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

[email protected]

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


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


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


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


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]

http://www.jaif.or.jp/


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

http://www.jaif.org.ja/


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


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


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


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”


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


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


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


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


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


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

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