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

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 2
The question of total WIPP facility risk at a number of acceleration levels and under a number of
assumptions about source zone parameters is addressed graphically in Figure 2.5-31, where several
extreme cases are considered. Four curves in all are shown. Curves 1 and 2 both assume maximum
source zone magnitudes of 7.8, 6.0, and 5.5 for the Basin and Range subregion (or Rio Grande rift),
Central Basin Platform, and WIPP facility source zones, respectively, and recurrence formulas suggested
by the Roger and Malkiel 15 magnitudes. That is, curve 1 of Figure 2.5-31 is the result of combining
individual source zone risks at the WIPP facility represented by curve 4 of Figure 2.5-27, curve 8 of
Figure 2.5-28, and curve 4 of Figure 2.5-29. Similarly, curve 2 of Figure 2.5-31 is the result of
combining individual source zone risks at the site represented by curves 2 and 4 of Figures 2.5-27
through 2.5-29, respectively. The difference between curves 1 and 2 of Figure 2.5-31 is that curve 2 uses
source zone geometries taken from Algermissen and Perkins, 21 while curve 1 uses the slightly more
conservative alternate source zone geometries discussed in Section 2.5.4.2. Curves 3 and 4 of Figure 2.5-
31 both assume smaller maximum source zone magnitudes of 7.8, 5.0, and 4.5 for source zones taken in
the same order as above and recurrence formulas suggested by Sanford et al. 14 The individual risk curves
used to generate these two total risk curves may be deduced from the above description and Table 2.5-4.
The differences between curves 3 and 4 are precisely the geometric differences between curves 1 and 2.
It is clear from the four total site risk curves of Figure 2.5-31 that the geometric differences considered
for the source zones do not introduce important differences in total WIPP facility risk at any acceleration
level, although what small differences do exist are most evident at low accelerations. More importantly,
for all parametric variations allowed in this study, extremum curves as shown in this figure imply
accelerations associated with 10 -3 /y risks ranging between about 1.31 and 2.46 ft/s 2 (40 and 75 cm/s 2 ),
accelerations associated with 10 -4 /y risks between 75 and 130 cm/s 2 , and 10 -5 /y risk accelerations between
4.27 and 8.04 ft/s 2 (130 and 245 cm/s 2 ).
2.5.5 Design Basis Earthquake
The stringent seismic criteria for nuclear power plants do not apply to the WIPP facility due to the unique
character of the design and function of the facility. In particular, the terms "Operating Basis Earthquake"
(OBE) and "Safe Shutdown Earthquake" (SSE) are not applied to the WIPP facility. Rather, the term
"Design Basis Earthquake" (DBE) is used for the design of Class II and IIIA confinement structures and
components (Section 3.2.7). As used here, the DBE is equivalent to the design earthquake used in
Regulatory Guide 3.24 (U.S. Nuclear Regulatory Commission). ? That is, in view of the limited
consequences of seismic events in excess of those used as the basis for seismic design, the DBE is such
that it produces ground motion at the WIPP facility with a recurrence interval of 1,000 years (Section
3.1.3). In practice the DBE is defined in terms of the 1,000-year acceleration and design response
spectra.
The generation of curves expressing probability of occurrence or risk as a function of peak WIPP facility
ground acceleration is discussed in detail in Section 2.5.4 for a number of possible characterizations of
WIPP facility region source zones and source zone earthquake parameters. The most conservative (and
the least conservative) risk curves are shown in Figure 2.5-31.
2.5-18 January 24, 2003