Tritium Leak at Vermont Yankee

It’s been all over the news for the past few days. Water contaminated with tritium, a radioactive substance, has been leaking out of the Vermont Yankee nuclear power plant. The discoveries began with water containing 22,000 picocuries per liter (ppl, more on this later) in a test well near the plant, continued with water containing one to two million ppl in an open trench, and keeps accelerating today with a report of 150 gallons at 720,000 ppl in an underground storage room.

Part of the story is that Entergy, the owner of Vermont Yankee, told Vermont regulators there were no underground pipes carrying radioactive materials at the plant. Entergy spokesman Rob Williams claimed that this was a mistake rather than a lie. This merely adds the alternative of gross incompetence to the probability of dishonesty. Entergy is searching for the leak while an underground plume of tritium-laced water heads for the nearby Connecticut River.

Those are the reports so far, but there are a number of basic questions confronting Vermonters, as well as our neighbors downstream. What is tritium? Where does it come from? How dangerous is it? What can be done about it?

Tritium is a radioactive isotope of hydrogen. Ordinary hydrogen is made up of one proton and one electron. It is the lightest and most common element in the universe, and, of course, one of the two elements in water. When exposed to radiation, as in a nuclear plant, some hydrogen becomes tritium, consisting of one proton, two neutrons, and an electron. This arrangement is unstable and will eventually decay into helium, releasing beta radiation. Beta radiation is essentially high-powered electrons. Tritium has a half life of about 12.3 years, meaning that if you put 1000 atoms of tritium in a jar and wait 12.3 years you will have 500 atoms of tritium. 500 will have decayed. Another 12.3 years and you will have 250. The rule of thumb for radioactive materials is that they need to sit around for 10 to 20 half-lives (120-240 years in the case of tritium) before they are safe.

So what is a picocurie, and what is a million picocuries in the scheme of things? A curie is a measurement of a radioactive material in terms of disintegrations per second. If a sample of material has 37,000,000,000 (3.7 x 1010) atoms decaying and emitting radiation every second, then that is one curie. A picocurie is a trillionth of a curie, which amounts to 2.2 disintegrations per minute. Thus, a million picocuries per liter (ppl) means that each liter of water emits 2.2 million beta particles a minute.

What does that mean for human health? How dangerous is this stuff? Federal regulations put the safe limit for drinking water at 20,000 ppl. In Europe the limit is 2,000, and in California the limit is 500. I have read that research indicates no safe threshold for tritium. There are a few unpleasant problems with the stuff. Being an isotope of hydrogen, it is part of water molecules themselves. This means it can’t be filtered out of water by any practical means. If it is ingested in water it clears out of the human body in about 10 days, as long as that human body doesn’t drink more tritium-laced water. However, if it is ingested by humans in food it can integrate itself into our tissues and remain for ten years, quietly bombarding us from the inside. It can lodge in our DNA, damaging the genetic code all around it. Its ability to insinuate itself into our systems has caused researchers at Lawrence Livermore Laboratory to assign it an RBE (radiobiological effectiveness) ratio of 1.5 to 5 times that of other radioactive materials. That means that given the same ppl, tritium will cause 2 to 5 times the actual damage of something emitting gamma radiation or x-rays.

Tritium causes all the usual radiological effects: cancer, genetic defects, cell death, birth defects, and loss of fertility.

How much tritium is normal? Tritium is caused not only by nuclear reactions in power plants, but also by cosmic rays hitting our atmosphere. There is a background level of tritium in water of 3 to 24 ppl. That puts the tritium-contaminated water in that trench at somewhere between 42,000 and 660,000 times the usual background level and 50 to 100 times the federal limit.

My conclusion from all this is that the present tritium leak at Vermont Yankee is no small thing. The material is dangerous at low concentrations, persistent in the human body, impossible to filter, and hard to contain. The leak is limited to the area in and around the plant for now, but I can’t imagine the isolation and cleanup is going to be easy.

I’d also conclude that the management at Entergy should start planning for decommissioning Vermont Yankee on schedule in 2012. Even the Douglas administration, long time servant of Entergy, has reacted strongly. I predict that more damning evidence will come out, more tritium will leak, and Entergy will continue its tone-deaf attempts at smoothing things over. Vermont Yankee is a turkey, folks, and it has been in the radioactive oven for a few decades now. Stick a fork in it, it’s done. Let me update that cliché: Stick a really long-handled fork in it and then carefully encase that fork in concrete and let it sit a couple of centuries.

Update on Tuesday, January 26, 2010 at 10:26AM by Minor Heretic

It gets better, or worse, depending on your enjoyment of shadenfreude. An article in the Times Argus this morning reports that VY officials submitted documents showing over 40 buried pipes at the plant. A year ago they said there were none. The scenario of incompetence or ignorance has now been completely superceded by the reality of blatant, unrepentant lying. I would predict that the Vermont Legislature will now stick a fork in Vermont Yankee, hard, with both hands.