LEADER/ELECTRA Safety Workshop: Petten 27-28 February 2013 IRSN presentation on its document “ Overview of Generation IV (Gen-IV) reactor designs Safety

LEADER/ELECTRA Safety Workshop:Petten 27-28 February 2013

IRSN presentation on its document

“ Overview of Generation IV (Gen-IV) reactor designsSafety and Radiological Protection Considerations “

D. BLANC

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Contents

1.Scope of the IRSN document

2.Safety aspects specific to the concept

3.Aspect of the safety analysis

4.Resistance to the Fukushima Daiichi TEPCO events

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• The IRSN has issued in September 2012 a document entitled « Overview of Generation IV Reactor Designs – Safety and Radiological Protection Considerations “

• For each of the six reactor concepts considered by the GIF, the following topics are considered:

• Presentation of the concept and development status• Safety aspects specific to the concept • Aspects of the safety analysis• Resistance to the Fukushima Daiichi TEPCO events

• This document is based on open documents (from IAEA, technical articles from scientific reviews, etc.) and on previous safety papers issued in France

LEADER/ELECTRA Safety WS (27-28 Feb 2013) : IRSN presentation

Scope of the IRSN document

4LEADER/ELECTRA Safety WS (27-28 Feb 2013) : IRSN presentation

Safety aspects specific to the concept

• This document is available on the public IRSN website in French and English

• INTERNET link: http://www.irsn.fr/FR/Larecherche/publications-documentation/collection-ouvrages-IRSN/Pages/documents-reference.aspx

• The main aspects of the four above mentioned topics are given here after (except the first one: presentation of the concept…)

http://www.irsn.fr/FR/Larecherche/publications-documentation/collection-ouvrages-IRSN/Pages/documents-reference.aspx




1. Risk of erosion/corrosion of the structures

• The management of this risk is a key issue for the LFR development• The corrosion phenomena depend greatly on the LFR temperature and may

limit the temperature rise through the core • The life time of some components immersed in lead may be limited and the

replacement of these components has to be envisaged• The lead velocity has to be limited to avoid erosion risks

2. Risk of embrittlement of steels immersed in lead

• Some ferritic steels (such as T91) may present a risk of embrittlement when in lead and this phenomenon may be increased by the irradiation effect



3. Risks related to the chemical reaction between lead and water or air • The main point is that there is no exothermic reaction between lead water or

air (to the opposite of sodium…) Possibility to have the steam generators inside the primary circuit

• Nevertheless, lead in contact with water or air will produced hydrides or oxides able to increase the lead viscosity, to reduce the heat transfer and to cause subassemblies blockages

See the accident occurred on a Soviet submarine reactor in 1968

4. Risk of coolant freezing

• The high lead freezing temperature (327°C) will determine the temperature at core inlet (not lower than about 380°C).

• Safety devices are required to avoid freezing during long shutdown period

• As sodium, lead expands when it melts (to the opposite of water)



5. Chemical and radiological risks • Lead is chemically toxic: the Occupational Exposure Limit is 20 times lower

than that for sodium hydroxide (considered in case of sodium releases)

• The source term may be highly influenced by the production of Polonium 210 in particular when LBE is used

6. Natural convection capability

• The high expansion coefficient of the lead and with its high density are in favour of natural convection

7. Risk of thermodynamic interaction

• Even if lead does not react chemically with water, contact between liquid lead and liquid water is able to give a “vapor explosion” with the risks of gas ingress in the core and possible reactivity increase



1. Normal operation • The management of the corrosion risk is crucial and will require in service

inspection

• In service inspection techniques have to be developed (opacity of lead)

• The possibility to remove easily large components is a good aspect

Aspect of the safety analysis


2. Accidents without core melt

2.1 Control of reactivity

• IRSN has no information on the control rods design but they must be inserted into the core despite the high density of the lead

2.2 Containment

• Given the high toxicity of lead, the containment requires special attention to prevent releases to the environment




2.3 Core cooling

Decay heat removal

• The neutronic characteristics of LFR core allowed the designers to “space out” the fissile material and to have low pressure drop through the core

• This low pressure drop combined with the lead capability for natural convection are in favour of possibility of core cooling without any electric supply

• The high thermal inertia of the coolant limits the temperature increase versus time and provides grace periods for recovery of DHR means

• IRSN has noticed that ELSY projects use two diverse and redundant DHR systems immersed in the primary vessel with also a system able to cool the vessel and the concrete of the reactor pit




2.3 Core cooling

Reactor under neutronic power

• The low power density (regard to the SFRs one), the high thermal inertia of the coolant, the high boiling temperature of the lead and its capability for natural convection make LFR concept tolerant to unprotected transients (ULOF, ULOHS) accidents even if the “void effect” is positive

Important characteristic in particular for “inherent safety”



3. Accidents with core melt

• Available analyses on accident sequences performed for the ELSY project do not reveal any scenario that may lead to global core melt

• IRSN does not have information on the molten fuel behaviour and its relocation in LFRs

• Nevertheless MOX fuel may float on the lead and, for this reason, the use of a core catcher at the bottom of the primary circuit would be of no use

• What about the risk of recriticality of molten fuel at the lead surface?



1. Earthquake

• The large mass of the lead inside the primary vessel requires design precautions to prevent large loadings on the structures during earthquake (in particular in case of waves effect)

• IRSN has noticed that anti-seismic pads are planned on ELSY project and also the existence of the EC project SILER

2. Flooding

• Measures to avoid contact between water and lead have to be taken in order to limit the lead releases in the environment

Resistance to the Fukushima Daiichi TEPCO events


3. Total loss of electric supplies

• A good point is the capability to cool the core by natural convection as already said

• A difficult situation for LFRs could result from the loss of heating means and, in this case, the integrity of the primary vessel containing frozen lead has to be demonstrated



3. Loss of the ultimate heat sink(s)

• Good point : there are two ultimate heat sinks (water and air)

• Air stacks of the DHR system may be a sensitive area in case of large earthquake or aircraft crash (but no typical for LFRs..)

• The possibility of water top-up into the tanks associated to one of the DHR systems seems to be necessary

4. Severe accident management

• In case of LOCA, provisions would be desirable in particular to re-inject lead in the core (the same for SFRs..)



Thank you for you attention

Documents

LEADER/ELECTRA Safety Workshop: Petten 27-28 February 2013 IRSN presentation on its document “ Overview of Generation IV (Gen-IV) reactor designs Safety