High-level nuclear waste to go underground

The designing of a “deep geological repository” for storing high-level waste from South African nuclear reactors might start soon, according to a paper tabled by the Pebble Bed Modular Reactor (PBMR) company yesterday.

Among the sites considered was Vaalputs, a radioactive waste-disposal facility managed by Nuclear Energy Corporation of SA (Necsa) about 100km south-east of Springbok, according to the document, submitted to parliament’s environmental affairs portfolio committee.
The committee is holding public hearings on nuclear energy.
The Vaalputs site is licensed to accept low to medium-level waste only.

PBMR (Pty) Ltd was established in 1999 to develop and market small-scale, high-temperature reactors, locally and internationally.
According to the paper, a national policy and strategy for the disposal of high-level waste (HLW) is still being prepared.
“There is as yet no HLW disposal methodology or facility for dealing with this category of waste from Koeberg (nuclear power station), Necsa (which operates the Safari-1 reactor at Pelindaba), or the PBMR.”

A draft policy and strategy document did, however, indicate that investigations for the establishment of a deep geological facility should go ahead in the interim.”This directive would imply that work be initiated on the selection of a suitable site (which could be Vaalputs), the conceptual design of a repository, as well as geological modelling and associated studies to support the safety assessment and licensing of this facility.”

The deep geological storage of high-level waste involves encapsulating spent nuclear fuel from a reactor in specially-engineered casks, and placing these underground in a mined-out chamber in a geologically stable rock formation.

Experts consider this a viable and safe long-term method of isolating highly-radioactive waste, which remains dangerous for centuries.
The bulk of South Africa’s high-level waste is produced by Koeberg in the form of spent fuel rods, most of which are stored underwater in the power station’s fuel storage pools.

“Except for some fuel assemblies in four dry storage casks, all spent fuel at Koeberg is stored in the spent fuel storage pools, which would be able to accommodate the rest of the spent fuel for the full expected 40-year lifetimes of the two reactors,” the paper says.

It warns, however, that should the plants’ operational period be extended for 10 years, “the dry storage capacity of Koeberg would have to be expanded to make provision for a total of almost 4 000 spent fuel assemblies”.

The paper says reprocessing some of the spent fuel would mean no dry storage would be needed.

Dry disposal or storage involves placing the spent nuclear fuel rods in so-called castor casks, specially-designed steel and concrete cylinders.

The paper says spent fuel from the pebble bed reactors the PBMR company is hoping to develop will be stored on site.
“The first option… implies on-site storage of the spent fuel for … 40 years after the closure of the reactor, after which it can be transferred to shipping casks for storage and disposal at the HLW repository.”