ML25069A620
| ML25069A620 | |
| Person / Time | |
|---|---|
| Issue date: | 03/16/2023 |
| From: | Mazaika M NRC/NRR/DEX |
| To: | |
| References | |
| Download: ML25069A620 (1) | |
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8 The existing commercial LWR fleet in the United States is deployed in the lower 48 States Some advanced reactor designs may be deployed in Alaska (and other cold regions)
Current NRC dispersion models are old and based on limited field studies in the lower 48 States conducted many years ago; model results are generally conservative in accordance with the defense in depth concept Current regulatory guidance was developed based on the above but with caveats on model use Other models (e.g., EPA, national laboratories), Met data, and other model inputs are alternate approaches = custom analyses by applicants + custom reviews by NRC staff Atmospheric dispersion may be different in cold regions (e.g., longer persistence of poor dispersion conditions = potentially higher doses)
Dispersion conditions vary by location and may need different seasonal modeling approaches Logistical issues for Met monitoring include weather, remote sites, maintenance, QA/QC, and wildlife
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- Duration of sunlight and intensity of solar radiation
- Frequency of calm winds and low wind speeds
- Boundary layer, mixing height, and temperature inversions
- Persistence of restrictive dispersion conditions
- Presence of thermal internal boundary layers
- Precipitation frequency and intensity
- Length of growing season
- Topography (including presence of sea and river ice)
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- Atmospheric dispersion has two parts:
Transport where does a release go and how fast does it get there Diffusion how much does a release spread in the horizontal and vertical directions as it travels
- Transport:
Where depends on wind direction(s) at plume height Plume height depends on release temperature, exit velocity, and ambient temperature How fast (or slow) depends on wind speed
- Diffusion or plume spread:
Plume spread defines the volume of air that the release mixes into Volume controls dilution, and dilution depends on physical and mechanical turbulence The NRC defines turbulence (physical by stability class, mechanical by structural wake)
11 Barrow Fairbanks Anchorage Annette Jan 0:00 4:03 5:40 7:17 Feb 4:16 6:59 7:48 8:47 Mar 9:25 10:10 10:26 10:47 Apr 14:17 13:39 13:25 13:07 May 19:50 17:05 16:15 15:18 Jun 24:00 20:37 18:45 17:02 Jul 24:00 21:26 19:11 17:18 Aug 23:33 18:10 17:05 15:54 Sep 15:40 14:37 14:14 13:46 Oct 10:59 11:17 11:24 11:33 Nov 5:49 7:49 8:30 9:17 Dec 0:00 4:40 6:05 7:34 Source: NASA, Goddard Institute for Space Studies, ModelE AR5 Simulations
12 Barrow Fairbanks Anchorage Annette Jan 1.67 20.02 39.19 77.30 Feb 34.11 73.40 97.81 139.95 Mar 130.47 174.24 198.58 237.80 Apr 269.97 301.19 318.91 346.97 May 409.45 413.11 420.47 433.88 Jun 483.29 467.83 468.44 473.25 Jul 440.78 436.88 441.08 450.58 Aug 313.81 337.10 351.37 374.67 Sep 171.29 212.73 235.20 271.40 Oct 59.13 101.44 126.14 167.92 Nov 7.13 30.86 51.63 91.06 Dec 0:00 7.01 23.47 59.22 Source: Adapted from NASA, Goddard Institute for Space Studies, ModelE AR5 Simulations
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- Boundary Layer:
Lowest 1 to 2 kilometers above Earths surface
- Mixing Height:
Depth above earths surface through which relatively vigorous mixing of air (and pollutants within it) takes place Varies seasonally and from day to day depending on cloud cover, wind speed, weather patterns, etc.
- Temperature Inversions:
Ambient temperature usually decreases with height An inversion is an increase of temperature with height that acts like a lid Usually at high altitudes during the day, starts at or closer to the ground at night due to radiational cooling Photo of Salem Power Plant in Massachusetts by Ralph Turcotte, Beverly Times
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- 1. Size of advanced reactor and site footprint doesnt affect all disciplines and technical reviews in the same way.
- 2. Design development is a business decision and should account for the range of climate and Met conditions when considering potential site locations.
- 3. Met monitoring is generally a long lead-time item; even more so in remote locations subject to extreme or persistent cold or both.
- 4. NRC modeling and Met monitoring guidance is preferred. Alternate approaches are allowed if justified, but customized analyses by applicants and reviews by NRC staff are needed.
- 5. Maximum dispersion impacts, locations, doses, and sizing of the emergency planning zone may be affected by location, persistence, and time of year.
- 6. Multiple long-and/or short-term modeling analyses or modeling approaches may be needed for licensing if conditions vary significantly.
- 7. Community relations may be important as consent-based siting approaches for nuclear facilities continue to develop.
19 Contact for additional information:
michael.mazaika@nrc.gov