Andra s Safety Options of French underground facility Cigéo- a milestone towards the licensing application

Transcription

1 Andra s Safety Options of French underground facility Cigéo- a milestone towards the licensing application S. Voinis, M. Rabardy, L. Griffault

2 From 1991 towards the licensing application- successive safety milestones More than 25 years of acquisition of scientific and technical knowledge and the development of safety methods appropriate to deep geological disposal. Since 2011, the DGR project entered an industrial design phase and has become the Industrial Center for Geological Disposal- Cigéo

3 The Cigéo project will comprise consecutive phases: An industrial pilot phase will start during the Cigeo s initial construction and will end when reaching repository s routine operations. This phase comprises inactive operations such as tests performed on installed equipment and active operations, i.e. operations in the presence of waste packages A Challenge is to be able to tell a story with solutions but also with open options to make it «as evolutionary as possible». During operation, periodic safety examinations will be conducted conference - Nov- 2016

4 Siting - A progressive and converging approach Detailed survey in Location of repository surface facilities to be presented during the Public Debate 3- Area defined for location of repository U/G facilities after local consultation (2009) and detailed geological survey from the surface Additional above-ground geological survey Transposition zone of URL results (proposed 2005) 1- Siting started in 1992 with a National call for volunteering; URL licensed 1998

5 A Key milestone - The Cigeo 2015 Safety Options According to article 6 of the French decree n 1557 the 2 nd of November 2007 : Submitting Safety Options is a possibility for nuclear operators to plan for the construction license application process and the related ASN review of their safety principles and approach To begin the review process required as part of the construction license application process They do not constitute a safety demonstration Nor a detailed description of the technical solutions Nor a detailed description of scientific supporting evidence Key objectives of the safety options: Stabilize the safety standards reference documents, approaches, and input data, particularly the package design assumptions used; Stabilize the design and safety options and identify potential evolutions of the design; Stabilize the various scenario categories (encompassing those used as the basis of design calculations, those not included in DOS-Expl, normal evolution scenarios and "what-if" scenarios); Present an initial "bounding scenarios" impact assessment conference - Nov- 2016

6 Specificity of Cigéo Surface and underground facilities «classical» nuclear surface facility : Receiving, handling and preparing waste packages «underground nuclear facility» Depth > 500m Limited geometry Ramp ( ~ 4 km) Post- closure phase After the closure of the disposal facility, the protection of human health and the environment must not depend on institutional monitoring or control as there is no certainty that this can be maintained for more than a limited period

7 Safety options a challenge issue - to show that all families of waste envisaged to Cigéo are covered Andra has integrated the various families of waste (around 100) and their level of knowledge Lifetime > 100,000 years, ~10,000 m 3 of HLW, ~70,000 m 3 of ILW-LL 60% of ILW-LL and 30% of HLW destined for Cigeo have already been produced For operational phase - The waste package is an important safety component Establishment of sizing characteristics Allocation of operational safety functions between waste package components ( matrix, container, overpack..) For post closure phase - The radiological inventory is an important input for the post-closure quantitative safety assessment Post-closure safety functions of waste packages Application of factors of margins according to knowledge level Distribution of the radioactivity inventory to have a safety demonstration independent of delivery schedules for a bounding field for impact Method to retain safety model for waste release

8 Illustration - IL-LLW canisters : a wide variety of primary packages Design results mainly from operational requirements ( standardization, containment, criticality..) concrete can contribute to post-closure safety (favorable conditions) but is not a requirement (brings margin) a need to verify that they do not disturb the safety function ( e.g void, chemical..) 7 models of canisters ILLW In concrete 6 different partitioning design 6 different cover design

9 Illustration - A need to take into account the uncertainties regarding the location of waste packages with time There are plans for the emplacement of each ILW waste package family into one specific vault of the architecture. However, as present availability chronicles cannot be granted till the closure date, waste package families have been re-arranged in order to get conservative (high) radioactive content

10 Need to adapt classical guidance to take into account the underground characteristics Nuclear safety authority guidance Need to adapt some of the rules currently applied to surface nuclear facilities to an underground nuclear one (e.g. fire) Illustration on Fire Guidance Two apparently opposite approaches : Nuclear approach Underground construction/tunnel approach Necessity of reconciling these two approaches Guidelines set up by Andra with the contribution of fire experts from nuclear operators from various bodies (tunnels, firemen, industrial risks)

11 Safety options - both operational and post-closure safety functions and associated requirements 1 Operation safety functions 2 Post closure safety functions Contain radioactive substances Limit dose rate Avoid criticality Avoid heat accumulation Avoid radiolysis gas accumulation Isolate the waste from surface phenomena and human actions limit the transfer into the biosphere of the radioactive substances and toxic elements in the waste 1 oppose water flow; 2.limiting the release and immobilizing of radionuclides and toxic elements 3.delaying and reducing the migration

12 Very favourable characteristics of the Callovo-Oxfordien- the pillar for post closure safety High depth : > 400 m High thickness : > 140 m Very low permeability Stability with time High capacity of retention Post-closure safety Main Safety options Organization of the Layout and engineered barriers play complementary rules Ramps/shaft seals HLW ( vitrified matrix, overpack)

13 Need to conduct operational and post closure safety analysis in parallel Complementarity of operational and post closure safety analysis Both based on science/technological knowledge

14 The safety options present the four classes of post-closure scenarios Normal evolution domain Altered Evolution Scenarios Human Intrusion scenarios What-if scenarios Quantitative assessment of the scenarios (indicators) Normal Evolution Domain To check that the disposal satisfies the protection objectives (radiological and toxicological) and the safety functions Consider expected evolution of the disposal (time and space) from its closure to the long term Assuming all safety functions are realized Considering a set of evolutions which appear quite probable referring to the NSA guide of 2008 Includes two situations A reference situation considering the disposal as designed (assumptions rely on the best available knowledge) A situation based on the post-closure safety requirements applicable to Cigéo and most conservative data when no specified requirements

15 Altered Evolution Scenarios and What-if scenarios Identified through the qualitative safety analysis of risks and uncertainties and Based on the design and safety functions Based on the scientific and technological knowledges and associated residual uncertainties The understanding of internal processes (including their coupling) and their evolution with time From the closure (initial state at closure To the long term (up to one million years) Includes a comparison with international OECD FEP s database of 2012 Comprehensiveness of the analysis

16 The malfunction scenarios - list of AES and what-if malfunction scenarios of closure structures 3 AES Scenarios Malfunctioning at the interface between the clay core and the Callovo-Oxfordian of seals ( surface-bottom, drift ) 3 What-if Scenarios Malfunctioning due to a combined/cumuli of the clay core failure and malfunction at the interface between the clay core and the Callovo-Oxfordian

17 Inadvertent human intrusion scenarios

18 Safety options presents dimensioning situations, excluded scenarios during operational phase Normal mode situations corresponds to the operation of the facility which includes statuses and operation including maintenance and scheduled shutdowns Dimensioning incident and accident situations All operating situations outside normal operation which may change the protection of the interests but whose design measures limit the consequences for the public and the environment Dimensioning extension accident situations Very unlikely situations which may occur following multiple failures of safety systems or accumulations of events Situations excluded Physically impossible situations or situations for which a sufficient number of measures enables exclusion conference - Nov- 2016

19 Illustration of main safety and design options Reduce fire risks and heat loads Choice focused on funicular system compared to truck for the ramp, Electric driven equipment Using life rail (only emergency batteries) Optimization: Water based hydraulic fluid Use of proven equipment Vertical descent = no feedback for such masses Funicular = mostly used for transport of persons Reduce human occurrence and improve automation Reduce human failure Reduce dose rates

20 Illustration - Bounding dimensioning accident situations and preliminary assessment Room/zone Scenario Impact (msv) Unloading cell 6-meter fall of a primary waste unloaded by the overhead crane in an ET-V following material failure of the lifting chain 10-4 Unloading cell Cask fire involving a primary package at the centralized control station < msv (0.4) ILW-LL hot cell Fall of a disposal package following failure of the forklift 10-6 ILW-LL disposal cell Fire on stacking crane involving a disposal package < msv (0.1)

21 Now and future.. National review of all Cigéo 2015 files by the TSO : Is ongoing Standing committee in May 2017 based on review report by IRSN Official nuclear safety authority position mid 2017 International review by IAEA experts on behalf of the nuclear safety authority (Focus on safety) Seminar in mid November 2016 Official oral presentation on 2016 (positive views and suggestions/recommendations towards licensing) Andra is now preparing the overall safety case ( 2018) towards the licensing application

22 Thank you for your attention