This article gives suggestions for disposing High Level Waste (HLW). The remarks below apply to both vitrified waste after reprocessing and spent fuel, both in the UK and for disposal throughout the world.
In 1981, a comprehensive comparison of options for burial of UK vitrified HLW was published by UKAEA Northern Division (Burton and Griffin ND-R-514 (R)). The study was carried out by a highly experienced team of engineers and technologists. Three main classes, all of which involved surface storage for 100 years or so to reduce the heat load on rock after burial, are outlined below.
A. Deep burial of the waste in relatively thin steel packages lowered down vertical boreholes in the floors of access tunnels, followed by a relatively thin bentonite backfill.
B. Deep burial of HLW containers overpacked in thick (300cm) steel or cast iron in a horizontal mode in tunnels surrounded by a thick backfill of bentonite.
C. Horizontal tunnel emplacement as in B but above sealevel, where host rock could be drained, bypassing the backfilled region, into the original access tunnels.
In A, the barrier to activity migration is mainly geological. Being below the water table, activity could eventually be leached by groundwater, whose movement would be slow; absorbers in the rock would further delay activity transport. Difficulties could be:
(1) The surface store for the highly active packages would need high active operations during periodic refurbishing in the 100 years of storage.
(2) Manipulation of packages from vertical to horizontal and the reverse would be necessary and tunnel heights increased to do this at load points.
(3) The high active operations in (2) and (3) would have to be done by future generations.
(4) Obtaining the data to predict water movement round the waste would require extensive drilling in the host rock – itself a possible source of increasing water flow. Using the complex data in a large computer programme will only mask uncertainties.
(5) Any accidents such as jamming of packages in boreholes could be difficult and dangerous to put right.
In system B, previously referred to as TSD, the thick overpack would allow conventional engineering in storage (open air with a light security fence) and in manipulating the twenty-ton packages horizontally into the tunnels, followed by backfilling with bentonite. All operations would be hands-on. The thick shield and bentonite would inhibit corrosion and hence access of water to the waste for a very long time. The hazard from the disposed waste would then be reduced to a tiny level, probably below that of dumped LLW or non-active toxic waste. The first few tens of metres into the access could eventually be sealed to prevent unauthorised tampering; though inconvenient, backfill could be removed if necessary to take packages away. Finding of sites should then be akin to that for LLW or toxic waste with an overhead erosion cover. They should be acceptable to the public and convenient for surface transfers e.g. from Sellafield to Black Combe. The UKAEA report concluded, moreover, that system B would be cheaper than system A, and, having extra and thicker engineered barriers, be much safer. This remains true, regardless of site or emplacement depth.
The concept of B can be further enhanced as in option C by having the emplacement zone above or just below the water table as in a hillside. The original access tunnels would slope up towards it and after backfill round the waste, the water in the host rock would by-pass the load zone to flow into the access tunnels (where it could be channelled through actinide absorber beds to a sump from which seepage into non-potable water zones through a geological barrier could be arranged as recommended in toxic waste disposal). A set of slightly downsloping tunnels and boreholes just above the emplacement zone and draining outwards would reduce water flow near the waste to a slow rate. The main drainage tunnels are wide and will not block; the tunnelling merely removes resistance and improves natural drainage. If it did block, the hazard would merely revert to that of Concept B. This concept C, described in earlier publications as Drained Disposal, would be cheaper in construction than B and have more migration barriers. (Emplacement just below the water table would probably be preferred, to give a positive compression on the bentonite, as in conventional backfilling).
Overall, B and C require little verification and in a rational world there would be no concern over HLW disposal – in fact with the systems of the earlier article for ILW, there are no serious disposal problems with nuclear waste at all. Unfortunately, in the UK, NIREX/NDA have persistently chosen to ignore the UKAEA work. Recent NDA reviews of global approaches in this field have only mentioned other countries – the UKAEA recommendations of tunnel disposal are decades in front of those abroad.
The author has contacted NIREX/NDA on numerous occasions. No sensible technical objections to Thick Shield/Drained (TSD) systems have been raised. Priority has been given to looking at concept A, even though it is clearly inferior. In spite of setting up public consultancy meetings (MRWS) TSD or Drained Disposal ideas have never appeared on the agenda. Complaints to CoRWM and DECC have revealed that neither have control over NDA, in spite of the latter spending vast sums of taxpayers money. (Since NIREX/NDA have spent 30 years investigating System A, it is unlikely that they will be successful in the next 30 years! Meanwhile, the UK will pour billions into an inferior concept). Hopefully, the basics of this article may be discussed sometime at MRWS meetings or open publications; they are easy to understand and the public can then decide there and then the general direction of new investigations. Huge savings could be made, which should be welcomed by the UK Government and public in the present straitened finances of the nation. Similar reactions would probably arise abroad.
Bob Burton is author of Nuclear power, pollution and politics (1990, ISBN: 978-0-415-03065-6)Related ArticlesOld meets new