Aerosols deposition qualification of Stack Monitors for Research Reactors (RR) & Medical Isotope Production Facilities (MIPF)

Transcription

1 Aerosols deposition qualification of Stack Monitors for Research Reactors (RR) & Medical Isotope Production Facilities (MIPF) Eduardo Nassif INVAP S.E. Bariloche - Argentina Fabian Rossi - ANSTO - Australia

2 Context - Relevance of Aerosols Deposition (& Iodine Plate Out ) on Sampling lines of Stack Monitors On measuring stack effluents in nuclear facilities, aerosols deposition and iodine plate out on sampling lines should drive relevant attention in order to optimize design of sampling lines, minimize sample losses and improve accuracy (on determination of stack releases). A number of considerations on sampling lines geometry, analysis of suitable materials and flow rate ranges shall be taken into account. Design recommendations and guidance are defined on Standards like, for instance- ANSI 13.1 and M11 (see References below on this presentation). This lead designers to often focus their attention on monitor s location and disposition inside the plant, and reactor s stack sampling lines design. While this a rather common practice to be considered when connecting air effluent monitors to process (stack), less attention is driven regarding design and qualification of monitor s internal sampling lines, related to aerosol deposition and iodine plate out effects.

3 Scope : Main goals.. To determine actual penetration factors inside monitor s sampling lines. This is relevant, since may affect measurement accuracy when estimating stack emissions. In addition to review calculations on deposition effects expected for specific connections of stack monitors to process, an experimental method to quantify relevance of deposition effects inside monitoring equipment in comparison with the effects observed on main connection to process- is described. Previous analysis is complemented with a review of Iodine Plate-Out effects on stack monitor s sampling lines is presented.

4 Stack Monitors Installation Requirements Many RMS suppliers produce and install Stack Eflluent monitors on (new or upgraded) nuclear facilities. Different facilities do have specific air sampling requirements. Due to quite diverse lay-out arrangements, etc ), installation requirements for sampling lines may be quite different. Installation in already existing upgraded plants usually do present more complex restrictions for sampling line connections from monitoring units up to the stack. Specific customer s requirements does impose also additional restrictions on monitoring units themselves. (Example: closed structures may be required as prevention for shower spreads being installed in the vicinity of the equipment as part of fire systems..), while in other cases open racks can be used, thus giving other internal sampling lines design opportunities. In the following slides, some remarks on these design options, considered for several equipment installed by our company at different facilities are presented...

5 Installation & Monitoring Requirements Real Time Off-Line Automatic Stack Effluents Surveillance (some examples) RPF/ETRR-2 Radioisotope Production Facility (Egypt) OPAL Nuclear Research Reactor (Australia)

6 Stack Effluents & Air Ventilation Radiation Monitors (Most Usual Features) ISOKINETIC SAMPLING STACK EMISSIONS IN RR STACK EMISSIONS IN MIPF * (High Activity - Pulsed «batch» emissions follow-up) PARTICULATE IODINE NOBLE GAS independent channels NG CHANNEL: GROSS β - GROSS γ DETECTION and γ SPECTROMETRIC CAPABILITIES ( 41 Ar 133 Xe and other specific measurement channels) GROSS β - GROSS γ DETECTION FOR AEROSOLS (currently α/β measurement requirements) 131 I DETECTION ON IODINE CHANNEL DETECTORS: Use of plastic scintillators last generation Lanthanum halide scintillators CdTe Solid State detectors Si PIPS 4 User s Interface Communication Levels (Local x 2 Remote x 2) CUSTOMIZED PROCESS ORIENTED SOFTWARE INTERFACE PROCESS CUSTOMIZED STRUCTURE & SAMPLING SYSTEM*

7 Typical Internal Architecture (possible Options) Interconnection & Communications (example) Structural OPEN GEOMETRY SAMPLING RACK STANDARD 19in. RACK WITH TOUCH SCREEN LOCAL INTERFACE OR.. SEISMIC QUALIFIED CUSTOM STRUCTURE after IEEE 1E 344 IP 65 COMPLAINING - WATER TIGHT -

8 2 Main Tracks to be considered.. Stack to Monitor Monitor s internal sampling lines Adjustment of Penetration Factors should be available within Monitor s Software capabilities

9 Determining Aerosols Deposition.Stack to Monitor INPUT DATA From Stack to Monitor...(by calculations) Vertical section (stack level +37 to llevel +16) 21 m Horizontal section 3.7 m Elbows 4 x 90 Pressure Kpa Temperature 300 K Diameter of the aerosol particle to be considered 10 m* * according to ANSI 13.1, pages 29 and 39 Shorter sampling lengths between Stack and Monitor is achievable when installing the monitor at higher reactor building levels.but..this implies higher seismic requirements impact on structure and internal sampling lines design

10 The Real Emissions..determining Aerosols Deposition Stack to monitor sampling line - Aerosols Deposition mechanisms Gravitational settling: Significantly only on horizontal sections or on an angle above 30 degrees with respect to the vertical Brownian diffusional deposition: Generally quite low for velocities above 1m/s Turbulent inertial deposition: Quite significant and rising with velocity at an exponent close to 2.6, depending on the correlation Electrostatic deposition: It depends on the electrostatic load accumulating on the piping Thermophoretic deposition: Registered when there are temperature gradients between walls and flow, or between flows at different temperatures Diffusiophoretic deposition: Due to aerosol concentration gradients in the same fluid, it is negligible in turbulent rates and in those of low deposition by other mechanisms

11 The Real Emissions..determining Aerosols Deposition Stack to monitor sampling line - Aerosols Deposition mechanisms Penetration of the Piping System as the result of the individual penetrations of each fitting and straight section for each mechanism. total i, j i, j Where i, j is the penetration of fitting i for deposition mechanism j Correlations are used for the entire sampling piping that calculate separately each mechanism and distinguish elbows, contractions and expansions as global deposition. Deposition on bends may be calculated through the following equation when the curvature radius inner diameter ratio is equal to or above 5. is the elbow angle. Stk = Stokes Number bend Stk e where,

12 Stack to monitor sampling line - Aerosols Deposition mechanisms Calculations being considered/performed on all straight sections after the specific mechanisms Mechanism Gravitational settling Turbulent inertial deposition Brownian diffusional deposition Electrostatic deposition Thermophoretic deposition Diffusiophoretic deposition Calculation being performed Yes, for all non-vertical sections -main mechanism- Yes Yes, for verification purposes No: as metallic pipelines grounded through anchors are considered and fluid is air with 50% +/- 10% controlled humidity. No: as it is considered that there are no RELEVANT temperature gradients on the pipeline (hence effects are negligible: < 0.1%). No: only one gas (air) -perfectly mixed and uniform - is present in the sampling line

13 Item Alternative Stack to Monitor sampling lines Different sampling line design alternatives being analyzed i = m (25.4mm, BWG16, e=1.65 mm) Q = 75 l/min U = 3.26 m/s i = m (25.4mm, BWG16, e=1.65mm) Q = 65 l/min U = 2.85 m/s i = m (34.9 mm, BWG16, e=1.65mm) Q = 94 l/min U = 2 m/s i = m (38.1mm, BWG16, e=1.65mm) Q = l/min U = 1.85 m/s i = m (38.1mm, BWG14, e=2.11mm) Q = 100 l/min U = 1.85 m/s Vertical section Horizontal section Elbows Total Reynolds fluid (Ref) Gravitational penetration Diffusional penetration Turbulent penetration Total ( i ) Reynolds fluid (Ref) Gravitational penetration Diffusional penetration Turbulent penetration Total ( i ) Reynolds fluid (Ref) Gravitational penetration Diffusional penetration Turbulent penetration Total ( i ) Reynolds fluid (Ref) Gravitational penetration Diffusional penetration Turbulent penetration Total ( i ) Reynolds fluid (Ref) Gravitational penetration Diffusional penetration Turbulent penetration Total ( i )

14 The Real Emissions..determining Aerosols Deposition (Aerosols) Stack to Monitor sampling: Conclusions Case Item 5 : A tube of a 38 mm diameter and BWG 14 (ID 33.88mm) at a nominal flow of 100 l/min was adopted. Global penetration of 58.3% -reached with previous adoption-, is above the 50% deemed as sufficient design value for the transfer of aerosols with a 10 m diameter.

15 Stack To Monitor Sampling Lines.. Iodine Plate Out..? The following equation given by ANSI N , Annex C (C-1) is used to calculate iodine plateout: iodine e VL 4 d Udt Vd: Deposition speed in [m/s] interpolated to 50% rel. humidity L: Total Length [m] U: Air Flow speed [m/s] dt: Piping diameter [m] Species I2 HOI CH3I The calculation considers fixed length L= 25m Inner diameter [m] Velocity [m/s] Vd (50 % humidity) 1.43E-03 m/s 3.85E-05 m/s 7.50E-08 m/s Penetration iodo

16 Stack To Monitor Sampling Lines.. Iodine Plate Out..? (Iodine) Stack to Monitor sampling lines: Conclusions All penetrations are above 50%, except for chemical species I2, in which values are quite low, mainly as a result of the small Vd (Deposition Speed)* for this species. Case Item 5 adopted before, i.e. a tube of a 38 mm diameter and BWG 14 (ID 33.88mm) at a nominal flow of 100 l/min, showed acceptable conditions for Iodine Plate-Out, for HOI and CH3I species. * Deposition speed being considered is that reported by M.J. Kabat, Deposition of Airborne Radioiodine Species on surfaces of metals and plastic, Ontario Hydro, mentioned as reference in standard ANSI , and corresponding to stainless steel.

17 Iodine Plate Out - A look to internal monitor s sampling lines: Comparison among Iodine Species Note here for I2 (Plastic): Much LOWER Vd than SS! Smaller L than external Smaller d than external Much efficient Penetration!

18 The I2 Species: comparison between stack monitor s external & internal sampling lines: the I2 Case Vd: Iodine Deposition Speed [m/s] interpolated considering 50% de humidity L: Total Length [m] U: Air Flow rate [m/s] dt: Piping diameter [m] Note here for I2 (Plastic): Smaller L Smaller d Much higher Vd! Calculations for I2 Stack to Monitor SS 304L Monitor internal lines SS304L Stack to Monitor Poliethylene Monitor inte rnal Poliethylene Vd(I2) 1,43E-03 1,43E-03 9,50E-05 9,50E-05 L 25 1, ,42 U 3,26 4,46 3,26 4,46 d 0,0221 0,0195 0,0221 0,0195 L/( U x d) 347, , , , ηd 13,74% 91,08% 87,65% 99,38%

19 Monitor s internal Iodine Plate Out : (not obvious..?) Lessons learned Iodine depositions are extraordinary sensitive to geometrical parameters. Using Plastic - instead of SS dramatic improvements may be reached when focusing on I2 species (I2 is «more anomalous» in terms of deposition on SS..) Iodine Plate Out and Aerosols deposition goes in opposite directions in terms of design for optimum penetration (Design helps on finding a compromise.. not an optimum solution..!) If I2 were the predominant species, Plastic should be used instead of SS...but (because of chemical stability and relative abundance in air), I2 is not the most common species for radioactive Iodine, therefore.. SS is still- a good relative solution in terms of Iodine penetration.

20 Now..how Does Behave the Aerosols Deposition inside Monitor s Internal Sampling Lines? Experimental Determination needed!! Ideal representation..but Complex real Geometry

21 Monitor s internal sampling line: Why Experimental Determination.?..since Monitor s sampling circuit do present non-regular geometrical arrays Non perfectly cylindrical sections (¾ ID Poliethylene Poliethylene pipes). Valves of different types and sections Curves Fittings (7) Elbows T reductions Adapters Theoretical calculations & modelling do not bring fully reliable data.. (as may be developed in case of for regular piping sections for stack to monitor sampling lines)...experimental Validation Tool is required for Aerosols Deposition factors determinations (Similar criteria as in case of calculation of Hydraulic losses in complex equipment/sampling circuits where experimental validation is current used tool, beyond finite elements calculations).

22 Aerosols sampling depositions: Experimental Determinations To quantify aerosols deposition from monitor s flange connection to process (stack sampling lines), up to the particulate measurement chamber. Calibrated Spherical Particles - 5.4* microns diameter are injected at monitor s inlet. (* available particle diameter size in occasion of the measurement) Quantification is performed using differential weighing technique. Simultaneous measurement of particle concentration with APS at monitor s inlet. (Aerodynamic Particle Sizer). Each measurement comprises a collection filter at monitor s entrance, and a collection filter inside particulate measurement chamber. More than 30 measurements were conducted. Measurements were performed at INVAP s Testing facilities.

23 Aerosols sampling depositions: Experimental Array Particulate generation is performed using a high speed N2 jet Jet-driven depression sucks and atomizes the particulate suspension The Measurement Array does include: A particle spray generator A Heat Exchanger (for water evaporation on water drops attached to the particle A Dryer for absorption of water steam A Flow compensation device (between particulate injection flow and monitor s air flow) An APS (Aerodynamic Particle Sizer) Glass Fiber filters fro Aerosols collection Injection system components (i.e., N2 cylinder, flowrate meters, valves, etc.)

24 Aerosols sampling depositions: Experimental Set-Up (schematic)

25 Experimental Set-Up : Filter Removal at Aerosols Measurement Chamber location

26 Experimental Set-Up APS

27 Measurement Sequence A previously weighed filter, is set at the entrance of the monitor to collect aerosols during a defined time interval. After collection and remotion of this filter, another weighed filter is set inside the monitor at the regular particulate measurement location (without interrupting particulate generation), so that particulates are collected for a similar (time) interval. Both filters are weighed again,after collection, in order to get by difference the deposited net mass inside monitor s internal sampling lines. Using APS measurements, the sampling flow rate and the collection time interval, the total mass being injected is calculated. Four measurements were performed: two for mass (monitor s input and output), corresponding to filter weighing, and two for concentration (direct measurements performed with APS at monitor s inlet).

28 Results Several statistical methods were applied to handle experimental data: Adjustment by minimum squares Minimum Modules Analysis Pairing Data Analysis The results obtained for Aerosols relative deposition, namely the ratio between Mass Deposition (Md) to the mass at the entrance of the equipment (Me), lead to: (Mdep/Me) ~ (14 +/- 5) % regarded as the envelope of the most conservative results brought with each one of the individual statistical analysis.

29 Conclusions Particulate material deposition inside internal sampling lines on Stack Monitors is NOT NEGLIGIBLE, and should be taken into account for proper estimation of aerosols actual stack emissions. Type,Sizeandmaterialsofinternalpiping, are indeed a relevant issue on designing Stack Monitor s. Plastic is still a good option to be considered on specific cases (with some remarks on Electrostatic issue and exceptive life if installed outdoors.. Combined together with external sampling lines deposition calculations, characterization of sample losses inside monitor s internal circuits may bring an integral picture in order to get a more accurate adjustment of sample losses by Aerosols Deposition and Iodine Plate Out. (Calculated & Measured) Penetration factors may be integrated into equipment software and user interface in order to facilitate estimations of real emissions of aerosols coming out through the stack. To include strategic sampling points in the system to do predictive maintenance and calibrations to take into account the variation along the time of the sampling line performance.

30 Conclusions (Cont.) In situ adjustments of monitor s sampling system during life cycle operation can be done, in order to optimize equipment performance and accuracy. Optimize the instrumentation to monitoring and control the flow performance. Flow affects the isokinetic hypothesis at the nozzle. System with smart adaptation to the real online conditions can be implemented on next generation of instruments e.g. adaptive flow- Finite element is a very useful calculation tool to predict: best point to install sampling point main isokinetic nozzle and test point-, minimum mixing length required, flow patron alteration under different condition in the stack, ambient changes (wind temperature), etc.

31 REFERENCES Aerosol Measurement: Principles, Techniques, and Applications by Pramod Kulkarni, Paul A. Baron, Klaus Willeke, Paul A. Baron, Wiley Third Edition (2 nd. Edition 2004) Gaseous Radioiodine Deposition Losses in Nuclear Reactor Sample Lines, Byung Soo Lee, William A. Jester, Pennsylvania State University, Nuclear Engineering Department Deposition of Airborne Radioiodine Species on surfaces of metals and plastic, M.J. Kabat, Ontario Hydro Monitoring of Radioactive releases to Atmosphere from Nuclear Facilities, Tech. Ref. M-11 (UK). Sampling and Monitoring Releases of airborne Radioactive Substances from the Stack and Ducts of Nuclear Facilities. Standard ANSI/HPS N

32 Aknowledgements Thanks are due to Mr. Marcelo Caputo and to Mr. Marcelo Gimenez from Centro Atomico Bariloche (CNEA-Argentine National Atomic Energy Commission) for technical support on implementation of the experimental technique Thanks are due also to Mrs. Mariana Di Tada and Mr. Román Pino (INVAP S.E.) for valuable technical discussions

33 Thank you! Questions..?