Aug 19 The Health Assistant's Evening Routine
It is late afternoon over Risø, and the shadows from the silver poplars have grown long. However, DD's security personnel remain on duty, even as the lights in the offices are switched off one by one. There are always people present at the Risø site, around the clock, year-round, where DD's guards, among other tasks, patrol and inspect the buildings and take samples.
HHealth Assistant Jens Heidelbach retrieves a log sheet and reviews the notes left by the outgoing guard. In addition to the usual duties, the log sheet contains a message instructing him to perform a control measurement on a concrete milling machine. It has been used in the reactor hall, and nothing may leave the area without being checked for radioactivity. This also applies to personnel.
Jens takes a handful of small, numbered paper bags and a checklist, then sets out on his evening round. This evening, his tasks include going behind the DR3 reactor to inspect the area near the cabin where demolition waste is being sandblasted. Along the way, he bends down and vigorously wipes the floor at the locations indicated on the checklist. Precisely the same locations are wiped and control-measured every Thursday. Precisely the same every Tuesday. This round is part of DD's quality assurance, as stipulated by the nuclear regulatory authorities:
Continuous measurements of radiation levels, surface contamination, and airborne contamination must be performed at the nuclear facilities, and levels must be established that trigger predetermined action plans.
This means that every evening, the health assistants patrol DD's site, taking wipe samples from the floor at several locations and checking them for radioactivity. Approximately 8,000 samples per year. After each round, the samples are placed in a drawer in the multi-counter in the laboratory. It measures alpha and beta activity, and all results are verified and stored.
Air Monitoring
Jens carries a long glass flask with him on his round. It is a cold trap designed to capture radioactive contamination from the air. The cold trap collects atmospheric moisture along with any substances that may be suspended within it. Jens removes a frozen cold trap and inserts a new one. He also replaces the air filter through which the dry ventilation air from the DR3 reactor is passed. This procedure is covered by the Operational Limits and Conditions. Wipe samples are taken and air filters are checked daily.
Inside the DR3 reactor itself, Jens checks the computer screen of a so-called iCAM, which measures airborne dust. The acronym stands for Continuous Air Monitor, and the instrument constantly draws air through a filter. The measurements are stable and show no anomalies. However, the day's work of milling concrete from the reactor's facade is visible on the filter. The underside is white, as it was when the filter was installed. The upper side is dark grayish-brown. The work has been dirty, but no unexpected radioactivity has been detected on the filter.
Filter Measurement
Jens inspects the various instruments in the reactor hall, but none show readings or levels exceeding the expected background level. He then proceeds to the laboratory and, using tweezers, places the wipe samples into the multi-counter's drawer. It takes approximately ten minutes to obtain the results from the samples. The dry air filter from the ventilation system takes considerably longer. The filter must remain in a lead shield for 10,000 seconds, or just under three hours, while being measured with a gamma spectrometer. The instrument's sensitive sensor or detector is made of germanium, which is cooled with liquid nitrogen. The container is empty, so Jens grabs a glove and refills it. Liquid nitrogen is minus 196 degrees Celsius and causes immediate frostbite if it comes into contact with skin.
Inspection of Tools and Laundry
While samples and the air filter are set aside for measurement, the cold trap slowly thaws on the table. The liquid must be poured into a flask, which will be sent for analysis to DTU Nutech, located in the adjacent building. DTU Nutech is Denmark's research center for radioactive substances, and DD collaborates with them in several areas. Jens goes out to perform the remaining inspection tasks. The concrete milling machine is on a pallet in the AH hall, and Jens carefully scans it with a handheld measuring instrument, a so-called plastic scintillation counter, but finds no trace of radioactivity. The milling machine then receives a label indicating that it is cleared to leave the area. Two green waste bags and six red laundry bags are also inspected and marked as acceptable.
Evening falls, and it is time for dinner. DD's health assistant on duty stays overnight on site and hands over the shift to the reliever the next morning.