astec status and perspectives 2019 - presentations...enhancing nuclear safety astec status and...

Enhancing nuclear safety

ASTEC status and perspectives

CHAILAN Lionel - ASTEC project leader

On behalf of the ASTEC development team

Severe Accident Department

IRSN Nuclear Safety Division

9th Conference on Severe Accident Research, ERMSAR 2019,

March 18 - 20, 2019 - Prague, Czech Republic

Outlines

▌Recent safety applications with ASTEC V2.1 at IRSN

▌ASCOM project

▌Under development ASTEC V2.2 version

▌ASTEC+ trajectory and perspectives


March 18 - 20, 2019 - Prague, Czech Republic 2/24

Outlines


▌ASCOM project





Safety analyses: expertise of EDF proposals for Operating Fleet Lifetime Extension

▌Safety study: expertise of EDF proposals for Plant Lifetime Extension in the frame of the post Fukushima CSE

In the frame of the Plant Life Extension program for Gen II PWRs operation beyond 40

years, the French regulator supported by IRSN requested improvements to increase the

safety levels towards those of the Gen III EPR safety level. For SA, limited in space and

time population protection measures are targeted.

First set of modifications to avoid reactor concrete basemat melt-through by the

molten core after vessel failure : dry spreading in an area larger than the reactor

vessel pit rapidly followed by a passive top cooling of the corium.



Second set of modifications to remove the decay heat from the containment

without opening the EFCVS (U5 line including metal pre-filter and sand bed filter)

5


Ultimate heat sink has to be

lined by the EDF nuclear rapid

response force (FARN)

Delay time for ultimate heat

sink implementation is

evaluated by EDF to 24 hours



CSARP Technical Review Meeting, Washington,

June 5-7, 2018

▌ PWR 900 MWe ASTEC reference datasets have been updated to include these

proposed modifications, including the corresponding severe accident

management actions and taking into account the various basemat concrete

composition of the fleet that significantly impacts the concrete top cooling.

▌ Corium top cooling during MCCI models have been updated specifically for these

safety analyses.

water

injection concrete

bubbling

corium

pool

quenched

upper crust

dry upper

crust

water

ingression

erupted melt

debris




Heat exchange at corium/water

interface: Nukiyama curve

Ingression : Lister

Eruption: Fontaine / Ricou & Spalding

Assessment on SSWICS and CCI

experiments (including the recent

ANL/EDF program)

6/24

EDF Rescue team activation (24 h)

Safety study: expertise of EDF proposals for Plant Life Extension

Containment over-pressurization

Depending on the concrete composition, two

main hazards are challenging the

containment integrity:

• Silicious concrete implies strong basemat

melt-through risk

• Limestone concrete enhances fast

containment pressurisation

In any case, the delay for the activation of

EDF nuclear rapid response force is crucial

Basemat melt-through

▌ ASTEC V2.1 results regarding MCCI phase



Safety study: Spent Fuel Pool Accident Mitigation

CPA nodalization of SFP building Thermal-hydraulic validation of CPA model

by comparison with FLUENT computation

Total, Aerosol and gas releases

Main releases are in aerosol form: I2O5, CsI,

Cs2I2

Main gaseous released species are: CH3I, I2



SFP – evaluation of mitigation strategies

▌Several mitigation strategies were evaluated

External spray outside the SFP building

Spray in a small room disposed between SFP building and environment

Internal SFP building spray


External spray Small spray located in an

exit lock

Internal spray



SFP building

9/24


▌Preliminary Observations

Without mitigation strategy applied:

Non-negligible retention of SFP building itself

No H2 explosion risk

Main gaseous release carried by organic iodine

With mitigation:

Negligible effect of sprays when located outside the SFP building

Efficient effect of spray located inside the SFP building

Work to be continued in particular in the frame of H2020 MUSA project



Outlines


▌ASCOM project





12/13

▌ASCOM Project conduct

4-year long in-kind R&D project (Oct. 2018 - Sept. 2022) coordinated by IRSN in the

frame of the NUGENIA/TA-2 (SARNET)

▌ASCOM Project objectives

ASCOM main objective is to help amplify and accelerate the on-going process of

making ASTEC a fully reliable tool for SA analyses and accident management in a

wide range of nuclear safety applications by strengthening the various R&D

activities of the ASTEC COMmunity in a consistent way

▌ASCOM Project partnership

Today, ASCOM gathers 25 partners (TSO, research, universities, industry) :

IRSN, EDF R&D (France), KIT, HZDR, RUB-PSS (Germany), ENEA, Univ.Pisa (Italy), CIEMAT (Spain), NUBIKI (Hungary), IVS (Slovakia), UJV (Czech Rep.), INRNE (Bulgaria), RATEN ICN (Romania), LEI (Lithuania), VTT (Finland), IJS (Slovenia), FER (Croatia), JRC (EC), Tractebel-ENGIE (Belgium)

SEC NRS, NRC-KI (Russia), Energorisk (Ukraine)

NSC (China), NUS (Singapore)

Univ. Utah (U.S.A)

ASCOM : General introduction to the project



13/13

▌ASCOM project structure

ASCOM is spread over 6 Work-Packages, whose major ones cover:

Continuous validation of ASTEC V2 series

ASTEC applications at plant scale, along with cross-walk activities with other

reference SA analysis codes (MELCOR, MAAP, …) for Gen.II LWRs

Development of few new “generic” reference open input decks to extend

the ASTEC V2 applicability to some other kinds of nuclear installations:

– Gen.III & III+ PWRs with IVMR strategy (e.g. AP1000)

– Gen.III & III+ VVERs (e.g. VVER-1200)

– SMRs

– SFPs

▌Yearly workshops

Next workshop to be hosted by KIT in September 2019

▌A crucial community for best-estimate calculations

SA codes necessitate experienced users

Sharing experience and best practice is essential for reliable calculations

ASCOM : General organization of the project



Outlines


▌ASCOM project





ASTEC V2.2

▌DEBRIS modelling: a new generation of degradation models in ASTEC

MAGMA

Melting and eutectic

formation

Relocation for

liquid fraction>0

DEBRIS

Granular flow,

interaction with

MAGMA

Creation on

several criteria

Melting temperature

of oxide lowered,

based on PHEBUS

experiment

Criteria of creation

currently investigated

on several scenarios

Fuel melting and relocation of the liquid fraction to magma was the unique

degradation mechanism assumed in ASTEC

Core degradation through creation of solid particles (so-called “debris”) is intended

to provide ASTEC with a complementary way to describe the degradation course

when solid debris can be generated under their melting temperature



ASTEC V2.2

▌DEBRIS modelling: models are operational, now ongoing validation

tasks are being conducted

Kingery/Vortmeyer*2

(best results with ASTEC V2.1)

Heat transfers models in porous media:

best fit of thermal conductivity in porous

media

Re-assessment against FPT4 experiment

(PHEBUS FP experiment characterized by an

initial debris bed), showed a good agreement

Thermal-hydraulic in porous media:

sensitity w.r.t wetting angle

PEARL experiments have been intensively

used to set up and validate the two-phase

thermal-hydraulic models in porous media



ASTEC V2.2

▌Current validation tasks aim re-assessing integral experiments and

accident with respect to the gain of debris models



PHEBUS-FP FPT1 and FPT3 experiments

These experiments showed essentially melting

phenomena without clear evidence of debris creation:

how considering the debris in such situation?

PBF SFD-1.4 experiment

This experiment is considered being more representative

of TMI-2 accident and should be well adapted for

assessing the debris creation criteria

TMI 2 accident

The Three Mile Island accident revealed a large amount

of debris creation, likely related to strong thermal

gradient during reflooding

17/24

ASTEC V2.2

▌Thermal hydraulic models for high incondensable gases rates

Conditions frequently arising in the reactor cooling circuit components in

various situations:

Shutdown states scenarios calculations,

During reflooding after a large H2 production in the core,

SFP accidents and air-ingress scenarios

Models are required to operate in a large range of conditions, i.e. from pure

steam flow to pure incondensable gases flow

Implementation of adequate models is finished, re-assessment of improved

thermal hydraulic module CESAR is underway



ASTEC V2.2

▌ Several modelling improvements have been implemented to better

address the IVR strategy issues

Over-filling of the lower plenum: will be delivered with next V2.1 patch

planned in April 2019

• This situation will be handled by ASTEC V2.2

• Radiation through cavity has also been extended in this case, allowing

lower plenum pool to exchange by radiation with upper part of the core

and the vessel wall

ASTEC V2.2



Outlines

▌Safety applications with ASTEC V2.1 at IRSN

▌ASCOM project





▌ASTEC+: a new pathway for ASTEC development

Where most of the codes we are using have been developed for years

(or decades), we need to address their sustainability : ASTEC+ is an

evolutionary trajectory of the development of the future versions of

ASTEC targeting their modernisation.

New trajectory based on standardized software programming

approaches using the C++ scientific software programming platform

PELICANS (Open Source, developed by IRSN)

Where significant knowledge, methods and tools have been developed

for power reactors, there is a need to globally consider the radiological

risks : extension of the scope of ASTEC to address with a risk-rated level

of accuracy - spent fuel pool, fuel reprocessing facilities, MTR, SMR,

naval…

Development of a set of tools and methodologies allowing coupling

with dedicated codes (internal/external)



▌ASTEC+: a new pathway for ASTEC development (ctd)

Where budget constraints apply to most of our organizations, there is a

need to streamline severe accident prognosis/diagnosis capabilities :

deterministic plus uncertainties, PSA, EP&R, desktop simulator.

Capitalization of knowledge and methods in SA framework,

progressive integration of modern algorithmics including surrogate

modelling

Where budget constraints apply and where the spectrum of potential

simulation objects is widening, this new trajectory also target at short

term a facilitated potential external co-development.

ASTEC+ project started in 2019 using so-called agile « user oriented » approach

In coherence with the global IRSN approach for the digital shift IRSN

2030

In close coordination with similar approaches implemented in the US



Chaining ASTEC and

aero-dispersion code pX

ASTEC V3.0 : new applications for ASTEC

Generalisation of

Surrogate models and

Bayesian Networks

Red oils accidents in

reprocessing facilities Coupling ASTEC and CFD code for SFP



That’s all, folks!

Thank you for your attention!



PEARL Experimental facility

▌ IRSN, Cadarache, France

▌Coolability of large heated debris beds

▌Steel particles heated by induction

▌Effect of pressure (1-10 bar), velocity, initial temperature (400°C-1000°C) on reflooding behaviour

▌Bypass around the debris deb simulates less degraded zone

Subcooled

water

Steam ↑↑↑ Overview

PEARL Experimental facility

Initial conditions

▌ Temperatures

▌ Liquid level

Boundary conditions

▌ Flow inlet

▌ Pressure outlet

▌ Electrical power

Experiment ASTEC

Modelling in ASTEC V2.1

IRSN CONTRIBUTION TO FASTNET PROJECT

▌FASTNET : an European H2020 project dedicated to emergency preparedness and response.

Use of Bayesian Networks and ASTEC code to help diagnosis in a SA

Three prototypic tools have been developed

A situation selector in a calculation grid

An iodine source term predictor (prognosis)

A diagnosis tool for plant state assessment at a given time of the accident

Scenario specification

ASTEC Simulations

DataBase

Data Learning

Validation



▌WP1: a calculation grid composed of 57 best estimate ASTEC calculations, simulating a PWR 1300 MWe

All ASTEC modules implied, various kinds of situation (LOCA of different sizes, SBO,

LFSG), various failure times of safety systems

▌WP2 phase 1 : Source term prediction ~30 000 SOPHAEROS calculations (~6 hours on 25 computing nodes)

Various kinds of ambient situations: dose rate/temperature in gas/liquid phase,

degradation, pH, various hypothesis about iodine behavior, Iodine related kinetics

reactions uncertainties as underlying variables

▌WP2 phase 2 : Vessel state prediction ~30 000 ASTEC calculations simulating a simplified PWR 900 MWe (~2 months on 25 computing nodes)

All ASTEC modules implied, LOCA with SI or not, CSS available or not, break size

between 1 inch to 12 inches, break located in hot or cold leg, containment overall

leak rate between 0.01 to 100 of “normal” leak rate

28

IRSN CONTRIBUTION TO FASTNET PROJECT



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