Transcript 09_Tritium_Retention.PPT

Tritium Retention in Vessel Tiles & Oil
Charles A. Gentile
D&D Lessons Learned Workshop
June 25-26, 2002
PPPL
June 25-26, 2002
D&D Lessons Learned Workshop
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Acknowledgement of Others
Working on these Issues:
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P. LaMarche
G. Gettelfinger
S. Langish
R. Parsells
June 25-26, 2002
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J. Parker
S. Raftopoulos
K. Rule
R. Feder
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Presentation Outline
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Introduction to TFTR, Tritium History
Scale Model Testing
Decontamination
Results
Summary/Conclusion
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Tokamak Fusion Test Reactor
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TFTR Tritium History
• T fueling by neutral beam injection (NBI)
• Small amount by direct gas puffing
• T captured on NB enclosure cryopanels
• Batch processed to holding tanks
• D/T mixture with trace hydrocarbon
• Early stages of TFTR Ops scrap gas oxidized and shipped offsite
for reprocessing
• Total T processed through facility - 99g
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Tritium Retention in TFTR 6000 Ci “tenaciously bound” in torus
• Carbon tiles - Major location of T inventory
• Approximately 1 ton of carbon tiles
• Codeposited Layer
• Plasma generated Carbon/Tritium coating
• Most tritium inventory in codeposited layer
• Carbon dust and debris
• Highly contaminated
• Smearable hazard to personnel
• Low total inventory
• Stainless Steel vessel wall
• Modest inventory
• Low outgassing rates at room temperature
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Requirements for Safe
VV Segmentation
• Cut up TFTR vacuum boundary while:
• Minimizing worker exposure to T-contaminated and activated
materials
• Leave internal components inside TFTR
• Remove tiles from cut lines
• Minimizing amounts of T or T-contaminated material released to
the environment
• Minimizing waste
• Waste disposal cost is a significant fraction of D&D cost
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Concrete/Tile Test
• Mock-up of TFTR VV conditions in a TypeA waste container
• Eight tiles placed in container
• About 10Ci of tritium in tiles
• Three lifts (about 10 gallons each) loaded in
container on successive days
• Passive measurements taken after each lift
• Core samples of cured concrete measured
for T
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Test Results
• Great deal of moisture was released as the
concrete cured
• T monitors gave false high signal (moisture
and foam agent) during curing time
• Once concrete cures, smearable
contamination was low
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Test Results – Core Samples
Sample
2001-1262
2001-1263
2001-1724
2001-1725
2001-1726
2001-1727
June 25-26, 2002
Tritium (µCi/gm)
0.0178
0.1342
0.0201
0.0226
0.0353
0.0231
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Empirical Data - Conclusion
• Level of tritium in concrete
• DAC ≈ 40.9 g/m3 (estimate)
• Very difficult to suspend 41 g/m3 and greatly exceeds the TLV for
silica (0.005 mg/m3)
• Miniscule hazard from tritium in the dust!
• Conclusion from empirical data
• Low level of tritium to be released in concrete fill
• Concrete dust will have very low level of T
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Safe Disposal of VV - Plan
• Strategy to contain T while concrete filling
and segmenting vessel:
• Concrete/Foam Filling of the vacuum vessel (VV)
• Displaced air passed though bubblers to reduce T release
• Detritiation factor ≈10X
• Possible to go directly to stack via E-trunks
• Segmentation of the VV using Diamond Wire Cutting (DWC)
• Dry process - no large volumes of cutting fluid or gas
• Containment of particulates generated by the DWC during the
segmentation process
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Diamond Wire Cutting
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Actual Results on TFTR
• Concrete pour on three separate days in
Summer 2001
• Vessel segmentation commenced in
Summer 2001
• Completed Spring 2002
• No whole body doses detected for this task
• Tritium released is modest over plant
chronic release (CY 2001 totals)
• HTO: 191Ci vs 115Ci/yr chronic rate prior to pour
• HT: 39Ci vs 10Ci/yr chronic rate prior to pour
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Activity in Stack During D&D Task
Monthly Total Stack Releases (2001-2002)
70
HTO (Ci)
HT (Ci)
Monthly Total (Ci)
59.94
50
August 2001
DWC Started/
NB's on trunks
40
33.173
30.8
30
25.638
21.802
21.428
21.136
18.178
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15.46
11.044
12.775
12.337
10.482
9.945
7.79
10
5.753
Apr
Mar
Feb
Jan
Dec
Nov
Oct
Sept
Aug
July
June
May
Apr
Mar
Feb
0
Jan
Tritium Release (Ci)
60
Month
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Impact on Workers
• Full face supplied air respirators worn in
enclosures
• Reduces/eliminates facial skin exposure
• Facial skin exposure is only credible internal exposure risk
• Full anti-contamination protective clothing
worn in enclosures and cutting lay-down
area
• Minimal T exposure to workers. No whole
body uptakes from activated components
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Sector Disassembly
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Worker Inside DWC Enclosure
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Sector Removal
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Tritium Activity in Oil
• 2 types of oil used for TFTR
• Krytox
• Hydrocarbon
• Both types of oil found to have great
affinity for “collecting” tritium
• Personnel exposure to oil is hazardous
• Oil easily sticks to and passes through skin
• High specific activity of tritium in oil – makes it extremely
hazardous
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Tritium Activity in Oil
• Oil removed from primary (nuclear)
pumping system measured to levels of
200µCi/g
• Approximately 2-3 g of oil (due to high
specific weight) per drop
• A single drop of tritiated oil exposed to skin
would lead to an uptake of approximately
30 mRem
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