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Information Notice No. 83-23: Inoperable Containment Atmosphere Sensing Systems
SSINS No.: 6835 IN 83-23 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 April 25, 1983 Information Notice No. 83-23: INOPERABLE CONTAINMENT ATMOSPHERE SENSING SYSTEMS Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is being issued to remind all licensees of the importance of assuring that procedures are both properly developed and carefully followed. The instances cited relate to the containment system, an important element in the "defense-in-depth" approach to nuclear safety and are of particular concern because some had apparently existed for several months without detection. Description of Circumstances: Seven instances have been compiled since April 1981 that indicate insufficient licensee management attention is being given to maintaining containment integrity, and to the operability of equipment related to the containment function. At LaCrosse Nuclear Generating Station on two separate occasions in April 1981, a containment high-pressure sensing switch was temporarily isolated while the plant was at power, thus defeating automatic emergency core cooling system actuation. A proposed design change was being implemented without proper review and authorization. Subsequently, it was determined that under 10 CFR 50.59, the change should not have been made without concurrence by the Nuclear Regulatory Commission. At Oconee Nuclear Station, in March 1982, an NRC inspector found that a pipe cap had not been reinstalled on a test connection to a containment pressure sensing line, as required by the relevant test/calibration procedure last performed in July 1981. As a result, containment integrity had been violated for that interval, and the sensing system (although operable) was degraded. Containment pressure as sensed by the system could be significantly lower than actual containment pressure. At Dresden Unit 2, there is a local sight (gage) glass on the side of the suppression pool to show the level of the water in the pool. In October 1982, the 8303040025 . IN 83-23 April 25, 1983 Page 2 of 3 licensee reported finding the upper isolation valve and the vent valve open. This violated containment integrity, and allowed free communication between the inerted atmosphere of the suppression pool and the outside atmosphere. In fact, both the upper and lower isolation valves should be closed, except when calibrating other level-sensing devices, while shut down. At Kewaunee Nuclear Station, the licensee reported in October 1982 that all containment pressure-sensing lines were found to have pipe caps installed, thereby defeating the entire containment pressure-sensing systems, including alarm and emergency core cooling functions. The licensee believes the caps were improperly left in place after required testing and calibration about five months earlier. At Arkansas Nuclear One on December 16, 1982, during performance of routine refueling surveillance of the reactor building pressure transmitters, the licensee discovered that the inlet ports on two transmitters were blocked with brass pipe plugs. One of the two inoperable transmitters provide an input to a recorder; however, the other instrument provides a signal to one of three engineered safeguards actuation system (ESFAS) safety channels. With this transmitter input plugged, the ESFAS logic for reactor building high pressure was reduced from a 2 out of 3 to a 2 out of 2 trip logic required for the initiation of engineered safeguards. It was determined that the plugs were installed on February 20, 1981, as a prerequisite for a containment integrated leak rate test and remained installed until their discovery on December 16, 1982 during the next refueling outage. The licensee attributed the specific cause to use of an inadequate temporary test procedure change which allowed plugs to be installed in the pressure transmitters but did not contain a step specifically requiring their removal. At Calvert Cliffs Nuclear Power Plant on June 18, 1982, an NRC inspector and licensee representative were examining containment system boundaries of Unit 1 in preparation for a containment integrated leak rate test. They discovered two of the four safety-related containment pressure sensing lines were isolated with pipe caps inside containment, thus deactivating containment pressure monitoring instruments which provide protection signals to the safety systems. A review of records and logs from the previous operating cycle revealed that this inoperable condition did not exist prior to the last refueling outage. The licensee reviewed records and conducted an investigation but was unable to determine who installed the pipe caps; when they were installed; or with what authorization. It was however assumed that they were installed by mistake during the prior outage. In each of the above instances, in normal operation there is little difference between containment pressure and ambient atmospheric pressure. For pressure differences of the magnitude expected in normal containment system operations, verification techniques such as trend plotting of averaged output values may be beneficial to supplement visual verification of individual component status. At Salem Nuclear Station, on October 17-18, 1982, the licensee found during containment purge operations that radiation monitor sensing lines, which provided high radiation level automatic containment isolation signals, had been temporarily capped while making a design change, and the caps had not subsequently been . IN 83-23 April 25, 1983 Page 3 of 3 removed as required. The work had been performed during a refueling outage which terminated on April 11, 1982. Systems for sensing airborne radioactivity typically include a blower or air pump to extract a sample of the air being monitored and direct it through or past sensors. For the very low levels of activity normally expected, some technique is required for integrating total activity over a known time interval. To achieve acceptable accuracy of calibration, the actual flow (quantity of air in the total sample) must be known. Periodic observation of the flow measuring device provides a simple means of verifying this aspect of system operability, and would have detected the capped lines at Salem. Although all the examples cited above involve sensing of containment atmosphere conditions, (pressure and radioactivity) and the licensee event reports do not in each case identify why the anomalous condition existed undetected for so long a time, the NRC staff is of the opinion that inadequate surveillance procedures, or inadequate implementation of the procedures, or both, were the underlying cause(s) of the situations. Further, a variety of other instances have appeared in licensee reports indicating that surveillance of operability of other safety-related systems could be improved. No specific actions are required of any licensee by this Information Notice. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: J. B. Henderson (301) 492-9654 Attachment: List of Recently Issued IE Information Notices .
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