BRATTLEBORO -- A recent security violation at Vermont Yankee nuclear power plant in Vernon has been dealt with in an acceptable manner, stated the Nuclear Regulatory Commission in a notice to Christopher Wamser, site vice president.

The nature of the Severity Level IV violation is not public knowledge however, because it involved "security matters that are considered sensitive information," stated the letter.

The NRC's investigation of the April incident found that Entergy Nuclear Operations had "identified the issue, took immediate corrective actions to address any security-related vulnerability, entered the issue into its Corrective Action Program, and notified the NRC Region I office."

After review of the violation and Entergy's reaction to it, the NRC characterized it as a non-cited violation.

Though he wouldn't divulge any information related to the violation, Rob Williams, spokesman for Vermont Yankee, said at no time was the health, safety or security of the public or plant employees ever at risk.

"Entergy Vermont Yankee is absolutely committed to safe and secure operation of the plant," he said. "Because Entergy took appropriate steps to address the situation and promptly report it to the NRC, the NRC concluded that it had minor security significance and today notified the plant that it was issued a Severity Level IV, non-cited violation."

Neil Sheehan, spokesman for the NRC, also refused to reveal the nature of the incident.

"As is always the case with security-related violations, we can't go into detail about the issue," he said. "However, the fact that this was classified as a Severity Level IV non-cited violation indicates that we considered this to be of very low significance."

A Severity Level IV violation is comparable to a "Green" inspection finding, said Sheehan.

"As with a ‘Green' finding, the plant owner gets a chance to put the issue into its corrective action program. With security violations, our security inspectors do not leave the site unless the company has fixed the issue or put in place compensatory measures until a permanent fix is in place."

Though Sheehan wouldn't release any details about the incident, he did offer a generic example of what a Severity Level IV non-cited violation might be.

"In the area of security it could be a security officer failing to check if a door is properly locked during rounds. The overall impact on the plant's security is minimal, but we still want to call attention to it and ensure the plant owner takes action to prevent recurrence."

David Lochbaum, the director of the Union of Concerned Scientists Nuclear Safety Project characterized the NRC's letter as "cryptic as to the underlying security problem."

"On the plus side, the letter indicates that the owner 'took immediate corrective actions to address any security-related vulnerability,' so the problem -- whatever it was -- doesn't pose undue hazard to people around the plant today," said Lochbaum.

Each year, the NRC sends an annual report on nuclear plant security to Congress, he said. In 2012, the NRC had 130 total findings in security inspections that didn't involve force-on-force tests, about 1.3 findings per rector.

"Of those findings, only three were Severity Level IV," noted Lochbaum. "On its surface, this might suggest that Yankee had some unusual, atypical problem, found only three of 130 times elsewhere last year. But that's misleading. Severity Level IV findings are similar to 'Green' findings in terms of significance. The majority of security findings in 2012 were of the same significance -- 121 green and three Level IVs out of 130 total."

Lochbaum said he takes comfort in the fact the NRC and the industry appears to be taking security very seriously, even after more than a decade after Sept. 11, 2001.

"It can be tempting to let old problems and threats fade and focus on newer threats, like the Fukushima lessons," he said. "The evidence suggests that while security threats may not be getting as much attention by the NRC as Fukushima threats, security threats haven't fallen off the table."

Severity Level IV violations are defined in the NRC's Enforcement Policy as violations of more than minor concern which, if left uncorrected, could lead to a more serious concern. Violations at Severity Level IV, the least significant of the four severity levels established in the NRC Enforcement Policy, involve noncompliances with NRC requirements for which the associated risks are not significant.

Bob Audette can be reached at raudette@reformer.com, or at 802-254-2311, ext. 160. Follow Bob on Twitter @audette.reformer.