Abstract. In Finland, Olkiluoto Island has been selected for constructing a spent nuclear fuel disposal facility. With the approaching licensing step, submitting the application for nuclear construction licence in 2012, all components of the safety case are becoming more site-specific. In order to assess compliance with regulatory requirements, a prospective deterministic dose assessment methodology based on the ICRP concept of assessing doses to the representative person was developed and implemented in the interim safety case 2009, to be further refined for the safety case 2012. To facilitate the assessment of doses to the most exposed people and other people at the evolving site, full dose distributions are derived, comprising the dose to each potentially exposed person in each generation.

Different numerical strategies in searching for orphan radioactive sources in the environment by means of a mobile detector system have been evaluated. A carborne 3- by 3-inch NaI(Tl) spectrometric system was used with an unshielded 2 GBq 137Cs source as a test source. In this paper, a previous method (MB method), based on a moving average algorithm applied on the gross count rate, was extended and compared with three moving average algorithm methods involving different natural background subtraction strategies. For each method the distance from the road that an orphan source can be detected with a probability of 50% (the critical distance, CD) when driving by is determined. The CD for a 2 GBq 137Cs source improved from 105 m to 130 m when the interference from 40K was subtracted from the 137Cs spectral window. However, when the contribution of other natural gamma-emitting nuclides also was subtracted, the ability to find the 137Cs source was reduced.

A car-borne NaI(Tl) spectrometric system was used together with a 137 Cs source to obtain realistic data in the search of unshielded and semi-shielded orphan sources. The PSC (potassium stripped counts) method was used to estimate the influence by the shielding on the detection ability. A reduction of about 5% in the critical distance was obtained for the semi-shielded source. A curve fitting method was also developed and evaluated. The results showed inferior ability to find the source, compared to the PSC method. However, it can be a useful complementary tool, for characterization of the source shielding, and estimation of the distance from the road.

The role of excavation damaged zone (EDZ) in a KBS-3 type repository for spent nuclear fuel depends significantly on the design of the engineered barrier systems such as tunnel backfill since one obvious function of the backfill is to prevent the growth of EDZ. Main results of EDZ studies based on using 14C-PMMA method carried out at Äspö Hard Rock Laboratory in Sweden, and at Research Tunnel at Olkiluoto in Finland by Posiva and SKB in co-operation are presented. The significance of the results is evaluated quantitatively and qualitatively. The EDZ around the deposition hole on migration of radionuclides diffusing out of a waste canister was found unlikely to be a significant migration route in the absence of large hydraulic gradients. According to the study the EDZ caused by state-of-the-art drill and blast excavation adjacent to walls and roof of deposition tunnels was found negligible, however the EDZ adjacent to deposition tunnel floor is evidently more extensive and more significant.

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