Appendix AI - Oceanography FINAL.pdf - PBMR

Pebble Bed Modular Reactor Demonstration Power Plant
Environmental Impact Assessment
Assessment of Oceanographic Impacts
Compiled by Dr T.B. Robinson
Tel: (021) 671 6724
trobins@botzoo.uct.ac.za

Table of Contents
Executive Summary
i
1. Introduction 2
2. Methodology 2
3. Impact assessment 2
3.1 Potential impacts during normal operations 2
3.1.1 Flooding from the sea 2
3.2 Interruption in supply of marine cooling water 3
3.3 Seawater temperature 5
3.2 Potential impacts as a result of non-nuclear accidents 12
3.3 Potential impacts of a nuclear accident 12
4. Conclusions and recommendations 12

Executive Summary
This report offers a review of the report prepared by Prestedge Retief Dresner
Wijnberg (Pty) Ltd and an assessment of oceanographic impacts surrounding the
proposed PBMR DPP during the construction, commissioning and operational phases
of development.
The threat of flooding from the sea during all phases of the proposed development
stems from extreme waves, extreme water levels and tsunamis. Should the PBMR
DPP be constructed at least 8m above mean sea level, there is no risk of flooding
under the current parameters.
Exposure of cooling water intake pipes, damage to cooling water intake pipes,
sedimentation within the mouth of the intake basin and blockage of cooling water
intake pipes by sand, oil slicks, debris or marine fauna and flora may threaten the
supply of seawater for cooling purposes. These threats will be encountered during the
commissioning and operational phase of the development.
The temperature of seawater taken up for cooling purposes has implications for the
efficiency of the cooling system. It is anticipated that the likelihood of the sea
temperature increasing above the 42C margin is extremely low
It is concluded that the proposed PBMR DPP are not expected to be significantly
impacted by the oceanography of the surrounding area. Additionally, the development
is not anticipated to affect the oceanographic characteristics of the marine
environment.
1

1. Introduction
SHE Cape Environmental were appointed by Arcus Gibb to prepare a specialist report
on Meteorology and Oceanography aspects of the Koeberg PBMR DPP. Prestedge
Retief Dresner Wijnberg (Pty) Ltd were in turn appointed by SHE Cape
Environmental to provide specialist oceanographic input into this study. As
engineering specialists Prestedge Retief Dresner Wijnberg (Pty) Ltd described
potential oceanographic impacts on the PBMR DPP development but were unable to
assess the implications of these impacts. Due to unforeseen circumstances SHE Cape
Environmental have not been able to conduct an assessment of the impacts identified
by Prestedge Retief Dresner Wijnberg (Pty) Ltd. As such, this report serves to review
the report prepared by Prestedge Retief Dresner Wijnberg (Pty) Ltd and assess all
possible environmental impacts identified within that report.
2. Methodology
The assessment provided in this report is based on the potential oceanographic
impacts identified within the report provided by Prestedge Retief Dresner Wijnberg
(Pty) Ltd (Attached here to as Appendix 1).
3. Impact assessment
3.1 Potential impacts during normal operations
3.1.1 Flooding from the sea
(a) Extreme waves
Using wave data collected at Koeberg Nuclear Power Station (KNPS) mathematical
modelling (using the widely accepted Weibull distribution method) was used to assess
the return period of extreme waves (See Appendix 1 for more detail). These best fit
predictions indicate that if the PBMR DPP is build at the same elevation as KNPS
(i.e. 8 m above mean sea level (MSL)) flooding from extreme waves is very unlikely.
(b) Extreme water levels
Extreme water levels are influenced by wave action, tides, meteorological effects (e.g.
onshore winds, low barometric pressures, shelf waves and edge waves) and tsunamis.
Based on the predictions of Prestedge Retief Dresner Wijnberg the extreme water
level that would cause flooding of the power station from the sea has a recurrence
interval of 1 in 10 6 years at the 68% confidence level and would be 6.09 m above
2

MSL. These estimates are considered reliable as two separate studies arrived at the
same figure (See Appendix 1).
Accompanying global climate, sea levels are anticipated to rise over the long-term. It
is predicted that global sea level will rise at a rate of about 4 mm/year to reach
between 0.22 and 0.44 m above 1990 levels by 2090 (Appendix 1). At this rate of
increase extreme water levels are not anticipated to threaten the PBMR DPP.
(c) Tsunamis
When considering potential of flooding due to a Tsunami it is recommended that the
maximum credible tsunami run-up (i.e. 4 m above still water level) be combined with
the level of highest astronomical tide (i.e. 1.20 m above MSL based on the 2005 Tide
Tables). Under such conditions a maximum flood level of 5.20 m above MSL is
predicted. As the reoccurrence interval of the highest astronomical tide is 1 in 18.6
years the likelihood of a tsunami co-occurring with such a tide is small. Nonetheless,
should this occur a flood level of 5.20 m will not affect the PBMR DPP should it be
build at an elevation of 8 m above MSL (as is KNPS).
The above assessment of the threat of flooding from the sea from extreme waves,
extreme water levels and tsunamis applies throughout the construction,
commissioning and operational phase of the development
3.1.2 Interruption in supply of marine cooling water
(a) Exposure of cooling water intake pipes
It is proposed that the PBMR DPP will obtain marine cooling water from the CRF-
SEC backup line of KNPS. As the centre line of the openings to the backup line occur
at -1.75m MSL and the uptake pipe has a diameter of 1.2m, intake water will be
totally cut off at a level of -2.35m.
Additional consideration should be given to the potential of exposure of cooling water
intake pipes by tsunamis. Under conditions of the maximum credible tsunami
described above, the draw down of water at the site of the proposed development is
predicted to reach 4 m below still water level. Should this occur at lowest
astronomical tide the extreme low water level could be -4.9 MSL.
3

(b) Damage to cooling water intake pipes
As the cooling water abstraction pipe for both KNPS and the PBMR DPP are located
within the intake basin, damage to the breakwaters of the basin may result in damage
to the pipes and subsequent reduction in volume of cooling water. In order to
minimise the risk of such damage from storms or collisions with ships, the
breakwaters were designed according to a ‘zero percent damage’ criteria (as defined
in the Koeberg Site Safety Report). As a result, damage to the breakwater would not
jeopardise the immediate availability of water in the basin and as such no significant
threat is posed to the supply of emergency cooling water.
(c) Sedimentation
Regular monitoring since the construction of KNPS has shown that no long-term
erosion or accretion of the seabed or surrounding beach has been caused by the
building of the intake basin and breakwaters. Additionally, repair of only minor
erosion damage has been required on the south side of the basin.
Silting-up of the intake basin entrance occurs at a rate of 132 000 m 3 /year and in the
last 26 years dredging of encroaching sediment has been required only seven times.
Based on this tack record it is considered unlikely that sedimentation will result in
blocking of the entrance to an extent which would impede the inflow of cooling water.
(d) Blockage of cooling water intake pipes
A number of structural and operational aspects of the pumphouse and water intake
system to be used by the PBMR are designed to minimise the possibility of blockage
of intake water (see Appendix 1 for details). The threat of blockage of the cooling
water system stems predominantly from sand, oil slicks, debris and marine fauna and
flora. Current mitigation measures have reduced the chance of a significant blockage
occurring. However, in the last six years jellyfish blooms have had dramatic effects on
cooling water intake on three occasions. A current study is investigating this impact in
detail and additional mitigation measures are presently being implemented.
The interruption in supply of marine cooling water may impact on the PBMR DPP
during the commissioning and operational phases.
4

3.1.3 Seawater temperature
As the cooling system of the PBMR DPP ultimately relies on heat transfer from the
hot reactor to cold seawater, the temperature of seawater taken up has implications for
the efficiency of cooling. By design the PBMR DPP requires that the temperature of
uptake water does not exceed 42 ºC, by comparison KNPS requires that the
temperature of cooling water remains below 23 ºC. Mathematical modelling based on
daily temperature measurements collected at KNPS over twenty years indicates that
the return period of a seawater temperature above 22 ºC is 40 years while the return
period of 23 ºC seawater is 133 years. It is thus clear that the risk of uptake water
exceeding 42 ºC is not considerable but will have an effect on efficiency. It is
anticipated that the likelihood of the sea temperature increasing above the 42ºC
margin is extremely low. Therefore, no impacts are anticipated.
5

Table 1: Potential oceanographic impacts during normal operations
Impact Nature Intensity Extent Duration Probability Non-
Reversibility*
Impact 1: Flooding due to extreme waves Negative High Local Short term Improbable Not considered
Mathematical modelling of data collected over
relevant
seven years indicates that extreme waves are
very unlikely to cause flooding at the site of the
proposed development.
Irreplaceability*
Not considered
relevant
Confidence
High
With Mitigation
Should the PBMR DPP be built at least 8m above MSL no mitigation measures are considered necessary
Impact 2: Flooding due to extreme water
levels
The probability of flooding of the power station
due to extreme water levels is considered low as
this would require a water level of 6.09 m above
MSL and has a recurrence interval of 1 in 10 6
years.
Negative High Local Short term Improbable Not considered
relevant
Not considered
relevant
High
With Mitigation
Should the PBMR DPP be built at least 8m above MSL no mitigation measures are considered necessary
Impact 3: Flooding due to Tsunamis
The maximum credible tsunami for the
proposed site is predicted to be 4 m above still
water level. When combined with the level of
highest astronomical tide (i.e. 1.20 m above
MSL), a maximum flood level of 5.20 m above
MSL could occur. While the probability of such
a tide co-occurring with a tsunami is low, a
water level of this height will not flood the
PBMR DPP if it is built 8 m above MSL.
Negative High Local Short term Improbable Not considered
relevant
Not considered
relevant
High
With Mitigation
Should the PBMR DPP be built at least 8m above MSL no mitigation measures are considered necessary
6

Impact Nature Intensity Extent Duration Probability Non-
Reversibility*
Impact 4: Exposure of cooling water intake Negative High Local Short term Improbable Not considered
pipes under tsunami conditions
relevant
Under conditions of the maximum credible
tsunami, the draw down of water at the site of
the proposed development is predicted to reach
4 m below still water level. Should this occur at
lowest astronomical tide the extreme low water
level could be -4.9 MSL.
Irreplaceability*
Not considered
relevant
Confidence
High
With Mitigation
Under such unlikely conditions as described
above, alternative cooling water would have to
be sourced in order to maintain operation of the
cooling system.
Impact 5: Damage to intake basin
The intake basin is designed in such a way that
damage to the breakwaters would not jeopardise
the integrity of the intake pipes or the
immediate availability of water in the basin. As
such no significant threat is posed to the supply
of emergency cooling water.
Negative High Local Short term Improbable Not considered
relevant
Negative High Local Short term Improbable Not considered
relevant
Not considered
relevant
Not considered
relevant
High
High
With Mitigation
No mitigation measures required
Impact 6: Erosion or accretion of
surrounding sediment
As no long-term erosion or accretion of the
seabed or surrounding beach has been caused by
the building of the intake basin and breakwaters
since the construction of KNPS. As such it is
highly unlikely that this will occur in the future.
With Mitigation
Negative Medium Local Short term Improbable Low No High
No mitigation measures required
7

Impact Nature Intensity Extent Duration Probability Non-
Reversibility*
Irreplaceability*
Confidence
Impact 7: Sedimentation within the intake
basin
As dredging of encroaching sediment has been
required only seven times in the last 26 years it
is considered unlikely that sedimentation will
result in blocking of the entrance to an extent
which would impede the inflow of cooling
water.
Negative High Local Short term Improbable Not considered
relevant
Not considered
relevant
High
With Mitigation
No mitigation measures required
Impact 8: Blockage of cooling water intake
pipes
The threat of blockage of the cooling water
system stems predominantly from sand, oil
slicks, debris and marine fauna and flora. The
structural and operational mitigation measures
currently applied to the pumphouse and water
intake system to be used by the PBMR are
deemed sufficient to minimise the possibility of
blockage of intake water.
Negative High Local Short term Improbable Not considered
relevant
Not considered
relevant
High
With Mitigation
No further mitigation measures are required
*These categories are not considered relevant to this particular study as it considers the impact of oceanographic features on the design and placement etc of the PBMR DPP
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Table 2: Consequence of oceanographic impacts during normal operations
Impact
Impact 1: Flooding due to
extreme waves
Consequence Probability Confidence
Low Improbable High
With mitigation
Impact 2: Flooding due to
extreme water levels
With mitigation
Impact 3: Flooding due to
Tsunamis
With mitigation
Impact 4: Exposure of cooling
water intake pipes under
tsunami conditions
Should the PBMR DPP be built at least 8m above MSL no
mitigation measures are considered necessary
Low Improbable High
Should the PBMR DPP be built at least 8m above MSL no
mitigation measures are considered necessary
Low Improbable High
Should the PBMR DPP be built at least 8m above MSL no
mitigation measures are considered necessary
Low Improbable High
With mitigation Low Improbable High
Impact 5: Damage to intake
basin
With mitigation
Impact 6: Erosion or accretion
of surrounding sediment
With mitigation
Impact 7: Sedimentation within
the intake basin
With mitigation
Impact 8: Blockage of cooling
water intake pipes
With mitigation
Low Improbable High
No mitigation measures required
Low Improbable High
No mitigation measures required
Low Improbable High
No mitigation measures required
Low Improbable High
No mitigation measures required
Table 3: Significance of potential oceanographic impacts during normal operations
Impact Consequence Probability Significance Confidence
Impact 1: Flooding due to
extreme waves
Low Improbable Low High
With mitigation
Impact 2: Flooding due to
extreme water levels
No mitigation measures required
Low Improbable Low High
9

With mitigation
Impact 3: Flooding due to
Tsunamis
With mitigation
Impact 4: Exposure of cooling
water intake pipes under
tsunami conditions
No mitigation measures required
Low Improbable Low High
No mitigation measures required
Low Improbable Low High
With mitigation Low Improbable Low High
Impact 5: Damage to intake
basin
With mitigation
Impact 6: Erosion or accretion
of surrounding sediment
With mitigation
Impact 7: Sedimentation within
the intake basin
With mitigation
Impact 8: Blockage of cooling
water intake pipes
With mitigation
Low Improbable Low High
No mitigation measures required
Low Improbable Low High
No mitigation measures required
Low Improbable Low High
No mitigation measures required
Low Improbable Low High
No mitigation measures required
10

3.2 Potential impacts as a result of non-nuclear accidents and incidents
No non-nuclear accidents are anticipated to affect the oceanography of the
surrounding area.
3.3 Potential impacts of a nuclear accident
The oceanography of the surrounding area is not anticipated to cause or be affected by
a nuclear accident.
4. Conclusions and recommendations
The threat of flooding of the PBMR DPP originates from extreme waves, extreme
water levels and tsunamis. Although present during all stages of the development, this
threat is, however, not significant.
The temperature of seawater taken up for cooling purposes has implications for the
efficiency of the cooling system. It is anticipated that the likelihood of the sea
temperature increasing above the 42C margin is extremely low
It is concluded that construction, commissioning and operation of the proposed
PBMR DPP are not expected to be significantly impacted by the oceanography of the
surrounding area. Additionally, the development is not anticipated to affect the
oceanographic characteristics of the marine environment.
11