ML20012A350

Comments on Three Questions from 900123 Senior Reactor Operator & Reactor Operator Written Exams

ML20012A350
Person / Time
Site:	Neely Research Reactor
Issue date:	01/26/1990
From:	Karam R Neely Research Reactor, ATLANTA, GA
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20012A334	List: ML20012A350
References
NUDOCS 9003090301
Download: ML20012A350 (7)

Text

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.. . -3 Georgia Institute of Technology

~

M' NEELY NUCLEAR RESEARCH CENTER OCC ATL ANTIC ORIVE I t ATLANTA, GC ORGLA 30332-0425 l January 26, 1990

)

l Mr. Thomas A. Peebles, Chief j operation Branch  !

Division of Reactor Safety (

U.S. Nuclear Regulatory Commission, Region II .!

'101 Marietta St.,-N.W. 3

~ Atlanta, Georgia 30323 l

Subject:

The SRO and RO Written; Examination for GTRR perssonnel j of January. 23,,1990. -

t

Dear Mr. Peebles:

l

, ' I wish to thank the1NRC;for the. opportunity to comment on three l questions.out of 60 given at the Operator' Licensing, Examination  !

of January 23, 1990'. l

1. ' Question A-5 . "Enough reactivity is added to a shutdown  ;

reactor to double the countirate. If this same amount l of' reactivity ~is again added to the reactor, then'the i

reactor will.be' 1

, 1

a. subcritical  :

b ~. critical ,

.l c'. super; critical l d.

prompt critical." i l

The answer given'on the NRC's list of answers'is.(c),:1.0. super- '

critical'. ~The reference-to this problem is given as INP-1971 '

p.110-19. ' Additional material-intsupport'of A-5 was supplied by.

Mr; Richard Baldwin of your staff'on 1/23/90. This material is  :

appended. i Comments reactivity, p , may be defined as 1

'C p= Ikm) -

1; ref 1NP 19':!, p. 10-19  ;

(k,)  !

'A'better definition ist p= Ikm)' - Ikm) j (k,)

9003090301 900226 PDR ADOCK 05000160 D .

V PDC $lCi 7 4 1 Teles:: 542507 GTRIOCAATL Fax: 404-8944120 (Verify 404 8944951) ,

A Unit of the Urwereity System of Georgia An Equal Educaten and Employment Opporanty instiamon

pa ;,.

1 .

. =

i Where k,,' is the perturbed k,,of the system and where in the second  ;

definition it is recognized that reactivity is simply the  !

fractional' change in keff regardless of whether or not the reactor i is critical. From the statement of the problem and the normal l 6 -

simple multiplication approach, it can readily be shown that w IrJQ, = 1 - I km ) . l (CR), 1 - ( k,, ) ,  ;

For A-5 (CR),/(CR), = 1/2 .j Consequently, k,,, = 1 + I k_ ) , j 2

-l If one assumes that (k,,), = 0.99, one obtains a' value for k,,, =0.995  :

i and p = ( km ) - (km).

( k,,) ,

= .995 - 0.990 = 0.00505 '

0.990 if one adds p to (kef f), one gets 0.99500 + 0.00505 = 1.00005 i I don't believe that a reactor with keff = 1.00005 qualifies to be called super critical.

?

L  !

2. Question C-8. "Which one of the following Nuclear instrument channels is the special instrument channel that will permit the cross checking required in the low flux  ;

environment of a subcritical reactor? j t -

I a. Count rate meter channels '

i b. -Micro-micro Ammeter channel L c. B10 proportional detection channels '!

d. Log-N and period amplifier channels. "  ;

1 ,

y Comment: The answer to C-8 is (c), in accordance with the statment l appearing on page 66 of the SAR. However, the GTRR does not have

any .B-10 proportional counters. The B-10 channels are all l ionization chambers. When approaching criticality for the first [

time back in 1964, the GTRR had B-10 proportional counter for start-up purposes. Under current condition answer (a) would be more appropriate.

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3. Question C-15. "According to Technical Specifications.  :

while operation in Mode 2, which one of the following parameters is abnormal for steady state, forced convection mode of operation?

a. Reactor coolant inlet temperature 124 degrees F. I

b. Moderator level within 10 inches of overflow. i

c. Reactor coolant outlet temperature 138 degrees F. )

d. Reactor coolant flow 1650 gpm."

l Comment: The correct answer for question C-15 is (a). But (b) is i also correct. When moderator level is below overflow, the GTRR will  ;

scram. 3 We appreciate your willingness to reconsider the above questions. ,

1 Sincerely, j k./9 ' hk" .

R. A. Karam, Director  ;

Neely Nuclear Research Center RAK/arr i j

t a

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Se ::untrate :n Se cut-cf-c:re nuclear instrumentanen will increase ,

ue :: Se :ncrease m subct:ucal muluplicaten. There :s no reason '

why 4101 :urve cou!d act be plotted f:r the startup of a fuuy 1

'caced react:r. :n pr:cuce, hewever, it is seldcm done. First

• nere :s Se ;eeme r:c pr:biem with respect to detec cr locaten.

Th:s ::uid precably be : vere:me, as bef:re, by proper averaging techniques. A see:nd pr:blem :s chocsing a quanuty against ,

wn:ch is pict 1. M. The !cq1 cal chetce is agarnst con:r:I red positen.

H: wever, s:nce the rescuvity strength Of different centr:1 rods var:es

ensiderably. Se K,ff Of the c:re depends str:ngly upon which

n:::1 ::ds are withdrawn as well as how many c ntrol reds are wt2-

rswn. Th:s int:ws an adcitenal ::mplicaung fact:r ints Se pict.

But e.e ma:n reasen whg no 1.M plot :s made is simply because :t is net worta de effert. Cnce the reactor has been br:ught crtucal

• ne first ume, the data item this first criccality (called physics test-mg) :an be used to predict de red positions on subsequent

_ isppr

acnes to crtucal. As for predicung the red pattern on the I firs: :r:ucal, the Operster usually uses the results of physics tests T.ade durtng the intual ! cad:ng plus design predictions suppbed by the manufacturer. This informauen is c mpiled

.n:: s reacuv:r/ balance precedure and the operater uulizes

• nts :ata :: predict :ne crincal red posit!cn. (Reacuvity

a;an: As w:H te :iis::ssed !ater in Chapter 5. Secuen II.

NCTI: The Operator must be able to discuss what is happening in the react:r during the approach to cr:ticall:7

-3 . 5U3CR:T: CAL MULTIPLICAT!ON " RULES CT THOtB"

a. Scme c:nvenient rules Of dumb that may be used by the

perat:r as an aid in deter aning the point of criucality are as f:1!:w s :

-:* ' e nf. re:::i::ire h.:i ?ee- :isci :: :

s'.a

- i:: re::::r w i:.i-;e R :n~: .~::c, : ;i;;e : :a-: :, re:::i::iry :iii-i:n .: *;; ::.a:e -;.e n::::: :: ?c:: e , raper :: ::i::;.

1

r:ci: Using equanen (3-40). Assume an intual K,f*, of 0.3. CR t c

= 20 :ps and CR2 = 40 cps. )

l CR b i

=

l-Ke-ri: . ,r C3 IS eff

t (

5.:st:uung: 00 1-K,ff

- =

40 1 .3 190 ,

y -

,0-And: (.5) (.2) = 1-K,ff, ,

.1-1

• Kef, K = 0,9 eff; -

1: sing equatien (3 41)-

p,'eff: "' e f f i 2=

eff: eff t

.8 Subsutuung: # * (.9 .9)(,8) 2 = .1389

-w eacuvit" added to double the countrate was 0.1389 .iK/K.

If

• e e aSd the same amount of reacuvaty again and using equauon (3-41) we 'ind :

E eff; ~

O.1389 =

.9 K,ff, 0.1250 K,ff, -Keff,

• 9 (0.1250-1) =- .9 K,gg,

• 9-

-* 1.028 getf,a . 875 One can see that the reactor is supercritical. The cperators shcuid convince themselves that regardless of the iniual K,ff the accve relat:ensh:p holds true and the reactor will always ce supercr:ucal under these condiuons.

. . .: . . - -hw-; U 9.;; i,' the OFCP::: P 038#8 ;b# 5'{$ f ##".). .

'N - 'en " '

• L~ C S The TC20;:? $8 EY.' 0'###

,i

g 4

130 i . _ _ . _ _ _ -=_-m - _ _ _ _ _ _ _ = _ - . _

.: .o -

i *4

-

• Assume de instal concutens as de prev cus prcblem.

l That :s K, ,

• 3 and :nital : unts CR i = 20. Rememcer the sub-Or: cai Cplicaten formulas to ect held when K'If > ;; therefore assu ::e a :r:::si K ., Of .999.

et.

Pr:cf: 00 :ps d ubled seven tmes = 2560 :ps Us:ng equaten (3 40) l'E CR eff 1

a CR  ;-K effa  ;

S ub st:tutr.;: 20 c:s , 1 .999 l CR 2 1 .6  :

CR = 90 aas

',335

• 4000 cps

[

The estmate: ::::: cal CR of 2560 cps : mpares very favorably with 7.e :3.:u. ate:: Or:t: cal CR cf 40C0 cps and the reacter is indeed verv

• r

2. 3 e *,0 e tr.Q O r10 c al . [

. The :perater should always remember that any critical

rec ct

n .s :nly a guide, and it is generally very fortunate if

• tne react:r actually gees cridcal at exact!y the point which was  ;

pr e::ctec . Cn tne other hand, if the predicted critical' rod pattern  ;

.s puned and de core sell appears to be considerably subertucal, tne :perat:r shculd make an investigauon before pulling additional  :

r:cs t: ver:fy that the discrepancy is simply the result of calculation na::urse:es ender than an indication of mere serious problems such is a malfun:u:n in the red centrol system. In all cases, the operator T.ust use n:s judgment, c upled with the information ebtained from his e.

.nstrumentat:n to insure that crincality is approached in a safe manner. t 2

U SECTION IV T'.,UX DISTRIBUTION AND REACTOR CONTRCL I 94, CONTROL METHODS, CRITERIA, AND MEANS

~

f:

L Two ::neellable parameters existing in a nuclear react:r " -" 82

reaty affe

t de reacuvity balance within the system. These are .U

nr:i .ater:3.s pensening and soluble poison ::ncentraten. D t:

si 1

h

O C-3 s

,, .w .

t.

L ENCLOSURE 4 t

NRC Resolution of facility Coments R0/SRO Examination Question A-5 NRC Resolution: The definition of reactivity given in INP,1971 and documen-tation supplied for Suberitical Multiplication " RULES OF THUMB" are both accepted by Industry and by the Academic Society. Even though the problem may be calculated to indicate a very small amount of Keff, the reactor would still be considered supercritical. The examination question stands as is.

Question C-8 NRC Resolution: Comment acknowledged. Page 66 of the SAR indicated the GTRR

,- utilized B-10 proportional counters, and there was no facility comment during the preexamination review process. The GTRR presently does not utilize B-10 counters, therefore, answer (a) is the appropriate answer. The answer key was modified to indicate (a) as the correct response. The facility is reminded to 1

update reference material to reflect current plant equipment, c Question C ,

NRC Resolution: There was no comment generated during the preexamination '

review process. A close review of the Technical Opecifications indicates two possible responses could be correct.

NRC policy, concerning questions with more than one possible correct answer, is ,

to delete the question. The examination and answer key was changed to reflect deletion of the question.

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