Databank

POSIVA Report 1996-17

Back

Name:

Interim Report on Safety Assessment of Spent Fuel Disposal TILA-96

Writer:

Timo Vieno; Henrik Nordman

Language:

English

Page count:

187

ISBN:

951-652-016-2; 1239-3096

Summary:

Working report: INTERIM REPORT ON SAFETY ASSESSMENT OF SPENT FUEL DISPOSAL
TILA-96



The TILA-96 study, a continuation and update of the TVO-92 safety analysis, confirms that the
planned system for spent fuel disposal fulfils the proposed safety criteria. Provided that no major
disruptive event hits the repository, initially intact copper canisters preserve their integrity for
millions of years and no significant amount of radioactive substances will ever escape from the
repository. Impacts of potential canister failures have been analysed employing conservative
assumptions, models and data. In the case of single canister failures, the results show that the
margin to the proposed regulatory criteria is more than three orders of magnitude in the dose rate
and more than four orders of magnitude in the release rates into the biosphere. Even in the extreme
cases, where all 1500 canisters are assumed to be initially defective or to ”disappear”
simultaneously at 10 000 years in the "worst possible location" in the repository, all the proposed
safety criteria would be passed. When realistic modelling and data are used in the consequence
analyses, the results show negligible releases and doses.

The most apparent difference between the candidate sites for the spent fuel repository is that
Olkiluoto is presently located at the coast of the Baltic Sea, whereas Kivetty and Romuvaara are
inland sites lying about 200 metres above the sea level. At the depth of 500 metres, groundwater is
brackish or saline in Olkiluoto, whereas it is fresh in Kivetty and Romuvaara. Because of the
ongoing postglacial land uplift Olkiluoto, too, is likely to become an inland site after some
thousands of years.

No extraordinary characteristics are required from a site in the crystalline bedrock to ensure the
long-term safety of a deep repository for spent fuel. Local variability and heterogeneity within the
investigation sites are of greater importance than the differences between the general properties of
the areas. Attempts at an "objective" ranking of the candidate sites in terms of a quantitative post-
closure performance index are not meaningful. There seems to be little prospect to discriminate
between inland sites with non-saline groundwater in terms of radionuclide transport.

The site of the spent fuel repository shall be selected in the year 2000. Characterisation and
evaluation of the candidate sites should now emphasise three topics: i) Evaluation of the
geological structure and fracturing of the bedrock, ii) Identifying of bedrock volumes, where the
repository could be constructed, and their assessment from the construction point of view, iii)
Assessment of geochemical conditions (the role of brackish and sulphate-rich, saline, and very
saline groundwaters).
INTERIM REPORT ON SAFETY ASSESSMENT OF SPENT FUEL DISPOSAL
TILA-96



The TILA-96 study, a continuation and update of the TVO-92 safety analysis, confirms that the
planned system for spent fuel disposal fulfils the proposed safety criteria. Provided that no major
disruptive event hits the repository, initially intact copper canisters preserve their integrity for
millions of years and no significant amount of radioactive substances will ever escape from the
repository. Impacts of potential canister failures have been analysed employing conservative
assumptions, models and data. In the case of single canister failures, the results show that the
margin to the proposed regulatory criteria is more than three orders of magnitude in the dose rate
and more than four orders of magnitude in the release rates into the biosphere. Even in the extreme
cases, where all 1500 canisters are assumed to be initially defective or to ”disappear”
simultaneously at 10 000 years in the "worst possible location" in the repository, all the proposed
safety criteria would be passed. When realistic modelling and data are used in the consequence
analyses, the results show negligible releases and doses.

The most apparent difference between the candidate sites for the spent fuel repository is that
Olkiluoto is presently located at the coast of the Baltic Sea, whereas Kivetty and Romuvaara are
inland sites lying about 200 metres above the sea level. At the depth of 500 metres, groundwater is
brackish or saline in Olkiluoto, whereas it is fresh in Kivetty and Romuvaara. Because of the
ongoing postglacial land uplift Olkiluoto, too, is likely to become an inland site after some
thousands of years.

No extraordinary characteristics are required from a site in the crystalline bedrock to ensure the
long-term safety of a deep repository for spent fuel. Local variability and heterogeneity within the
investigation sites are of greater importance than the differences between the general properties of
the areas. Attempts at an "objective" ranking of the candidate sites in terms of a quantitative post-
closure performance index are not meaningful. There seems to be little prospect to discriminate
between inland sites with non-saline groundwater in terms of radionuclide transport.

The site of the spent fuel repository shall be selected in the year 2000. Characterisation and
evaluation of the candidate sites should now emphasise three topics: i) Evaluation of the
geological structure and fracturing of the bedrock, ii) Identifying of bedrock volumes, where the
repository could be constructed, and their assessment from the construction point of view, iii)
Assessment of geochemical conditions (the role of brackish and sulphate-rich, saline, and very
saline groundwaters).

Keywords:

File(s):

Interim Report on Safety Assessment of Spent Fuel Disposal TILA-96 (pdf) (8.4 MB)


Back


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.
Close

Cookies

To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see aboutcookies.org. You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.

Close