PWR Upgrades Emerge
Table 3 lists the number of plants where the owners have already contacted the NRC about an EPU, but the real number of prospective uprates is far larger. At least 60 nuclear units are most likely candidates for an EPU program in the near future, and about 50 of those units are PWRs, which represent 6 to 12 new plant equivalents. The increased interest by PWR owners has been prompted, in part, by advances in technology and, perhaps more importantly, improvements in available fuels. Fuels with slightly higher enrichments, improved cladding, low noncondensable gas releases, and improvements to burnable poisons and better structural stiffness that make the fuel less vulnerable to vibration and fretting have become available over the past couple of decades.
Table 3. Expected applications for extended power uprates. Source: NRC
Also, improved manufacturing processes result in better process control, which leads to less statistical variation design margin. With less design margin required, an uprate in output is possible. Additionally, engineers have found ways to safely place more fuel in existing reactor vessels, all of which leads to greater thermal power output. Improvement to neutron fluence through the use of low-leakage cores has provided additional margin in NSSS components and helps to accommodate higher power levels over the long term.
The added thermal power output can be achieved with little to no increase in output steam pressures (based on redesign and replacement of the HP turbine rotor) through increasing steam mass flow. In some cases, an increase of 2% to 3% pressure has been adopted for increased fuel margins.
Many Economic Advantages
The economic incentive of an EPU is to increase power output at competitive costs while avoiding the long lead times for constructing new generation. Information provided in a June 2008 Nuclear Energy Institute Seminar, based on a small number of plants currently involved in EPU programs, indicates that the capital cost of this incremental power ranges from about 15% to 50% on a cost per kilowatt basis, compared with the cost of a new nuclear plant. Of course, these costs are very site dependent and tend to increase on a per kilowatt basis with larger uprates, so it is difficult to generalize other than to suggest that on a capital cost per kilowatt, EPU uprates are very competitive with constructing new power plants.
There are also other intangible benefits associated with an EPU. Many of the plants have been operating for 30 years or more and require some major replacement of equipment. These and other plants either have already completed, or are contemplating, license renewal. Combining an EPU with a maintenance upgrade and/or a license extension allows some of the cost and cost recovery to be shared among programs. Integrating the total project would minimize future outage risks because upgraded/modified equipment would be used that had already considered the new life-extension requirements.
The added power from uprated units is also effective in reducing greenhouse gas emissions for the entire utility fleet of plants in a timely fashion. It can also reduce utility costs.
Although not necessarily an economic advantage, a utility doesn’t have to wait as long to reap the benefits of an EPU. An EPU can be brought into operation in about one-half the time required to license and build a new plant.
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