United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-17: Supplement 4, Failure of Control Rods to Insert During a Scram at a BWR

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, D.C. 20555

                               December 18, 1980

IE Supplement 4 to Bulletin No. 80-17: 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 BWR 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, including:

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.



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                                                      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 appratus 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 recommendations.

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.



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                                                      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 per  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 fill 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.



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                                                      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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