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Training Nuclear Watchdogs

17/01/2006

Long before arriving on site, novice and seasoned inspectors alike take part in rigorous training. It kicks off with classroom exercises and lectures before inspectors take their knowledge to the field. The IAEA organizes about 50 training exercises each year, for up to 12 inspectors at a time.

In Sweden, the fuel fabrication facility in Västerås houses the entire chain of the fuel making process – from the arrival of enriched uranium to conversion into pellets and final bundling of fuel rods into "assemblies". The facility is operated by Westinghouse Electric Sweden AB and regulated by the Swedish Nuclear Power Inspectorate (SKi), a longstanding IAEA partner for training inspectors.

After each day’s work, inspectors – and their tools – are scanned for any sign of radiation contamination. Radiation doses at a typical fuel fabrication plant are low, and safety is a top priority.

Fuel for most of the world's nuclear power plants is made from enriched uranium at "fuel fabrication" facilities. Each year, teams of IAEA inspectors verify the peaceful nature of civil nuclear programmes – their work includes fuel fabrication plants in more than 20 countries.

Once at the facility, inspectors test their new skills. To untrained eyes, the factory floor is a spaghetti of wires, tubes and pipes giving the impression of organized chaos. Inspectors must learn about a variety of plant configurations so they can detect indications to divert sensitive material.

A Westinghouse operator lifts the cover of a rotary filter containing a batch of “yellowcake”, technically called ammonium uranyl carbonate. It is processed into purified uranium dioxide (UO2) for use in fuel rods.

Inside a control room, inspectors view displayed schematics of the plant’s operational flow. The computer monitors key operations – temperatures in the pipes, conductivity measurements, batch weights, precipitation levels, Ph balance and chemical flows, among others. TV cameras zoom in on gauges giving the operator critical information.

An inspector checks the declared inventory of UF6 cylinders -- they contain approximately 2000 kg of uranium hexafluoride. The cylinders arrive at Västerås from enrichment plants in Europe, the USA and Russia.

Checking the cylinder is one thing. Checking what's inside is another. As most enriched material emits gamma rays, inspectors rely on sophisticated instruments – such as sodium iodide detectors pictured here (inset - thickness gauge instrument). These tools of the trade help inspectors verify the accuracy of facility records.

Randomly selected cylinders are weighed as part of the verification procedure.The inspector checks the cylinder, weighing nearly 3000 kilos on to a load cell. These measurements are all part of piecing together the inspection data.

Once the cylinder's contents are verified, inspectors attach an IAEA metallic seal -- commonly used to prevent tampering. The seals provide important evidence of any unauthorized attempt to gain access to the secured material.

Another step for inspectors is to verify levels of enrichment during the uranium conversion process. Here, inspectors observe a plant operator carefully extracting a UF6 sample to be analyzed for isotopic composition.

The inspector looks on as the operator shows the process of precipitating the UF6 sample with ammonium hydroxide.

The UF6 sampling process ends up with concentrated uranium dioxide, a form of "yellowcake". The sample is baked in a furnace for three hours to mimic the uranium conversion process. Thereafter, the sample is sent to the IAEA's Safeguards Analytical Laboratory in Seibersdorf, Austria, for analysis of enrichment levels.

Before shipment to analytical labs, scales are diligently calibrated by the inspector. Base measurements are taken on empty bottles before a sample is placed inside and weighed.

During an inspection, samples can be secured with a temporary paper seal.This is done to maintain the continuity of knowledge and prevent tampering in the inspector's temporary absence. The inset shows a sample secured with a permanent metallic seal in preparation for shipment.

To make nuclear fuel, the UF6 is converted into UO2 powder, then pressed and sintered into fuel pellets. Here, inspectors check the "hoppers" -- capsule-shaped buckets -- of UO2 powder against the facility records. Any inconsistency is a red flag for further investigation.

A Westinghouse operator carefully takes a sample from the tilted hopper. The powder sample is poured into two small glass bottles (inset).

Inspectors check the storage area where boxes of fuel pellets are kept. Pellet boxes are randomly selected for verification.

Metal boxes hold trays of finished fuel pellets. Each pellet, slightly larger then a pencil eraser, contains enriched uranium dioxide that will be used at nuclear power plants in and outside of Sweden. It's been said that one single pellet contains enough "fuel" to provide a year's worth of energy for a Swedish home.

Each pellet tray contains approximately 2 kg of enriched uranium. The operator weighs each pellet tray. Inspectors compare the measured weights against the operator's declared weight that is indicated on the boxes.

Inspectors randomly select two pellets from the tray. One pellet is destined for an on-site archive; the other sample will be shipped back to the IAEA Safeguards Analytical Laboratory for further analysis.

An inspector verifies the pellet's enrichment on-site using a Mini Multi-channel Analyzer with a sodium iodide detector that attaches to a palm-sized computer.

Fuel pellets are loaded into thin rods, then bundled into “fuel assemblies”. Inspectors check the fuel rod enrichment levels using a sodium iodide detector together with the HM-5 (foreground) to confirm the amount of enriched uranium.

Going up to the source is sometimes the only way to access the assemblies for critical measurements. In this case, an inspector rides an electrically operated crane to measure the length of fuel rods.

A neutron detector provides an "active measurement" of uranium content and ultimately provides the total weight of the uranium in the assembly. For the reading to be accurate, inspectors have to ensure that the fuel assembly is perfectly positioned within the polyethylene "collar" – also known as a Uranium Neutron Coincidence Collar. Errors in total weight can be an indication of diversion, and all inconsistencies need to be reconciled.

Inspectors spent seven days in training at Västerås. Once fully trained, inspector teams can spend over 100 days a year on the road at various sites throughout the world, to help make sure that peaceful nuclear materials and activities stay that way.

Natural uranium contains three different isotopes, U-238, U-235, and U-234. In industry, the isotopes are separated to increase the concentration of one isotope relative to another. The aim is to achieve higher – or "enriched" -- concentrations of U-235, which can sustain a nuclear chain reaction. Low-enriched uranium used for nuclear fuel is not useful for making nuclear weapon devices. But the material could be diverted and become feedstock for developing them – prime reasons why the IAEA safeguards it.

UO2 powder in hoppers is verified for enrichment levels using a gamma measuring instrument with a germanium detector. The weight of UO2 is verified using the operator's calibrated scale.

Training Nuclear Watchdogs: In Sweden, IAEA safeguards inspectors learn the "ins and outs" of safeguarding nuclear fuel.

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