Ghent University Research Reactor THETIS: Unloading and Conditioning of Spent Fuel

Transcription

1 Ghent University Research Reactor THETIS: Unloading and Conditioning of Spent Fuel Myriam Monsieurs, Hubert Thierens, Isabelle Meirlaen, Karel Strijckmans, Ghent University, Luc Noynaert, Luc Ooms, Patrick Lewandowsky, Marnix Braeckeveldt SCK.CEN, Belgoprocess, NIRAS/ONDRAF Paul Luycx, Frankie Vermierdt Transnubel

2 Overview 1) History of the Thetis research reactor. 2) Problems and their solutions. Finding a destination for the spent fuel. Compensating for the lack of documentation of an old facility. Checking for micro-leaks in the fuel elements. Linking the manual operations at the Thetis site to the remote control operations at the Belgoprocess site. 3) Conclusions and lessons learned.

3 1)History of the Thetis research reactor.

4

5 Thetis research reactor: Type: Pool type Fuel: Low enriched uranium Moderator: Light water Reflector: Graphite

6 Construction of reactor Thetis

7 Thetis 1967: Commissioning Power: 15 kw

8 Thetis 1972 Core enlargement. Power: 150 kw nominal, 250 kw maximum.

9 Mainly used as a neutron source for : - Radionuclide production (material analysis) - Activation analysis.

10 Thetis final shutdown 19 th December 2003: Final shut down. Decommissioning strategy: In 2 phases: : Removal of fuel elements : Dismantling of the infrastructure.

11 2) Problems and their solutions.

12 2) Problems and their solutions. Finding a destination for the spent fuel. Overcoming the lack of documentation of an old facility. Checking for micro-leaks in the fuel elements. Linking the manual operations at the Thetis site to the remote control operations at the Belgoprocess site.

13 26 fuel elements present, (irradiated and non-irradiated) = 583 fuel rods. Possibilities: 1) Re-using the spent fuel. 2) Reprocessing of the spent fuel. 3) Storage and disposal of the spent fuel. Evaluation criteria: 1) Feasibility, 2) Safety, 3) Waste reduction, 4) Total cost

14 1) Re-use. Fuel rod: - Active pin height: 376 mm - Containing 5 % enriched UO 2 - Graphite plugs on both ends - Cladded AISI304L stainless steel - Average burn-up: 3.15 GWd/tIHM, - Maximum burn-up: 5.15 GWd/tIHM Fuel = exotic no end user. NO

15 2) Reprocessing. - Fuel = exotic. Acceptance criteria not OK. - Technical issues: cutting, repackaging, reprocessing, final storage. Total cost = high. Waste reduction = minimal NO

16 3) Intermediate storage + final disposal - New technique developped. - Technically feasible and available. - Total cost = lower than reprocessing. - No extra waste produced YES

17 Proposed scenario: Unload fuel at Thetis facility Place fuel in transport container Unload transport container at PAMELA facility Conditioning and storage at Belgoprocess

18 Installations at Belgopocess site: building PAMELA 131-X : treatment & conditioning building 127-X : storage 131-X 127-X

19 Conditioning of the spent fuel: Cut top and bottom plugs from each element. Conditioning in 400 l drum. Internal basket containing 4 concentric cylinders for fuel elements. Additional central cylinder for cut plugs. Use of special cement mixture containing LiNO 3 due to presence of Aluminium. Criticality.

20 Cutting at Belgoprocess

21 Proposed scenario: Unload fuel at Thetis facility Place fuel in transport container Unload transport container at PAMELA facility Conditioning and storage at Belgoprocess Cut elements

22 2) Problems and their solutions. Finding a destination for the spent fuel. Overcoming the lack of documentation of an old facility. Checking for micro-leaks in the fuel elements. Linking the manual operations at the Thetis site to the remote control operations at the Belgoprocess site.

23 Problem: - Thetis facility > 40 years of exploitation. - No update of the original safety report. - Changes made during exploitation without proper documentation. - Staff = mostly retired. no up-to-date technical information.

24 Solution: Consultation of retired staff members to share practical information of Thetis start-up and reconfiguration. Camera inspection of the reactor pool Creation of an up-to-date safety report of the Thetis facility.

25 Visual inspection Identification

26 Anomalies spotted: Standard bottom pin Off-center top pin Central top pin Round bottom pin

27 Proposed scenario: Up to date safety report Unload fuel at Thetis facility Place fuel in transport container Unload transport container at PAMELA facility Conditioning and storage at Belgoprocess Cut elements

28 2) Problems and their solutions. Finding a destination for the spent fuel. Overcoming the lack of documentation of an old facility. Checking for micro-leaks in the fuel elements. Linking the manual operations at the Thetis site to the remote control operations at the Belgoprocess site.

29 Problem: Only intact fuel elements can be transported to and accepted at the PAMELA facility - Fuel has been in Thetis pool for > 40 years. - No leaks evident from pool water samples: no major cracks. But: - How to check for micro leaks of the fuel? - How to make sure that the fuel element does not get damaged during transport?

30 Sipping test: Searching for micro-leaks in the fuel elements by reducing hydrostatic pressure. Technique: Element placed in sipping tube, - Tube hoisted to the surface, - 2h delay (sipping), - Water pumped in tube (15 min). - Sampling of sipping water. - Gamma-spectrometry of sample. Decision: leak or no leak.

31 Sipping test

32 Transport under special arragement by means of a leak-tight container (TNB 145) provided by Transnubel.

33 Leaktesting of tranportcontainer at Thetis and Belgoprocess.

34 Scenario: Unload fuel at Thetis facility Up to date safety report Sipping test Place fuel in transport container TNB 145 Transport Gent Dessel under special arrangement Unload transport container at PAMELA facility Conditioning and storage at Belgoprocess Leak test Leak test Cut elements

35 2) Problems and their solutions. Finding a destination for the spent fuel. Overcoming the lack of documentation of an old facility. Checking for micro-leaks in the fuel elements. Linking the manual operations at the Thetis site to the remote control operations at the Belgoprocess site.

36 Problem: THETIS Small facility. Original tools available on-site. Hands-on operation possible. PAMELA Large facility. Remote control cranes. Hands-on operation not possible. Interface necessary

37 Thetis: Original manual tools used for handling of fuel elements

38 Belgoprocess: All handling is done by remote-control

39 Solution: Placing sleeve into transport-container at Thetis. Creation of a specially designed lifting tool for the PAMELA installation.

40 Scenario: Unload fuel at Thetis facility Conditioning and storage at Belgoprocess v v Place fuel in transport container TNB 145 Transport Gent Dessel under special arrangement Unload transport container at PAMELA facility with special tool Up to date safety report Sipping test Place sleeve Leak test Leak test Cut elements

41 3) Conclusions and lessons learned

42 The unloading of the Thetis fuel was completed during the summer of The cumulative dose for the team at Thetis was only 404 µsv l drums of conditioned fuel were produced and stored at Belgoprocess.

43 Distribution costs 8% 25% On- site U Ghent 36% 31% Transport Treatment&conditioning Storage&disposal

44 Lessons learned: 1) Interface between Thetis facility use of transportcontainer unloading in Pamela installation, posed important challenges for all parties (licensing, technical, respect of planning) 2) Visual inspection by remote-controlled under water camera proved very usefull 3) Succesfull termination of project was important for the further dismantling of Thetis reactor

45 Thank your for your attention Acknowledgements: Operations and transport: Transnubel NV. Photography UGent : Courtesy of Hilde Christiaens, Communications Department, UGent UGent Memorie.