gases are stripped from the liquid using a gas stream, and the resulting liquid is analyzed for beta radiation of the energy level indicative of the presence of tritium using a detector such as a scintillation counter.
Other methods are also known which monitor tritium levels in liquids and gases. For instance, Corbett et al, U.S. Pat. No. 4,244,783, disclose a method for monitoring tritium levels in the coolant fluid and reactor cover gas of a sodium-cooled nuclear breeder reactor. The tritium is separated by a hydrogen-permeable tube and diffused into a gas discharge device that ionizes the gas. The tritium is monitored by measuring the ionization current produced.
McManus et al, in U.S. Pat. No. 4,835,395, disclose a method and apparatus for continuously monitoring the tritium concentration in liquid aqueous solutions. A series of air streams direct water and tritiated water from the liquid sample to a flow-through ionization chamber. The ion chamber response, along with humidity and temperature measurements, are ultimately used to calculate the tritium content.