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MEMPHIS STATE UNIVERSITY AGN-201 NUCLEAR REACTOR FACILITY LICENSE R-127, DOCKET N0. 50-538 FOLLOW-UP REPORT TO REPORTABLE OCCURRENCE NO. 79-3 Date of Report:              November 26, 1979 Date of Occurrence:          November 16, 1979 Initial NRC Notification: November 16, 1979
MEMPHIS STATE UNIVERSITY AGN-201 NUCLEAR REACTOR FACILITY LICENSE R-127, DOCKET N0. 50-538 FOLLOW-UP REPORT TO REPORTABLE OCCURRENCE NO. 79-3 Date of Report:              November 26, 1979 Date of Occurrence:          November 16, 1979 Initial NRC Notification: November 16, 1979
: 1. Reactor.
: 1. Reactor.
AGN-201, Serial 108. Located at the Center for Nuclear Studies, Memphis State University, Memphis, Tennessee. Facili ty Operating License No. R-127; Docket No. 50-538.
AGN-201, Serial 108. Located at the Center for Nuclear Studies, Memphis State University, Memphis, Tennessee. Facili ty Operating License No. R-127; Docket No. 50-538.
*
: 2. Reportable Occurrence.
: 2. Reportable Occurrence.
Shield Water Level Float Switch Assembly failed to initiate protective trip signal during Prestartup Checkoff. Item 6.9.2.a(5) of the Facility Technical Specifications applies.
Shield Water Level Float Switch Assembly failed to initiate protective trip signal during Prestartup Checkoff. Item 6.9.2.a(5) of the Facility Technical Specifications applies.
Line 30: Line 27:
: b. Shield water level was 8 inches below the highest point on the tank manhole opening which is the normal operating level for the system.
: b. Shield water level was 8 inches below the highest point on the tank manhole opening which is the normal operating level for the system.
: c. Prestartup Checks of the Shicld Water Level Safety Channel were in progress per Facility Operating Procedure OP-2.
: c. Prestartup Checks of the Shicld Water Level Safety Channel were in progress per Facility Operating Procedure OP-2.
                                                                              .
1555 061 79121SO625f
1555 061 79121SO625f
                                  .
    .
  ,
.
      .
: 4. Narrative.
: 4. Narrative.
At 1:10 p.m., CST, on November 16, 1979 Prestartup Checks of the AGN-201, Serial 108 Reactor were being performed to verify operability of the Shield Water Level Safety Channel.
At 1:10 p.m., CST, on November 16, 1979 Prestartup Checks of the AGN-201, Serial 108 Reactor were being performed to verify operability of the Shield Water Level Safety Channel.
                                                                            '
The check is a Channel Test which consists of manually depres-sing the water level float to operate an associated microswitch and thereby interrupt the Interlock Line continuity circuit.
The check is a Channel Test which consists of manually depres-sing the water level float to operate an associated microswitch and thereby interrupt the Interlock Line continuity circuit.
Interruption of the Interlock Line initiates a protective trip signal by deenergizing the system's main scram relay which removes power from--and/or prevents application of power to--
Interruption of the Interlock Line initiates a protective trip signal by deenergizing the system's main scram relay which removes power from--and/or prevents application of power to--
Line 48: Line 37:
Maintenance records indicate that the microswitch had been installed by MSU personnel on September 15, 1978 as part of a routine surveillance procedure. The Shield Water Level Safety Channel had been calibrated to initiate a reactor scram at a water level of 9 inches below the highest point on the manhole 5  062 2
Maintenance records indicate that the microswitch had been installed by MSU personnel on September 15, 1978 as part of a routine surveillance procedure. The Shield Water Level Safety Channel had been calibrated to initiate a reactor scram at a water level of 9 inches below the highest point on the manhole 5  062 2


I
I opening, which confoms to the Limiting Conditions for Operation specified in Table 3.1 of the Facility Technical Specifications.
    -
.
opening, which confoms to the Limiting Conditions for Operation specified in Table 3.1 of the Facility Technical Specifications.
Subsequent Channel Tests required by Item 4.2.d of the Technical Specifications had been satisfactorily performed at least once each month, the trip set-point verified annually, and Channel Tests satisfactorily conducted during approximately 90 Prestartup Checkoffs since the time of switch installation. The most recent satisfactory Channel Test had been perfomed within 27 hours of the time of failure.
Subsequent Channel Tests required by Item 4.2.d of the Technical Specifications had been satisfactorily performed at least once each month, the trip set-point verified annually, and Channel Tests satisfactorily conducted during approximately 90 Prestartup Checkoffs since the time of switch installation. The most recent satisfactory Channel Test had been perfomed within 27 hours of the time of failure.
The microswitch was replaced with a new switch of the same type, was tested satisfactorily, and nomal operations were resumed at approximately 2:30 p.m., CST, on November 16, 1979.
The microswitch was replaced with a new switch of the same type, was tested satisfactorily, and nomal operations were resumed at approximately 2:30 p.m., CST, on November 16, 1979.
Line 58: Line 44:
At nomal operating power, an undetected loss of shield water co.ld increase the gama dose-rate at the reactor exterior by a factor of 7-8, and the neutron background by a factor of several hundred. Compounding an undetected loss of shield water with a nuclear runaway and additional scram circuit failure could result in an exposure of 200-300 Rem of fast neutrons to a person standing next to the reactor.    (Reactor Hazards Summary Report for the AGN-201 Nuclear Reactor: Aerojet-General Nuclecnics Report No. 23, Revised April 1,1959.)
At nomal operating power, an undetected loss of shield water co.ld increase the gama dose-rate at the reactor exterior by a factor of 7-8, and the neutron background by a factor of several hundred. Compounding an undetected loss of shield water with a nuclear runaway and additional scram circuit failure could result in an exposure of 200-300 Rem of fast neutrons to a person standing next to the reactor.    (Reactor Hazards Summary Report for the AGN-201 Nuclear Reactor: Aerojet-General Nuclecnics Report No. 23, Revised April 1,1959.)
1555 063 3
1555 063 3
  .
    .
.
: 6. Redundancy.
: 6. Redundancy.
There is no design redundancy in the Shield Water Level Safety Channel. However, a loss of shield water would be indicated by the following additional mcans:
There is no design redundancy in the Shield Water Level Safety Channel. However, a loss of shield water would be indicated by the following additional mcans:
Line 67: Line 49:
(2) Visual inspection of areas which would receive shield water leakage is made and documented as part of each Pre-Startup Checkout.
(2) Visual inspection of areas which would receive shield water leakage is made and documented as part of each Pre-Startup Checkout.
(3) An increase in radiation levels may be observed during Pre-Startup radiation survey.
(3) An increase in radiation levels may be observed during Pre-Startup radiation survey.
      *
: b. Durina Operation (1) An increase in reactor room radiation levels sufficient to activate the facility evacuation alarm would be detected by the area gamma monitor located approximately 6 feet from the reactor.
: b. Durina Operation (1) An increase in reactor room radiation levels sufficient to activate the facility evacuation alarm would be detected by the area gamma monitor located approximately 6 feet from the reactor.
(2) Shield water levels below s 20 inches from the tank top are visible from the control room via a viewing window directly in front of the AGN console and viewing window in the reactor shield tank (0perator is approxi-mately 17 feet from shield tank 32h x 274 inch viewing window).
(2) Shield water levels below s 20 inches from the tank top are visible from the control room via a viewing window directly in front of the AGN console and viewing window in the reactor shield tank (0perator is approxi-mately 17 feet from shield tank 32h x 274 inch viewing window).
Line 75: Line 56:
           . plunger, was insufficient to overcome the corrosion effects; thus, the switch contacts remained closed and prevented interruption of of the Interlock Line.
           . plunger, was insufficient to overcome the corrosion effects; thus, the switch contacts remained closed and prevented interruption of of the Interlock Line.
4 1555 064
4 1555 064
    .
.
      -
  .
: 8. Corrective Action.
: 8. Corrective Action.
The microswitch was replaced with a new switch of the same type on November 16, 1979.
The microswitch was replaced with a new switch of the same type on November 16, 1979.
Line 93: Line 69:
1555 065 5
1555 065 5


  .
..  ,
d    Il Output terminal to Interlock NC terminal                          Line continuity circuit (not used) '          ;
d    Il Output terminal to Interlock NC terminal                          Line continuity circuit (not used) '          ;
uc;                  m
uc;                  m
                                                                            ' '        *
                                                      ,
: s. 'N'-      -
: s. 'N'-      -
                               '                                                                        Input terminal Plunger actuator                  :    !'                                              '
                               '                                                                        Input terminal Plunger actuator                  :    !'                                              '
from Interlock
from Interlock
                              - -
                                                                         ) __-
                                                                         ) __-
                               \\                                          P'                    om    Ljnecontinuity Leaf spring                        !''  ;' ' ,
                               \\                                          P'                    om    Ljnecontinuity Leaf spring                        !''  ;' ' ,
                                                                                    '
                                                                                            -
                                                            -
                                                                                         's i
                                                                                         's i
                                             / lNp' L ' (- l /
                                             / lNp' L ' (- l /
                                             /
                                             /
                                                                                       'l
                                                                                       'l N
                                                                                          .
circuit
N circuit
                                                                   ~
                                                                   ~
Corroded k    -/'[.              .
Corroded k    -/'[.              .
                                                                         ,#y$^
                                                                         ,#y$^
                                                                          -
operating lever
operating lever
[C
[C
                                                                  -    .
                                   ; l'                                                              (stuck to housing) g\';IO-MICR0 SWITCH Microswitch plunger ceramic housing (shown depressed) 8" Nomal Water Leve]                                                            _
                                   ; l'                                                              (stuck to housing) g\';IO-
                                                    ''
                                                                    ,
                                                                      "        '
MICR0 SWITCH Microswitch plunger
                                                      .
ceramic housing (shown depressed)
                                                          !
8" Nomal Water Leve]                                                            _
l Float N          'y (showndepressed to below its normal operating level)
l Float N          'y (showndepressed to below its normal operating level)
                                                                                   /
                                                                                   /
NOTE: Not drawn to scale.
NOTE: Not drawn to scale.
FIGURE 1. Shield Tank Float Switch Assembly (Microswitch shown in failed position) 1555 066 6}}
FIGURE 1. Shield Tank Float Switch Assembly (Microswitch shown in failed position) 1555 066 6}}

Latest revision as of 16:25, 1 February 2020

Followup Rept to RO-79-3:on 791116,during Prestartup,Shield Water Level Float Switch Assembly Failed to Initiate Protective Trip Signal.Caused by Gradual Buildup of Corrosion Products in Internal Mechanism of Microswitch
ML19290B743
Person / Time
Site: 05000538
Issue date: 11/26/1979
From:
MEMPHIS STATE UNIV., MEMPHIS, TN
To:
Shared Package
ML19290B738 List:
References
NUDOCS 7912130628
Download: ML19290B743 (6)
v • d • e


Text

.

MEMPHIS STATE UNIVERSITY AGN-201 NUCLEAR REACTOR FACILITY LICENSE R-127, DOCKET N0. 50-538 FOLLOW-UP REPORT TO REPORTABLE OCCURRENCE NO. 79-3 Date of Report: November 26, 1979 Date of Occurrence: November 16, 1979 Initial NRC Notification: November 16, 1979

1. Reactor.

AGN-201, Serial 108. Located at the Center for Nuclear Studies, Memphis State University, Memphis, Tennessee. Facili ty Operating License No. R-127; Docket No. 50-538.

2. Reportable Occurrence.

Shield Water Level Float Switch Assembly failed to initiate protective trip signal during Prestartup Checkoff. Item 6.9.2.a(5) of the Facility Technical Specifications applies.

3. Conditions at Time of Occurrence.
a. The reactor was shutdown with Cadmium Shutdown Rod installed in the Glory Hole.
b. Shield water level was 8 inches below the highest point on the tank manhole opening which is the normal operating level for the system.
c. Prestartup Checks of the Shicld Water Level Safety Channel were in progress per Facility Operating Procedure OP-2.

1555 061 79121SO625f

4. Narrative.

At 1:10 p.m., CST, on November 16, 1979 Prestartup Checks of the AGN-201, Serial 108 Reactor were being performed to verify operability of the Shield Water Level Safety Channel.

The check is a Channel Test which consists of manually depres-sing the water level float to operate an associated microswitch and thereby interrupt the Interlock Line continuity circuit.

Interruption of the Interlock Line initiates a protective trip signal by deenergizing the system's main scram relay which removes power from--and/or prevents application of power to--

the control rod drive / latch magnets. The Channel Test is per-formed while the reactor is shutdown and with normal water level in the Shield Tank.

Upon depressing the float to its lowest level, simulating a water level of approximately 9.5 inches below the tank top, the operator did not hear an audible " click" of the associated microswitch which is physically located about 2h inches above the water line; nor was the Interlock Line continuity circuit interrupted as observed by the Senior Operator stationed at the control console.

Operation of the reactor was prohibited. The event was reported to the Region II, U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement via telephone conversation between the AGN-201 Reactor Supervisor and Mr. Paul J. Kellogg, and confirmed by mailgram on November 16, 1979 in accordance with Section 6.9.2a of the Facility Technical Specifications.

Maintenance records indicate that the microswitch had been installed by MSU personnel on September 15, 1978 as part of a routine surveillance procedure. The Shield Water Level Safety Channel had been calibrated to initiate a reactor scram at a water level of 9 inches below the highest point on the manhole 5 062 2

I opening, which confoms to the Limiting Conditions for Operation specified in Table 3.1 of the Facility Technical Specifications.

Subsequent Channel Tests required by Item 4.2.d of the Technical Specifications had been satisfactorily performed at least once each month, the trip set-point verified annually, and Channel Tests satisfactorily conducted during approximately 90 Prestartup Checkoffs since the time of switch installation. The most recent satisfactory Channel Test had been perfomed within 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br /> of the time of failure.

The microswitch was replaced with a new switch of the same type, was tested satisfactorily, and nomal operations were resumed at approximately 2:30 p.m., CST, on November 16, 1979.

5. Safety Sionificance of the Occurrence.

In the event of a shield water leak, failure of the Shield Water Level Safety Channel to initiate a reactor scram at water levels > 10.5 inches below the highest point on the manhole opening during critical operation would.have violated the speci-fied Limiting Conditions for Operation; and at levels greater than 12 inches below the top of the tank, adequate biological shielding would not be provided during reactor operation as specified by the Safety Limit of item 2.1, Technical Specifica-tions.

At nomal operating power, an undetected loss of shield water co.ld increase the gama dose-rate at the reactor exterior by a factor of 7-8, and the neutron background by a factor of several hundred. Compounding an undetected loss of shield water with a nuclear runaway and additional scram circuit failure could result in an exposure of 200-300 Rem of fast neutrons to a person standing next to the reactor. (Reactor Hazards Summary Report for the AGN-201 Nuclear Reactor: Aerojet-General Nuclecnics Report No. 23, Revised April 1,1959.)

1555 063 3

6. Redundancy.

There is no design redundancy in the Shield Water Level Safety Channel. However, a loss of shield water would be indicated by the following additional mcans:

a. Prior to Startuo (1) Shield tank level is verified at the proper level by visual observation and documented as part of each Pre-Startup Checkout.

(2) Visual inspection of areas which would receive shield water leakage is made and documented as part of each Pre-Startup Checkout.

(3) An increase in radiation levels may be observed during Pre-Startup radiation survey.

b. Durina Operation (1) An increase in reactor room radiation levels sufficient to activate the facility evacuation alarm would be detected by the area gamma monitor located approximately 6 feet from the reactor.

(2) Shield water levels below s 20 inches from the tank top are visible from the control room via a viewing window directly in front of the AGN console and viewing window in the reactor shield tank (0perator is approxi-mately 17 feet from shield tank 32h x 274 inch viewing window).

7. Cause of Failure.

Gradual buildup of corrosion products in the internal operat-ing mechanism of the microswitch due to its location in the humid atmosphere of the shield tank resulted in the internal switch operating lever being stuck to the ceramic switch housing (Figure 1).

Spring pressure, which normally opens the active switch contacts when the float operating arm permits movement of the microswitch

. plunger, was insufficient to overcome the corrosion effects; thus, the switch contacts remained closed and prevented interruption of of the Interlock Line.

4 1555 064

8. Corrective Action.

The microswitch was replaced with a new switch of the same type on November 16, 1979.

Manufacturer: Micro-Switch Company; Freeport, Illinois Type- V3-101, SPDT, 0.5 A 0 125 volts D.C.

Mechanical Life: 10,000,000 cycles Minimum Release Force: 2 oz.

9. Measures to Prevent Recurrence.

The microswitch casing is of riveted construction which precludes periodic disassembly and cleaning of switch internals.

Thus, the availability of a model more suitable to a humid environment or a model constructed such that periodic cleaning of switch internals is possible will be investigated. If installation of such a switch is not feasible, then routine replacement of the microswitch with a switch of the same type on an annual basis will be incorporated into the facility surveillance procedures.

10. Applicability to Other Equipment in the Reactor System.

None. Microswitches of similar internal construction but with different terminal connectors and actuating mechanisms are utilized for interlocks and position indication devices in the Rod Control System. However, due to their location outside the humid atmosphere characteristic of the Shield Tank and due to the greater frequency with which they are exercised during normal reactor operation, it is anticipated that corrosion will not be a problem throughout the mechanical life of the switches.

11. Similar Reportable Occurrences.

MSU Followup Report dated June 27, 1977.

1555 065 5

d Il Output terminal to Interlock NC terminal Line continuity circuit (not used) '  ;

uc; m

s. 'N'- -

' Input terminal Plunger actuator  :  !' '

from Interlock

) __-

\\ P' om Ljnecontinuity Leaf spring  !  ;' ' ,

's i

/ lNp' L ' (- l /

/

'l N

circuit

~

Corroded k -/'[. .

,#y$^

operating lever

[C

l' (stuck to housing) g\';IO-MICR0 SWITCH Microswitch plunger ceramic housing (shown depressed) 8" Nomal Water Leve] _

l Float N 'y (showndepressed to below its normal operating level)

/

NOTE: Not drawn to scale.

FIGURE 1. Shield Tank Float Switch Assembly (Microswitch shown in failed position) 1555 066 6

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