United States Nuclear Regulatory Commission - Protecting People and the Environment

General Information or Other Event Number: 37985
REP ORG: INOVISION NOTIFICATION DATE: 05/11/2001
LICENSEE: INOVISION NOTIFICATION TIME: 15:05[EDT]
CITY: CLEVELAND REGION: 3 EVENT DATE: 05/10/2001
COUNTY: STATE: OH EVENT TIME: [EDT]
LICENSE#: AGREEMENT: Y LAST UPDATE DATE: 05/11/2001
DOCKET: PERSON ORGANIZATION
VERN HODGE (FAX) NRR
NRC NOTIFIED BY: JANICE BROWNLEE
HQ OPS OFFICER: FANGIE JONES
EMERGENCY CLASS: N/A
10 CFR SECTION:
CCCC 21.21 UNSPECIFIED PARAGRAPH

EVENT TEXT

10 CFR 21 REPORT - INTERIM REPORT ABOUT R-11 MONITOR PROBLEM

The following is taken from a faxed report:

Deviation being evaluated: An R-11 Monitor installed in Korea has been reported as having a rapid increase in displayed concentration and analog output values. Initial evaluation of the problem indicates the cause may be in one of the base 960 firmware modules, which are also installed in some US nuclear power plants. The significance of the problem is still under evaluation to determine if it could create a substantial safety hazard. The initial report was received on March 15, 2001.

Evaluation information to date: The problem is a rapid increase in displayed concentration and analog output values. The problem is not apparent at low levels of activity where low count rates and statistical variation mask the increase. When activity is near the upper range of the monitor, this spike in calculated activity has triggered radiation alarms and could place the channel into over range. The spiking in activity is believed to be due to the microprocessor being unable to read and clear a register within the allotted time. This results in a higher accumulated count value when the register is finally read. Since the problem is directly related to processor workload, the problem is most likely to occur in a complex channel with multiple detectors (such as a PIG or Extended Range) and where the microprocessor is highly tasked with RMS computer or isolator communications.

For single range channels, the result of the spike would be a false radiation alarm and possibly an over range condition as well, although this has not been reported to the best of our knowledge. The other possibility is that this situation could occur on an Extended Range monitor thereby placing the channel in 'accident' or high range mode. If this occurs, the normal range is shut down and/or by-passed. If the accident range detector is online below its minimum operating range and the normal range detector is shut down, an unmonitored release might be possible.

A more detailed analysis of the firmware in specific channels is needed to determine if this last condition is possible.

The possible defect is believed at this time to only affect Model 960 firmware modules upgraded or purchased since 1992.

Evaluation completion date: July 10. 2001

Page Last Reviewed/Updated Thursday, March 29, 2012