Colorado State University

Decontamination of a Fume Hood Contaminated with Tritiated Thymidin

K. J. Walter, A. E. Draine, and T. E. Johnson Colorado State University Fort Collins, CO

Contaminated Fume Hood

Background

• Contaminated in 2003 with Tritiated-Thymidine
• Inadvertently volatilized
• From 2003 to 2007, have been attempting decon
  • Still contaminated after almost monthly attempts
  • Tried both soap/water and Radiacwash
• RSO will not release until counts are at background

Proposed Solution

Polymer-hydrogel strippable-coating from CBI Polymers. (CBI)

Process

• Spot tests demonstrated to RSO that gel was capable of removing tritiated-thymidine contamination
• Gained approval to continue decon efforts
• Removed expendable materials and put in radioactive waste
• Painted hood with 2 formulations of gel for comparison
  • ½ Decon 1101
  • ½ Decon 1101EXP
• Gel applied and allowed to set for 3 days

Materials

• Tried two formulations in development
  • Decon Gel 1101
    • Polymer B + Thixotrope A
  • Decon 1001EXP
    • Polymer B + Thixotrope B
• Multiple surfaces of hood
  • Glass
  • Painted metal
  • Cement board countertop
  • Copper pipe

Decon 1101EXP vs. DeconGel™ 1101

 

Application & Removal

Decon 1101EXP	DeconGel™ 1101
• More difficult to paint even thickness • Horizontal surfaces: - Thick, uneven application • Vertical & inverted surfaces : - Thick, uneven application - Dripped less	• Easier to paint • Horizontal surfaces: - Thick or thin, even application • Vertical & inverted surfaces: - Thinner application - Dripped more
• Removed in smaller brittle pieces • Thicker films Easier to peel • Longer dry time • Thinner films • Difficult to peel - tended to tear	• Removed in large pliable sheet • Thicker films Easier to peel • Longer dry time • Thinner films Peeled satisfactorily

Scintillation Wipe Map

12-14 = Inside ceiling; 15-17 = Inside hood window center; 18-20 = water pipe; 21 = floor

Area #	Before decon	3 days after	1 month later	% removed	11 Weeks later	% removed
1	30	0	0	100	0	100
2	261	0	0	100	0	100
3	89	0	0	100	0	100
4	21	0	0	100	0	100
5	1180	0	0	100	0	100
6	1920	11	47	98	0	100
7	202	0	0	100	0	100
8	754	0	0	100	0	100
9	1184	0	0	100	0	100
10	33	0	0	100	0	100
11	209	0	0	100	0	100
12	154	0	0	100	0	100
13	341	0	0	100	0	100
14	758	21	19	98	0	100
15	0	0	0	100	0	100
16	0	0	0	100	0	100
Paper wipes counted for 5 min using dark-adapted Beckmann Liquid Scintillation Counter Reported in cpm / 100cm2 above background

Conclusions

• Decon Gel 1101 was preferred for application and removal ease
• Decon of tritiated-thymidine accomplished
• Leaching controlled after one month
• Hood checked again 11 weeks later
• Additional coat was applied to area still contaminated
• Leaching still controlled

Questions?

 

 

Application Areas

• D&D Sites
• Commercial Nuclear Power Plants
• Nuclear Medicine & Research Labs
• Hazardous Chemical Clean-Up
Department of Defense
• Other Successful Applications