1. Vincent MASSAUT SCK•CEN and EFDA
ALARA from the decommissioning to the design stage in the nuclear field
Vincent MASSAUT
SCK•CEN and EFDA
10th European ALARA Network Workshop on
“Experience and new developments in implementing ALARA in occupational, public and patient exposures”
Prague, Czech Republic, September 2006
Vincent MASSAUT September 2006 EAN workshop

2. A piece of history…
: we started the BR3-PWR decommissioning project, as a European pilot project….
V. Massaut September 2006 EAN Workshop

3. Content of the presentation
ALARA : not only a good practice, but an optimization process…
Some examples of application in decommissioning project
In D&D, the aspect of industrial safety is also important and lead to introduce the ASARA principle
Helping tools for the evaluation and optimization
What can ALARA bring for the design and construction of new facilities ?
The regulation
The optimization
The systematization
Overall positive input of the application of the principle
Conclusions
V. Massaut September 2006 EAN Workshop

4. The application of the ALARA principle in the industry: not only a good practice…
The tendency is often to consider the ALARA approach as a reduction of the foreseen dose by applying principles of good practice
But the ALARA approach is more than that; it implies a real optimization, taking into account financial and practical aspects and implying the analysis of alternatives. It does not always lead to a reduction of doses (or at least of dose rate) !
V. Massaut September 2006 EAN Workshop

5. A practical example: the dismantling of the reactor upper internals
On one hand, use deep water shield, using long tools, remote controlled and tele-vision  lower dose / high risk and high costs
On the other hand, use reduced water height, easier tools, direct vision  higher dose / lower risk and lower costs
Finally after optimization analysis, this solution was selected.
RPV
=source
RPV
=source
V. Massaut September 2006 EAN Workshop

6. View of the platform with low water depth
Short Handling Tools
Working Platform
Internals to dismantle
V. Massaut September 2006 EAN Workshop

7. The optimization process
EAN - Prague
14/09/2006
The optimization process
Definition of the operation
Identification of the options, factors and boundary conditions
Factors characterizing different options:
Collective dose
Individual dose
Investments
Dose transfer
Quantification of the options depending on the factors
Comparison and selection
Decision aiding techniques
Sensitivity analysis
Decision
V. Massaut September 2006 EAN Workshop

8. For simple operations this scheme seems simple, but in actual decommissioning operations …
One has to take several complicating factors into account:
Changing environment
Moving sources
Dismantling of shielding
Precise data often not well known (for physical and radiological data)
Difficult access zones (even for measurements)
Contamination hazard
Industrial hazards
“One-shot” operations
Non usual working areas
...
V. Massaut September 2006 EAN Workshop

9. Some specific aspects
Difficult access zones - Dismantling requires sometimes to go in areas which were not foreseen to be dismantled... - Shieldings have thus not be foreseen - Dose rate measurement difficult to carry out - Use of assumptions and good practice
V. Massaut September 2006 EAN Workshop

10. Dismantling: the detailed data are often not well known
Most of the current facilities in decommissioning were not built under QA
Archives often difficult to retrieve
Modifications during plant life not fully documented
Loss of the installation knowledge (retirement of the operators, and disappearing of the living installation memory)
Radiological state rather unknown in some areas (as not useful during operation)
Difficulty to retrieve records of small incidents (leaks, spills...) able to cause contamination
Archives
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11. Some examples Temporary waste storage (new radiation source)
Proximity of the sources
(and contamination hazard)
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12. Some examples Industrial and radiological hazards Shielding demolition
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13. Some examples Sources Transport and handling
Sometimes difficult access
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14. Some examples
Opening of contaminated loops and components (internal contamination hazard)
Handling of contaminated or activated equipments (contamination & irradiation)
V. Massaut September 2006 EAN Workshop

15. Dismantling: other hazards are present
Industrial (conventional) hazards: - open flame cutting tools - use of corrosive products and acids (decontamination processes) - Noxious gaseous effluents (opening of loops, CO2decontamination, chemical decontamination and production of H2, O3...)
- presence (and removal thus mobilization) of toxic products (asbestos, Beryllium...) - working in height - handling of heavy loads - difficult access - etc.
V. Massaut September 2006 EAN Workshop

16. These aspects have lead to two main actions
EAN - Prague
14/09/2006
These aspects have lead to two main actions
To develop a 3D tool for helping evaluating the radioprotection and the optimization (so-called VISIPLAN)
To develop an optimization process not only based on radiological impact but also on the overall operator safety impact: the ASARA principle (As Safe As Reasonably Achievable)
This last aspect is mostly evaluated in the appreciation of the options selection and optimization
V. Massaut September 2006 EAN Workshop

17. Example of a 3D evaluation and optimization tool
Establish scenarios and procedures including trajectory and station time
Analyze the process, propose alternative options and report
Introduce the geometrical and physical data
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18. …and at the other end of the plant life?
V. Massaut September 2006 EAN Workshop

19. ALARA for the design of new installations ?
The design of new and future installations is nowadays very concerned by the occupational safety of the operators. Moreover, the safety authorities are requesting an ALARA optimization analysis.
Therefore the ALARA approach, including the options selection, can be a powerful tool to optimize the occupational exposure and to improve the overall design.
The approach will be highlighted on an example: the fusion plant design
V. Massaut September 2006 EAN Workshop

20. Setting the scene: some short reminders about fusion principles
Courtesy from JET
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21. In order to reach the necessary parameters for producing net energy
One need to get a threshold in the so-called “triple product”: nτT > m-3 s keV for the reaction D+T
Sufficient high density (n) : 2-3 x 1020 particles m-3 (approx. 1/1000 gram m-3)
Energy confinement time (τ): τ ≈ E/P a measure of how long the energy in the plasma is retained before being lost. The confinement time increases dramatically with plasma size (goal : 1-2 sec)
Temperature : above 100•106 K needed for the Deuterium-Tritium reaction to occur
V. Massaut September 2006 EAN Workshop

22. What is the meaning of the confinement time tE?
Temperature
1/e tE
tE is a measure of how fast the plasma looses its energy
The loss rate is smallest, tE largest
if the fusion plasma is big and well insulated
V. Massaut September 2006 EAN Workshop

23. The way towards power plants
Courtesy from JET
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24. For plasma physics grounds there is a need to have large plasma volumes
Hence large fusion machines….
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25. Fusion is characterized by… (for occupational exposure aspects)
No long lived radio-nuclides
High potential activation around the plasma (14 MeV neutrons)
Tritium contamination potential
Large machine (e.g t for a power plant tokamak)
Regular replacements of plasma facing components (divertor and blanket modules)
V. Massaut September 2006 EAN Workshop

26. Moreover, as in the decommissioning,…
There are other industrial occupational safety aspects:
Presence of Beryllium (can be in powder/dust)
Presence of hydrogen and dust (explosion hazard)
Handling of large components
Strong magnetic fields
Therefore, here also there is need to balance radiological exposure optimization with classical safety and occupational safety optimization (avoid transfer of risk)
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27. The ALARA process implemented in ITER design
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28. The ALARA optimization during design phase brings some focus on…
Design facilitating maintenance
Reducing maintenance frequency or number of components to handle
Simplify components handling
Reduce handling of activated components
Optimize shielding / location / frequency (including financial aspects)
Optimized use of remote handling
V. Massaut September 2006 EAN Workshop

29. Some examples from ITER analysis
Concerning vacuum vessels port plugs configuration, various technical solutions have been compared in order to retain the best option in terms of radiological protection :
ECH port : design parameters such as plug composition and plug thickness have been studied ;
Divertor port : different layouts have been studied to reduce high dose rates due to large opening in the vacuum vessel ;
Cryopump port : comparative study of five different shielding configurations ;
Diagnostics systems plugs : some of the plug layouts do not alter the bulk efficiency but in other cases, the diagnostic access apertures affect the effective blanket/vacuum vessel shielding capability. Several configurations have been studied to counterbalance this effect and lead to acceptable dose rates
V. Massaut September 2006 EAN Workshop

30. Some examples from ITER analysis
Major changes in the TCWS design that have contributed to significant ORE reduction are :
Enhancement of CVCS efficiency (from DF = 2 in 1996 to DF = 50 in 1998) ;
Reduction of number of components (from 18 to 5) leading to lower maintenance frequency,
Improvement of inspection and maintenance strategy : the use of RH tools has been once envisaged but not retained since its gain was estimated to less than 1%,
Modification of operating scenario : delay intervention time from 24 h to 5 days after shutdown has contributed to an ORE reduction of 50%. As shown here, increasing this delay would not contribute to further ORE reduction.
TCWS : Tokamak Cooling Water System
CVCS : Chemistry and Volume Control System
V. Massaut September 2006 EAN Workshop

31. This ALARA approach in the design phase is a stepwise process
Iterative process, starting on rough pre-design phase and improving in parallel with the design evolution
The design and concept can change, not only (and often mostly not) to comply to the ALARA approach and optimization
A good evaluation of the occupational exposure and effects of design changes is needed to evaluate the direction of the evolution and the effectiveness of the changes.
V. Massaut September 2006 EAN Workshop

32. The ALARA implementation brings positive input by…
the dose evaluation
Implying very detailed analysis of the operating and maintenance procedures, access, tooling etc.
Requiring a systematic approach
Highlighting the difficulties and issues
the design improvements
Application of good practice and pinpointing of bugs and design errors
Implementation of easy design changes and improvements
the actual optimization
Involving complex evaluation and sometimes complete design review
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33. Overall conclusions of application of ALARA at different phases of the facilities life
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34. Conclusions
The ALARA approach is not only applied in operating facilities, for routine operations (although it can probably bring here large benefits)
The regulatory bodies are currently requiring to demonstrate that operation and maintenance in operating, dismantling or future facilities have been optimized following the ALARA principle.
The return of experience from the application of ALARA to actual operation is important in evaluating and optimizing occupational exposure for future plants and facilities
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35. Conclusions (continued)
The availability of interactive evaluation tools plays a central role in the whole process, as well for decommissioning as for design purposes.
Even if the ALARA approach seems, in a first stage, a cumbersome and heavy process, it proved (as well in decommissioning as in the design phase) to be very effective in optimizing design and/or procedure set up.
The approach should be broadened towards overall operator occupational safety, by applying a wider principle philosophy based on the ASARA “As Safe As Reasonably Achievable” principle.
V. Massaut September 2006 EAN Workshop

36. Conclusions (continued)
But there are limitations in the application of the principle and its optimization:
Very difficult to use the concept of “the cost of the man-Sv”
An overall ALARA approach should consider the whole life of a component, including its evacuation and disposal. This is not always possible.
The dose evaluation and attached calculations do not need to be very precise: there are so much uncertainties in the actual time spent for an operation and in the actual dose exposition. The most important aspect is the relative comparison.
V. Massaut September 2006 EAN Workshop

37. Concluding remark: Alara in the engineering process
New design / New operation (procedure)
Boundary conditions
Feasibility / design
ALARA / ASARA optimization philosophy
Enhanced design / procedure
Gain in terms of
Doses
Money
Safety
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38. Thank you for your attention
V. Massaut September 2006 EAN Workshop