L-75-237, Response to Request for Information on Capability of ECCS to Provide Adequate Cooling in Case of Loss of Coolant Accident When Operating Plant with One Idle Loop

Response to Request for Information on Capability of ECCS to Provide Adequate Cooling in Case of Loss of Coolant Accident When Operating Plant with One Idle Loop

ML18227B025
Person / Time
Site:	Turkey Point
Issue date:	05/19/1975
From:	Robert E. Uhrig Florida Power & Light Co
To:	Rusche B Office of Nuclear Reactor Regulation
References
L-75-237
Download: ML18227B025 (5)

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Mr Rusche ORIG one signed CLASS UNCLASS PROP INFO INPUT DE SC R I PTION:

Ltr re our request....furnishing info with.regard to ECCS analysis for two loop operation'.....'C OTHER NO CYS REC'D ENCLOSURES:

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REGULATORYDOCKIiTPILE COPM FLORIDA POWER 5 LIGHT COMPANY May 19, 19.75";

L-75-237,

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Mr. Benard C.

Rusche Office of Nuclear Reactor Regulation U.

S. Nuclear Regulatory Commission washington, D.

C.

20555

Dear Mr. Rusche:

Re:

Turkey Point Units 3 & 4 Docket Nos.

50-250

& 50-251 ECCS 'Anal 'sis'or Two Loo erato.'on This is in response to a request by your Staff that we supply information on the capability of the Turkey'oint Emergency Core Cooling System (ECCS) to provide 'adequate cooling in case of a Loss of Coolant Accident (LOCA) when operating the plant with one idle loop.

On March ll, 1975 we submitted to you the 'ECCS analysis for. 3 loop operation at design.power.

The'onsequences of a LOCA when operating this plant, which has no isolation valves, with one idle reactor coolant pump at a maximum of 60% of full power will not be as sevexe as those of a LOCA occurring with 3 loop operation.

at full power.

Reasons 'for this become "clear by considering the comparison of the various phases of the accident transient for thxee 'loop and two loop operating conditions.'.

Blowdown:

In comparing three 'loop and two loop LOCA's 'the predominant factor influencing the blowdown'ransient is the effect=of reduced core powex required during two loop operation.'or any given break size, including the "limiting" break, the core mass flow transient vill remain essentially the same for the cases because the energy and driving forces in the reactor coolant system, i.e. pressure and.temperature, are similar.

The idle reactor coolant pump may cause a slight t'ime shift in the 'core 'flow charact'er'istics,'ut

'the trends will remain the

'ame.

Thexefore, be'cause 'of,the reduced core power', coolant quality in the core during bl'owdown'ill be significantly lower for two loop operation and the 'clad and pellet temperatures will be 'lower at the 'end of blowdown.

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Mr. Benax'd C,

Rus ch.e May 19, 1975 2.

Refill:

Since the blowdown hydraulic transients are similar and emergency.

core cooling syst'm performance for the two cases is the

same, lower plenum refill and bottom of core recovery will not be altered significantly.

3.

Reflood:

One important factor that influences.the reflood transient is. the containment pressure.

The conservatively calculated ECCS containment pressure 'transient will be only slightly affected because the'CCS'ass, RCS energy and rate of ezplusion of the primary coolant to containment'ill be about the 'same for the two cases'.

Another factor in the reflood calculation that must be

'onsi,der'ed is, again, core powe'r'.

Sensitivity studies'er'formed with 'the westinghouse

'Appendix K ECCS evaluation model show that decreasing core 'poorer'nd core 'heat release in the '.reflood calculation res'ult in a more effective 'core 'reflood transient with 'res'pect to core cooling.. The decrease in. core 'power for two loop operation will, therefore,"'mprovethe

'reflood transient.

In summary, since the 'core 'conditions at the 'end of blowdown will be 'improved for the two loop 'oper'ation analysis and the,refill/reflood transient -ia, at worst, the 's'arne 'for three 'loop and two loop operation, a LOCA postulated to occur. during two loop operation will'esult in lower calculated peak clad t'emperaturesthan for 100% power'.

For additional conservatism it is proposed that the pres'ent echn'al Specifications be amended so that fox two loop operation the 'permissible maximum peaking factor, Fq, be'educed to 80% of the value permitted by Section 3.2.,6a of the Turkey Point Technical Specifiations, This would lower the peak linear heat rate 'during two loop oper'ation to 10.9 kw(ft,'ompared to the '13".62.kw/ft 'value used in the.'3 loop ECCS analysis.

According to sensitivity studies described zn WCAP-8340, thepeak 'clad temperature following a LOCA would be lowered another'. 360oF as a result of this reduction in heat rate, bringing the.'clad temperature 'we'l below 1840~F.

.Very truly yours,

)girl'obert.

E. Uhrig Vice Presi,dent REU:nch

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Mr. No'rman Moseley Jack R.

Newman, Esquire