United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-17: Failure of 76 of 185 Control Rods to Fully Insert During a Scram at a BWR

                                                      SSINS No.: 6820      
                                                      Accession No.:       

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION

                                 JULY 3, 1980



Description of Circumstances:

On June 28, 1980, 76 of the 185 control rods failed to fully insert during
a  routine shutdown at TVA's Browns Ferry Unit No 3 located at Athens
Alabama.  The reactor was manually scrammed from about 30 percent power in
accordance  with routine shutdown procedures. The shutdown was initiated to
repair the  feedwater system. The 76 control rods that failed to fully insert
were all on  the east side of the core.

Following scram discharge volume (SDV) high level bypass and a short drain 
period of the SDV, a second manual scram was initiated and all partially 
inserted rods were observed to drive inward, but 59 remained partially 
withdrawn. A third manual scram was made, again following high level in the 
SDV and bypassing for another short drain of the SDV, with the result that
47  rods remained partially withdrawn. Following a longer drain of the SDV,
an  automatic scram occurred that was initiated by a scram discharge volume
tank  high water level signal when the scram reset switch was placed in
"Normal";  with this scram all remaining rods fully inserted. The total time
elapse from  the initial scram to the time that all rods were inserted was
approximately 15  minutes. Core coolant flow, temperature and pressure
remained normal for plant  conditions. The unit is now shutdown and
additional testing indicates that a  possible cause of the malfunction was
the retention of a significant amount of  water in the east bank scram
discharge volume. In view of these interim  findings and pending results of
continued investigation, the following actions  are to be taken.

Actions To Be Taken By Licensees:

All General Electric Boiling Water Reactors with operating licenses which are 
operating at any power on the date of this Bulletin shall perform the 
following steps in the time stated. Those that are presently shutdown shall 
perform the following steps prior to operating at power.

1. Within 3 days from the date of this Bulletin, perform surveillance tests
to  verify that there is no significant amount of water in the Scram
Discharge  Volume (SDV) and associated piping and that the SDV vent valves
are operable  and vent system is free of obstruction.


IE Bulletin No. 80-17                                        July 3, 1980 
Page 2 of 4

2. Within the next 20 days, perform one manual and one automatic scram in
that  order at normal operating temperature and pressure and with more than
50  percent of the rods fully withdrawn, and obtain the following information
on  each scram:

a) All rod insert times and as many individual rod scram times as

b) Voltage at the scram solenoid valve buses to verify that these solenoids 
are de-energized upon receipt of scram signal.

c) Verify that scram valve air is relieved through the backup valves and that 
the backup valves are fully open and remain open during the presence of a 
scram signal.

d) Measure fill time of the instrument volume from scram initiation to
closure  of the scram instrument volume high level alarm switch, to closure
of the rod  withdraw block switch on the instrument volume and to the closure
of the scram  instrument volume reactor scram switch.

e) Measure vent and drain valves opening and closing times utilizing the
valve  stem mounted switches. This measurement may be made independent of the

f) Measure the delay time from scram initiation to closure of the SDV vent
and  drain valves utilizing the stem mounted position switches.

g) Sample water from the instrument volume discharge after each scram for 

h) Measure the time to drain the SDV down to a repeatable reference level.

i) Monitor the SDV and associated piping for residual water.

j) Verify that the ten (10) second delay on scram reset is functioning 
properly to prevent resets of momentary scram signals.

k) Compare the results of the two sets of data taken above with each other
and  with any previously obtained data.

3. At the conclusion of the scram tests and all other scrams, verify that all 
vent lines on the SDV are functional. Verify that there is no significant 
amount of water in the SDV and associated piping.

4. Within 10 days, complete a review of emergency operating procedures by the 
licensee and the NSSS vendor to assure that, for scram, operator actions 


IE Bulletin No. 80-17                                        July 3, 1980 
Page 3 of 4

a) Place the reactor mode switch in a position other than RUN.

b) Determine whether either of the two conditions below exist:

(1) Five (5) or more adjacent rods not inserted below the 06 position.

(2) Thirty (30) or more rods not inserted below the 06 position.

c) If either condition 4.b.(1) or 4.b.(2) exists:

(1) Trip the recirculation pumps.
(2) Insert rods manually. If rods cannot be inserted manually, alternately 
reset the RPS and scram the reactor until all rods are fully inserted. 
(3) Vent the scram air header.
(4) Manually open or bypass the scram instrument volume drain and vent
valves,  if possible.

c) If, at any time, either condition 4.b.(1) or 4.b.(2) exists and either RPV 
water level cannot be maintained or suppression pool water temperature cannot 
be maintained below the suppression pool water temperature scram limit, 
initiate the SLCS.

e) Review the Browns Ferry occurrence with all licensed operators and train 
them in the procedures to recognize and mitigate the event. Verify that 
preliminary training of operators is completed within 10 days of the date of 
this Bulletin and that full training is completed within 30 days of the date 
of this Bulletin.

5. Review and develop surveillance procedures such that scram discharge
volume  is monitored daily for residue water for 6 days and, if results are
acceptable  the interval may be extended to 7 days.

6. In order to mitigate the consequences of an ATWS event, enhanced 
operability of HPCI, RCIC, SLCS, RPT/RHR/pool cooling and main steam bypass
is  essential. Accordingly, the following actions are requested:

a) Prompt notification (within 24 hours) of any of the above systems when it 
is less than fully operable and when it is restored to service. Operability
of  both pumps in the SLCS is required for full operability. Surveillance
tests  and preventive maintenance less than 24 hours need not be reported.

b) Operate all the available suppression pool cooling whenever the
suppression  pool exceeds the normal operating temperature limit.

c) Perform a 50.59 review to increase SLCS flow to the maximum consistent
with  safety (2 pumps, unless unsafe).


IE Bulletin No. 80-17                                       July 3,1980 
Page 4 of 4

7. For plants without ATWS related RPT, perform an analysis of the net safety 
of derating such that, in the event of an ATWS, calculated peak pressures do 
not exceed the service Level "C" limit (~/1500 psig) by taking into 
consideration the heat removal capability of safety valves, isolation 
condenser, bypass to the main condenser and other available heat removal 

8. Report in writing within 5 days of the performance of each of the tests 
results (except for the daily tests) and the results of your review and 
include a list of all devices which respond as discussed above, actions taken 
or planned to assure adequate equipment control, and a schedule for 
implementation of corrective action. Report in writing within 10 days, the 
analyses specified by Item 7 above. This information is requested under the 
provisions of 10 CFR 50.54 (f). Accordingly, you are requested to provide 
within the time periods specified above, written statements of the above 
information signed under oath or affirmation. Reports shall be submitted to 
the Director of the appropriate NRC Regional Office and a copy shall he 
forwarded to the Director NRC Office of Inspection and Enforcement, Division 
of Reactor Operations Inspection, Washington, DC 20555.  

For all boiling water power reactor facilities with a construction permit, 
this Bulletin is for information only and no written response is required.

Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was 
given under a blanket clearance specifically for identified generic problems.

Page Last Reviewed/Updated Tuesday, July 23, 2013