ML20148K109

Hazards Evaluation Branch Memorandum Supporting Amends 7,8 & 10 to OL Application

ML20148K109
Person / Time
Site:	Yankee Rowe
Issue date:	05/11/1959
From:	Beck C US ATOMIC ENERGY COMMISSION (AEC)
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ML20148K099	List: ML20148K094 ML20148K103 ML20148K109 ML20148K115
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NUDOCS 8012020632
Download: ML20148K109 (5)

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}gQEANDIN BY THE CHIEF. BAZARDS EVALUATION BRANCH IN THE MATTER OF YANKEE ATOMIC ELECTRIC COMPANY AMENDMENTS 7. 8 AND 10 .

gg I - In re Amendment No. 7 to the Yenkee anolication.

Introduction N

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. Amendment No. 7 to the Tatkee license application is concerned with the effect on the reactor's nuclear parameters of the buildup of plutonium in the core over the reactor lifetime. It had been suggested by the Commission's Advisory Committee on Reactor Safeguards, in its report dated September 16, 1957, that the effects 'of plutonium buildup in the Yankee reactor be determined experimen-tally in a part-core critical assembly. using synthetic fuel elements containing

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long-exposure plutonium. Tankee is of the opinion that determination of'the effect of plutonium buildup in a part-ecre critical facility would be difficult to interpret because of the impossibility of duplicating the temperature and neutron spectrum of the actual Tankee reactor in this facility. As an alterna- .

tive and more dependable procedure for determining the effect on plutonia, Yankee has proposed to conduct an experimental program to measure the to apera-  :

ture coefficient and other core parameters affecting operation in the actual power reactor at startup, after 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> ~ of operation, and at intervals while =

plutonium is building up in the core. To establish that the reactor could be operated safely while plutonium is building up in the core during the interval =

between experimental measurements, Tankee has calculated the effects on the temperature coefficient, void coefficient, delayed neutron fraction and neutron lifetime. The temperature coefficient was also calculated for Yankee by the Nuclear ~xvelopment Corporation of America as an independent check on the method used by Westinghouse Electric Corporation, the firm which is designing the Yankee reactor. These theoretical calculations show that the buildup of plutonium dur-ing'even the entire anticipated fuel lifetime of 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> vill have only a minor eff ect on the reactor's nuclear parameters.

Discussion of__the Calculations The temperature coefficient was calculated using the standard four-factor formula with lak;ge terms added. As can be seen from Table Sa, page 101:21 in the revised Yankee hazards report (7/1/58), the coefficient is strongly i

negative at operating temperature throughout the lifetime of the core. This is principally due to the stronc negative effect of the change in the resonance ese' ape probability with temperature. At temperatures belov the operating point and with a clean core, the coefficient ic less negative than at high tempera-tures, while at the end of the core lifetime at temperatures below the operating I

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• point, the coefficient is calcul'ated to be slightly poaltive. _ However, this calculation-involves taking the difference in two relatively large numbers and, therefon, may be'in error by a large amount. At any rate, whether the.coef-  :.. ?

ficient is positive or negative at these low temperatures is not significant, E]

since Yankee plans to heat up the reactor water with the circulating pumps to 4 '

at least 250 F' before the reactor is~ made critical. At this temperature, the ~'

coefficient is expected to be' negative with a value of.at least 10-4/0F.

The void coefficient is expected to become more negative as the core .is burned E up. The. delayed neutron fraction decreases during the core lifetime from about 0.70% to 0,.56%. Prempt neutron lifetime also decreases, from 24 microseecnds

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to,21 microseco.nds. . All' of.the abwe calculations were made t.ssuming uniform - g

' plutonium. concentration throughout the core. An-additional calculation of the  :.9=

above nuclear parameters was made' assuming the plutonium concentration was y;

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three times the equilibrium value. This calculation was intended to show that the greater plutonium buildup at the center of the core where the flux is -

higher than average does not appreciably affect the core nuclear parameters. -

w The only appreciable changes were that the delayed neutron fraction was de-creased to 0.47% and the prompt neutron lifetime was decreased to 14 micro-seconds. It is not clear, however, thpt the assumed concentration of three ....;;y

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. times equilibrium covers the largest variation in concentration that could occur if non-uniform buildup due both'to higher flux values at the center of p.m.,

the core and self-shielding effects which would cause plutonium buildup ~ pre-

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dominantly at the surfscarof fuel elements and enhanne the importance of Pu '

relative to U 2K are eonsidered.

Reoort of the Advisoiv Q;gp.ittee on Reactor Safeguards In its report of Octobe'r 21,Il958,.the Advisory Committee..on. Reactor Safeguards stated that the Committee . concurs with Yankee's proposal to determine the, temperature coefficients,in the actual reactor rather than.in.the part-core  ;

critical fccility and. agrees with Tcakee'.s judgment that the effect of plu- _

tonium buildup on these coefficients vill be small. enough to permit these '

measurements to be made with safety in t,he actual reactor.

Cenclusion With the method of reactor startup proposed, i.e., heating the. reactor coolant to 2500F before making' the reactor critical, ve. concur with Yankee that theoretical calcula~tions give adequate assurance that the. temperature . . d coefficient should be sufficiently negative when the reactor is first critical.

to ensure safe operation. Even.in the unlikely event that.this is not correct, the coolant could be preheated to a higher temperature before startup which d would insure that all coefficients are negative. We also concur with Yaakee ,

that measuring the temperature coefficient of the part-core critical with plu- tI tonium fuel elemento and then extrapolating the results to the full size Iankee. .,

reactor core would mt he a very practical or adequate way to detemine the actual +

temperature coefficient, and that results so obtained could be relied on only to .l give a general indication of the trend. It is our opinion that proposed. measure ,(

cent of the temperature coefficients on the actual reactor.before the initial y reactor startup, followed by re-measurement after 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> of operation and , j at intervals thereafter could provide the necessary confirmation of the theo- i retical predictions regarding the effect of plutonium buildup. The need and  ;

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3-frequency of later measurements can be determined from the information obtained in these first two measurements.

Yankee has not provided a description of the proposed experiments or experimental procedures to be used at the beginning of core life or when plutonium 1 tarts.to buildup .in the reactor to d_etermine the.. temperature coefficit it .and othey paran meters affecting the operation of the reactor. One method that might be utilized would be controlled transients experiments, with known sinusoidal or step changes in reactivity, as suggested by the Advisory Committee on Reactor Safeguards in its report of October 21, 1958 Before the staff can recommend that an operating licenso be granted for this g facility Yankee should furnish a description of specific experiments to be per-formed on the reactor and the experimental procedures to be followed, together  ;

with justification showing that the proposed experiments and procedures will provide inforsation necessary to predict the effect of plutonium buildup on reactor characteristics.

JI - In re Amendment Nos. 8 and 10 to the Yankee acolication.

Zntroduction knendments No. 8 and No.10 to the Yankee license application provide a current and more detailed description of the. Yankee vaste disposal system and its oper-ation. Ths description of this system provided at _the time the Construction Permit was issued was quite general, but did indicate in some detail the fune-tional requirements of the system. There are now sufficient details of this system provided to reach the : conclusion that there is reasonable assurance that the proposed system provides adequate safeguards to the health and safety of the public.

Law for Svg_teLDesien The system is designed to agfely handle the total quantity of radioactive liquid, gaseous and solid vaste originating in the primary plant, secondary plant and service building, based on primary plant operation 330 days per year, two com-plete shutdowns per yesr, and 15 days for inspection and maintenance during each shutdown. The estimate of the total quantity of radioactivity entering the gys-tem is based on an equilibrium fission product activity in the main coolant of 37.64 microcuries per milliliter resulting from cladding defects in 1% cf the total number of fuel rods, and a main coolant equilibrium corrosion proddet activity of 0.83 microcuries per milliliter. The figures for claddin6 defects and corrosion product activity are based on comparable data from similar reactors and are considered conservative.

The Yankee estimate of the total quantity of radioactivity which might have to be handled by the system was made on the same basis as was us.ed for,the design of the PWR vaste disposal system, and is believed to be a conservative one. 7f the number of shutdowns per year exceeds the number used-as a design basis for the system, the capacity would not be overtaxed; however, if the intirval between shutdowns is less than 15 days, plsnt startup would have to be delayed since this ir, the amount' of time required to process the quantity of radioactive water '

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_4 expected as a result of a plant shutdown and startup from a cold condition. H Although this might result in an operational problem, there vould be no hazards from such an occurience, since the applicant has indicated.that startup would be celayed if this were to occur. $

Details of System Deshm The components and procedures for the disposal of liquid vaste are conventional with one exception., Yankee proposed to use an electrede type evaporator for concentrating liquid vastes to elimimte corrosion problems and sealing of heat L h

transfer surfaces. . Although there appears to be no actual . operating experience using radioactive liquids in an evaporator such as this, there is no apparent reason to doubt that it would be suitable for this service, or that the decon-tamination factor expected would be nehieved. The capacities of the various . h_

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tanks of the vaste disposal system indicated that they are conservatively sized.

The components for the disposal of gaseous vaste are likewise conventional and -

conservatively sized. The only question that might be raised concerning the proposed procedures for atmospheric disposal of gaseous vaste is whether or not L there .is need for meteorological control of the discharge from the strek, as  ?

proposed by Yankee. Using the applicant's estimate of the maximum activity of the radioactive geses at the top of the stack, a dilution factor of only 5 to 10 would be required to reduce this concentration to an acceptable value for p@

unrestricted areas. Xankee feels that atmospheric dilution might not be ade- Q, quate to attain this dilution under adverse weather' conditions, and therefore h has made plans to restrict gaseous discharges during such times. It may later n be determined that it is possible to achieve the desired reduction in concen-tration regardless of weather conditions. However, since the plans for meteorological control represent a more conservative approach to the problem, and since Yankee has indicated that they expect to conduct meteorclogical expsriments at the site to determine the actual dilution from this stack, there is no apparent safety problem.

The procedures and equipnent for the disposal of combustible solid vastes appear to present no safety problems.

In regard to non-combustible solid vaste, additional information vill be required befor.s the staff can recommend that the procedures for the on-site burial of such vastes are acceptable, since no details have been provided by the applicant. How-ever, this concept is acceptable for the disposal of low-level vastes provided they are properly packaged. If disposal of more highly contaminated pieces of l plant equipment is contemplated, it might be necessary to ship such equipment 7 off-site after being dismantled or cut-up and pachged. In any event, details concerning proposed procedures and criteria for on-site burial of vastes must be furnished before the staff can de.termine whether this method of dispasal is acceptable, gnrM the Adviso-v Comittee on Reactor _Saf.eruards i In its report of October 21, 1958, the Advisory Committee on Reactor Safeguards stcted that it was the Ocmmittee's opinion that the proposed Yankee vaste dis-posal systea would permit disposal of vastes without undue hazard to on-site or j off-site personnel.

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Cenelusion

- Based on the foregoing, we have concluded that if the vaste disposal system is ~

constructed and operated substantially as proposed in Amendments 8 and 10 there . .llj

'is reasonable assurance that the health and safety of the public would not be ,

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Cliff d K. Beck Chief, Hazards Evaluation Branch  ;;Q

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Division of Licensing and Regulation Date: MAY 111959 5

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