ML19084A214
| ML19084A214 | |
| Person / Time | |
|---|---|
| Issue date: | 03/14/2019 |
| From: | Anton S Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| P YADAV DUWP | |
| Shared Package | |
| ML19084A209 | List: |
| References | |
| Download: ML19084A214 (14) | |
Text
www.holtec.com Advances in Spent Fuel Storage Technologies to support Prompt Decommissioning Dr. Stefan Anton, Vice President of Engineering Holtec International 31st Annual Regulatory Information Conference March 12 to 14, 2019
www.holtec.com l Page 2 Overview Decommissioning Strategies Spent Fuel Loading Strategies Spent Fuel Pool Inventories Loading Software Summary
www.holtec.com l Page 3 Decommissioning Strategies Traditional Plant Shutdown Plant put into SAFSTOR Spent Fuel Pool continues to contain fuel for 10 or more years after shutdown, until decay heat of assemblies comes down to levels manageable by traditional dry storage systems. Assemblies then placed into dry storage Final decommissioning decades after shutdown
www.holtec.com l Page 4 Decommissioning Strategies (cont.)
Prompt Decommissioning Plant Shutdown Decommissioning activities start almost immediately Spent Fuel Pool is emptied as early as 2 years after shutdown.
This is possible due to the advances in spent fuel storage technologies, in both system design and analysis Final decommissioning not delayed by need to continue spent fuel pool operation Advantage: Returning the site decades earlier Main Challenge: Decay heat of fuel assemblies
www.holtec.com l Page 5 Spent Fuel Loading Strategies for Dry Storage Systems Uniform (pre 2000)
Limited systems performance Steel (stainless or carbon) baskets 5 to 10 years cooling time, 20 kW total decay heat capacity Main Goal: Load what you need to load to keep the plant running, i.e. oldest fuel
www.holtec.com l Page 6 Spent Fuel Loading Strategies for Dry Storage Systems (cont.)
Regionalized or Preferential (2000 to 2015)
Improved system performance Initially Steel (stainless or carbon) baskets, later Aluminum based baskets Overall higher heat loads through improved analytical tools and regionalized placements of assemblies in the basket 2 or 3 regions with different heat load limits 3 years cooling time, >30 kW total decay heat capacity Main Goals Reduce dose rates around cask by placing hotter assemblies on the inside Keep more low heat load assemblies for later
www.holtec.com l Page 7 Spent Fuel Loading Strategies for Dry Storage Systems (cont.)
Individual Cell Decay Heat Limits (2015 onwards)
Further improved system performance Aluminum-based baskets Higher heat loads through better basket materials, and individualized cell heat load limits Optimized heat load pattern for storage of entire SFP inventory after plant shutdown As low as 1 year cooling time, >40 kW total decay heat capacity Main Goal: load entire spent fuel pool inventory as early as possible to support prompt decommissioning, while optimizing both total heat loads and dose rates
www.holtec.com l Page 8 Canister Decay Heat Loading Pattern Examples 0.9 0.9 0.9 0.9 1.7 1.7 1.7 0.9 0.9 1.7 1.1 1.1 1.1 1.7 0.9 0.9 1.7 1.1 1.1 1.1 1.7 0.9 0.9 1.7 1.1 1.1 1.1 1.7 0.9 0.9 1.7 1.7 1.7 0.9 0.9 0.9 0.9 Example of a Decay Heat Pattern for regionalized Loading, Values in kW.
0.55 0.55 0.55 0.55 3.2 0.55 3.2 0.55 0.75 2.4 0.55 0.65 0.55 2.4 0.75 0.75 0.55 0.65 0.55 0.65 0.55 0.75 0.75 2.4 0.55 0.65 0.55 2.4 0.75 0.55 3.2 0.55 3.2 0.55 0.55 0.55 0.55 Example of a Decay Heat Pattern with individual Cell Limits, Values in kW.
www.holtec.com l Page 9 Spent Fuel Pool Inventory depending on Strategy Equilibrium Pool (for uniform strategy)
Same set of assemblies discharged from Core after each cycle Same set of assemblies moved from Pool to dry storage between cycles Pool inventory remains the same Transient Pool (for regionalized strategy)
Regionalized loading requires different set of assemblies to be moved to dry storage than uniform.
Different equilibrium pool inventories Transient from one equilibrium to the other
www.holtec.com l Page 10 Spent Fuel Pool Inventory depending on Strategy (cont.)
Pool after Discharge (for multilevel strategy)
Highly diverse burnups and cooling times. Example:
1/3 burnup, 1 year 2/3 burnup, 1 year Full burnup, 1 year Full burnup, 2.5 years Full burnup, 4 years Full burnup, 20 years
www.holtec.com l Page 11 Cask Loading Plan Software Sophisticated loading plan software is developed to match up pool inventories and cask loading patterns Goals
- Minimize time to empty spent fuel pool
- Optimize heat load distribution over all casks
- Minimize dose rates Graph on the right shows heat loads for the same inventory loaded into casks, but for different loading assumptions
www.holtec.com l Page 12 Cask Loading Plan Software Example of Dose Rate Minimization using software to optimize loading plans 35 40 45 50 55 60 65 70 75 80 1
3 5
7 9
11 13 15 17 19 21 23 25 27 29 31 33 35 Average Transfer Cask Surface Dose Rate (mrem/hr)
Loaded MPC Number
www.holtec.com l Page 13 Summary Technological advances in both system design and analytical tools for dry storage systems allow prompt decommissioning shortly after shutdown of the plant This allows a return of the site decades earlier than the more traditional SAFSTOR approach
www.holtec.com Advances in Spent Fuel Storage Technologies to support Prompt Decommissioning Dr. Stefan Anton, Vice President of Engineering Holtec International 31st Annual Regulatory Information Conference March 12 to 14, 2019