Development and implementation of seismic design and evaluation criteria for NIF Page: 4 of 11
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Following the successful completion and DOE approval of
the Conceptual Design Report , the NIF Project was formally
initiated with a total project cost of $1.2 Billion. It was planned
that about 75% of the project cost goes to U.S. industrial
partners for equipment and materials or design and construction
services. For example, the design and evaluation of the
conventional facility portions of NIF are being performed by the
NIF A&E, the Ralph M. Parsons Company, with support from
Albert C. Martin & Associates. Several industrial partners, such
as Science Applications International Corporation, TRW, Inc.,
and CSA Consulting, are providing design and evaluation
expertise for numerous aspects of the project. Since NIF is a
national research facility, a multi-laboratory team led by LLNL is
participating in the engineering design and evaluation of the
special equipment that will be used in NIF. The multi-laboratory
team consists of LLNL, Los Alamos National Laboratory, Sandia
National Laboratory, and the University of Rochester Laboratory
for Laser Energetics. While the system start-up of one bundle
of eight beams is planned for late 2001, all 192 beam lines are
planned to be operational by the end of 2003.
NIF has four main groups of SSCs: a laser system with its
associated optical and diagnostic SSCs, the target area with its
associated optical and diagnostic SSCs, an environmentally
controlled building housing the laser system and target area,
and an integrated computer control system. For structural
design purposes, these SSCs are considered as alignment-
sensitive and nonalignment-sensitive special equipment and
conventional facility equipment. In general, the nonalignment-
sensitive SSCs protect and support the alignment-sensitive
SSCs. Examples of nonalignment-sensitive SSCs include the
laser building, mechanical utilities, and the HVAC system.
Special equipment (SSCs) is typically for the laser system and
is being designed and evaluated by the multi-laboratory team,
while conventional facility equipment (SSCs) provides services
and environmental protection for the laser system and is being
designed and evaluated by the NIF A&E.
The alignment-sensitive special and conventional facility
equipment comprise the largest optic bench for ICF research.
As shown in Figure 1, the optic bench consists of the laser bay
foundations, the laser bay support structures, the switchyard
spaceframe, the target area building, and the target chamber.
Since ICF experiments with NIF will use a short pulse length of
about one to twenty nanoseconds, the alignment-sensitive
optical components in the NIF system must be aligned properly
and remain stable with that alignment in order to position the
beams on target as desired. It is also important to accurately
align and center the beams in the laser system in order to
minimize losses due to beam clipping, to maximize the laser
performance at the target, to avoid diffraction patterns that
result from the bean interacting with hard apertures, and to
prevent laser-induced damage to hardware on the beam
perimeter. Proper alignment of the NIF laser is accomplished
with precision alignment procedures, mechanical designs with
adequate adjustability, and stable optical support structures.
The stability budget is used to evaluate the performance of
NIF alignment-sensitive structures when they are subjected to
conditions that can cause drift. Drift is defined as a change
during the alignment procedures before a shot in the position of
an optical element from an aligned position. Conditions which
can cause drift include ambient vibration input, acoustical
excitations, wind fluctuations, and thermal transients. The
flowdown in the stability budget results from Section 2.1.5 of the
NIF Functional Requirements and Primary Criteria  which
requires that "the (rms) deviation in the position of the centroids
of all beams from their specified aiming points shall not exceed
50 micrometers ( m) at the target plane or its equivalent". The
beam position on target is influenced by three major categories
of contributions. First, there are multiple sources of input or
excitation, such as ambient vibration, acoustical excitation, and
wind fluctuations. Second, there are multiple optical elements
contributing to the beam position on target and these elements
are on two separate foundation systems. Finally, there are 192
independent beams which must satisfy the requirement for the
root-mean-square (rms) deviation of all the beams not
exceeding 50 microns. In addition to meeting the stability
budget requirements, the alignment-sensitive structures must:
(1) maintain clean operations by supporting laser components
over 10 feet above the foundation in order to use a line-
replaceable-unit (LRU) concept and to maintain a downflow of
air past the components and (2) typically use conventional
materials and fabrication techniques in order to minimize costs.
With these constraints, the alignment-sensitive structures are
hybrid structures of reinforced concrete and steel as shown in
NIF Seismic Provisions
NIF seismic design and evaluation provisions are based on
information in the NIF Functional Requirements and Primary
Criteria, DOE-STD-1020 , the UBC , the MEDSS  and
several NIF seismic criteria memos  . Consistent with DOE
policy on the mitigation of natural phenomena hazards, a
graded approach is implemented for the seismic design and
evaluation of NIF SSCs. The NIF Functional Requirements and
Primary Criteria specify a maximum recovery time from design
level seismic events of three months and dictate the use of PC2
seismic design and evaluation criteria, as a minimum. An
evaluation of the DOE-STD-1020 seismic design criteria for
PC2 SSCs indicates consistency with the three month recovery
requirement. Table 1 provides the qualitative seismic
performance characteristics or goals of PC2 SSCs as compared
to other DOE performance categories.
As discussed in DOE-STD-1020, PC2 SSCs have
performance goals of occupant safety and continued operation
with minimum interruption while meeting a seismic hazard
exceedance level of 1 x 10-3. The seismic design and
evaluation requirements for PC2 SSCs are based, in general,
on the UBC requirements for essential facilities (importance
factor of 1.25), such as hospitals or fire stations. In comparison,
PC1 facilities are typical office buildings and PC4 facilities are
commercial nuclear power plants. For alignment-sensitive
SSCs in NIF, the PC2 criteria is augmented with additional
dynamic analysis provisions and termed "PC2-A". For NIF
nonalignment sensitive SSCs, the PC2 criteria has additional
considerations of seismic anchor motion and the effects of the
nonalignment-sensitive SSCs on alignment-sensitive SSCs.
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Sommer, S.C. & MacCalden, P.B. Development and implementation of seismic design and evaluation criteria for NIF, article, March 17, 1998; California. (digital.library.unt.edu/ark:/67531/metadc680795/m1/4/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.