Fuel Management in EWN

Transcription

1 Fuel Management in EWN Fuel Management in EWN Dr. Helmut Förtsch, EWN GmbH Eberhard Thurow, EWN GmbH

2 Fuel Management in EWN Part 1: Status in 1990 Part 2: Spent nuclear fuel strategy of EWN Part 3: Technical requirements Part 4: Licensing requirements Part 5: Loading procedure for CASTOR 440/84

3 Fuel Management in EWN Part 1: Status in 1990

4 Status in 1990 After the final shut down of the nuclear power plants in Greifswald (KGR 5 units) and Rheinsberg (KKR 1 unit) there were on the sites: 934 fresh fuel elements (FE) and 5283 used fuel elements FE in the reactors of units 1 to 5 in KGR 1628 FE in the cooling ponds of units 1 to 5 in KGR partly in two levels, 3 of them damaged 2398 FE in a wet interim storage on KGR-site 246 FE in the cooling pond of KKR, 26 of them damaged In addition, 68 Pu/Be-sources and 53 ionisation chambers with nuclear fuel had to be disposed of in KGR. In Germany a final storage for nuclear spent fuel does not exist.

5 Fuel Management in EWN Part 2: Spent nuclear fuel strategy of EWN

6 Spent nuclear fuel strategy of EWN Due to political reasons, the efforts to return the spent fuel elements to Russia according to the former procedure did not succeed. Also negotiations on the reprocessing of these fuel elements in France and England were not been successful due to economical reasons. According to the unification treaty of the two German states from 1990, it was possible to use the existing wet interim storage facility (ZAB) on the KGR-site for spent fuel storage (exclusively for EWN needs).

7 Spent nuclear fuel strategy of EWN With the decision to build an interim storage facility (Interim Storage Facility North - ISN) at the Greifswald site, the following strategy for the disposal of nuclear fuel was realised: Sale of all fresh FE and low burned- up FE from unit 5 to interested foreign customers Transfer of the FE from the units 1-5 of the KGR to the wet interim storage facility according to licensed technology Temporary storage of the remaining FE which could not be stored in the wet interim storage facility (only 4680 places available) in CASTOR casks 440/84 in the units 3/4 This strategy was realised in the period between 1994 to 1997.

8 Spent nuclear fuel strategy of EWN After the construction of the ISN and the installation of the reloading unit in unit 3 (ULE 3) it was possible to transport the FE from the wet interim storage facility (ZAB) by C-30-casks (wet) to the reloading pond of unit 3 and reloading into CASTOR-casks; transport and storage of CASTOR-casks (dry) in the new ISN (The loading of CASTOR-casks in the wet storage facility was not possible, because the building was not designed for higher crane loads. There was also not enough space for the clearance of the casks.) pack the off-standard FE, load them into special CASTOR casks and transport them to the ISN pack of the Pu/Be - sources and the ionisation chambers (with nuclear fuel) and load into a CASTOR cask 440/84 These activities started in 1998 and were completed in June In Rheinsberg 4 CASTOR casks were loaded, one of them with a special basket for damaged FE, and transported to ISN by train in 2001.

9 Spent nuclear fuel strategy of EWN Greifswald site

10 Fuel Management in EWN Part 3: Technical requirements 3.1 CASTOR 440/ Reloading unit Drying equipment 3.4 Cooling down equipment 3.5 Transport means 3.6 Dry interim storage facility (ISN) 3.7 Special equipment for damaged FE

11 Technical requirements CASTOR 440/84 The CASTOR 440/84 has been developed for the transport and storage of 84 hexagonal spent FE, fuel parts of control assemblies and different core components of pressurized water reactors (type WWER 440 and 70). The cask consists of a thick-walled cylindrical body made of cast iron with ball graphite and a double lid system as well as a basket for the FE. The basket consists of 84 hexagonal tubes of borated stainless steel. The two lids (primary and secondary lid) enclose a special controlled pressure area (buffer space) with a higher pressure than in the cask inner room and the exterior environment. Thus, in connection with a pressure switch, the cask tightness during the storage can be controlled. For the protection against mechanical and weather influences, a protection plate is placed above the double lid system. In the cylindrical body of the cask, there are rods of Polyethylene for the improvement of neutron absorption. Radial fins at the outer surface of the cask increase the heat transfer. At the top and bottom ends, trunnions are attached for handling.

12 Technical requirements CASTOR 440/84 mass (empty cask): 94.7 Mg outside length : 4.08 m diameter with trunnions: 2.72 m diameter of the cask shaft: 1.8 m

13 Technical requirements Reloading unit 3 It consists of: - reloading pond with the original deposition place for C-30 casks - reconstructed cooling pond with a new deposition place for CASTOR 440/84 casks - ion-fork for fuel elements control by EURATOM/IAEA - different reflectors and TV-cameras (mobile on vertical rails) - water cleaning equipment (pumps and filters) - reloading machine equipped with improved instrumentation and for automatic operation. The reloading process from C-30 to a CASTOR cask was performed FE by FE with the reloading machine.

14 Technical requirements Reloading unit 3 C-30 cask water cleaning filters / pumps ion-fork CASTOR 440/84

15 Technical requirements Reloading unit 3 reloading machine

16 Technical requirements Drying equipment The mobile filter and drying facility (MOFTA) consists of: - vacuum pump with condenser and filter systems, - valve and measurement instrument unit, - power supply and control unit, - compressed air tank. The condenser system separates the humidity part of exhausted inner cask gas, collects the condensate for volume measurement and for sampling. The filter system (5µm) separates solid air particles. The remaining humidity and the pressure can be measured with the valve and measurement instrument unit. In case of power failure all valves close by compressed air.

17 Technical requirements Cooling down equipment In case the tightness criterion of the primary lid was not fulfilled the cask had to be cooled down and the sealing had to be exchanged (or the cask had to be unloaded). The surface temperature of the FE were about 140 C, which required a specia l equipment for cooling down. Design of cooling down unit - supply unit for demineralised water with measurementand control- equipment - discharge unit for steam and demineralised water with measuring- and control- equipment - equipment for Kr 85 - detection of the exhausted inner cask gas The cask was de-aerated and filled with demineralised water. Heated demineralised water and generated steam were discharged into the reloading unit. The activity concentration of Kr 85 was measured before and after filling with demineralised water. With the help of these results conclusions could be drawn about additional un-tight FE resulting from the cooling down process.

18 Technical requirements Transport means C-30 (86 Mg - loaded cask) Can be placed on a railway wagon or a road heavy load platform; standing transportation with a protection cover The CASTOR 440/84 (116 Mg - loaded cask) Lying transportation in a rack, with buffers on both sides, can be placed on a railway wagon or on a road heavy load platform.

19 Technical requirements Dry interim storage facility (ISN)

20 Technical requirements Dry interim storage facility (ISN) Storage Hall 8 area: ca m² length: ca. 192 m width: ca. 17 m height: ca. 18 m equipped with: 120 potential deposition places for spent fuel casks cask monitoring system (tightness control) for 80 casks bridge crane (140 Mg) with coordinate control passive ventilation. Only 65 storage places are needed for the casks with FE from NPP Greifswald and NPP Rheinsberg. The remaining places serve as a reserve.

21 Technical requirements Dry interim storage facility (ISN) Caisson 5 is used as a service place for secondary lid change in case of untightness, for adjustment of the pneumatic pressure switch and the He-atmosphere between primary and secondary lid before the cask is connected to the cask monitoring system in hall 8 of ISN.

22 Technical requirements Special equipment for damaged FE The different parts of the 3 damaged FE were packed by special gripping devices into sleeves and special pennals (canister). New baskets were constructed for the CASTOR KRB-MOX. These baskets are a welding construction and accommodate the sleeves and the special pennals. After successful cold testing the 3 CASTOR KRB-MOX casks were positioned in the reloading pond of unit 1. The canisters with the different parts of damaged FE were put into the baskets under water. The clearance of the loaded CASTOR KRB MOX casks comprises nearly the same working steps as for the CASTOR 440/84 cask. Due to the small heat power of the inventory, the CASTOR KRB MOX casks were heated during drying.

23 Technical requirements Special equipment for damaged FE Damaged spent FE

24 Technical requirements Special equipment for damaged FE The CASTOR KRB MOX mass (empty cask): outside length: diameter with trunnions: cask shaft: 53 Mg 4.9 m 1.97 m 0.52 m

25 Technical requirements Special equipment for damaged FE The loaded CASTOR KRB - MOX

26 Fuel Management in EWN Part 4: Licensing requirements

27 Licensing requirements For the loading and handling of the CASTOR casks 440/84 in the plant, a licence was required according to 7 of the Atomic Law. The transports from the KGR plant to the ISN were considered as internal transports on the site, whereas the rules for theses transports had to follow the legal traffic regulations. For the storage of the casks in the ISN, a licence is required according to 6 of the Atomic Law.

28 Licensing requirements Requirements for CASTOR loading and storage max. number of fuel assemblies 84 max. residual heat power kw 12.5 max. activity Bq 2.7 E+17 max. residual humidity after drying - inner cask room - buffer space - between sealings g/m³ g/m³ g/m³ permissible water mass in total in the CASTOR atmosphere g 21 He-leak rate of the first barrier hpa l/s 1.0 E-7 He-leak rate of the second barrier hpa l/s 1.0 E-7 gas environment Helium gas pressure after tightness test hpa min. 450 max. 500 gas (He) pressure in the buffer space hpa 6000 number of adsorption candles 2 surface dose rate surface contamination msv/h Bq/cm² special permissible FE - configuration to decrease ambient dose outside the cask (γ) 0.3 (n) (ICRP-60) 4 (β,γ) 0.4 (α)

29 Licensing requirements FE-tightness For the residual humidity after drying of the inner cask room, it is important to know, how much water is in the untight fuel rods. Because these untight fuel rods can not be dried and so the remaining water of these rods can be released during the storage. That s why we have to differ between: tight (intact) FE - untight (defect) FE - i.e. all 126 fuel rods inside a fuel element are tight; i.e. the number of untight fuel rods inside a fuel element is unknown. Note: Individual fuel rods could not be removed from a fuel element.

30 Licensing requirements Variants of FE-tightness test 1. Sipping test was performed only for the reactor core of unit 1 in 1990 with a special equipment of SIEMENS, i.e. with a sipping bell for 7 FE. The indicated nuclides were I-131, Cs-134, -137 (this equipment was suitable only for the reactor core configuration and for a high level of residual heat power) 2. Integral measurement of loaded C-30 casks (thermal test) in 1997 and 1998 with measurement of the difference of radioactivity concentration (mainly caused by Cs-137) before and after heating up of at least 10 K. 3. The suction head is an EWN-construction. It is placed on top of the FE and interrupts the natural circulation through the FE. The indicated nuclide is Cs-137 measured by the inner suction head water before and after placing the head.

31 Licensing requirements FE-tightness test - results sipping test in 1990 (only for the reactor core of unit 1; after final shut down): 4 untight FE of 276 FE successful integral tests with the C-30 cask (tests of up to 30 FE in total - without untight FE): 36 C-30 with 1069 FE (including 235 sold FE) suction head method (individual testing of FE): 88 untight FE of 1484 FE (maximum 8 FE of a KB-30 basket were untight) The total rate of untight FE was ~ 3.6 %. (Note: In each KB-30 basket, which had not been investigated, we assumed 8 untight FE.)

32 Fuel Management in EWN Part 5: Loading procedure for CASTOR 440/84

33 Procedure 1. Loading and clearance of C-30 casks in the wet storage facility

34 Procedure 2. Transport of the a C-30 cask with the heavy load platform to the reloading unit and preparation of the C-30 for unloading

35 Procedure 3. Transport of empty CASTOR 440/84 through rail corridor into the reactor hall unit 3/4 to a service place 4. Dismantling of the secondary/primary lid 5. Deposition of the CASTOR in the reloading unit 6. Loading of CASTOR with 84 FE from 3 C-30 casks (under water)

36 Procedure 7. Placing the primary lid 8. Lifting the CASTOR from the reloading unit and 9. cleaning of the cask during lifting with a spray system 10. Transport to a service place

37 Procedure 11. Emptying and drying of the CASTOR, test of remaining humidity of the inner room, tightening and He-tightness test of primary lid 12. Mounting of the secondary lid 13. Drying and test of remaining humidity of the buffer space between lids 14. He-tightness test of the secondary lid

38 Procedure 15. Transport of CASTOR to the ISN

39 Procedure 16. Measurement of gamma and neutron dose rate 17. Transport from the reception area to caisson 5

40 Procedure 18. Adjustment of the pneumatic pressure switch and the heliumatmosphere between primary and secondary lid 19. Helium- tightness test 20. Mounting of the protection plate

41 Procedure 21. Transport into hall 8 of the ISN 22. Connection of the cask to the monitoring system

42 Procedure 23. Storage in hall 8

43 Fuel Management in EWN Thank you for your attention!