Tritium Puzzle

By Philip Elmer-DeWitt

The mystery was great enough to disturb even the most jaded cold warrior. Somewhere between Oak Ridge, Tenn., and two manufacturers in England, a total of five grams (0.175 oz.) of radioactive tritium had vanished without a trace. What made the disappearance especially alarming was that the quantity of tritium involved was sufficient, when combined with other ingredients, to build a small nuclear weapon. The U.S. Department of Energy, sensitive to the dangers of nuclear proliferation, last July halted U.S. sales of the gas and moved quickly to explain the losses and assure the public that the missing tritium had not ended up in the hands of a terrorist state.

A little too quickly, it seems. According to a report by the Energy Department's inspector general made public last week, the DOE not only failed to locate the missing tritium but never adequately addressed the possibility that the gas was stolen. In a sharply worded statement that raises questions about what exactly the Government has been doing for the past five months, the inspector general said that earlier explanations attributing the losses to procedural errors or mismeasurements were based more on "speculation than fact." More than a year after the first shortfalls occurred, the report charges, "basic questions concerning ((the)) discrepancies remain unresolved."

Tritium, an isotope of hydrogen that contains two neutrons and a proton in its nucleus, occurs naturally in minute quantities in raindrops and groundwater. But the radioactive gas took on strategic importance in 1952, when the U.S. exploded its first hydrogen bomb. That explosion demonstrated the destructive force that can be released when tritium fuses with deuterium, another hydrogen isotope, to yield helium and a burst of nuclear energy. Today, tritium is used both to enhance the power of atom bombs and in the trigger mechanism of the far more destructive H-bomb. Because it decays at the rate of 5.5% a year, the gas must be regularly replenished if atomic weapons are to maintain their full explosive potential.

Until recently, it was the problem of tritium replenishment that concerned most nuclear experts. Last year the DOE was forced to shut down its only source of tritium, the aging Savannah River nuclear weapons plant in South Carolina, when the reactors there developed cracks and other safety problems. The risk that the U.S.'s nuclear arsenal might soon run out of gas provoked long and acrimonious debates in Congress. In the midst of that controversy word came that the DOE had been making millions of dollars a year by selling surplus tritium overseas. Some of the gas, it was revealed, had vanished while being shipped to British lighting manufacturers.

The tritium in question followed a circuitous route that began at the Savannah River weapons plant. The vast majority of the plant's tritium output ; was purified and stored for use in nuclear warheads. But some 300 grams (10.5 oz.) a year was sent to Oak Ridge, where it was packaged in uranium sponge and sold for commercial use -- primarily as a radioactive marker in biological research or as a source of light in everything from airport runways to luminous watch dials. The apparent losses were discovered when customers complained of discrepancies between the amount of tritium ostensibly exported and the amount that was actually received.

Three separate investigations were launched to explain the discrepancies, but according to the inspector general's report, none of the probes seriously pursued the possibility of illegal diversion. Experts say that although the material was packed in sealed containers, it was sent by commercial carrier and did not receive the special safeguards used for shipments of plutonium or enriched uranium. Last week's report urged a fresh investigation and a tightening of procedures. Critics welcomed the recommendations but wondered why they came so late. Asked Congressman Edward Markey of Massachusetts, who released the report to the press: "Do we have to wait until Pakistan, Libya or South Africa announce they have got an H-bomb before we start taking the risk of diversion seriously?"

With reporting by Seema Paul/Washington