UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION 

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555

August 4, 2003

NRC INFORMATION NOTICE 2003-10: CRITICALITY MONITORING SYSTEM

DEGRADATION AT BWX TECHNOLOGIES, INC.,

NUCLEAR PRODUCTS DIVISION, 

LYNCHBURG, VA

Addressees:

All U.S. Nuclear Regulatory Commission (NRC) licensees authorized to possess a critical mass

of special nuclear material.

Purpose:

NRC is issuing this information notice (IN) to inform addressees of a safety concern in EC1-X

and EC2-X Thermo Electron (formerly Eberline) analog monitors. The safety concern arises

when these systems, used as either in-line monitors or criticality monitors, are exposed to

power surges, such as in a lightning storm, causing a failure of the alarm function of the EC1-X

and EC2-X monitors without indication. It is expected that licensees will review this information,

and consider actions, as appropriate, to avoid similar problems. However, suggestions

contained in this IN are not NRC requirements; therefore, no specific action nor written

response is required.

Background:

Under 10 CFR 70.24(a), certain licensees are required to maintain, “in each area in which such

licensed material is handled, used, or stored, a monitoring system...using gamma- or neutronsensitive radiation detectors that will energize clearly audible alarm signals if accidental

criticality occurs.”

Description of Circumstances:

Recently, a lightning storm triggered several alarms in a fuel facility’s criticality monitoring

system. A storm watch procedure was in effect at the time and the criticality monitoring system

alarms had been disabled to prevent inadvertent activation by the lightning storm. The storm

watch procedure is a compensatory measure, whereby individuals are stationed throughout the

facility with monitors, to compensate for loss of detection or inadvertent alarm sounding

because of a lightning strike. After the storm, all alarms were reset except one, which had been

damaged to the point of failure. After replacement of the failed monitor/detector pair, there was

no indication of any further problems and the system was released for operation.

ML032160016
IN 2003-10

Page 2 of 2

Later, a criticality monitor trouble indication was received. A technician’s subsequent

investigation revealed that the lightning strike on May 10 had damaged the alarm circuitry of six

EC1-X and EC2-X monitors, causing a failure in the ability to generate alarms, but had not

affected the ability of the analog meters to accurately indicate radiation levels. The licensee’s

investigation revealed that the lightning “surge” caused the logic chip in the A6 location to fail. 

After the investigation, the licensee took the following corrective actions: 1) evaluated the

placement of criticality monitoring components and modifications to prevent lightning damage;

2) evaluated other potential causes for failure of the alarm circuits; 3) established procedures to

source-check all monitors after a lightning storm or whenever the operability of a single monitor

was in question; and 4) implemented a formalized checklist that contains step-by-step

instructions for use following a storm or system component failures. At the time of this IN,

analysis was continuing to determine if additional actions were needed to address this safety

concern.

Discussion:

The EC1-X and EC2-X monitors have a Thermo Electron modification for criticality detection,

the main feature of which is a “saturation” circuit, which provides an alarm signal caused by

high GM detector current in a high gamma field. In the monitor, the criticality signal is jumpered

from pin 7 to the OR gate on the A6B chip. If damaged by lightning, the defect allows the

monitors to indicate radiation levels, but the monitors will not alarm. During this failure, the

monitors’ “NORMAL” indicator light remains lit. These devices fail to operate in a “fail safe”

mode and give external indications after becoming disabled.

NRC is aware that other licensees use the Thermo Electron equipment discussed in this notice

for similar purposes. Therefore, licensees should consider actions, as appropriate, to mitigate

this vulnerability. These actions could include consulting technically qualified individuals for

recommendations to mitigate this vulnerability, implementing changes to the hardware, and

revising the procedures for responding to these events.

This IN requires no specific action nor written response. Questions about this matter may be

referred to the technical contact listed below or the appropriate NRC facility Project Manager.

/RA/ /RA/

William D. Beckner, Chief Robert C. Pierson, Director

Reactor Operations Branch Division of Fuel Cycle Safety and Safeguards

Division of Inspection Program Management Office of Nuclear Material Safety and Safeguards

Office of Nuclear Reactor Regulation

Technical Contact: Billy Gleaves, NMSS

301-415-5848

E-mail: bcg@nrc.gov

Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices