ML20046B031

LER 93-012-01:on 930524,turbine & Reactor Tripped During Mussel Cook (Thermal Backwash) Due to Lack of Heat Removal Capabilities from Main Generator Stator Water Cooling Sys. Installed Thermoconductivity filler.W/930723 Ltr

ML20046B031
Person / Time
Site:	Millstone
Issue date:	07/23/1993
From:	Haynes H, Hoagland Z NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-012, LER-93-12, MP-93-590, NUDOCS 9308030024
Download: ML20046B031 (6)

Text

_ _ _

• e  :

. l NORTHEAST tmLITIES oenere' = ces saenS"eet Beran connecocut l

3 w sin 7/aIsIenYk tUE1e cC an7 P.O. BOX 270

( '

N[r$r*I[$InNYery a c7c*Nuany

' Northeast Nuc' ear Erggy Company e

HARTFORD, CONNECTICUT 06141-0270 (203)665-5000 l

1 July 23, 1993 MD-93-590 .

Re: 10CFR50.73(a)(2)(iv) 10CFR50.73(a)(2)(ii)(B) i l

U.S. Nuclear Regulatory Commission l Document Control Desk Washington, D.C. 20555

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336 Licensee Event Report 93-012-01 Gentlemen: l l

This letter forwards an update to Licensee Event Report 93--012-01.  ;

Very tru.'y yours, i NORTHEAST NUCLEAR ENERGY COMPANY FOR: Stephen E. Scace Vice President - Millstone S*ation

(

mi ,

7 Lt _

BY: Harry F. ( 'i ) ne.

. , (..

Millstone UnJt 1 irector  !

SES/ZH:bjo

Attachment:

LER 93-012-01 cc: T. T. Martin. Region 1 Administrator P. D. Swetland, Senior Resident inspector, Millstone Unit Nos.1, 2 and 3 G. S. Vissing, NRC Project Manager, Millstone Unit No. 2 n

s DR ADO [ ,

g

• i i

NRC FO'm 360 US nucle AR REGULATORY COMM:SS10N APPROVED OMB NO 3160-0104 8 i

@ 89) E.xPtRES 4 /30/B2 Estimated bs oen per response to compty w!n te ns {

g

{

informa1 eor coue: tion reavest . 50 C rn Forwarc a comments rer,arding buroen estimate to tne r<eco ds LICENSEE EVENT REPORT (LER) ana Reports Manager =nt e enen m-sact u s Navear Rega:atory Comm:suon Wasmngton DC 20f,55, and to tw Paperwom Recuction Prorect (3150-0104i Office et Management anc Bsapet. Aasnmgton DC 20503 f F ACILrrY NAME (t j DOCKE I NUM68 (21 CV- -

l Nidlstone Nuclear Power Stanon Unit 2 ofsiololol3l3is 1 lod 0l5 i T;TLE i4)

Turbine and Reactor Tnp Dunng N1ussel Cook (Thermal Backwash) eve NT oiTE (5 - L E A NUMPEG @ AFDOAT D ATE m OT HE A F A01UTIE S INvot vFO @

VONTF DAY VEAR VEAA y [g* MONTH DAY VEAq F ACluTY NAME5 '

ofslofofol 1 1

~ ~

0l5 2l4 9 3 ol.3 ol1l2 ol i ol7 2 l3 9l 3 olslolofof l l OPE R/, TING T45 AEPORT 15 BEING SJOCTED PURSUANT TO THE PEQJREME NTS OF 10 CFA 6: (Cheo one or rnye c41% fonowng)(11) 20 4;2(c) 2; 402;c) V SD 73(al f21 hv) 73 71 4) pOwpp 2:: 405: a : (11 t o 60 36scir11 50 73(al(2;M 73 71gc)

Y ll0l0 20 435 f a a f

• i t u i 50 36(cli21 SC 73 la)(2)(m) -

OTHEA f 5pecW m Aostract timow anc 'n e :: C5ialf t lim 50 73(alt ro 50 73la)(211vao t Ai l ext. NRC Forrn 366 A) 20 405:a!(liev N 50 73:a] Teit0 50 73!ali2i f wo Gs J 4Wat P1 t 3 SC 73(a6:2)imi 53 73f alf2) f N UCENSEE CON'ACT COA TH 9 LEP Im NAME TE LEPHONE NUMBER AREA CODi Zan Hogland. Engmeer. X 4725 2l0l3 4l4l7l-l1l7l9l1 COMPLETE ONE UNE FOR E ACM COMPDNENT F AtiUAE DE SOA BED rN TH'S REPOAT tt3) [

CAUSE S Y S T E PJ CoupONENT Th[ QMI CAUSE SYSTEM C OMPONE NT $$ ,p,Yg l l II I I I I II I I I I l i I l l I I 1 II 1 I I I SJPP .EMEV AL 8;E PO47 EXPECTED 114)

MONTH DAY YEAR suevassioN

] vE S gg ves wwete E XPEcED SUEMSStON C ATE) NO l l l ABSTRACT pm:t tc 14D0 En::es as. notommatch 5*4eq singesrace twewntter tines) (SE)

On Niav 24,1993. at 0043 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br />, wnh the p! ant m N1 ode 1 at 100G power. a reactor inp occurred due to a turbine tnp. The turbine inp was caused by high generator stator cooling water temperature resulting from mussel cookmg (thermal backwash) operanons on the 'B' condenser waterbox. During the subsequent transient, a malfunction caused the 'A' feedwater regulating salve to stay at approximately 569 open which caused the #1 steam generator water lesel to increase to the high level setpomt. The reactor operator tripped the running feedwater pump bated on the high steam generator water level. Steam generator water levels were subsequently controlled usmg the auxiliar> feedwater system. Operators performed Emergency Operating Procedure 2525.

" Standard Post Tnp Acuansf All safety related equipment. wnh the exception of the mam feedwater regulating valves, responded as expected and the umt was pl3:ed in a stable condmon. Durmg the event investigauon subsequent to the inp, n was discosered that during the muuel cook, Reactor Buildmg Closed Cochng Water

( R BCCW ) temperatures momentan13 exceeded 55'F which potentially resulted in the plant bemp outside of its design b.eis. RBCCW temperatures immedmteh returned to normal.

l These everm are being reported pursuant to the requirements of Paragraph 50.73(a)(2)(iv) and Paragraph 50.73(a)(2(ii)(B) reporung any event or cond;uon that resuhed m manual or automauc actuation of any l Enpneered Safety Feature Ss stem mcluding the Reactor Protection system and to report an event or condition that potennall) resuhed m the nuclear power plant bemp in a condition outside the design basis of the plant. l NH C V orm 366 1 (649) )

I 1

FAC Fo-m 366A U.S. NvCLE AR REGLL ATORY CoMM:SSION APPROVED OMB NO 3 ' 50-O Kae r6-69i EWRE S. C30 92 Estenatec becer, per resconse to compty wetn this

'"'o"""

• c"* * **5 0 SD 0

• 5 * * 'd LICENSEE EVENT REPORT (LER) Comme"'s rega' ding buroen est msie to the RecorCS TEXT CONTINUATION ana secons Maragemed Enncn p530L U S Nacw Regulatory Commission A a smngton Dc 20555 and to tne Paperwork Aecsctcon Project (3150-01041 Ottice et Management anc Buapet. Wasmngton DC 20503 FACIUTV NAMEqT) DoCdI NUMeER (2)  !(' A NUf GF Q @ PAGE (31 VEAR mem NUWm Millstone Nuclear Power Stauon Unil -

0l5l0l0l0l3l3l6 9l3 0l1l2 0l 1 0l 2 OF 0l5 TE AT P' more scace rs 'ewee use aci tions' NRc Form 3R A si il7)

1. Descrmnon of Esem On May 24,1993, at 0920, with the plant at 1009 power, mussel cooking (thermal backwash) operanons on the 'B' waterbox w ere imnated. At approximately 0940 hours0.0109 days <br />0.261 hours <br />0.00155 weeks <br />3.5767e-4 months <br />, the ume hmit for elevated temperature m the 'B' waterbox was sausf ed and restoration of the waterbox was underuay.

Dunny the course of the restoranon, the elevated temperature in the 'B' circulaung water intake bay was affecung the sernce water temperature and Turbme Building Closed Cochng Water temperature. It was deterrmned that the service water mlet isolanon vahes for the Turbme Buildmg Closed Cochng Water (TBCCW) heat exchangers were restnctmg the flow and heat removal capabihues. The service water l inlet solanon valves were then opened from 30 degrees to 40 degrees open m response to elevated TBCCW temperatures.

Approximate!) 0940 hours0.0109 days <br />0.261 hours <br />0.00155 weeks <br />3.5767e-4 months <br />. a common alarm for the mam generator stator cochng cabinet was annunciated m the Control Room. A Plant Equipment Operator was dispatched to invesupate this alarm.

l The mam generator stator wmdmg inlet temperature was found to be 51 degrees Celsius, which was I abose the alarm setpomt of 47 degrees Celsius. This condmon was reported to the Shift Superusor by l the Plant Equipment Operator. When the Plant Equipment Operator returned to the mam generator l stator coolmp cabinet, the " Generator Protecuan Tnp Circuit Energized" alarm uas observed to be l

annunciated followed shortly b3 the turbine tnp. When the alarm energized, the process computer mdicated that the stator coolmg water heat exchanger outlet temperature was 75 degrees Celsius. The setpoint for the " Generator Protecuon Tnp Circu t Energized" is 81 depees Celsius.

l

! The feedwater reculatmc vahes receive a ramp close signal as part of the normal inp response. During l the subsequent transient. a malfunction caused the 'A' feedwater regulatmg valve to stay at approximately 5(M open causmg the #1 stearn generator water lesel to increase to the high level setpomt. In response to this condmon, the reactor operator closed the bypass valve and the blockmg valve for the 'A' i feedwater regulating vahes. Then the 'B' steam generator lesel went high. The 'B' feedwater regulating I valve mdicated 109 open. The bvpass vahe and the blocking vahe for the 'B' feedwater regulatmg vahes were closed. Additionally, the reactor operator tnpped the running feedwater pump based on the l high steam generator water level. Steam generator water levels were subsequently controlled usm; the auxihary feedwater system. Operators performed Emergency Operatmg Procedure 2525, " Standard Post Tnp Actions All safety related eqwpment responded as expected unh the exception of the main feedwater regulaung valves and the umt was placed in a stable condition. j l

j Durmg tha transient, the Reactor Buildmg Closed Cooling Water (RBCCW System reached a l

temperature of 9 ' degrees Fahrenhen. The maximum normal operation RBCCW discharge temperature o 85 degrees Fahrenhen when the RBCCW heat exchangers are cooled by semce water up to a ,

maximum temperature of '5 degrees Fahrenheit.

l

11. Q use of Twent l 1. The reactor trip was caused by a turbme trip. The root cause of the turbine inp was the lack of heat removal capabihues from the Mam Generator Stator Water Coolmg System. The warm water bemg dscharged through the 'B' circulating water pump into the 'B' intake bay was being recirculated to the 'A' and 'C' intake bay s, causing an increased sernce water temperatures. The tide nas a significant f actor in the high semte water temperature. The low mcoming tide allowed the 'B' intake bay's high temperature to cause an aggravated ef fect on the adjacent bays. Some temperature stratification m the adiacent bays has been observed on prenous mussel cooks. The low tide placed the higher temperature water at the suction of the Serace Water pumps.

1 During the mussel cooking operations, all components cooled by the TBCCW System experienced j l elevated temperatures. The Mam Generator Stator Coohng Water outlet temperature increased )

greater than the tamperature switch setpoint. 81 degrees telwus, for greater than 70 seconds which resuhed in a Turbine tnp.

g n au

• a We Form 36f A L' s Nv0LE AR RE G.L A10RV COMM;55:ON APPAOVED Or4 NL 3150-0104 b fG E x r4RE S : 4 30'92 Estmatec bercea te recorre to comp <y w'tn tms M m a W " C& e:U m ro sest 500ms Forware LICENSEE EVENT REPORT (LER) 9 " * * * * '

TEXT CONTINUATION ""

and' Rep

'*"a'r*a"ge Y1s M 6'nent

• " Branc9

""* t (D-630)

• ' U S. N eear Peg.f atyy Comm%ori. W asnergtor. De PD$$5 and te the I"aDEvwork Recetton Ptoie:1 ;3150.-0104). c>tf ace et Management and 6scQet, W psmnyo% DC PD533 F ACUT v NAME (1; DOCC NW8E A 2 t r =; pf u:g r.; f i PACd (3, v:- , v n m nat avism usets co m Milktone Nuclear Power Station U t-0lSl0l0l0l3l3l6 ol3 0l1l2 0l1 0l 3 OF Oj5 w o, .we i.e ee 4 , ewe: ma=e #cro-r- 3cea s ; 72 2 The root cause of the ' A' feedwater regulating valve was vibrauon which caused the valve to go mio local manual controh The 'B' feedwater regulaung valve was 109 open due to the vahe stroke being out uf cabrrauon.

3. The root cause of the hich RBCCW temperatures was a lack of procedural go dance to address the 65 degrees Fahrenhen RBCCW temperature hmnanon.

Ill. Anah sis of Ei. en' Then esents are being repened pursuant to the requirements of Paragraph 50.73(a)f:)(iv) and Paragraph 50. 3(a n dni(B) reportmg ans event or condition that resulted m mar:ual or automatic actuauon of any Engmeered Safety Feature System. including the Reactor Protecuon System and to repon an esent or condinon that potentially resuhed in the nuclear power plant bemy in a condition outs:de the design basis of the plant.

There were no safets consequences from this reactor inp event. All safety equipment wnh the excepuon of one of the mam leeriuater regulaung vahes. responded as expected and plani operators executed appbcable Emergenc, Operaog Procedures accordmgly. All coohng water temperatures immechately returned to their normal salues.

IV. Cerrectn e Actmn

1. Post inp data review idenufied that the Mam Generator Stator Cochng Water outlet temperature, as monitored by a Resistance Temperature Device (RTD), only reached a maximum of the equivalent of 75 degrees Celsius, belou us computer alarm setpoint and the inp setpomt value of 81 degrees Celuus The tnp is imuated by a separate temperature swnch. Dunng the subsequent shutdown, the Mam Generator Stator Water Coohng water outlet temperature swuch calibrauon was checked and was found to operate within allowable ranges. Addiuonauy. the stator water temperature RTD cabbranon was checked it was found acceptable. It was determmed that the clearance between the RTD and the mner diameter of thermowell was excessive. This would cause a time delay for the mdicated temperature to read the actual temperature. A thermocanducuvny hUer was mstalled m the thermowen, at.d the RTD was remstaued. The presence of this gap explained the temperature chscrepancy observed between the stator coohng outlet temperature temperature sw tch, top setpomt and the stator coohng temperature. RTD. indication recorded by the process computer.

To present recurrence of this esent, procedure enhancements have been meluded m the Service Water System and the Circulaimg Water System procedures.

2. The feeciwater regulaung valves hand wheek were mechanicaH3 secured to prevent the large handwheel from vibrating to the manual engagement pomt. A design chance is beine evaluated for the next refuel outact i 1

On the 'B' feedwater regulatmg sahe, a cahbration of the poquoner and the pouuon indication j circu t was performed. The vahe was stroked f rom tne Control Room to verif y the stroke and the i posinon indicator. ~1 he vahe was verified sausfactors. l

3. Upon muuel cook restoranon. the Sernce Water temperature decreased to its normal value. To present recurrence of this condnion procedure change. have been made to secure mussel cooking if RBCCW temperature reaches greater than 83 degrees Fahrenheit.

1 NH c i or m 3ta I 16- M ) 1

• . j I

NAc Norm ?S6A U. S NUOLEAR REGULATORY COMM;SSION APPROVED OMB NO 315C-01(4 f6-89) EXPIRES- 4 /30/92 .

Estimated burden per response to compiy with tnis

at* c " ct ** '*os t 60 0 h's. For ward LICENSEE EVENT REPORT (LER) Com"ments"rega'O+ng burce" n estimate to tne ReCDros e TEXT CONTINUATION a,o Reports uanagement e anen ::-sa:n u s. Nuc. ear ,

Regulatory Comrnission. Washington DC 2055E. and to l'5p PaperwD'k Reductan Pro lect (3150-01C41. Omce of Management and Buopet W ashmoton DC 20503.

FAOUTY NAME 11) DOcn.ET NUMBER (2) MP NUMArm @ PAGE [3i YEAR N N nuem m hiillstone Nuclear Power Station Unit 2

~

0l 5l 0l 0l 0l3 l3 l6 9l3 0 l 1l 2 0l1 0l 4 OF Ol5 TEXT tti more space is rewed. use accitea NRC Form 366A s) (17)

Y. Addninnal Inf ormnion Similar LERs: None .

Ells Codes for referenced components:

+

N1ain Feedwater Reculatine Valves: SJ-FCV-C635 hiam Feedwater Regulating Bypass Valves: SJ-FCV-C635 Stator Coolmg Water Outlet Temperature Switch: TJ-TS-G054 Turbine Building Closed Cooling Water Heat Exchangers KB-HX-530S Stain Feedwater Blocking Valve: SJ-ISV-C684

+

Auxihary Feedwater Pump: B A-P- 1075

+ Niain Feedwater Pump: SJ-P-1075

=

Slam Generator Stator Cochng Water Heat Exchanger: TJ-HX-G054 hiam Generator Stator Coolmg Water RTD TJ-23-GO S4 Reactor Buildmg Closed Cooling Water Heat Exchangers CC-HX-5445 1

I l

l l

i NRC Form 366 (6-t'9) l 4

. . .. . l A orm 366A U.S NUOLEAR REGJLATORY COMM:SSiCN APPROVE O BtO $0-0104 Estimated buroen per response to comply w;tm this LICENSEE EVENT REPORT (LER) g;m*,'g',cy,qt *ng,q5l,1?on,0,l(5, ,l,"n*go, TEXT CONTINUATION and Rewr:s Management Branch 1p-630L U S. Nuc1 ear Repatory Comm ssion. Washington DO 2005E. anc to the Paperwork Recuction Pro,ect (3150-01D4) Othee of Management and Bucpet, Wasnington DO 20503 F AO!UTY NAME tij DOOKET NUVEER (2) LCD tJUMBFA #6 PAGE (3',

YEAR mcm met Millstone Nuclear Power Station Unit 2 0l5l0l0]0[3l3l6 9l3 0 l 1l 2l 0l 1 0l 5 OF 0l5 TEXT in more space is reostf ac. use accitener PJRC Form 300A s) (17)

MUSSEL COOK (THERMAL BACKWASH) LINEUP Traveling Screens Traveling Screens Traveiin;; Screens Travehng Screens O O O  ;

C SW Pump B SW Pump A SW Pump D C B A DC Pump CCW ump BC Pump AC Pump  !

h 12C 12D LA LA l rT r3 V Y Y  !

[11E { 11F {11G {11H D Condenser C Condenser B Condenser A Concenser Wateroox Waterbox Waterbox Waterbox 12B A 12A LA k/2' r, VN y V

[11D 11C

^

2, V V V To Discharge Canal

• Throttle 11 A to maintain inlet temperature of 'B' Circulating waterbox between 110 - 120 F.

geg-maa

_ - _ _ _ _ _ _ - _ _ _ - _ _ _ _ . _ _ - .