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Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
Page 1
SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Status of Safety Analyses for the ESS Target
R.Moormann, R.Bongartz, W.Kühnlein, J.Marx, H.Schaal, K.Verfondern (FZJ)
P.Berkvens (ESRF), P.Wright (RAL)
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Artist‘s view of the ESS Facility
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Main parameters
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Scheme of ESS target and of mercury circuit (15 t Hg, max. operation temperature: 250°C, max. temperature increase by decay heat: 35 °C)yellow =target block, red = mercury
Proton beam
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
-The target is the only component in Spallation Sources, which requires detailed accident analyses: accidents, harming the public, are imaginable only for the target due to its substantial radiotoxic and chemical toxic inventory. Other components (accelerators etc.) need safety considerations for normal operation/- abnormal events only.
The preliminary safety analysis report (PSAR including updates) for the SNS target is under review with respect to its applicability for ESS
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Short description of PSAR Procedure of PSAR
(preliminary safety analysis report) :- screening of possible events- rough estimation of consequences and
frequencies (limited credit on safety measures = ‘unmitigated’ estimations)
- identification of relevant accidents by ‘risk
binning’; (risk = dose * frequency)
- cut off criteria: low frequencies (< 1.e-6/a) and low consequences (< 1 mSv)
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
- more detailed estimation of source term and consequences for relevant accidents (‘unmitigated’ estimations)
- in case of transgression of dose limits:repetition of source term/consequence/- frequency estimations assuming additional ‘mitigating’ safety measures
- stepwise increase of accuracy, until dose limits are met (advantage: reduction of effort, identification of really important safety measures)
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Relevant accidents identified:• Fire within the target building• Hydrogen/moderator explosion with and without
subsequent fire• Loss of confinement (Leak in the target circuit)
– [Loss of mercury flow]– [Loss of heat sink]
• [Target hull heat-up by misadjusted proton beam]• Earthquake followed by explosion with and
without following fire• Crane drop accident
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Safety work at ESS
Main results of PSAR/SNS review are:
- PSAR/SNS is a valuable basis for ESS safety work
- Additional accident to be considered in case of a Be-reflector: Be-reflector fire
- European conditions require a more detailed safety analysis than performed within PSAR/SNS for the following reasons:
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
• larger ESS radioactive inventory• smaller distance ESS – receptor• conservative consequence model for ESS
required, not a realistic one as for SNS• consideration of ingestion pathway for ESS
accidents required (contrast to SNS)• lower dba dose limits in EU:
effective dose/dba: 50 mSv in D 250 mSv for SNS
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Safety relevant nuclides in mercury target:
nuclide boiling point [K]
ESS target inventory
[GBq]
half life [d]
radiation type
dose/emission 1) ground cloud inhalation ingestion shine (γ) [ / ]Sv GBq
H-3 ( )HTO 373 2.3e-9 3) 4.6e-8 2) H-3 ( )HT 14
5.6 5 e( )total
4500 weak β 0 0 1.5e-11 3,4) 3.3e-9 4)
I-124 387 3100 4.2 β,γ 2.8e-6 1.0e-8 3.0e-5 3.4e-3 I-125 „ 14000 60 γ 1.8e-6 1.0e-10 1.8e-5 2.3e-3 I-126 „ 630 13 β,γ 3.9e-6 4.2e-9 6.3e-5 7.6e-3
Hg-193 629 1.9 6e 0.16 γ 3.6e-8 1.7e-9 6.5e-9 2.5e-10 Hg-194 „ 2.1 5e 1.9 5e γ 6.1e-3 1.3e-13 1.3e-6 5.0e-7 Hg-195 „ 3.2 6e 0.42 γ 7.5e-8 1.7e-9 8.1e-9 6.3e-10 Hg-197 „ 2.2 7e 2.67 γ 1.1e-7 5.2e-10 2.0e-8 3.0e-9 Hg-203 „ 1.5 7e 47 β, γ 7.5e-6 2.2e-9 1.8e-7 8.1e-9 Gd-148 3546 3.5 4e 2.72 4e α 0 0 2.2e-3 4.0e-7 Hf-172 4875 7.3 5e 683 γ 2.8e-4 7.7e-10 1.3e-5 1.9e-9 Au-195 3081 4.2 6e 186 γ 3.1e-6 6.2e-10 2.2e-8 5.9e-10
1) , (70 ), German directives for design basis accidents infant a continuous ingestion and ground shine effective doses (except for iodine ), : 250 , : 25 , thyroid minimum distance m emission height m2) preliminary ingestion model of , German rules3) ( ), including HTO resorption by skin preliminary model4)HT- oxidation to HTO in soil considered
: = , = Volatility classes green high volatile blue me ( ), = rcury intermediate volatility yellow low volatile
Overview on radiologically most relevant nuclides in the ESS-target (5 , 30 )MW y continuous operation
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Note: Long lived actinides are not found in spallation sources
Comparison of activities in LWR and ESS
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Conclusion on comparison of inventories:• Determination of spallation yield for long-lived
nuclides (Hg-194, Gd-148) is of particular relevance: ESS will perform evaluation of Hg irradiation experiments of ORNL, performed at SINQ
• Even for individual short lived nuclides the spallation yield is fairly uncertain (which is compensated by the large number of nuclides). Accordingly, short term Hg irradiation experiments are advisable
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Comparison of radiotoxicity and chemical toxicity of mercury
• Comparison is problematic, because only incorporation effects are comparable
• Comparison for toxicity by inhalation between the total inactive Hg-inventory and the inventory of one individual nuclide (Hg-197) reveals, that the chemical toxicity is about a factor of 10 - 30 higher than the radiotoxicity of Hg-197
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
• Nevertheless, due to strong ground shine (Hg-194) and due to the large number of other radiotoxic nuclides, we expect, that radiotoxicity dominates the overall toxicity.Chemical toxicity may however not be neglected.
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Loss of confinement accidents1. Probabilistic and system studies
No Released media
Released activity
Probability / dose limit (mSv)
Unmitigated dose (mSv)
Counter measures
Remarks
Large failure of target confinement, release of Hg and cooling water into core container at operating temperature; release into environment via vacuum system, off gas system and stack
3.1-4
Hg, cooling water
H-3, Hg-,I-isotopes
SNS: U/50 ESS: A/0.3 per path
SNS: 3.2 ESS: > Limit
HEPA-Filter H-3-filter ?
Large failure in target circuit, release of Hg into target cell at operating te mperature; release into environment via Primary Containment Exhaust System (PCE) and stack
3.1-7
Hg “ SNS: A/5 ESS: A/0.3 per path
SNS: 2.2 ESS: >Limit
HEPA-Filter Hg-Adsorber
“
Failure of Hg-flow, local boiling, Hg- and cooling water release into core vessel via leak generated by proton beam, partial evaporation of Hg, release into environment via overpressure valve and stack
3.1-12
Hg, cooling water
“ SNS: A/5 ESS: A/0.3 per path
SNS: 200 ESS: >> Limit
Beam shutdown
Time for beam shutdown?
Failure of target heat sink, Hg- and cooling water release into core vessel via leak generated by proton beam, partial evaporation of Hg, release into environment via overpressure valve and stack
3.1-13
“ “ SNS: A/5 ESS: A/0.3 per path
SNS: > 250 ESS: >> Limit
Beam shutdown
Time for beam shutdown?
Leak in cooling water system (target shroud), release via target cell or core container and stack into environment
3.3-1
Cooling water
H-3 SNS: A/5 ESS: A/0.3 per path
SNS: 0.05 ESS: > Limit
H-3 filter in –PCE?
HT, HTO ?
Leak in reflector cooling system, release of cooling water into auxiliary system building, release into environment via stack
3.3-12
D2O H-3 SNS: A/5 ESS: A/0.3 per path
SNS: 0.22 ESS: > Limit|
H-3 filter in SCE?
“
Relevant ESS dba
A = anticipated within ESS lifetimeU = unlikely
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
2. Deterministic examinations• Hg/H-3 thermochemistry has to be examined • JSNS work indicated, that mercury iodides (lower volatility than I2) may be formed:
- PSAR/SNS assumes a pronounced iodine release in loss of confinement accidents, because the chemical status of iodine is considered as elemental (high volatile). Resulting emissions are too high for ESS conditions.- Thermochemical calculations (using ORNL-code SOLGASMIX-PV) at ESS quantified the chemical composition. Validation will be performed.
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Equilibrium composition of an Hg/I and of an Hg/I/Fe system
Results of SOLGASMIX-PV
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
Additional target and moderator safety work
Other accident classes in examination for ESS (probabilistic, system, source term and dose studies) are:
• External events (earthquake, fire, airplane crash..)
• Internal explosions
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
• CFD (CFX-Code): calculations on distribution of moderator within target cell/- building in accidents (burnable gas mixtures etc.):
Leak in H2-pipe with spontaneous evaporation
1.5 kg of H2 released in 30 s
Air ingress with 0.15 kg/s at 288 K
• CFD-calculations on particle (Hg-droplets) transport in case of accidents
Examinations on moderator explosions
Status of safety analyses for the ESS target Rainer Moormann, PES-FZJ
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SAFERIB I - CERN/Geneva30.10. - 01.11.2002
General ESS safety work• Decommissioning, final waste disposal
• Activity transport with ground water flow
• Consequence estimations for accidents using COSYMA model (planned)
• Selected design work for safety systems
• Shielding philosophy and design