A radioactive gauge’s shutter failed at a Freeport, Texas, site holding cesium-137

The source shutter on a fixed radioactive gauge at Blue Cube Operations in Freeport, Texas, failed to function as designed, according to a Nuclear Regulatory Commission event report. The gauge holds a sealed 300-millicurie cesium-137 source. It was found with the shutter stuck open, which is the position the device uses in normal operation, and the licensee says the failure poses no additional radiation risk to the public or workers.

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Texas regulators relayed the event to the NRC on Oct. 13. It is logged as event 58494, and the state said more information will follow. The Texas Department of State Health Services supplied the report, and the licensee’s explanation that no added risk results comes from the licensee, not from an independent survey, so the state’s follow-up is the next document to watch.

A stuck shutter on a Ronan SA1-F37 gauge

The NRC event report says the licensee told the Texas Department of State Health Services on Oct. 13 that the shutter on a Ronan model SA1-F37 gauge had failed. The problem surfaced during a visual inspection and shutter check on Oct. 12, the event date in the record. Sindiso Ncube reported for the state, and the NRC’s headquarters operations officer, Sam Colvard, took the notification at 3:09 p.m. Eastern on Oct. 13. Texas assigned incident number 10338, and the licensee holds Texas license L-06926.

The state classified the event as non-emergency and as a stuck shutter. The record adds that further information will follow under SA-300 reporting requirements. It also says the condition was found by the licensee itself during a routine check rather than after any harm, which is the kind of discovery an inspection-style test is meant to produce.

Why an open shutter is the normal state, and why a stuck one still counts

In general, a fixed process gauge keeps its source inside a shielded housing, and a shutter lets radiation cross the material being measured when open and blocks it when closed. The report’s wording matters here: the shutter was stuck open, which the record describes as the normal operating position. The reported failure is a shutter mechanism that did not function as designed, and the record does not describe any release of the source. Whether the shutter can still be closed, and what servicing the licensee plans, are not stated.

Cesium-137 is a long-lived industrial isotope. The Environmental Protection Agency lists a half-life of about 30 years and says it is used in industrial gauges that monitor the flow of liquids through pipes and measure the thickness of materials such as paper or metal sheets. The agency adds that a large external exposure, most likely from mishandling a strong industrial source, can cause burns, acute radiation sickness and death, and that its gamma radiation raises cancer risk.

The source here is 300 millicuries. A millicurie is a thousandth of a curie, and the curie is defined as 37 billion disintegrations per second, so 300 millicuries is about 11 billion per second. The sealed source remained inside the gauge; the record describes no leak, no contamination and no exposure.

The same isotope turns up in many places outside heavy industry. The EPA page says small amounts of cesium-137 are used to calibrate radiation detectors such as Geiger-Mueller counters, and larger amounts appear in medical radiation therapy devices for cancer treatment. Its long half-life means a source stays active for decades, so a gauge installed years ago is still a working radiation source today. The licensee describes finding the stuck shutter through a visual inspection and shutter check on Oct. 12.

Freeport, the licensee and the state regulator

Freeport is a Gulf Coast city in southern Brazoria County, near the mouth of the Brazos River, with a 2020 census population of 10,696, according to its encyclopedia entry. Its economy leans on heavy industry, including Dow’s Texas Operations, Port Freeport and the Freeport LNG export terminal. The NRC report does not say which unit of the plant uses the gauge or what process it monitors.

The regulator is the Texas Department of State Health Services, whose Radiation Control Program licenses radioactive materials, registers X-ray machines and runs inspections and complaint handling. The NRC page lists the report as an Agreement State event, meaning the state regulator, not the NRC itself, holds the licensing relationship with Blue Cube Operations and relayed the notification to Washington.

As of the Oct. 13 update, the record gives no cause for the shutter failure, no repair date and no statement on whether the process the gauge serves was stopped. Those details, if they emerge, would come through the state’s follow-up report on incident 10338. Until then, the documented facts are narrow: one gauge, one 300-millicurie cesium-137 source, a shutter that did not function as designed, a Texas regulator tracking it, and an NRC log entry that reports no added risk to the public or to workers. Anything beyond that, including how long the shutter had been stuck, remains unreported.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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