in the summary report that TEPCO updates everyday, but I don't remember seeing the formal press release nor I can find one from their site. I'll keep looking (update: they've been found, see below), but according to their daily "Status of TEPCO's Facilities and its services after the Tohoku-Chihou-Taiheiyou-Oki Earthquake" report, tritium has been found at the water intake canal and in the sub drain water near the turbine buildings.
From the latest "Status" report as of 3PM, August 14:
We detected Tritium in the Tritium analysis contained in the seawater sampled at the water intake on June 13.
(Discussing the nuclide analysis of the sub drain water near the turbine buildings) We detected Tritium at the sumpling [sic] survey on June 13.
The June 13 survey seems to be the one and only survey that they have done on tritium, according to TEPCO's status reports. No further detailed information that I've found.
(UPDATE: TEPCO's announcements on tritium, as follows. H/T anon reader)
I do not know the significance of tritium, but from what little I read from a European Commission paper on tritium in 2007, titled "Emerging Issues on Tritium and Low Energy Beta Emitters", it doesn't seem like a very good thing to have around you, to say the least:
Tritium is an isotope of the element hydrogen which is both naturally occurring and manufactured. Its half-life is 12.26 years, decaying to helium (3He) while emitting a beta particle. The beta particles, while of low energy (18.6 keV maximum, 5.7 keV average), have enough energy to produce ionizations and excitations of molecules in their path. Tritium poses no external hazard since the beta particles released during tritium decay cannot penetrate the outer layer of dead skin cells due to their average range in tissue of less than 1 μm, and maximum range of only 6 μm (ICRP, 1983). Because of the low beta energy, dilution throughout all of the soft tissues, and elimination with an average biological half-life of around ten days in adults, tritium as HTO (tritiated water) has relatively low radiological toxicity when compared to other pure beta emitters, such as 32P or 90Sr, or to common betaemitters, such as 131I or 137Cs (ICRP, 1979-82).
Although tritium is not considered as a particularly toxic radionuclide, it presents a concern since it can become part of the biologically necessary hydrogen pool. If released into the environment, the tritium poses a potential internal radiation hazard since compounds containing tritium undergo various chemical transformations resulting in forms which can enter in the body. The majority of tritium in the environment exists as HTO. Because of its mobility in the environment and its biological importance, water is one of the most important compounds of tritium. As HTO, tritium can enter in the body by inhalation, ingestion, or diffusion through the skin. Once inside the body, the HTO diffuses freely and rapidly across cellular membranes, equilibrating throughout the total body water pool. The uniform concentration of HTO will result in the radiation dose being uniformly distributed throughoutthe body.
On the other hand, the tritium from HTO may exchange with hydrogen atoms and thereby become incorporated into organic molecules. HTO is the primary chemical precursor for other chemical forms of tritium. Essentially any organic molecule can incorporate tritium in this manner. Each will have a specialized metabolism associated with it that may result in inhomogeneous distributions of tritium within the body, within individual organs, and even within individual cells.
In general, the more rapidly a molecule is turned over, the more tritium will be incorporated per unit of time and the more rapidly the tritium will be removed from the same molecule. For longer-lived molecules, such as the structural protein collagen, or the phospholipids of some nerve cells, fewer tritium atoms will be incorporated per unit of time and those that are incorporated will be retained for longer periods of time (NCRP, 1979).