*TTACHMENTH

)CO NEE E MER'3 N C Y PROCEU RE C I.. lE..1 1IE

.1 ..... ... .I .3 ... .... I: .... (. ... ... .. .. .... .... ... ..... . 1 . .... ui. .. ... ....- J 1

IN DEU1-.JT C..,..R COIN .G MONITRN G INSTRUMENTAT -41 . z.IO IUIDA1

.Ol PURPOS

3J 1. 1pro c to . C : Mitig a ti

44- 2,.) 1% RCP OI::r t o Wi Lh ICC

, , I C C R : : e

4.1 Int rr<..:ipt in a-E a . .a1 ir:.. '.a.I v.: A.

VC, JOI IETFCTO ANDMT .TO

5.,2d -od M t g t o J. Ol t.UMMAARY-3,

F60710032 PDR ADOC 05000269 F

1 0. OP.RPOSE

The enclosed infornation is provided in accordance with item

IIII.5 of the Order for Modif ication of License dated December

10, 1982. This item requests information +or NRC review and,:

approval regarding proposed emergency prac:edure revi sians which

imr.:lement the Iinadequate Core Cooling Monitoring (ICCM) instr-.

mentation.

2.0 S: COPE

The intent of this doc::ument is to outline r::raposed modifications

to the Emergency Procech.ure Gut..Aidelines (EPG) relative to the

irnatallation of ICCM irnstrumentation. The EPS p1:rovides the. tech

nical basis from which the unit specific emergenc:y procedures are

written,

The co mplete safety gracde ICCM packiage incl.des sulc::t:::oled margin

monitors,, core e:x.i thermoc.o<..uples (CETC), redundent reaictor

vessilel head and hot leg level indications as well as the ncon

safety grade reactor coolant pt..unp (RCP) amme.r I' c es:1.n

description of this system has been su:mitted p:reviosly

(References 1) . The IRC staff has: reviewed this design and

resporn::ed w:i:t a Safety Evaluat:i.on Rep::rt (SER) ac::pting the

design .concept (Ref erence 2).,, Duk: has present ed carnceptu.:al

emergency poce::rce.re gu.idance regarding ICCM level instru.mentatio

in Reference . The information contained herein is intended to

s.ul::pLament and cArify this guidance.

EPG g.iidance cu'.<rrently e:.ists which prescribes operator actions

based :i ::n l .<c::cooled nargin and i dic::ET(: ir::ications.. Pcrtiorns of

this e c:::ist in g. .idance aIr . in cu e t o ::rovie a cJ L, Jle ov .' r V:

o the sever e ac ci ent mitigation tr atey. p:::1ic:ation f the

IC:M instl:rt..ment4:ati1on w~illI be demAcio onsatrcated byc i ;i. ustrat 1 in h~ciow th.elI

11Jnuss tis in t r ment ati to id e ntif y mi t i ate and p vnt

t e a proach to act a I CC c cl iti. dditional a p p .p . icat ion

of CC level instrumentatijon will .1 also be~cic d:icseid.

,: IC D n EN tII CTION nND MIT _ TON

: ). .1 a cr ah t . ioi c C .t.; vaI.. c a

a l.c of bcoold marM in reg ard l e of r the initi Li at o bi nd event

[he EPaIca.c. ic th re :fore(** tre' at t h : i is. incmptom i thJ 1 absic;olut.ti: pr icor it .y, andc

ccecondr ~c on, toCE::: idi iccatinc that iCC '~ odiion already

ei t., n ~ ~ St.<::cole cmrin ci:ndilcaiol;ns are~~c a alal to the ope:~ra

tc fro a variet of iouc es~ci in lui ng dig ital m ters. F/

di p aiy:iea o a d C0m:n.teri.i 'i ar:: t e n w ia et Is:lt d I

a:.. T ... be mi

p

errors i~crreciF -Ionc cin: c li..ed i1n e~ac~h I indi catin., The opl~ecrator :i.

i n t r c e d. . ... ..... ... an.. . o .... . t h e E.. .. .. i o t.. i : M r.i n p r.::..

cJ.. artt:.ci eh Iea i I::: c:oo inC cna i I I:i :c tiat io i n cc. ci ccci d c r e ase toI : F

The in: L os of uc ooii ed Marain i:c:inzc i. c 0 p cril:::e v a-c In oL :. c p er

tcor ac ti ion - c ei n edI to: c ain Ft.ic :i L f po sil e , Ir r a

: :re pre f, 14v nti c r:cver.i of thei .i:C o l d mar , _k .c. i a i c

earco dcay: hi [eati removl are establishedc , The 1firt and

m o. iportc c'.:e ctepn I 1in this p..r::::ecl.. .ire: I.to...' ip ll reac. tor

.I I Lm C.; . . I i.a 1ci on i a Ie. n a( 1 . in the preventi

of .C1 : on cii ton a ince c t: nt..u .. rU...r cov0r = t.. , * , 1r n I c... . t .r..;

wi At h a bLOCA, may ress.it i a hiih l o tiea r eac:a or co 0C.a n

yst eIn (RCS) and poss ibl.e cnore on -, a The EI- e I .i dancei

e i. ci. t thr Io- u 00 g h out e ard ri p p ing . I of RCC on l of r.I:

cD oo lId mlar 1in Ei an d t h e op er at. or are t razin . n e to (. r ertand th Ie

imp or ta o fi 0 ic : this action andi repond promptly.. Cn ol i n uo u .

op erat i on wi.th sat ur at e: cIool ant cld 1 t i cons i s not per mi tte d or

e:p ec d c c.e to th e c: n tir.. ed emp*h*iS pl ac e , &: : n P t i '

loss of subooled m: 0a r g . I in , C R(..;:F's are nI-t en t i on a llI.y r et artd wi t h

satl.trated coolant onl when severe IC c .ondition dic tate Such

dr ast ic actIon i order to cool the ore by 4 orce d c oo i ng

1ter t :i et erini n thiat a sev e r e over co o.l :Lnci nI d :i d notC c ause t he

10n. of subc:ool ino thle ... qaIC of -iuboo 1 ed Margi pr oc:edure

1 iraust ruci:t the oi::s r at1.or t.o in:iti at e Iin .:.iec~ itin fl ::>w and~ ci so.Iatea

a::: I File RCS 3 leal . The Hteam ener ator level. arethen rai sd

co the atur ate nati.. ral circltion setoin in anti ci pation oI

h bo Sl I.r-.denr h at. tranS er pha of a SPL...L.C Al l

..k. Actio s none nt at o t r eat ini oIth c r p sibl cym I:: I- it m

cr :: l c ar gi. r v :it nn- nte symptom.

ce trhe pmay c r olant ib co eat at.. r at. c, th. op e ra tor y

.t rI c hanges i1 C oo . ant: inv n or y by oh ser v ng the ICCM pl I am a

displ T i d iplay J. Vir ::: 1.. de in tr..utat ion d J. . w hih w4il. J t in i

c:at e an d , r end c:oola leve in I h legs andI in th reactor

ve l head . Pro rcoral ud ' ( nance hn a d I eve lped to ta 1::

cad van-- ta c--F . t h i J :i nst r wrenta atiJ.Ion and assi th.....e oper at or.

identifying the approach to !Ci. conditions. The criteria for

transfer to the !CC section of the EPG was enhanced by including

low reactor vessel head level in addition to superheated CETC

temoeratures. These parameters will indic:ate the approach to MC

conditions and the actual onset of ICC conditions. A reactor

vessel head level setpoint equ..ivalent to the bottom o:f the hot

leg ( istrument errors incl.uded.) was chosen to initiate a trans

*fer to the ICC section. ' Belc:w the setpoint, reli able coolanit

level indications will no longer be available to the operator to

ensure that the core remains covered.

3.2 ICMt.8i9

The CETCs prov:idce a relative in:sication of high core teimperat..res

once level indic:ations are off-scale low.i.::ETC temperatures are

therefore the basis +or operator action once the CC secti:on of

the EPG is entered. initial efforts in this section focus on

max:1.:::ing ECC.:: i :.jecti on flow and attempting to restore some

form of core cool.ing. All furt.her actions are based ..pon the

succ:es . 0+ these actions is indicated by CETC temperatt.ures. If

CETC temperatures remain superheated and are not decreasing, th n

.RCPs are use:: to initiate forced cooling.

3.2.1 RCP Operation With ICC

Contiruous -RCP iperation with satu..orated coolant conditions is rnt

permitted in the EPG with one exception. S.5<stained CC condi

tions is the one circumstance which warrants poissible RCP damage

in lieu of severr core damage. A RCP is thus restarted iF

3ei-ous efforts. to restore core coolini are un..tci:essful and.

CETC temperatures remain superheated and are not decreasing.

S: ucc ev. 1V C are res.x i ta rt 8 o ,,as e essary, unti the M Cc at r c.ui.

tion is mitigated.

3.2.2 ICC Recovery

The recovery from an ICC condition may t::en ;gauged by the core exi.t

sabcooled margin, reac:tor vessel head level , or RCP amps if any

RCPs are opera t ing.. Each of these parameters are used in the

revised ELPG to provide the operator with an onambiguot iindica

tion that actions performed in the ICC section have mitigated the

ICC condition.,

All RCPs which may have been restarted du..ring ICC mitigation are

secured prior to transferring cout of the ICC section. This is

at:::complished once the CETCs are leis than 400 F and the core emit

subcooled margin is saturated or .st..ibcooled., RC:::P c:rrent must be

stal e and::1 greater than th:i nominal cur<rrent at f.1. power o:era-

tion prior to. s curi :::: .. r- 1 na a RCP. Stable RCP .cu o-.rrent is an indi c: a

tion that single ph ise coolant is being punped and the c. rrent

setpoint assures that the coolant is indeed in tlhe li quid :phase.

Correlat io::ns relating cocn::tan void fraction to ::n.un:: apm::mp amp are no.

used due to the limited appl:1icability of these correlations and..

the diffia..mIlty of use they ;.present to the o::pere or.a Cuo rrent

stability will 1:::rovide a more practical and less ambigoios..ts indi

cation of the relative c:oolant ph ase content..

Once all RCPs (if any) have been secured, rea:::tar vessel heild

level i observed to ensure that the c:ore remains covered. A

transfer o.mtt of the ICC section is made only after tela core exit

, c.. . ::..ai... mI. L ma --ag-:in is ve=arified greiater than or eq.a. to F and

reactor vessel. head .i 1 3. a on scale. hIne :ot.tom of the hot: .leg

(instrumIent errors included) is the setpoint chosen for this

level since it is the same setpoint .s eci to transfer into the .ICC

section.

4.0 SA TURATED NATUR=AL CIRCULT....TION COOLING

Natrt..ral circulation cooling is assured in a B&W NSSS provided an

adequ.ate heat sin: exists and the primary coolant remains s..b-

cooled. Primary coolant saturation presents a unique :c.:oncern to

a B&W plant, particularly when a BiL.OCA res..ults in draining of

the hot leg piping and the subsequent interrtuption of saturated

natt.iral circulation cooling. Guidance based poL::pn ICCM hot lec

level has been included in the EPG to assist. the operator in

identifvinc conditions where natural c:irctulation may be interrup

ted.

4,. 1 In e r ryag' p;.:1.ant i i of 1 Natural~. L.:. C:: ul..a :.t i

The interru:pti:on of natural, :irculation may resl..lt when a hot leg

void di sp laces pr i mary cool ant Iel ow the Ui-bend sp illover el eva

tion. Interr.u::tion of heat transfer can result with an r nt ..":ng

heatu: of the primary Toant. This condition will first be

recogized throucih loss of heat transfer symptoms a:arn::d may be

Corifirmed with the ICCM hot leg lee l instrE.tumentation. The EPG

prescribes guidance designed to condernse or vent hot leg voichs:

and restore heat transfer,

4. He toat Tr'ansel i r -! ec:: vetry

Once loss at heat trarnsfer sympEtoms are recogn:E1.:zct., several

acti. + are p..orm±:-tined to rcstabl i sh heat transf er. If t chi core

e:it is saturated and hot leg level is below the Ul-bend spillover

elevation (instrument errors considered) , then the .hot leg high

point vents are opened in each loop with low level. This level

will confirm that vo:cc:is have formed in the hot legs and are

blocking natu..<ral circulation flow. By opening the high point

vents., the o:perat:3r will lessen the RCS prees.ure increase cue to

coolant heatup. ECCS injection flow will therefore be ma:imized

and the void will be vented as :nj n:.ect:. on flow ref ills the hcit

legs.

The EPS u ses RCP pump bt.unps to he.p restore iitural circulation

flow since they are an effective means of condensing steam vo ids.

H::t leg level indications are used to help determine which RCP to

Lm..unp and assist in evaluating the effectiveness of each bump.

RCP ai. are b::.iunped in the loop with the lowest hot lec level and

level is trended to determine if the p..ump bump was effe:tive.

This process is::. r:epeated u.intil the voids have been conr:ensed or

the RCP su..caessive restart limit is reached..

If no RCPs are :::peral.Ie or noncondensible gcases are present, ::p..ump

bum:::. may not sicces..isaully restore nat..iral circulati .,on The hot

leg high point vents are then u.sied to vent the voids and allow

ECS in jection law to ref ill the hot legs and restore heat.

transfer. If all .. effct fail to restocre natural circulati on

heat transfer, then the feed -and-bleed cooling made :s in tered -to

p:::rovide decay heat reovain wh:AP1 efforts continu..e to restore

ea m n orator heat tr ans r.r

5 .0 ll.) VOI ENTIFICATION AND MITIGATION

O..ne of the more obvious applicat:i.ns of .the ICCM instrumentation

is the ability to identify void formation in the reactor vessel

head and the hot legs dou.tring subcooled operat:in. T e I CN M level

instru.amentation has therefore been included in the ERG as a

direct indication of void formation and is used to determine when

the voild hat been removed.

5, 1 St.<bcoo ed:t a NIilatuoral C i r: co..1 at 4 i on Cool dowvsn

The current EPG stbcooled natural circulation couldown strategy

relies on reactor vessel head venting to prevent a head void from

forming,. This strattegy has been reviewed and approved by the NRC

(Ref erence 4). It was suggested that additional quidance be

provided should a v::id form du...ring the couldown., The natural

circulation cooldown gui..idance has ::been modified to monitor for

head- void formation and tfake appropriate actions as. suggested. A

step has been added to the gi.oidance which monitors vessel head

level and redu:s t::a the cooldown and depressu riz:ation rates, as

necessary, to limit the void size. Vessel head level .s main

taineci at the top of the head with insIitru..<ment uncerta:i.nties

considerea.

5..2 Vi:3d Mi!it igaat i on

The ICCM level instrumentation is also utilized to prepare the

operator for the conseqcluences of a RCP restart. Whenaver a

.mus .al transient has res..tited :1 :i .primary coolant s.at..ration and

st.:.bcooling is st :bsequently recovered , steam voids May still

e:x ist in the reactor vessel head and/or .the h::t legs. These

voids Will be rapidiy condensed -when a RCP is restarted. As a

resut, a drop in both pressurizer .level and RCS pressure will be

observed which is proportional to the void size. The E: ca...

tions the operator about this phenomenon and instructs him to

increase pressurizer level prior to the restart: if the level

instrumentation indicates a void. The setpoint at which a void.

is indicated is chosen as the top of the hot leq ar the top .:f

the reactor vessel head. Instrument errors were not factored

into these setpoints for conservatism siceri: the higher pressuri

zer level setpoint will not adversely affect the restart

procedu..re.

The final applications of the .ICt..;t..;M level instrumentation assist

the opaerator in itdentifying and removing voids when the primary

coolant is subcooled and rno RCPs are operating. TheI setpoint

below which a head void is indicated with certainty is chosen as

the top of the vessel (instrument errors incuded). The :::(::rreaa :

panding hot leg level setpoint is the top of the hot leg (inst..t

ment errors inluded). When a void external to the preassu1<rizer

is indicated., one at several options are exercised to remove the

void. These o::.ations :.ncl.de RCS represast..rization, high point

vantin , and RCP restart.. in all :1.nstances , preanst..rizer level :is

ria:::rased to accomodate the liquidvol...ime requiret:1 to. refill the

void volume. Level instrumentation is then u..sed to verify that

the void has been successfyi*11 removed.

The basic applications of ICCM irnatr.metoa.n incl.nu::ed in the EPG

are summarized in Able 1 . Althgca h sn.:<bcooled margin is used for

.i

a variety of operator actions, only those actions related to C IC

monit:orinyc and mitigation are presente in ti. t iable.,

Th iICCM instrumentation, when coupled with the pro posed

proced ural guidance, should provide the operator with a deiniM~

tive means of identifying the approach to ICC conditions. If

actual ICC c:onditions resu..11t, the severity of this condition may

be deter mined and the effectiveness of operator actions may be

promptly evaluated.

The procedural cuidance has been designed to .tili:::e the

instru.rmentation in a manner consistent With its capabilities and

accuracy. Complicated interre::retations of these indications by the

operator have been avoided to enhance the diagnostic capabilities

ni the ins trimentation.

7.U -EFER:NL.E.

1) Duke Power Company Firnal Desian Description, instrt..mentati on

to Detect Inadeaquate Core Cooling, submitted July 1, 1985.

2) NRC letter, J. F. St:o to H. B. Tucker, Safety Eval uat i on

Report (SER), NUREG-0737,II.F.2, Submittals of March 10 and

Aucu.tst 25, 1983.

3) Duke Power Company resp:3nse to. "Order for Modific:ation of

License", NUREG-0737, I I. F.2, December 10, 1982, submitted Marc

10., 198m.

4) NRC letter, j., F. Stlz to H. BS. Tu...<cker., Safety Evalu.ation

Report of Natural Coaldown Strateg., j..ne 5, 1985.

able 1

Summar ogf El G ICM...RelatdGi ac

Instrt.ment ___ arct ion

St.<bcooled Margin -Trip all RCPs when sat.urated

Monitors .- Maximize ECCS in.jection f low -Increase SG levels to saturated setpoint at saturation

-Indicate recovery from ICC conditions

Reactor Vessel -Transfer to ICC section on low vessel

Hot Leg Level s head level. --Ensure recovery from ICC conditions

-Operate high point vents to restore heat transfer

-Establish appropriate pressurizer level

prior to RCP restart -Identify and mitigate voiding when subcool ed

-Identify and:1 mitigate a head void during a natural circtulation cool down

CETC Temperatures -Transfer to ICC section when superheated

--Determine the severity of action performed during !.C mitigation

-Ensure recovery fro:m !CC conditions

RCP Current -- Indicates no significant RCS voidin::g

during~ satu.rated RCP!- operation

c-Used to secure RCs d..ring ICC recovery

12