IEB 80-17 Supplement 4, Failure of Control Rods to Insert During a Scram at a BWR (Generic Letter 80-111)

                                                            SSINS No.:  6820
                                                            Accession No. 
                                 UNITED STATES              IEB 80-17 Sup. 4  
                         NUCLEAR REGULATORY COMMISSION 
                           WASHINGTON, D.C.   20555 

                               December 18, 1980 

IE Supplement 4 to Bulletin N. 80017:  FAILURE OF CONTROL RODS TO INSERT 
                                       DURING A SCRAM AT A BWR 

NRC staff evaluation of failures of the continuous monitoring system (CMS) 
for the scram discharge volume (SDV) at an operating DWR has identified the 
need for licensee actions in addition to those requested by IEB 80-17 and 
Supplements 1-3.  The purpose of these actions is to provide assurance that 
the CMS has been tested to demonstrate operability as installed, remains 
operable during plant operation, and is periodically surveillance tested to 
demonstrate continued operability. 

The occurrence of CMS failures at Dresden Nuclear Power Station was 
discussed in IE Information Notice 80-43, which was issued on December 5, 
1980 to those operating BWR's with CMS recently installed.  Subsequently, 
investigation into the cause of the failure to receive the alarm with the 
SDV essentially full revealed several items which required correction, 

1.  Excess portions of transducer cable were placed in physical positions 
    which would increase external noise sensitivity. 

2.  The UT transducers were not placed in a physical position to optimize 
    system sensitivity. 

3.  A certain amount of "cross-talk" was occurring between redundant 
    transducers located a few feet apart on the same run of 4" pipe. 

Station and vendor personnel shortened and rerouted transducer cables to 
improve noise rejection.  Vendor specialists optimized transducer placement 
and synchronized both transducers to the same ultrasonic instrument internal
clock to minimize cross-talk and improve signal to noise characteristics. 
Following these actions the CMS appeared to function properly. 

Further difficulties were encountered when apparently minor quantities of 
water leaked into the SDV as a result of control rod drive scram valve 
maintenance activities and minor scram outlet valve leakage.  It appears 
that the transducers are located on a section of SDV piping which forms a 
local low point.  Accordingly, small amounts of water can accumulate to a 
depth which triggers the high level alarm (at 1-1/4") before the water 
drains to the instrument volume.  The licensee in conjunction with the NSSS 
vendor, performed a unit specific analysis for a conservative high alarm 
setpoint and reset the alarm point to 2-1/2".  The system now appears to 
function properly. A five second alarm time delay was also installed to aid 
in rejecting spurious alarms. 

                                                          IEB 80-17 Sup. 4 
                                                          December 18, 1980 
                                                          Page 2 of 4 

Potential malfunction modes which are still of concern are: 

1.  The capability of the CMS to adequately determine level of water for the
    entire range of depths which may occur during slow and rapid fill 
    conditions, that is, beam penetration capability. 

2.  The potential for loss of transducer sensitivity during periods of rapid
    flow, or when the water being detected is turbulent or mixed with 
    entrained air or steam bubbles. 

The ability of the CMS installed in your facility to operate in respect to 
these concerns should be considered in the preparation of your response to 
this bulletin.  The following actions are requested in addition to those 
specified in IE Bulletin 80-17 and Supplements 1 through 3. 

Actions to be Taken by Licensees of Operating BWR's Using CMS 

1.  Bench Test of CMS 

    Make available the following information which describes the CMS design 
    and the bench tests which have been performed to demonstrate system 
    operability and sensitivity: 

    (a)  System description including a schematic of the apparatus and 
         associated electronics. 

    (b)  Type of sensing device and characteristics (include response 
         characteristics versus temperature). 

    (c)  Calibration criteria, including transmission losses. 

    (d)  Training and testing of personnel performing the calibration test. 

    Items a through c above may be referenced by the licensee if the 
    information has been submitted to the NRC by the equipment manufacturer.

2.  Operability Test of CMS 

    Prior to conducting the operability test, verify that the CMS on the SDV
    is installed and calibrated in accordance with the vendor 

    In order to provide assurance of operability of the CMS, if not already 
    performed conduct an operability test within 14 days of the date of this
    bulletin.  In this test, inject a sufficient amount of water into each 
    SDV header to determine that the ultrasonic transducers are adequately 
    coupled to the SDV piping and that the trip alarm function of the CMS 
    will perform satisfactorily.  The test may be performed by single 
    (multiple) rod scram tests while operating.  No water may be introduced 
    into the SDV header while the reactor is operating except using the 
    scram function.  Independent level measurement must be used to verify 
    CMS operation and proper calibration. 

                                                          IEB 80-17 Sup. 4 
                                                          December 18, 1980 
                                                          Page 3 of 4 

3.  Interim Manual Surveillance 

    In the interim 14-day period before the operability test is completed, 
    perform a manual surveillance for the presence of water in the SDV at 
    least once pe shift and after each reactor scram.  In order to provide 
    assurance that manual surveillance can detect water accumulation in the 
    SDV, verify that the method and the operator have been qualified by 
    testing which uses or simulates the SDV piping and has the ability to 
    detect different levels of water in the SDV. 

    Surveillance of SDV manual measurement techniques should be done before 
    completion of the operability test described in Item 2 above. 

4.  Full Test of CMS to be Conducted During a Planned Outage 

    During a planned outage within six months, perform a full CMS test using
    the SDV headers: 

    (a)  Admit water into the SDV to establish full rates for several (not 
         less than three) in-leakage flow rates.  The in-leakage rates 
         should range from approximately the minimum which results in water 
         accumulation in the SDV to a full scram. 
    (b)  Establish and record the response of the CMS indication and alarm 
         functions from the trip level to a full SDV.  Provide criteria for 
         replacement or adjustment when exceeding design specifications of 
         the system. 

    (c)  Verify by independent measurement that the alarm initiates at the 
         proper level setpoint. 

5.  Operability of CMS During Reactor Operation 
    The CMS shall be operable prior to reactor startup and during reactor 
    operation.  If the CMS becomes less than fully operable, within 8 hours 
    perform a manual check for water in the SDV and institute procedures 
    for a manual check of the SDV each shift and following scram until the 
    CMS is fully operable.  When not fully operable, the CMS should be used 
    to the extent practical in addition to the manual checks. 

    If the CMS is not operable within 7 days, the frequency of the manual 
    check should be increased to once every 4 hours.  If the CMS is not 
    operable within 30 days the plant shall be shutdown. 

    To demonstrate continued operability of the CMS during reactor 
    operation, perform periodic surveillance tests for operability of the 
    CMS.  For these periodic surveillance tests, test as much of the CMS as 
    practical during reactor operation without injecting water in the SDV.  
    Establish criteria for repair or replacement when the system design 
    criteria or estimated service life limitations are exceeded.  The 
    frequency of these periodic surveillance checks should be determined by 
    the licensee. 

                                                          IEB 80-17 Sup. 4 
                                                          December 18, 1980 
                                                          Page 4 of 4 

    These periodic surveillance tests should include the following: 
    (a)  determination that the response and power output of the transducer 
         has not degraded; 

    (b)  visual inspection for adequate condition of the transducer to SDV 
         coupling material; and 

    (c)  a calibration check of the electronics to assure alarm initiation 
         in the control room. 

    Water should be periodically injected into the SDV to perform a CMS 
    operability and calibration check similar to that specified in Item 2 
    above.  This check should be performed semiannually and during startup 
    after plant outages where maintenance operations may have taken place 
    near to CMS equipment. 

6.  Operating Procedures 
    Develop procedures for operation, periodic testing and calibration of 
    the CMS and for repair or replacement when system design specifications 
    are exceeded.  Develop procedures for the calibration and use of the 
    hand held UT device in the event of a malfunctioning CMS.  Notify the 
    NRC before changing the established CMS alarm level setpoints. 

Licensees of all operating BWRs with a CMS shall provide the information 
requested in Item 1 and shall submit a report summarizing action taken in 
response to each of the above items within 45 days of the date of this 
Bulletin Supplement.  Accordingly, you are requested to provide within 45 
days as specified above, written statements of the above information signed 
under oath or affirmation under provisions of Section 182a of the Atomic 
Energy Act of 1954.  Reports shall be submitted to the Director of the 
appropriate NRC Regional Office and a copy forwarded to the Director, NRC 
Office of Inspection and Enforcement, Washington, D.C. 20555. 

This request for information was approved by GAO under a blanket clearance 
number R0072 which expires November 30, 1983.  Comments on burden and 
duplication should be directed to the U.S. General Accounting Office, 
Regulatory Reports Review, Room 5106, 441 Eighth Street, N.W., Washington, 
D.C. 20548. 


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