ITER Safety and Licensing issues

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ENEA
Evaluation of external Occupational Radiation
Exposure and optimisation of the
radioprotectionM. T. Porfiri
Garching 10th October 2006 Meeting on
Occupational Radiation Exposure ALARA in ITER
further refinement
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Outline

• Results of 2005 analysis
• Difficulties met in the past analysis
• Cross check with the existing data base
• Data necessary for the ORE refinement
• Tool
• Schedule

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2005 analysis (1) configuration
Reference document Design Description Document
(DDD 5.3) Neutral Beam Heating Current Drive
(NB HCD) System N 53 DDD 29 01-07-03 R 0.1,
July 2001, ITER
Radiation field dose rates below the mezzanine
floor are generally below a value of 25 ?Sv/h,
while above they are generally below 2 ?Sv/h
(Polunovskiy 2005). A notional value of 10 ?Sv/h
for all hands-on operations, to take into account
other contributors to dose rate, such as piping
and the collective effect of other activated
equipment.
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2005 analysis (2)type of maintenance

• The NBI is activated by plasma neutrons,
  maintenance on components inside the box will be
  performed by remote handling operations. Human
  assistance will be limited to preparatory work in
  the NB cell.
• Hands-on maintenance is possible only on
  components that are located inside the NB cell,
  but outside the shielded NB box.
• Hands-on maintenance can be performed on cooling
  system components, cryogenic system components,
  electrical power supply system components, gas
  supply system components, pneumatic/hydraulic
  system components and instrumentation and control
  system components.
• The proviso is that the machine, for maintenance,
  is in the shutdown state.

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Results of 2005 analysis (3) Number and Type of
Components to be Maintained Inside NB Cell
NB Component Temper/ Press. Sensor Flow Meter Control Valve Isolation Valve Current/ Voltage Meter Transmitter/ Multipl. Servo Mechanism Actuator Total
Beam Duct 2 1 1 2 1 1 8
Drift Duct 4 2 2 4 1 2 15
Fast Shutter 4 1 5
Calorimeter 2 1 1 2 1 2 3 12
Residual Ion Dump 2 1 1 2 1 1 8
Neutralizer 2 2 2 4 1 2 13
Beam Source 11 7 7 14 85 1 7 132
Beam Line Vessel 7 13 26 1 13 60
Magnetic Compensation Coils 2 1 1 2 7 1 14
Totals 32 15 28 60 92 8 3 29 267
Assumption each of the above components requires
one person-hour of maintenance/testing per
intervention, and each component is maintained
once per year
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Results of 2005 analysis (4)
Serviceable equipment refers to those system
components located inside the NB Cell (above the
mezzanine floor), which are believed to require
regular maintenance.
NB Major Component Serviceable Equipment Work Effort (p-h) Worker Dose (p-?Sv)
Beam Duct 8 8 80
Drift Duct 15 15 150
Fast Shutter 5 5 50
Calorimeter 12 12 120
Residual Ion Dump 8 8 80
Neutralizer 13 13 130
Beam Source 132 132 1,320
Beam Line Vessel 60 60 600
Magnetic Compensation Coils 14 14 140
Totals 267 267 2,670
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Results of 2005 analysis (5)

• The hands-on annual dose associated with port
  openings and closings
• will depend on both the unit dose and the
  maintenance frequency.
• The unit dose for a RH port is about 14
  p-mSv/port, estimated in 2001 ORE assessment.
• The maintenance frequency of the beam ducts is
  likely dictated by
• water leaks in the cooling tubes.
• Therefore, assuming a leak frequency of 0.1
  leaks per year,
• per beam duct, gives a maintenance frequency of
  0.3/a.
• Each maintenance intervention requires the
  opening and closing of two
• ports, hence, the associated worker dose would
  be in the range of 8.4 p-
• mSv/a.

Operation Worker Dose (p-mSv/a)
Maintenance of NB Cell Components 8.1
Beam Duct Maintenance (RH port opening/closing) 8.4
Hot Cell Maintenance of NB Injector Components Not Estimated
TOTAL 16.5
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2005 resultscontribution to ORE in ITER of the
systems
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Difficulties met in the past analysis

• 1. The reference documents (DDD) was based on a
  previous version of the design.
• 2. The maintenance procedures were not defined
  when the ORE
• assessment was performed.
• 3. The maintenance frequency was unknown at that
  time
• 4. The tritium was not taken into account because
  not evaluated yet
• when the ORE studies was carried on
• 5. Rough assumptions for the instrument and
  control system were
• necessary, because a clear strategy on this
  field was not ready
• 6. Extrapolation of the radiation field values in
  zones not covered by the activation analysis was
  necessary

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Cross check with the existing data base

• One of the main points in the work effort
  evaluation, that is the basis for the ORE
  assessment, is the achievement of standardized
  rules for the evaluation of the type of
  activities and for the duration of each single,
  elementary activity.
• The optimization of the maintenance phases, from
  the worker safety point of view, requests,
  besides the knowledge of the procedures, also a
  good knowledge of the system lay out in order to
  plan the intervention on the basis of
• normal maintenance frequency,
• prediction of accidental maintenances ,
• sharing of the available spaces between different
  system allowing simultaneous maintenance
• sharing of the intervention time on the base of
  the worker shifts
• overlap of different interventions to reduce the
  number of port opening and closing actions, when
  possible.

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Data necessary for ORE refinement

• NBI design documents
• Ventilation and detritiation systems
  flow rates, set point for
  intervention and stop, decontamination factors
• Radiation field in NBI box, NBI cell and gallery
• Tritium contamination in the maintenance zones
• Components maintenance frequency

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Tool (1)ORE_Code
To handle the large quantity of data and to allow
user friendly updating of data as the design
evolves and the maintenance knowledge base
improves, a software tool, named ORE_Code has
been developed in Excel spreadsheet format.
Dedicated Excel workbooks have been formatted to
record data for maintenance procedures and,
dedicated Visual Basic routines have been
developed to easily manage such data. The
workbook dedicated to ORE data recording is made
up of several worksheets set for data recording
in structural way.
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Tool (2)Relations between worksheets in ORE_code
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Worksheets
The meaning of the different worksheet
is Maintenance Tasks used to list all
operations related to the maintenance tasks to be
evaluated. Rooms auxiliary sheet used to list
information on the Rooms where maintenance is
performed. Equipment used to list information
on equipments subjected to maintenance. Worker
Groups used to define Worker Groups who are
implicated in the maintenance to be
performed. Elementary activities used to list
elementary operations and related numerical data,
such as time required for the single operations,
involved people and work effort in terms of
person-hour. Notes auxiliary sheet used to
list all the notes used in the other
sheets. ORE_Sheets.xls
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What are the elementary activities

• Category
• Standard activity
• Operation Time (h)
• Involved people
• Elementary WE (p-h)

• Testing, monitoring inspections
• Making and breaking services connections
• Installing and removing thermal insulation and
  pipe hangers
• Pipe cutting and welding
• Tube cutting and welding (e.g., wave-guide tubes)
• Flange bolting/unbolting
• Flange lip seal welding/cutting
• Transportation of components
• Set-up/remove work platforms (scaffolding)
• Set-up/remove temporary equipment supports

cut small diameter pipe weld small diameter pipe

• weld lip seal on small flange
• cut lip seal on small flange
• weld lip seal on port flange
• cut lip seal on port flange

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Schedule

• 1. Achievement of the main documents of the
  updated design
• and radiation field data
• December 2006
• 2. Draw up of the data base for elementary
  activities, minor activities, mayor
  activities, maintenance frequency
• January 2006
• 3. Discussion with the NBI designers of the
  maintenance procedures
• and on the reliability of the data base
• February 2006
• 4. Design of the more suitable maintenance
  scenarios and relating ORE assessments
• March 2006
• 5. Final report
  May 2006