05000259/LER-1979-001-01, /01T-0 on 790118:reactor Scrammed Due to High Flux Actuating Intermediate Range Monitor high-high Neutron Monitoring Circuit;Reactor Neared Criticality.Caused by Withdrawal of High Reactivity Worth Rod

/01T-0 on 790118:reactor Scrammed Due to High Flux Actuating Intermediate Range Monitor high-high Neutron Monitoring Circuit;Reactor Neared Criticality.Caused by Withdrawal of High Reactivity Worth Rod

ML19270F310
Person / Time
Site:	Browns Ferry
Issue date:	01/31/1979
From:	TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19270F305	List: 05000259/LER-1979-001, Forwards LER 79-001/01T-0 05000259/LER-1979-001-01, /01T-0 on 790118:reactor Scrammed Due to High Flux Actuating Intermediate Range Monitor high-high Neutron Monitoring Circuit;Reactor Neared Criticality.Caused by Withdrawal of High Reactivity Worth Rod
References
LER-79-001-01T, LER-79-1-1T, NUDOCS 7902060235
Download: ML19270F310 (2)

LER-1979-001, /01T-0 on 790118:reactor Scrammed Due to High Flux Actuating Intermediate Range Monitor high-high Neutron Monitoring Circuit;Reactor Neared Criticality.Caused by Withdrawal of High Reactivity Worth Rod

Event date:
Report date:
2591979001R01 - NRC Website

text

N ORM 366 U. S. NUCLEAR REGUL ATORY COMMISSION 0

UCENSEE EVENT REPORT CONTROL BLOCK: l l

l l

l lh (PLE ASE PRINT OR TYPE ALL REQUIRED INFORMATION) i e

AlLlBlRlFl1l@l0lGl- 0l0 0l0 0 - l0 0 @l 4 l 1 l 1 l 1 1l@i l

l@

o 1 F

8 9 LICENSEE CODE 14 15 LICENSE NUMBE H 25 26 LICENSE TY PE JO

$7 CAT $8 CON'T lOlil [g]lL @ 0l5]0 0l0l2l5l9 @l011l1l8!7 9 @LOI il 31 11719 @

?

8 60 61 DOCKET NUMBE R 68 69 EVENT DATE 14 75 REPOR T DATE 80 EVENT DESCHIPTION AND PROBABLE CONSEQUENCES h lal2l lWhile pulling rods at the end of a refueling outage, the reactor scrammed due to high l lo tal flux actuating the IRM high-high neutron monitoring circuit. The reactor was approachF ing criticality in the B1 number 1 rod sequence. The estimated reactor period l

o 4 [o ig approached 5 seconds. Reactivity anomaly is reported in accordance with T.S. 6.7.2.a.4p o 6 There have been no previous occurrences. There was no hazard to the public health or 10171 i safety.

l 0 H l

l 80 7

8 9 SYSTEM C A US E

CAUSE

COMP VALVE CODE CODE SUBCODE COV'ONENT CODE SUBCODE SUBCODE O 9 Il Dl

[ A l@

Z lZ lZ lZ lZ lZ l@ g@ ]@

F 8

9 10 11 12 13 18 19 20 SEQUEN TI AL OCCURRENCE REPORT REVISION LE R RO 6%ENT YE AR REPORT NO.

CODE TYPE NO.

@R P,c R T l7 [9 l l_l l0 0 l1 l jfl l 0l 1 lTl g

l0 l

_2t 22 23 24 26 27 28 29 Ju 31 32 TAKEN A T ON ON PL ANT M TH HOURS 22 SUBMITT D FOR b B.

SUPPLI MANUF CT RER 1@1@

[ C_j@

l C l@

l0 0 l1 2l y@

lN @

l@

Z lZ lZ Zp Z

33 34 35 36 J1 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS lilol The fast period was caused by withdrawal of a high reactivity worth rod.

Normal plant l t i l i I l practices were being followed. Administrative controls shall require the first rod I

i 7 l in a RWM group to be notched prior to criticality. Precautions have been placed into l lil3l operating instructions.

i FrT41 1 I

7 8 9 80 STA S

% POWER OTHE R ST A TUS iSC HY DISCOVERY DESCH PTiON iTT 1 Bl@ l 0 l 010 l@l NA l

y @l NA l

ACTivlTY CONTENT RELE ASED OF RElf ASE AMOUNT OF ACTIVITY L OCA110N OF HELE ASE Ii is I LZJ @ LzJ@l NA l

NA 7

8 9 10 tt 44 45 80 PE RS JNNE L E R POSURE S

.s -OER TYPE DESCRtPTION -

M { 0l 0 0l@ ] @l NA l

n n SONNu',N;unS DE SCn<P TION @

NuMu R [0 0l0l@l NA l

i a 7

8 9 11 17 80 L OSS OF OH (J AM AGE TO F ACILITY TYPE DE SC RIP T ION LzJ@l NA l

' 9 7

8 9 10 80 PUBL ICI T Y NHC WE ONLY

'ggpsc"'"'o~

7902060ca35 lj y

i i,,ii,,,,

1 8 9 to 68 69 80 ;

N AME OF PREPAREH--._

PHONE:

Fonn BF-17 BF 15.2 6/09/78 LER SUPPLEMENTAL INFORMATION BFRO 259 /

791 Technical Specification Involved None

)

Reported Under Technical Specification 6.7.2.a.4 T! ate of Occurrence 1-18-79 Time of Occurrence 2328 Unit 1

Identification and Description of Occurrence:

Reactor scrammed due to high flux detected by the IRM neutron monitoring circuit.

Conditions Prior to Occurrence:

Pulling control rods to obtain criticality.

Action specified in the Technical Specification Surveillance Requirements met due to inoperable equipment. Describe.

None Apparent Cause of Occurrence:

Too rapil withdrawal of a high reactivity worth control rod.

Analysis of Occurrence:

Withdrawal of high reactivity worth control rods must be slow enough to allow full development of ensuing reactor periods.

Corrective Action

The fast period was caused by withdrawal of a high reactivity worth control rod.

The operator, following normal practice, allowed the rod to continuously withdraw since neutron monitoring instruments indicated the reactor to be far subcritical.

Operator action to reinsert the rod failed to reduce the period and resulted in a reactor trip. Administrative controls have been implemented to require the fiist Failure Data: rod in a RWM grbup to be notched before criticality.

Precautions pertaining to high rod worths have been inserted into operating instructions.

None Tennessee Valley Authority - Browns Ferry Nuclear Plant