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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Prior to Decommissioning
Wilhelm Kukla, EnBW Kernkraft GmbH, Obrigheim NPP
Christian Topf, AREVA NP GmbH, Erlangen
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History of NPP Obrigheim
Considerations
Decontamination Targets
Systems included in decontamination
Technical description of the decontamination
Results
Energie
braucht Impulse
Full System Decontamination at the
Obrigheim Nuclear Power Plant
time of construction:
design
1. criticality:
thermal reactor power:
exchange steam generators:
operating time:
total gross production:
capacity factor:
2
1965 – 1968
two loops
Oktober 1968
1,050 MWth
1983
01.03.1969 – 12.05.2005
90,828 TWh
81.4 %
Full System Decontamination at the
Obrigheim Nuclear Power Plant
Considerations
After final shut down of the NPP
- decontamination of primary coolant system
- wait until activity is reduced by decay
Decision
Carrying out decontamination
- activity is reduced faster as by natural decay
- ensures that the experienced plant personal with intimate system
and operating knowledge is still available
- functionality and usability of all NPP systems is already given
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Decontamination Targets:
• Reduction of the activity inventory in all systems included in the
decontamination
• Reduction of the ambient dose rate in working areas
• No significant shift of the gamma/alpha ratio
• Minimum waste generation
• Average decontamination factor of more than 10
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Systems and components included in decontamination:
• Reactor pressure vessel with internals, no fuel
• Pressurizer
• Primary circuit (two loops) including steam generators
as well as part of:
• Residuel heat removal system
• Volume control system
• Emergency injection system
• Mechanical filters of the chemical purification system
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Total volume:
160 m³
Surface total:
8,100 m²
Is composed of:
Incaloy 800 (SG)
austenitic weld cladding (primary circiut)
austenitic CrNi steel (auxilary systems)
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6,200 m²
1,100 m²
800 m²
Full System Decontamination at the
Obrigheim Nuclear Power Plant
Additional supporting systems:
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chemical injection system
component cooling system
coolant storage
building drains
spent resin tanks
Full System Decontamination at the
Obrigheim Nuclear Power Plant
Technical description of the decontamination:
AREVA NP GmbH obtained the contract, performance: first quarter 2007
AREVA NP used HP/Cord UV decontamination technology in
combination with the AMDA equipment.
HP:
Permanganic acid (the chemical used for preoxidation).
CORD: Chemial Oxidation Reduction Decontamination; represents the
chemical decontamination process.
UV:
Represents the in-situ decomposition of the decontamination
chemical with an ultraviolet light source.
AMDA: Automated Mobile Decontamination Appliance, is the synonym
for the external decontamination equipment of AREVA NP.
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
HP/CORD UV process is a multi-cycle process including following
steps:
Step 1:
Pre-oxidation with HP
Step 2:
HP reduction with the decontamination chemical
Step 3:
Decontamination
Step 4:
UV decomposition of the decontamination chemical
and solvent clean-up
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Results:
A total of four HP/CORD UV cycles were performed
cation removal
224 kg
activity removal
5.6 E12 Bq (151 Ci) with > 95 % Co60
ion exchange resins 6.7 m³
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Doserate [mSv/h]
Full System Decontamination at the
Obrigheim Nuclear Power Plant
Dose rates before and after decontamination (given in log.scale)
Full System Decontamination, Evaluation
100,000
before: SG 2100 µSv/h; channel head 72 mSv/h
10,000
after:
1,6 µSv/h;
DR before 1st cycle, empty
1,2 mSv/h
1,000
0,100
0,010
0,001
DR after 4th cycle,empty
Full System Decontamination at the
Obrigheim Nuclear Power Plant
Results:
Average decontamination factors (DF)
DF auxilary systems
29
DF primary system
736
DF steam generators tubing
DF overall average
Gamma/alpha nuclide ratio:
Total man dosis
Estimated
12
1409
625
increased about factor 10
46.1 mSv
97 mSv
Full System Decontamination at the
Obrigheim Nuclear Power Plant
RESULTS
- Reduction of the ambient dose rate in the different areas:
steam generators
residuel heat removal
heat exchangers
chemical volume control system
recuperative heat exchanger
- Easy handling for dismantling and disposal of these components,
especially for the steam generators
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
RESULTS
- No controlled rooms more in this area, the single hot spots were
shielded and will be decontaminated in a special prozess
- Man-Sv savings for upcoming dismantling acitivities (1 - 1,5 Sv)
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Full System Decontamination at the
Obrigheim Nuclear Power Plant
Thank you
for your
attention!
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