LFR Safety Design Criteria - Nucleus Documents... · IAEA HQ, Vienna, Austria, 4-8 September 2017 ....

Overview and Status

Giacomo Grasso – FSN-SICNUC-PSSN

LFR Safety Design Criteria

TM on “Challenges in the Application of the Design Safety Requirements

for Nuclear Power Plants to Small and Medium Sized Reactors”

IAEA HQ, Vienna, Austria, 4-8 September 2017

Titolo della presentazione - Luogo e data

The Lead-cooled Fast Reactor

LFR Safety Design Criteria: Overview and status – IAEA HQ, Vienna, Sept. 4-8, 2017


The Lead-cooled Fast Reactor in GIF

GIF context

3 LFR Safety Design Criteria: Overview and status – IAEA HQ, Vienna, Sept. 4-8, 2017


Signatories Observers



• EURATOM

• Japan

• Republic of Korea

• Russian Federation

• People's Republic of China

• United States of America

GIF LFR provisional System Steering Committee


SSTAR

(USA)

Small-sized, battery type reactor with long core life

BREST-OD-300

(Russia)

Medium-sized, «pools-in-loop» type reactor + associated fuel cycle



(Europe)

Large-sized, integral type reactor closing the fuel cycle

ELFR

CLOSURE HEAD

CO2 INLET NOZZLE

(1 OF 4)

CO2 OUTLET NOZZLE

(1 OF 8)

Pb-TO-CO2 HEAT

EXCHANGER (1 OF 4)

ACTIVE CORE AND

FISSION GAS PLENUM

RADIAL REFLECTOR

FLOW DISTRIBUTOR

HEAD

FLOW SHROUDGUARD

VESSEL

REACTOR

VESSEL

CONTROL

ROD

DRIVES

CONTROL

ROD GUIDE

TUBES AND

DRIVELINES

THERMAL

BAFFLE

Reference systems for the GIF LFR pSSC


GIF Roadmap as of 2002 GIF Roadmap 2014 update

The LFR potential


Technological readiness

+10 y

+7 y

+5 y

+10 y

≈

+10 y


The LFR potential

Acknowledged features

• Fast spectrum

For full management of natural resources

and waste through closure of the fuel

cycle

• High temperatures

For multiple applications along with

electricity production, e.g., hydrogen

production, co-generation, etc.

• Flexible design

For deployment into many and different

market segments, e.g., micro-batteries,

SMRs, large plants



The LFR potential

A growing interest

• BREST-OD-300 by ROSATOM-NIKIET (Russian Federation)

• SEALER by LEADCOLD (Sweden)

• CLFR by Westinghouse (USA)

• LFR-AS-200 by Hydromine Inc. (USA)



European situation

Framework objective



European situation

Framework objective


Energy Union

Sustainability

Competitiveness

Security of Supply


European situation

Framework objective



European situation

Context



European situation

Context


Commercialization

Commercialization

Commercialization

…


European situation

EU LFR roadmap


ELFR

Commercial deployment

ALFRED

Demonstrator

Prototype

FoaK


Main strength Main weakness

European situation


EU LFR roadmap

Extremely robust (prudent?) approach

to commercial maturity

• no excessive jumps between sizes

of reactors in successive steps

• progressive shift from proven (off-

the-shelf) to innovative (advanced)

solutions

• progressive increase of system

temperatures (for corrosion)

• progressive increase of system

performances

Perspective for market deployment

not earlier than 2050

• scarce attractiveness for industry

due to the seen time-to-pay

• very limited will to get involved in a

lengthy development, even for

specific innovative solutions

• issues in securing funds only from

public investment

• weakening of governmental

commitments following the poor

involvement of industry


(few applications)

(few remote areas)

(high temperature

applications)

(proven technology

is better)

A Lead-cooled SMFR

Potential of SMFR in Europe


Complement to

intermittent

energy sources

Replacement of

fossil PP

Non-electrical

applications

Military

applications

Power remote

areas

New nuclear

countries

Match

incremental

demand

(renewables target:

20% in 2020)

(proper power

range)

(no rapid growth)

Power required

Market potential

in Europe

Most interesting

opportunities for

SMFRs in Europe

Credits:

EU FP7 project

Grant # 605172


A Lead-cooled SMFR

Perspective features


• Simplification of design

significant reduction of capital cost thanks to elimination of unnecessary

components (e.g., intermediate loop)

System «Worthy» steel [kg/kW(e)]

GCR 20

Large SFR 5÷10

Gen-III/+ passive LWR 3

Gen-III/+ LWR SMR >3 (4÷5)

LFR 2

Mass of

concrete also

follows

proportionally


A Lead-cooled SMFR

Perspective features


• Simplification of design

significant reduction of capital cost thanks to elimination of unnecessary

components (e.g., intermediate loop)

reduction of O&M costs

• Extreme flexibility

excellent neutronics to easily target different missions (from battery to

iso-breeder)

• Enhanced safety

no safety implications from one unit to any other on the same site

• Potential for high-temperature operation

net efficiency from 38% to upper 40s (always >> than LWR SMRs)

opening to different applications and multiple market segments


European situation

EU LFR roadmap


ELFR


ALFRED

Demonstrator

Prototype

FoaK


A Lead-cooled SMFR

EU LFR roadmap


Demonstrator

Prototype

FoaK ELFR


ALFRED Prototype

SMFR FoaK Anticipated

commercial deployment


A Lead-cooled SMFR

An evolving deployment

• Materials for lower temperature

operation exist today

a first off-the-shelf design can be sold

to market in a very short term

(time for demonstration)

opportunity to match the retirement of

the reactors of the fleet presently

operating

• Advanced materials are being

developed and qualified

an improved design can be

developed with minor modifications

even higher performances can be

sought for a mid-term deployment


Short-term SMFR

Medium-term upgraded

SMFR


LFR Safety Design Criteria


The information presented in the following slides

is based on material produced by the

GIF LFR pSSC.

Acknowledgement



References and position

Hierarchy of standards




Reference documents



Development process

Objective

To present a set of reference criteria for

the design of systems, structures, and

components of LFR systems with the

aim of achieving the safety goals of the

Generation-IV reactor system



Development process

Rationale

To demonstrate that IAEA safety

requirements for design (SSR-2/1) are

essentially applicable to LFRs, and

require only minor modification



Development process

Approach

To minimize differences between the

LFR SDC and the IAEA safety

requirements (SSR 2/1) to the extent

necessary



Development process

Methodology

• Present draft of LFR SDC has been developed by GIF LFR pSSC in

2014-2015

• The work has been based on the SDC for the Sodium-cooled Fast

Reactor (SFR), since the GIF LFR and SFR systems share a

number of design solutions and some safety-related phenomenology

• It was also found useful to use the same structure and methodology

of the already existing SFR SDC



Development process

Methodology

• Specific technical features of LFRs are considered

• Latest knowledge is incorporated, incl. R&D results & lessons

learned from the accident at the TEPCO Fukushima Daiichi NPP



Development process

Criteria†

• Applicable as is

• Applicable with interpretation

No modification is required, but the rationale for the application of the

requirement to the design is different than that of the standard light water

reactor

• Application with modification

Modification is required to be applicable to the design

• New criteria

• Not applicable


†The primary focus is on heavy liquid metals, more specifically lead, as reactor coolant, but

other lead-based coolant options (especially lead bismuth eutectic, LBE) are also considered.

Where considerations for LBE coolant differ from those of lead, additional commentary is

included as footnote in the LFR SDC.


LFR safety aspects

GIF safety goals

• Generation-IV systems shall excel in safety and reliability:

• will have a very low likelihood and degree of reactor core

damage

• will eliminate the need for off-site emergency response



LFR safety aspects

GIF safety approach

Based on a combination of the following

principles:

• Defence in Depth and its further

improvements (as a fundamental principle)

• Risk informed approach

• Simulation, prototyping and demonstration

• Utilization of passive safety features

• Prevention of cliff edge effects (in severe

accidents)

• Provision against internal & external

hazards

• Considerations of non-radiological and

chemical risks



LFR safety-relevant characteristics considered

Core and Fuel Characteristics


• Fuel assemblies are operated in a fast neutron spectrum under the

conditions of high power density, high burnup, and high temperature

of lead.

• The reactor core is not in the most reactive configuration under

normal operating conditions and it is possible to have a positive void

reactivity in the central area of the reactor core the reactor core

should be designed to prevent excessive reactivity insertion.

• The high boiling point of the lead coolant (1749ºC) makes coolant

boiling highly unlikely, but gas/void might appear in the core or its

vicinity, for example as a consequence of a fission gas release from

ruptured fuel pins or due to steam generator tube leakages or

ruptures.



Physical and Chemical Properties of Lead Coolant


• The low partial vapor pressure (correlated to the available margin to

boiling) allows operating the system close to atmospheric pressure.

• The high density generates buoyancy forces which have to be

considered in design of in-vessel structures; challenges to the main

vessel and reactor components in terms of seismic response need

to be specifically addressed.

• The freezing temperature of lead is 327ºC coolant solidification

needs to be considered and prevented.

• The high volumetric heat capacity (ca. 1.54 J/cm3/K for lead),

combined with the inventory of the coolant present in the primary

circuit, provides high thermal inertia.



Physical and Chemical Properties of Lead Coolant


• The large volumetric expansion coefficient (1.2∙10-4 1/K for lead) and

the possibility to operate in a large range of temperatures, without

boiling or excessive material corrosion/erosion, enhance the

possibility of core cooling by natural convection.

• Due to opacity, in an LFR it is preferable that each component inside

the reactor vessel is designed as removable ensuring adequate in-

service inspection (ISI) and maintenance.



Induced radioactivity, coolant activity, retention of volatile products


• Pure lead is not exempt from the polonium formation, however, the

rate of polonium production is very small and the volatility of

polonium is lowered, typically by several orders of magnitude with

respect to LBE, through strong chemical reaction with the lead

coolant (e.g., via the formation of lead-polonide).

• Only a very small fraction of polonium, depending on lead

temperature, is expected to be vaporized into the cover gas system.

• Lead provides a relatively good capacity for retention of important

fission products as well as activation products. E.g., volatilized

fractions for 137Cs, 90Sr, and 131I at 700ºC are 1.1∙10-6, 5.1∙10-14 and

3.7∙10-6, respectively.



Chemical interactions


• The relative chemical inertness of lead with water or air provides

conditions for the elimination of the intermediate circuit in LFRs.

• However, in case of steam generator tube rupture (SGTR) event,

water interaction with lead needs to be considered and adequately

prevented and/or mitigated.

• Specifically, over-pressurization of the primary circuit, sloshing and

steam/water entrainment, which might result in a positive reactivity

insertion as well as formation of solid PbO possibly causing flow

blockages, need to be considered.

• Fuel-coolant interactions have shown to exhibit low energetics,

favouring safety. Further investigations are however ongoing to

better assess the phenomenology.



Structural material compatibility with coolant/environment


• Flowing heavy liquid metals are corrosive and can induce or

accelerate a material failure under a static loading (brittle fracture) or

under a time-dependent loading (fatigue and creep).

• LFRs are consequently designed to operate at a low temperature

range (400-520ºC to maintain the fuel cladding temperature below

ca. 570ºC) maintaining a controlled concentration of dissolved

oxygen in the primary coolant.

• The concentration of dissolved oxygen has to be high enough to

support the formation of protective layers on surfaces of structures,

while at the same time low enough to prevent the formation of large

amounts of PbO precipitation.





• For traditional materials at temperatures above 500ºC, the corrosion

protection through the oxide barrier seems to fail and the application

of corrosion surface coatings (for example Al2O3, SiO2 or aluminum

alloy) or the use of innovative steels with addition of silicon or

aluminum is therefore considered.

• Fuel cladding, upper core regions and primary coolant inlet regions

to the heat exchanger are particularly sensitive to corrosion, because

temperatures are the highest.

• The integrity of the protective layer needs to be ensured during all

plant operating conditions, including long-term transients, in order to

ensure the integrity of the components.





• As an LFR operates at a relatively high temperature compared to an

LWR and in high fast neutron fluence conditions, due consideration

of creep and radiation effects on fuel and structural materials is also

necessary.

• Because of the good thermal conductivity of lead and the relatively

large temperature differences between inlet and outlet of the reactor

core, thermal striping needs to be considered and must be

accounted for in the design to prevent structural damage.



Operation under low pressure condition


• As an LFR is operated in low pressure conditions, close to

atmospheric pressure and temperatures well below the boiling point

(1749ºC), coolant leakage or pipe break does not lead to the type of

loss of coolant accident experienced in an LWR with

depressurization, coolant boiling and the loss of cooling capability:

• an emergency core cooling systems for coolant injection

under high and low pressure conditions, as used in the LWR,

is therefore not necessary in an LFR;

• the only requirements for LFR core cooling are the

maintenance of the lead coolant level above the inlet of the

Steam Generator (SG) or Decay Heat Removal (DHR) heat

exchangers, to provide a heat removal flow path.


Lessons learned from Fukushima Daiichi accident

LFR advantages

The LFR is particularly suited, thanks to

the inherent characteristics of the

coolant and the extended use of

passive safety features, to face

Fukushima like events




Additional provisions to improve plant response to extreme events


Extreme earthquake

LFR concepts are designed to withstand the Design Basis Earthquake,

with margins. Due to the high density of lead, the response of a plant to

extreme earthquakes needs to be however carefully considered, incl.

sloshing effects and need for their damping. 2D seismic isolators under

the primary building (to reduce loads caused by horizontal oscillations),

or design features of the reactor vessel, can address this issue.





Extreme flooding

LFR concepts, notably the DHR systems, shall be protected from the

consequences of a flooding. This is both from a mechanical point of

view, to prevent the component damage, and from a functional point of

view since their actuation is to be accomplished by protected energy

devices. However, the relative chemical inertness of lead in contact

with water permits an extensive use of water cooling.





Total loss of an electric power supply and/or heat sink(s)

Intrinsic characteristics of lead cooled reactors provide an increased

robustness of the plant in response to the total loss of electric power

supply and/or heat sink(s) because:

• the liquid lead can maintain an adequate degree of natural

convection to accomplish decay heat removal function completely

passively;

• the heat sink is usually diverse: water or air.

In case of loss of a normal heat sink, fully passive DHR systems are

able to fulfil the safety function.





Total loss of an electric power supply and/or heat sink(s)

In the very unlikely event of a Fukushima-like scenario leading to the

loss of all heat sinks (both secondary and dedicated DHR systems),

heat can be possibly extracted by injecting water into the reactor cavity

between the reactor and safety vessels (based on the specific design

features) and/or the decay heat can be removed by a dedicated heat

removal system that cools the concrete of reactor cavity walls.

Lead provides a relatively good capacity for retention of important

volatile fission products as well as activation products, e.g., Cs and I.


The GIF LFR SDC

outlook


• First draft elaborated by GIF LFR pSSC in 2014-2015

• Eighty-four (84) reference design criteria identified for

GIF LFRs

• Draft submitted to GIF-RSWG for review in December

2015

• Comments received by GIF-RSWG and by IRSN and

partners of the Euratom collaborative project “ARCADIA”

• Presently under review for final issue

• Further steps include the development of detailed Safety

Design Guidelines for selected topics


The GIF LFR SDC

Applicability Number

As is 70

With interpretation 6

With modification 6

New requirement 2

Not applicable 0


Summary of development process


LFR safety issues

addressed:

Criterion 42bis: Plant system performance

The overall plant system shall be designed considering the specific characteristics of the reactor coolant and, in general, of the fast reactor system. This includes coolant inherent characteristics, such as its freezing and boiling point, volumetric heat capacity, degree of opacity, chemical reactivity in contact with air and water, as well as corrosion and erosion effects, and the reactor neutronic characteristics, such as its susceptibility to reactivity variations due to coolant heat-up and voiding as well as due to the loss of core geometry. Coolant-specific requirements, including the impurity and toxicity limits, need to be considered in the design as well.

• Corrosion/erosion, opacity

and high coolant freezing

point of lead (327ºC)

• Ruptures of steam

generator tubes might lead

to over-pressurization of the

primary side, sloshing and

steam/water entrainment

resulting in a positive

reactivity insertion

• Loss of core geometry (core

compaction) might lead to a

positive reactivity insertion

and power increase



LFR safety issues

addressed:

Criterion 47: Design of reactor coolant systems

6.15bis: The components of the reactor coolant systems shall be designed with due account taken of creep properties, thermal fatigue, fast neutron fluence, coolant-induced environmental effects, and other ageing effects, as well as its compatibility with lead, and with thermal stress and dynamic load on structures used under low pressure and high temperature conditions.

• Operation at relatively high

temperatures compared to

an LWR and in high fast

neutron fluence conditions

• Molten lead is corrosive and

oxidizes without oxygen

concentration control

• Metallic impurities produced

by corrosion can be

transported in the primary

system and form blockages

• Molten lead might erode

structural materials

• Large quantities of primary

coolant in pool LFRs may

lead to complex flow

patterns and interactions

with structures



LFR safety issues

addressed:

Criterion 76bis: Coolant Heating Systems

Heating systems shall be provided for primary coolant as necessary to prevent loss of primary coolant circulation by coolant freezing. These heating systems and their controls shall be appropriately designed to assure that the temperature distribution and rate of change of temperature are maintained within the limits.

• High freezing point (327ºC)

with a potential for coolant

solidification

• Mechanical stresses might

be exerted on structures

during unfreezing if a

proper melting sequence is

not applied



LFR safety issues

addressed:

Criterion 20: Design extension conditions

5.31. The design shall be such that design extension conditions that could lead to significant radioactive releases are practically eliminated. Since a fast reactor core is not in its most reactive configuration under normal operating conditions, the following design features for prevention and mitigation of severe accidents in postulated design extension conditions shall be considered:

a) Additional reactor shutdown measures against failure of active reactor shutdown systems,

b) Mitigation provision to avoid re-criticality leading to large energy release during a core degradation progression,

c) Means for decay heat removal of a degraded core, and

d) Containment function capability to withstand the thermal and mechanical loads generated by severe accident conditions.

• LFR reactor core is not in

the most reactive

configuration; it is possible

to have a positive void

reactivity in the central area

of the reactor core

• Corrosive properties of

molten lead could challenge

confinement barriers



Giacomo Grasso

[email protected]


LFR Safety Design Criteria - Nucleus Documents... · IAEA HQ, Vienna, Austria, 4-8 September 2017 ....

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