Operational Experience Topic

1. Operational Experience Topic Millstone Dry Shielded Canister Loading

2. Millstone Power Station ISFSI • ISFSI Loading began 2005 • NUHOMS 32PT canisters • Model 152 HSMs • 34 canisters currently stored on Pad 1 • 31 with Unit 2 fuel (CE 14x14) • 3 with Unit 3 Fuel (W 17x17)

3. 2015 Dry Storage Campaign • May – June 2015(7th campaign) • 7 canisters, all Unit 2 fuel • 2 DSCs loaded and transferred to ISFSI with no issues

4. DSC Loading Process

5. DSC Loading Process Vent Exhaust RM 8132B Vent Suction Registers RM 8145 SFP Area Vent Duct Stack Frisker DSC Venting Helium DSC Blowdown DSC Spent Fuel Pool Cask Wash Pit

6. DCS 21 (3rd cask) • 5/10/15 • 1300: Stack Radiation Monitor (RM8132B) trending up • 5/11/15 • 1502: Grab sample negative <MDA • 5/12/15 • 1200: RM8132B declared non functional • ϒ Spec of sample negative for principle ϒ emitters • Action statement entered • 1400 initial DSC21 drain down • 2358 He blowdown -> friskers alarm • Air samples indicate 0 DAC • 5/13/15 • 0035: He blowdown -> friskers alarm • 0100-0330: He blowdowns -> no alarms • 0330-0530: He blowdowns -> friskers alarm (1200-1400 ccpm) • 0530: ISFSI Operations suspended

7. What did they see? • Krypton 85 • 10.76-year half-life • considerably longer half-life than virtually all other gaseous fission products (I-129 being the exception, but in low abundance) • increasingly the dominant nuclide in the accident source term for gap releases as decay times increase.

8. Radiological Risk Plan (Rev. 0) • Discussed personnel risk • No discussion of effluents • Neither rad risk plan nor procedure required effluent monitors

9. Dominion Response • Initial actions • DSC maintained in inert state with required He overpressure • Fuel integrity assessment • Chemistry calculation - releases < NRC limits • HP exposure calculation • Convened Prompt Issue Response Team (PIRT) • Ongoing dialogue with NRC • Focused on the fuel characterization/integrity • Courtesy call to DEEP Radiation Director • Focused on radiological release

10. DEEP Actions • Challenged organization • release calculation • Rad risk plan • HP knowledge • Ops decision making • Ensured CGS compliance for posting releases • Off site samples • Reviewed PIRT, dose calculations • Concurrence with continued operations

11. Interim Corrective Action (PIRT) • Compliance (DSC technical specifications) • Calibrations (Rad monitors) • Procedural Controls (rad monitor operation and response) • Off-site dose calculation • Relocate floor monitors • Worker exposure calculation • Revised Rad Risk Plan • HP briefing • Ops Standing Order for rad monitor inoperability

12. Fuel Integrity Requirements • AREVA TN CoC 1004 Tech Spec requirements • Intact fuel only • Structurally sound • If leaking rods, may only have hairline cracks or pinholes • No damaged fuel or grossly failed fuel permitted • Damaged fuel cans or failed fuel end caps not part of the current license • Dominion does not load known failed fuel in canisters

13. Fuel Integrity Assessment • Three-step approach • Confirm that fuel was intact (not failed) prior to loading in DSC • Confirm that the failure that occurred was not a gross defect • Confirm that the failure will not degrade to a gross defect

14.  All fuel in DSC 21 was intact prior to loading • All 32 assemblies either • from a cycle determined to be clean by radiochemistry analysis • tested by UT/sipping • All 32 assemblies visually inspected prior to loading (4-side video); no anomalies observed • Total Kr-85 gas volume released - rod not previously failed

15. No gross fuel failure • Most failures in core initiate as small defects • Typically result of considerable thinning of cladding during operation (grid to rod fretting wear and corrosion) do not exist in dry storage • Dry storage operations would be highly unlikely to create a large, open defect in a fuel rod • Gas pressure inside rod much lower than during operation • Increases to differential pressure during draining/vacuum drying are very slow compared to reactor conditions and self-limiting • No evidence of grossly failed fuel in water/condensate samples • Heavy metals or other fission products = gross failure • Vacuum drying condensate - only activated Co-60 seen • From vacuum pump – only elevated Cs compared to SFP water

16. Failure will not degrade to a gross defect • Assessment of Degradation Possibility • Pressure differential creating the increased stress is relieved • Stable temperature with helium backfill • Inert atmosphere; no water/oxygen present • Handling of cask is slow • ISG-1: “unlikely to degrade since the atmosphere is inert and the temperature is controlled.” • Rod that fails during dry storage evolutions will not degrade to a gross defect

17. Safety Culture Principles • Questioning attitude - Individuals avoid complacency and continuously challenge existing conditions and activities in order to identify discrepancies that might result in error or inappropriate action. • QA.2 Challenge the Unknown: Individuals stop when faced with uncertain conditions. Risks are evaluated and managed before proceeding. Continuous Learning • Decision Making – Decisions that support or affect nuclear safety are systematic, rigorous, and thorough. • DM.2 Conservative Bias: Individuals use decision making practices that emphasize prudent choices over those that are simply allowable. A proposed action is determined to be safe to proceed, rather than unsafe in order to stop. • Continuous Learning - Opportunities to learn about ways to ensure safety are sought out and implemented • CL.1 Operating Experience: The organization systematically and effectively collects, evaluates, and implements relevant internal and external operating experience in a timely manner

18. Long-term Corrective Actions • Procedural controls for radiation monitors • Contingency actions • Verify effluent monitors prior to cask loading • Accountability for supervisors involved • HP training • Relocate Kr85 monitors (friskers) • Relocate exhaust vent exhaust pipe • Contingency release in web reportingof releases

19. Challenges With Current Requirements • Confirming older fuel is intact (unfailed) prior to loading • Incomplete or missing records from early reactor operation, change of plant ownership, old inspection data, old fuel not tested in timely manner, etc. • NDE limitations (no test is 100% accurate) • Visual exams - limited to exterior of assembly • Providing objective evidence that failed fuel is pinhole leak/ hairline crack • “Reasonable Assurance” - use accepted industry inspection methods, thorough radiochemistry analysis, and plant operating information

20. Lessons For Radiation Professionals • It’s hard to measure betas with gamma spec • Know your instrumentation • Understand the process you are measuring • STOP when unsure…get help • Be intrusive early…Trust but verify • A good zero says more than a long explanation….or…one sample is worth a thousand words • Expected to think.

21. Jeff SemancikDirector, Radiation DivisionCT DEEPJeffrey.Semancik@ct.gov