This report is being made pursuant to
10CFR50.72(b)(3)(v)(A), event or condition that at the
time of discovery could have prevented the fulfillment of a safety function of systems that are needed to shutdown the reactor and maintain it in a
safe shutdown condition. A scheduled load reduction for surveillance testing and
control rod sequence exchange was in progress. During the
control rod sequence exchange, the core monitoring software system (3DMonicore) was used to obtain a 'case' which records various calculated and actual core parameters (i.e. core thermal power, Power Range Monitor indication). The 'case' data is used to evaluate the Technical Specification (TS) Surveillance Requirement (SR) acceptance criteria for
SR 3.3.1.1.2 to verify the absolute difference between the average power range monitor (
APRM) channels and the calculated power is less than or equal to 2% rated thermal power (
RTP) while operating at greater than or equal to 25%
RTP. The 'case' showed that all 3 A
RPS Trip System
APRM channels exceeded the allowable 2% difference threshold in the non-conservative direction (i.e.
APRM power reading less than calculated thermal power, difference of 2.9, 3.1, and 2.5% respectively).
TS 3.3.1.1 requires at least 2 operable
APRM channels per trip system (there are 2
RPS trip systems, A and B). At least 1 of 2 TS required
APRM channels are required to maintain the Safety Function (i.e.
SCRAM). In this situation, none of the A
RPS TS required
APRM channels met their SR and were declared inoperable.
TS 3.3.1.1 allows delaying entry into the associated Condition and Required Action for this inoperability for up to
2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> when the inoperability is solely due to
APRM indication not within the 2% limit; therefore no TS Required Action tracking timeclocks were entered. A confirmatory 'case' was performed that validated that the subject SR was not met. Prompt action was taken to restore the
APRM indications to within limits (this action took approximately 22 minutes to complete) and the subject
APRMs were declared operable, restoring the A
RPS Safety Function.
The licensee notified the NRC Resident Inspector and the
Illinois Emergency Management Agency.
