The Problem
There is a growing need for a method to immobilise radioactive
nuclear waste safely. In principle this can be done by
encapsulation in a material which forms an effective barrier to
potential release into the environment. The waste in question
arises primarily from nuclear power stations, with some also from
decommissioned nuclear weapons. Safe immobilisation of nuclear
waste is critical to the future of the nuclear power industry, but
regardless of this the amount of currently stored non-immobilised
waste is already large enough to be of concern.
The Challenge
It is important to assess the consequences of the irradiation on
the performance of the encapsulating medium over long timescales -
up to tens of thousands of years for some isotopes. In order to
study how the properties of waste forms can change over time it is
necessary to perform massive parallel molecular dynamics (MD)
simulations on high energy recoils in materials of interest. These
simulations need to be sufficiently large in terms of number of
atoms (tens of thousands) requiring significant compute capacity
with parallel, distributed memory functionality.
The Solution
Using the Daresbury MD code DL-Poly3, simulations were performed
on the UK supercomputer located at Daresbury - HPCx. A highly
energetic particle is driven into the system giving rise to
cascades of displaced atoms in the encapsulating material. The
study covered materials currently proposed for waste containment
(glasses) and also new ceramic forms such as zirconium silicate
(shown), which promise considerably higher durability. The recoils
studied are designed to simulate an alpha decay event during which
a heavy recoil causes extensive damage in the structure, resulting
in several thousand permanently displaced atoms.
Molecular simulation of zirconium silicate after a
highly energetic particle has been driven into the
system
The Benefits
- The simulations demonstrate that the permanent residual damage
to the containment material can be limited to a few thousand atoms.
This is important to the customer when comparing encapsulation
materials
- The customer can use such simulations to point the way to the
development of novel, high performance containment materials
- The simulations are only possible due to the benefits available
from high performance
parallel computing