A stochastic assessment using LISA

European Union

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Industrial research and development

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• Sciences et techniques

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• Publié par: EUROPEAN-UNION
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 4 Mo

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Commission of the European Communities
Study of the Feasibility and Safety of the
Disposal of Heat Generating Wastes into
Deep Oceanic Geological Formations
Part 1 : Radiological Safety Assessment
A stochastic assessment using LISA: models, data and results.
Directorate-General for Science, Research and Development
Joint Research Centre
EUR 11754 EN July 1988 Commission of the European Communities
Study of the Feasibility and Safety of the
Disposai of Heat Generating Wastes into
Deep Oceanic Geological Formations
Part 1 : Radiological Safety Assessment
A stochastic assessment using LISA: models, data and results.
Carlo Flebus* and David Stanners**
* University of Liege
Mécanique des Fluides Géophysiques - Environnement
B5, Sart Tiiman
400 Liege, (Belgium)
** Commission of the European Communities
Joint Research Centre - Ispra Establishment
Radiochemistry Division Bid. 46
21020 Ispra (VA) Italy
Contract N° 2847-85-12 ED ISP Β
Series Editor: C.N. Murray
Directorate-General for Science, Research and Development
Joint Research Centre
EUR 11754 EN July 1988 Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person
acting on behalf of the Commission Is responsible for the use which might
be made of the following Information.
Cataloguing data can be found at the end of this publication.
The articles published in the JRC series "Study of the Feasibility and
Safety of the Disposal of Heat Generating Wastes into Deep Oceanic
Geological Formations" are grouped into five topical areas:
1. Radiological Safety Assessment
2. Geochemical and Geotechnical Studies
3. Engineering Investigations for Sub-Seabed Emplacement
4. Deep Ocean Instrumentation Development
5. Simulation and Testing Facilities.
The articles have been written by specialists at the request of the Joint
Research Centre, and form an integral part of the programme of research
carried out by the Commission of the European Communities on this option.
Luxembourg: Office for Official Publications of the European Communities, 1988
© ECSC - EEC - EAEC, Brussels-Luxembourg, 1988
Printed in Italy TABLE OF CONTENTS
Page
PREFACE
1. INTRODUCTION 1
2. ASSESSMENT METHODOLOGY 5
2.1 Uncertainty Analysis 8
2.2 Sensitivitys 13
3. CALCULATION TOOLS5
3.1 Description of the LISA Code
3.2 Data Post Processing - The LISAG and
SPOP Codes 21
4. THE APPLICATION OF LISA TO THE SUB-SEABED OPTION 27
4.1 Models and Data
4.2 Waste Package and Radionuclide Inventory8
5. MATHEMATICAL AND TECHNICAL DESCRIPTION OF THE
LISA SUB-MODELS 3
5.1 The Near-Field Model1
5.1.1 Penetrator and canister degradation
model2
5.1.2 Release model of radionuclides from
the glass matrix 35
5.1.3 The Near-Field computer model 40
5.2 The Far-Field Model 49
5.2.1 Transport equation for radionuclides
in the sediment column
5.2.2 Far-Field Computer model and input
parameters 5
5.3 The Biosphere Model
5.3.1 The Mark-A ocean box model 64
5.3.1.1 Mathematical model description 62 The computerl 7
5.3.2 Pathways to man model and dosimetry9
5.4 Processing of the Biosphere Model Output Doses 8
6. RESULTS OF THE PRELIMINARY LISA SUB-SEABED SIMULATIONS 91
7. RESULTS OF THE STOCHASTIC-UNCERTAINTY ANALYSES FOR THE
GME AND SNAP SITES 103 Page
8. SENSITIVITY ANALYSES 115
8.1 GME site results6
8.2 SNAP sites 127
8.3 Comparison of sites 131
9. SUMMARY AND CONCLUSIONS3
10. ACKNOWLEDGEMENTS
11. REFERENCES9
APPENDIX: DATA USED FOR THE STOCHASTIC-UNCERTAINTY ANALYSIS 14
A.l FOREWORD 14
A.2 GME SITE
A.2.1 Basic radionuclide data 143
A.2.2 Waste inventory and canister data4
A.2.3 Sediment column data5
A.2.4 Ocean parameters used in the Mark-A model 147
A.2.5 Pathways and dose model data 15
A.3 SNAP SITE 15
A.3.1 Basic radionuclide data
A.3.2 Waste inventory and canister data7
A.3.3 Sediment column data
A.3.4 Ocean parameters used in the Mark-A model 158
A.3.5 Pathways and dose model data9 PREFACE
Research has been underway in a number countries for some years now
aimed at assessing the feasibility and safety of the proposed sub-sea­
bed disposal option for high-level radioactive wastes. In 1977 the in­
ternational Seabed Working Group (SWG) was set up to study this option
under the auspices of the Nuclear Energy Agency of the Organisation for
the Economic Cooperation and Development (OECD-ΝΕΑ). The work described
in this report springs from this cooperative research effort.
Towards the end of 1985 the Radiological Assessment Task Group (RATG)
of the SWG requested the Commission of the European Communities' Joint
Research Centre (JRC) to perform the probabilistic analysis of the be­
haviour of the sub-seabed disposal option using the LISA code (Long
term Isolation Safety Assessment), developed by the Risk Assessment
Group at Ispra. The results of the stochastic-uncertainty/probabilistic
analysis contained herein are the outcome of this work and form part of
the overall radiological assessment conducted by the RATG /l/.
The purpose of the present report is to give a comprehensive descrip­
tion of the work conducted by the JRC. This will enable the reader to
enter into the details and background of the models employed for the
probabilistic analysis, their development, interpretation into FORTRAN
computer code and application to the probabilistic framework of the
LISA safety assessment code /2/. Close reference is made throughout the
report to the co-operative work of the RATG and the other SWG task
groups. This mainly concerns the part they played in the formulation of
some of the models and in the assembly of the input data set. 1. INTRODUCTION
The proposal to use the uniithified sediment strata under the deep
oceans as a repository for high-level radioactive waste has received
much attention over the last decade. The assessment of the feasibility
and safety of thi:; disposal option involves many tasks including the
investigation of the performance of the major barriers (waste form,
canister, sediments) and biosphere components (ocean and biota). Model­
li rig is required to help interpret data from such studies and evaluate
consequences of results, especially when an understanding oí the per-
formance oí the whole system is required.
Modelling a repository system and its evolution is a complex task. It
requires the identification of sets of scenarios for analysis, corre­
sponding, for example, to an expected evolution of the disposal system
over the period of time considered. This might include normal and acci­
dent situations. Moreover, the assessment must include a probabilistic
treatment of the system uncertainties, both in the input data and on
the model results. The present work covers this latter aspect, being a
stochastic-uncertainty analysis of the normal or base case evolution
scenario for sub-seabed disposal. Two sites are investigated, Great Me­
teor East (GME) in the Madeira Abyssal Plain of the North-East North
Atlantic, and the South Nares Abyssal Plain (SNAP) in the South-West
North Atlantic.
The term "stochastic-uncertainty" analysis has been used throughout
this report in place of the more commonly used term "probabilistic
analysis" for two main reasons. Firstly, the functions used to describe
the variable parameters are not strictly probability distributions due
both to the paucity of appropriate data in many cases and with the fre­
quent difficulty of determining the relevant information from the
available data. Secondly, no account of the probability of occurrence of the analysed events vis taken into consideration, so that the end
results of the analysis aya dose rates and not risks.
The normal evolution or tase case scenario corresponds to the following
sequence of events. The starting point is the successful emplacement of
the waste packages at thtLr prescribed depth (mean value 50 m) in the
selected zones of the study site (GME or SNAP). The packages (penetrat-
or and canister) slowly corrode eventually leaving the vitrified waste
exposed to the sediment pore water. As the glass gradually dissolves
into the interstitial water the radionuclides are released to migrate
into the surrounding sediments. The nuclides undergo interactions with
the sediments leading to varying degrees of retardation in their move­
ment depending on the chemical properties of each nuclide and of the
host sediment. The radionuclides reaching the sediment-ocean interface
at the sea bottom are released into the water column by diffusion where
they slowly disperse, becoming involved in various mixing and scaveng­
ing processes. Eventually they enter the food chain contaminating ma­
rine foodstuffs where they become available to man through ingestion
and inhalation.
The models and data used here for evaluating the consequences of this
base case s