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RADIOACTIVE WASTE DISPOSAL IN SOUTH AFRICA IN 2015:

STATUS AND RESEARCH AND DEVELOPMENT STRATEGIES

M.A.G. Andreoli1, E. Raubeheimer

2, A.C. Carolissen

2, J.F. Beyleveld

2

1School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa

2South African Nuclear Energy Corporation, Pretoria, South Africa

1. Introduction .............................................................................................................. 2

2. Sources of Radioactive Waste in South Africa ............................................................. 2

3. Necsa-managed Radioactive Waste Storage Facilities in South Africa ......................... 3

4. Research and Development at Vaalputs ..................................................................... 4 4.1 General Approach ........................................................................................................... 4 4.2 Earth and Environmental Sciences ................................................................................... 5 4.3 System Engineering ...................................................................................................... 10 4.4 BDF Site Screening and Selection ................................................................................... 12 4.5 Material Sciences: Ceramics as Waste Immobilizers ....................................................... 13

5. Acknowledgments ....................................................................................................13

6. References................................................................................................................14

Abstract

The South African government has established the National Radioactive Waste Disposal

Institute (NRWDI) since the Fourth Worldwide Review of 2006. The NRWDI is a state owned

institution and it is currently being staffed and put into operation. The strategic mandate of

the NRWDI is to manage the whole spectrum of radioactive waste on a national basis. While

the process of putting the NRWDI into operation is evolving Necsa (the South African

Nuclear Energy Corporation) is continuing to perform the day-to-day disposal operations for

the LLW (Low Level Radioactive Waste) of Necsa and the Koeberg nuclear power plant

(operated by Eskom). The Vaalputs National Radioactive Waste Disposal Facility is licensed

to receive this LLW and will be managed by Necsa until the official transfer to the NRWDI.

Necsa, together with the IAEA and its consultants has developed a Borehole Disposal

Concept (BDC) for the disposal of disused sealed radioactive sources. This concept has been

identified as being the optimal solution for the countries disused sources inventory. A site

selection process for the disposal of spent sources has been initiated on the Necsa owned

property surrounding the current disposal area for LLW at Vaalputs. A suitable site has been

selected for a Borehole Disposal Facility (BDF) next to the current disposal area using the

extensive scientific database available for Vaalputs gathered since the early 1980’s.

Further research on various geotechnical and environmental parameters has been

undertaken that will contribute to the Safety Case of Vaalputs and which will also strengthen

the scientific data base for potentially new types of radioactive waste or nuclear facilities at

Vaalputs. The Nuclear Waste Research (NWR) Group at Necsa is carrying out research and

development on post reactor materials such as the chemical treatment and encapsulation for

disposal of such waste.

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1. Introduction

Since the Fourth Worldwide Review of 2006, the South African Government established the

National Radioactive Waste Disposal Institute (NRWDI) as a state-owned institution through

the NRWDI Act (Act 53 of 2008), which also describes the functions of the NRWDI and the

relevant powers to perform such functions. The NRWDI was formally launched by the

Minister of Energy in March 2014, and currently is in the process of being operationalized.

The strategic mandate of the NRWDI is to manage radioactive waste on a national basis,

independently of the producers of such waste. NRWDI’s role and functional scope comprises

the management of a national inventory of all radioactive waste to be disposed, including

long-lived waste, high level waste, used nuclear fuel, and disused, sealed radioactive sources.

This means that the NRWDI must initiate an appropriate research and development process to

investigate alternative disposal concepts for obtaining, characterizing and constructing

disposal sites.

While the NRWDI is in the process of being operationalized, the South African Nuclear

Energy Corporation (Necsa) continues to discharge the functions of the NRWDI for day-to-

day disposal operations, to conduct low-key geological investigations, and to develop

innovative technologies for immobilization and disposal of radioactive materials. In

particular, a site was selected to dispose disused (spent) and sealed radioactive sources in

boreholes at Vaalputs, which is the only South African radioactive waste-disposal facility.

The Vaalputs Radioactive Waste Disposal Facility is operated by Necsa. The facility is

located about 100 km southeast of Springbok, in the Northern Cape. It covers approximately

10,000 hectare, measuring 16.5 km from east to west, and 6.5 km from north to south at its

narrowest point (from https://en.wikipedia.org/wiki/Vaalputs). The borehole disposal has

been identified as being the optimal disposal solution for the country’s nuclear waste

inventory, which is currently scattered among a variety of unregulated sites. In this current

review, the authors highlight the most significant, recent achievements in the characterization

of the Vaalputs and Pelindaba sites, and in the disposal and immobilization of radioactive

materials.

2. Sources of Radioactive Waste in South Africa

The main generators of Used Nuclear Fuel (UNF) and other long-lived waste potentially

destined for a geological disposal facility in South Africa are Necsa, with its SAFARI-1

reactor for isotope production and research, and Eskom’s Koeberg Nuclear Power Station

(KNPS). Necsa’s location is ca. 20 km west of Pretoria, and Koeberg ~30 km north of Cape

Town (see Figure 1-inset). Current projections show that SAFARI-1 will produce about 5 m3

of UNF and the KNPS about 3,000 USF assemblies (including ~1,500 tons of uranium)

during their lifetimes. About 10,000 m3 of long-lived bulk waste and an unknown quantity

from industrial and medical industries are also potentially earmarked for geological disposal.

In the Fourth Worldwide Review (Andreoli et al. 2006), the authors mentioned a possible

pebble bed modular reactor program being implemented in South Africa. Since then the

program has been discontinued for various technical and political reasons. However, a

program by the South African Government to build additional nuclear power stations,

including the successor to the Safari-1 reactor (which recently celebrated its 50th

anniversary),

remains a possibility.

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Figure 1. Satellite-derived outline of the Vaalputs property and major infrastructure locations. The disposal site lies 100 km south of Springbok and to the east of the Namaqualand highlands which form part of the escarpment (left of the Stofkloof and Garing facilities) running along the western coast of South Africa.

3. Necsa-managed Radioactive Waste Storage Facilities in South Africa

Currently, radioactive waste (Used/Spent Nuclear Fuel [USF], “hot cell” waste, and other

historical waste) produced by Necsa and its Nuclear Technology Products (NTP) subsidiary,

are stored at several interim storage facilities within the Necsa site. More specifically, the

USF from the Safari-1 reactor is currently stored in the authorized Thabana dry-storage

facility at the Necsa’s Pelindaba site, which is currently being extended to increase its storage

capacity. Low Level Waste (LLW) generated by the Koeberg Power Station and by Necsa is

disposed at the Vaalputs National Radioactive Waste Disposal Facility in the Northern Cape.

Vaalputs complies with the general guidelines deemed suitable for the safe disposal of LLW

as considered in typical Generic Post-Closure Safety Assessments (van Blerk et al. 2007). In

addition, the Vaalputs facility, in operation since 1984, also presents a logistical advantage

that makes it the logical solution for disposal of disused sources (Figure 2).

Airfield

Garing

Stofkloof

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Figure 2: The site infrastructures within and around the security fence. Red dashed lines are the main electrical infrastructures (power line, high-security perimeter fence). Green blocks (Sites A and B) are areas considered for the potential boreholes disposal of radioactive sources (see text for discussion).

4. Research and Development at Vaalputs

4.1 General Approach

The limited resources available to characterize the geology of the Vaalputs site continue to be

offered to researchers from South African and overseas institutions who are interested in

pursuing areas of specific academic interest. Efforts are also made to insure that the

knowledge base accumulated in past decades is transferred to a new generation of students

and academics, so that it may benefit future initiatives by the NRWDI. In general, the focus

of current research has now shifted from the study of the crystalline basement to the

sedimentary and soil cover, regional geology, tectonics, seismicity, groundwater

characteristics, rock stress, climate change, and natural radioactivity. The immediate aim of

such investigations is to contribute to the Safety Case for the currently disposed low level

radioactive waste.

On the engineering side, Necsa scientists played a major role in an IAEA/AFRA project to

develop a BDF (Borehole Disposal Facility) system, this being the final step of a

technological process called BOSS (Borehole Disposal of Spent Sources). The BOSS/BDF

concepts are designed to provide a detailed, engineered level system which allows for: a) pre-

disposal activities, such as characterization and conditioning of disused sources, and b) the

safe and permanent disposal of disused sealed radioactive sources (DSRS’s) in specifically

built boreholes.

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4.2 Earth and Environmental Sciences

Mineral Potential of the Precambrian Geology. An important issue for Precambrian geology

is the search for pathfinders to economic mineral deposits that may be present in the

~1,000 my old Namaqualand belt basement under the blanket of Cenozoic deposits (Maier et

al. 2012). Of particular interest are the (Th-) monazite deposits of the so-called

Steenkampskraal type (Andreoli et al. 2006, and references therein; Clay et al. 2014).

Because granite veins with monazite, and thorium anomalies occur in and around the

Vaalputs site, the possibility of a 10 m thick lode of Th-rich under the site, albeit unlikely,

may not be excluded until more is understood about the geology of the site. The

Namaqualand monazite occurrences are now being re-investigated by Dr. Daniel Harlov,

monazite specialist at the German GeoForschungsZentrum (GFZ)-Potsdam.

Cenozoic Geology: Clues to Climate Change and Soil Disturbances. Much progress has been

made since the last review in characterizing Cenozoic sediments and palaeo-sols exposed in

the increasing number of trenches cut at the Vaalputs site (Figure 2). These sediments are

now recognized as precious archives recording climatic change going back in time to the end

of the Cretaceous. The University of the Witwatersrand, Johannesburg, is currently using

infra-red stimulated luminescence to date the deposition of the red sand that covers the

Vaalputs site is currently underway, while the University of Johannesburg is using the 40

Ar-39

Ar method to determine the age of the illite of the underlying fluvial, clay-bearing

arenaceous sediments. These latter rocks are critical to understanding the site performance in

terms of dispersion of the radioactive waste into the environment (Figure 3). Among the

various multidisciplinary investigations of the trenches (the Near Field; Andreoli et al. 2014,

2015), we are also studying the origin and evolution of the silicified ferruginous layer that

typically lies between the red sandy soil and the clay-bearing sediments of the trenches

(Figure 4; Clarke et al. 2015). This rock, often cut by vertical soil tongues and low angle

shear fractures, probably defines a major episode of climatic/geohydrological change, and

stress release between ~70 and ~60 ka BP (Evans et al. 2015; Andreoli et al. 2014). The

processes leading to widespread pockets of oxidized sediments (see the “oxidized “bowl” in

Figure 3) are also being investigated because the latter suggest still undetermined phenomena

of stratigraphic disturbance and open-system behaviour by near-surface water.

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Figure 3. Representative stratigraphic profile in Trench B (1, 2).

Figure 4. Detailed stratigraphy of Late Pleistocene palaeosols in Trench A (0,5), Vaalputs:

arrows mark band of sepiocrete nodules at the contact between calcretized, pale-coloured

greywackwe (age of calcrete: ≥70 ka) and light brown dorbank (DB). Top: red sand (≤60 ka;

Evans et al. 2015).

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Site Seismology and Neotectonics. The monitoring of the sporadic seismicity of the broader

region around Vaalputs (mentioned in our contribution to the 4th

Worldwide Review) has

continued in the following years until 2011, when the two Necsa seismic stations installed in

1989 finally ceased functioning. The seismic activity is now monitored by a new network of

three seismic stations (one being broadband) forming a triangular array positioned to include

the largest number of expected future epicenters. Substantial effort is currently placed on

interdisciplinary research to identify the origin of the tectonic force responsible for these

events. The available data suggest that the seismicity in the Vaalputs area derives from the

interplay of several forces, the weakest being predominantly extensional and induced by the

southern propagating East African Rift. The main force, named the Wegener stress anomaly,

is horizontal and strike slip in character with a NNW-SSE orientation (see ellipse in Figure 5;

Bird et al. 2006). The cause of the Wegener compressive, coast-parallel stress remains

unidentified (Andreoli et al. 1996; Viola et al. 2012; Andreoli et al. 2013). As part of the

effort to explain the seismic activity in the greater Vaalputs area, Necsa continues to invest in

a number of initiatives. These include support for a) a M.Sc. project to obtain neotectonic

stress orientation data in South Africa from off-shore borehole break-out measurements

(successfully completed; University of Cape Town), b) a Ph.D. project on the seismicity of

the Northern Cape (University of the Witwatersrand), c) a M.Sc. project to establish a GIS

database of neotectonic faults in South Africa (University of Pretoria). Additional research

initiatives on the subject of neotectonics focus on issues of surface development and land

stability (Evans et al. 2015; Andreoli et al. 2015) and morphotectonics. The latter study is

greatly aided by recent developments in Digital Terrain Model (DTM) analysis (Figure 6) to

assess the reactivation potential of the basement faults in the Vaalputs area (Viola et al.

2012). The evolution of the landscape, and, in particular, the age of the 1-km uplift of the

Vaalputs plateau are also the subjects of careful investigation, as they are controversial

(Kounov et al. 2009).

Figure 5. Intraplate indicators of stress regime (indicated by colour) and azimuth of the most compressive horizontal principal stress. Ellipse: approximate region of the Wegener stress anomaly (Bird et al. 2006).

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Figure 6. Digital terrain model, with vertical exaggeration of the Vaalputs (green polygon) and adjacent areas of the Northern Cape (credit: Dr. F. Eckardt, University of Cape Town).

Alexandre et al. (2006; 2007) studied the regional geology and tectonic stability of the area

around the Pelindaba site. An additional investigation was also conducted at the Pelindaba

site as part of the discontinued pebble bed modular reactor project. This latter investigation

included a study of the regional Brits graben fault that underlies the Pelindaba site. Trenching

across the fault indicates that it lies buried under an undisturbed Cenozoic soil cover and, as

such, it is inactive under the foreseeable geodynamic conditions.

Geohydrology: Natural Radioactivity and Pathways Modeling. The study of groundwater, its

age, movement/recharge dynamics and interaction with the naturally occurring radioactive

minerals of the granitic country rocks has taken centre place in recent years by supporting two

M. Sc. projects (University of the Free State). It must be stressed that these studies are based

on water sampled from fractures in granitic host rocks at a depth of about 54 m. The first

project involved statistical processing of more than 20 years of groundwater analyses for the

period preceding the disposal of uranium bearing waste at Vaalputs. As such, the study by

Pretorius (2012) provides a baseline insight of the behavior of uranium and its decay chain

radionuclides as they have partitioned through time between host rock minerals and

groundwater. The available data show evidence of occasional, statistically significant releases

of radionuclides, mainly 234

U, into the groundwater for reasons that are currently under

investigation (Figure 7). The second M. Sc. is based on the reconceptualization of the

groundwater regime in the Vaalputs site and surrounding farms, and aims to address

N

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uncertainties that were raised in the post-closure radiological safety case assessment (

currently being reviewed by the regulator) to gain understanding of the groundwater regime,

namely hydrogeochemistry and recharge. The major and minor element data (Figure 8)

confirm a Na-Mg-Cl rich stagnant groundwater under stagnant conditions (Levin, 1988).

Figure 7. Radioanalytical data of groundwater from boreholes in the Vaalputs site and nearby areas. A: Timeline

of total α radiation for boreholes from zones of increasing distance from the trench area (Zones A, B and C: boreholes <2 km, <6 km, and >6 km from disposal trenches respectively). B: cumulative contributions of α emitting radionuclides to the measured total α levels of the year 2009 (Pretorius 2012).

Figure 8. Piper and Piper Expanded plots of groundwater from boreholes at Vaalputs and surrounding farms. The

concentration of points in the last two 8 and 9 segments suggests old water (unpublished Necsa data by M. Mandaba).

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4.3 System Engineering

BDF in a nutshell. This technological development provides a safe, economic, simple and

permanent solution to spent sources management, and is particularly suitable to countries that

do not have an established nuclear infrastructure for radioactive waste management and

disposal. The concept, which consists of a system of multiple, physical and chemical barriers

(near-field engineering), is widely applicable, as it is versatile and suitable for a range of

geosphere, biosphere and climatic conditions. It provides for:

Selection and characterization of a disposal site

Construction of a dedicated disposal borehole

Transport of sources (conditioned in stainless steel capsules) from storage to disposal

site

Containerization of sources into high integrity, stainless steel disposal containers

Emplacement of the disposal containers in the borehole

Sealing and closure of the borehole, including restoration of the site

Site maintenance as per operational and post closure safety assessment requirements

A schematic illustration of the disposal of the sources in a borehole according to the BDF is

shown in Figure 9. As indicated in the checklist above, a key component of BDF/BOSS

system is the selection of an appropriate disposal site. Lessons learned from decades of

investigations for the nuclear industry have taught that “the perfect site” is like a safe, high

yield investment: impossible to find, given the inherent complexity of every natural system,

irrespective of how simple it may appear at first. Table X.1 lists a number of prominent

guidelines (Quintessa 2003, 2005) that will nevertheless assist in the site selection process in

order to find a suitable site to implement the BDF concept. For the reason indicated above, it

is the aim of a selector to find, if not necessarily the”perfect site” at least one which is suited

to meet all key requirements for safety in a way that can be appropriately justified.

Figure 9. Schematic representation of the emplacement borehole (Chaplow and Degnan 2010).

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Table X.1: A Checklist of Desirable Characteristics in Disposal Systems (Quintessa 2004)

Geology

Low tectonic and seismic activity

Absence of geological complexity

Distance from present or potential mineral exploitation (open cast/underground mining)

Low geothermal heat and gas resources potential

Geomorphology

Limited geomorphological activity

Borehole disposal zone below local erosion base level

Hydrogeology

Simple hydrological system

Stability of water table (limited fluctuation of saturate/unsaturated zone interface)

Slow moving ground water (long travel times from borehole to biosphere)

Appropriate dilution along the geosphere to biosphere pathway

Geochemistry

Significant sorption of radionuclides (e.g., through reducing conditions)

Avoidance of conditions impairing the longevity of engineered barriers (e.g., high SO42-

, Cl-)

Climate Dry conditions (low rainwater percolation, weathering rates)

Society Avoidance of urban areas

In the case of an application of the BDF concept at Vaalputs, this facility was originally

selected as it satisfies and incorporates most of the criteria set out in Table X.1 as best suited

for LLW disposal sites. In particular, the low rainfall/low recharge and the great depth of the

water table make the Vaalputs site particularly suitable for LLW and spent sources disposal.

Similarly, the outcomes of the neotectonic and seismological investigations satisfy the

requirements for tectonic stability at the disposal site (low ground acceleration and seismic

hazard probability). For the BDF concept, however, there are additional constraints and

criteria to consider (Raubenheimer 2012), these being of a rather practical and operational

nature. More specifically, the following considerations are envisaged:

Placing the BDF area for spent sources adjacent to the current security fence of the

LLW disposal site. Following the emplacement phase, when a temporary security

fence might be built to protect the waste, an easier-to-control permanent fence will

enclose the perimeter of all security areas.

Siting the BDF beyond the existing security fence will provide a >200 m buffer space

from the trenches of the LLW disposal area. This will prevent the co-impact of the

different facilities on each other.

Avoiding the LLW infrastructures (e.g., roads, experimental areas) will minimize

operational disruption and risks to existing nuclear licenses and operations.

Avoiding areas of deeper, clay-bearing overburden, as these may be needed should

the current LLW disposal site require future expansion.

Avoiding electrical infrastructures to minimize any risk of electrocution or damage to

wiring. Given the current position of the power line, the latter will need to shift

northeast by establishing a 30 m exclusion zone. A 15 m exclusion zone will also run

parallel to the potentially electrified security fence (see Figure 2).

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Allowing generous dimensions for the BDF site (~100 m × 300 m) to provide

disposal space to last at least a few decades, and unhindered expansion should more

space be needed in the far future.

4.4 BDF Site Screening and Selection

Using the above criteria, two candidate areas (see Sites A and B, Figure 2) were selected from

which a smaller final site will be chosen for borehole disposal. Sites A and B are both

feasible, considering both geotechnical/geological and non-geotechnical aspects. Should a

specific area be selected on the basis of specific considerations (see below), the next step will

involve the acquisition of site-specific parameters for a rigorous Post Closure Radiological

Safety Assessment.

Logistic/geotechnical considerations. Both sites are adjacent to the current security perimeter

and accessible by the current road network (Figure 2). They satisfy most of the

abovementioned considerations. If a distance of 10 m between the disposal boreholes is

maintained, a large number of disposal boreholes can be accommodated within Site A south

of the power line, even without shifting the adjacent road, for many years.

Environmental and geological considerations. In a previous section mention was made of

several types of structural//sedimentary features within the overburden. However, such

features (low angle shear fractures, penetrative soil tongues, etc.; Andreoli et al. 2014, 2015)

are confined to the top few metres and will not be considered further in terms of potential

hazard to the sources disposed in the boreholes. Sufficient casing and grouting would

minimize the risks associated to water percolation along such features. Drilling and

geophysical data further indicate that the basement geology underlying Sites A and B consists

of high grade, >1.0 Ga old granitic rocks largely free of mafic/anorthosite intrusions,

potentially prone to deeper weathering. High resolution (airborne, ground) magnetic survey

data indicate, however, that both Sites A and B are in close proximity to NW-SE trending,

probably normal faults which should be avoided not because of their unlikely reactivation

potential, but rather because they may represent potential nuclide migration pathways.

Geohydrological considerations. The groundwater levels are frequently monitored throughout

the Vaalputs site, especially around the security area, and contribute to a uniquely detailed,

30-year database of fluctuating water levels. It is therefore with a high level of confidence

that the water table beneath Zones A and B is assumed to be at a depth of 50 m, which is

35 m below the basement/cover unconformity (see Figure 10). This configuration allows up

to ~15 m of stacked sources below the required 30 m intrusion limit, and even provides a 5 m

safety margin against the underlying water table. The sulphate and chloride content in the

groundwater measured in boreholes close to Sites A and B shows values of about 1000 mg/l

and 300 mg/l for chloride and sulphate respectively. However, in the unsaturated zone, these

concentrations are likely to be much lower, and close to the X-Ray Fluorescence detection

limits for granite-hosted groundwater.

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Figure 10: Illustration of the BOSS concept based on the available geological and hydrological data.

MON 11/12 represents nearby groundwater monitoring boreholes.

4.5 Material Sciences: Ceramics as Waste Immobilizers

Research and development at Necsa is not only concerned with siting new and ongoing

assessment of existing nuclear waste disposal facilities, but also with the development of

innovative techniques of radioactive waste isolation. This program is the responsibility of the

Nuclear Waste Research (NWR) Group, a team within Necsa that carries out research and

development on post reactor materials; more specifically, to supply consulting service to

different clients (locally and internationally) regarding the chemical treatment and disposal of

post reactor waste. This includes in-house research projects as well as international contract

research. Contract research completed in 2015 for Argonne National Laboratories (ANL)

presented scalable, innovative solutions for the recovery of high-and low-enriched uranium

from post-reactor material using proliferation-friendly alkaline technology. The Aim of this

project is to enable the reuse of uranium for medical target plates or nuclear fuel, and of target

plates for Mo manufacturing (Carsten et al. 2015). In a second contract for the ANL, and in

partnership with Australia’s Ansto, the Group is investigating how to encapsulate and dispose

different radioactive waste streams produced while purifying uranium from used nuclear fuel

using alkaline technology

5. Acknowledgments

We thank our colleagues M Mandaba and WCMH Meyer for valuable data provided on the

Vaalputs groundwater chemistry and on Materials Sciences research respectively and the

management of Necsa for permission to publish this paper. Frank Eckardt (University of

Cape Town) kindly provided Figure 6.

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