Environmental Engineering Reference
In-Depth Information
The impact of core melt on reactor internals and reactor vessel
integrity.
The effects of long-term wet and dry storage as well as environmen-
tal conditions in any long-term disposal site on the integrity of the SiC
cladding.
Phenomenological models for the behavior of SiC-composite structures
as a function of temperature, stress, and radiation.
9.2.4 Increasing the life and accident tolerance of control
rods, blades and other fuel assembly structures
There are other components in the core which, while they do not directly
contain fi ssion products, do affect the ability of the cladding to do so and
have a major effect on the ability of the nuclear plant operators to con-
trol the reactor as the plant ages. These components include the structural
materials in the fuel assembly such as the top and bottom nozzles, springs,
fasteners, grid structures, skeleton, and the control members (rods in a PWR
and blades in a BWR). In a BWR there are also water channels that chan-
nel the coolant fl ow. Many of these structures are currently made of various
zirconium alloys and some are of stainless or high alloy steels. The inside
components of the PWR control rods are Ag-In-Cd alloy while BWR con-
trol blades contain B
4
C. The research areas of interest are:
Understanding and predicting the corrosion of the current alloys in their
respective BWR and PWR environments.
Development of new materials such as SiC composites for PWR control
rod cladding and BWR water channels.
Development of new control rod materials including gray rods (con-
trol rods with much lower thermal neutron absorption materials, such
as tungsten, than control rods but higher than steel or zirconium) for
P W R s .
9.3 The primary system - the second fission barrier
The second line of defense for nuclear plants is the primary system bound-
ary in any LWR. The primary system for a PWR consists of the reactor
vessel, the primary side piping, steam generators, pressurizer and coolant
pumps. For a BWR, the primary system consists of the reactor vessel, pip-
ing, steam turbine, condenser and coolant feed pumps. In both cases, main-
taining the integrity of this boundary is crucial to maintaining the cooling
functions for the reactor and therefore its long-term ability to prevent the
release of fi ssion products into the environment. Loss of integrity of this
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