Liquid Metal Fast Breeder Reactor Program. Volume III. Environmental Statement Page: 85 of 622
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pressure changes caused by coolant thermal expansion and contraction as plant
loads change, and to prevent coolant pressure from exceeding the design pressure
of the entire primary system. Like the reactor vessel, the steam generators, the
pumps, and all other parts of the primary system, the pressurizer is also located
in the containment.
The major function of the emergency core cooling system of a PWR is to supply
sufficient water to cool the core in the event of a break that permits water to
leak from the primary system. The break most probably would be very small but
accommodation of the effects of rupture of the largest coolant pipe in the system
is a design requirement. PWR emergency core cooling systems consist of several
independent subsystems, each characterized by redundancy of equipment and flow
path. This redundancy assures reliability of operation and continued core cooling
even in the event of failure of any single component to carry out its design
functions. Although the arrangements and designs of PWR emergency core cooling
systems vary from plant to plant, depending on the vendor of the steam supply
system, all modern PWR plants employ both accumulator injection systems and pump
injection systems, with redundancy of equipment to assure desired operation.
More detailed discussions of design considerations for specific safety systems,
practices for assuring safety and analyses of hypothetical accident sequences are
presented in refs. 1 and 12.
Most present-day PWR containments are constructed of reinforced concrete with a
steel liner (Figure 6A.1-22). All are sized and designed to withstand the maximum
temperature and pressure that would be expected from the steam produced if all the
water in the primary system were expelled into the containment. Refinements in
containment technology are still being made, and containment systems vary widely
from plant to plant. For example, in some PWR plants, the containment space is
kept at slightly below atmospheric pressure so that leakage through the containment
walls would, at most times, be inward from the surroundings. Other systems have
double barriers against escape of material from the containment space.
Two kinds of additional measures are taken in PWR plants to minimize the potential
for escape to the environment of any accidental release of radioactive materials.
In some plants, cold-water sprays are provided to condense the steam resulting from
a major escape of primary system coolant into the containment; in other plants,
stored ice is used for this purpose. By condensing the steam, and thus lowering the
containment pressure, the driving force for outward leakage is reduced. Another6A.l-40
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Liquid Metal Fast Breeder Reactor Program. Volume III. Environmental Statement, report, December 1, 1974; Washington, District of Columbia. (https://digital.library.unt.edu/ark:/67531/metadc1019855/m1/85/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.