Rethinking Used Fuel Management-France-M Chiguer; AREVA
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Transcript of Rethinking Used Fuel Management-France-M Chiguer; AREVA
Rethinking Used Fuel Management
Paper Ref. IAEA-CN-209-026.
International Experts’ Meeting on Reactor and Spent Fuel Safety in the Light of the Accident of Fukushima
Vienna, March 19th -22nd , 2012
Mustapha CHIGUER AREVA
1, Place Jean Millier
92082 Paris-La-Defense
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.2
Background and issues at stake Before Fukushima
Used Fuel was perceived as one of the crucial unresolved issues when referring to nuclear energy
Several Opinion Surveys launched by Governments, National and international institutions, Industry,..
Critics often leveled against nuclear is the large accumulation of stored used fuel [1]
Stakeholders poor awareness of solutions despite the importance of the stake
Recycling used fuel is the preferred route for a large majority of polled people in the US and Europe [2] & [3].
Used Fuel Management was something of an afterthought in many National Fuel Cycle Policies
“Wait and See” strategy spreading
Implementation of DGRs, the crucial pillar of Once-through strategy, faded away in many countries
Short-term solutions, such as SFP densification, were the preferred solution in many countries…
Leading to much larger used fuel inventories in SFP
[1] Eurombarometer 2005 & 2008
[2] US DOE/NEI nationwide Opinion Survey conducted by Bisconti Research Inc 2009 & 2010
[3] Tns-Sofres Nuclear Energy and Recycling opportunities: the perceptions in Europe & the US 2010
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.3
Background and issues at stake After Fukushima
Shock and surprise among public and relayed by the media
SFP turned out to be far more vulnerable than initially assumed and could lead to concerns of radioactive release
Apparent inadequacy of contingency plan and preparedness at the plant
Months later, Operator still facing a difficult situation to restore normal condition in the SFPs
All pre-Fukushima critics and weakness underlined by Stakeholders are rushing back…
… and regaining stakeholders/public confidence will be a long road
Used Fuel Management options at reactor are likely to be re-evaluated, if not reconsidered following safety margins re-assessment
Choosing an outcome to the Used Fuels stored currently in
SFPs involves a large combination of technological, financial, political and licensing parameters
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.4
Originally, a shared view among Nuclear Safety Regulators “No used fuel storage at reactor pool”
But…unavailability of off-site routes due to
Postponement of Back-end strategy implementation
Wait & See strategy
Used Fuel stored in SFP rather than shipped for Recycling
or DGR[1]
To help NPP continue their operations, Industry has applied
best practices and Safety Regulators have allowed…
…Storage and high density racking in SFPs
Resulting in increasingly large inventories as much as 5
times those of reactor cores
Leading to pool densities close to reactor core
Trend continued with reactor lifespan extensions
Risk analyses and best practices impacted further
Outage duration reduction
Increase in discharged fuel burnup
Degradation of neutron absorbing capability of
permanently installed neutron absorbers [3]
Higher density racking to accommodate
the larger used fuel inventory in SFP [2]
Comments
For decades, SFP requirements have remained contingent on the timely opening of DGR[1] or other Disposition
[1] DGR stands for Deep Geologic Repository
[2] NUREG/CR-0649 “Spent Fuel Heatup Following Loss of Water During Storage”
[3] US/NRC “On Site Spent Fuel Criticality Analyses, NRR Action Plan” TAC n° ME0372
May 2010
Early Accident Risks Assessment in NPP
Tightly packed
Closed frame structures Widely spaced
Open frame structures
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.5
SFP was an aggravating factor in the difficult emergency
situation faced by the operator at Fukushima
Loss of power and damage to cooling capabilities in the aftermath of the natural disaster [1]
While cooling reactor core has been the first priority…
…Early challenges faced by operators have also been to:
Adequately cool used fuel
Keep the pools filled with water
With the following potential issues at stake
Heat up and steam build up in SFP building
Loss of shielding from the loss of water
Loss of fuel structural integrity
Hydrogen accumulation [2]
Fuel fires [3]
Radionuclide releases
The biggest risk to the plant was the SFP N°4 ”, concluded[4] Mr. Kondo, Chairman of JAEC
Reported [4] on March 25th, 2011 to former Prime Minister Mr. Naoto Kan
Spraying water into buildings (helicopter, fire trucks,
water pumps ) for cooling reactor and pools
Comments
[1] Source: IAEA , March 24, 2011 reported 17 March by Japan’s METI
[2] Oxidation of the Zirconium cladding exposed to water vapor, resulting in hydrogen
generation and risk of explosion
[3] Zirconium fire: The cladding ignition point is about 800~900°C compared to the fuel
melting point of ~2880°C
[4] JAEC’s Chairman report to former Prime Minister of Japan on March 25th 2011 (2
weeks after the accident): "Contingency scenario outline of Fukushima Daiichi Nuclear
power plant“, as reported on Feb. 28, 2012
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.6
Facts and figures in the aftermath of the Fukushima accident
SFP Status and Fuel Inventory
All assemblies, 1535, were in the pool on March, 11th the core had been off-loaded since Nov. 2010
1331 Used Fuel
204 Fresh Fuel
SFP fuel Inventory, 1535, to compare to 548 FAs as total Reactor Core Fuel Capacity (more than twice!)
Immediately after the earthquake & tsunami [2]
March 14: water temperature in spent fuel pool at 84°C
Explosion in reactor building on March 15th
Fires on March 15 & 16th (TEPCO could not confirm fire on the ground)
Scenario by JAEC and presented on March 25th
A challenging situation up to 5 months later [2]
TEPCO judged that most fuels were not damaged [3]
on May 31st (2.5 months later)
4.5 months later (July 28th) ,water temperature was still as high as 88°C [2]
Circulating cooling with thanks to a new Heat Exchanger erected on July 31st
Water temperature cool down below 60°C since August 3rd to reach as low as 42°C on August 10th (5 months after the earthquake and tsunami!)
Since then TEPCO reported that [2]
Operation of desalting facility started Aug. 20th
Temperature around 22°C (update on Jan.19, 2012)
Fukushima Unit 4, SFP water level and temperature[1] & [3] Sequence Events and Status of SFP #4
[1]- TEPCO Report to NISA, Sep. 2011
[2]- Reports by JAIF (Japanese Atomic Industrial Forum at www.jaif.or.jp)
[3] JAEC’s Chairman report to former Prime Minister of Japan on March 25th
2011 (2 weeks after the accident): "Contingency scenario outline of Fukushima
Daiichi Nuclear power plant“, as reported on Feb. 28, 2012
Measured
Th
e w
ate
r le
ve
l (F
ue
l ra
ck
to
p a
t 0
m)
Po
ol w
ate
r te
mp
era
ture
in
°C
__ Estimated
SFP Water Level
SFP Water Temperature °C ▲ Measured
__ Estimated
DS: stands for Dryer Separator Pit
Surface Temperature
Inflow of the water from
Well + DS pit after water
level droping
3/16 Water level checked
by helicopter
3/15, building damage confirmation
Gate closed after recovery of the
water level by pouring water
Transition to a the water level
of SFP, DS Pit and Well
Layout of BWR Sequence Envents
Worst-Case Scenario [3]
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.7
Safety Regulators require Post-Fukushima upgrades of SFP Safety
Fukushima accident clearly demonstrates the importance of defense-in-depth philosophy/approach [1]
Although the radiological consequences from Fukushima due to airborne releases has so far been dominated by the releases from reactor cores [2] & [3]
SFPs presented a considerable potential threat given that there was no containment to prevent releases[4]
SFPs were an aggravating factor[5] in the difficult emergency situation faced by the operator
Based on the Saiakusinario (Worst-case Scenario) Mr. Kan, JAEC’s Chairman, concluded that the biggest risk to the plant was the SFP at the reactor N°4
“Contingency scenarios outlined”[5] on March 25th, 2011 to Prime Minister
Confluence of various factors going along the defense-in-depth will cause SFP’s requirements and risk assessment to become more complex
Complete changes will require time before being defined, reviewed and implemented
Short-term with “Complementary Safety Assessments”, “Stress Tests”, “Tier-1”
Medium-term with “Upgrade by Regulators” and … Stakeholders!
[1] US NRC, Recommendations for enhancing reactor safety in the 21st century, July 12, 2011, page 20, WENRA (Western European Nuclear Regulators Association) Task Force
“Stress tests specifications” April 21, 2011, Report of Japanese Government to the IAEA, June 2011 at www.iaea.org
[2] TEPCO Press Release on May 31st (reported also by JAIF at www.jaif.org.ja) based on detailed analysis of radioactive materials in the pools in Units 2 and 4
[3] High amounts of Iodine-131 Vs. Caesium-137 found at sampling points away from the Fukushima site, and reported by UK/HSE Sep. 2011
[4] UK-HSE Report on implications of Fukushima for the UK nuclear Industry Interim Report, p.27/106- May 2011
[5] JAEC’s Chairman report to former Prime Minister of Japan on March 25th 2011 (2 weeks after the accident): "Contingency scenario outline of Fukushima Daiichi Nuclear
power plant“, as reported on Feb. 28, 2012
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.8
US: Pool Safety a Top NRC Priority[1] and “the transfer of used fuel to dry cask storage” is Now[3] under considerations
Improving SFP safety is in the “top-tier” out of three tiers priority NTTF [1] recommendations
Tier 1 include those NRC proposes be started without unnecessary delay
Tier 2 & 3 consist of those that cannot be initiated in the near term
Additional issues[3] under NRC considerations
the early transfer of spent fuel into dry storage before it is operationally necessary
How Fukusima Lessons Learned should apply to
independent Spent Fuel Storage Installations (ISFSIs)
Shutdown reactor that still maintain fuel in SFP
NRC Chairman confirmed on Nov. 4th , 2011 during STST [4] Regulatory conference that
Everything is shaped by Fukushima which raised issues about spent fuel storage, and led the country to rethink how the US handles spent fuel”
Fukushima NTTF “is still considering several additional recommendations, including addressing the transfer of spent fuel to dry cask storage”
Final BRC Report [5], issued on Jan. 2012, adds a new recommendation for
“prompt efforts to prepare for the eventual large transport of SF & HLW to consolidated storage…”
“The term storage, is understood to mean storage for an interim period prior to disposal or other disposition”
Spent Fuel Pool Safety a Top NRC Priority according its Policy issue Oct. 3, 2011 (SECY-11-0137) and briefing Oct. 11, 2011
[1]: Recommendations of the Fukushima US-NRC Near-Term Task Force (NTTF), July 12, 2011
[2]: NRC NTTF recommendations dated July 12, 2011, monitor key SFP parameters (i.e. water level,
temperature, and are of radiation levels) from the control room
[3]: “Although NRC’s assessment of these issues is incomplete at this time (Oct, 3 2011), several of
these issues have already been judged to warrant further consideration and potential prioritization
based on relative safety significance” NTTF recommendations, SECY-11-0137
[4] STST stands for Spent Fuel Storage & Transportation
[5] BRC for Bleu Ribbon Commission on America's Nuclear Future
CSN ONR
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.9
Safe and Optimized Used Fuel Management Or, how to get back to basics
Reduce used fuel and radionuclide
inventories in reactor pools
Refueling/Defueling
pool
(On-site or Off-site)
Interim Dry Storage
Used Fuel Recycling
Recycled Fuels (MOX & ERU)
• Safe & Robust
• Volume / 5
•Radiotoxicity / 10
•No Safeguards
Constraints
3 to 5 years of cooling
1 to 2 years of cooling
Should Recycling not foreseen in the
near term, Transfer Used Fuel to Dry
Storage (3 to 5years of cooling)
Harden pools to meet potential new
safety guidance & requirements
Safety and risk Analysis
Safety Upgrades (ex. Improving
robustness of cooling capabilities, remote
control, SFP make-up)
Safety procedures (ex. Enhancing
contingency arrangements and training)
Near term, by shipping used fuel for
Recycling (1 to 2 years of cooling)
Enhance racking configurations as a
consequence of density reduction
Thank you for your attention
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.11
Used Fuel Management at Fukusima
background and status before the accident
Used Fuel Strategy in Japan is Recycling
Used overseas recycling up to 90s’
Developing domestic recycling infrastructure
Delays of domestic recycling have led to increase used fuel inventories at NPP
At the time of natural disaster, Used Fuel is stored in a number of locations [1]
Six reactor pools (~40%)
A common pool (~56%)
On-site dry storage (< 4%)
Reactor pools inventories are much higher than those of reactor cores
The total inventories, 4546 used FAs[2] , is equivalent to 8 reactor cores
Used Fuel inventories at reactor pools [1] Comments
[1] Source: IAEA , March 24, 2011 reported 17 March by Japan’s METI and NEI World Nuclear Industry
Handbook, 2010
[2] FA, stands for Fuel Assembly
When the earthquake struck and tsunami hit, about an hour
later, Japan’s east coast:
•Reactors Units 1, 2 and 3 were operating at power
•Reactor Units 4, 5 and 6 were already shutdown. Unit 4’s core
had been off-loaded to its pool
4546
UnitReactor Core FA
capacity
Pool FA
capacity
Used Fuel at
reactor pool
Fresh FA at
reactor pool
Most recent
additions of used
FAs
1 400 900 292 100 Mar. 2010
2 548 1240 587 28 Sep. 2010
3 548 1220 514 52 Jun. 2010
4 548 1590 1331 204 Nov. 2010
5 548 1590 946 48 Jan. 2011
6 764 1770 876 64 Aug. 2010
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.12
Appendix to “Facts and figures in the aftermath of the accident”
1) Status of SFP water inventory
before the accident
2) Decrease of water inventory after
SBO (Station Black-Out) and
consequential LOCA (Loss-Of-
Coolant-Accident) that followed the
earthquake and the tsunami
3) An opening of the moveable gate
as soon as an unbalanced water
pressure is detected as a matter of
passive response to the loss of
water inventory in the SFP
4) The closing of the moveable gate
due to water pressure balance,
though a drop in the SFP water
level (shielding and grace period
reduction)
Reactor #4 - SFP make-up capability
RPV: Reactor Pressure Vessel
SFP: Spent Fuel Pool
DS Pit: Dryer Separator Pit
Transition of SFP water level to the water level equilibrium of “SFP”, “Well” and “DS Pit”
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.13
Appendix to “Facts and figures in the aftermath of the accident”
1) Video camera for water level
2) Thermocouple
3) Container for sampling
4) Gamma dosimeter
Reactor #4- measurement of SFP
parameters
RPV: Reactor Pressure Vessel
SFP: Spent Fuel Pool
DS Pit: Dryer Separator Pit
Transition of SFP water level to the water level equilibrium of “SFP”, “Well” and “DS Pit”
1 2
3
4
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.14
Generic BWR used fuel pool
Most BWR are designed for SFP within the secondary containment
In Mark I and Mark II, SFP is located at the operating level (30~45 m above grade)
In Mark III, SFP is located on the ground level
The water in the pool is demineralized water
* Layout of used fuel pool and transfer system for
BWR reactor (source NUREG-1275, 1997)
2nd Containment
building Typically range from
9 to 18 m in length
6 to 12 m width
~12 m deep
Constructed of
Reinforced concrete
Sufficient thickness to meet radiation shielding and structural requirements
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.15
Containment
building
Generic PWR used fuel pool
Generic PWR used fuel pool
Located generally outside the containment
…though adjacent to it in a separate auxiliary building (named BK in France)
Using Borated water
* Layout of used fuel pool and transfer system for
PWR reactor (source NUREG-1275, 1997)
Auxiliary
building
Typically range from
9 to 18 m in length
6 to 12 m width
~12 m deep
Constructed of
Reinforced concrete
Sufficient thickness to meet radiation shielding and struc-tural requirements
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.16
Safety Regulators might require Post-Fukushima upgrades of used fuel Management Safety
Appendix to 1 /2 and 2/2 slides
Below is a collection of ongoing or potential/likely upcoming requirements: Robustness Assessment of SFPs related to a set of graded criteria defined and/or approved
by National Safety Authorities (stress tests and Complementary Safety Assessments)
Safety and Risk Assessment Methodology and Tools have likely to be adapted, if not developed
Enhancing SFP (Evaluate, Upgrade and Harden) Remote Monitoring Instruments and Equipments
Ventilation of SFP (containment, Hydrogen build-up & accumulation, building ventilation rate)
Post-accident Spray and plug & play to Critical Systems (accident mitigation)
Used fuel cooling, including ultimate Heat Sink and SFP make-up capability enhancement.
Reducing Used Fuel density and Inventory in SFP (accident risk prevention and mitigation)
Differences are introduced further due to: Existing Natural and Extensive Damage Mitigation Plans (Earthquake, flood, tornado, sea-
shore or inland sitting, terrorist events…)
Structural integrity of the SFP (example: pool structures, fuel storage building, SFP racks)
Reactor characteristics (PWR, BWR, Generation type or Mark) and core management (BU, outage duration, power up-rate consequences such as Fuel reactivity/enrichment,
Regional fuel cycle services (Recycling facilities and services, interim storage,…
National back-end policy
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.17
UK: potential implications for the UK nuclear industry, including new reactors
Office for Nuclear Regulation (HSE Agency) report on implications of Fukushima for the UK nuclear industry
Interim report on May 18, 2011
Final report in September 2011
Potential implication for the UK installed Base
Point 318: “…The configuration of the fuel assemblies relative to its neighbours will affect the efficiency of heat transfer,…
Point 325:The response to the interim report recommendations and the European council “Stress Tests” being carried out in the UK should demonstrate whether the UK SFP are passively “safe” by design, and in some cases whether ALARP [1] to impose relatively straight forward minimum cooling times or racking configurations to ensure that with a total loss of active cooling (possibly even a catastrophic loss of water inventory) the fuel should remain substantially intact
Recommendations for new reactors
Point 319: Some racking arrangements are less susceptible than others and may represent good practice in the future
2 reports posted by UK safety regulator
[1] ALARP stands for As Low As Reasonably Practicable
IAEA International Experts’ Meeting – Rethinking Used Fuel Management - Vienna, March 19-22, 2012 – M. Chiguer p.18
Spain: Potential Implications foreseen by the CSN, the Spanish Nuclear Safety Council
The Spanish Nuclear Safety Council :
Submit on Sep. 15, 2011 Preliminary Report on the
stress tests carried out by the Spanish NPP
The CSN approved on Oct. 13, 2011 a proposal
limiting cooling time at SFP
The Stress Test Preliminary report [3]
Presents the NPP Licensees proposal for
improvements to diversify the possibilities for water
make-up and cooling of SFP to address important
accident
The CSN “considers the approach presented to be
adequate, although the information submitted
should be completed in the final reports”
As Post-Fukushima Lessons Learned, the CSN
take a dramatic step towards
Questioning the limitation of used fuel cooling time
in SFP at all Spanish NPP
This issue has been put under considerations
On October 13th, 2011
milestone to CSN staff: 1 year time
CSN Preliminary report on Stress Tests and additional issue in connection of SFP used fuel inventory reduction
[1] Report posted at www.csn.es
[2] Ref. Acta del Pleno del CSN – N°1.208, Madrid Oct.13, 2011 other European Stress Tests
reports available at www.ensreg.eu