Tritium Release Limits for Fusion Facilities

1. Tritium Release Limits for Fusion Facilities David Petti INEEL Fusion Safety Program APEX/ITER TBM Meeting, UCLA November 3-5, 2003

2. Method for Establishing Release Limits • Determine the allowable dose limits • Reverse calculate from these doses to find allowable releases • Use ALARA • Document the effort

3. Allowable Dose Limits • Nuclear reactors under 10CFR20.1301 must meet an airborne release limit of 1 mSv/yr with the expectation that ALARA would be applied. • The DOE Fusion Safety Standard (DOE-STD-6009) adopted 0.1 mSv/yr as a more stringent fusion requirement for routine releases considering ALARA • Federal rules in 40CFR61.92 (from the EPA), “National Emission Standards for Radionuclides other than Radon from Department of Energy Facilities”, set airborne releases to the ambient air at a level of 0.1 mSv/yr for public doses from DOE facility routine releases. • Federal rules in 40CFR141.16 (from the EPA), “National Primary Drinking Water Regulations,” set liquid releases into community drinking water at 4 mrem/year (0.04 mSv/year) for the public, or 20,000 pCi/liter of Tritium in drinking water. • These new DOE federal rules are without ALARA. ALARA will have to be considered. • Sometimes State rules are more stringent. For example, the New Jersey State Bureau of Radiation Protection (in NJAC 7:28) set a limit of 1 Ci/year of tritium release to waste water discharges.

4. Reverse-calculating Release Amounts from Doses • The standard Gaussian plume dispersion models are used for annual releases as well as accident releases. • Site distance and site terrain are important to determine release dispersion. Factors of 100 difference in small versus large sites, rural versus urban sites are not uncommon • For annual doses, weather conditions over an average year are used to make the evaluation. • Routine releases are generally elevated releases (up the stack). • Releases via permeation through the steam generator ARE NOT elevated. These ground level releases are 10 times more restrictive. • HTO is generally assumed because of conversion of any HT in the environment

5. Annual Release Calculations for the FIRE Design in 1999 • Used ITER methodology for annual releases assuming a 100-m elevated stack release. • Assumed total conversion of T2 to HTO. This is a routinely used conservative assumption. • Since the DOE Fusion Safety Standard requirement (0.1 mSv/yr) implemented ALARA no additional reduction factor was explicitly applied. • The result was an allowable airborne stacked release of 8 g-T/year, or 80,000 Ci-T/year, or ~9 Ci-T/hour release. • Given the new EPA limit of 0.1 mSv/yr, ALARA may have to be applied to reduce the FIRE release limit.

6. Annual Releases from US Tritium Facilities • The Tritium Systems Test Assembly at LANL has had a good record. With ~100 g-T on site, annual releases were below ~1 Ci/week. (R. V. Carlson, Fus. Tech., 30 (1996) 900-904) This was relatively easy to achieve given the low temperature processes involved • The Replacement Tritium Facility at SRS has been operating since 1994. The 0.1 mSv/yr is shared with Kr-85 releases. • From Environmental Reports, the entire SRS site released: • 96.7 kCi T in 1995 • 55.3 kCi T in 1996 • 58.0 kCi T in 1997 • 82.7 kCi T in 1998 • 51.6 kCi T in 1999 • This is in reasonable agreement with the 8 g/year calculated for FIRE but much greater than the stricter ITER limits (discussed later)

7. Design Targets for New US Tritium Facilities • The Tritium Extraction Facility (TEF) at SRS is planned to remove tritium from commercial light water reactor irradiation targets. • TEF is currently under construction, scheduled to begin operation in FY-07. It is the newest US facility at this time. • The TEF inventory is ~ 8 kg-T. • The annual release limit for TEF is set at 1 g-T/year (DOE/EIS-271, 1999). TEF will use a 100-foot stack, stripper systems, and assumes continuous operation. 1 g-T would be 0.02 mrem annual dose for the SRS site boundary, using site-specific weather and terrain data. • The use of stricter limits for new facilities is consistent with regulatory tightening of release limits over time. Also public acceptance will be easier with lower limits. • Fusion needs to be able to be as good as current facilities to demonstrate its S&E advantages

8. ITER EDA Country Release Limits • The US airborne limit is 0.1 mSv/yr and liquid limit is 0.04 mSv/yr as stated earlier • The Japan public dose limit for normal operational releases of all kinds is 1 mSv/year • The France public dose limit for normal operational releases is also 1 mSv/year. • The Canada public dose limit for normal operational releases is 5 mSv/year, but in 2002 there was a proposal to Environment Canada to reduce to 1 mSv/year. The proposal is still under review. • The Spain public dose limit for normal operational releases was not found, it is probably 1 mSv/year. • The Swedish limit is 0.1 mSv/year • The Russian limit is 0.2 mSv/year airborne and 0.05 mSv/year liquid • All countries apply ALARA but the different regulatory cultures in the different countries result in different mass release limits • ITER adopted 0.1 mSv/yr and implemented a factor of 10 reduction on the release limit because of ALARA implementation, the release of other radionuclides that also count against the limit, and the recognition that 1 km site may be too generous in some countries that could be ITER sites.

9. What Tritium Level Can an ITER TBM Release each Year? • ITER Project Guidelines for annual release limits are 0.1 g-T as HTO/a ground level and 1 g-T as HTO/a airborne, and 0.0004 g-T/a liquid. • The 1 g-T as HTO corresponds to 0.01 mSv/yr, one-tenth the dose limit that ITER adopted. • These could change when the site is selected. • A key issue is that the 0.01 mSv/yr limit is for the entire site. All airborne releases of all radionuclides must sum to meet the 0.01 mSv limit. • The TBMs are just a small part of the ITER facility. ITER will have releases of tritium and other radioactive gases (e.g., Ar-41 from activated air) and aerosols (e.g., activated tokamak dust). There are sources in the tokamak and cooling systems, the tokamak cell, the tritium plant, inefficiencies of tritium cleanup systems, and the hot cells. • As a first approach, apportioning some fraction (e.g.,10%) of the annual release limit to the set of TBMs seems reasonable from a safety perspective. The ability to meet it given the high temperature permeation issues is unclear. Analysis will have to be done to evaluate the releases even for these small TBM systems

10. Summary • Translation of dose limits to release limits depends on the site terrain, meteorology and site boundary distance. • The 0.1 mSv/year US DOE FSS limit corresponds to ~ 10 g-T as HTO per year stacked and ~ 1 g-T as HTO per year ground level for a 1 km site. • ITER used 0.1 mSv/year as the dose limit and imposed a factor of 10 reduction in calculation allowable mass releases recognizing the potential for smaller sites and ALARA. The project guideline of 1 g-T/year may change depending where ITER is sited. • The 1-g T/year is recommended as the baseline for any future assessments given the tightening of regulations in the US and around the world, the precedent set for the new DOE tritium facility at SRS, the need for local public acceptance and our goal to demonstrate the S&E advantages of fusion • Permeation releases for the ITER TBMs through the ultimate heat sink may be very limiting because they are ground level releases • A 10% portion of the annual release limit for the entire set of TBMs may be difficult to achieve given the high temperatures of the TBMs. Analysis is required.