DOE 2000. - Waste Isolation Pilot Plant - U.S. Department of Energy

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 2
H.C.S. Thom has developed a procedure for estimating the probability of a tornado striking a given
point. 9 The method uses a mean tornado path length and width and a site specific frequency. Applying
Thom’s method to the WIPP facility yields a point probability of 0.00081 on an annual basis, or a
recurrence interval of 1,235 years. An analysis by Fujita yields a point tornado recurrence interval of
2,832 years in the Pecos River Valley. 10
According to Fujita, the WIPP design basis tornado with a million year return period has a maximum
wind speed of 183 mi/hr (294.6 km/hr), translational velocity of 41 mi/h (66 km/hr), a maximum
rotational velocity radius of 325 ft (99.1 km), a pressure drop of 0.5 lb/in 2 (3.4 kPa), and a pressure drop
rate of 0.09 lb/in 2 /s (0.62 kPa/s).
2.4.1.2.4 Freezing Precipitation
The region of the WIPP facility has about 1 day of freezing rain or drizzle a year. 4 An ice accumulation
of more than 0.25 in (0.63 cm) has not been observed. Any ice accumulation that does occur is thin
because of the scarcity of precipitation during the winter months and because daytime temperatures rise
well above freezing.
2.4.1.2.5 Strong Winds
The maximum 1-min wind speeds recorded at Roswell are shown in Table 2.4-1. The fastest 1-min wind
ever recorded at Roswell was 75 mi/h (120.7 km/h) from the west in April 1953. 11 Windstorms with
speeds of 50 knots (93 km/hr) or more occurred ten times (during the period between 1955 and 1967)
about one a year. 7 The mean recurrence interval for annual high winds at 30 ft (9.1 m) above the ground
in south eastern New Mexico is shown in Table 2.4-2. 9,12 The 100-year recurrence 30 ft (9.1 m) level
wind speed in southeastern New Mexico is 82 mi/h (132 km/hr). Based on a gust factor of 1.3, 13 the
highest instantaneous gust expected once in 100 years at 30 ft (9.1 m) above grade is 107 mi/h (172.2
km/h). The vertical wind profile for two 100-year recurrence intervals has been estimated from the 30 ft
(9.1 m) values using the 1/7 power law 16 and is presented in Table 2.4-2.
2.4.1.2.6 Restrictive Dispersion Conditions
Hosler 14 and Holzworth 15 analyze records from several National Weather Service stations with the
objectives of characterizing atmospheric dispersion potential. Seasonal and annual frequencies of
inversions based at or below 500 ft (152.4 m) for the WIPP facility region are shown in Table 2.5-3.
Most of these inversions are diurnal (radiation-induced) and occur because the radiation cooling at the
earth’s surface is increased by conditions that frequently exist at the WIPP facility. The conditions are
lack of moisture, clear skies and low air density. When these conditions exist in the early morning,
radiation lost from the surface is not adequately absorbed and re-radiated by upper level air to heat the air
at the surface sufficiently. Consequently, the air at the surface quickly becomes cooler than the upper
level air and the colder surface air becomes trapped.
Holzworth gives estimates of the average depth of vertical mixing, which indicates the thickness of the
atmospheric layer available for the mixing and dispersion of effluents. 15 The seasonal afternoon mixing
heights for the region (Table 2.4-4) range from 1,320 m (4,329.6 ft) in winter to 3,050 m (10,004 ft) in
summer. Seasonal morning mixing heights in the region range from 300 m (984 ft) in winter to
680 m (2,230.4 ft) in summer.
2.4-2 January 24, 2003