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. 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

5. 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

6. 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
: He blowdowns -> no alarms
: He blowdowns -> friskers alarm ( 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.
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.

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 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

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
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

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

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