POWER March 2022 - 30

COMBINED HEAT & POWER
District Heating Supply from
Nuclear Power Plants: Technical
and Economic Aspects
In the February 2022 issue of POWER, an overview of existing district heating
systems that utilize nuclear power for their energy source was presented and best
practices of successful installations were reviewed. In this article, the technical and
economic aspects of these combined heat and power systems are examined.
Ishai Oliker, PhD, PE
T
he heat delivery systems from
nuclear power plants are based on
a tertiary (in relation to the reactor
core) circuit. Pressure in this circuit is
kept higher than the maximum possible
pressure of the extracted steam. This
prevents radioactive products from getting
into the district heating water.
District Heating Design
Considerations
District heating piping size is determined
by the heat load and the water temperature
drop in the system. In most cases,
the required amount of heat is provided
to the customer by varying the temperature
in the supply network at the power
station as a function of outdoor ambient
temperature. A substantial temperature
drop between the supply and return lines
reduces the flow rate of the circulating
water and, as a result, piping size and
pumping power. However, a high supply
temperature at the nuclear combined
heat and power (NCHP) plant reduces
electrical generation.
To maximize electric power production,
the optimum supply temperature
is generally set at about 250F; this is
increased to as much as 300F on the
coldest days by peaking boilers. Return
temperature is usually about 160F. For
long-distance transport, supply temperatures
up to 400F have been considered.
Typically, 60-inch-diameter pipes will
carry about 2,400 MWth, and 40-inch-diameter
pipes will carry about 700 MWth.
Installation of underground district heating
piping in the U.S. typically costs from
$800/ft. to $1,500/ft. However, despite
the high piping cost, it may be economical
to transport hot water as far as 100
miles to cities with heat loads of 1,500
MWth to 2,500 MWth.
One-way heat transport pipelines with
30
1. Diagram of a nuclear combined heat and power (CHP) plant with extraction/condensing
steam turbine. Courtesy: Joseph Technology Corp.
use of large electric driven heat pumps
to increase the quantity of useful heat
is also possible. In this case, at the user
end the water can be cooled to temperatures
acceptable for discharge.
Optimum Heat Load
It is generally not economical to supply
district heat to areas with heat densities
less than 90 MWth per square mile
(MWth/mi2
). Commercial and high-rise
residential areas with heat densities
of 130 MWth/mi2
to 180 MWth/mi2
are
It is generally not economical to supply
district heat to areas with heat densities
less than 90 MWth per square mile.
most suitable for district heating.
The problem of heat load is especially
important when NCHP systems are being
considered. Such plants would usually be
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District Heating Turbines
To heat water in an NCHP system, it is
necessary to regulate the amount of
heat extracted from the cycle to follow
POWER | March 2022
far from the urban area and require long
pipelines. Because large quantities of
heat transported reduce the specific cost
of heat transmission, large cities are the
most favorable for NCHP supply systems.
However, large district heating systems in
U.S. cities, such as New York (Figure 1),
Philadelphia, Boston, and Indianapolis,
are mostly medium-pressure steam systems
(150 psi to 400 psi), and extraction
and long-distance transport of steam with
those parameters is not economical.
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POWER March 2022

Table of Contents for the Digital Edition of POWER March 2022
