Study of the Performance of Sealing Systems for Access Shafts in a High-Level Waste Repository

1992 ◽  
Vol 294 ◽  
Author(s):  
A. Saotome ◽  
K. Hara ◽  
J. Okamoto
Keyword(s):  
Host Rock ◽  
Ground Surface ◽  
Sensitivity Analyses ◽  
High Level Waste ◽  
Radionuclide Transport ◽  
Radionuclide Migration ◽  
Backfill Material ◽  
Disturbed Zone ◽  
Waste Repository ◽  
High Level

ABSTRACTShaft sealing in a high-level waste(HLW) disposal system functions to minimize the water flow passage, and retard the radionuclide transport from the repository to the accessible environment. It is important to estimate the radionuclide migration along the sealed shaft from the viewpoint of the design and the performance assessment of the sealing system.This study presents the results of sensitivity analyses on the radionuclide migration in the vicinity of the access shaft of a repository in order to evaluate the effects of the length of a plug, as well as the number of plugs, and curtain grouts.In this study, the upward hydraulic gradient of the groundwater flow along shafts was used, based on transient coupled thermo-hydraulic analyses around a repository. Hydraulic conductivities of the backfill material and the disturbed zones around the shaft tunnels were also assumed to be one order and two orders of magnitude higher than that of the host rock, respectively.The results show that the velocity of the groundwater within the shaft and the disturbed zone is reduced by a factor of one third by installing a few plugs into the shaft filled with backfill material. The curtain grouts have the effect of retarding the radionuclide migration from the repository to the ground surface at a factor of approximately five. A few plug installations have the same effect. The sealing system properly constituted with backfill, plugs, and grouts can provide the same performance as the original host rock.

Bentonite as a Backfill Material in a High-Level Waste Repository

MRS Bulletin ◽  
1994 ◽  
Vol 19 (12) ◽  
pp. 43-46 ◽  
Author(s):  
Rolf Grauer
Keyword(s):  
Host Rock ◽  
High Level Waste ◽  
Rock Fractures ◽  
Swelling Properties ◽  
Northern Switzerland ◽  
Backfill Material ◽  
Thick Steel ◽  
Waste Repository ◽  
High Level ◽  
Good Retention

The concept for the disposal of high-level radioactive waste (HLW) in Switzerland is illustrated in Figure 1: the waste, solidified in a borosilicate glass matrix, is encapsulated in a 25-cm-thick steel canister which has a minimum life expectancy of 1,000 years. After this time, the heat produced by 90Sr and 137Cs will have dissipated and the repository will have adjusted to the host rock ambient temperature of around 60°C.The steel canisters will be placed in horizontal tunnels, 3.7 m in diameter, at a depth of around 1,000 m in the granite of northern Switzerland, and the tunnels then backfilled. The backfill material, an important link in the chain of engineered and natural safety barriers, satisfies both physical/mechanical and chemical requirements. The most important of these are:• Low hydraulic conductivity compared to the host rock;• Good swelling properties to seal construction-caused joints and rock fractures;• Plasticity to absorb rock movements and to distribute pressure homogeneously;• Good retention of radionuclides; and• Stability over a period of at least 106 years.Economic aspects and availability should also be considered: each canister requires 88 tons of backfill material, or of the order of 250,000 metric tons for the planned repository.

scholarly journals Insights to Repository Performance through Study of a Nuclear Test Site

2000 ◽  
Vol 663 ◽  
Author(s):  
D.K. Smith ◽  
A.B. Kersting ◽  
J.L. Thompson ◽  
D.L. Finnegan
Keyword(s):  
Tectonic Setting ◽  
Test Site ◽  
Yucca Mountain ◽  
Nuclear Test ◽  
High Level Waste ◽  
Radionuclide Transport ◽  
Source Terms ◽  
Nevada Test Site ◽  
Waste Repository ◽  
High Level

ABSTRACTUnderground nuclear test sites offer an unprecedented opportunity to evaluate processes relevant to high-level waste repository performance in the absence of engineered barriers. Radionuclide migration programs at the Nevada Test Site represent a twenty-five year systematic investigation of the diverse radiologic source terms residual from weapons testing and the evolution of the hydrologic source term which comprises those radionuclides dissolved in or otherwise available for transport by groundwater. The Nevada Test Site shares actinide source terms, correlative geology, an identical tectonic setting, similar climate, and a thick unsaturated zone with the adjacent potential Yucca Mountain high-level waste repository and provides a natural laboratory to assess long-term radionuclide transport in the near field. Analog studies may ultimately help validate predictions of radionuclide transport from the potential Yucca Mountain repository.

Effects of Aging on the Solubility of Palladium

1995 ◽  
Vol 412 ◽  
Author(s):  
C. Oda ◽  
H. Yoshikawa ◽  
M. Yui
Keyword(s):  
Aqueous Solution ◽  
Aging Time ◽  
Room Temperature ◽  
High Level Waste ◽  
Anaerobic Conditions ◽  
Dilute Aqueous Solution ◽  
Waste Repository ◽  
Ph Range ◽  
Effects Of Aging ◽  
High Level

AbstractPalladium solubility was measured in a dilute aqueous solution at room temperature in the pH range from 3 to 13 under anaerobic conditions. Crystalline Pd metal was clearly visible and the concentration of palladium in solution decreased gradually with aging time. The palladium concentrations in solution were less than 9.4×10-10M in the pH range from 4 to 10 and increased to 10-7M in the pH range greater than 10. This study suggests that palladium concentrations in certain high-level waste repository environments may be limited by Pd metal and may be less than 10-9M.

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