Tritium Technology and Regulation Issues for Power Plants Lee Cadwallader Fusion Safety Program ARIES Meeting Bethesda, MD October 25-26, 2010

Tritium System Technology ITER serves as a reference design for machines of the future. ITER will use equimolar D-T, with gas puffing, pellet injection, and NB injection of D for fuelling. ≤ 4 kg-T on site. Tritium handling, storage, delivery and repurification technologies are fairly mature, judging from TSTA, TFTR, JET, and experiences outside of fusion (e.g., SRNL). These systems should be at a TRL of 6 due to small masses handled, with ITER operation moving these systems to TRL 7. As Tillack et al pointed out, tritium handling from breeder materials is at TRL 3 development with work proceeding to reach TRL 4 (Fus. Sci Tech., 56 (2009) ). The tritium fuel breeding and extraction will be addressed on a small scale by ITER test blanket modules. The TRL for this technology depends on the breeding material under consideration.

Building Layout for ITER T Systems Figure taken from Glugla et al, Fus. Eng. Des. 82 (2007)

US NRC Approach to Tritium –When the AEC was divided into ERDA-DOE and NRC, the DOE retained the concerns for weapons and the NRC focused primarily on fission power. –In fission power, tritium is a fission product mingled with others and the NRC regulations address it with other fp’s. – Graphs for the entire US BWR and PWR fleet, from Harris and Miller, “Trend Analysis of Commercial U.S. Nuclear Power Plant Radiological Effluents,” IRPA-11, Madrid, 2004

US and ITER Tritium Regulations –ARIES had G. G. Hofer review NRC regulations in 1995, these documents are on the ARIES web site. The overall conclusion was that the NRC was not specifically addressing tritium safety, safeguards, or accounting. –Hofer noted that the NRC does not give occupational dose values per radionuclide. That is still the case now. –NRC and DOE occupational dose limits remain in 10CFR20 and 10CFR835 as 5 rem/y (50 mSv/y). –DOE made administrative control levels of < 2 rem/y (20 mSv/y) in DOE-STD-1098, July 1999 (most recent version is May 2009). The NRC has not done this. The typical fission worker dose is ~180 mrem/y (NUREG-0713 for 2008) –The ITER occupational dose limit is 1 rem/y (10 mSv/y).

US and ITER Tritium Regulations-con’t –NRC public dose limit in 10CFR is 100 mrem/y (1 mSv/y). An NRC dose goal in 10CFR50 Appendix I is 3 mrem/y from drinking water. The NRC also referenced the EPA 40CFR190.10, to limit the public dose to the U fuel cycle to 25 mrem/y. –NRC annual release limit into sanitary sewerage is 5 Curies of tritium, given in 10CFR –ITER release goals are 0.05 g-T as airborne oxide, 1 g-T as elemental gas in air, and g-T (4 Curies) as HTO in water. –EPA in 40CFR61.92 limits DOE facilities to 10 mrem/y (0.1 mSv/y) from all airborne radioactive materials and 4 mrem/y (0.04 mSv/y) from all radioactive materials released to drinking water (20,000 pCi-T/liter = 4 mrem/y) –ITER public dose limit is 10 mrem/y (0.1 mSv/y) for all releases (airborne and liquid)

Tritium Safeguards –Hofer noted that the NRC does not have any safeguards documents that specifically address tritium. 10CFR73 gives safeguards against nuclear material sabotage and theft, which includes tritium found in spent fuel. –DOE published a nuclear material control and accountability manual, DOE M The latest edition is –The DOE approach is that T is a nuclear material of strategic importance; it requires protection from theft and diversion. Safeguard Category III is defined as 50 g-T. Safeguards are graded according to usefulness of the material; Category III means physical inventory every 2 years, locked storage, and attended when in use. Power plant security and access control systems would meet Cat III requirements. –The NRC could augment its safeguards regulations to address T since fusion would have large quantities of pure T.

Tritium Accountability –Hofer noted that the NRC does not have any specific tritium accountability requirements. This situation is unchanged; the main NRC concern is public safety against T fission product releases. –Basic tritium accounting is a mass balance, shipment mass in minus mass lost to effluent streams; the result is compared to the measured mass contained in the facility. ITER will follow that same approach - the TBMs will only create small amounts. TBMs could be a mini-experiment in accounting. Power plants will breed tritium onsite - the TBR and extraction make accounting difficult. –DOE M (2006) gives tritium accountability standards. DOE tritium must be accounted for to the 0.01 g-T level. Even sophisticated equipment cannot accurately determine to 0.01 g-T once the quantity exceeds ~5 g-T. This is a very challenging requirement!

Tritium Accountability-con’t –The ITER team believes they can determine tritium amounts to within 3% during a shift and to within 1% accuracy over longer time periods in the ZrCo storage beds by calorimetry. One bed could hold 1 to 70 g-T. (E.S. Lee et al., Fus Eng Des 83 (2008) –The DOE manual states that tritium in water that is used as a moderator in a nuclear reactor is not an accountable material. –The NRC could follow what DOE has done, or generate its own accountability regulations for fusion power plants.

Conclusions –Since the Hofer documents were published, the NRC has not made any new regulations on tritium. Since the NRC views tritium as a low mass (~gram scale), mingled fission product rather than as a high mass (~kg), pure fuel, they are unlikely to make regulations on tritium until they exercise their regulatory authority over fusion power. –Tritium handling systems are fairly mature in fusion and ITER is expected to advance these systems in both T inventory and operational time. –The largest issue for tritium systems in fusion is tritium production and extraction. The ITER TBM program is a step toward addressing this issue.