ML19345B049

Safety Evaluation Supporting Mod of 800211 Order by Providing for Use of Mini Decay Heat Removal Sys

ML19345B049
Person / Time
Site:	Crane
Issue date:	11/14/1980
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML19345B041	List: ML19345B040 ML19345B043 ML19345B045 ML19345B049 ML19345B050
References
NUDOCS 8011260031
Download: ML19345B049 (11)

Text

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i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION METROPOLITAN EDISON COMPANY JERSEY CENTRAL PCWER AND LIGHT COMPANY PENNSYLVANIA ELECTRIC COMPANT D_ OC= r NO. 50-320 THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 2 Introcuction i

By letters cated July 31,1980 (Reference 1) and Augast 5,1980 (Reference 2),

the Metropolitan Edison Company (licensee) proposed changes to the Recovery Mode technical specifications for Three Mile Island Unit 2 (TMI-2) dealing with the implementation of.the Mini Decay Heat Removal System (MDHRS). Although several modes for removing decay heat would De available, the MDHRS woula provide a forced ficw system for removing decay heat from the TMI-2 reactor fuel. Accordingly, the proposed changes would impose operaDility requirements for tne MDhRS anc would also delete tne operaoility requirements for certain Balance of Plant (50P) systems wnich i

have been used since the March 28, 1979, acciaent, but would no longer ce requirea, for removing tne decay heat. The operability requirements for tnese BOP systems haa esen imposed by the Order of the Director of the Office of Nuclear Reactor Regulation on FeDruary 11,1980, (F.R.11282) in tne form of proposed Technical Specifications.

4 Sumrary The licensee has requested ilRC staff approval of an additional long term core cooling metnca. Tne proposed change would rake available a newly installed 1

!!DHRS to remove decay neat rather nan the present method wnicn accorolisnes this function by using tne "A" steam generator in a steaming mode to the condenser.

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. Tne licensee's proposal required certain modifications to meet our requirements witn wnich the licensee has agreed. tfith the incorporation of tnese staff re-quired modifications, we have found the proposal to be an acceptable metnod for removing the decay neat and nave tnerefore granted the licensee's request i

to nodify the nethod used for long term core cooling.

Evaluation The TMI-2 Reactor Coolant System (RCS) is currently operating in a natural cir-culation heat removal moce with heat rejection from it Deing accomplished oy Doth loss to amoient (reactor building atmosphere and surp water) anc througn sne "A" steam generator. The reactor ouiloing is in turn being cooleo by tne reactor ouiloing f an coolers while the "A" steam generator is steaming to tne concenser througn the turoine by-pass valve. This mode of core cooling has been in effect since late April 1979. With tne passage of time and the associated reduction of cecay heat generation rate (presently approximately.75 kw), the natural circulation flow has enangeo from continuous to cyclic with increasing intervals between the cyclic flow "ou rp s".

Heat rejection through the "A" steam generator by steaming to the concenser requires tne operation of several major 80P systems including: circulating water system, main steam system and the "A" steam generator, condensate and feeowater systems, main condenser and package boiler.

Conversion to and use of the HDHR5 for core cooling woula simplify the plant operations since use of tne MDnRS woula eliminate tne need for operating the previously noted B0P systems.

The M0 HRS is classified as a nonsafety grace system out it is cesignec ano installed to seismic Category I requirements up to and including the secona isolation valve in its supply ano cischarge lines. The balance uof tne system is cesigneo anc installed to Operating Basis Earthquake requirements. The MDHRS takes suction from tne "B" f

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' loop of the Decay Heat System (DH) outlet from the reactor vessel via a connection to the Alternate Decay Heat Removal System (ADH). After passing through one of the MDhRS's parallel heat exchangers and pumps, the reactor coolant is returnec 1

to tne reactor coolant system through the "B" Core Floocing injection nozzle via 1

a connection to the ADH anc DH systems. Connection of the ADH to the DH was evaluatec anc approvec in NUREG-0557. The MDHRS is sizec such that one pump and one neat exchanger (two of each are installed) could remove up to approximately 1 N of q

cecay heat. Therefore the MDhRS has more than acequate cooling capacity for removing the present anc future cecay neat loads. Tne MDHRS would De ccolec oy tne Nuclear 1

Services Cluseo Cycle Cooling System whicn is requirec to De cperaole by proposec Tecn-nical Specification 3.7.3.1.

The power supply ~for the MDHRS pumps anc motor cperatec valves is from recuncant Class lE cuses which woulc be manually loaced on tne Class' IE ciesel generators in the event of a loss of of f-site power. A cetailec cescription of the MDMRS anc of its principal moces of operation is proviced in the enclosure to Reference 3.

1 In the event the MD F 3 is not usec or becomes inoperaole, Dackup cooling modes are available for removing tne cecay heat from the RCS. These oackup cooling moces incluce the long term "B" steam generator cooling system anc " Loss to Amoient".

Tne long term "B" steam generator cooling system has oeen previously evaluatec anc its operability woulc continue to be requirec Dy proposed Technical -Specification 3.7.1.

In its analysis of tne " Loss of Amoient" cooling mode (ciscussec in References 1 anc 2;,

the licensee calculated that with the present decay neat generation rate, the reactor coolant bulk temperature would initially increase at a rate of approximately U.4 F/ncur snc that this heatup rate would graoually-cecrease sucn tnat at a RCS temperature of J

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. 4 approximately 190 F,- the heatup ' te would oe approximately zero. At this RCS tempera-ture, tne heat loss from the RCS to amotent -(reactor building atmosphere and sump aater) would be equal to the aecay heat generation rate. The RCS operating pressure i

curing MDHRS cperation would be maintained at 9010 psig; therefore a substantial margin to the saturation temperature exists and the plant concitions would reacn a staole, equilibrium condition.

The NRC staff has reviewed the licensee's results of tne J

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" Loss to Amoient" cooling moce and has performed an incependent analysis, tne results of ahich are in agreement with the licensee's conclusion. Therefore, we have conciucec tnat any one of tnese cooling methoos provides an acceptaole means for long term cooling i

of the reactor core.

1 Written procedures for operating the MDHRS and for operation in the " Loss to Amoient" cooling moce wiii ce requirea for operation in either of these cooling moces.

Tnese pro-cecures will be preparea ano submitted to the NRC staff in accorcance witn the recuire-ments of proposea Technical Specification 6.8.1 and 0.8.2 prior to implementation.

The MDHRS has a design pressure of 235 psig. Therefore, consiceraticn was given to possible sources of oysrprs:surization of tne MDHRS. Three potential sources of MDHRS overpressurization were identified. These sources were:

(1)

Makeup pump operation with MDHRS in operation, (2) Pressurizer heater operation, and (3) Malfunction of the Standby Pressure Control (SPC) System.

To creclude operation of a makeup pump curing operation of tne MDHRS, tne licensee proposed to celeta tne requirement for an operaole maceup pump from tne proposea Technical Specifications out to retain the option to operate tne ; ump for certain operations (e.g. cegassing). The licensee further statea tnat tne electrical B

power supply circuit breakers for the makeup pumps woula De "racKea out" when valve I

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1 DH-VI cr DH-Vl71 is open. Since operation of a makeus pump may be required in one or more of the backup cooling modes or for degassing operations, we will retain a requirement for its operability in proposed Tecnnical Specification 3.1.1.1.

However, to provide assurance that the MDHRS will r.ot be overpressuri:ed due to operation of a makeup pump, we propose to add a requirement to proposed Technical Specification l

3.1.1.1 that all makeup pumps be made inoperable when valve DH-VI or DH-V171 is open by " racking out" their electrical power supply circuit breakers. We n>c;1d also add a surveillance requirement to tne Recovery Operations Plan tu periodically verify trat these breakers are " racked out".

These actions provide assurance that the MDHRS would not be overpressurized due to operation o' tne makeup pumps.

l Operation of tne pressurizer heaters while operating the RCS in a water solic mode with the MDHRS in operation creates the potential for overpressurization of the MDHRS due to volumetric expansion of the reactor coolant as a result of heat input to tne reactor coolant. The licensee has calculated that the electrical energi:ation of all the pressurizer heaters (1638 kw) would result in a volumetric expansion o#

the reactor coolant which would require a compensating relief capacity of S.6 gpm.

The MDHRS has an installed relief valve capacity of 53.5 gpm. The NRC staff nas reviewed the licensee's result of tnis potential overpressurization event and has performed an independent check, the results of which are in agreeraent with the licensee's conclusion. Therefore, we agree tnat operation of the pressurizer neaters while operating the MDHRS with a water solic RCS would not result in overpressurization of the MDHRS.

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i I Overpressurization of the MDHRS due to a malfunction of the SPC system has been precluded by reducing the SPC in-service nitrogen bank pressure to a new operating range of 225 to 400 psig and by tne installation of a SPC systems pressure relief valve (SPC-R14) whicn has been set to provide overpressure relief if the SPC system pressure exceeds 125 psig which is substantially below the MDHRS design pressure of 235 psig. The change in the nitrogen bank pressure was approved on July 25, 1980 (Reference 4).

The licensee also proposed deleting from proposed Technical Specification 3.1.1.1 the requirements for a boric acid storage system and ar associated flow patn to the RCS.

We have reviewed this proposed cnqc and since redundant boron injection flow paths f rom the BWST to the RCS via the makeup pump ano decay heat removal pump exist, we find the proposed change acceptable.

l The licensee's proposeo Technical Specification for the MDHRS woula require only one-operable MDHRS pump and heat exchanger with an action statement provicing instruc-tions to De taken il the event of tneir inoperability. Our position is that this Tecnnical Specification should require the operaoility of both MDHRS pumps anc neat exchangers and the associated aw path and that applicable action statements shoulc be supplied dealing with the inoperability of the various compcnents in tne MDHRS.

Tne staff's position is consistent with the operability requirements for similar sys-tems (e.g. proposed Technical Specifications 3.7.2.1, 3.7.3.1 and 3.7.4.1) i n whica the redunaant systems are required operaDie and action statements are provicea for when one or Doth systems are inoperable.

Unless Doth MDHRS pumps are required oper-able and periodically cemonstrated so in accordance witn applicable surveillance requirements, there is no assurance of the operability of the redundant pump snoulo its use be required for any reason. We have therefore modified the Technical Speci-

. fication proposed for the MDHRS to be in accordance with our position.

The licensee nas agreed with our pcsition on this matter. We have also adced appropriate surveillance requirements to the Operations Recovery Plan to periodically demonstrate the operability of the MOHRS.

The Licensee also proposea to celete from proposec Tecnnical Specification 3.8.2.1, the operaDility requirements for several electrical power busses.

Its basis for proposing to delete these requirements was tnat they suppliec electrical power to the various 80P systems which were proposed for celetion from the pro-posed Technical Specifications upon incorporation of tne MDHRS. However, in our review of these proposed changes, we ceterminee that four of the Dusses proposea i

for celetion (480 volt Busses 2-35, 2-36, 2-45 and 2-46) alsc supplied electrical power to tne auxiliary building and the fuel handling builcing air cleanup systems i -

which are in turn required operaole per proposed Technical Specification 3.9.12.

1 Tnerefore, to ensure tne electrical power supply for these air cleanup systems, we have retained the operability requirements for these four busses ir proposec Technical Specification 3.6.2.1.

The licensee has agreea tnat the oreraoility re-quirements for these four busses shoula De retainea in proposec lecnnical Specification 3.8.2.1.

We agree that the operaoility requirements for the otner Dusses can De celeted from tne proposea Technical Specifications as proposea oy tne licensee since the otner ousses proposed for celetion do not supply electrical pcwer to any systems required for maintaining the plant in its safe shutcown concition.

Tne licensee has postulateo an accicent involving isolation of tne MDHRS at

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inlet anc outlet isolation valves folicwec by approximately 1200 gallons of coolant i

water inventory being cumped on the floor of the auxiliary ouilcing. Since the MDHRS operating tenperature is shown by the licensee's thermal analysis never to exceec

4-I 4 L 190 F, even when the system heat removal capacity i's' lost, dumping of tne coolant r

is no: expected to result. in any flasning.

In the an 'ysis, the licensee assumed 4

that the airborne source term will not exceed lt of tne total. coolant inventory of radionuclides censisting primarily of cesium and strontium. The airborne source term in tne auxiliary building is then released to the atmosphere as a puff of i

radionuclides. As a result of this analysis, the licensee calculated a site boundary i

cose of 1.16 x rem.

We aise considered the possioility of recriticality of tne reactor core curing t

operation of the M0 HRS. The potential for recriticality with the reactor coolant system operating in cyclic natural circulation was evaluated in Reference 5.

Tne i

only method identified therein tnat could leac to recriticality was by boron ci-lution. of the reactor coolant.

In Reference 5 it was concluded that the timing l

'of sucn an accicent war !?ry long and that several weeks of continuous.coron cilu-tien at tne then present make.0 rate woulo be requirec to reach criticality. Tne present makeup rate is lower Dy a f actor of at least two than the makeup rate usec in that analysis. Due to the mixing action provideo by tne MDnRS pumps, use of the MDHRS will ensure unif orm coron concentrations in the core and, as cescribec in Reference 3. will provice a more representative sample of tne reactor coolant l

anc therefore a potential Doron cilution accicent would De cetected even more reactly 1

than as cescrioec in Reference 5.

Therefore, we concur tnat the accicent pcstulatec oy the licensee is the severest accicent. We performec a consequences analysis uti-lizing the source term calculated from the racionuclice cacentrations measurec in TMI-2 coolant samples; by Oak Riege ' National Lacoratory. The cata showed aDsence of any noble gases, presence of extremely small concentrat ons of iocine, anc presence of i

cesium anc strontium. - The source term was therefore calculated Dy neglecting noole g :?s and iodines.

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Based upon tne review of tne vapor pressure of cesium ano strontium at the O

maximum coolant temperature of 19C F calculated by the licensee, we Delieve that l

the licensee's assumption of 1". o.- the coolant racionuclices being airDorne is conservative, and have used this value in our evaluation of off-site doses (Exclusicn Area Bouncary) shown in Table 1.

I For the postulated accident, the staff has used a "small fraction" (about 1 percent) of the 10 CFR 100 dose guidelines as a criterion for the radiological consequences 4

. which would not present an undue risk to the public.

Since the doses calculated for a f ailure of the MDhRS, as shown in TaDie 1 are st.sstantially less than a "small fraction of Part 100," it is concluoed tnat the postulated accicent would not cause an undue risk to puolic health ano safety.

TABLE 1 4

Offsite Doses For Mini Decay Heat Removal System Failure Whole Bocy Coolant Samples X/0 Dose i

Nuclice Concentration

1. Ci/gm sec/m mrem CS-134 20 1,1x10 -3 2.4 Cs-136 0.5 1.1x10 -

1.5x10

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-Cs-137-100 1.1x10 5.8

'Sr-89 300 1.1x10 ^

0.85'

-3 Sr-90 20 1.1x10 29.2 TCTAL 39.3 l

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, Environmental Consideration We have determined that the modification coes not authorize a cnange in effluent j-types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this oetermination, we nave furtner concluded that the modification involves an action which is insignificant from tne i

standpoint of environmer,tal impact and, pursuant to 10 CFR Section 51.5(d) (4), tnat an enviro.cental impact statement or negative declaration ano environmental impact i

appraisal aeed not be prepared in connection with the issuance of the mocification.

Conclusion Basea upon our review of MDHR5 moaification, the attendant Tecnn: cal Specifica-l tions, and our findings that the proposed mode provice cooling options wnich are reliable and less complex means for long term core cooling, we find tne licensee's l'

request to De acceptable and grant the request to make saia modifications. The measures authorizec in connection with this evaluation will assure the continuec maintenance of the facility in a safe, stacle, long-term cooling concition, as ciscussea j

aoove. Baseo on these considerations, we have concluced that:

(1)

ne modification does not involve a significant-increase in the probacility or consequences of accicents previously consicerec or a significant recuction in a margin of safety ana aces not involve a significant hazaras consideration, (2) there is reasonaole assurance that 4

the health and safety of the public will not be endangereo by operation in tne mocifiec manner, and (3) such E.tivities will De conouctea in compliance witn tne Commission's j

regulations and the issuance of this modification will not be inimical to the common cefense and security or to the healtn ano safety of tne public.

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REFERENCES 1.

Letter to B. Snycer, USNRC, from R. C. Arnold, Met. Ed/GPU, Technical Specification Change Request No. 24, dated July 31, 1980, (TLL 372).

2.

Letter to B. Snycer, USNRC, from R. C. Arnold, Met. Ed/GPU, Technical Specification Cnange Request No. 24, cateo Augus t 5,1980, (TLL 362).

3.

Letter to John T. Collins, USNRC, from G. K. Hovey, Met. Ea/GPU, MDHR System Description. Revision 3, cated Septemoer 8,196u, (TLL 436).

4 Lette. to R. C. Arnolo, Met. Ed/GPU, from John T. Collins, USNRC, TMI-2 Recovery Operations Plan C.iange Request ho. 4, dated July 25, 1960, (NRC/TMI-60-115).

5.

Memorancum for William J. Dircks, from Normal M. Haller, " Report of Special Task Force on inree Mlle Islanc Cleanup", cateo Feoruary 28, 1980.

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