SEMINARIO SAFETY IN NUCLEAR FUSION PLANT 24 Aprile 2015 T. Pinna Safety report for a nuclear fusion...

SEMINARIOSAFETY IN NUCLEAR FUSION PLANT

24 Aprile 2015

T. Pinna

Safety report for a nuclear fusion plant: generalities

2Seminario Fusione 2015 – Safety report for a nuclear fusion plant: generalities

Pericoli e rischi nella fusione nucleare

Un pericolo è qualsiasi fonte di danno potenziale o di danno per qualcosa o di effetti

negativi sulla salute di qualcuno in determinate condizioni di lavoro.

In sostanza, un pericolo è qualsiasi cosa od evento in grado di provocare danni o effetti

negativi ad individui e/o ad attrezzature e/o ambiente.

Talvolta viene definito come pericolo il danno reale o l'effetto sanitario causato piuttosto

che l’entità che è in grado di generare il danno. Per esempio, la tubercolosi (TBC)

potrebbe essere definita un pericolo, ma, in generale, dovrebbe essere definito come

pericolo il battere od i batteri che causano la tubercolosi

It is a physical situation with potential for human injury, damage to property, damage to

the environment or any combination of these

HAZARD:PERICOLO



Rilascio incontrollato di energia

un oggetto che potrebbe cadere da un'altezza (energia potenziale o

gravitazionale),

una reazione chimica (energia chimica),

il rilascio di gas compresso o vapore (pressione, temperatura

elevata),

apparecchiature rotanti (energia cinetica), o

scariche elettriche (energia elettrica),

sostanze radioattive (radiattività).

HAZARD:PERICOLO



Si identifica con il termine rischio la possibilità o la probabilità che un

evento indesiderato avvenga in un tempo specificato e/o in specificate

circostanze. Ad esempio, che una persona sia danneggiata in caso di esposizione a un pericolo, che proprietà subiscano dei danni o attrezzature vadano perse.

Un modo di definire il rischio è ad esempio:

tra un numero di persone "N", esposte ad un pericolo (hazard), un certo

numero, "Y", di persone subisce un danno – > Rischio = Y/N

It is the likelihood of undesirable events (hazard) to occur within specified

time and/or specified circumstances

RISK:RISCHIO



Identificazione dei pericoli

Analizzare e valutare i rischi associati a ciascun pericolo

Identificare dei modi appropriati per eliminare o ridurre i

pericoli

In caso non sia possibile eliminare o ridurre i pericoli,

identificare i modi appropriati per eliminare o ridurre i

rischi associati

Cosa è un’analisi di rischio?



Generazione di malattie

Ferite sul corpo

Cambiamenti delle funzioni corporali

Cambiamenti nella normale crescita e sviluppo degli individui

Effetti sulla crescita dei feti e modificazioni genetiche

Effetti sui bambini e sugli anziani

Diminuzione delle aspettative di vita

Stress e traumi mentali

Effetti sulle capacità di affrontare in futuro nuovi stress o situazioni di

pericolo

Tra i pericoli che si analizzano, al primo posto: Pericolo per la salute dell’uomo


Fundamental safety and environmental characteristics of fusion

• No climate-changing emissions

• Power excursions self-limited by inherent processes

• Products of fusion reaction are not radioactive

• Structures are activated by neutrons but:

– Low power density (“decay heat”) after termination of burn

– Short decay of radiotoxicity

• No fissile or fertile material, no actinides or fission-products

A Demonstration Power Plant should demonstrate that these characteristics lead to excellent Safety and

Environmental performance.


Mobilizable Radioactive Inventory in ITER and in DEMO

Radiological source terms are

• Tritium: in VV, PFCs, fuel cycle and Hot Cell and Radwaste. Main relevant

contribution in term of safety is the tritium inventory in the VV, tritium

building and Hot Cell

• ACPs: the activation of the corrosion products present in in the primary

cooling loops

• Activation products:

• in-vessel components activation

• in-vessel dust from FW-plasma interaction

• liquid metal activation products


Realizing the potential safety and environmental benefits of fusion

Design choices can help to make the most of the S&E potential benefits

• Materials selection

– “low activation” materials for components that experience significant neutron fluence

– combinations of coolant and in-vessel materials to be considered (e.g. avoid water + beryllium)

• Passive rejection of decay heat after loss-of-coolant

• Minimise dependence on active safety systems, or operator actions(passive safety)

• Extensive use of Remote Maintenance to avoid personnel doses


Safety Approach for ITER and DEMO

• To protect workers, the public and the environment from harm;

• To ensure in normal operation that exposure to hazards within the facility and due to

release of hazardous material from the facility is controlled, kept below prescribed limits

and minimized to be as low as reasonably achievable;

• To ensure that the likelihood of accidents is minimized and that their consequences are

bounded;

• To ensure that the consequences of more frequent incidents, if any, are minor;

• To apply a safety approach that limits the hazards from accidents such that in any event

there is no need for public evacuation on technical grounds;

• To minimize radioactive waste hazards and volumes and ensure that they are as low as

reasonably achievable.

ALARADefence in depth Passive safety

Top-level safety objectives

Employ established safety principles

Mitigation of consequences of significant releases of radioactive material

Off-site emergency response (e.g. evacuation) – should not be necessary for fusion


“Defence in Depth” approach to safety

Main safety function is confinement of radioactivity,achieved by multiple layers of protection:

Prevention of accident progression, mitigation of consequences

Control of accidents within design basis

Control of abnormal operation and detection of failures

Prevention of abnormal operation and failures

• Multiple barriers

• Natural shutdown

• Filtering and detritiation systems

• Small inventories

• Conservative design

• Safety systems

• High quality construction

• Use of passive means wherever possible

Safety Approach for ITER and DEMO


A Nuclear Fusion Plant needs to be licensed

• The unlicensed operation of a nuclear installation is prohibited in any country.

• The risk associated to Fusion Plants are different from those of NPP– presence of huge amount of tritium and dust– Easy end of the fusion reaction, no risk of excursion (self-limited by

inherent processes)– Products of fusion reaction are not radioactive– Structures are activated by neutrons but:

• Low power density (“decay heat”) after termination of burn• rapid decay of radiotoxicity

– No fissile or fertile material, no actinides or fission-products

• The licensing is focused on Structure, Systems and Components (SSE) Safety Important Classified (SIC) performing a safety function necessary to bring and maintain the plant into a safe state in any circumstance (normal and accidental)


Safety Functions in ITER

1. Confinement of radioactivity– Static barriers (mainly process barriers and some building walls)– Systems for maintaining depression and filtering/detritiation

2. Limitation of exposure– Shielding – Access control

3. Protection of systems for confinement and limiting exposure

– Management of pressure– Management of chemical energy– Management of magnetic energy– Management of heat removal and long term temperatures– Fire detection/mitigation – Mechanical impact (including seismic, load drop, etc.)

4. Support of systems for confinement and limiting exposure

– Services supporting systems implementing safety functions such as instrumentation and control, electrical power

– Provide transport/lifting of radioactive components/materials– Monitoring of safety functions

Main functions

Supporting functions


Confinement: in-vessel inventoryConfinement strategy:

• Two confinement systems

• each with one or more static barriers and/or dynamic systemsTritium

(adsorbed in plasma-facing surfaces, in dust)

Active dust(tungsten eroded from plasma-facing surfaces)

Activated corrosion products

(in accidents with in-vessel loss of water coolant)

First confinement systemVacuum vessel and its extensions

Second confinement systemBuilding walls and slabs surrounding tokamak, rooms served by ventilation with filtering and detritiation systems.Other boundaries (e.g. cryostat under discussion)

Safety Functions in ITER


Main safety functionConfinement concept – Glove box

1st Static barriersLeaktight process

Dynamic systems- filtration- detritiation

2nd Static barriers- filtration - detritiation

1st confinement system – closest to radioactive material, protects the worker

2nd confinement system– protection of population and environment in case of failure of first system

3H

Building - Filtration- Isolation

P

P

worker


Safety analysis in ITER

Metodologia applicata ad ITER per l’analisi di sicurezza

PIE Postulated Initiating EventsFMEA Failure Mode and Effect AnalysisPST Process Source TermEST Environmental Source TermDCF Dose Conversion Factor

SOURCE

TERMS ASSESSMENT

Normal working conditions Occupational dose

IEAS

Thermodynamic transients Aerosols and H3 transport

Containments Release from the plant DCF

Overall Plant AnalysisFFMEA

Radioactive waste Operational&Decomm waste

Identification&classification

Management•On-site•Recycling•Final disosal

Effluents

PST

PST EST

DCF

man*Sv/y

dose/sequence to MEI

frequency*dose

Quantity and waste categories

mSv/y

SOURCE

TERMS

Normal working conditions Occupational dose

PIE Thermodynamic transients Aerosols and H3 transport

Confinements Release from the plant DCF

Overall Plant Safety AnalysisFMEA

Radioactive waste Operational&Decomm waste

Identification&classification

Management•On-site•Recycling• Final disposal

Effluents

PST

PST EST

DCF

man*Sv/y

dose/sequence to Public

frequency*dose

Quantity and waste categories

mSv/y

(Courtesy of S. Ciattaglia)


ITER Safety objectives

Objective for ORE: 500 mSv person/year

General safety objectives

For personnel For the public and environment

Situations in design basis

Normalsituations

As low as reasonably achievable, and in any case less than:Maximum individual dose

≤ 10 mSv/yrAverage individual dose

≤ 2.5 mSv/yr

Releases less than the limits authorised for the installation,Impact as low as reasonably achievable and in any case less than:

≤ 0.1 mSv/yr

Incidental situations

As low as reasonably achievable and in any case less than:

10 mSv per incident

Release per incident less than the annual limits authorised for the installation.

[i.e. 0.1 mSv per incident]

Accidental situations

Take into account the constraints related to the management of the accident and post-accident situation

No immediate or deferred counter-measures (confinement, evacuation)

< 10 mSvNo restriction of consumption of animal or vegetable products

Situations beyond design basis

Hypothetical accidents

No cliff-edge effect; possible counter-measures limited in time and space


The licensing procedure: the application• Early examination of the project

– Safety options (not compulsory)Presentation by the operator of safety objectives and main characteristicsReview by the ASN’s relevant advisory committee of expertsInformation of the operator on issues to be addressed in its applicationFor ITER: Safety options report consulted by the committee of technical experts in 2002

– National Public debate : compulsory when dealing with a new nuclear electricity generating site or a new site

not generating electricity but costing more than 300 million euros FOR ITER : debate closed in May 2006

• Application file– Content Description of the installation and of the operations to be carried out Report on the consequences on the environment Preliminary safety analysis report (hazards presented by the installation and steps

taken to prevent them ; measures capable of reducing the probability and the consequences of an accident)

Decommissioning plan


ITER Licensing process

• ITER is to be licensed in France as a Basic Nuclear Installation (Installation Nucléaire de Base, INB)according to the law on transparency and security in the nuclear field (Loi

Relative à la Transparence et à la Sécurité en Matière Nucléaire, TSN)• In order to obtain the decree to authorise ITER, at this stage, ITER has

submitted to the French nuclear safety authorities(Autorité de Sûreté Nucléaire, ASN):

The DAC files(Demande d’Autorisation de Création)

Request for authorisation, comprising 14 files including

Preliminary Safety Report (Rapport Préliminaire de Sûreté, RPrS)

Impact Study (Etude d’Impact)


Preliminary Safety Report • At the end of this stage, construction authorization is given• Needed information : studies and calculations• Need to assess loads on buildings and structural confinement

barriers : – internal loads (normal operation, incidents and accidents) and

external loads (site and environmental loads) to be applied, combination of loads for: all that allow to set-up the design

• Studies and associated calculations of all “plausible” conservative internal and external hazards to consider for the design of rooms, buildings and non reversible components in order to demonstrate the adequacy of safety systems vs workers and public protection (e.g. in order to assess confinement systems, pre-requites of potential contamination level)


Preliminary Safety Report

• Calculation of the worst “plausible” scenario and to assess potential impact on the construction

• Accident approach in particular fire risk (in order to assess whether static or dynamic confinement could be used, assessment of escape routes for workers)

• List of components and structures with safety requirements• Radiation protection approach in order to assess zones and

biological• Shields, radiological monitoring in rooms and stacks


Preliminary Safety Report • All “plausible” conservative internal hazards = Postulated initiating events

Similar as in nuclear power plants such as Loss of flow accident (LOFA),

Loss of offsite-power (SBO), Leaks (VV, Primary System, …), Fire & explosion Fusion specific events: loss of cryogenic system, arcing , magnet system faults affecting

barriers


Safety report for a nuclear fusion plant: generalities

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SEMINARIO SAFETY IN NUCLEAR FUSION PLANT 24 Aprile 2015 T. Pinna Safety report for a nuclear fusion...

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