# Presentation: 693637

## Concrete Filling of the TFTR Vacuum Vessel

- Steve Raftopoulos
**D&D Lessons Learned Workshop**
**June 25-26, 2002**
**PPPL**

## Requirements

- The concrete shall provide:
- Stabilization of tritium.
- Void fill as required for Rad Waste burial.
- Shielding from gamma.
***Cleaning of the diamond wire***

## Concerns

**Would tritium (that was bound in graphite tile at ambient conditions) be released by:**
- The moisture introduced during the concrete pouring?
- The heat generated during the curing process?
**Would hydrostatic pressure rupture windows and/or bellows?**
**Would pressure increase during curing period vent tritiated gas?**
**Would slumping of the concrete leave graphite tiles exposed at the top of the vacuum vessel?**
**Would the vendor’s equipment become contaminated during the pouring process?**
**Could the room HVAC pressure zones be maintained during the pouring process?**

## Prototype Test of Concrete

- We filled two sets (4 total) surrogate vacuum vessel segments with low density concrete.
- Various height lifts were attempted; It was determined that filling the vacuum vessel in three lifts was best.
- Some settling was always observed. We suspected that the final lift was being collapsed by the increase in pressure generated during curing.

## “Tile-in-Concrete” Test

***1⁄2 gram tritium co-deposited in the vacuum vessel inner walls (st.steel) and graphite tiles.***

- Actual tiles removed from the TFTR vacuum vessel and used in experiments to verify concrete stabilization of tritium.  These tiles were placed into a 5 gallon container which was filled with the lightweight concrete.
- Temperature, pressure and tritium concentrations were monitored as the concrete cured.  Results indicated that tritium was NOT liberated from the tiles in appreciable quantity.

**Notes:**
Concrete filling of VV
Concerns
1⁄2 gm T2 in tiles
Would the pouring/hydration of the concrete release this tritium?
Would the concrete stabilize the T2 and make the DWC process safe?

## Vacuum Vessel Preparation

- All re-entrant devices removed from the vacuum vessel
- Probes, illumination devices, etc.
- Hydrostatic integrity of the vacuum vessel upgraded by:
- Removal or re-enforcement of vacuum windows
- Removal or re-enforcement of bellows
- Lexan inspection/lighting ports installed at several locations.
- Concrete-fill measuring system,“dip sticks”, installed at two locations.
- Filling station,vent and recirculation ports installed at top of vacuum vessel.

## Concrete that Floats!!!

- The **CO****2**** cooling** of the diamond wire provided adequate cleaning, therefore the requirement for the concrete to “scrub” the wire was eliminated.  This allowed the use lightweight concrete.
- The concrete is a **low density** (~ 35ft3) product, that is commercially available.
**Geocell **foam additive replaces aggregate, and provides aeration.
- Cement and Geocell additive are combined to achieve the low density.
- Cure times are consistent with conventional concrete, (i.e. hours to set, 28 days full strength).
- Concrete adds **94,000 lbs to VV weight**, or 9,400 to each removed segment.

## Vendor Mobilization

## Vendor Mobilization

- Vendor provided a turnkey system for delivering concrete to the TFTR Test Cell.
- D&D personnel handled the filling process, while Vendor operated only his equipment.
- Containers provided to Vendor for flushing of effluent(s).  Engineering and administrative controls prohibited effluents from entering the storm drain system, or running off to the watershed.
- With ERWM and HP concurrence, the Vendor was allowed to release limited quantities of water to graveled areas (where it slowly percolated into the soil).
- Vendor returned on subsequent days and provided concrete for each lift.
- 105 cubic yards of concrete were pumped into the vacuum vessel.

## Filling Hardware

**Aerated concrete would not withstand the nine-foot drop from the top of the vacuum vessel.**
**A pouring station, with tubes that minimized the drop, was installed.**
**The shorter tubes were used on the subsequent days’ pours.**

## Pouring the Concrete

**Technicians connecting the concrete hose to the pouring station.**

## Controlling Effluent Gas

- During the concrete filling of TFTR, the vacuum vessel was a controlled, sealed volume. (as it had been all along)
- As the concrete was poured into the vacuum vessel,  the displaced air had to be exhausted.
- Provisions were made to exhaust to:
- The stack via the vacuum vessel ventilation system
- The stack via bubbler
- Torus Cleanup System via the Diagnostic Exhaust Vent
- The default venting path was the stack via bubbler (10:1 Decontamination Factor “DF”).
- Switch over to other paths was dictated by the measured released tritium.

## Gas Handling System

## Concrete Filling of Vacuum Vessel

- Results
- Vacuum vessel filled in three lifts.
- No slumping observed.
- Complete wetting of inner surfaces.
- ~15 curies total released during pouring and curing periods.

## Conclusion/Lessons Learned

**The concrete was a very effective means of stabilizing the internal contamination.  The filling/curing process ****did not liberate tritium**** from the graphite tiles.**
**The gas handling system was effective in controlling overpressure during the curing process.  The result was ****NO**** slumping of the concrete.**
**The ability to route exhaust gasses, to systems with various levels of detritiation, allowed us to ****minimize the release of tritium,**** without unnecessarily burdening the tritium oxidation system.**