Fission Stories #188
The previous Fission Stories commentary described a problem at the Grand Gulf Nuclear Station near Port Gibson, Mississippi that prevented workers from transferring fuel bundles from the new fuel vault to the spent fuel pool. This post describes a problem encountered shortly after that problem was eliminated and the transfers began.
I was the reactor engineering supervisor at Grand Gulf as Unit 1 approached its first refueling outage. The new fuel bundles that would be placed in the reactor core during the refueling outage had been received, inspected, and placed into the new fuel vault.
The next task involved transferring the fuel bundles from the new fuel vault to the spent fuel pool. To accomplish this task, workers would use the overheard crane to latch onto one fuel bundle at a time in the new fuel vault, raise it out of the vault, move it over the spent fuel pool, and lower it down into an empty position within a storage rack.
Spent fuel storage racks
Because Grand Gulf had not yet had its first refueling outage, the only things in its spent fuel pool at that time were the storage racks and water. I took the picture below from the railing around the spent fuel pool looking down at the empty storage racks. There’s no water shown in this picture. The large holes to the left were used to store control rod blades and canisters holding damaged fuel bundles. New and spent fuel bundles were stored in the rest of the holes.
Workers at Grand Gulf had reviewed experience from other nuclear plants about moving fuel bundles into the storage racks. A recurring problem involved the bottom of a fuel bundle missing the hole and catching an edge of the storage rack framework. As workers continued lowering the boom thinking the fuel bundle was descending into the storage position, the top of the “stuck” fuel bundle sometimes worked loose from the latch. The freed fuel bundle would then fall over to lie horizontally across the top of the storage rack.
Seeking to avoid this recurring industry problem, we lowered the water level inside the spent fuel pool to below the top of the storage rack. We placed plywood boards on top of some of the racks for workers to walk on. Workers standing on the plywood boards would guide the bottom of each fuel bundle into storage holes to prevent the interference problem.
Because the water inside the spent fuel pool had been recycled from reactor cooling water during the plant’s operation, it contained small but measurable amounts of radioactivity. Consequently, the workers entering the spent fuel pool had to wear protective clothing to prevent them from being contaminated through contact with the walls and racks.
A metal cage attached to the overhead crane was used to get workers into and out of the spent fuel pool. Two workers would enter the basket as it rested on the refueling floor. The overhead crane would lift the basket, carry it over the pool, and lower it down to the level of the racks. The workers would step out of the basket onto the plywood boards lying across the top of the racks. This process would be reversed to get workers out of the pool.
Because the storage racks had been contaminated by the radioactivity in the spent fuel pool water, the health physics department instructed us to keep the bottom of the basket from contacting the top of the storage racks. This measure prevented the basket itself from getting contaminated and spreading contamination outside the pool. We planned to lower the basket to within about four inches of the rack and let workers step out of and into the basket from that elevation.
Monitoring the transfers
I went to the refueling floor to monitor the initial transfers, joining a crowd on the refueling floor:
- Two of my reactor engineers were there—one to ensure the proper fuel bundle was moved from the new fuel vault to the correct storage location within the spent fuel pool rack and the second to independently verify that movement.
- A crane operator and a spotter were there to handle the overhead crane movements.
- Two workers and a foreman were there to perform the in-pool function.
- A quality control inspector was there to verify the activities were performed in accordance with approved procedures. A health physics technician was there to monitor radiation levels.
- A mechanic maintenance supervisor was there to monitor his crane operators and craft workers.
- And a quality control supervisor was there to oversee his inspector.
The crane operator stood on the refueling floor. A control box at the end of a long cable running up to the cab of the overhead crane allowed him to operate the crane remotely. Workers stepped into the basket on the refueling floor. The spotter used hand signals to direct crane operator in lifting the basket, moving it over the spent fuel pool, and lowering it down into the pool.
When it came time for the workers to step out of the basket onto the plywood boards atop the storage rack, a minor problem cropped up. The workers yelled up to the spotter standing at the spent fuel pool railing. The spotter did not understand the workers. Eventually, the crane operator left the remote control station and walked over to the railing to communicate with the workers in the basket. They expressed concern that when exiting the basket, it might swing back and forth and unintentionally contact the contaminated rack. A revised plan was developed to raise the basket to about a foot above the racks to provide additional margin. The crane operator returned to the remote control station and jogged the basket upward a few inches. Soon the workers were on the plywood and the uncontaminated basket was back on the refueling floor.
After watching several fuel bundles successfully transferred from the new fuel vault to the spent fuel pool, I left the refueling floor and returned to my office. By the end of the day, all of the new fuel bundles had been transferred to the spent fuel pool.
A safety violation?
I attended the management meeting the following morning thinking the matter would be off the agenda since the transfers had been completed. But it was item one.
The quality control supervisor stated that his quality control inspector wrote a top level corrective action report for a procedure violation during the new fuel bundle transfers that jeopardized worker safety. The supervisor did not describe the nature of the violation, but did state that it reflected “careless disregard” for worker safety. I glanced at the mechanic maintenance supervisor who shrugged—it was the first either of us had heard about it. Senior managers were not happy about our putting workers in harm’s way and directed the three of us to resolve the problem as quickly as possible.
The mechanical maintenance supervisor and I followed the quality control supervisor to his office immediately after the morning meeting. He handed the corrective action report to me to read. It said that the crane operating procedure stated that the crane operator is not to leave the controls with a load suspended from the crane. Despite that requirement, the quality control inspector observed the crane operator abandon the remote control station with two workers suspended in the basket over the spent fuel pool storage rack. The report went on to state that the procedure violation put the workers in great jeopardy.
I handed the report to the mechanical maintenance supervisor. He read it and then asked something to the effect, “Let me get this straight. Your inspector sees a violation that places workers in harm’s way and instead of telling them, or you, or me, or him [pointing to me], he leaves the area and returns to his office to write up a safety report. Are you telling me that he left my workers in danger to fill out some paperwork?” The volume of his voice increased throughout his remarks until he was shouting by the end.
The quality control supervisor took back the report, ripped it up, threw it into his trash can, and said softly, “our inspection report will reflect that the fuel transfers were successfully completed.” The matter had been resolved.
Technically, the quality control inspector was right. The crane operating procedure did not permit the controls to be abandoned with a load suspended from the crane. The controls had been abandoned with workers inside a basket suspended from the crane, albeit by only about four inches.
Technically, the quality control inspector was wrong. If he perceived the violation to have ongoing worker safety implications, he was supposed to intervene immediately.
Technically, two wrongs should not make a right even though they did in this case. Tearing up the corrective action report wiped out the crane operating procedure violation and the leaving the scene of a dangerous activity miscue.
What should have happened was the quality control inspector should have immediately notified workers and supervisors about the apparent violation of the crane operating procedure. That notification should have resulted in the process being revised to adhere to the procedure or the procedure being formally revised to permit the practice.
“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.