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SSINS No.: 6835 IN 83-62 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 September 26, 1983 Information Notice No. 83-62: FAILURE OF REDUNDANT TOXIC GAS DETECTORS POSITIONED AT CONTROL ROOM VENTILATION AIR INTAKES Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as notification of events that involve the degradation and subsequent common-cause failure of toxic gas detectors for control room ventilation systems. It is expected that recipients will review the information herein for applicability to their facilities. No specific action or response is required at this time. Description of Circumstances: During the five-year period, 1977 through 1982, approximately 64 licensee event reports have involved the failure of one or more chlorine and ammonia detectors positioned at the air intakes of control room ventilation systems. To date, for the present year, there have been four such failures. The frequency of events corresponds to a significant failure rate, since not all nuclear power plants have toxic gas detectors. There have been several instances of releases of toxic gases at nuclear power plant sites. Although these events apparently were not complicated by concurrent failure of toxic gas detectors, this certainly is a possibility. During 1977 to 1982 actual chlorine gas releases occurred at Millstone (March 1978) and Browns Ferry (June 1979). While neither release involved more than a gallon of liquid chlorine, a total of 20 persons, including one control room operator, were hospitalized because of chlorine gas inhalation during both incidents. IE Circular No. 80-03 titled "Protection From Toxic Gas Hazards" provided detailed information pertaining to the Millstone and Browns Ferry releases, potential source's of toxic gas, and applicable regulations for toxic gas hazards. Information Notice No. 82-43 also dealt with deficiencies in LWR air filtration and ventilation systems. 8308300342 . IN 83-62 September 26, 1983 Page 2 of 2 More recently, an incident involving a chlorine gas release occurred on June 6, 1983 at the Oyster Creek nuclear plant. A plastic pipe failed on the outlet side of an evaporator, expelling the toxic gas. The reactor and the turbine buildings were evacuated. Of the 25 people transported to the hospital, all but one were permitted to leave the same day. This occurrence and the other two previously noted, typify the significant and potentially fatal repercussions associated with chlorine or ammonia gas releases, and the need to have operable toxic gas detectors. The toxic gas detector most susceptible to failure is the type which utilizes a dripping electrolyte. This detector can fail because of a clogged electrolyte wick or orifice, excess electrolyte consumption between scheduled replenishments, and absorption of the electrolyte by dust accumulation. Other factors contributing to failures are dust raised by nearby construction, periods of high wind or low humidity, and seasonal high pollen counts. Redundant toxic gas detectors are exposed to the same intake airflow for ventilation systems, and may therefore fail from a common cause, i.e., exposure to the same source of dirty air. The personnel of some facilities using such toxic gas detectors are considering either increased surveillance or replacement with a more reliable type of detector to preclude continuing failures. 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: R. M Young, IE (301) 492-7275 Attachment: List of Recently Issued IE Information Notices .
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