Page 256 - Materials Chemistry, Second Edition

246 G. A. da Silva et al.

3.3 Product System Boundaries Definition

Boundary definition is probably the most controversial step in the development of
a hydropower LCI, generally divided into two separate definitions: time boundary
and spatial boundary.
0
Regarding time boundary, hydropower LCI s must consider the process that
occurs within the power plant, and also the capital investments in materials, and
the energy required to build and to operate the dam. This approach is recom-
mended since the construction phase is claimed to be the most relevant source of
environmental load.
Hydropower dams are expected to ‘‘last forever’’, if proper maintenance
practices would be applied. So, construction impacts should be distributed to all
the energy produced by the plant during its whole operative lifetime. Thus, the
definition of how long the plant will last, or the amount of energy generated by the
system, is decisive in terms of scope definition. This question is, maybe, the most
controversial aspect of hydropower LCA. The solution commonly adopted by the
examined studies was to establish a fixed value.
Originally, this value was determined as being 60 years (Brännstrom-Norberg
et al.1996); however, after a review of the time horizons of systems under oper-
ation, a 100 years of operation has been considered more adequate (Swedish
Environemntal Management Council 2002a, b, 1999; IEA 1998, 2000). As a
requirement, all environmental burdens associated with maintenance activities
must be included.
Another important definition on this kind of studies refers to the stages to be
considered in the whole life cycle. In general, the studies used to separate it on
construction and operation of the power plants. Demolition was not considered on
any case, and mainly, because it is recognized that the dismantling of a dam could
lead to severe environmental impacts, once the local ecosystems are adapted to the
lacustrine situation. Thus, hydropower dismantling is not included, except on
special cases when public security is endangered.
The spatial boundaries of hydropower LCIs are the same for the consulted
studies. The refinement of boundaries is considered a key element on hydropower
LCI development because of the large amount of mass and energy flows
exchanged between the product system and the environment, especially during the
construction stage of the project. In fact, all the considered studies had started their
LCA screening adopting Vattenfall’s boundary definition (Brännstrom-Norberg
et al. 1996).
According to that procedure, the initial boundaries included material and energy
flows from: the operation of civil work machines; extraction and/or production of
construction materials (cement, sand, aggregate, rocks, steel, and diesel); and
materials transportation. It were also included within the boundaries the envi-
ronmental aspects associated with the production and the transportation of the
materials necessary to manufacture the most important equipment (as steel, cop-
per, lubricant, etc.), and also aspects related to civil workers transportation,