Quality Assurance Issues in France: Implications for U.S. Plants?

Kerri Kavanagh
Chief, Quality Assurance and Vending Inspection Branch

The NRC doesn’t just oversee how nuclear power plants operate. We also oversee the quality of the important components that go into the reactors. That’s why NRC staffers are working with the French Nuclear Safety Authority and AREVA, a manufacturer of reactor components, to determine if a quality assurance investigation underway in France has implications for U.S. plants.

ASN – the acronym for the French regulator — requested the probe in early May after a flaw was discovered in the vessel of a reactor under construction at Flamanville in France. So AREVA checked the manufacturing records of the Le Creusot Forge, in central France. They found anomalies in the records of about 400 parts manufactured there since the plant opened in 1965. (Le Creusot Forge was purchased by AREVA in 2006.)

investigationsASN says these are paperwork irregularities – inconsistencies, modifications or omissions in production files concerning manufacturing parameters or test results. The irregularities are troubling because complete documentation provides assurance the components were forged to the proper procedures and specifications.

They do not mean, however, that any parts or components manufactured at Le Creusot are defective.

AREVA announced at the end of May that it had completed two-thirds of its review and found no indications of safety issues. The company told the NRC about 10,000 documents are still under review. The company pledged to provide us with a list of U.S. plants affected by these paperwork irregularities when the investigation is completed around the end of July. We’ll continue to engage with ASN and AREVA to make sure we have a complete picture of how these irregularities may affect any components provided to U.S. nuclear power plants.

NRC’s regulations in 10 CFR Part 21, “Reporting of Defects and Noncompliance,” require any entity that identifies reportable issues to evaluate them and inform the users of any impacted components. The users then have 60 days to do their own safety evaluations. If the users identify significant safety hazards, they must report these to the NRC by phone within two days, and in writing within 30 days.

AREVA and Le Creusot Forge are under contractual obligations to their U.S. customers (who are NRC licensees) to follow these reporting requirements. We’ll take appropriate regulatory and enforcement action if we find issues of safety significance. At this time, there is no indication of a safety issue with any components from Le Creusot covered by this quality assurance audit.

Regarding new reactors, Westinghouse Electrical Co., the architectural engineering firm for the AP1000 reactors under construction at Vogtle and V.C. Summer, has confirmed that no components at these plants were supplied by Le Creusot Forge.

Once AREVA completes its audit and we have a complete picture of the situation, the NRC has several options. We may issue a generic communication to keep the broader nuclear industry informed. We may also perform inspections to ensure conformance and compliance with our regulations.

More information will be coming on this issue. If the NRC determines that Le Creusot Forge has provided components to U.S. nuclear power plants, we’ll make sure those components are fully evaluated to determine any impact the documentation irregularities might have on their safety-related functions.

Dry Cask 101 – Radiation Shielding

Drew Barto
Senior Nuclear Engineer

CASK_101finalWe’ve talked before about how the uranium in nuclear fuel undergoes fission during reactor operations. The fission process turns uranium into a number of other elements, many of which are radioactive. These elements continue to produce large amounts of radiation even when the fuel is no longer supporting a chain reaction in the reactor. So shielding is necessary to block this radiation, and protect workers and the public.

As we discussed in an earlier blog post, the four major types of radiation differ in mass, energy, and how deeply they penetrate people and objects. Alpha radiation—particles consisting of two protons and two neutrons—are the heaviest type. Beta particles—free electrons—have a small mass and a negative charge. Neither alpha nor beta particles will move outside the fuel itself.

drycaskshieldingBut spent fuel also emits neutron radiation (particles from the nucleus that have no charge) and gamma radiation (a type of electromagnetic ray that carries a lot of energy). Both neutron and gamma radiation are highly penetrating and require shielding.

Shielding is a key function that dry storage casks perform, but the two main types of dry storage casks are configured in slightly different ways.

For welded, canister-based systems, shielding is provided by a thick (three feet or more) steel-reinforced concrete vault that surrounds an inner steel canister. The thick concrete shields both neutron and gamma radiation, and may be oriented either as an upright cylinder or a horizontal building.

In bolted cask systems, there is no inner canister. Bolted casks have thick steel shells, sometimes with several inches of lead gamma shielding inside. They have a neutron shield on the outside consisting of low-density plastic material, typically mixed with boron to absorb neutrons.

drycask101_radiationshielding_CompimagesThe NRC reviews spent fuel dry cask storage designs to ensure  they meet our limits on radiation doses beyond the site boundary, under normal and accident conditions, and that dose rates in general are kept as low as possible. Every applicant must provide a radiation shielding analysis as part of the application for a new storage system, or an amendment to an existing system. This analysis uses a computer model to simulate radiation penetration through the fuel and thick shielding materials under normal operating and accident conditions.

We review the applicant’s analysis to ensure it has identified all the important radiation-shielding parameters. We make sure they’re modeled conservatively, in a way that maximizes radiation sources and external dose rates. We may create our own computer simulation to confirm the dose rates provided in the application. That helps us to ensure the design meets off-site radiation dose rate requirements under all conditions.