Upon arrival at the site, the inspectors conferred with control room personnel regarding
emergency plan event classification and actions being taken by the site. On April 18, 2008 at 04:38 a.m., security officers within the protected area at Quad Cities felt vibrations associated with an
earthquake. The officers reported the tremors to the control room at 04:38 a.m. and the control room entered QCOA 0010-09,
Earthquake. At 10:17 a.m. plant staff in the service building and security officers within the protected area again reported feeling tremors. In both cases, the shift manager reviewed the Emergency Action Levels and associated thresholds for an
earthquake (natural and destructive phenomena affecting the PROTECTED AREA) and determined that the Emergency Action Level (
EAL) for the event was not met and that the event was therefore not reportable. The
EAL Threshold for an Unusual Event at Quad Cities is established to coincide with
NEI 99-01 Revision 5, Methodology for Development of Emergency Action Levels, and states, Seismic event as indicated by any TWO of the following:
Earthquake felt in plant, Seismic event confirmed by station seismic monitor procedure, or National
Earthquake Center. The shift manager determined that the
earthquake was not felt in the plant because no one within the power block or the main control room felt the tremors (the residents confirmed with the site
emergency preparedness group that this is how the site trains the emergency response organization to classify this event). The quake and subsequent aftershocks were only 0.002 0.003 gs on the seismograph and did not reach the actuation set point of .025g. The shift could not contact the National
Earthquake Center but did get confirmation of the southern
Illinois earthquake via a web page. Thus in the shift managers evaluation, only one of the criteria was met and the site did not declare an Unusual Event. While executing the steps of QCOA 0010-09, operators and engineers walked down the plant looking for damage and possible leaks, including the fuel pools and their associated cooling systems, steam piping, safety systems and outbuildings/surrounding area. Air sample activities were monitored for the drywell and turbine building. Key plant parameters such as offgas flow, drywell
sump flow, steam flow, feed flow, etc. were also monitored for abnormal indications. These actions had just been completed when the 10:15 a.m. aftershock we reported to the control room, so the procedure was re-entered and the steps were executed again. All walkdowns and monitoring activities were completed with no impact to the plant identified. The resident inspectors performed an independent assessment of plant condition, including area walkdowns to confirm the reports of the operators and engineers performing the plant walkdowns. The inspectors questioned whether the first
EAL threshold value was being interpreted correctly by the licensee. Specifically, the site interpretation that
earthquake felt in plant is limited to the control room and power block does not seem to support the
EAL for issues affecting the protected area or the NEI bases discussion in
NEI 99-01 for this event. The NEI bases document states, As defined in the EPRI-sponsored Guidelines for Nuclear Plant Response to an
Earthquake, dated October 1989, a \"felt earthquake\" is: An
earthquake of sufficient intensity such that: (a) the vibratory ground motion is felt at the nuclear plant site and recognized as an
earthquake based on a consensus of control room operators on duty at the time, and (b) for plants with
operable seismic instrumentation, the seismic switches of the plant are activated. As Quad Cities had transferred this statement to their own bases document, the use of felt in plant and felt at the nuclear plant site do not appear to be as limiting as the site interpretation. Examples of risk-significant or safety equipment such as underground piping that could be impacted outside of the power block were of particular concern. This issue is considered an unresolved item pending clarification of the apparent conflict in the reference documents for the
EAL (
URI 05000254/2008003-02;
05000265/2008003-02)
