ANNALS ANNALES - Academia Oamenilor de Stiinta din Romania

Mărgărit Pavelescu, Alexandru Octavian Pavelescu, Ioan Ursu 48
NWW is the redundant material from nuclear weapons programs. This has to be
converted into the waste forms that meet the stringent standards required by the
safety case. If it has in view the plutonium, there are two sound options for disposing:
use it in existing reactors as mixed oxide fuel, or convert it into a stable waste form.
The last one consists from highly insoluble glass or ceramic waste form that can be
emplaced into a secure deep geological facility.
2. CONVENTIONAL REPOSITORY CONCEPT
For all waste types to be emplaced in the conventional repository concept as an
underground mine in geological stable formations, a safety case must be performed
(Brian Looney, 2000).
This must demonstrate that their disposal will be safe for present and future
generation. Although the need for a safe disposal of nuclear waste has been
universally acknowledged for a number of years, the discussion on how the long-term
safety of the disposal practice should be assessed is still proceeding. Indeed, on one
hand, option feasibility studies as well as sites investigations and selections activities
must be implemented today in order to achieve operating repository systems in the
coming years, and this involves considerable assessment work.
On the other hand, due to the complex task that the analysts working in this field are
facing, new methodologies and techniques are being developed in order to give the
best answers to the questions raised by the safety evaluation of the underground
disposal.
A few remarkable characteristics may be identified that make the safety assessment
task unique for nuclear waste disposal practice, namely:
1) the complex nature of the multibarrier system to be described;
2) the very long time span to be covered by the analysis;
3) the uncertainties affecting some of the input parameters and model
assumptions;
4) the fact that a complete repository system does not exist, yet;
5) the public concern for the safety aspects.
There are two primary functions for a normal geological repository:
1) to physically isolate the waste from environment and
2) to prevent or minimize processes that could result in the transport of the
radioactive materials from the repository back to the biosphere.
Physical isolation is readily achieved for geological repositories situated at sufficient
depth to avoid erosion by rivers or glaciers, even for the long time frames required by
the repository.
The primary issue of concern at a most potential repository sites is to ensure that
there will be minimal groundwater flow in the repository vicinity. It could be shown
that even a small amount of groundwater is capable over long periods of time of
dissolving and transporting radioactivity to the biosphere.
A central concept for repository design is the use of multiple barriers against the
release of radioactivity to the biosphere. This makes that if one barrier fails to perform
as expected, the others still operate.
Because they are quite different, it is common to divide release barriers into
engineered barriers and natural ones. Indeed, the consensus of the scientists and