Figure 1-1 Evolution of the Reactor System Design
The first BWR containments were spherical
“dry” structures, similar to those still used today in
PWR designs. The BWR, however, quickly moved
to the “pressure suppression” containment design for
its many advantages. Among these are:
Chapter 1 — Introduction
recirculation loops, that allows the containment
(and, by extension, the reactor building) to be more
compact.
The Mark I containment was the first of the new
containment designs. The torus used to house a large
water inventory in the Mark I gives this design its
characteristic light bulb configuration. The conical
Mark II design has a less-complicated arrangement,
based on steel-lined reinforced concrete. A key fea-
ture is the large containment drywell that provides
more room for the steam and ECCS piping. The
Mark III containment design, used worldwide with
BWR/6s and some BWR/5s, represented a major
improvement in simplicity. Its steel containment
structure is a right circular cylinder that is easy to
construct, and provides ready access to equipment
and ample space for maintenance activities. Other
features of the Mark III include horizontal vents to
reduce overall loss-of-coolant accident (LOCA)
dynamic loads and a free-standing all-steel structure
to ensure leak-tightness.
The ABWR containment is significantly smaller
than the Mark III containment because the elimina-
tion of the recirculation loops translates into a sig-
nificantly more compact containment and reactor
building. The structure itself is made of reinforced
concrete with a steel liner from which it derives its
name—RCCV, or reinforced concrete containment
vessel. Figure 1-2 illustrates the evolution of the
BWR containment from the earliest versions to
today’s ABWR RCCV design.Where the reactor
building is also shown, the containment is outlined
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