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VOLUME REDUCTION AND SAFE STORAGE OF PRESSURE TUBES (FROM EMCCR OF MAPS-I) FOR FUTURE RECYCLING OF

PRECIOUS HAFNIUM-FREE ZIRCONIUM

D. Anji Reddy*, G. Chenna Keshavulu and Biplob Paul Centralised Waste Management Facility, Kalpakkam

*Corresponding author email: [email protected] Shri Biplob Paul, Nuclear Recycle Board and his team received the Shri Biplob Paul, Nuclear Recycle Board and his team received the Shri Biplob Paul, Nuclear Recycle Board and his team received the Shri Biplob Paul, Nuclear Recycle Board and his team received the

DAE Group AchiDAE Group AchiDAE Group AchiDAE Group Achievement Award for the year 2013evement Award for the year 2013evement Award for the year 2013evement Award for the year 2013

Abstract At Centralised Waste Management Facility (CWMF), Pressure Tubes (PTs) were received from MAPS Unit–I & II during en-masse replacement of coolant channels as part of life extension. In 2002 campaign, Unit–II PTs were received as waste; cut into two half’s and permanently disposed in Tile Holes (TH) at CWMF. But in 2005 campaign, Unit–I PTs were stored in an SS lined pool under DM water for further processing for the recovery of hafnium free zirconium. At the end of the pool storage period, a process was evolved to reduce the volume of the PTs and store in dry condition in Tile Holes on campaign basis in a retrievable manner till a process for the recovery of zirconium is available in plant scale. A detailed process flow sheet was prepared; sub-systems were designed, fabricated and erected. Inactive trials were carried out successfully. Active operations involving retrieval of pressure tubes, removal of shield plugs, compaction & shearing into small size pieces, collection of the pieces in SS drum and storage of the drum in Tile Holes were demonstrated to safety committee. After obtaining clearance, campaign of processing of 300 Pressure Tubes was completed successfully. This campaign was executed with due consideration to safety, minimization of radiation exposure and minimum use of precious waste disposal space. This paper outlines the design, erection and commissioning of the system and its component equipment. It also summarizes the challenges overcome and experiences gained during this maiden campaign for storage of a wealth of 11 tons of zircalloy for future retrieval of Hf-free zirconium. Introduction The MAPS is a heavy water cooled and heavy water moderated Pressure Tube type CANDU reactor. Each pressure tube is inside an outer tube called Calandria tube. Pressure tubes play an important role by isolating the high pressure primary coolant and the moderator. During 2005, the PTs of the MAPS-1 reactor were replaced enmasse due to various factors like induced neutron / hydride embrittlement, creep / growth, fatigue & corrosion etc. After their removal from the reactor, the PTs (contact dose ~1000s of R/h) were transported to CWMF in shielded casks as Category-III radioactive solid waste1 and stored in an SS lined pool in racks under DM water. Figure-1 shows the view of the pool before and after storing of PTs.



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Fig.1: View of the pool before and after storing of PTs

The irradiated pressure tubes with shield plugs had a large inventory of activation product radionuclides; namely Cr-51, Co-58, Fe-59, Co-60, Zr-95, Nb-95, Hf-181, Zn-65, Sb-124, Sb-125. The longest half life amongst these radionuclides was of Co-60 i.e.5.3 years. The radioactive wastes inventory as on 2010 2 measured before the campaign for design requirements were as given in Table-1.

Table 1: Inventory of Radioactivity as on 2010

Item Qty(Nos.) Activity content Dose rate on contact

PT with shield plugs

inside

298 441040 TBq (11920 Ci)

250 -300 R/h

Calandria tube

2 2960 TBq (80 Ci)

At the end of the pool storage, it was decided to reduce their volume and store them retrievably in tile holes for future recovery of zirconium. A detailed process flow sheet was prepared for these operations. The sub-systems were designed, fabricated, erected and commissioned. Safety committee approval obtained for campaign on the retrieval of pressure tubes (PT) from pool, their volume reduction and storage of the drums in Tile holes. The Campaign In each cycle of the campaign, one pressure tube, now with surface dose of 100-150 R/h (reduced from 1000s of R/h due to decay of short lived radionuclides), was retrieved from the



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pool using a split cask and processed. The following paragraphs describe the equipment used and operations carried out during the various steps of the campaign. Retrieval of PTs from Storage Pool The specialty of the split cask is that it is split horizontally with a removable top-half and at the same time, has ports at both ends for axial movement of the PT. To retrieve the PT from the pool, the bottom piece of split cask was lowered using 20 Te gantry crane and placed on the pad provided inside the pool. A pressure tube was taken out from the rack using a pneumatic tube handling device and placed in the cavity of the split cask. Split cask cover was next placed over the lower portion. The entire assembly of split cask was then lifted out of water and held over the pool for sufficient time to allow the water to drain completely. The cask was then shifted to Shield Plug Removal Station (SPRS) which is a 150 mm MS shielded and ventilated enclosure. Figure-2 shows the operation carried out in the storage pool.

Fig.2: Operation carried out in the storage pool Removal of Shield Plugs from PTs

Before transfer of pressure tubes from MAPS, two shield plugs on either ends were pushed into the tubes. So, prior to taking up compaction and cutting of PTs, the shield plugs were to be removed and it was carried out in Shield Plug Removal Station (SPRS). The split cask, with the pressure tube inside, was placed on a trolley at one end of SPRS with the help of the crane and mated with enclosure port. A shield plug collection device was placed on its trolley on the other side of the enclosure, aligned and sliding doors of the ports were opened. The tube was fed into the enclosure using pusher ram.It was held there with clamps and burr on ID of the PT removed using wedge shaped conical cutter. Next, the shield plug was pulled out of the PT into the cask with a special shield plug removal tool. After closing the ports, the shield plug was transferred to a drum and disposed in RCC Trenches. The pressure tube was retracted into split cask, sliding door closed and the split cask was rotated by 180°. The other shield plug was also removed similarly and the cask with

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PT was next transferred to Compaction and Cutting Station (CCS). FigureShield Plug Removal.

Volume Reduction of Pressure Tubes Compaction and Cutting Station (CCS) was also a 150enclosure. Compaction and cutting machine was housed in the enclosure. It also had a manipulator to collect the PT pieces which get dislocated from the up cutting, the split cask was aligned to the enclosure port of CCS, sliding door was opened and the tube was fed into CCS in incremental movements of 200After each feed, the length of 200sheared with 100 Te ram. The operation was controlled using a PLC based control system supported by view through a CCTV camera. The chopped pieces were collected through hopper in an SS drum located on the retrieved into the drum disposal cask through bottom opening door. Figureof volume reduction operations at CCS.

Fig. 4: Views of Volume Reduction Operations



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PT was next transferred to Compaction and Cutting Station (CCS). Figure

Fig.3: Shield Plug Removal Station

Pressure Tubes

Compaction and Cutting Station (CCS) was also a 150 mm MS shielded and ventilated enclosure. Compaction and cutting machine was housed in the enclosure. It also had a manipulator to collect the PT pieces which get dislocated from the intended position. For taking up cutting, the split cask was aligned to the enclosure port of CCS, sliding door was opened and the tube was fed into CCS in incremental movements of 200 mm by operating the feeding ram. After each feed, the length of 200 mm was flattened using the 150 Te compaction ram and

Te ram. The operation was controlled using a PLC based control system supported by view through a CCTV camera. The chopped pieces were collected through hopper in an SS drum located on the trolley below the hopper. Five tubes were cut and the drum was retrieved into the drum disposal cask through bottom opening door. Figureof volume reduction operations at CCS.

4: Views of Volume Reduction Operations

PT was next transferred to Compaction and Cutting Station (CCS). Figure-3 shows the view of

mm MS shielded and ventilated enclosure. Compaction and cutting machine was housed in the enclosure. It also had a

intended position. For taking up cutting, the split cask was aligned to the enclosure port of CCS, sliding door was opened and

mm by operating the feeding ram. Te compaction ram and

Te ram. The operation was controlled using a PLC based control system supported by view through a CCTV camera. The chopped pieces were collected through hopper

trolley below the hopper. Five tubes were cut and the drum was retrieved into the drum disposal cask through bottom opening door. Figure-4 shows the views



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Storage of PT pieces in Tile Holes

The SS drum with five PTs cut pieces in the disposal cask was transported to Near Surface Disposal Facility and stored retrievably in tile holes for future recovery of zirconium. Obstacles Overcome During Inactive Trails

After completion of fabrication and erection works, trials were carried out with inactive zirconium alloy tubes to validate operating and maintenance procedures. This resulted in the following improvements:

� Compensatory shielding was provided at enclosure ports of CCS minimizing radiation field in the working area during the actual campaign.

� Chamfering was carried out on split cask door port for smooth movement of the shield plug from PT into the cask.

� PT guiding unit was modified to fully encase the Pressure tube to prevent fragments from spilling out (and remain in guiding unit) & for smooth retraction of PT into the cask.

� Machine base and hopper was modified so that the cut pieces fall automatically into the SS drum.

� Modification was carried out on SS drum lid hinges to limit the angle of rotation of lid and automatic closing during its movement to cask bottom position.

Active Trails – Further Challenges Faced

Active operations with actual 5.2 meter long pressure tubes with surface dose rate of few hundreds of R/h were demonstrated to safety committee representatives. During the trials following difficulties were faced and overcome successfully.

• Shield plugs could not be taken out of the tubes due to presence of burr on inner diameter of the PT. This was because PT's were cut out from their original location at MAPS using a chip-less cutting machine with a disk cutter feeding from ID to OD. Due to this, deformation occurred on the inner surface of the PT, reducing its ID by about 1mm at cut ends. Hence, an additional step of removal of burr using a wedged shaped cutting tool was introduced in the procedure for the removal of shield plugs. With this modification in the SP removal procedure, all the shield plugs could be removed without any difficulty during actual operations.

• In Compaction and Cutting Chamber, after flattening of the PT, while shearing it was observed that a few pieces are travelling like projectiles and falling outside the chute provided for collecting the pieces. The shortcoming was overcome by providing a hood to the cutting ram.



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Operational Experiences

Some interesting experiences are shared below:

� During the campaign, the burr removal tool wore out twice i.e. after processing about 60 and 220 tubes; the tool was changed with new tool and operation continued.

� During the campaign, the shearing tool was changed after processing 29 PTs. Since the available shearing tools were found to wear out too soon, after a review of the tool material, shock resistant tool steel was selected and tool fabricated. The new tool needed replacement only once i.e. after processing 222 PTs.

� Replacement of HEPA Filters: First and Second filters were replaced during processing of 23rd and 43rd PTs. To reduce the load and to prevent contamination of ducting, a pre-filter was installed at enclosure exhaust. The third & fourth HEPA filters needed replacement at 154th & 252nd PTs. Final HEPA filter was disposed after completion of campaign.

� Cut pieces of only 5 PTs were placed in one drum against envisaged 10. About 60 drums have been stored in 12 Tile Holes

Conclusion

� The campaign of retrieval, volume reduction and storage of high active pressure tubes involving their handling in heavy lead shielded casks and enclosure was completed successfully.

� About 11 tones of pressure tubes could be reduced to a minimum volume and safely stored retrievably in Tile Holes from where these can be taken out at a later date for recycle & reuse of precious zirconium.

� The NSDF area consumption was about three times less when compared to the MAPS Unit–II PTs disposal that was carried out in 2002.

� No overexposure or internal contamination reported in the campaign. Post-Campaign Activities And Campaign Closure

The campaign was closed after completing the following Post-campaign activities:

� The Pre-filter (dose rate~3.5 R/h) & HEPA filter (dose rate~1.5 R/h) of the Compaction & Cutting Enclosure were removed and disposed in RCC trenches.

� The clear liquid from the PTs storage pool was transported to liquid effluent treatment plant for further processing.

� The slurry was collected in four drums (each with ~100 l slurry) and fixed in cement matrix. The CWP drums were disposed in RCC Trench.

� The PTs storage pool was decontaminated. � The decontaminated SS lined pool has been kept for future use.

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Before Decontamination

Fig.5: Storage pool before & after Decontamination

Acknowledgement

The authors are grateful to Shri R C Sharma, Director, Reactor Group & Chairman, ULSCNRG for his valuable guidance provided at crucial points during the campaign. We also acknowledge the contribution of Shri B Madhu, HP, CWMF who played a very important rby not only ensuring radiological safety during the entire campaign but also by working closely with the engineers in solving the problems encountered. The authors also would like to thank the core team of CWMF for their support during the campaign, esSmt S Chitra, Shri V. Subba Rao and Shri References

1. International Atomic Energy Agency, Standardization of radioactive waste categories, Technical Report Series No. 101, IAEA, Vienna, 1970

2. Safety Report on Retrieval, Volume Reduction and Storage of Pressure Tubes from EMCCR- 2005 (MAPS



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After Decontamination

Fig.5: Storage pool before & after Decontamination

The authors are grateful to Shri R C Sharma, Director, Reactor Group & Chairman, ULSCNRG for his valuable guidance provided at crucial points during the campaign. We also acknowledge the contribution of Shri B Madhu, HP, CWMF who played a very important rby not only ensuring radiological safety during the entire campaign but also by working closely with the engineers in solving the problems encountered. The authors also would like to thank the core team of CWMF for their support during the campaign, especially Shri G

Chitra, Shri V. Subba Rao and Shri K. Paramasivan.

International Atomic Energy Agency, Standardization of radioactive waste categories, Technical Report Series No. 101, IAEA, Vienna, 1970 Safety Report on Retrieval, Volume Reduction and Storage of Pressure Tubes from

2005 (MAPS-1) campaign.

After Decontamination

The authors are grateful to Shri R C Sharma, Director, Reactor Group & Chairman, ULSC-NRG for his valuable guidance provided at crucial points during the campaign. We also acknowledge the contribution of Shri B Madhu, HP, CWMF who played a very important role by not only ensuring radiological safety during the entire campaign but also by working closely with the engineers in solving the problems encountered. The authors also would like to thank

pecially Shri G J M Coelho,

International Atomic Energy Agency, Standardization of radioactive waste categories, Technical Report Series No. 101, IAEA, Vienna, 1970 Safety Report on Retrieval, Volume Reduction and Storage of Pressure Tubes from

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