Proposed pebble bed modular reactor


SECTION 2: ASPECTS OF THE PROPOSED ACTIVITY



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SECTION 2: ASPECTS OF THE PROPOSED ACTIVITY

introduction


To provide an overview of the life cycle impacts (potential and real) of the proposed Plant, inputs and outputs were developed for each life cycle phase. These are presented below in tables and text. The in- and output tables, in turn, were used to develop the impact tables for each of the life cycle phases.

1.8supplementary information on inputs and outputs of the proposed activity21

1.8.1Input data


  • Nitrogen/Helium

  • Nitrogen for installation and commissioning period

For the initial clean up and commissioning nitrogen gas rather than helium gas will be used due to the cost of helium gas.

Approximately 1 000 kg nitrogen is required for the initial clean up of the MPS22 and gas systems. For completion of the installation and commissioning period the demonstration module will require an additional 3 576 kg of nitrogen.



  • Helium for normal operations

The expected helium loss during normal operations is specified as 0.1% of inventory per day. The inventory is approximately 7 290 kg and the helium loss is approximately 2 661 kg per year. The inventory loss is based on the THTR/HTR specification, although less inventory loss was experienced. Actual loss will be determined during operation.

  • Helium for planned outages

During each sixth year planned outage, a helium loss of approximately 898 kg is expected. An additional 250 kg is required during the outage when the core reflector is replaced.

  • Graphite spheres

The central graphite column in the reactor will be replaced once in about 20 years of the plants life. A total of 110 000 graphite spheres will be removed from the graphite storage tank to replace those in the central column. The spheres removed from the storage tank will have to be replaced to maintain the de-fuelling capability.

The usage of graphite spheres due to normal wear and maintenance activities is expected to be about 3 000 spheres over the life of plant.



  • New Fuel Spheres

The Fresh Fuel Storage Area is designed to store six months’ supply of fresh fuel, i.e. approximately 70 000 fresh fuel spheres.

The Spent Fuel Storage Area in the basement of the building will provide storage space for all the spent fuel produced during the lifetime of the reactor, which is 35 Full Power Years (FPY). This amounts to about 6.0 x 106 spent fuel spheres. The spent fuel spheres will be stored in 10 Spent Fuel Storage Tanks.

Only two of the 10 Spent Fuel Tanks will be in operation at any given time. Spent fuel is loaded in daily batches into the two tanks, until the tanks are full. Thereafter, the tanks will be sealed and the next pair of tanks is brought into operation. A total of about 425 spheres are loaded into the tanks per Full Power Day (FPD).


  • Demineralised water

The initial filling of the module’s closed water circuits will be obtained from Koeberg and transported in tankers. Approximately 500 m³ of demineralised water will be required for the first fill.

For make-up water, decontamination and other cleaning processes, demineralised water at an average of 10 m³ per month is required.



  • Potable water system

During normal operation, the volume of potable water required per month is indicated in Table 4.

Table 4: Volume of External Service Water Required During Normal Operation



Plant Configuration

Normal Operation

Potable Water Consumption
(m³/month)

Services & auxiliary buildings + 1 module

200

During an outage about 50m³ of water per day is required.

Ideally, any PBMR plant should be built on sound bedrock. In the case of this site, drilling results show that such bedrock exists at a depth of some 20 to 22 m below ground level. This is particularly appropriate for the PBMR, since the design of the plant is such that it ideally requires to be embedded to a depth of some 22 to 25 m.

The information regarding foundation conditions, was confirmed by information gathered during the construction of the Koeberg NPS.



  • Excavation conditions

Drilling results at the proposed site have shown that the local water table is some 5 m below ground level. Since the site is immediately adjacent to the Atlantic Ocean and about 8 meters above sea level, it must be assumed that during the excavation process, continuous dewatering of the area will be required via pumping. This dewatering will continue during construction, until such time as the building’s walls have reached ground level and backfilling of the excavation is completed. Thereafter the groundwater level will be left to resume normal levels.

Except for the bottom one or two meters of partially fractured rock the material to be excavated will be compacted sand.

No decisions have been made on methods of limiting water ingress to the excavation, or to the excavation methodology to be used. These are dependent on the evaluation of proposals to be received from civil engineering contractors and will be environmentally managed to acceptable levels in the EMP.


  • Site access

Access to the proposed site would be via the existing normal access routes to Eskom's KNPS, i.e. via the R27 Highway from the directions of either Cape Town or Saldanha Bay. Although a private Eskom owned road from Duynefontein to Koeberg exists, traversing through the Koeberg Nature Reserve, this route would be designated as off-limits to construction traffic, to and from the PBMR site.

Shipments of equipment of normal mass for the demonstration plant would be imported via Cape Town harbour. In the case of components of extreme mass, route studies have shown that several of the road bridges between Cape Town harbour and the proposed site could not handle these loads. It is therefore proposed that these abnormal components be imported via Saldanha Bay harbour and transported to site by road via the R27 Highway. Surveys of this route show that that there is only one highway bridge, which would not be capable of handling the loads. The bridge can be bypassed via a temporary road.



  • Availability of cooling water

It has been established that the cooling water supply for the demonstration plant will be taken from Koeberg's cooling water pump house, and that the heated water from the demonstration plant will be routed into Koeberg's thermal water discharge channel. This will result in PBMR not having to build new water intake and discharge structures, with a resultant considerable cost saving. Piping connections between the Plant and the Koeberg structures will, however, have to be provided.

Skilled labour is readily available in surrounding towns such as Atlantis, some 25 km from the site. Unskilled labour is readily available from any number of the townships surrounding Cape Town. In both cases, the mass transporting of this labour to and from site by PBMR contractors will be essential.

  • Availability of local nuclear infrastructure

Being immediately adjacent to Eskom's KNPS, the proposed site of the demonstration Plant is ideal from a nuclear infrastructure point of view. Although it is planned that the demonstration plant will run independent of Koeberg, it will use some of Koeberg's facilities, such as Radiation Medicine and to some extent, the decontamination facilities.

The PBMR requirement for a 400 m radius exclusion zone around the demonstration Plant will have no additional effect on adjacent land use, since the entire area defined by such a radius falls well within Koeberg's existing and much larger exclusion zone.

  • Employment

During construction about 1 400 job opportunities will be created with emphasis on local recruitment. During operations about 40 permanent employees will be required to operate the proposed Plant.

1.8.2Output Data


  • Sewerage system

The sewerage requirements for the demonstration plant are catered for by the existing Koeberg sewerage reticulation system. The sewerage flow is estimated at 140 m³ per month.

The expected sewerage effluent is as indicated in Table 5.

Table 5: Average Sewerage Effluent


Plant Configuration

Average Estimated

Sewerage Effluent
(m³/month)

Services & auxiliary buildings + 1 module

140

  • Local authority garbage/refuse disposal

The average volume of garbage/refuse on site is as indicated in Table 6:

Table 6: Average Volume Of Garbage Removal



Plant Configuration

Compacted Average Estimated

(m³/month)

Non-compacted Average Estimated

(m³/month)

Services & auxiliary buildings + 1 module

3.6

1.5

  • Ultimate heat sink

The demonstration plant’s ultimate heat sink system will be interfaced with the existing KNPS seawater basin. The seawater temperature at Koeberg is 18 °C (weighted maximum average).

For a constant heat load of 158 MW for the module, a main closed circuit water flow rate of 1 300 litres per second, a closed circuit heat exchanger inlet water temperature of 50 °C, and a closed circuit heat exchanger outlet temperature of 21 °C, sea water at a rate of 1 700 litres per second is required. The seawater outlet temperature is 40 °C at this rate.




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