LBNF Tritium mitigation by scrubbing Jim Hylen TSD topical meeting - - PowerPoint PPT Presentation

▶
lbnf tritium mitigation by scrubbing
SMART_READER_LITE
LIVE PREVIEW

LBNF Tritium mitigation by scrubbing Jim Hylen TSD topical meeting - - PowerPoint PPT Presentation

Nov 15, 2023 106 likes •324 views

LBNF Tritium mitigation by scrubbing Jim Hylen TSD topical meeting 21 November 2019 DAC (Defined Air Concentration) DAC is amount of radiation in air that: Would gives 5 rem dose to workers in 2000 hr work year. = 2.5 mrem/hr, = 100

slide-1
SLIDE 1

LBNF Tritium mitigation by scrubbing

Jim Hylen TSD topical meeting 21 November 2019

slide-2
SLIDE 2

DAC (Defined Air Concentration)

11/21/2019 Jim Hylen | LBNF Tritium mitigation 2

  • DAC is amount of radiation in air that:

Would gives 5 rem dose to workers in 2000 hr work year. = 2.5 mrem/hr, = 100 mrem in 40 hr work week.

  • For tritium in form of HTO, DAC is 20 pCi/cc of air. (Humidity)
  • At 25 C, 100% RH, it translates to about 852,000 pCi/ml of water

At FNAL, we don’t let water get tritiated much beyond 800,000 pCi/ml, so that leaks/spills can’t get the air above a DAC.

  • Work restrictions required if Tritium in air > 10% DAC

Note we are trying to design LBNF to stay below 10% DAC

slide-3
SLIDE 3

During NuMI operation, MI-65 ventilation

11/21/2019 Jim Hylen | LBNF Tritium mitigation 3

AHU 1 AHU 2 AHU 3 Pile Dehum Evap EAV2 Absorber Condensate stair shaft Hi-Bay Target Pile Target Hall Shield door

AHU condensate up to 1,720 pCi/ml, AHU1, AHU2, AHU3 fairly similar Evaporator ~ 500,000 pCi/ml

  • f water in air

600 cfm 6,000 cfm

AHUs release condensate to sewer

slide-4
SLIDE 4

9/11/2018 short circuit to AHU during access at NuMI

11/21/2019 Jim Hylen | LBNF Tritium mitigation 4

AHU 1 AHU 2 AHU 3 Pile Dehum Evap EAV2 Absorber Condensate stair shaft Hi-Bay Target Pile Target Hall

Target pile open, target hall shield door open, pile dehumidifier off worst condition for exposure

Shield door

24,300 pCi/ml

  • f water in air

41,500 pCi/ml

  • f water in air

66,600 pCi/ml

  • f water in air

950 / 819 / 17,500 pCi/ml condensate to sewer 4% of DAC in target hall

slide-5
SLIDE 5

11/21/2019 Jim Hylen | LBNF Tritium mitigation 5

Yearly shutdown Yearly shutdown

Yearly shutdown

Yearly shutdown 300 kW

  • ps

540 kW

  • ps

700 kW

  • ps

700 kW

  • ps

1) Large jump in tritium release when Duratek steel shielding got to ~ 100 C

(not smooth exponential in diffusion versus temperature)

2) Lower emissions during beam-off

No beam, upgrade for NOVA

Tritium concentration in dehumidifier water, evaporated to air

slide-6
SLIDE 6

Designing for LBNF access

Higher beam power -> more tritium

  • NuMI 700 kW beam power
  • LBNF eventually 2,400 kW beam power

Potential to trap tritium until a shutdown, then release in extended puff

  • NuMI leaky pile with humid air continually getting rid of tritium
  • LBNF sealed pile with dry Nitrogen fill could trap tritium

until open pile for access when humid air gets in

11/21/2019 Jim Hylen | LBNF Tritium mitigation 6

slide-7
SLIDE 7

GH local exhaust local exhaust airline mask anorak suit air supply line

The work wearing airline mask and anorak suit is hot and extremely tough. 2-hour is the upper limit for one work.

NBI-2019 “Muon Target Replacement” by N. Kawamura (JPARC)

slide-8
SLIDE 8

LBNF

Mitigation strategies being implemented for LBNF

  • Remove most tritium during beam operations by scrubbing with humidity (NuMI

experience)

  • Operate inner layer of steel (the cooling panels) at higher temperature (~100 C)

during operation, then cooler (room temperature) during access to encourage higher/lower release during running/access. (NuMI experience)

  • During access, increase air ventilation rate to dilute the HTO

– 1,091 cfm -> 22,300 cfm of air through target hall

  • Draw the air (to the extent practical) away from workers to a release stack

– Ventilation once-through, from target hall down into target pile, then up stack

11/21/2019 Jim Hylen | LBNF Tritium mitigation 8

slide-9
SLIDE 9

LBNF

LBNF: scrub tritium out of target pile with humidity during beam

11/21/2019 Jim Hylen | LBNF Tritium mitigation 9

Target Hall N2 in vessel Steel shielding releasing tritium

Comparison NuMI LBNF Target pile gas air N2 H2O in gas (ppt) 5 1 Condensate (gallon/day) 170 17

Plan to remove most of the tritium released from the shielding during beam running the same way we do for NuMI – pick it up with water vapor to HTO, and dehumidify. Require addition

  • f mist injection
  • f humidity

Dehumidifier for N2 gas was already in design Goal: Don’t build up large amount of tritium, which would come out in puff when

  • pening up

Calculations indicate parameters shown will

  • maintain the tritium transport path
  • keep built up tritium to reasonable levels

We are also optimizing ventilation to protect workers during access

slide-10
SLIDE 10

LBNF

During Target Pile access

11/21/2019 Jim Hylen | LBNF Tritium mitigation 10

Pre-target chase Target hall Target pile vessel Steel shielding Gas handling room Nitrogen vessel Filter chiller dehum. fan 22,300 cfm air Ventilation to help mitigate high Tritium release in target pile vessel

  • Pull tritium away from workers in nitrogen vessel
  • Use existing filter to pick up contamination before exhaust

Fresh air for workers Access target pile and gas handling just one at a time 22,300 cfm Exhaust to stack

OPEN OPEN CLOSED

Target pile gas system

slide-11
SLIDE 11

LBNF

During Target Pile Gas Handling access

11/21/2019 Jim Hylen | LBNF Tritium mitigation 11

Pre-target chase Target hall Target pile vessel Steel shielding Nitrogen vessel Filter chiller dehum. fan Ventilation modification stay away from high Tritium release in target pile vessel

  • CLOSE off main tritium reservoir (target pile shielding)
  • Turn off gas handling fan, use some small local ventilation

Access target pile and gas handling just one at a time Exhaust to stack

OPEN CLOSED CLOSED OFF or LOW

Gas handling room 0 cfm from absorber 22,300 cfm fresh air 22,300 cfm exhaust Target pile gas system

slide-12
SLIDE 12

LBNF

For the tritium scrubbing with humidity

11/21/2019 Jim Hylen | LBNF Tritium mitigation 12

Have set up a framework for tritium transport, and done 1st pass calculations:

  • Model elements – follow the Tritium path:
  • Tritium production in steel shielding (MARS MC)
  • Diffusion rate of tritium through steel
  • Steel to surface water layer tritium transfer
  • (surface water is few molecules thick)
  • Surface layer tritiated water to humidity exchange
  • Humidity turnover rate (injection and dehumidification)

The model calculations indicate the parameters shown earlier are sufficient to:

  • Maintain the surface physical-water layer that underpins the transfer calculations
  • Maintain a high gradient from steel to surface water layer for tritium transport
  • Keep the amount of tritium stored in the target pile humidity to reasonably low level

The model will be further refined and checked, and some prototyping may be done

Steel Surface water Humidity In N2 gas Dehumidifier Evaporter & stack to air

slide-13
SLIDE 13

First model iteration – assume equilibrium, locate possible rate limiting steps

The steel blocks need thin layer of water – (OH layer possible as base)

  • Nishikawa et al, Journal of Nuclear Materials 277 (2000) 99-105 “Tritium trapping capacity
  • n metal surface” subdivides surface water as

– Structural water – Chemically bound water – Physical water – most easily exchanged with gas

  • The formula they provide for physical water is calculated from partial pressure of

H2O, temperature, and a constant that depends on the metal surface

– In the range of 20 C to 100 C for their materials this is around a few E-4 mole/m2 – I put 1e-4 mole/m2 in the model to check if this essentially covers the surface, or we end up with partially dry surface -> looks fully covered to me – Note: used input H2O pressure 101 Pa (i.e. 1 atm at 1000 ppm H2O) – Note: very generic rough; our blue blocks and water cooling panels may vary

  • To get order of magnitude estimate of tritium stored in the water on surface of

steel, took WAG of 5000 m2 of steel surface, 3e-4 mole/m2 of water: get ~ 1 mCi

11/21/2019 Jim Hylen | LBNF Tritium mitigation 13

slide-14
SLIDE 14

11/21/2019 Jim Hylen | LBNF Tritium mitigation 14

slide-15
SLIDE 15

First model iteration – assume equilibrium, locate possible rate limiting steps

Molecular exchange between humidity and surface layer

  • I used our NuMI experience with tritium leaching out of the air when it went down

the decay pipe passageway to WAG how fast the humidity exchanges with a water layer. The time constant for NuMI was << 1 hr. I cross-checked this with some literature where people were doping tritium onto samples, and removing tritium from samples. It needs to be documented in a more refined manor, but this exchange rate appears to be fast enough to not be rate-limiting in this version of the calculation. Recall time scale of the diffusion in steel to water layer is days.

11/21/2019 Jim Hylen | LBNF Tritium mitigation 15

slide-16
SLIDE 16

First model iteration – assume equilibrium, locate possible rate limiting steps

Exchange rate between surface water and steel

  • My impression from those same studies of tritium is the transport between water

layer and near-surface steel is fairly fast, and should not be rate-limiting, but need better documentation.

  • Note there are barriers, like an oxide layer on stainless steel, that can significantly

slow down the transport. A cautionary statement in fusion research is “barrier layers tend to break down in radiation environment”.

  • The T in the steel can basically trade places with an H in the water layer
  • Is the layer of black iron-oxide at T2K on the vessel walls why there seems to be

significantly less release of tritium at T2K than NuMI?

11/21/2019 Jim Hylen | LBNF Tritium mitigation 16

slide-17
SLIDE 17

First model iteration – assume equilibrium, locate possible rate limiting steps

Equilibrium between water layer and steel

  • Assume ratio of tritium densities in the surface water to steel is the ratio of Tritium

Solubilities in water to steel

  • There is a measured solubility for tritium in stainless steel, but I have not located a

paper documenting solubility in more normal steel. Using some web information, assuming it is not hugely different between tritium and hydrogen, I used

– hydrogen solubility estimate of 0.3 (mole H/m3)/sqrt(Patm), (ref Ispat) – which given a water solubility estimate of 4E4 (mole H/m3)/sqrt(Patm) (very rough extrapolation from Sharpe et al “Tritium migration to the surfaces of stainless-steel, aluminum 6061, and oxygen free high-conductivity copper”) – and an assumption that both solubilities are at 1 atm, – gives a solubility ratio of 1.3E5

  • This is a very rough number now, but use it to do some calculations.
  • In humidify/dehumidify scheme, steel builds up concentration of equilibrium value

in a few minutes, so this transfer should not be rate limiting

11/21/2019 Jim Hylen | LBNF Tritium mitigation 17

slide-18
SLIDE 18

First model iteration 8 – assume equilibrium, locate possible rate limiting steps

Steel near target

  • 18% of produced Tritium is in the volume of the cooling panels nearest the target

– 2 sides x 7.32m x 2.24 m x 0.1016 m= 3.33 m3

  • > 26 metric tons

– ~ 1 mCi if entire block was at equilibrium

  • At that rate, the time constant of production build-up toward “equilibrium” is a few

minutes for those panels Conclusion: for tritium scrubbing with humidity as shown (1 ppt H2O in N2), diffusion through steel is the rate limiting effect, and that time scale is days for the highly irradiated cooling panels.

11/21/2019 Jim Hylen | LBNF Tritium mitigation 18

slide-19
SLIDE 19

LBNF/DUNE 11/21/2019 Jim Hylen | LBNF Tritium mitigation 19

Prototype test of tritium transport rate through steel through paint through surface water to gas

Is the tritium monitor a mass spec?

  • If use NuMI condensate

as HTO source, source is about 3e-10 HTO to H2O; need pretty sensitive monitor or some other Tritium source Is the tritium monitor a water sample to scintillation detector?

  • But need a significant

amount of water Is the tritium monitor the continuous monitor we have?

  • Detection level on edge?

Fe

Humidity

STEEL Separator

Humidity with HTO

Chamber One Chamber Two Tritium Monitors (what kind?)

HTO

T NuMI condensate?

  • Fig. curtesy of Sawtell
slide-20
SLIDE 20

Experiment outline

Can run experiment as function of:

  • Thickness of steel (1 mm, 10 mm)
  • Paint / no paint
  • Temperature: 20° C to 100° C
  • Humidity: e.g. 1 ppt H2O as proposed for LBNF, 5 ppt as NUMI
  • Gas: Nitrogen vs air (vs helium)
  • Radiation: none, or up to …

Like to Disentangle:

  • rate of transfer between gas and surface
  • rate of transport through steel
  • effect of paint on transport
  • effect of temperature on transport
  • effect of humidity on transport
  • possible effect of radiation on transport

Main point: want to baseline a tritium transport rate with close to LBNF conditions

11/21/2019 Jim Hylen | LBNF Tritium mitigation 20

slide-21
SLIDE 21

LBNF

LBNF: scrub tritium out of target pile with humidity during beam

11/21/2019 Jim Hylen | LBNF Tritium mitigation 21

Target Hall N2 in vessel Steel shielding releasing tritium

Comparison NuMI LBNF Target pile gas air N2 H2O in gas (ppt) 5 1 Condensate (gallon/day) 170 17

Plan to remove most of the tritium released from the shielding during beam running the same way we do for NuMI – pick it up with water vapor to HTO, and dehumidify. Require addition

  • f mist injection
  • f humidity

Dehumidifier for N2 gas was already in design Goal: Don’t build up large amount of tritium, which would come out in puff when

  • pening up

Calculations indicate parameters shown will

  • maintain the tritium transport path
  • keep built up tritium to reasonable levels

We are also optimizing ventilation to protect workers during access