- About NRC           - The Commission
      - Statutory Authority
      - Strategic Plan
      - Budget &  Performance
      - Organization & Functions
      - Locations
      - History
      - Values
      - Policymaking
      - Radiation Protection
      - Fire Protection
      - How We Regulate
      - Grants
      - Civil Rights
      -     
    - NuclearReactors           - Operating Reactor Locations
      - Reactor Quick Links
      - Power Reactors
      - Research and Test Reactors
      - Operating Reactors
      - Operator Licensing
      - New Reactors
      - Operator Licensing for New Reactors
      - Reactor Safety Research
      - Advisory Comm (ACRS)
      - Decommissioning of Nuclear Facilities
      -     
    - NuclearMaterials           - Fuel Cycle Facility Locations
      - Uranium Recovery Locations
      - Materials Quick Links
      - Special Nuclear Material
      - Source Material
      - Byproduct Material
      - Med, Academic & Ind Uses
      - Source Materials Facilities
      - Uranium Recovery
      - Fuel Cycle Facilities
      - Materials Transportation
      - Materials Research
      - Advisory Comm (ACMUI)
      - Decommissioning of Nuclear Facilities
      - Materials Environmental Reviews
      -     
    - RadioactiveWaste           - Waste Quick Links
      - Low-Level Waste
      - Waste Incidental to Reprocessing
      - Incidental Waste Criteria
      - High-Level Waste
      - Uranium Mill Tailings
      - LLW Disposal
      - HLW Disposal
      - Spent Fuel Storage
      - Spent Fuel Transport
      - Waste Research
      -     
    - NuclearSecurity           - Security Spotlight
      - NRC Responsibilities
      - Domestic Safeguards
      - Radioactive Material Security
      - Facility Protection
      - Nuclear Material Control
      - International Safeguards
      - Information Security
      - Emergency Preparedness
      - &;   
    - Public Meetings& Involvement           - Public Meeting Schedule
      - Commission	    Schedule
      - Conferences & Symposia
      - Documents for Comment
      - Brochures & Fact Sheets
      - Involving Stakeholders
      - Info Quality Guidelines
      - Rulemaking Process
      - Licensing
      - Enforcement
      - Hearing Process
      - Hearing Applications
      -     

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001

February 17, 1998

**Addressees**

All holders of operating licenses for nuclear power reactors except those licensees who have permanently ceasedoperations and have certified that the fuel has been permanently removed from the reactor vessel.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing a Supplement to Information Notice (IN) 97-45 to alert thelicensees of erratic indications from high-range radiation monitors (HRRMs) as result of a problem with their associatedcoaxial cables. It is expected that recipients will review the information for applicability to their facilities and consideractions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRCrequirements; therefore, no specific action or written response to this notice is required.

**Description of Circumstances**

IN 97-45 addressed issues relating to a potential environmental qualification (EQ) deficiency for cables and containmentpenetration pigtails for HRRMs. After IN-45 was issued, the staff became aware of an additional issue that could result inmisleading the operators in assessing the radiation levels in the containment during an accident scenario. This issue wasidentified as a temperature-induced phenomenon.

During a periodic test of the containment emergency coolers at the San Onofre Nuclear Generating Station (SONGS),Unit 3, the HRRM indicated a "fail" alarm for periods of up to 15 minutes. After completion of the cooler test, an upscalereading of approximately 1 R/hr occurred, decaying back to zero in about 15 minutes. Southern California EdisonCompany's (SCE's) follow up provided more detailed information and evaluation on the transient response of allchannels of the HRRM under postulated accident conditions.

The licensee documented the transient response evaluation and EQ testing results in two internal memorandums that wereprovided to the NRC in an SCE letter (Accession No. 9708250123) dated August 20, 1997. In one of thesememorandums, the licensee concluded that Rockbestos RSS-6-104/LE coaxial cable used previously with the SONGSUnits 2 and 3 HRRMs would undergo significant positive and negative current flow when exposed to transienttemperature conditions. The induced current is the result of temperature stress, specifically the rate of temperature change.Another conclusion was that the detector "keep alive" signal of 1R/hr would provide a false high radiation reading, forapproximately 15 minutes, when exposed to extreme temperature transient conditions inside containment, such as thosepostulated during a loss-of-coolant accident (LOCA) or a main steamline break (MSLB). The magnitude of the falsereading may be in the range of the low thousands of R/hr. The low thousands of R/hr indication spike would last less than1 minute, drop down to hundreds of R/hr, then return to below the alarm setpoint (less than 10 R/hr) in approximately 15minutes.

**Discussion**

The licensee concluded from EQ testing that the magnitude and direction of the spurious signal is a function of thetemperature gradient across the cable insulation. When the cable is heated, the induced current signal is positive and whenthe cable is cooled, the induced current signal is negative. A negative current signal could cause the HRRM to alarm"fail." Consequently, when the cable begins to cool following the initial accident temperature transient, the effect on theHRRM system could be to indicate a false fail signal in the control room if the cooling transient induces a current ofsufficient magnitude to overcome the "keep alive" and/or detector dose rate signal.

A comparison of steam environment test results for 250-foot coaxial cable lengths indicated that cable routed completelyin conduit does not provide relief from thermally induced currents. The test specimens routed completely in conduitdemonstrated a time delay of approximately 60 seconds. The cable samples completely in conduit and partially in conduitexperienced spurious signals of equal magnitude that ranged up to thousands of R/hr.

The results of the testing program performed for the temperature-induced signal phenomena demonstrated that both falsehigh and fail indications could mislead the operators during LOCA and MSLB environmental conditions insidecontainment. The licensee made the following conclusions from the Wyle Laboratory test results:

Operators could be misled in the required actions during an accident scenario if they are not sensitized to the potentialspurious signals from HRRMs. As previously reported IN 97-45, SCE replaced the Rockbestos coaxial cables withstainless steel jacketed mineral-insulated (MI) cables. SCE concluded that the MI cables are not significantly sensitive tothermal transients, moisture intrusion, or sudden air flow across the cable. SCE believes that the stainless steel jacketedMI cable is of a more robust design and will provide a significantly more stable signal than the previously installedRockbestos RSS-6-104/LE coaxial cable during LOCA environmental conditions. However, the MI cable does notcompletely eliminate the temperature-induced signal phenomena in that erroneous signals up to 100 R/hr could existduring severe temperature transients. SCE revised its operator training to ensure that operators were aware of the MI cableresponse for this phenomena.

This information notice requires no specific action or written response. If you have any questions about the informationnotice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation(NRR) project manager.

----