Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – Surrounding with specified material or structure
Patent
1996-02-14
1998-04-14
Mai, Ngoclan
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
Surrounding with specified material or structure
588 17, 106738, 106792, 106817, 405128, 976DIG323, G21F 900
Patent
active
057405468
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with the disposal of radioactive waste and in particular with a method of forming a repository for such waste and with a filling material for use in backfilling such a repository.
Proposals for the disposal of low level and intermediate level radioactive waste materials include the long term disposal of such materials in repositories comprising subterranean vaults. In some proposals natural caves or old mine workings are to be used and in other proposals the vault is excavated specifically for the repository.
There has been particular discussion concerning the selection of the appropriate geological conditions for such repository vaults, particularly with a view to avoiding the possibility of ground water seeping into the vault during the very long storage periods contemplated.
Hitherto, proposals for repository vaults have contemplated backfilling the vault to fill voids between radioactive waste disposal packages with a filling material which is impervious to water or becomes impervious. Grouts which have been proposed for this purpose include mixtures of sand and bentonite. Such materials are proposed for backfilling repository vaults in "Management of Radioactive Waste from Nuclear Power Plants"--IAEA-TECDOC-276, a paper presented at a seminar on the management of radioactive waste from nuclear power plants organised by the International Atomic Energy Agency and held in Karlsruhe, October 1981; and also GB-A-2128800 and EP-A-0198808.
In addition, GB-A-2181883 discloses backfilling a repository vault with a "weak filler" to facilitate the possibility of re-opening the vault to remove stored radioactive packages in the event of some need. In this proposal, voids between storage packages in the vault are first partially filled with removable concrete blocks, and then the interstices between the blocks, the vault and the packages are in turn filled with the "weak filler" which is typically a mixture of bentonire and sand. In all the above mentioned prior art documents, the purpose of the filler is to provide an impervious barrier to ground water seepage into the vault. However in spite of proposals to backfill with impervious material, there remain concerns with the possibility of ground water ingress.
The present invention proposes a method of forming a repository for radioactive waste comprising locating the waste in a subterranean vault and backfilling the vault with a filling material which is water permeable and provides a substantial reservoir of available alkalinity such that any ground water permeating through the filling material to the waste has a pH of at least 10.5. Thus, the present invention takes a different approach and rather than attempt completely to prevent ground water seepage, instead contemplates a filling material which is in fact water permeable but which will so load any water seeping through (called pore water) with alkalinity that any such water permeating through to the contained waste will have a very high pH which will inhibit the solubility of the radioelements in the disposed radioactive waste by amounts up to several orders of magnitude. In essence, the vault backfilling material is designed to provide a large reservior of alkaline material in order to buffer i.e. chemically condition the porewater at a high alkalinity for a time scale of 100,000 years or more.
Preferably the filling material has a buffering capacity such that, for ground water (assumed to be deionised) discharging at a rate of 10.sup.-10 meter per second uniformly into one face of a one meter cube of the filling material, the column of water emerging from the opposite face is buffered at pH 10.5 or above for a column length of 2.5.times.10.sup.3 meters over a period of 10.sup.5 years or longer.
Preferably also, the filling material has an hydraulic conductivity at 28 days cured in a sealed condition of between 10.sup.-8 to 10.sup.-10 meter per second. The fractional porosity of the filling material may be in the range 0.4 to 0.6, and the pore radius distribution in the r
REFERENCES:
patent: 4026716 (1977-05-01), Urschel, III et al.
patent: 4205994 (1980-06-01), Moyer, Jr. et al.
patent: 4354877 (1982-10-01), Kawano et al.
patent: 4773934 (1988-09-01), Colin
patent: 4950426 (1990-08-01), Markowitz et al.
patent: 5169566 (1992-12-01), Stucky et al.
patent: 5328508 (1994-07-01), Lin
patent: 5340235 (1994-08-01), Milliken
A. Haworth, et al. "Evolution of the Groundwater Chemistry Around a Nuclear Waste Repository", to be presented at the Scientific Basis for Nuclear Waste Management Symposium of the MRS 1987 Fall Meeting, Boston, U.S.A. 30th Nov.-3rd Dec. 1987.
U. Berner.sup.(1), A Thermodynamic Description of the Evolution of Pore Water Chemistry and Uranium Speciation during the Degradation of Cement PSI-Bericht Nr. 62, Jun. 1990.
U.R. Berner.sup.(2), Thermodynamic modelling of cement degradation: Impart of redox conditions on radionuclide release; 1992, Cement and Concrete Research, vol. 22, pp. 465-475.
"Management of Radioactive Waste from Nuclear Power Plants" IAEA-TECDOC-276 a paper presented at a seminar on the management of radioactive waste from nuclear power plants organized by the International Atomic Energy Agency and held in Karlsruhe, Oct. 1981.
Mai Ngoclan
United Kingdom Nirex Limited
LandOfFree
Repository for radioactive waste-vault backfill does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Repository for radioactive waste-vault backfill, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Repository for radioactive waste-vault backfill will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-649178