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[Editor’s note: On Dec. 29, former NASA scientist Dr. James Hansen wrote a piece on advancing nuclear energy to help address climate change and air pollution. The article below, by Stanford professor Mark Jacobson, provides a response to Hansen’s comments.]

Comment 1 by Dr. James Hansen:

The urgency of expanding clean energy implies that nuclear power, presently the largest source of carbon-free energy and historically the clean-energy source of fastest scale-up, likely must play an important role in meeting needs for dispatchable electric power, carbon-neutral fuels and fresh water.

Photo credit: Shutterstock
Dr. James Hansen argues that nuclear power “must” play an important role in the future. However, there is no scientific basis for this statement and his claim does not address the problems with nuclear power identified by the international community. Photo credit: Shutterstock

Summary Response:

Nuclear is an opportunity cost relative to clean, renewable wind, water and solar energy because of

a. the significant lag time between planning and operation of a nuclear plant relative to a wind, solar, or geothermal plant;

b. higher carbon emissions of nuclear per unit energy; and

c. nuclear weapons proliferation risks, meltdown risks, waste disposal risks, and uranium mining risks. As such, the only basis for nuclear growth is if 100% wind, water and solar is not possible. However, because the technical feasibility of 100% wind, water and solar across 139 countries and 50 states has been shown to be possible, evidence suggests at this time that a solution can be obtained without nuclear.

Response 1a:

The scale-up time for existing nuclear (10-19 years between planning and operation compared with 2-5 years for wind or solar) is too slow to help solve climate problems. Nuclear power requires 10-19 years between planning, permitting, financing and operating in all countries of the world.

This time includes 3.5-6 years to find a site, obtain a permit for the site, and obtain financing for the reactor, 2-3 years for the review and approval of the construction permit, 0.5-1 years between permit approval and issue, and 4-9 years for construction. (Jacobson, Energy and Environmental Science, 2, 148-173, 2009).

On the other hand, onshore wind and solar require an average of 2-5 years. A wind farm takes an average of 1-3 years for siting, purchasing or leasing land, monitoring winds, negotiating a power-purchase agreement and permitting. The construction period for a large wind farm is 1-2 years. A solar photovoltaic or concentrated solar power plant is also 2-5 years. Geothermal requires 3-6 years. (See citations in Jacobson, Energy and Environmental Science, 2, 148-173, 2009).

Response 1b:

Nuclear is not carbon free and emits 6-24 times more carbon-dioxide equivalent emissions than wind per unit energy produced over the same 100-year period. Such emissions include those during (a) planning, permitting, constructing, operating, refurbishing and decommissioning a nuclear plant versus a wind turbine and (b) the emissions associated with reducing carbon sequestration in soil by covering the soil with impermeable material or by mining.

Whereas, the emissions associated with constructing, operating and decommissioning a plant are accounted for in the standard lifecycle assessment (LCA), those associated with the timelag between planning and operation and downtime due to refurbishment (OC, opportunity cost emissions) and emissions associated with the loss of carbon from soil, are not.

IPCC (2014) Section 7.8.1 (P. 540) suggests that the range in lifecycle carbon emissions from nuclear is 4-110 g-CO2-eq/kWh: The ranges of harmonized lifecycle greenhouse gas emissions reported in the literature are … 4-110 gCO2eq/kWh for nuclear power.

The high-end of IPCC (2014) is 40 g-CO2-eq/kWh, higher than the high end of 9-70 g-CO2- eq/kWh provide in Jacobson (Energy and Environmental Science, 2, 148-173, 2009), suggesting the LCA results of Jacobson (2009) are well within the range of accepted norms.

However, when comparing different energy technologies for mitigating climate change, it is essential to account for the full emissions associated with the choice of one technology over the other over a similar period. This necessitates including emissions from the background grid associated with the difference in time-lag between planning and operating one technology versus another, the difference in emissions from the grid during downtime of each plant due to refurbishment, and the emissions associated with covering the soil with impermeable materials in each case.

Table 3 of Jacobson (Energy and Environmental Science, 2, 148-173, 2009) summarizes the opportunity cost emissions of nuclear power (59-106 g-CO2-eq/kWh) relative to wind and solar (0 g-CO2-eq/kWh), since the opportunity cost is taken relative to the generators with the shortest time-lag).


The figures in this document further summarize the comparison of all emissions from nuclear (LCA, OC, soil emissions and others) relative to all wind, water and solar technologies.

The net result of the data in the figures is that nuclear carbon-equivalent emissions per unit energy range from 6-24 times those of wind power, thus they are not zero.

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