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The 1st COE-INES Int. Symposium, INES-1 Oct 31 – Nov 4, 2004, Tokyo, Japan 1

Research Center JuelichInstitute for Safety Research and Reactor Technology (ISR)

The Particular Safety Aspects The Particular Safety Aspects of of the the Combined Combined HTTR/HTTR/Steam Reforming Complex Steam Reforming Complex

for Nuclear Hydrogen Productionfor Nuclear Hydrogen Production

bybyKarl VERFONDERN Karl VERFONDERN 1)1) and and Tetsuo Tetsuo NISHIHARA NISHIHARA 2)2)

1)1) Research CenterResearch Center JuelichJuelich, Germany, Germany2)2) Japan Atomic Energy Research Institute, Japan Atomic Energy Research Institute, OaraiOarai, Japan, Japan



Combined Combined HTTR/HTTR/Steam Reforming Steam Reforming SystemSystemHTTR

SteamGenerator

SteamReformer

Naturalgas

Water (H2O)

Hydrogen

IHX10MW

IsolationValve

950°C

30MWFeed gas preheater

395°C

Pressurized water cooler

20MW

150°C Radiator

Heliumcooler

905°C

Steamsuper heater



Combined Combined HTTR/SR HTTR/SR ComplexComplexReactor System Hydrogen Production system

Steam reforming

Hot gas duct

Control center

IHXReactorvessel

Containment vessel

CH4 + H2O → 3H2 + CO



Potential Potential HazardsHazards in HTTR/SR in HTTR/SR ComplexComplex

Tritium transportation from core to product gases;

Thermal turbulences induced by problems in steam reforming system;

Fire and explosion of flammable mixtures with process gases.



Tritium and Tritium and Hydrogen Flow PathsHydrogen Flow Paths

Sources:- fission (51%)- lithium (34%)- helium (15%)



Problem TritiumProblem TritiumHigh mobility of both HT and H2 at high temperatures- radiation problem to consumer- corrosion problem in graphitic core structuresMeasures of reducing HT and H2 transport- oxide layers (doping with O2)- gas purification system- intermediate circuit (doping with H2O)

Results from JAERI calculations and tests- HT level in product gas deemed sufficiently low- permeability of oxide layer reduced by factor 100-1000Limit as defined in German legislation- 0.5 Bq/g (applies to any fabricated product)



He circulator

Electricheater

Steamreformer

Steamgenerator

H2; 120m3/h, COFlow Diagr am an d Ma in Tes t Item s ofOut-o f-Pile Demo nstrat ion Te st Fac ility1/30sc ale mod el of HT TR hyd rogen product ion syst emReplace ment o f nuclea r heat with ele ctricity

６００℃

８８０℃

４５０℃６５０℃

H2:110Nm 3/h, CO

Mainte st items Desig n verific ation ofhigh- temperat ure comp onents - Stea m reform er - Stea m gener atorInves tigation o f static a nd trans ient beha viorEstab lishmen t of opera tionalandc ontrol te chnology

Pump

LN2 tankLNG tankPum pPum pEvapo ratorEvap oratorSu rge tank

Water ta nk Air c ooler

Steam g enerator S teamre former

Flare sta ckSu rge tank

Helium gas cir culation line

Product gasInert g as feed line Produ ct gas combus tion lin e

Natura l gas fe ed lineSteam feed lin e

880℃

Condenser

Steam generator

Steamreformer

Electric heaterCirculator Hot gas duct

Helium gas circulation system

Product gas

Nitrogen feed lineProduct gas combustion system

Natural gas feed system

Steam feed system

600℃

650℃

450℃

Shematic Diagram of Simulation TestSteam Reforming Steam Reforming OutOut--ofof--Pile Pile Pilot PlantPilot Plant



HTTR/SR System HTTR/SR System ControllabilityControllability TestTest

1200

1000

800

600

400

200

140

120

100

80

60

400 4 8 12

Hyd

roge

npr

oduc

tion

rate

(m3/h)(°C)

Time (h)

H2 production

He temp. at SR outlet

He temp. at SG outlet

Start of hydrogen production

Hel

ium

tem

pera

ture

Startup operation



HTTR/SR System HTTR/SR System ControllabilityControllability TestTest

0

1

2

3

4

5

6

0

100

200

300

400

0 2 4 6 8 10-1200

400

600

800

1000

0 2 4 6 8 10-1

Hel

ium

gas

tem

pera

ture

[oC

]

SG

pre

ssur

e [M

Pa] S

team production

and circulation rate [g/s]

Steam reformer inlet

Steam generator outlet

Steam reformer outlet

Elapsed time after suspension of methane feed [h]

Elapsed time after suspension of methane feed [h]

Steam productionSteam circulation

Loss of feed gas (chemical reaction)



Safety Safety Design Design against Fireagainst Fire and Explosionand ExplosionReactor System Hydrogen Production system

Take safe distance

Take safe distance to storage tank

- Prevent leakage and ignition- Prevent inflow into

nuclear building- Detect leakage and

shut off natural gas line



Equilibrium ProcessEquilibrium Process Gas DistributionGas Distribution



Possible EffectsPossible Effects of of FireFire/Explosion /Explosion AccidentsAccidents



Flame Flame VelocitiesVelocities of Hof H22--COCO--Air Air MixturesMixtures

Breitung, FZK, 2000



Potential Potential HazardsHazards of LNG of LNG StorageStorageBoil-off;Tank „roll-over“ (e.g., by ageing, heat input);Change of material properties at cryo temp.;BLEVE type catastrophic failure of storage tank(Boiling Liquid Expansion Vapor Cloud Explosion);Rupture of tank or pipeline;Cryogenic burns of personnel.



Safety Safety DistanceDistance

R = k * M 1/3

with R: safety distance [m]

M: mass of flammable substance [kg]

k: factor 2.5-8 for working building

22 for residential building

200 for no damage



German BMI German BMI Guideline Guideline (1974)(1974)for thefor the

ProtectionProtection of NPP of NPP against External Explosionsagainst External Explosions

R = 8 * M 1/3

100% for unsaturated HC and non-liquefied gases50% for gases liquefied under pressure10% for gases liquefied at low temperatures0.3% for combustible liquids

TNT equivalent for explosives

Minimum Distance: R ≥ 100 m

Protection by means of safety distance



German BMI German BMI Guideline Guideline (1974)(1974)Protection by means of design against pressure wave



German BMI German BMI Guideline Guideline (1976)(1976)Guideline was the result of experts‘ opinion.

Guideline was confirmed by PNP gas cloud program that gas mixtures typical for PNP cannot generate pressures beyond the design curve.

However, Guideline is not to be applied to process heat HTGRs.

If applied to HTTR/SR:k = 3.7 R = 205 m for LNG storage tank(not considered: inventory in steam reformer)



US Regulatory Guide 1.91 (1975)US Regulatory Guide 1.91 (1975)

LNG: 400 m3 169 t 1859 t TNTR = 2.2 km

(or show that attendant risk be sufficiently low)



Conclusions Conclusions (1)(1)Methane combustion occurs most certainly as flash fire with insignificant pressure wave.Detonantion of methane-air vapor cloud has never been observed in field trials nor accidents.Only for more reactive gases, overpressures > 30 kPa could be measured. Here partial detonations may not be excluded (IAEA).BLEVE type combustion has never been reported to have occurred in an LNG storage vessel. Cannot occur in underground container.



Conclusions Conclusions (2)(2)

Safety distance of „more than 300 m“ betweenHTTR and LNG tank would meet German BMI Guideline, but not the US Regulatory Guide 1.91.

If reactor building is well designed to withstandpressure wave from outside, impact on components inside is covered by resp. Design against airplane crash and earthquake.

the particular safety aspects of the combined httr/steam ... · igafd duc cbstlin e natural...

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