2008 ISOE EUROPEAN SYMPOSIUM Turku Finland 25 27

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Unexpected radiological exposure during removal of the Lower Vessel Internals at Ascó 2 NPP Francisco González Tardiu Turku, Finland, 25 -27 June 2008 ISOE EUROPEAN SYMPOSIUM

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Index 1. Background description 2. Event description 3. Radiological consequences 4. Cause analysis 5. Corrective actions 6. In summary

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 1. Background description

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Background description (1/2) Ø 17 Refuelling outage Unit I (September 2004) while the Lower Internals were being replaced, three workers receiving doses of 8. 0, 7. 8 and 5. 2 m. Sv, respectively. Collective dose 27. 4 m. Svp. ØRadiation Protection measures, based on previous experience of this type of manoeuvres, were: • Specific radiation work permit (RWP), with access limitation to the affected area (elevations 42. 5 and 50). • Installation of shielding on the floor and handrail of the handling crane and polar crane. • Protection of the personnel directly involved in the manoeuvre by means of lead aprons. • Blocking of high radiation alarms of radiation transmitters TR- 2603 and 04 to facilitate communications between the operators on elevation 50.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Background description (2/2) CAUSES • Difficulty in orienting the lower internals with respect to the vessel guides • Interference between the support for the lifeline at the edge of the cavity, and the handling crane • Nor was there a contingency plan CORRECTIVE ACTIONS • Instructions for preliminary verifications to determine the exact position of the polar crane prior to the transfer to lifting over the vertical axis of the vessel. • Schedule of greasing the axial bearing and checking of the mobility of the hook during each refuelling outage. • Study on interferences between the hoisting device handrail and the upper cable run of the handling crane, and the lifeline support. • Establishment in the radiation work permit (RWP) of the maximum times in each position. • To include a contingency plan • Study of the possibility of modifying the components conditioning the correct entry of the lower internals in the guides and of the possibility of installing a remote control for the polar crane, allowing it to be used from the cavity.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 2. Event description

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (1/7) On 8 th October 2005, within the programme of activities for the 16 th refuelling of Unit 2, the personnel of a contractor firm were removing the lower internals, in accordance with the corresponding procedure, “Disassembly of the lower internals” Prior to the initiation of this manoeuvre • Radiation Protection measures, based on previous experience before detailed. • Detailed reading of Procedures, Human Factors and Lessons Learned from previous experiences (28 th and 29 th of September 2005) • ALARA meeting. The corrective actions deriving from the event in Unit I (2004) had been implemented. • RP, in accordance with the agreements reaching during the ALARA meeting, had authorised a work permit with an individual dose of 8 m. Sv, and times maximum stay of 3 and 2 minutes

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (2/7) Persons directly involved Manoeuvre Responsible Manager (1) Handling crane Maximum dose rates planned in the handling crane: 300 m. Sv/h Supervisor (1) Dose rates planned: 10 m. Sv/h Persons providing support (3) Two, to pull on the ropes attached to the tool One camera operator Operators Polar Crane (2) One, to relever Reactor Vessel

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (3/7) Radiation control Radiation Protection Supervisor (1) Elevation 50 At elev. 57 in Rx. General control and to evaluate the dose rate in the lower internal vertical axis. Radiation Protection Technician (1) At elev. 50. To control the dose in lower internal adjacent area, close to the position of the maximum exposure. Radiation Protection Technician (1) At elev. 50. To control exposure times. Radiation Protection Technician (3) To control accesses and people in the corridor at elev. 50 and down to lower elevations and to control dose rates in the stand area Handling crane

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (4/7) 1. Check that the level of the water cavity was at 49. 5 m, as established in the procedures. 2. The manoeuvre responsible manager stood over the fuel handling crane + 49. 5 m Stand Lower Vessel Internals Level 1 of the cavity Reactor Vessel

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (5/7) Handling crane 3. The manoeuvre responsible manager ordered the internals to be raised gradually. 4. He had to operate the internals hoisting tool in order to avoid a minor interference with upper beam of the handling crane. 5. The manager in charge, assisted by the Supervisor, determined the moment at which the operation should be interrupted (upper part < 52. 6 m and the neutron plate submerged at least 75 mm), through cameras in Level 1 and visual observation. 6. It was impossible to confirm that internals did not exceed 52. 6 m. Lower Vessel Internal

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (6/7) 7. Radiation Protection Supervisor from the wall of PZR measured 330 m. Sv/h instead 80/90 m. Sv/h expected. 8. Radiation Protection Technician that control the dose in lower internal adjacent area, could not contact the technician responsible for time controls (is in the wall of PZR, initially they were together), and tried to warn to responsible manager but he was unable to understand him. 9. The responsible manager started to rotate the internals from the handling crane. This operation should have been carried out in the storage area (Stand). Wall of the pressurizer

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Event description (7/7) Nozzle inlet 10. The Radiation Protection technician commented on the situation with the Supervisor, pointing out that the manager might be affected by a high dose rate; however, given the position of the internals it was decided to continue with the operations, since they were moving towards a radiologically safer position. 11. The internals were then moved towards their storage position and were submerged slightly more on entering level 2 of the refuelling cavity. Reactor Vessel Wall of the pressurizer

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 3. Radiological Consequences

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Radiological Consequences Collective Dose 39, 17 m. Svp Maximum Individual Dose 24, 52 m. Sv The legal limits were not exceeded (100 m. Sv in 5 years and 50 m. Sv in 1 year).

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Summary of radiation exposure received at the plants (m. Svp)

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Actual Source Term of the Lower Vessel Internals (m. Sv/h)

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 4. Cause Analysis

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Cause Analysis (1/5) perform… INAPPROPIATE ACTION THE RESPONSIBLE FOR THE MANOEUVRE EXTRACTED THE INTERNALS FROM THE WATER FURTHER THAN NORMAL by failing to properly implement the…. PREVENTION TECHNIQUES ERROR USE AND COMPLIANCE PROCEDURES that would have avoided. . DUE TO THE FACT THAT…. Ø THE PROCEDURE DOES NOT DEVELOP SPECIFIC INSTRUCTIONS TO CHECK THAT THE INTERNALS DO NOT PAS ELEVATION 52. 600

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Cause Analysis (2/5) perform… INAPPROPIATE ACTION THE MANAGER RESPONSIBLE FOR THE MANOEUVRE STOOD ON THE FUEL HANDLING CRANE by failing to properly implement the…. PREVENTION TECHNIQUES ERROR UNCLEAR OR COMPLEX WORDING that would have avoided. . DUE TO THE FACT THAT…. Ø THIS IS EXPRESSLY PROHIBITED IN THE PROCEDURE.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Cause Analysis (3/5) perform… INAPPROPIATE ACTION IS NOT ACTIVATED THE EXPOSURE TIME CONTROLS by failing to PREVENTION TECHNIQUES properly implement ERROR the…. PRE JOB BRIEFINGS TOM CONSERVATION DECISION COMMUNICATION that would have avoided. . DUE TO THE FACT THAT…. Ø Ø Ø THE PREJOB TOM REFERENCE THE INSERTION THAT GAVE PROBLEMS, THAT IS NOT REMOVAL OF THE LVI. THE CONTINUATION OF THE MANOEUVRERESTS ON THE REMOVAL OF BARREL WHEN THIS HAS JUST PRODUCED PRECISELY INCREASED DOSE. BETTER COMMUNICATION WAS SUITABLE FOR THIS MANOEUVRE.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Cause Analysis (4/5) perform… INAPPROPIATE ACTION THE RESPONSIBLE FOR THE MANOEUVRE NOT DETECTED AN ABNORMALLY HIGH ACCUMULATED DOSE by failing to properly implement the…. PREVENTION TECHNIQUES ERROR COMMUNICATIÓN that would have avoided. . DUE TO THE FACT THAT…. Ø RESOURCES SHALL BE USED INSUFFICIENT/INAPPROPRIATE FOR THIS SPECIFIC SITUATION. Ø NO ENSURES THAT THE MESSAGE IS UNDERSTOOD AT THE TRANSMISSION DON’T INSIST ON IT.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 Cause Analysis (5/5) perform… INAPPROPIATE ACTION THE RESPONSIBLE FOR THE MANOEUVRE ATTEMPTED TO ROTATE THE INTERNALS FROM THE HANDLING CRANE by failing to properly implement the…. PREVENTION TECHNIQUES ERROR • USE AND COMPLIANCE PROCEDURES • PRE JOB BRIEFING that would have avoided. . DUE TO THE FACT THAT…. Ø THE PROCEDURE SAY THAT TJIS MANOEUVRE SHOULD BE PERFORMED AT ANOTHER TIME. ü THE PRE JOB BRIEFING PREVIOUSLY HAD TO MAKE IT CLEAR TO ALL PARTICIPANTS WHAT ARE THE CRITICAL MOMENT.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 6. Corrective actions

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 33 corrective actions were proposed Procedures (2) Work practices (5) Verbal communications (2) Resources (1) Supervision (1) Work organization (5) Training (5) Others (12).

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 1. Corrective Actions directed at avoiding elevated levels of area radiation. Revision of the procedures: v To raise the refuelling cavity water to the maximum possible elevation. v To minimize the elevation of the lower internal to provide a maximum margin of 171 mm from the vessel flange. v Specific precautions, in order to minimise the degree of exposure to the parts of the internals implying the highest dose rate (nozzle inlets). v Installation of a laser level to set the maximum extraction quota. v Instructions regarding the number of cameras to be used to control the level of extraction of the internals over the vessel flange and possible interferences with the handling crane. v Contingency for remote polar crane stopping in the event of uncontrolled rising of the shroud.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 2. Corrective Actions to avoid high exposure of personnel ØLocation of the handling crane during manoeuvre in the transfer canal side, so that no personnel are in the reactor verticality, through which the Lower Internal is introduced or extracted, thereby avoiding interferences in its extraction or introduction. ØAssessment of the installation of an electrical spindle on the header of the polar crane avoiding the need to use ropes to rotate the lower internals, allowing the rotation to be maintained for alignment with the guide pins.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 3. Corrective Actions directed at covering all possible incidents. Development of an Action Plan: v Develop supervision criteria applicable to Radiation Protection, such that the different operations associated with movement of the internals be assessed as regards the dose rates to be received in each case. v Develop the control procedures required to prevent the persons participating in the manoeuvre from possibly having doubts or basing their actions on situations not associated with actual performance when taking decisions or applying existing procedures (Pre-job briefing). v Use all the resources required and/or available for the correct dosimetry control of all persons participating in the manoeuvre. v Establish adequate mechanisms for correct communications between Radiation Protection and Mechanical Maintenance, as well as between the persons participating in the manoeuvre.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 4. Corrective Actions in relation to human factors and training. v Assessment of training needs in relation to human factors for the operating personnel. v Inclusion of this event in the Radiation Protection Training programme applicable to all the exposed personnel. v Inclusion of this event in the programme of the annual on-going training course for the Radiation Protection Service personnel. v Extension of training on radiation protection and the ALARA policy for Radiation Protection, Maintenance and Operations performers and supervisors.

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 5. In summary

2008 ISOE EUROPEAN SYMPOSIUM. Turku, Finland. 25 -27 June 2008 The incident has been caused by three fundamental aspects 1 Elevated levels of area radiation caused by failure to minimize a Lower Internal refuelling cavity water surface extraction due to the lack of technical resources and optimal procedures relating to this. 2 Use of the handling crane as a work zone with high risk of exposure for the carrying out of visual inspections and the resolving of interferences. 3 Radiation Protection supervision criteria and associated technical resources not sufficiently developed to cover all the possible incidents which can occur while carrying out the manoeuvre.

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