Embed Size (px)
Citation preview
Copyright © 2013
SCK•CEN
The new radioprotection
implications of fusion reactors
V. Massaut; L. Di Pace; F. Druyts; P. Van Iseghem; F. Vermeersch
SCK•CEN/ ENEA (I)
International Symposium
on the occasion of the 50th anniversary
of the Belgian Association
for Radiological Protection BVS-ABR (April 2013)
Copyright © 2013
SCK•CEN
Fusion: a fast reminder of how it works
Fusion brings together light atoms to produce energy
Today system is based on the reaction D + T implying the use
and handling of massive amounts of tritium and the production
of highly energetic (14 MeV) neutrons.
Copyright © 2013
SCK•CEN
Fusion: a fast reminder of how it works
Fusion brings together light atoms to produce energy
Today’s system is based on the reaction D + T implying the use
and handling of massive amounts of tritium and the production
of highly energetic (14 MeV) neutrons.
To overcome the positive ion mutual repulsion, one needs to
have either VERY high temperature or VERY high pressure.
This leads to several types of confinment systems.
Tokamaks, Stellarator Huge Laser pulses Sun, stars
Impossible on
Earth
Less developed
today Let us focus on this one
Copyright © 2013
SCK•CEN
Fusion: further reminders
Tritium is a weak (mean 5,7 keV) beta emitter.
But it is an HYDROGEN isotope, thus forming easily organic
compounds and difficult to confine.
Fortunately, it has a very LOW radio-toxicity !
For tritium gas (T2): 1.8 10-15 Sv/Bq
For tritiated water (HTO): 1.8 10-11 Sv/Bq
But the amount of circulating tritium is rather huge:
E.g. in ITER, 1 kg cycling in the plant, 3kg total storage on site;
to give an idea, 1g T2 = 10 000 Ci …
To compare : annual amount of tritium generated by cosmic rays 200 g
Copyright © 2013
SCK•CEN
Different aspects of radioprotection in fusion reactors
During operation (handling of T; production of energetic
neutrons 14 MeV)
During maintenance (activated products, presence of
tritium, contamination of cooling loops, presence of
activated dust)
In case of accident (activated dust, presence of tritium,
presence of hydrogen, presence of toxic materials,…)
Waste management (huge amount of exposed and
activated materials, presence of tritium and detritiation,
recycling,…)
See further
Copyright © 2013
SCK•CEN
Radioprotection aspects During operation
Handling of tritium:
Tritium is needed for the D-T reaction
there is continuous tritium cycling through
the reactor;
TBMs: (Test) Blanket Modules, with breeding
of Tritium from Lithium and treatment of the
gas
Copyright © 2013
SCK•CEN
The tritium plant in ITER: a real gas plant on 7 floors ! !
Courtesy from M. Gugla’s presentation, SOFT 2006
Copyright © 2013
SCK•CEN
Radioprotection aspects During operation
Handling of tritium:
Tritium is needed for the D-T reaction
there is continuous tritium cycling through
the reactor;
TBMs: Test Blanket Modules, with breeding of
Tritium from Lithium and treatment of the gas
Production of energetic neutrons
14 MeV neutrons specific shielding and
long range activation
Activation with threshold reactions
No access to the "galleries" during operation.
Copyright © 2013
SCK•CEN
Just an idea of the ITER reactor scale
Copyright © 2013
SCK•CEN
ALARA approach for maintenance and operations
Dose targets for personnel (for the public)
Maximum individual dose in normal
operation < 10 mSv/y (≤ 0.1 mSv/y)
Average individual dose < 2.5 mSv/y
Collective dose < 500 mSv/y
Maximum individual dose per incident
<10 mSv (≤ 0.1 mSv)
ALARA in design and operation
Work descriptions and dose evaluation
Dose Simulation programs
VISPLAN 3D ALARA planning tool selection of the optimal solution
Work task description
(manpower, duration,
frequency, personnal
protective equipment)
Work area description
(doserate, radiation
sources, contamination,
shielding…)
Prediction of doses (individual, collective, internal,
external)
Study of different variants, modification of processes and
protections, identification of solutions leading to dose
reduction
"Galleries"
Copyright © 2013
SCK•CEN
Radioprotection aspects During operation
Handling of tritium:
Tritium is needed for the D-T reaction there is continuous tritium cycling through the reactor;
TBMs: Test Blanket Modules, with breeding of Tritium from Lithium and treatment of the gas
Production of energetic neutrons
14 MeV neutrons specific shielding and long range activation
Activation with even threshold reactions
No access to the "galleries" during operation.
Presence of high magnetic field, of beryllium, hydrogen, etc (i.e. other safety aspects to be taken into account)
Copyright © 2013
SCK•CEN
Heavy maintenance is foreseen
The divertor has to be replaced regularly (in ITER
after about 3 years of operation) and this
replacement requires opening the tokamak and
handling huge and heavy activated components
Copyright © 2013
SCK•CEN
Heavy maintenance is foreseen
The divertor has to be replaced regularly (in ITER
after about 3 years of operation) and this
replacement requires opening the tokamak and
handling huge and heavy activated components
The First Wall of the Torus chamber will probably
have also to be replaced (at least partially). This
requires the use of complex remote handling system
and the handling of large activated components
Copyright © 2013
SCK•CEN
Heavy maintenance is foreseen
The divertor has to be replaced regularly (in ITER
after about 3 years of operation) and this
replacement requires opening the tokamak and
handling huge and heavy activated components .
The First Wall of the Torus chamber will probably
have also to be replaced (at least partially), This
requires the use of complex remote handling system
and the handling of large activated components.
When opening the vacuum vessel, the risk of
contamination by tritium (detrapping from the walls)
and activated dust has to be considered.
While replacing the divertor and first wall, the
primary cooling loop will be open.
Dust traces
in JET
Copyright © 2013
SCK•CEN 15
Remote Handling
Specificity of fusion regarding radioprotection
Hot Cells
Remote handling will be important, however
hands on work will still be necessary.
Copyright © 2013
SCK•CEN
As for all nuclear installations, the case of accidents have to be considered
One has to take into account the presence
(and potential mobilization) of tritium,
activated dust, activated corrosion products
etc…
Copyright © 2013
SCK•CEN
As for all nuclear installations, the case of accidents have to be considered
One has to take into account the presence
(and potential mobilization) of tritium,
activated dust, activated corrosion products
etc…
Specific isotopes from fusion (due to the
materials used for the PFC and the high
energetic neutrons) have to be taken into
account,
Copyright © 2013
SCK•CEN
As for all nuclear installations, the case of accidents have to be considered
One has to take into account the presence
(and potential mobilization) of tritium,
activated dust, activated corrosion products
etc…
Specific isotopes from fusion (due to the
materials used for the PFC and the high
energetic neutrons) have to be taken into
account,
Nevertheless, the current simulations have
shown that for the worst case accident, no
population evacuation would be needed.
Copyright © 2013
SCK•CEN 19
SOURCE
TERMS
ASSESSMENT
Normal working
conditions Occupational dose
IE
AS Thermodynamic transients
Aerosols and H3 transport
Containments
Release from the plant DCF
Overall Plant Analysis
FFMEA
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 Analysis
FMEA
Radioactive waste
Operational&Decomm waste
Identification&classification
Management
• On site • Recycling • Final disposal
Effluents
PST
PST EST
DCF
person*Sv/y
dose/sequence
to Public
frequency*dose
Quantity and
waste
categories
mSv/y
Probabilistic Safety Analysis
Overall Safety Analysis “Course”
DCF = Dose Conversion Factor; PIE = Postulated Initiating Event
PST = Process Source Term; EST = Environmental Source Term
Copyright © 2013
SCK•CEN 20
SOURCE
TERMS
ASSESSMENT
Normal working
conditions Occupational dose
IE
AS Thermodynamic transients
Aerosols and H3 transport
Containments
Release from the plant DCF
Overall Plant Safety Analysis
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
FMEA
Radioactive waste
Operational&Decomm waste
Identification&classification
Management
• On site • Recycling • Final disposal
Effluents
PST
PST EST
DCF
person*Sv/y
dose/sequence
to Public
frequency*dose
Quantity and
waste
categories
mSv/y
Deterministic Safety Analysis
Overall Safety Analysis “Course”
DCF = Dose Conversion Factor; PIE = Postulated Initiating Event
PST = Process Source Term; EST = Environmental Source Term
Copyright © 2013
SCK•CEN
The Waste management requires specific approach, also from a radioprotection standpoint !
There will be a very huge amount of activated material produced:
During maintenance of the plant (exchange and removal of activated divertor and first wall)
At decommissioning (one of the European designs of DEMO assumes 90,000 tons of activated metals !!! To compare with PWR RPV + internals < 1,000 tons)
Here again, the presence of tritium, exotic materials and dust is an important factor (calculation of the impact of the waste storage or disposal for the biosphere)
The main strategy is to recycle (or release when possible) the materials: needs for specific rules and regulations regarding the specific isotopes.
Copyright © 2013
SCK•CEN
Release and Recycling
Release from Regulatory Control
• By exemption or clearance (conditioned or not)
▪ it is necessary to develop internationally agreed limits being
complete and fusion specific
▪ Issues on control and measurement with emphasis on the
correct evaluation of impurities.
Recycling in or out the nuclear industry
• Development of radiation-resistant recycling equipment to
handle high dose rates > 10,000 Sv/h.
• Handling, cutting and dismantling of active material using
remote techniques, particularly the separation of high
activity items.
• Issues of removal and transportation of tritium-containing
materials.
Copyright © 2013
SCK•CEN
Radioactive Waste generated in a future Fusion Reactor (Ms thesis M. Desecures)
Case study: activation analysis of two W-based divertor designs
Classification of radwaste as LLW or HLW (according to US regulations) or as MA-VL (according to French regulations) is very dependent on the choice of materials, alloying elements (such as Re, Mo, Ni and Cu), and impurities (especially Nb, Ag)
The main lesson learned is that radioprotection and waste management issues should be taken into account in the first steps of developing new alloys for fusion applications (impurities management down to ppb levels)
Copyright © 2013
SCK•CEN
Conclusions
Specificities of fusion for radioprotection purposes
Activation products (exotic PFC materials; high energy neutrons)
specific isotopes for fusion
Contamination products in cooling loops (high energy n + complex
loops)
Tritium aspects (handling, confinment, water/gas)
No fuel (normally no long lived isotopes, but huge amount of
activated materials)
Complex and regular heavy maintenance of the plant
(removal/exchange of PFC and divertor)
Thus: needs for specific approach, at least for operational
planning, for the release and recycling, and probably also for the
accident analysis, for the impact of tritium, etc
This approach should start now !
Copyright © 2013
SCK•CEN
Thanks for your attention !
Copyright © 2013
SCK•CEN
Copyright © 2013 - SCKCEN
PLEASE NOTE!
This presentation contains data, information and formats for dedicated use ONLY and may not be copied,
distributed or cited without the explicit permission of the SCK•CEN. If this has been obtained, please reference it
as a “personal communication. By courtesy of SCK•CEN”.
SCK•CEN
Studiecentrum voor Kernenergie
Centre d'Etude de l'Energie Nucléaire
Belgian Nuclear Research Centre
Stichting van Openbaar Nut
Fondation d'Utilité Publique
Foundation of Public Utility
Registered Office: Avenue Herrmann-Debrouxlaan 40 – BE-1160 BRUSSELS
Operational Office: Boeretang 200 – BE-2400 MOL
