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Receptor Height: 1.5 m in Dispersion Modeling

This article discusses the importance of choosing the appropriate receptor height in dispersion modeling and the potential impact on results. It also explores a case study involving beryllium contamination.

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Receptor Height: 1.5 m in Dispersion Modeling

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  1. Receptor Height: 1.5 m in Dispersion Modeling J.C. Laul SB-EWM, Los Alamos National Lab P.O. Box 1663 Los Alamos, NM 87545 505-665-9791 jclaul@lanl.gov LA-UR-12-01536

  2. Background • EPIcode (chemicals) and HOTSPOT (radionuclides), approved codes in DOE “Toolbox”, recommend a receptor ht of 1.5 m, which is typical for “chest ht and breathing zone”. • MACCS2 and other codes use zero meter receptor ht, and yield a highly conservative value at short distances. A ground level (0 m ht) means that a receptor is lying on the ground, which is not the typical case. • A conservative value is not necessarily realistic. • A sensitivity analysis by EPIcode at 0 m and 1.5 m receptor ht for Be and Cl2 showed that 0 m ht yields values about 144 times higher at 30m than with 1.5 m ht, which is highly unrealistic from field measurements. • EPP use 30 m (Alert) and 100 m (SAE). Safety Basis use 100 m for HC for nuclear and non-nuclear facilities. A value at 100m is 60% higher with 0 m ht than with 1.5m ht.

  3. MDA-B: Incident Description on February 22, 2011 • During excavating a trench (15 ft W x 15 ft deep) in the middle of Enclosure 9, operators observed a significant quantity of beryllium (Be). • 34 glass (Mason) jars from ~30 inches (in.) below grade were excavated from the trench, and then placed in the sorting area. • An unknown number of jars were broken so the material was dispersed in the soil. About 50% jars were uncovered and 50% were covered. • Industrial Hygienist removed a jar from the dig face, took to a nearby safe area, and took samples for evaluation. • The Lab analysis showed the wipe sample to contain 40 mg/100 cm2, which is interpreted as a combination of Be powder (i.e., small metal spheres) and dust (loose contamination in oxide form), and loose soil (i.e, dirt). Proportion of Be powder, Be dust, and dirt is unknown.

  4. MDA-B: Incident Description on February 22, 2011 • Bulk sample analysis also showed that it was 97.2% Be shaving/chip (2mm) and remaining Pb and Ni. • With in 30-45 min, an IH set up an air sampling equipment on a table (1.3 m ht) at about 10 m from the dig face, using NIOSH approved filter for Be. Total airflow passes through was 271 L in 2. 5 hr (150 min), which is 1.81 L/min. Measurement was unmitigated. • Analysis showed 4.4E-4 mg/m3 or 0.44 µg/m3 or, which is very low concentration. • How does this measured value fit with the dispersion model? • Does this support 1.5 m receptor height for modeling?

  5. Glass Jars shows mainly Be powder/chips

  6. Glass Jars show mainly Be powder/chips; dust is unnoticeable in jars. Blue color is due to blue film

  7. Beryllium Blue Film: Oxidation (2Be + O2 2BeO); “blue film”, (a few microns; 1.2% to 8.1% wt), tight coating on the Be metal.

  8. Enclosure #9 Description • Dome: 296 ft (L) x 75 ft (W) x 32 ft (H) ; Vol. 7.10E+5 ft3 • Air Exchange: 4.5 air/hr ( no negative pressure) • Exhaust Systems: 8 ; Each has 4 HEPA; Each HEPA filter – 1,500 cfm • Total air flow: 8 x 4 x 1,500 = 48,000 cfm • Air flow perpendicular to exhaust fan; 276 ft x 32 ft = 8,832 ft2 • Velocity, airflow: 48,000 cfm/ 8,832 ft2 = 5.4 ft/min or 0.03 m/sec • Observed Be concentration: 4.4 E-3 mg/m3 or 0.44 ug/m3 • Bkg level: <0.03 ug/m3, below LANL action level

  9. Enclosure #9 Description

  10. TA-21 MDA B Enclosure 9 HEPA Ventilation Units • IH Monitoring Equip • CAM • Sampling • Equip D& D Conex • North Changeout Approx. Location of Be. jars. Control Clean Fill Trench • Anomaly • Bins

  11. Source Term (ST) • Observed 34 jars; estimated wt 20 lb; Some jars were broken, 50% uncovered and 50% covered. • Used 10 lb for calculations using 0 m vs 1.5 m and 1.3 m ht. • ST = MAR x ARF x RF x DR x LPF (DR and LPF = 1.0) • MAR : 10 lb ; ARF x RF = 1E-3 x 1E-1 ; 1E-4 • ST = 10 lb x 1E-4 x 454 g/lb ; 0.454 g ; modeled as Term release • ARR: DOE-HDBK-3010-94, P 4-10, ARR is 4E-5/hr or 1E-8/s; RF 1.0 • Rate: 1E-8/s For 10 lb, rate = 1E-8/s x 10 lb x 454 g/lb = 4.54E-5 g/s • Air sampling for 150 min; 4.54E-5 g/s x 60s x150 min = 0.41 g ; modeled as continuous release by EPIcode

  12. EPIcode: Approved Code in “DOE ToolBox” for chemical dispersion; Parameters Used for Spill • Release type: Term release and continuous release are modeled as a ground level release with no plume buoyancy and centerline plume concentration provides the maximum exposure to the receptor. Both releases are conservative. • Stability Class: F, which is stable and a conservative estimate. • Wind speed: 0.03m/s (calculated value) at 2 m height is used. • Release effective height: 0 meter, which is ground level release. • Receptor height is typically 1.5 m, normally chest height and breathing zone, but 1.3 m table height is used, and zero height is also used for comparison. • RT = ST = 150 min each, because air monitoring equipment was run for 2.5 hrs. • RF =1.0; ERPG/TEEL-3 assumes total concentration exposure to a receptor. • Terrain Standard: Open country which is more conservative than City terrain.

  13. EPIcode: Beryllium Concentration at zero, 1.5 m and 1.3 m Ht

  14. EPIcode: Beryllium Concentration at zero, 1.5 m and 1.3 m Ht

  15. EPIcode: Beryllium Concentration at zero, 1.5 m and 1.3 m Ht

  16. Be Concentration Vs Distance, Zero Receptor Ht (Wind speed 0.03 m/sec)

  17. Be Concentration Vs Distance, 1.5 m Receptor Height (Wind speed 0.03 m/sec)

  18. Be Concentration Vs Distance, 1.3 m Receptor Height (Wind speed 0.03 m/sec)

  19. Conclusions • Experimental value of Be 0.44 ug/m3 by an air monitoring equipment at short distance from spill is 0.29 ug/m3 , an excellent agreement with the value by EPIcode modeling with receptor ht of 1.3 m. • This further strongly supports 1.5 m receptor ht (chest ht and breathing zone) modeling at short distances. • The values calculated at 1.5 m ht are reliable and close to being realistic than values at 0 m ht, which over-estimates the concentration by several orders of magnitude as compared to the air monitoring result. • Receptor ht is important at short distances (e.g, 300 m). Beyond 300 m, it is not important.

  20. Conclusions: Cost Benefits • With zero receptor ht, the concentrations are overestimates at 100 m by 60% as compared to 1.5 m ht, which reduces the TQs for facility CHC. • For chemical safety analysis, consequences will be also an overestimate by 60% at 100 m with zero receptor ht for collocated workers, which will require controls (ML1) and involves significant costs that become cumulative over time. • For nuclear safety analysis there can be significant costs savings for the selection of controls (SSCs) to mitigate consequences for the workers at 100 m by using 1.5 m ht instead of zero receptor ht. • Overall, the use of 1.5 m receptor ht is highly beneficial for CHC, FSA (chemical) and DSA (nuclear) facilities.

  21. EPIcode: Beryllium Concentration at zero, 1.5 m and 1.3 m Ht

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