Handling of Future Human Actions in the safety assessment SR-Site

Eva Andersson

Outline

•The Swedish system and SR-Site

• Methodology for handling FHA at SKB

• Calculation cases for FHA covered in SR-Site

• Results of FHA assessment in SR-Site

The Swedish system

Backfill

Rock

Buffer

Canister

Spent fuel repository according to KBS-3 at Forsmark

4

SR-Site: safety assessment for a deep repository for spent nuclear fuel. SKB’s licence application march 15 -2011

Strategy and results of Future human actions reported in TR-10-53

• General considerations of FHA

• Methodology applied

• Representative cases

The report can be downloaded from www.skb.se

Development of the methodology used at SKB

• SKB has worked with FHA since late 1990ies.

• The methodology is based to on the conclusion of the NEA working group assessment of future human actions at radioactive waste disposal sites (NEA 1995) and three SKB workshop in1997 and 1998

• Provide a comprehensive picture – involved people from different field of knowledge

• Methodology used in a number of safety assessments at SKB: SR97, SAFE, SR-Can and now in SR-Site. Inputs from the authorities on each safety assessment has been used to update the methodology and calculation cases

General considerations

• Potential for exposure inescapable consequence of deposition in a final repository

• Main focus of FHA assessment is a time period when institutional control has ceased to be effective (300 y or more after repository closure)

• Restricted to global pollution and actions that:

– take place at or close to the repository site,

– impair the safety functions of the repository’s barriers.

– are carried out after the sealing of the repository,

– are unintentional, i.e. are carried out when the location of the repository is unknown, its purpose forgotten or the consequences of the action are unknown, Future generations are responsible for their own actions if they are aware of the consequences

• In line with guidelines from Swedish authorities Future human actions are evaluated separately and not included in base scenarios and risk summations in the safety assessment.

The following systematic approach has been used:

• Technical analysis: Identify human actions that may impact the safety functions of the repository and describe and, in technical terms, justify that such actions may occur.

• Analysis of societal factors: Identify framework scenarios (framework conditions) that describe feasible societal contexts for future human actions that can affect the radiological safety of a deep repository.

• Choice of representative cases: The results of the technical and societal analyses are put together and one or several illustrative cases of future human activities are chosen.

• Scenario description and consequence analysis of the chosen cases.

Technical analysis:

• Actions divided into the categories

– Thermal (heat stores, extract energy etc)

– Hydrological (well construction, dams, drainage systems etc)

– Mechanical (drilling, build rock caverns, shafts, mining etc)

– Chemical (dispose hazardous waste, acidification, chemical accidents)

• Conclusions from the technical analysis

– Actions including drilling or construction in the rock have the greatest potential to impair safety functions

– The site is more favourable for heat extraction than other similar sites

– Someone or something must cover the costs for the action

societal analysis

Conclusion from societal analysis

• It is difficult to imagine inadvertent intrusion given a continuous development of society and knowledge

• However, owing to the long time horizon it is not possible to rule out the possibility that the repository and its purpose will be forgotten, even if both society and knowledge make gradual progress

A set of representative cases

Representative cases for a sealed repository:

• Canister penetration by drilling

• Rock facility in the vicinity of the repository

• Mine in the vicinity of the Forsmark site

In addition:

• Complementary analysis for an incompletely sealed repository

Rock facility in the vicinity of the repository

• Very high water conductivity in the tectonic lens in the upper 150 meter of the bedrock above the repository

• Unfavorable site for tunnel or rock

• Analysis also show that a tunnel at this depth would not affect the ground water flow at repository depth

Mine in the vicinity of the Forsmark site

• The ore potential has been investigated in Forsmark. Siting of the repository has been chosen after this

• An area south west of the repository have potential for iron oxide mineralisation

• No influence on repository safety functions

Deep drilling

Canister penetration by drilling- dose to drilling personnel

Canister penetration by drilling – dose from well

Canister penetration by drilling – dose from using the contaminated soil for agriculture

Incompletely sealed repository

• Repository is left without backfilling and sealing of all parts of the repository

• Results imply that backfill in the deposition tunnels may be lost and that the safety functions in the deposition holes close to the entrance are violated

• If corrosion breakthrough in canisters occur during the next glaciation radionuclides are calculated to reach the surface systems and give rise to dose.

Conclusions

• The calculation cases illustrate that drilling a deep borehole into a canister could give high doses both to drilling personnel and humans settling on the site afterwards

• Leaving the repository without complete backfilling and sealing could violate the safety functions of deposition holes close to the entrance of the repository