Inspection of PUSPATI 1 Reactor (RTP) Core and Control Rod

Transcription

1 TM Assessment of Core Structural Materials and Surveillance Programme for Research Reactors, June 2010, Vienna, Austria Inspection of PUSPATI 1 TRIGA Reactor (RTP) Core and Control Rod Zarina Masood Malaysian Nuclear Agency 1

2 Introduction

3 PUSPATI TRIGA Reactor 3

4 PUSPATI TRIGA Reactor PUSPATI TRIGA Reactor (RTP) is a 1MW pool type TRIGA MkII First critical: 28 June

5 PUSPATI TRIGA Reactor - Specification Type: 1 MW TRIGA MkII Critical: 28 June 1982 Fuel: 19.9% enriched U-ZrH No. Fuel : 112 (Core #14) (10@20%wt/, 16@12%wt, 86@8.5%wt) Coolant: Light Water Moderator: Light Water Reflector: Graphite Control Rod: Boron Carbide - 3 FFCR & 1 AFCR Neutron Source: Americium Beryllium Cooling System: Primary (natural convection), Secondary Irradiation Facility: PTS, Central Thimble, Dry Tube, 4 Beamports, Rotary Rack,Thermal Column, NuR2, SANS, Maximum Flux: 1x10 13 n/cm 2 /s 5

6 PUSPATI TRIGA Reactor Vertical Cross-section section 6 6

7 PUSPATI TRIGA Reactor (RTP) Horizontal Cross-section Radial Beamport 2 7 Radial Beamport 1 Rotary Rack Radial Beamport 3 Tangential Beamport 4 7

8 Fuel Element 8

9 Surveillance Method

10 Surveillance of Fuel Element, Control Rod & Core 10% of total number of fuel element and all fuel follower control rod inspected annually First visual inspection of core structure in Sept 2008 Type of inspection: Visual Inspection - underwater camera, boroscope Physical Dimension measuring tool (check for bowing or expansion) 10

11 Visual Inspection of Control Rod SHIM Control Rod REGULATING Control Rod Blemish 11

12 Position of Control 12 Rod in Core Top Core Grid Plate REGULATING Control Rod SHIM Control Rod 12

13 Water Quality & Radioactivity Water taken from the reactor tank was checked for ph, conductivity presence of ions radionuclides Poor quality of water would precipitate corrosion of the stainless steel SS304 cladding material and aluminium 6061-T6 core structure materail. The presence of fission products would indicate that there has been a cladding integrity loss. 13

14 Results and Discussion

15 Blemish on Regulating Control Rod Close up view of the blemish 15

16 Position of Blemish 40.6cm (16ins) 16

17 Visual Inspection of Core Grid Plate Boroscopy inspection of top grid plate 17

18 Water Quality and Radioactivity The PH of the reactor water (within the limit of 5.5 and 6.0 set by General Atomics) Conductivity < 2µmhos/cm 3 (or above 0.5MΩ/cm 3 ) as recommended by General Atomics. Anions tested: Fluorine, Chlorine, Bromine, NO2, NO3, PO4, SO4. analysis of these anions in reactor water does not show any abnormality when compared to de-ionised water. Chlorine content is between 0.01 and 0.06 µg/ml which is just slightly higher than that in de-ionised water (0.01 µg/ml). 18

19 Water Quality and Radioactivity It can be concluded that the water quality is within the specified limits set by the manufacturer and amount of anions present would not lead to corrosion of the stainless steel cladding. The radioactivity analysis carried out on the reactor water over several months before and after the control rod inspections showed no traces of fission products. Since there are no fission products detected in the reactor water, it can be concluded that there is no loss of cladding integrity. 19

20 Consultation with Manufacturer General Atomics replied via personal communication as below: the source of discoloration is exactly where the FFCR rubs against the bottom grid plate during operation. This rubbing is probably caused by either a bent connecting rod or some misalignment of the control rod drive. We have seen similar discoloration on some our FFCRs in the past and they have not been a cause of concern 20

21 Consultation with other TRIGA User Consultation via personal communication with Dr Sean O Kelly, Manager of the 1 MW TRIGA Reactor, University of Texas at Austin, USA, was carried out. It was explained that Similar blemishes in approximately the same location on all control rods were also observed.the stainless steel develops a high temperature corrosion layer which is dark and the occasional contact with the grid plate when the reactor is operating makes a cooler spot on the rod (less limiting). The control rods move slightly all the time due to the diffuser and primary pump flows on the connecting rods. This vibration cannot be avoided and is not a cause of concern normally. Changing connecting rods or aligning them will not remove the flow oscillations unless they are visibly bent which would be indicated by deep scratches on the fuel rod and changes in the rod drop times. 21

22 Action Taken

23 Control Rod Replacement The Safety Sub Committee recommended the replacement of both SHIM and REGULATING fuel follower Control Rod as a precautionary measure There were two spare fuel follower control rods and the replacement was carried out in Mac-April 2009 The core had to be re-configured since the control rods added fresh fuel into the core 23

24 Surveillance Programme Continue with present surveillance programme Enhance the online parameter monitoring of primary coolant ph, conductivity Annual dimensional measurement of control rods Explore other techniques for core structure assessment 24

25 Conclusion

26 The possible causes for the blemish found on the SHIM and REGULATIING control rods were investigated water quality was within the set limits no traces of fission products detected which indicate that the control rod cladding was still intact phenomenon is prevalent among TRIGA reactors. As a precautionary measure, both controls were replaced A new core configuration was implemented to account for the addition of the fresh fuel contained in the control rod. Currently the reactor is operating normally. 26

27 Reactor Staff during 25 th Anniversary,

28 The End. Thank You

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