ML20148F873

Hazard Analysis Supporting Proposed Change 10 to License DPR-3,subj to Encl Conditions

ML20148F873
Person / Time
Site:	Yankee Rowe
Issue date:	09/12/1961
From:	Case E US ATOMIC ENERGY COMMISSION (AEC)
To:
Shared Package
ML20148F870	List: ML20148F868 ML20148F873
References
NUDOCS 8011060817
Download: ML20148F873 (3)

Text

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HAZARDS" ANALYSIS BY THE RESEARCH'AND' POWER REACTOR SAFETY BRANCH l h

DIVISION OF LICENSING AND REGULATION _ g

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j YANKEE ATOMIC-ELECTRIC COMPANY  ;

i a PROPOSED CHANGE NO.I l0

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' Yankee Atomic Electric Company's license presently provides;that the reactor Q,]

s will, not be " operated ' above!15 Mw electric unless: the. boron concentration in the ' +

i main coolant; system 'is-less than 80 ppm. Yank'ee, pursuant to paragraph 3.A. of .

License No. DPR-3, has; requested authorization to perform a test-demonstration of t the-use of boriciacid at' higher concentrations.while operating the' reactor at full. =G "

a' power. KThis test would sontinue 'for .a period 6f 'from .two, to six ' weeks , with con-tinuation of the test beyond the initial two week. period depending on Yankee's 7=?

evaluation.~cf data obtained during'the first two weeks.;

During the. test, the concentration of- boron in the system would be limited  :;= d to' values less than 400 ppm. The negative reactivity which 'would be provided ' , j.g

by 300. to 400 ppm of boron'in the coolant is approximately equivalent to that  : W=

of the reactivity worth of the equilibriuni xenon concentration in the' reactor, . . . ==;

1.e. , 2.57. delta k/k. ;Tht ' ability 'to operate the reactor for short periods of

[:] y time with boric l acid:present would allow a portion of the excess reactivity to *

! be poisoned 'out during startup operations-unti1 xenon equilibrium is established.

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5 This might permit' an' increase in the initial reactivity 'of subsequent core load-  :

ings with a consequent increase in core lifetime.

Boric acid has been used in the main coolant system during initial testing I of the Yankee. reactor and is injected into the system during the process of-cooldown. During the first year of operation, Yankee has had considerable ex- M perience in the .use of boric acid and hae reporti.d that it has had no problema j with' boron injection, residence or dilution. One phenomenon which has been ob-served'during operations at Yankee involving beric acid is that the' acid acts as a mild decontaminant and solvent of the established corrosion product film,

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and tends to increase the crud level in the coolant. However, this.has resulted >

in a beneficial effect in that the crud level after cleanup of the borated system has been found to te lower than before the sL adown, and a lower crud equilibrium

. level has. persisted for a period of time following's subsequent startup. Al-though there is no conclusive evidence to indicate whether or not the crud re-' -

leased as a consequence of boric acid injection tends to deposit on heat t'ransfer y"

.urfaces', Yankee ~1ntends to operate a cation purification syetem during the' pro-

.pj ed. tests'in order to hold the crud concentration to 10 ppm, and to minimize q this effect should it occur.

The - (n, alpha) reaction which would take. place with boron present in the l coolant with the reactor at power will result in some' disassociation' of water d ss a result of the ionizatica produced by the alpha particles. Yankee has Q considered the increased disassociation'which might result from operation un-  ?

' der the conditions of the proposed teste.. They have concluded, and we agree, ,

that such 'an increase is not a cause for concern, since it would not be signi- q cficant in relation to the dieaesociation normally taking pla:e which has been- 1

. ade'quately ; controlled during previcue ope. rations.

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2-U There has been concern expreesed in the past that initially dissolved boron in the coolant might react under irradiation with other chemicals present in the primary system. Should this occur, the boron might initially be deposited on surfaces in the reacter (boron hideout), and then suddenly

" fall out" and cause a step increase in reactivity. There has been some experimental evidence that Tithium metaborate is one such insoluble com-pound that might be ' formed if lithium it ,irement in the reactor coolant.

However, since:the only additive which Yankee plans to have present in the primary system is- the boric . acid, there seems to be no possibility of a sudden removal of boron from the Yankee reactor due to possible chemical .

reactions. Although it is conceivable that other phenomena might aleo cause boron hideout, there is no known mechanism for such an occurrence in the Yankee reactor. Accordingly, Yankee believes, and we agree, that the only indisputable means of proving or disproving this possibility is to conduct a test demonstration under carefully controlled conditions of the use of boron in the coolant with the reactor at power. .

Yankee has stated that chemical analysis will be routinely performed -

during the proposed tests which will define the boron concentration in'the -

main coolant within 1% of the actual concentration present. In addition, by a

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monitoring control' rod withdrawal rates , any losses in reactivity greater than .43% delta k/k can be detected. The .43% delta k/k, therefore, _

represents an upper limit on the uncertainty in measuring reactivity. Yankee 1

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has otated that the test will not be continued past the initial two week c. .-

period if the value of the uncertainty in reactivity plus any unexplainable reactivity change exceeds .8% delta k/k. Thue , the largest unexplainable .

change which could be present at the end of the two weeks, and the test etill be allowed to continue, is .37% delta k/k.

In order *.o estimate the upper 7 im!.c of hazard from there proposed teste ,

Yankee has analyzed the conasquences cf ar. inetantaneoue insertion of 1.5%

delta k/k of reactivity into the reacter. They have concludsd, and we agree, that the resulting excursion would peak at about 200% of tte steady etate power, with a minimum DNB tatio greater than 1 at the time of the peak due .

to the inherent negative power coefficient of the reactor. The reacter would automatically be scrammed on high neutren flux (any two of three independenc channels could cause such a scram) and the integrity of the fuel v:uld not be impaired. As noted previously, Yankee har stated that the teet would not be extended past the initial two week period if the value of the uncertainty in reactivity measurement plus any unexplainable reactivity change exceeds .8% >

delta k/k. Since the resulting excursion following the instantaneous insertion of this amount of reactivity would be less severe than that caused by the 1.5%

step which was analyzed, we believe that the .8% delta k/k limit is adeauste to determine if the test should be permitted to continue at the end of cce initial two week period. Further, we believe that an additional condit:

should be impose.d that will require that the tests be discontinued if at say time during the testing perted the a:m of uncertainty plus unexplainable

. reactivity values exceeds .8% delta k/k. An existing license condition requires 1 that Yankee provide the Commitrian with a complets repert on the resulta and significance of these tests af ter they hsve been completed.

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Based on the foregoing' analysis, we have concluded that Yankee should be authorized tu perform the pr6 posed tests with the additional restriction that

. the: test be discontinued if at any time the sum of uncertainty _ plus the H unexplainable reactivity values exceeds .8$ delta k/k. With'this restriction, 6=

it is our . opinion that the proposed tests do not present significant hazards considerations not described or implicit in the license application and there is reasonable assurance that the health and safety of the patblic will not be endangered by operation of the facility as described above.

Original Signed b/

E. G. Case -

Edson G. Case, Chief Research & Power Reactor Safety Branch Division of Licensing and Regulation Date SEP 12 461 .

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