Upgrades underway28 September 2012
Physical upgrades and revisions of emergency plans are in progress at fuel cycle plants post-Fukushima. By Caroline Peachey
As with nuclear power plants, fuel cycle facilities, including conversion (see also pp. 26-30), enrichment (see also pp. 32-36), fuel fabrication and reprocessing plants, have conducted safety reviews in response to the Fukushima accident. The safety reviews consider the capability of facilities to withstand extreme events (such as earthquakes or flooding) and their emergency response capability. Some of these reviews have been completed and some are ongoing. As with nuclear power plants, the recommended upgrades resulting from these reviews could take some years to implement.
Most assessments to date, covering facilities in Canada, the USA, Russia and the UK, have concluded that the facilities’ level of safety is sufficient to allow continued operation, with one notable exception.
The United States Nuclear Regulatory Commission (NRC) announced in October 2011 that it would conduct inspections to evaluate seismic hazards, internal and external flooding hazards, wind and tornadoes, extended loss of AC or emergency power, and fire impacts at all operating fuel cycle facilities. It inspected seven US operating fuel facilities, mostly in early 2012:?Paducah Gas Diffusion Plant, B&W Nuclear Owners Group, Global Nuclear Fuels, Nuclear Fuel Services, and Westinghouse. Louisiana Enrichment Services (Urenco USA) and USEC’s American Centrifuge Project sites were not inspected because they are new.
In mid-July, Honeywell announced that it would not restart production at its Metropolis (Illinois) conversion plant, which entered annual maintenance in May 2012, until reaching an agreement with the US Nuclear Regulatory Commission (NRC) on the necessary plant upgrade project and timing.
Although the NRC confirmed that the facility poses ‘no immediate safety concern,’ the inspection “raised concerns that Honeywell may have underestimated the amount of uranium hexafluoride that could be released into the environment should the process equipment be damaged by such an event,” NRC said in a 13 July statement. In a Confirmatory Action Letter issued on the same date, NRC revealed that: “the design of the process equipment in the Feed Materials Building lacked seismic restraints, supports, and bracing that would assure process equipment integrity during a credible seismic event, or tornado.”
Honeywell agreed to suspend conversion operations until it has fixed the problem. The timeline for the upgrades has not been determined, but completion could take approximately 12 to 15 months, it said.
USEC said the Paducah Gas Diffusion Plant completed a massive seismic upgrade project in 2000 to install dozens of steel braces at key locations in the process buildings, at a cost of more than $70 million. Earlier projects replaced rigid piping expansion joints with flexible joints, reinforced control room walls and more securely anchored electrical equipment.
Similar work is underway in Russia to strengthen the seismic stability of fuel cycle facilities, fuel company TVEL told NEI. Like Honeywell, work was already underway prior to Fukushima, for example at the uranium enrichment plant Angarsk Electrolysis Chemical Combine (AECC).
“Before the 1990s, seismic hazard in the JSC AECC siting region did not exceed 7 points,” TVEL said, referring to the Richter scale of earthquake magnitude. “Based on studies carried out by the Institute of the Earth’s Crust of the Siberian Branch of the Russian Academy of Sciences, a reassessment of seismic hazard was carried out and now the value is 8 points.”
It said: “In 2010, a work schedule to ensure seismic stability of buildings and structures until 2015 was produced. The schedule includes a total of 74 buildings ranked by a safety degree. Given the Fukushima-Daiichi events, about US$1 billion was additionally allocated out of special reserve funds to accelerate works to strengthen essential process building structures.”
Cameo told NEI that the primary hazards at its Port Hope Conversion Facility are chemical: hydrogen fluoride, nitric acid and ammonia. “Radiological risk is considered low due to the type of uranium we handle,” it said.
The UK regulator echoed this assessment in its ‘stress test’ of non-power-generating nuclear facilities: “Unmitigated release of uranic material or hydrogen fluoride (HF) presents a predominantly chemotoxic hazard. On release to the environment, UF6 reacts with moisture in the air forming uranyl fluoride (UO2F2) and gaseous HF. The chemotoxic hazard is primarily from gaseous HF and the heavy metal toxicity of uranium.”
For example, in the USA the limit for public exposure to soluble uranium is 30 mg, and of hydrogen fluoride gas is 20 parts per million for one hour. USEC told NEI that the Paducah plant’s Safety Analysis Report shows that a seismic event at the plant could cause UF6 releases that could result in an exposure of 4 mg of soluble uranium compounds and 2 ppm of HF gas at the site boundary.
Once the Paducah GDP is shut down, process temperatures and pressures drop rapidly; there are no residual heat issues, and so the loss of offsite power does not create a safety hazard, it said.
In France, AREVA has been asked by French nuclear regulator ASN to study and implement complementary means for mitigating the consequences of a toxic product leak (such as gaseous hydrogen fluoride, uranium hexafluoride, chlorine, chlorine trifluoride) at its Tricastin and Romans-sur-Isère sites. For the La Hague site silos, AREVA has been asked to conduct feasibility studies with a view to setting up technical arrangements, such as geotechnical containment, with the aim of protecting the underground and surface water in the event of a severe accident. It must also implement measures to reduce the risk of fuel becoming exposed in spent fuel pools at various reprocessing facilities.
AREVA has also committed to deploying new emergency response and communications equipment at its sites.
Cameco commissioned a third-party study of the safety of its fuel cycle operations that reported [largely positive] results to the Canadian nuclear regulator in August 2011. “Our emergency response plan will be tested in early September 2012, when we conduct a day-long exercise involving local emergency responders,” Cameco said.
In Russia, measures have been taken to improve the process for notification of events to management with a 24-hour duty dispatch service (DDS).
This article was published in the September 2012 issue of NEI magazine.
|Sources of information|
This article draws on responses from Cameco, Honeywell, Rosatom and USEC, and other information in the public domain. AREVA was unable to provide information for our deadline; Urenco did not respond to our queries.