Decommissioning and dismantling of the moata reactor a radiation protection perspective- maharaj
1. Decommissioning and Dismantling of the
Moata Reactor-
A Radiation Protection Perspective
Prashant Maharaj
Australian Nuclear Science &
Technology Organisation
2. A History of Moata
• Graphite
moderator /
reflector
• Cooled by light
water
• Shielding - high
density and low
density concrete
• Constructed at ANSTO in 1961
• ARGONAUT type reactor
• Built as a 10 kW reactor, but modified
in 1972 to 100 kW
3. The Moata Reactor
From 1961 to 1995:
– Neutron
radiography
– Soil analysis
– Cancer
treatment
research
– Quality Control
for HIFAR
4. Shutdown & Decommissioning
Two phases of dismantling:
– Preliminary Dismantling – the removal of the internal components of the reactor,
including the steel core structures, graphite moderator and beam line facilities
– Structural (Biological Shield) Dismantling – the cutting and removal of the concrete
shielding and the floor area below the shielding.
1995 1996 1997 1998 2009
Shutdownafter4,519start-ups
Fuelunloaded
DecommissioningProjectTeam
established
Primarycoolant(lightwater)
drained
ReactorControlSystem
removed
Planningcommencedfor
dismantling
PreliminaryDismantlingbegan
PreliminaryDismantlingcomplete
Containmenttentinstalled
2010
BiologicalShieldDismantlingbegan
BiologicalShieldDismantlingComplete
6. Structural (Biological Shield) Dismantling
• Reactor housed in a building used for
other operational task
• A containment tent with HEPA filtered
extraction system built around the
reactor
7. Getting There…
The steps involved in planning, completing and evaluating the
success of the Biological shield Dismantling:
– Radiation Protection Plan
• Characterisation
• Radiation Management & Monitoring
• Dose Estimation & Constraints
• Personal Protective Equipment
• Final Status Surveys
– Outcomes & Lessons Learnt
8. Characterisation – Survey
• A radiological survey was carried out to determine
the dose rates within the empty cavity areas.
• The data from this exercise was used to prepare a
dose estimate for the Biological shield dismantling.
• This helped us estimate the maximum individual
and collective dose for this part of the project.
Measured dose rates ranged from 7-4000 Sv/hr
11. Radiation Management & Monitoring
Controlling exposure using shielding
Steel Plates for shielding
12. Radiation Management & Monitoring
Controlling exposure using shielding
Shielded containers for
activated waste:
– Specially designed
6mm steel boxes for
active concrete
14. Radiation Management & Monitoring
• External gamma monitors
and air samplers were
placed close to work areas.
• Barrier and exit monitoring
equipment were used to
ensure that no
contamination was taken
out of the classified areas.
15. Personal Protective Equipment
• Since there was a high potential of
generating dust while cutting and
demolishing the active concrete it was
decided to start from the highest level
of PPE which included ;
Respiratory protection with
particulate cartridge)
Tyveks
Overshoes and gloves
• This was than downgraded as we
gained operational understanding of
the project risks.
16. Final Status Survey
• Dose rate surveys were carried out on
marked survey points (grid survey)
• Acceptance criteria of 0.5uSv/hr was
met to ensure a brown-field condition
was met
• Samples were taken in and around the
foundations of the reactor and analysed
for activity.
• The following guides were also used to
determine the exemption and clearance
criteria for the site
IAEA No. RS-G.1.7
ARPANSA Reg 1999, Schedule 2,
Part 2
18. Outcomes & Lessons Learnt
• From a radiation protection perspective the Biological Shield
Dismantling was completed safely and without incident.
– Dose estimates were higher than those recorded by staff.
This was attributed to being overly conservative and some
of the contributing factors were;
• Self shielding by the dismantled concrete
• Time taken to dismantle and remove the active concrete was
less than anticipated.
– No surface or airborne contamination was detected
throughout the project
– There were no personal contamination events
