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XYLENE POWER LTD.

FAST NEUTRON REACTOR (FNR) SITING

By Charles Rhodes, P.Eng., Ph.D.

INTRODUCTION:
Elsewhere on this website Fast Neutron Reactors (FNRs) have been identified as the primary source of energy for meeting mankind's future energy needs. This web page focuses on FNR siting criteria.
 

FNR SITING CRITERIA:
A liquid sodium cooled Fast Neutron power Reactor (FNR) should be sited sufficiently above nearby water bodies to ensure that even under worst case earthquake/tsunami/flood and sea level rise conditions the water level will never reach the bottom of the FNR primary liquid sodium pool, thus ensuring that there will never be any contact between the primary sodium and water.

The primary sodium pool of a 1000 MWt FNR typically contains about 4700 tonnes of liquid sodium at up to 450 degrees C. Hence sodium containment and safe isolation from water are paramount. The hot sodium is isolated from air using steel floats and argon cover gas. Once the sodium has cooled to room temperature it can be isolated from air using a thin layer of a low density low vapor pressure oil.

Since a FNR should not be sited close to a major water body a FNR normally dissipates heat via dry cooling towers and via a district heating system. Few people choose to reside adjacent to a natural draft cooling tower unless that tower is concealed inside another structure such as an office building or a high rise apartment building. The cooling towers must be higher than other nearby buildings.

A practical alternative is for every premises that uses district heat in the winter to have roof mounted fan-coil units that can dissipate a comparable amount of heat to the environment in the summer. Thus the district heating system can be configured to present a nearly constant thermal load to the reactor. In these circumstances the cooliing towers only have to be sized to dissipate fission product decay heat by natural circulation.

Ideally for both safety and long term structural stability the primary sodium pool of an FNR should be installed in a cavity cut out of a granite mountain. However, such ideal sites are seldom available in urban locations.

The FNR must either be set in a natural hill or must be surrounded by embankments about 15 m high that provide certain water exclusion and liquid sodium containment. The embankments need surface paving to ensure drainage of rain water off the surface and thus keep the embankment material dry. In addition to excluding water the embankments ensure containment of the liquid sodium above the highest possible local flood level under worst case earthquake conditions.

A reactor located in steep granite mountains might have a natural draft cooling tower concealed within a granite core mountain. This cooling tower concealment methodology might be applied in mountainous regions of British Columbia or Labrador but it is impractical in most of Ontario.

If there are not at least two redundant dry cooling towers a FNR must be located sufficiently close to a secure supply of water to enable safe removal of fission product decay heat by evaporation of water. In this case emergency cooling water must be stored in nearby reservoirs.

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. The shale that typically exists about 7 m below grade under Toronto has a maximum load bearing capacity of about 5000 kPa. Shale is not as good as granite but it is adequate for FNR support.

FNRs must be protected from both ground water and from malevolent attacks from above. To prevent a malevolent attack from above from causing serious consequences the primary liquid sodium pool surface must be sufficiently below local grade level that the surrounding ground or embankments can contain the liquid sodium, independent of the pool walls. Then in the event of a malevolent attack it is essential to rapidly remove heat from the liquid sodium to reduce its temperature to under 200 degrees C, to cover the sodium pool to exclude rain water and to maintain argon cover gas to prevent further sodium oxidation. A spare temporary sheet metal roof should be stored nearby and should be available for immediate deployment to exclude oxygen and rain water in the event of a major FNR roof failure.

When the temperature of the sodium approaches room temperature onging oxidation of the sodium can be prevented by flooding its surface with a low density oil such as kerosene.

To ensure containment and isolation of the liquid sodium after an earthquake that is sufficiently violent to rupture all three primary liquid sodium containment walls the surrounding ground should be impervious to liquid sodium and should be dry down to at least 21 m below the pool deck level. Thus ideally the FNR should be located within a broad rock hill that rises at least 22 m above its immediate surroundings. The top surface of the hill must be paved or otherwise sealed to cause rain water to drain off the sides of the hill instead of penetrating the hill.

The hill should be broad enough or the embankments thick enough to protect the FNR primary liquid sodium tank from a malevolent direct impact by a large aircraft travelling at close to the speed of sound.
 

SODIUM HANDLING:
There should be provision for nearby sodium storage with sufficient capacity to hold all the primary liquid sodium so as to permit future major maintenance/repairs to the FNR primary liquid sodium tank. There must be a means of easily and rapidly transferring heat emitting fuel bundles from the primary liquid sodium tank to fuel bundle transport cylinder and vice versa.

The sodium will likely be delivered to the reactor site either in tanker trucks or as a solid in open top 55 US gallon steel drums with removeable covers. There may be as many as 24,000 such drums. These drums need to be stored on pallets in groups separated by aisles that act as fire breaks and provide access for fire suppression. A safe drum pallet size is 30 inches X 30 inches. Hence exclusive of aisles the single level drum storage space requirement is:
(30 inches X 30 inches) / drum X (.0254 m / inch)^2 X 24,000 drums = 13,935 m^2

Allowing for aisle area equal to 3 X storage area implies a requirement for 41,806 m^2 = 0.042 km^2 for single layer sodium drum storage.

The sodium filled drums will likely arrive by rail. Hence the drum storage site will likely need additional area for a rail siding and cargo transfer of:
1 Km X 50 m = .050 Km^2

The FNR needs to have multiple adjacent cooling towers, to provide a secure heat sink. If there is only one dry cooling tower there must be an extremely secure source of cooling water.

The drainage required to ensure dryness of any hill where a FNR is installed below grade will likely have an adverse effect on any nearby water wells.

The combination of the hill and the cooling towers will be as prominent on the horizon as a cluster of wind turbines of similar height. In rural locations to avoid problems with neighbours it is recommended that the party that owns the FNR should purchase the land within a 0.5 km radius of the FNR. Hence from a land acquisition perspective it makes sense to locate several FNRs in a cluster to minimize land acquisition costs. To put this issue in perspective, if the average land area per FNR is 1 km^2 and the cost of rural land is $50,000 per hectare the cost of the land per FNR is about:
1 km^2 X 100 hectares / km^2 X $50,000 / hectare = $5,000,000.
 

ENERGY TRANSMISSION CORRIDORS:
Also important are the costs of an electricity and heat transmission corridors from the FNR to the electricity and thermal loads.
 

URBAN LOCATION ISSUES:
In order to access the district heating load FNRs should be located within urban developments. However, within a major metropolis the land acquisition cost will increase many fold.

Also important is the proximity of the FNR site to a metropolis where the highly trained personnel required to assemble, operate and maintain the FNR can comfortably live. These real estate considerations point to the wisdom of Ontario Hydro in establishing during the 1970s major thermal electricity generation sites at Bruce, Darlington, Nanticoke and Pickering and in laying out major electricity transmission corridors in Ontario. Today the whole issue of nuclear reactor siting and long term electricity and thermal energy transmission corridor planning needs to be revisited.
 

FNR SITE AND TRANSMISSION CORRIDOR RESERVATION:
Fully displacing fossil fuels will likely require at least a five fold increase in nuclear electricity generation and related energy transmission capacity in Ontario. Hence the government of Ontario should identify and prohibit new development on land that will be required for nuclear power stations and their related energy transmission and access corridors.
 

URBAN MARKET:
(a) To make economic sense SM-FNR must be able to reliably supply electricity, heat and cooling in urban markets in ratios that vary over time. To provide district heating and/or district cooling SM-FNRs must be sited in the middle of major cities which means that these SMFNRs must have no instability or failure modes that could impact persons outside the reactor site. Such SM-FNRs must incorporate a range of passive safety features that do not exist in current power reactors.

(b) Such reactors must tolerate almost any conceivable attack or act of God without causing a significant public safety problem.

(c)The reactors should be connected to their thermal and electrical loads without reliance on other electricity and natural gas utilities. The reactor owners must be able to obtain pipe and electrical easements under both public roads and private properties. The reactor owners must have the same legal status as an electricity or natural gas utility with respect to obtaining these critical easements. The reactor owners must be permitted to sell heat, cooling, electricity, kinetic energy or any combination thereof to end users without making payments to any other utility. For example the reactor owner must be able to sell electricity directly to major end users such as major building owners without paying a transmission-distribution charge to the electricity utility. The issues of electricity load island formation, disconnection, automatic re-synchronization and re-connection to the electricity grid must be faced. There are related control and load sharing issues that the Ontario Power Authority (now the IESO) has thus far refused to face, An important issue is short circuit fault clearance in grid connected loads that are closse to the nuclear generation.

(d) Obtaining public utility status generally requires an act of a provincial legislature. Selling SM-FNRs on a large scale will be all but impossible until a common industry body such as CNL takes on this legislative challenge. It is necessary to draft enabling legislation that any provincial legislature can easily approve. The legislative model for district heating is Enwave in Toronto. However, realizing utility status for Enwave required a many year effort by an association of major hospitals and office building owners. Even so, Enwave does not sell electricity in competition with the Toronto Hydro Electricity System. The number of actual SM-FNR installations will be negligible if each SM-FNR project proponent must first successfully run a major political campaign.

(e) A related issue is the prevailing end user electricity rate structure. Much of the value of nuclear power as compared to intermittent wind and solar power lies in the reliability of nuclear electricity generation. In order for nuclear to make financial sense to end users the electricity rate structure must properly reflect the value of kVA as compared to a kWhe. In the province of Ontario there are many electricity rate problems and there is almost no energy storage because the present electricity price plan charges too much per kWhe and too little per kVA.
 

This web page last updated April 19, 2018.

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