US TBM Meeting INL, August 10-12, 2005

B. J. Merrill and D. A. Petti Fusion Safety Program

Safety and Tritium R&D

Presentation Outline

• Overview of safety analysis of the Dual Cooled Lead Lithium (DCLL) test blanket module (TBM)

• Discuss safety issues that need to be resolved based on present analysis results

• Look forward from where we stand now to what will have to be accomplished both analytically and experimentally in order to obtain operation approval for the DCLL TBM

• Estimate the resources that will be required to reach the final goal and present a rough time schedule for the required work

• Summarize the key points to focus future safety activities

DCLL TBM Safety Analysis Overview

The safety analysis required by ITER for the DCLL TBM Design Description Document (DDD) focused on four areas of safety concern:

• Radioactive source terms that can be released during normal operation or accident conditions

• Pressurization events that could fail ITER radioactive confinement barriers (e.g., vacuum vessel (VV), confinement building rooms, etc)

• TBM decay heat removal by thermal radiation to the basic machine maintaining TBM FW temperatures < 350oC in the post-shutdown period

• Hydrogen and heat generation from chemical reactions between ITER cooling water and the PbLi and beryllium of the TBM

DCLL Radioactive Source Terms

• Where do we stand? An estimate can be made based on present ITER site boundary dose limit for TBMs of 0.5mSv during an accident, { assuming only a single nuclide is released, that the release is stacked, and allowing for two possible weather conditions, conservative weather (CW) and average weather (AW) }, as follows:– Tritium release of between 14 g for CW or 70 g for AW compared to a

total TBM system tritium inventory of ~0.3 g

– Po-210 release of between 1.4 Ci for CW or 15 Ci for AW compared to the TBM inventory of 1.8 Ci (possible problem area)

– Hg-203 release of between 1310 Ci for CW and 13,600 Ci for AW compared to a TBM inventory of 36 Ci

– F82H oxide release at 700ºC of between 8 days for CW and 80 days for AW compared to a building isolation time of 30 minutes

• The ITER in-facility annual release limit for TBMs will be ~100 mg-T; however the predicted system permeation rate is ~470 mg-T/a for a T2 pressures above the Pb-17Li of ~2 Pa (problem area)

Pressurization Events• The required ITER safety assessment of the DCLL TBM DDD examined three

loss-of-cooling-accidents (LOCA), which are:

– Ex-vessel LOCA to assess TBM vault pressurization

– Coolant leak into TBM breeder or multiplier zone to assess module and tritium extraction gas system pressurization

– In-vessel TBM coolant leak analysis to demonstrate a negligible pressurization of ITER’s first confinement barrier (i.e., ITER VV)

2800 2825 2850 2875 2900Time (s)

0.10

0.15

0.20P

ress

ure

(MP

a)

ITER-FEAT multiple tube in-vessel break

TBM base case

Pb-17Li - water reaction

VV pressure during andin-vessel TBM LOCA

2600 2800 3000 3200

Time (s)

.08

.10

.12

.14

.16

Pre

ssur

e (M

Pa)

.20

Test cell

Vault

VV

Test cell, TCWS vault and VV pressures during an ex-vessel TBM LOCA

• The safety function of the ITER VV pressure suppression system was not compromised and the vault design pressure were not exceeded, meeting ITER TBM safety requirements

Decay Heat Removal

• The ITER safety assessment for the DCLL TBM DDD demonstrated that the TBM decay heat could be removed by thermal radiation to the ITER VV

• The TBM FW temperature drops below 350ºC within 3days, with the primary reason for temperatures in excess of the ITER FW temperature during this time period being the latent heat capacity of the Pb-17Li and not decay heating

Hydrogen Generation from Chemical Reactions

• The chemical reactions of concern for the TBM are beryllium and Pb-17Li reacting with H2O

– ITER requires that the Pb-17Li volume be limited to 0.28m3 to ensure that H2 production is less than 2.5 kg

– Alternatively, a detailed analysis of PbLi/H2O interaction must be performed that considers a Pb-17Li spray into water (spray droplets that are ~ 2 mm in radius); this analysis is problematic because reaction rate data does not exist for such droplets

– Our DDD relied on data from a single test (pouring contact mode) that indicates that only ~50% of the Li will react; however only the quantity of H2 generated and the time to achieve this quantity of H2 were reported and very little additional information given regarding important modeling phenomena such as Pb-17Li fragmentation, transient temperatures, and reaction rates at various conditions.

• FW beryllium/H2O reaction will not produce more than 2.5 kg even if all of the beryllium is reacted

Jeppson’s* experiment for PbLi/H2O pouring contact mode is (2 g of 600°C PbLi into 4000 g of 95°C H2O, which gives an initial drop radius of ~8 mm)

*D. W. Jeppson, “Fusion reactor breeder material safety compatibility studies,” Nuclear

Technology/Fusion, 4 (1983), p. 277-287.

Looking Forward• Based on two presentation made at TBWG-15:

– Iseli’s (ITER-IT) presentation on TBM Safety described the ITER safety approach and confinement strategy

– J.-Ph Girard (EDFA) presentation described the evolving approach for Licensing of Experimental Devices for ITER, indicating that the safety approach is still under development

• It appears that TBMs will have to be licensed, and at the present time there is great deal of uncertainty regarding:

– Methods and guidelines for TBM safety analyses and documentation

Will the ITER radiological and hydrogen generation limits be acceptable or will new limits be established?

Will additional accidents need to be analyzed, and on what basis will they be selected?

What computer codes will be allowed for safety analysis and what level of quality assurance and design qualification will be required?

Looking Forward (cont.)Uncertainties:

– Licensing approach, three are being considered

Experiments considered and analyzed in initial safety files

This is presently the favored approach for ITER (Girard EDFA) but the worst possible approach for a staged TBM approach because all of the planned TBMs would have to be designed and qualified prior to ITER operating

Experiments with no extensive description

Approval as experiments mature but must stay within an initially defined safety envelope – more favorable for a staged TBM philosophy

Non-scheduled experiments

New licensing process per TBM

– CEA requirements (not yet defined), however rough cost estimates for design related safety work based on similar work done during the ITER EDA is:

Quality assurance, computer code V&V, historical control and design qualification could become dominate safety concerns for design activity requiring 1 to 1.5 FTE/yr effort for a safety analyst over the design life of the project for a full TBM approach and ~0.5 FTE/yr for a partial TBM or sub-module in EU TBM

Looking Forward (cont.)• If ITER analysis rules can be used as a guide, then we have identified several

areas of required safety R&D

– Additional Pb-17Li/H2O reactions test are required to support our contention that only 50% of the Li reacts when a hot atomized spray of Pb-17Li contacts relatively cool water

– Tritium permeation through cooling system pipe walls (Pb-17Li and He) will require permeation barriers. Alumina coatings on steel (50 μm) have been demonstrated to reduce permeation by 10 to 1000, but it is not clear that these coatings will survive the temperature swings of the helium piping during pulsed operation. These coating will be engineered administrative controls for personnel safety.

– The quantity of Po-210 produced approaches levels of a safety concern if we are asked to assume a complete release of this inventory directly to the atmosphere as a ground release. Cleanup of the Po-210 may be required; however if extraction columns are used to remove T2 from the Pb-17Li then most of the Po-210 will likely end up in the tritium purge gas system

– Present estimates of TBM tritium inventories are based on a prototype ferritic steel tube vacuum permeator keeping the tritium partial pressure to less than 2Pa. Test will have to be conduct to prove this technology. If extraction columns are used, then the tritium inventory could grow to 7 g, requiring more detailed accident mobilization and release calculations to demonstrate that the TBM meets radiological limits

Safety R&D• The anticipated Safety R&D projects required to resolve these

issues are:

PbLi spray/H2O reaction testing to determine percent of Li reacted for prototypical conditions. ($2 - 5 M - 3 to 5 years)

Tritium permeation barrier integrity during thermal cycling ($2 - 4 M; 3 to 5 years)

Tritium extraction tests to verify vacuum permeators ($2 - 4 M; 3 to 5 years)

Costs and schedules will be refined in more detail as we go forward and optimize conceptual approaches to each experiment

• Cost estimates are based on similar work done by the FSP during the ITER EDA.

Potential Safety ExperimentsSupporting the US ITBM Program

PbLi Reactivity During LOVA

• simulates LOVA with pooling water and sprayed molten PbLi

• single and multiple droplet sizes or streamed injection

• variable surface area of exposed water

• gas analyzer measures moisture content and H2 generation

• view ports allow imaging of reaction surfaces, temperature measurements, and droplet dynamics

Potential Safety ExperimentsSupporting the US ITBM Program, cont.

Thermal Cycle Performance of He Pipe Permeation Barriers

• simulates thermal stress degradation of permeation barrier coatings for He pipes

• configuration matched to TBM design for coated components

• utilize tritium for barrier technology qualification

• external thermal cycles followed by testing in permeation rig for integrated effects

• in-situ thermal cycling in permeation rig for barrier dynamic response

Summary