ML23296A113
| ML23296A113 | |
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| Site: | 05000610 |
| Issue date: | 10/23/2023 |
| From: | NRC/NMSS/DREFS/ENRB |
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GREENHOUSE GAS EMISSIONS ESTIMATES FOR A REFERENCE 1,000 MWe REACTOR AND THE ABLIENE CHRISTIAN UNIVERSITY MOLTEN SALT RESEARCH REACTOR The U.S. Nuclear Regulatory Commission (NRC) staff estimated the greenhouse gas (GHG) emissions of various activities associated with the building, operating, and decommissioning of nuclear power plants. The GHG emission estimates include direct emissions from the nuclear facility and indirect emissions from workforce and fuel transportation, decommissioning, and the uranium fuel cycle. The estimates are based on a single installation of 1,000 MWe output with an 80 percent capacity factor henceforth referred to as the reference 1,000 MWe reactor. The estimates may be roughly linearly scaled from the reference 1,000 MWe reactor for other reactor outputs. 1 This report discusses the calculation of GHG emission estimates for the reference 1,000 MWe reactor.
The estimated emissions from equipment used to build a nuclear power plant listed in Table 1 are based on hours of equipment use estimated for a single nuclear power plant at a site requiring a moderate amount of terrain modification (UniStar 2007-TN1564). Construction equipment carbon monoxide (CO) emission estimates were derived from the hours of equipment use, and carbon dioxide (CO2) emissions were then estimated from the CO emissions using a scaling factor of 172 tons of CO2 per ton of CO (Chapman et al. 2012-TN2644). The scaling factor is based on the ratio of CO2 to CO emission factors for diesel fuel industrial engines as reported in Table 3.3-1 of AP-42 Compilation of Air Pollutant Emission Factors (EPA 2012-TN2647). A CO2 to total GHG equivalency factor of 0.991 is used to account for the emissions from other GHGs, such as methane (CH4) and nitrous oxide (N2O) (Chapman et al. 2012-TN2644). The equivalency factor is based on non-road/construction equipment in accordance with relevant guidance (NRC 2014-TN3768; Chapman et al. 2012-TN2644).
Equipment emissions estimates for decommissioning are assumed to be one-half of those for construction equipment. Data on equipment emissions for decommissioning are not available; the one-half factor is based on the assumption that decommissioning would involve less earthmoving and hauling of material, as well as fewer labor hours, compared to those involved in building activities (Chapman et al. 2012-TN2644).
Table 1. Greenhouse Gas Emissions from Equipment Used in Building and Decommissioning (metric tons [MT] CO2(e))
Equipment Building Total(a) Decommissioning Total(b)
Earthwork and dewatering 12,000 6,000 Batch plant operations 3,400 1,700 Concrete 5,400 2,700 Lifting and rigging 5,600 2,800 Shop fabrication 1,000 500 Warehouse operations 1,400 700 1
The term model LWR" has also been used to describe a 1,000 MWe light water reactor for the purpose of evaluating the environmental considerations of the supporting fuel cycle to the annual reactor operations (WASH-1248, AEC 1974-TN23). It is assumed there are no significant differences between the 1,000 MWe reactor evaluated in WASH-1248 and the 1,000 MWe reference reactor evaluated in this appendix.
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Equipment Building Total(a) Decommissioning Total(b)
Equipment maintenance 10,000 5,000 Total(c) 39,000 19,000 (a) Based on hours of equipment usage over a 7-year period.
(b) Based on equipment usage over a 10-year period.
(c) Results are rounded to the nearest 1,000 MT CO2(e).
Table 2 lists the NRC staffs estimates of the CO2 equivalent 2 (CO2(e)) emissions associated with workforce transportation. Construction workforce estimates for the reference 1,000 MWe reactor are conservatively based on estimates in various combined license (COL) applications (Chapman et al. 2012-TN2644), and the operational and decommissioning workforce estimates are based on Supplement 1 to NUREG-0586 (NRC 2002-TN665). Table 2 lists the assumptions used to estimate total miles traveled by each workforce and the factors used to convert total miles to metric tons of CO2(e). The workers are assumed to travel in gasoline-powered passenger vehicles (cars, trucks, vans, and sport utility vehicles) that get an average of 21.6 mi/gal (9.1 km/L) of gasoline (FHWA 2012-TN2645). Conversion from gallons of gasoline burned to CO2(e) is based on U.S. Environmental Protection Agency (EPA) emission factors (EPA 2012-TN2643).
Table 2. Workforce Greenhouse Gas Footprint Estimates SAFe Construction Operational Decommissioning STORage Parameter Workforce Workforce Workforce Workforce Commuting Trips 1,000 550 200 40 (round trips per day)
Commute Distance 40 40 40 40 (miles per round-trip)
Commuting Days 365 365 250 365 (days per year)
Duration (years) 7 40 10 40 Total Distance Traveled (miles)(a) 102,000,000 321,000,000 20,000,000 23,000,000 Average Vehicle Fuel Efficiency(b) 21.6 21.6 21.6 21.6 (miles per gallon)
Total Fuel Burned(a) (gallons) 4,700,000 14,900,000 900,000 1,100,000 CO2 Emitted Per Gallon(c) 0.00892 0.00892 0.00892 0.00892 (MT CO2)
Total CO2 Emitted(a) 42,000 133,000 8,000 10,000 (MT CO2)
CO2 Equivalency Factor(c) 0.977 0.977 0.977 0.977 (MT CO2/MT CO2(e))
Total GHG Emitted(a) 43,000 136,000 8,000 10,000 (MT CO2(e))
(a) Values have been rounded.
(b) Source: FHWA 2012-TN2645.
(c) Source: EPA 2012-TN2643 2
A measure to compare the emissions from various GHGs on the basis of their global warming potential (GWP), defined as the ratio of heat trapped by one unit mass of the GHG to that of one unit mass of CO2 over a specific time period.
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Title 10 of the Code of Federal Regulations 51.51(a) (10 CFR 51.51(a)-TN250) states that every environmental report (ER) 3 prepared for an early site permit or COL stage of a light-water-cooled nuclear power reactor shall use Table S-3, Table of Uranium Fuel Cycle Environmental Data, as set forth in 10 CFR 51.51(b) (TN250) as the basis for evaluating the contribution of the environmental effects of uranium fuel-cycle activities to the environmental costs of licensing the nuclear power reactor. Section 51.51(a) (TN250) further states that Table S-3 shall be included in the ER and may be supplemented by a discussion of the environmental significance of the data set forth in the table as weighted in the project-specific analysis for the proposed facility.
Table S-3 of 10 CFR 51.51(b) (TN250) does not directly apply to non-light-water reactors (LWRs), nor does it provide an estimate of GHG emissions associated with the uranium fuel cycle; it only addresses pollutants that were of concern when the table was promulgated in the 1970s. However, Table S-3 states that 323,000 megawatt hour (MWh) is the assumed annual electric energy use for the Table S-3 reference 1,000 MWe nuclear power plant and that this 323,000 MWh of annual electric energy is assumed to be generated by a 45 MWe coal-fired power plant burning 118,000 MT of coal. These assumptions are based upon 1970s uranium enrichment technology, which has changed substantially since then. The older, energy-intensive gaseous-diffusion plants have been replaced with more efficient centrifuge-based systems. The current operating gas centrifuge uranium enrichment facility in the United States is URENCO-USA (Louisiana Energy Services), which is located in Eunice, New Mexico. The URENCO-USA facility does not rely solely upon coal as an energy source (Napier 2020-TN6443). If a 1,000 MWe plant is assumed to operate at 35 percent thermal efficiency and use uranium fuel enriched to 5 percent in uranium-235 (235U) with an average burnup of 40,000 megawatt days/MT for 40 years, then it will require about 1,043 tons of enriched uranium for fuel. To produce 1 ton of 5 percent enriched uranium with 0.25 percent 235U in the depleted uranium stream requires extraction of 10.3 tons of natural uranium and 7,923 separative work units, or SWUs (Napier 2020-TN6443). The 1,043 tons of uranium enriched to 5 percent 235U required over the 40-year life of the 1,000 MWe plant would then require 8,264,000 SWUs. Because a centrifuge enrichment facility requires about 50 kWh per SWU (WNA 2020-TN6661), a total of 413,200 MWh is needed to produce 40 years worth of uranium enriched to 5 percent 235U for fuel for the lifetime operation of the 1,000 MWe plant. For the existing U.S. centrifuge enrichment plant, the regional average CO2 emission factor is 1,248 lb/MWh, 4 and the total CO2 emission is about 243,000 MT.
Table S-3 also assumes that approximately 135,000,000 standard cubic feet (scf) of natural gas is required per year to generate process heat for certain portions of the uranium fuel cycle. The NRC staff estimates that burning 135,000,000 scf of natural gas per year results in approximately 7,440 MT of CO2(e) being emitted into the atmosphere per year because of the process heat requirements of the uranium fuel cycle. 5 For a 40-year operational life, this is 298,000 MT of CO2(e). This amount is in addition to the CO2(e) emissions from the enrichment process.
3 The NRC requires most applicants, including all reactor applicants, to submit an ER as part of the application. 10 CFR 51.45 and 10 CFR 51.50 (10 CFR Part 51-TN250).
4 The EPA provides estimates of emissions from electricity production for different regions in the United States at https://www.epa.gov/energy/emissions-generation-resource-integrated-database-egrid for CO2 in units of pounds per kilowatt-hour (lb/kWh). The value for southeastern New Mexico has been applied here (EPA 2023-TN9079).
5 The conversion is 0.0551 (metric tons CO2/thousand scf) (EPA 2023-TN9080).
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The NRC staff estimated GHG emissions related to plant operations from the typical usage of various onsite diesel generators (UniStar 2007-TN1564). Carbon monoxide (CO) emission estimates were derived assuming an average of 600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> (h) of emergency diesel generator operation per year (four generators, each operating 150 h/yr) and 200 h of station blackout diesel generator operation per year (two generators, each operating 100 h/yr) (Chapman et al. 2012-TN2644). A scaling factor of 172 was then applied to convert the CO emissions to CO2 emissions, and a CO2 to total GHG equivalency factor of 0.991 was used to account for the emissions from other GHGs such CH4 and N2O (Chapman et al. 2012-TN2644).
The number of shipments and shipping distances for transport of fresh nuclear fuel, spent nuclear fuel, and radioactive wastes are presented in Table S-5 of Supplement 1 to WASH-1238 (NRC 1975-TN216), for a 1,100 MWe LWR with an 80 percent capacity factor. WASH-1248 (AEC 1974-TN23) assumes that truck casks weigh 50,000 lb (23 MT) and rail casks weigh 100 t (91 Mt). For this analysis, emission rates of CO2 are calculated as 64.7 g/t-mi (44.2 g/MT-km) for trucks and 32.2 g/T-mi (22 g/MT-km) for rail (Cefic and ECTA 2011-TN6966). For the calculation, it was also assumed that return trips with empty casks double the total miles traveled by truck or rail. Table 3 presents estimated annual CO2(e) emissions from shipments associated with the reference 1,000 MWe reactor.
Table 3. Annual Number of Shipments for the Reference 1,000 MWe Reactor Annual Number of Shipments for the Annual Reference 1,000 MWe CO2(e)
Material Reactor Typical Distance (mi)(a) Emissions(b)
Unirradiated fuel (truck) 6 1,000 19 Spent fuel (truck) 60 1,000 194 Spent fuel (rail) 10 1,000 64 Radioactive waste (truck) 46 500 74 (a) Source: NRC 1975-TN216, Table S-5.
(b) Results are rounded to the nearest 1,000 MT CO2(e).
The total GHG emissions for fuel and waste transportation was approximately 352 MT per reference reactor-year as presented in Table 3. Over a 40-year operating life for the reference 1,000 MWe reactor, the total is approximately 14,000 MT of CO2(e) emitted.
Given the various sources of GHG emissions discussed above, the NRC staff estimated the total lifetime GHG footprint for the reference 1,000 MWe reactor to be about 990,000 MT CO2(e), with a 7-year building phase, 40 years of operation, and 10 years of active decommissioning. 6 These source categories of the GHG emissions footprint are summarized in Table 4. The uranium fuel cycle component of the footprint is the largest portion of the overall estimated GHG emissions and is directly related to the assumed power generated by the plant.
The GHG emission estimates for the uranium fuel cycle are based on newer enrichment 6 Under the NRCs regulations, a reactor licensee has up to 60 years to complete the decommissioning of a reactor facility commencing with the licensees certification that it has permanently ceased reactor operations (10 CFR 50.82(a)(3); TN249). The 60-year decommissioning period may be exceeded subject to NRC approval, if necessary, to protect public health and safety. Id. The estimated 10-year decommissioning period is a subset of the 60-year decommissioning period, during which significant demolition and earth-moving activities may occur (e.g.,
deployment and operation of equipment at the decommissioning site and shipments by truck or rail to remove irradiated soil, rubble, and debris from the site), as discussed in Supplement 1 to NUREG-0586 (NRC 2002-TN665).
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technology, assuming that the energy required for enrichment is provided by modern regional electric systems.
Table 4. Nuclear Power Plant Life-Cycle Greenhouse Gas Footprint Total Emissions Source Activity Duration (yr)(a) (MT CO2(e))
Construction equipment 7 39,000 Construction workforce 7 43,000 Plant operations 40 181,000 Operations workforce 40 136,000 Uranium fuel cycle 40 540,000 Fuel and waste transportation 40 14,000 Decommissioning equipment 10 19,000 Decommissioning workforce 10 8,000 SAFe STORage workforce 40 10,000 TOTAL(b) 990,000 (a) Nuclear power plant life-cycle for estimating greenhouse gas is assumed to be 97 years which includes building, operating, and decommissioning.
(b) Results are rounded to the nearest 1,000 MT CO2(e).
The Intergovernmental Panel on Climate Change (IPCC) released a special report about renewable energy sources and climate change mitigation in 2012 (IPCC 2012-TN2648).
Annex II of the IPCC report includes an assessment of previously published works on life-cycle GHG emissions from various electric generation technologies, including nuclear energy. The IPCC report included only reference material that passes certain screening criteria for quality and relevance in its assessment. The IPCC screening yielded 125 estimates of nuclear energy life-cycle GHG emissions from 32 separate references. The IPCC-screened estimates of the life-cycle GHG emissions associated with nuclear energy, as shown in Table A.II.4 of the IPCC report, ranged from 1 to 220 g of CO2(e)/kWh, with 25th percentile, 50th percentile, and 75th percentile values of 8 g CO2(e)/kWh, 16 g CO2(e)/kWh, and 45 g CO2(e)/kWh, respectively. The range of the IPCC estimates is due, in part, to assumptions regarding the type of enrichment technology employed, how the electricity used for enrichment is generated, the grade of mined uranium ore, the degree of processing and enrichment required, and the assumed operating lifetime of a nuclear power plant. The NRC staffs life-cycle GHG estimate of approximately 990,000 MT CO2(e) for the reference 1,000 MWe reactor is equal to about 3.5 g CO2(e)/kWh, which places the NRC staffs estimate at the lower end of the IPCC estimates in Table A.II.4 of the IPCC report. This placement is primarily because the IPCC estimates were for LWRs that used enrichment technologies that were based on the use of coal-fired generation as the electricity source.
The calculation of GHG emissions for the proposed Abilene Christian University (ACU) Molten Salt Research Reactor (MSSR) assumes that 1 megawatt thermal (MWt) advanced reactor would be installed. Assuming that GHG emission estimates for operation and extended SAFe STORage (SAFSTOR) for the proposed ACU MSSR, could generally be scaled based on the plants output, the estimates for these stages would be scaled down to 0.04 percent of the totals for the reference reactor calculated above. Since only one unit would be installed, no additional scaling was needed to account for the number of the reactors at the proposed site. As a conservative assumption, emissions from preconstruction/construction and decommissioning activities are assumed to be half of those estimated for the reference reactor. In addition, the 5
durations for preconstruction/construction activities would be shorter than the durations assumed for the reference reactor in Table 4.
The GHG emission estimates for the reference reactor for the uranium fuel cycle and transportation of fuel and waste are based on an annual capacity factor of 80 percent. Although this annual capacity factor assumed for the reference commercial power production would not necessarily apply to a research reactor, a capacity factor of 80 percent is assumed to be bounding for the ACU test reactor. Under this assumption, the staff estimated GHG emissions for uranium fuel cycle activities and fuel and waste transport associated for the proposed ACU MSRR facility as 0.04 percent of the totals presented for the reference 3,415 MWt (1,000 MWe) reference reactor. The assumed activity durations and total GHG emissions for these activities for the reference reactor and for the ACU reactor are shown in Table 5.
Table 5. Life-Cycle Assumptions and GHG Emissions for the 1 MWt Abilene Christian University Molten Salt Research Reactor 3415 MWt Reference Reactor 1 MWt ACU MSRR Activity Activity Total Duration Total Emissions Scaling Duration Emissions Source (yr)(a) (MT CO2(e)) factor (yr)(b) (MT CO2(e))
Construction equipment 7 39,000 0.5 2 5,571 Construction workforce 7 43,000 0.5 2 6,143 Plant operations 40 181,000 0.0004 20 33 Operations workforce 40 136,000 0.0004 20 25 Uranium fuel cycle 40 540,000 0.0004 20 99 Fuel and waste transportation 40 14,000 0.0004 20 3 Decommissioning equipment 10 19,000 0.5 10 9,500 Decommissioning workforce 10 8,000 0.5 10 4,000 SAFe STORage workforce 40 10,000 0.5 40 4 TOTAL(c) 990,000 25,000 (a) Nuclear power plant life-cycle for estimating GHG is assumed to be 97 years which includes construction (7 years), operations (40 years), and decommissioning (50 years).
(b) Nuclear power plant life-cycle for estimating GHG is assumed to be 72 years which includes construction (2 years), operations (20 years), and decommissioning (50 years).
(c) Results are rounded to the nearest 1,000 MT CO2e The NRC staff calculated that the GHG emissions for the proposed ACU MSSR to be approximately 25,000 MT CO2(e) using the assumptions discussed above to scale the emissions from the reference 1,000 MWe reactor. A scaling factor of 0.0004 is calculated from the ratio of power outputs between the reference 3,415 MWt reactor accounting for 0.8 capacity factor.
Scaling Factor = (1 MWt (3415 MWt x 0.8) = 0.0004 Yearly GHG emissions from the reference 3,415 MWt reactor is scaled down and then multiplied by the number of years of construction, operation or decommissioning as shown below:
Years of Activity for 1 MWt reactor ACU CO2 e = 3415 MWt Reactor CO2 (e) x Scaling Factor x Years of Activity for 3415 MWt reactor 6
A two-year of construction period and a 20-year operation period were assumed for the ACU MSRR. The period of decommissioning and SAFSTOR activities were kept the same as that for the reference reactor due to uncertainty with future post closure waste management activities.
The staff calculated that the GHG emissions for the ACU MSRR to be 25,377 MT CO2(e).
Comparing the entire life cycle estimated GHG emissions from construction, operation, uranium fuel cycle, transportation of fuel and waste, and decommissioning activities to 2019 total gross annual U.S. energy sector emissions, the projects GHG emissions would be about 0.0005 percent of the 2019 GHG emissions from the U.S. energy sector.
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