Databank

POSIVA Report 1997-11

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Name:

FEPs and Scenarios Auditing of TV0-92 and TILA-96 Against International FEP Database

Writer:

Timo Vieno; Henrik Nordman

Language:

English

Page count:

103

ISBN:

951-652-036-7; 1239-3096

Summary:

Working report: POSIVA-raportti POSIVA-97-11, 97 sivua
ISBN 951-652-036-7


FEPS AND SCENARIOS - AUDITING OF TVO-92 AND TILA-96 AGAINST
INTERNATIONAL FEP DATABASE


ABSTRACT

The NEA International Database of Features, Events and Processes (FEPs) relevant to
the assessment of post-closure safety of radioactive waste repositories has been
compiled by a working group within the Nuclear Energy Agency (NEA) of the OECD.
The main parts of the database are a master list of 150 generalised FEPs and the original
project-specific databases containing descriptions, comments and references on the
FEPs. The first version of the database includes in total 1261 FEPs from seven national
or international performance assessment projects. All project FEPs are mapped to one or
more of the FEPs in the master list.
The aim of the auditing was to discuss how the FEPs in the international database have
been treated in the TVO-92 and TILA-96 safety assessments on spent fuel disposal,
where no formal methods were applied to develop scenarios. The auditing was made
against all the 1261 project-specific FEPs in the international database. The FEPs were
discussed one by one and classified into categories according to their treatment in TVO-
92 and TILA-96 or in the technical design of the disposal system.
The International FEP database is a good first step towards to the proposed International
FEP Encyclopaedia and serves as a handbook, especially for the more exotic FEPs. The
exercise did not reveal anything substantially new from TVO-92 and TILA-96, nor did
it provide much new firewood for forthcoming assessments. The strong sides as well as
the weak points of TVO-92 and TILA-96 are comprehensively recognised and identified
in the reports itself and in their regulatory reviews. In the auditing, the most significant
open issues (for example, gas generation and release, saline groundwater, glaciation) fell
into the ”discussed” in TVO-92 and TILA-96 category. Most of the FEPs audited into
the ”not considered” category deal with factors which, in our mind, are not very
important issues.
A similar scenario approach as in TVO-92 and TILA-96 is proposed also for the
forthcoming TILA-99. This entails that the analysis will be based on a system of i)
a base case showing that in the expected normal repository conditions initially intact
copper-iron canisters will preserve their integrity for a very long time, ii) a set of
reference scenarios where the consequences of initially defective and later
”disappearing” copper canisters are evaluated, and iii) a large number of ”what if” type
sensitivity analysis scenarios (or variants). Steady, time-invariant boundary conditions,
circumstances and parameter values will be used within each variant. Special emphasis
shall be put on the weak points and issues identified in TVO-92 and TILA-96 and in
their regulatory reviews, including description of the normal evolution of the disposal
system, site-specific analysis of flow and transport, alternative fuel dissolution models,
potential poor performance of the bentonite barrier, gas generation and release, effects
of (very) saline groundwater, and postglacial faulting.

Keywords: FEP, scenario, safety, performance, assessment, analysis, spent fuel, nuclear
waste, disposal


POSIVA-raportti POSIVA-97-11, 97 sivua
ISBN 951-652-036-7


FEPS AND SCENARIOS - AUDITING OF TVO-92 AND TILA-96 AGAINST
INTERNATIONAL FEP DATABASE


ABSTRACT

The NEA International Database of Features, Events and Processes (FEPs) relevant to
the assessment of post-closure safety of radioactive waste repositories has been
compiled by a working group within the Nuclear Energy Agency (NEA) of the OECD.
The main parts of the database are a master list of 150 generalised FEPs and the original
project-specific databases containing descriptions, comments and references on the
FEPs. The first version of the database includes in total 1261 FEPs from seven national
or international performance assessment projects. All project FEPs are mapped to one or
more of the FEPs in the master list.
The aim of the auditing was to discuss how the FEPs in the international database have
been treated in the TVO-92 and TILA-96 safety assessments on spent fuel disposal,
where no formal methods were applied to develop scenarios. The auditing was made
against all the 1261 project-specific FEPs in the international database. The FEPs were
discussed one by one and classified into categories according to their treatment in TVO-
92 and TILA-96 or in the technical design of the disposal system.
The International FEP database is a good first step towards to the proposed International
FEP Encyclopaedia and serves as a handbook, especially for the more exotic FEPs. The
exercise did not reveal anything substantially new from TVO-92 and TILA-96, nor did
it provide much new firewood for forthcoming assessments. The strong sides as well as
the weak points of TVO-92 and TILA-96 are comprehensively recognised and identified
in the reports itself and in their regulatory reviews. In the auditing, the most significant
open issues (for example, gas generation and release, saline groundwater, glaciation) fell
into the ”discussed” in TVO-92 and TILA-96 category. Most of the FEPs audited into
the ”not considered” category deal with factors which, in our mind, are not very
important issues.
A similar scenario approach as in TVO-92 and TILA-96 is proposed also for the
forthcoming TILA-99. This entails that the analysis will be based on a system of i)
a base case showing that in the expected normal repository conditions initially intact
copper-iron canisters will preserve their integrity for a very long time, ii) a set of
reference scenarios where the consequences of initially defective and later
”disappearing” copper canisters are evaluated, and iii) a large number of ”what if” type
sensitivity analysis scenarios (or variants). Steady, time-invariant boundary conditions,
circumstances and parameter values will be used within each variant. Special emphasis
shall be put on the weak points and issues identified in TVO-92 and TILA-96 and in
their regulatory reviews, including description of the normal evolution of the disposal
system, site-specific analysis of flow and transport, alternative fuel dissolution models,
potential poor performance of the bentonite barrier, gas generation and release, effects
of (very) saline groundwater, and postglacial faulting.

Keywords: FEP, scenario, safety, performance, assessment, analysis, spent fuel, nuclear
waste, disposal


Keywords:

FEP; scenario; safety; performance; assessment; analysis; spent fuel; nuclear waste; disposal

File(s):

FEPs and Scenarios Auditing of TV0-92 and TILA-96 Against International FEP Database (pdf) (1.3 MB)


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