Operational Experience Topic Millstone Dry Shielded Canister Loading

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)

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

Transfer to Cask Wash Pit Immerse DSC Load SNF Install Shield Plug Transfer to Cask Wash Pit Decon Weld Shield Lid Blowdown Vacuum Dry He Purge Weld Inner Lid Leak Test Weld Outer Lid DSC Loading Process

Transfer to Cask Wash Pit Immerse DSC Load SNF Install Shield Plug Transfer to Cask Wash Pit Decon Weld Shield Lid Blowdown Vacuum Dry He Purge Weld Inner Lid Leak Test Weld Outer Lid 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

Transfer to Cask Wash Pit Immerse DSC Load SNF Install Shield Plug Transfer to Cask Wash Pit Decon Weld Shield Lid Blowdown Vacuum Dry He Purge Weld Inner Lid Leak Test Weld Outer Lid 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

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. In the event of a serious accident involving decayed spent fuel, protective actions would be needed for personnel on site, while offsite doses (assuming an exclusion area radius of 1 mile from the plant site) would be well below the Environmental Protection Agency's Protective Action Guides.

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

Dominion Response Initial actions Ongoing dialogue with NRC 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

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

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

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

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

 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 1 assembly was UT examined in 2004 7 assemblies canister sipped (2009 and 2015) 4 assemblies from Cycle 7 discharge (clean cycle) 6 assemblies from Cycle 13 discharge (clean cycle) 14 assemblies in-mast sipped at end of cycles 14/15

 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 Slowly increasing rod temperature increases internal pressure Vacuum drying further increases delta P These operations Failures resulting from gradual changes in pressure would be small

 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

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

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 reporting of releases

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

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.

Jeff Semancik Director, Radiation Division CT DEEP Jeffrey.Semancik@ct.gov