4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France “ALARA” versus reactor safety concern - A practical case - Staffan Hennigor & Berndt Ögren Forsmark NPP Sweden

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Europe Forsmark NPP 3 BWR units (F1 & F2 1980, F3 1985) - Total 3250 MW e Oskarshamn NPP Stockholm Ringhals NPP Barsebäck NPP Gothenburg Sweden Forsmark NPP

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France The case - Repair work on the steam dryer at Forsmark 2 Problem area

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France The basic problem - Corrosion!!! Challenge to the mechanical integrity of the steam dryer structure (more than 40 cracks detected on the 8 beams) Risk of loose parts in the reactor vessel Consoles welded on top of steam dryer

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Another problem - Very short planning time!!! No dose rate measurements with exposed upper part of the steam dryer performed during the outage year 2002 To short time to develop and implement robot techniques Limited time for optimizing cutting, grinding and welding methods (have to be based on more or less manual work methods) The upper part of the steam dryer above the water – limited shielding The work to be performed next two outages to short (9 days)

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Work preparation - Repair method & shielding Repair –Cutting of the beam consoles –Grinding the top surface of the beams –Welding of new beams upon the old Shielding –10 cm steel plates, forming a platform on top of steam dryer –Additional lead blankets over the beams not being worked on Target: Dose rate at platform  0,5 mSv/h

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France ALARA??? Preliminary dose predictions –Collective dose mmanSv –Individual doses close to 20mSv for several workers Proper optimization not possible (Work methods, tools & protective measures) –Lack of time! Continued operation without repair not considered possible –Due to reactor safety concern ALARA check points 1.Verify contractors working methods and tools) Check for work time required 2.After removing reactor vessel head) Check for source term accuracy 3.When the shielding is in place) Check the actual dose rate & compare with target 4.During work) Check collective dose and individual doses. 5.Constraints) Max collective dose = 350 mmanSv & max individual dose = 12 mSv

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Continued planning - Improvements Major improvements: Cutting the consoles by saw blade operated at slow speed –Using semiautomatic method (minimizing manual operations) Slow speed grinding Speedy welding method (only manual welding possible) –Cutting welding work time by 2/3 compared to the initial plan Training & verification performed in mock-up Special information regarding radiological & industrial safety matters Adjusted dose prediction based on planning & verification of work methods: Collective dose = 160 ‑ 180 mmanSv No planned individual dose > 12 mSv A skilled & interested contractor is extremely valuable!

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Dose rates higher than expected - Plan B! Measurements with shielding plates in place showed dose rates in working areas in excess of predicted values: –General dose rates in the range of 0,7 ‑ 0,8 mSv/h –2 mSv/h on working distance from unshielded beams –Work could not be performed within the given constraint of 350 mmanSv An alternative plan worked out: –Modification of only 4 out of 8 beams –The 4 “worst” beams chosen –Stress calculations verified that the integrity of the structure OK

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Work performance - Dose results Actual work performed according to the modified plan –without complications, accidents or incidents Daily meetings between contractor, operational staff and RP staff –Actual doses closely monitored and communicated to everyone involved Total collective dose= 165 mmanSv Max individual dose= 10,3 mSv Number of workers involved = 83 Number of workers with dose > 5 mSv = 12

4´th ISOE European Workshop on Occupational Exposure Management at NPP´s March 2004 – Lyon France Conclusions - Lessons learned! Allocate proper time for preparation & planning – At least 12 months seems appropriate Perform independent shielding calculations on complex geometries –Dose rates may easily be underestimated Perform a comprehensive risk assessment –Will place focus also on personal safety –Excellent base for communication between all involved parties, including contractors Have dedicated daily follow-up meetings –Coordinating the work –Communication of actual dose figures Perform pre mock-up training and dedicated information to personal involved –Greatly enhances workers involvement and awareness –Enhancing the quality of work performed. Establish well defined check points, including alternative plans –minimizes the risk for negative surprises, loss of outage time and poor quality of work