Frozen Trend Line on the Online Dose-Rate Monitor
An online gamma dose-rate monitor at the site boundary feeds an industrial PC that writes one record per minute to a file copied nightly to a NAS. On Monday morning the shift technician sees the trend on the display is a perfectly flat line at 0.11 µSv/h since Saturday noon, with no diurnal variation and no statistical jitter. She also finds that the NAS backup log shows the last successful copy was nine days ago, that a vendor-issued USB drive has been left in a front port since a service visit two weeks ago, that remote desktop is enabled with the shared password 'station123', and that the local data file's last-modified time is still updating every minute. When she holds a check source near the detector, the local display reading rises as expected. The station procedure states that continuous monitoring data are a regulatory record and that any gap must be covered by hourly manual readings and an entry in the logbook.
1. List the checks that would separate a detector fault from a data-path fault, and give your provisional conclusion.
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The check-source test is decisive for the front end: the detector, preamplifier and local electronics respond, so the radiation measurement chain is alive. That moves suspicion to the data path.
Checks:
- Compare the newest records in the data file with the value on the display - if the file holds a repeating constant while the display updates, the acquisition service has stalled.
- Confirm the file size and record count against elapsed time; a file that grows by writes of duplicate values is different from one that has stopped growing.
- Look at the acquisition service status, the event log and free disk space.
- Compare with an independent instrument - a portable survey meter or a second monitor - to confirm the ambient rate is normal, not genuinely constant.
- Check whether the display is computed from the same buffer as the file; some systems show a live value while the logging thread is dead.
Provisional conclusion: the flat line is a logging or display-pipeline fault, not a radiation event. The area must be covered by hourly manual readings until the logger is proven to be writing fresh, non-duplicated records.
2. What immediate IT security and record-integrity actions are required, and in what order?
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Order matters: preserve evidence before cleaning up.
- Do not use the USB drive on any other machine. Remove it only by handing it, bagged and labelled, to IT for scanning and quarantine; the vendor should be asked what it was for.
- Take a copy of the data files and logs with a hash and a timestamp, and record the machine's state before changing anything.
- Disable remote desktop and delete the shared account; issue named accounts with individual passwords and log the change.
- Have IT check for unauthorised access or scheduled tasks in the log, since the flat line began at the weekend when nobody was on shift.
- Restore the backup process: establish why the nightly copy failed nine days ago (NAS reachable? credentials expired? job disabled?), fix it, and run a verified test restore.
- Recover the last good copy and quantify the gap - up to nine days of data may exist only on the local disk, so it must be secured now.
- Raise the record gap with the RPS, start hourly manual readings, and log all of it.
3. The plant manager suggests quietly fixing the backup and re-running the system so the inspector sees no data gap. How should the technician respond?
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Refuse, and put the refusal in the logbook. Falsifying or concealing a monitoring gap on a regulatory record is a much more serious matter than the gap itself: it converts a technical fault into an integrity and compliance failure, and it removes the evidence that would show the site detected and corrected the problem.
The correct sequence is the one the procedure already describes: record the gap with its start and end times and its cause, cover it with hourly manual readings taken with a calibrated instrument by a named person, notify the RPS and site management, retain the corrupted and partial files as evidence, and state in the report what was done to prevent recurrence - backup verification, remote-access controls, USB policy, and a monitoring alarm for a stalled logger.
The technician should say plainly that she will not alter records, offer the compliant route as the fastest way to close the issue, and escalate through the safety officer if pressed. A documented gap with compensatory monitoring is normally acceptable to a regulator; a concealed one is not.