The First Matrix Diffusion Experiment in the Water Phase of the REPRO Project: WPDE 1


Antti Poteri, Peter Andersson, Kersti Nilsson, Byegård Johan, Mats Skålberg, Marja Kyllikki Siitari-Kauppi, Anna Marja Kerttuli Helariutta, Mikko Antero Voutilainen, Pekka Juhani Kekäläinen, Jussi Oskari Ikonen, Juuso Keffe William Sammaljärvi, Lindberg Antero, Jussi Timonen, Jukka Kuva, Lasse Koskinen

Tutkimustuotos: Kirja/raporttiTutkimusraportti


REPRO experiments analysed the matrix retention properties of the rock matrix under realistic conditions deep in the bedrock in ONKALO underground characterisation facility at Olkiluoto, Finland. The objective was to investigate tracer transport in the rock matrix, which was representative to the near-field of the nuclear waste repository, and to demonstrate that the assumptions made in the safety case of the final nuclear waste repository were in line with site evidence.

REPRO investigated the retention properties under different experimental configurations. The present Report describes the first in situ tracer test, the WPDE 1 test (Water Phase Diffusion Experiment). This experiment was performed from 8th of March to 21st of August in 2012 as a matrix diffusion experiment in a single drill hole. Tracer transport took place in the cylindrical circumference of a 2m long packed-off section of the drill hole. This set up enabled matrix diffusion through the wall of the drill hole into the rock matrix, which surrounded the experimental section.

Interpretation of the in situ tracer test was supported by a wide variety of parallel and independent laboratory experiments. This Report also summarises the results of these laboratory measurements of porosity, diffusion, permeability and batch sorption, as well as those of mineralogical and structural studies, which were made on the drill core samples taken from the experimental section of the in situ experiment.

WPDE 1 test was executed using a cocktail of four different tracers (HTO, 22Na, 125I and 36Cl) and when this cocktail was injected such that it created a pulse of short duration. The experimental performance of the test was successful. Measured breakthrough curves were successfully analysed using two independent models. Based on the analyses it was evident that matrix diffusion and sorption in the rock matrix had caused the retention observed in the test. The retention properties of the rock matrix resulting from these models were comparable within the uncertainties of the experimental results.

The tracer test results estimated from the in situ tracer test could be divided into three groups such that 22Na and 125I showed more retention than HTO, and 36Cl showed less retention than HTO indicating sorption and anion exclusion processes. Assuming a zero Kd for HTO and a rock matrix porosity of 0.6 %, based on the laboratory measurements, lead to Dp ~ 2×10‑11 m2/s for HTO in the rock matrix. Additional retention of 22Na and 125I compared to HTO could be addressed using Kd ~ (0.4…1.8) ×10-4 m3/kg, such that Kd for 125I was close to the lower end and Kd for 22Na was close to the upper end of the range. The results for 125I should however be considered very cautiously, because the behaviour of 125I appeared to include uncertainties which probably followed from the non-iodine species of the tracer cocktail during the test. A low retention of 36Cl in the rock matrix was thought to be affected by anion exclusion such that all the pores in the rock matrix were not available for matrix diffusion. The breakthrough curves lead to a diffusivity of 36Cl, which was about a half of an order of magnitude smaller than without anion exclusion, and to porosity available for diffusion, which was about a 1/3 of the values estimated otherwise for HTO.

Penetration depth of the HTO in WPDE 1 have been estimated to be 14–22 mm. Thus, indicating that depth of the connected porosity is at least over 2 cm.
JulkaisupaikkaOlkiluoto, Eurajoki
TilaJulkaistu - 2018
OKM-julkaisutyyppiD4 Julkaistu kehittämis- tai tutkimusraportti taikka -selvitys


NimiPosiva Working Report
KustantajaPosiva Oy


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