SF6 emissions from university and research particle

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ACCELERATORS

SF6 is used in university and research operated particle accelerators as an insulating gas. Typically, high voltage equipment is contained and operated within a vessel filled with SF6 at a pressure exceeding atmospheric pressure. Charges range from five kilograms to over ten thousand kilograms, with typical charges falling between 500 and 3 000 kg. When the equipment requires maintenance, the SF6 is transferred into storage tanks. SF6 losses occur primarily during gas recovery and transfer, when pressure relief valves are actuated, and through slow leaks.

Based on two recent studies annual SF6 losses range between 5 and 7 percent of vessel capacity per year and generally depend on the vessel opening frequency plus the efficiency of the recovery and transfer equipment. World banked capacity is roughly estimated to be 500 tonnes with annual SF6 emissions of 35 tonnes.

Switzerland has developed a voluntary program to reduce SF6 emissions from particle accelerators. Suggestions and techniques for reducing SF6 emissions from these sources exist.

Figure 8.3 Decision tree for SF6 from research accelerators

Figure 8.3 Decision tree for SF6 from research accelerators

Sacral Dimple Evaluation

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Tier 1 method - country-level method

In cases where individual user accelerator charge data is unavailable, one extremely rough method involves determining the total number of university and research particle accelerators in the country and using several factors to determine the country-level annual emission rate as noted in Equation 8.14. For this Tier 1 method, the only data that requires collection is the total number of university and research particle accelerators in the given country.

Equation 8.14

University and research particle accelerator emissions (country-level)

Emissions = (Number of university and research particle accelerators in the country) • (SF6 Use Factor) • (SF6 Charge Factor, kg) • (SF6 university and research particle accelerator Emission Factor)

Where:

Number of university and research particle accelerators in the country = The total number of university and research particle accelerators in the country. This rough method does not require countries to determine the number of accelerators that use SF6. To determine if a country has a particle accelerator, go to http://www-elsa.physik.uni-bonn.de/Informationen/accelerator_list.html

SF6 Use Factor = 0.33 Approximately one third of university and research particle accelerators use SF6 as an insulator.

SF6 Charge Factor = 2400 kg, SF6, the average SF6 charge in a university and research particle accelerator.

SF6 university and research particle accelerator Emission Factor = 0.07, the average annual university and research particle accelerator emission rate as a fraction of the total charge.

Tier 2 method - accelerator-level emission-factor approach

If data on the quantity of SF6 contained within each university and research accelerator are available, a default emission factor of 7 percent may be multiplied by the total SF6 charge contained in university and research accelerators in the country. The total country SF6 emission rate from university and research accelerators is therefore calculated from Equation 8.15.

Equation 8.15

UNIVERSITY AND RESEARCH PARTICLE ACCELERATOR EMISSIONS (ACCELERATOR-LEVEL

EMISSION FACTOR)

Total Emissions = SF6 university and research particle accelerator Emission Factor • Z Individual Accelerator Charges

Where:

SF6 university and research particle accelerator Emission Factor = 0.07, the average annual university and research particle accelerator emission rate as a fraction of the total charge.

Individual User Accelerator Charges = SF6 contained within each university and research accelerator. Tier 3 method -accelerator-level mass-balance method

SF6 emissions from university and research facilities operating particle accelerators may be most accurately determined at the user level on an accelerator-by-accelerator basis. Emission calculations are estimated by tracking accelerator charge as well as SF6 consumption and disposal. As detailed in Equation 8.16, the total emissions are equal to the sum of the individual users' emissions. Note, under this method, as the overall SF6 emission rate from particle accelerators is small compared to other SF6 uses, the associated SF6 lost in manufacturing is considered negligible and is not included in the calculation.

Equation 8.16 Total research accelerator emissions

Total Emissions = ^ Individual Accelerator Emissions

Each particle accelerator's emissions can be calculated as follows:

Equation 8.17

Research accelerator emissions (accelerator-level mass-balance)

Accelerator Emissions = Decrease in SF6 Inventory + Acquisitions of SF6 - Disbursements of SF6

- Net Increase in Accelerator Charge

Where:

Decrease in SF6 Inventory = SF6 stored in containers at the beginning of the year - SF6 stored in containers at the end of the year

Acquisitions of SF6 = SF6 purchased from chemical producers or distributors in bulk + SF6 purchased from accelerator manufacturers or distributors with or inside of new accelerator components + SF6 returned to site after off-site recycling

Disbursements of SF6 = SF6 contained in components transferred to other entities + SF6 returned to suppliers + SF6 sent off-site for recycling + SF6 destroyed

Net Increase in Accelerator Charge = SF6 Charge of New Components - SF6 Charge of Retiring Components

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