ML20087N997

Submits Test Results Demonstrating Steam Vented from Reactor Vessel Head Will Not Stratify in Hot Leg & Adversely Affect Core Cooling by Natural Circulation,Per Tm Novak 831025 Request & SER Open Item 9

ML20087N997
Person / Time
Site:	Midland
Issue date:	03/23/1984
From:	Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Harold Denton Office of Nuclear Reactor Regulation
References
27160, NUDOCS 8404050311
Download: ML20087N997 (4)

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@ Consumets power James W Cook Company vin n,u.n, - ~i. e+ a.

and Construction oeneral Offices: 1945 West Parnell Road, Jackson, MI 49201 e (517) 788-0453 March 23, 1984 Harold R Denton, Director

-Office of Nuclear Reactor Regulation.

-Division of Licensing US Nuclear Regulatory Commission Washington, DC 20555

' MIDLAND ENERGY CENTER PROJECT MIDLAND DOCKET NOS 50-329, 50-330 REACTOR VESSEL HEAD VENT SER OPEN ITEM #9 FILE B5.1, M1.50 SERIAL 27160

REFERENCE:

LETTER FROM T H NOVAK TO J W COOK DATED 10/25/83 In previous discussions and correspondence, Consumers Power Company (CPCo) has proposed venting the reactor vessel head through a small line connected to the top of the hot leg. ' The Staff position provided in the referenced letter

. requests the applicant to demonstrate by test or analysis that steam vented from the reactor vessel head will not stratify in a hot leg and adversely affect core cooling by natural M rculation.

We, therefore, plan to utilize the Multiple-Loop Integral Sy.c m Test-(MIST) facility to perform specific tests on the-interconnected head-hot leg vent design to address this concern.

= Testing of the interconnected head-hot leg vent design at the MIST facility will apply to the operation of both the Midland and the Davis-Besse plants.

The MIST tests.will be performed on a lowered loop configuration and the

-interconnected vent design will be essentially identical to the Midland design (ie, interconnection above the hot leg U-bend). These tests will be utilized to benchmark.the computer codes used to analyze the design and to verify the adequacy of operator actions to deal with system voids.. Final Abnormal

. Transient Operating Guidelines (ATOG) and operating procedures will reflect the results of the MIST testing when it is completed in 1986.

Having reviewed several alternate design modifications, including remotely isolating the line connecting the head vent to the high point vent, we firmly i

-believe that'the advantages of the proposed interconnected vent design far

-outweigh any potential disadvantages.

In summarizing the basis for our

. position,.we believe.that the assumption that excessive steam will collect in

.the hot leg U-bend does not allow credit for the' ability of the operators to vent steam from the system.

Correspondingly, if credit'is not allowed for 8404050311 840323

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operator action, then. separate head. vents-represent a less desirable design since operator action is required.to vent either point. However, if credit is allowed for. operatoriaction, then the concern' regarding the accumulation of

' ' MO-steam in the hot. leg:U-bend is' diminished and-the advantages of the

= interconnected vent design can be' realized without the complication of

~ additional linesiand' remotely operated valves. Operating procedures will

.E fprovide;several methods to reduce. system. voids. These methods will include venting ~from.the-high point' vent, establishing or increasing high pressure

- Linjection:(HPI) flow, and starting or bumping reactor coolant pumps.

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.,With-respect to the possibility.that steam. venting from the head to the hot

' leg'could cause:an earlier loss'of natura11 circulation than otherwise expected, we believe'that based on the'relatively low. capacity of the vent and the area ~available for condensation in the hot leg, an early loss of natural

-A Leirculation will'not occur.- Even if an earlyLloss of natural circulation

cooling occurs, a total ~ loss is precluded since the-vent-connection only goes Lto one hot leg U-bend. Loss of all natural circulation cooling due to c

! stratification in one hot leg-U-bend could'only occur coincident with the loss

of.the opposite steam. generator.

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lit l appears that in previous submittals, CP.Co.has not adequately pointed out

'the advantages of the: proposed interconnected vent design.. In arriving at

~this: vent design,'.there were-four important. features which were; considered desirable.

1.

The proposed ~ design provides'a method for extracting heat from the head

region to allow a more. rapid natural circulation.cooldown and

.depressurization of the system, without drawing a steam bubble in the

-head. This significant advantage'is~ achieved because of the continuous

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~ flow of-coolant.from'the reactor vessel upper head to the hot leg U-bend through the interconnection.

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. :2. : The proposed design should ' reduce the frequency and quantityL of steam and s

fluid vented into containment from the primary system. This feature is

-desirable as it minimizes the extent of-potential contamination and the

< consequential creation:of a harsh environment in the containment.

3; Likewise,1the' proposed design addresses margin to inadequate core cooling which,' among other parameters, is dependent on system inventory. The tinterconnected vent conserves inventory and. maintains margin.by:

a..Any steam collected in the reactor head will be directed to the primary side:of 'the. steam generator and condensed rather than being

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vented out'of the-system under normal recovery modes.

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In the' event'of a l'oss of natural circulation due to stratification in' 4

the hotileg U-bend, the boiler-condenser mode:of' natural circulation

- tcooling'would occur with a significantly. greater liquid ~ inventory.in the primary system than for designs without the interconnected vent.

Thiscadditional margin in inventory.is due

to the upper reactor vessel Du region;being filled with water rather than steam at onsets.

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4. :The proposed.'designLconsiders human factors enhancement during an accident 1 by simplifying 'the procedure required for the operator-to monitor the

primary, system' inventory for inadequate core cooling. The interconnected

' vent: design requires the operator toitrack only one level measurement (ie, the hot leg. level) tx) determine system inventory because the hot leg and

' head or vent line levels will be the same.

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It'is CPCo's. intention ~to proceed with.the installation land development of

' procedures :for operation of the interconnected. head-hot leg vent in order to Eresolve SER Open Item #9. 'If the: Staff. has any. questions regarding this design or the proposed testing to' confirm its-adequacy,.we would like to meet Twith you-as early-as.pos'sible to attempt to resolve'such concerns.

'JWC/JRW/MFC/bjw

'CCf JGKeppler

,. Administrator,jNRC Region III DSHood,'US NRC, Licensing' Branch No 4-RJCook,' Midland Resident Inspector 1

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CONSUMERS POWER COMPANY Midland Units 1 and 2

' Docket No. 50-329,'50-330 c

Letter Serial 27160 Dated March 23, 1984 At the request of.the-Commission.and pursuant to the Atomic Energy Act of 1954, Land the Energy Reorganization Act of 1974, as. amended and the

. Commission's Rules and Regulations thereunder, Consumers Power Company submits la commitment to. utilize the Multiple-Loop Integral-System Test facility to test the. int'erconnected head-hot leg vent ' design.

JCONSUMERS POWER' COMPANY h;

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-By' O-7

J Cooki Vice President-Proj'e s, Engineering and: Construction Sworn and subscribed before me this o?$. day of 7//g4cd,/9//

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~.. Notary P5bITc

. Jackson County,' Michigan

~My Commission Expires:

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