1. 2007 Vaalputs Post Closure
Radiological Safety Assessment
(PCRSA)
J.J. van Blerk, M.W. Kozak and
J.F. Beyleveld, A.C. Carolissen
International Workshop on A Common
Framework for the Safety of
Radioactive Waste Management and Disposal
2-6 July 2007 Cape Town South Africa

2. Vaalputs
Springbok
Vioolsdrif
Siyanda District Municipality
Karoo District Municipality
Frances Baard
District
Municipality
Namakwa District Municipality
Vaalputs Site
Designated facility for the disposal of
LILW in South Africa
Owned and operated by Necsa since
1986
Authorisation for the disposal of
LILW generated at the KNPS
Polokwane
Bloemfontein
Durban
East London
Cape Town
Johannesburg
Kimberley
Maseru
Mmabatho
Nelspruit
Pietermaritzburg
Port Elizabeth
Pretoria
Springbok
Ulundi
NORTHERN CAPE
WESTERN CAPE
EASTERN CAPE
FREE STATE
LESOTHO
KWAZULU NATAL
NORTH WEST
MPUMALANGA
GAUTENG
LIMPOPO
Atlantic Ocean Indian Ocean
O
range
Vaal
Caledon
Tugela
O
range
Vaal
Vaalputs
Pelindaba
Koeberg

3. Regulatory Authorization Review
 Changes to Regulatory Framework
 National Radioactive Waste Management Policy and Strategy
(2005)
 Safety standards (2006)
 Disposal of a national inventory of radioactive waste
 KNPS
 Reconsideration of nuclear power as an option
 Second PWR
 PBMR
 Necsa historical and future waste
 Safari-1 reactor (1965)
 Nuclear fuel production facilities (1970-1998)
 Decommissioning of facilities at the Pelindaba site

4. Purpose of the 2007 Vaalputs PCRSA
 Assess the post-closure radiological safety of the Vaalputs site for a
best estimate national inventory of radioactive waste
 Assess if current disposal concept of near-surface earth trenches
are sufficient to ensure long-term safety for the national inventory
 Derive nuclide specific activity limits for the disposal of LILW at the
Vaalputs site
 Provide insight with respect to qualitative waste acceptance criteria
necessary to ensure long-term safety
 Identify where further data or information would be most helpful to
improve the safety case

5. Independent Safety Assessment
 Parallel assessment in support of the Necsa assessment
 Increase credibility in the 2007 Vaalputs PCRSA
 Enhance confidence in the long-term safety of Vaalputs
 Common safety assessment methodology
 Consistent assessment context, system description and
exposure scenarios
 Independent model development process
 Necsa assessment more conservative
 Consistent assumptions and parameter values for consistent conceptual
and mathematical models
 Performed by Monitor Scientific LLC (Denver, USA)

6. Assessment Context
 Consistent with ICRP standards and recommendations
 Dose constraint of 0.25 mSv per year (SA safety standards)
 Target audience
 NNR identified as the primary audience
 Waste generators, state departments, statutory consultees, non-nuclear and
scientific communities, and environmental concern groups
 Operational period of 50 years
 2036 the starting point for calculations (all disposals completed)
 Institutional control period of 300 years
 No credit for controls after 2336
 Considered 10,000 years as the period of regulatory concern
 Analyses carried out to 100,000 years

7. Vaalputs System
 Near surface trenches
 Use standardized containers
 Semi-arid environment
 MAP of 74 mm per annum
 129 mm between 1986 to 2005
 30 mm min; 305 mm max
 Temperature
 Mean daily maximum: 34.8°C
 Mean daily minimum: 0.7°C
 Sparsely populated (52 people
are currently based in the area)
 Farming community (sheep and
game farming)
 Rain main source of drinking
water

8. Vaalputs System
 Near surface trenches
 Use standardized containers
 Semi-arid environment
 MAP of 74 mm per annum
 129 mm between 1986 to 2005
 30 mm min; 305 mm max
 Temperature
 Mean daily maximum: 34.8°C
 Mean daily minimum: 0.7°C
 Sparsely populated (52 people
are currently based in the area)
 Farming community (sheep and
game farming)
 Rain main source of drinking
water

9. Vaalputs System
 Near surface trenches
 Use standardized containers
 Semi-arid environment
 MAP of 74 mm per annum
 129 mm between 1986 to 2005
 30 mm min; 305 mm max
 Temperature
 Mean daily maximum: 34.8°C
 Mean daily minimum: 0.7°C
 Sparsely populated (52 people
are currently based in the area)
 Farming community (sheep and
game farming)
 Rain main source of drinking
water

10. Vaalputs System
 Underlain by unconsolidated
sand, calcrete, greywacke, clay,
granite and gneiss
 Bedrock extensively folded,
thrusted and fractured
 Underlying aquifer
 Situated in weathered and hard
granitic rock
 Piezometric surface at 50 to 60 m
 Very flat groundwater gradient
 Unsaturated zone
 Soil moisture increases in top
4 m after precipitation event
 Upward movement induced by
evapotranspiration is limited to 1
m below surface

11. Scenario Development
 Four natural exposure and two human intrusion scenarios
 Nominal Scenario
 Judged to be a reasonable future behaviour of the facility
 Late Subsidence Scenario
 Represent the uncertainty about the degradation of waste container and
materials in the LLW trenches
 Climate Change Scenario
 Seismic Scenario
 Drilling Intruder Scenario
 Assess the exposure of a driller to borehole cuttings brought to the surface
during a drilling intrusion event
 Post-Intrusion Resident Scenario
 Farmer builds a house on top of the disposal trenches, receive exposure from
the borehole cuttings, and uses the borehole for farming purposes

12. Model Development
 Compartmental modelling approach
 Amber (Necsa assessment)
 Ecolego (Supporting assessment)
 Near field was compartmentalised according to 5 waste types
 Necsa unstabilized LLW
 Necsa stabilized LLW
 Necsa stabilised ILW
 NPS unstabilized LLW
 NPS stabilized ILW
 Contribution of certain compartments was excluded
 Grounds of uncertainty (e.g. the saturated zone)
 Indications that the nominal fractions of activity accumulating in a compartment
would be limited (e.g. upward pathway due to evapotranspiration)

13. Model Development
Advective transport through
unsaturated zone
Saturated Zone
Backwarddispersivetransport
betweencompartments
Surface Soils
Cover
Necsa Unstabilized
LLW
Necsa Stabilized
LLW
Necsa Stabilized
ILW
NPS Unstabilized
LLW
NPS Stabilized
ILW
Unsaturated zone divided
into multiple compartments
Forwarddispersivetransport
betweencompartments
Advective
transport
Advective
transport
Upward
Advective
transport
Erosion
Borehole concentration
=
(Transfer rate into aquifer)/(Pumping rate)
Advective transport
Cap
Backfill
Waste
Atmosphere
Upper Soils
(Drilling
Residue)
Drilling
Crew
Elsewhere
Dilution
Dilution
Exhume
Deposition
Inhalation
(dust)
External
irradiation
Dispersion
Ingestion
External
irradiation
Erosion
Leaching
ExcretionDrilling
Re-suspension
A
B
C
D
E
F
G
1 2 3 4 5 76

14. Assessment Results
 Natural exposure scenarios
 Peak dose at 10,000 years: below 10-2 mSv/y
 Below 10-1 mSv/y at all times
 Dominant nuclides
 I-129, Tc-99 and Np-237
 Dominant pathway
 Water consumption
 Egg/mutton consumption
 Probabilistic analysis
 Deterministic analyses
represent 95th percentile
of uncertainty range
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+03 1.0E+04 1.0E+05
Time (Years)
TotalDose(mSvy
-1
)
Ac_227
Am_241
Am_242m
Am_243
C_14
Cd_113m
Cl_36
Cm_243
Cm_244
Cm_245
Co_60
Cs_135
Cs_137
H_3
I_129
Ni_63
Np_237
Pa_231
Pb_210
Pu_238
Pu_239
Pu_240
Pu_241
Pu_242
Ra_226
Se_79
Sm_151
Sn_126
Sr_90
Tc_99
Th_229
Th_230
Th_232
U_232
U_233
U_234
U_235
U_236
U_238
Cm_246
Total Dose
Advective Release : Nominal Scenario
I-129
Np-237
Tc-99

15. Assessment Results
 Natural exposure scenarios
 Peak dose at 10,000 years: below 10-2 mSv/y
 Below 10-1 mSv/y at all times
 Dominant nuclides
 I-129, Tc-99 and Np-237
 Dominant pathway
 Water consumption
 Egg/mutton consumption
 Probabilistic analysis
 Deterministic analyses
represent 95th percentile
of uncertainty range
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+03 1.0E+04 1.0E+05
Time (Years)
TotalDose(mSvy
-1
)
Ac_227
Am_241
Am_242m
Am_243
C_14
Cd_113m
Cl_36
Cm_243
Cm_244
Cm_245
Co_60
Cs_135
Cs_137
H_3
I_129
Ni_63
Np_237
Pa_231
Pb_210
Pu_238
Pu_239
Pu_240
Pu_241
Pu_242
Ra_226
Se_79
Sm_151
Sn_126
Sr_90
Tc_99
Th_229
Th_230
Th_232
U_232
U_233
U_234
U_235
U_236
U_238
Cm_246
Total Dose
Advective Release : Late Subsidence Scenario

16. Assessment Results
 Natural exposure scenarios
 Peak dose at 10,000 years: below 10-2 mSv/y
 Below 10-1 mSv/y at all times
 Dominant nuclides
 I-129, Tc-99 and Np-237
 Dominant pathway
 Water consumption
 Egg/mutton consumption
 Probabilistic analysis
 Deterministic analyses
represent 95th percentile
of uncertainty range
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+03 1.0E+04 1.0E+05
Time (Years)
TotalDose(mSvy
-1
)
Ac_227
Am_241
Am_242m
Am_243
C_14
Cd_113m
Cl_36
Cm_243
Cm_244
Cm_245
Co_60
Cs_135
Cs_137
H_3
I_129
Ni_63
Np_237
Pa_231
Pb_210
Pu_238
Pu_239
Pu_240
Pu_241
Pu_242
Ra_226
Se_79
Sm_151
Sn_126
Sr_90
Tc_99
Th_229
Th_230
Th_232
U_232
U_233
U_234
U_235
U_236
U_238
Cm_246
Total Dose
Advective Release : Climate Change Scenario
Pa-231

17. Assessment Results
 Natural exposure scenarios
 Peak dose at 10,000 years: below 10-2 mSv/y
 Below 10-1 mSv/y at all times
 Dominant nuclides
 I-129, Tc-99 and Np-237
 Dominant pathway
 Water consumption
 Egg/mutton consumption
 Probabilistic analysis
 Deterministic analyses
represent 95th percentile
of uncertainty range
Diffusive Release : Nominal Scenario
1.E-13
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1000 10000 100000
Time (y)
Dose
(mSv/y)
I-129 (mean)
I-129 (50%)
I-129 (5%)
I-129 (95%)
Tc-99 (mean)
Tc-99 (50%)
Tc-99 (5%)
Tc-99 (95%)

18. Assessment Results
 Driller Intruder Scenario
 Single drilling event in single waste category
 Peak dose below 1 mSv/y at all times (0.5 mSv at 10,000 years)
 Highest doses from
Necsa stabilized LLW
 U-238 and U-234
 No mass transfer
assumed
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+02 1.0E+03 1.0E+04 1.0E+05
Time (Years)
TotalDose(mSvy
-1
)
NPS Unstab LLW
Necsa Stab LLW
Necsa Unstab LLW
Necsa Stab ILW
NPS Stab ILW

19. Assessment Results
 Post-Intrusion Residence Scenario
 Companion scenario for drilling intrusion scenario
 Farmer builds house and is exposed under nominal conditions
 Radon dose dominates
 Peak dose at 10,000
years is 1 mSv/y
 Below 10 mSv/y at all
times
 No mass transfer
assumed
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
100 1,000 10,000 100,000
Time of Intrusion (Years)
TotalDose(mSvy
-1
)
Outdoor
Indoor
Total (Rn-222)
Nominal
Total Dose

20. Barrier Neutralization and Sensitivity
Analysis
 Issues unimportant from a long-term safety perspective
 Elaborate cap design
 Thickness important
 Concrete container lifetime
 Important in the broader context of radioactive waste management
 Unsaturated zone dispersivity
 Structural features in the unsaturated zone could alter this conclusion
 Horizontal dimensions of the waste trenches
 Vertical dimensions important
 Trench layout assumed for the disposal of LILW at the Vaalputs
site

21. Barrier Neutralization and Sensitivity
Analysis
 Issues important from a long-term safety perspective
 Refinement of the national inventory estimate
 Characteristics
 Extrapolation to future NPS
 Scaling factors used for radionuclide estimates
 Improved recharge estimates and near surface hydrological
processes
 Nominal and alternative scenarios
 Nature of the underlying aquifer
 Associated groundwater flow regime
 Near field and geosphere sorption properties
 Iodine, technetium, neptunium, carbon, uranium, and uranium decay
progeny

22. Barrier Neutralization and Sensitivity
Analysis
 Issues important from a long-term safety perspective
 Improve knowledge of human behavioral patterns
 Construction habits, eating habits, animal husbandry patterns, water use
patterns
 Biotic characteristics broadly relate to an “up and out” transport
pathway
 Insect excavation, animal excavation, rooting depths of local plants, and
root uptake and foliar shedding of eucalyptus trees
 Chemical nature of the waste
 Different chemical forms of U in the waste and the uncertainty of the
associated mass that may form corrosive agents
 Waste form characteristics
 Waste form evolution, effect of waste form moisture content

23. Question
 Why does one want to go through an exercise of this
nature?
“…to establish confidence that the basic principles of radioactive
waste management, namely to protect human health and the
environment at all times, are adhered to…”

24. Confidence
 The NEA (NEA, 1999) defines confidence as
“…to have reached a positive judgement that a given set of conclusions are
well-supported…”
 The NCRP definition for a post-closure safety assessment (NCRP,
2005) emphasises reasonable assurance of compliance
 It is neither possible nor desirable to argue absolute assurance
 What one really wants to achieve is to reach defensible decisions on the
extent to which the disposal system may comply with the regulatory criteria
 Both technical and non-technical arguments may be required for this
purpose

25. Confidence Building
 Process internal and external to the safety assessment
process
 Internal confidence
 Confidence the people performing the safety assessment has in their
results
 Proving that the analysis and the results are accurate, and
 Uncertainties are clearly identified and minimized where possible
 External confidence
 Building confidence in the regulatory body and in the public
 Providing an acceptable level of proof that the safety assessment is
suitable for the purpose of making or supporting a decision

26. Confidence in the Safety Assessment
 Used an internationally recognised, systematic and structured
safety assessment methodology
 Used site-specific data as far as possible, complemented with
justified literature values
 Selection of parameter values were conservatively biased
 Presented analyses results and finding in an accurate, traceable
and transparent manner
 Clearly identified and minimised uncertainties where possible
 Parallel assessments produced consistent and complementary
results over a wide spectrum of assessment conditions

27. Confidence in the Disposal System
 A robust disposal system can be described as a system
that continues to perform its expected global safety
function, no matter what kind of reasonable perturbation
may occur
 Integrating the concepts of robustness into the disposal
system or components of the system, lead to an increase
in the confidence of the disposal system

28. Confidence in the Disposal System
 Factors demonstrated to contribute to the intrinsic
robustness of the Vaalputs disposal system
 Comprehensive site selection process (1979-1982)
 Remoteness of the site
 Environmental site characteristics
 Limited contribution of disposal system components
 Trench Cover (cap)
 Concrete containers
 Trench layout
 Trench horizontal dimensions

29. Conclusions
 Given the assessment results and the conservative nature of the
assessment, the assessment concluded that most new data
collection activities (with a few key exceptions) would be expected
to lead to improved system performance
 The assessment concluded that the likelihood is high for post-
closure safety at Vaalputs to be demonstrated successfully for the
disposal of a national inventory of LILW
 It was concluded that, given the assumptions and conditions
imbedded in the assessment, the use of near surface disposal
trenches is effective and sufficient for the disposal of the national
inventory of LILW

30. Thank You for Your Attention!

31. National Inventory
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1.00E+12
1.00E+13
1.00E+14
1.00E+15
1.00E+16
1.00E+17
Am-241
Am-242m
Am-243
C-14
Cd-113m
Cl-36
Cm-243
Cm-244
Cm-245
Cm-246
Co-60
Cs-135
Cs-137
Eu-154
H-3
Ho-166m
I-129
Ni-63
Np-237
Pu-238
Pu-239
Pu-240
Pu-241
Pu-242
Se-79
Sm-151
Sn-121m
Sn-126
Sr-90
Tc-99
Th-230
U-232
U-233
U-234
U-235
U-236
U-238
Zr-93
Tru
Activity(Bq)