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Dial Trimphones This only affected dial Trimphones, which had the special luminous dials. The Hazards "The low-energy Beta radiation energizes the fluorescent coating and is then absorbed by the glass. The secondary radiation (Bremsstrahlung) which then arises has been confirmed by both the Post Office Radiological Officer and the Radiological Protection Service to be much less than the recommended maximum for luminous wrist watches. The tube is expected to have a useful life of at least 10 years." [Post Office Electrical Engineers' Journal, Vol 58 Part 1 April 1965] A continual fluorescent glow is thus emitted for immediate location and use in the dark. Tritium is a weak beta emitter, although the particles have enough energy to penetrate the human skin. However, they can be stopped effectively by plastic, glass, or metal. So unless the Betalight tube is broken, the risk is minimal. Recovery and Storage In the early Nineties, as old Trimphones were recovered from the field, the dials were separated, the GTLD (Gaseous Tritium Light Device) or Betalight was removed and held in a licensed secure storage facility pending the completion of a safe recovery process. In 1994-95 BT collected more than 24,000 Trimphone dials. In 1995-96 BT collected 13,341 Trimphone dials for safe storage. By 1996 a total of nearly 2 million Trimphones had been recovered and storage of so many dials was a potential hazard... Processing Thus in 1996, BT joined forces with the Atomic Energy Authority [AEA Technology] at Winfrith in Dorset to develop technology for recycling the gas. Using robotic arms, over 7,500 Trimphones were processed during 1996-97. In October 1997 AEA Technology reported... "The Recycling and Waste Management team at AEA Technology at Winfrith, Dorset, has reached a milestone in its £6.8 million contract with British Telecom to recover tritium from disused ‘Trimphones’. The team has now dismantled all of the dial mechanisms supplied so far - over one million, out of a total consignment of 1.8 million tritium devices to date. This represents a throughput of some 8,000 Trimphone dials a week over the three years of the project operations. It also paves the way for the final tritium recovery operations to begin in 1998. The project is scheduled to end in 2001 after four years of recovery work." The total amount of tritium involved was estimated to have an activity of 6,000 Terabecquerels. It was anticipated that over 90% of the original tritium would be recovered, purified and enriched, and then sold for use in medical and industrial applications, and the residual waste disposed of conventionally. |
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