New Developments in Tritium Monitors

Transcription

1 Overhoff Technology Corporation New Developments in Tritium Monitors 1

2 Overhoff Technology Design and manufacture of Tritium in Air monitors with ionization chamber detectors Portable Fixed 2

3 Overhoff Technology Also: Low Level Tritium in Air Gas Proportional Detectors Passive Samplers (Bubblers) 3

4 Safety Aspects for Tritium MDA Minimum Detectable Activity Basic performance capability of the instrument. MDA should be a fraction of expected levels 4

5 Tritium Monitoring Techniques MDA Minimum Detectable Activity Basic performance capability of the instrument. MDA should be a fraction of expected levels 5

6 Safety Aspects for Tritium Typical values: 20 C/m 3 (HTO) DAC 1 C/m 3 for the MDA 6

7 MDA versus Sensitivity The MDA is the minimum measurement with some certainty or reliability It summarizes measurement limitations of an instrument in a real environment The SENSITIVITY of an instrument is merely the partial differential (linear) relationship between a change in the tritium concentration and the change in the instrument display. 7

8 MDA Limitations Factors influencing the performance of tritium instrumentation: Electronic Noise Radon Contamination / Plateout Background Gamma Airborne Gamma Noble Gasses Temperature Changes Humidity Shock / Vibration 8

9 Defeating Real World Factors Noise, Electronic and Other Sources Ultimately affects the speed of response of the instrumentation. The tradeoffs are instrument sensitivity versus rate of response. Solution Include this factor when choosing an instrument. 9

10 Defeating Real World Factors Ambient Radon Typically equivalent to 1 to 5 C/m 3 of 3 H. Appears as sharp spikes/bursts in the signal. Solution OTC has special circuitry which renders our instruments immune to radon and its daughter products. 10

11 Defeating Real World Factors Contamination / Plateout HTO behaves like ordinary water and will be adsorbed by the walls of the ion chamber. Prolonged exposure at significant levels result in a semi-permanent offset in measurement. Solution Wire-grid chambers 11

12 Defeating Real World Factors Background Gamma For instruments with an MDA of 1 C/m 3 Solutions At modest levels, the use of two identical ion chambers gives good results. At higher levels, up to about 10 mr/hr, a quadruple cruciform arrangement is needed. 12

13 Defeating Real World Factors Noble Gases Kr 85, Xe 133, Ar 41 Solution Use two chambers (or four), and subtracting. One chamber contains both the tritium and noble gases, the other is just noble gases. Result: Only tritium oxide is measured. 13

14 Defeating Real World Factors Temperature drift Solution: Dual Channel Electrometer Result: Temperature drift 5-40 C < 1 MDA. Humidity Solutions: Electrometers are sealed. PTFE used for insulators. 14

15 Instrumentation Design Design of instrumentation is dictated by the applicable requirements and, to some degree, other factors such as: Reliability Serviceability Cost Maintenance Ease of Use 15

16 Hand Held Portables Extra Requirements: Extremely fast response if used a sniffer Instant warm up No drift Good MDA Light weight Low gamma response choice of chamber configuration Serial interface optional 16

17 Portable Model 400AC MDA of about 2 Ci/m 3 Immune to radon Dual channel Electrometer Quad chamber for total Gamma compensation Communication to PC via RS-232; Automatic Gamma Calibration Diagnostics; battery life, power supplies Rechargeable NiMH Batteries Constant flow; 2 LPM (5 volume changes/min) 17

18 Portable Model 200SS Non-Gamma compensated, uses both chambers for tritium measurement Successor to the Model 394 and AN/PDR cc volume; MDA of 2-3 Ci/m 3 Radon suppression Fast response, 10 seconds to 90% of final reading Low cost 18

19 Fixed Monitor Model 421-HTO Nuclear Power Plant Monitor (Heavy Water) High Sensitivity Monitor in the presence of high concentrations of Noble Gases Uses Nafion Dryer, only HTO passes through 19

20 Fixed Monitor Model 593 Revamped in 2012 Gas proportional detectors, MDA is 1 kbq/m 3 Measures T 2 and T 2 O, Oxidizer included Noble gas compensation Updated preamplifier Single Board Computer LCD touch screen 20

21 Tabletop / Rack Mount Monitors Model 357 MDA of 1 Ci/m 3 Immune to radon Available with plate out proof ionization chambers 21

22 Other Tritium Instruments Passive Sample Collectors (Bubblers) With enough sampling time and care they can measure down to 10-9 Ci/m 3 These can be built to separately measure HTO, T 2, and 14 C. 22

23 Thank You! Q and A 23

24 Questions and comments may be directed to: Dell Williamson Overhoff Technology Corporation 1160 U.S. Route 50 Milford, Ohio U.S.A. Ph , Fx