ML20207B761

Proposed Tech Specs Re Ice Condenser Flow Blockage

ML20207B761
Person / Time
Site:	Sequoyah
Issue date:	07/27/1988
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML20207B750	List: ML20207B746 ML20207B761
References
NUDOCS 8808040127
Download: ML20207B761 (12)

Text

. - i ENCLOSURE 1 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 .

DOCKET NOS. 50-327 AND 50-328 (IVA-SQN-TS-88-13 )

LIST OF AFFECTED PAGES Unit 1 3/4 6-27 Unit 2 3/4 6-28 O

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8800040127 DR 080727 ADOCK 05000327 ,

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CONTAINMENT SYSTEMS l 1

SURVEILLANCE REOUIREMENTS (Continued) one basket each from Padial Pows 1, 2, 4, 6, 8 and 9 for from i the same row of an adjacent bay if a basket from a designated row cannot be obtained for weighing) within each bay. If any basket is found to contain less than 1200 pounds of ice, a R8 representative sample of 20 additional baskets from the same bay shall be weighed. The minimum averace weight of ice from the 20 additional baskets and the discrepant basket shall not R7 be less than 1200 pounds / basket at a 95% level of conf,idence.

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The ice condenser shall also be subdivided into 3 groups of baskets, as follows: Group 1 - bays 1 throuch 8 Group 2 -

bays 9 through 16 and Group 3 - bays 17 through 24 The minimum average ice weight of the sample baskets from Radial Rows 1, 2, 4, 6, 8 and 9 in each group shall not be less than

. 120'0 pounds / basket at a 95% level of confidence. R7 The minimum total ice condenser ice weight at a 05t level of confidence shall be calculated using all ice basket weights determined during this weighing progran and shall not be less than 2,333,100 pounds. R7

2. "; r i fyi ng , by : ti:::1 'n::::tien Of :t le::t tre '!:r p::::ce:

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:nd:n: r b:y, that th: :::r elatier of 're:t er ice er NEPLAcfWrrH ficw pess g;; h:tw;;n i:: b::F:t;, ;::t 1:ttic #r: ::, thr ::'

INSE AT 'A'. th: int: cr.;dic t: :nd t:; d::E '1 :r ;r: tin:, er ;::t the 1:wcr

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, inl:t plong: :;;;;rt :truttart: :nd tur in: v:nt: i: r;;tricted t: ; thi:Ent:0 Of 1::: th:r r :nu;1 t: 0.3" ' :500. !' en:

fi w p::::p; per 5:y i; f end t: 5:v: Or :: u ul: tier Of ' ::t er f:: "ith : t'fckner: c' gre:te- th a e ecue' te 0.?9 da her,

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c. At least once per 40 nonths by liftino and visually. inspecting the accessible portions of at least'two ice baskets from each 1/3 of the ice condenser and verifyino that the ice baskets are free of detrinental structural wear, cracks, corrosion or other damace. The ice baskets shall be raised at least 10 feet for this inspection.

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Amendment 4 SE000YAH - l' NIT 1 3/a 6-27 1

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i CONTAINMENT SYSTEMS SURVEILLANCE REOUIREMENTS (Continued)

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one basket each from Radial Rows 1, 2, 4, 6, 8 and 9 (or from the same row of an adjacent bay if a basket from a designated row cannot be obtained for weighing) within each bay. If any basket is found to contain less than 1200 pounds of ice, a representative sample of 20 additional baskets from the same bay shall be weighed. Tbe minimum average weight of ice from the 20 additional baskets and the discrepent basket shall not be less than 1200 pounds / basket at a 95% level of confidence.

The ice condenser shall also subdivided into 3 groups of baskets, as follows: Group 1 - bays 1 through 8, Group 2 -

bays 9 through 16, and Group 3 - bays 17 through 24. The minimum average ice weight of the sample baskets from Radial Rows 1, 2, 4, 6, 8 and 9 in each group shall not be less than 1200 pounds / basket at a 35% level of confidence.

The minimum total ice condenser ice weight at a 95% level of confioence shall be calculated using all ice basket weights cetermined during this eighing program and shall not be less than 2,333,100 pounds.

2. '!:ri fyi ng , by : i:c:1 4 9:;;; tier c' at 'eset to: 'l:1 p::::ge: -

-per ice Condenser b y, that th :::umulation Of f r;;t Or it on f(PLActWWH flex panages-bet-weer f:0 b::kett, p::t 1:ttic: 'r::::, throug h

.JM5fRJ T the- 4 ten edist: and top deck 'l:Or grati g, er p::t the leuee 4-10t pl: ur :Uppert tructure: :n: tur 4 9; V:ne; i: re:trict:d t: ; thi: Pat:0 of 100; th:r Or equal t 0.39 d ech :.  !* :n

1. raw-p&%aje-pef' 4 y i; f 0end t h&Ve-&ft-3GCumulOti 0 Of f r;;t

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thicknet; Of grester th;n er- qu;l t: 0.23 inch::,

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repre:cr.t tiv ::npl; Of 20 Odditi0n:1

. are bay chall--be "itually i" pected. If th::: ::d!! fl0x p::: ::i n: 1 flew =

p::::ge: Orc f end ::: pt:ble, th: :urvei'l:ne:-pr;;c5m sey pr::::d cen:id:r'n; t*: sia;'e de'iciency 2: eaique and 2 : pt -

Oble. M: th:r : : rett-i:t:d '!:u ;::: ;; per t:y i:

evident: Of Obn:r:01 degr:::tien Of the .we wu Mun er.

c. At least once per 40 months by lifting and visually inspecting th'e accessible portions of at least two ice baskets from each 1/3 of the ice condenser and verifying that the ice baskets are free of detri-mental structural wear, cracks, corrosion or other damage. The ice baskets snall be raised at least 10 feet for this inspection.

4 SEQUOYAH - UNIT 2 3/4 6-28 4

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3. Verifying, by a visual inspection a representative random sample of at least 54 flow passages (33 percent) per ice condenser bay, that :

the accumulation of frost or ice on flow passages between ice .

baskets, past lattice frames, through the intermediate and top deck floor grating, or past the lower inlet plenum support structures and turning vanes is less than or equal to 15-percent blockage of the '

total flow area in each bay, with a 95-percent level of confidence.

If the summation of blockage from the sample fails to meet the acceptance criteria, then 100 percent of the passages of that bay shall be inspected, or 100 percent of the passages shall be cleaned.

If the 100-percent. inspection fails to meet the acceptance criteria, then 100 percent of the passages shall b,e cleaned. After cleaning, repeat the surveillance process.

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ENCLOSURE 2 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 .

DOCKET NOS. 50-327 AND 50-328 (IVA-SQN-TS-88-13)

DESCRIPTION AND JUSTIFICATION FOR ICE CONDENSER FLOW BLOCKAGE ,

SURVEILLANCE REQUIREMENT

ENCLOSURE 2 Description-of Change .

Tennessee Valley Authority (TVA) proposes to modify the Sequoyah Nuclear Plant (SQN) units 1 and 2 technical specifications (TS) to revise .

containment systems surveillance requirement 4.6.5.1.b.3. This change will repiece the visual inspection requireamnt utilizing a 0.38-inch criteria with a surveillance program to ensure that the flow blockage does not exceed 15 percent. .,

Reason for Change During preparation for unit 2 restart, the surveillance requirement (SR) of the SQN ice condenser, TS 3/4.6.5, was reviewed. The review revealed that SR 4.6.5.1.b.3 attempted to quantify the amount of allowable ice buildup in the ice condenser flow passages, but did not adequately reflect the intent of the TS. The TS is to ensure that adequate flow area exists in the ice condenser bays to allow passage of steam and air. Tha findings also showed that the surveillance of the ice condenser flow paths should be focused on the original intent of the TS and that a reasonable method of inspection be provided. The proposed method of inspection is more feasible and provides a more direct relationship to~ ne functional requirements of the ice condenser.

Justification for Change TS SR 4.6.5.1.b.3 requires by visual inspection of at least two flow passages per ice condenser bay that the accumulation of frost or ice in flow passages be restricted to a thickness of less than or equal to 0.38 inch.

j While this requirement attempts to quantify the amount of allowable ice i buildup in the ice condenser flow passages, it does not adequately reflee.

the intent of the TS, which is to ensure that adequate flow area exists through the ice condenser bays. In addition, the implementation of this SR is extremely difficult. Because of the inaccessibility of the 48-foot-long flow path, the current surveillance procedure requires that the inspector visually judge, from a distance of up to 24 feet, whether or not ice accumulation is less than or equal to 0.38 inch. This is a task that is extremely difficult. Therefore, the surveillanca of the ice condenser flow paths should be focused on the intent of the TS, which is to ensure that adequate flow area exists in the ice condenser bays and to provide a reasonable method to inspect such flow areas.

Frost or ice accumulation in flow passages between ice baskets may momentarily restrict the flow of steam through the ice condenser in the event of a hypothetical loss of coolant accident (LOCA). This rastriction will only be momentary, because the high energy steam will quickly melt any accumulation. Hence, the only design basis accident that may be affceted by such accumulation is the Short-Term Pressure Analysis (or Subcompartment Pressurization Analysis) presented in section 6.2.1.3.3 of the SQN Final Safety Analysis Report (FSAR). ,

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<4 This analysis is performed to ensure that-the subcompartment wall and the steel shell of the containment structure can maintain their structural integrity during the short-prcssure pulse (generally less than 3 second;)

that accompanies the rupture of a high-energy line within the lower -

compartment. A flow restriction in the ice condenser flow paths could result in a momentary pressure buildup in the lower compartment or lower plenum of the ice condenser bays and challenge the integrity of the operating deck, the upper or lower crane wall, or the containment steel shell. The analysis utilized an NRC-approved Westinghouse Electric Corporation Transient Mass Distribution (IMD) code employing the same assumptions used in the base analysis documented in section 6.2.1.3.3 of the FSAR with the exception that a 15-percent uniform flow area blockage assumption was employed. The 15-percent flow blockage assumptien corresponds to a 6.15-square-foot blockage area of a possible .

41.02-square-foot flow area in each ice condenser bay. The 41.02-square-foot value is the assumed flow area through the ice condenser bay at an elevation with a lattice frame. This flow area is ssumed to occur over the entire 48-foot flow passage length throughout tne ice cor. denser bays. This reduced flow area was assumed to be permanent throughout the duration of the accident, conservatively neglecting the fact that much of the blockage would be blown out by the high-energy flow through the ice condenser passages. As a result of TMD's one-dimensional ice condenser flow path model, the code conservatively neglects the benefits that cross-flow will provide in venting the steam and air around actual blockages in the ice bed.

In addition, the TMD analysis contains many other conservatisms. The hypothetical accident was conservatively assumed to be initiated by the instantaneous, double-ended guillotine rupture of one of the main coolant pipes. The break plane was assumed to be comple.tely displaced instantaneously, suca that the effective break flow area is twice the main coolant pipe flow area. Mechanistic pipe break technology has demonstrated that a double-ended guillotine break of the reactor coolant piping is highly unlikely. Even if such a guillotine pipe break were possible, the displacement of the piping would be limited by pipe whip restraints, which would significantly reduce the magnitude of the release of high-energy steam into the lower compartment of the containment. This conservatism was further compounded by the fact that the calculated mass and energy releaces assumed in the analysis were increased by 10 percent.

In addition, the analysis conservatively neglected the heat removal capability of the structural heat sinks. Hence, this 15-percent blockage analysis provides a conservative basis for defining an acceptable limit of effective flow blockage in the ice condenser. Therefore, the 15-percent blockage TMD Subcompartment Pressurization Analysis provides a conservative basis for determinin,~ the operability of the ice condenser flow paths.

The studies of flow blockage in the ice condenser established an effective flow blockage of not more than 15 percent of the total flow area, which is l sufficient to ensure that adequate flow area exists to limit the peak l

containment pressure below the design pressure of 12 pounds per square

, inch gauge (psig). The new surveillance method will inspect a sample of l the flow passages in each of the ice condenser bays against the acceptance l

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criteria ensuring that the fica blockage.is-less than the calculated blockage. A random sample of 54 (33 percent) of the flow passages in each bay will provide a 95-percent level of-confidence that the aggregate. flow. .

blockage is less than or equal to'15 percent of the' total flow area. -

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• ENCLOSURE 3 PROPOSED TECHNICAL SPECIFICATION CHANGE

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SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 ,

DOCKET NOS. 50-327 AND 50-328 (TVA-SQN-TS-88-13)

DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS 0

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4 ENCLOSURE I Significant Hazards Evaluation TVA has evaluated the proposed TS change and determined that.it does not represent ~a significant hazards' consideration based on. criteria established in 10 CFR 50.92(c)'. Operation of SQN'in accordance with the proposed amendment will on'ts' (1)' Involve a significant increase in the probability or consequences of an accident previ'usly o evaluated. The ice condenser: system is a passive system designed to absorb thermal energy released immediately following a LOCA or a high-energy line. break (HELB) for the purpose of limiting peak pressure inside containment.- The ice condenser :

serves no function during normal operation but is required in mitigating the consequences of a LOCA or HELB.

Existing TS SR 4.6.5.1.b.3 requires. verification that the accumulation of frost or ice on flow passages is restricted to a thickness of less than or equal to 0.38 inch. The intent of'this SR was to ensure that the flow areas in the ice condenser are consistent with those used by Westinghouse in analyses to determine containment design pressure. Frost or ice accumulation in the flow passages could momentarily add resistance to the flow of air and steam through the ice condenser. The Westinghotse analyses assumes a hypothetical ,

LOCA and utilized the TMD computer code. The TMD computer code was used for a sbert-term subcompartment pressure analysis that determined siart duration pressure transients across interior concrete walls, the operating deck slab, and the, containment shell during the. blowdown period. The mass and energy releases used in these analyses were increased by 10 percent over those calculated by the SATAN computer code, and no structural heat sinks were modeled to

, provide additional conservatism in the calculation of the pressure rise. Westinghouse performed sensitivity studies of flow blockages in the ice condenser, which established that the containment pressure was less than 12 psig with an effective blockage of 15 percent of the total available flow area in the ice bed. Additional conservatism in the sensitivity studies was that the blockages were assumed to be constant throughout the entire height of the ice bed and neglects the benefits that cross-flow will provide in venting the steam and air around actual blockage in the ice bed.

Additionally TVA performed calculations to confirm that the operating deck floor slab, refueling canal wall, crane wall above the ice condenser columns, and ico condenser end walls were structurally adaquate to withstand a design basis accident pressure increase because of ice condenser blockage up to 15 percent. These calculations confirmed that each area is structurally adequate for operation at the increased pressures.

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The use of 0.38-inch maximum ice buildup in the SQN TS for determination of blockage was intended to quantify the amount of allowable ice buildup in the flow passages because accumulation could momentarily add resistance to the flow of air and steam through the -

ice bed. Implementation of the existing SR is extremely difficult.

In some instances, inspectors must visually determine wheth2r ice buildup is less than or equal to 0.38 inch from a distance of up to 24 feet. The revision-of SRs will replace the specific 0.38-inch value for ice condenser flow passage inspection with a conservative, quantifiable, and reasonable method for verifying operability with respect to available flow nrea. The new surveillance method will inspect 54 (33 percent) of the flow passages in each of the 2,4 ice condenser bays against acceptance criteria where any bay with less than or equal to 15-percent calculated blockage shal? be considered to have acceptable flow channels for passage of air and steam through the ice condenser. Westinghouse has determined through sensitivity studies that up to 15-percent blockage will allow adequate flow through the ice condenser. The survelliance method to be used for

. flow passage inspection uses an acceptance criteria based on

, 15-percent blockage; the revision of the TS to replace the specific 0.38-inch value will not adversely affect the function of the ice condenser and will not increase the probability or consequences of any accident or malfunction previously evaluated.

(2) Create the possibility of a new or different kind of accident from any previously analyzed. The ice condenser is a passive system that functions to limit initial pressure inside containment following a LOCA or HELB as previously analyzed. Westinghouse verified that 85-percent available flow area is adequate for the ice condenser to perform its intended safety function; the c,hange in SR from requiring visual inspection to verify that ft.st/ ice accumulation does not exceed '.38 inch to visual inspection to verify that blockage does not exceed 15 percent of the total flow area will not affect the function of the ice condenser or create abnormal operating conditions. The new SR will provide a reliable and quantifiable means for conservative verification of blockage. Therefore, the change in SR does not create the possibility of a new or different kind of accident.

(3) Involve a significant reduction in a margin of safe;y.

SR 4.6.5.1.b.3 utilized a speci'ic value of 0.38 inch for

, determination of frost / ice blockage in the ice condenser. This specific value was used in an attempt to quantify the amount of blockage so that availabic flow area could be calculated and verified as acceptable. This specific value, however, does not establish the

safety limit for blockage of ice condenser flow area. Westinghouse has shown that with 85 percent of total flow area available, the ice condenser will perform its intended function. Therefore, the safety limit for ice condenser operability is less than or equal to 15-percent blockage. The new surceillance method to be used requires more extensive visual inspection than the surveillance program currently described in 4.6.1.b.3, thus providing greater reliability and a direct relationship to. analytical safety limits.

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Because the safety limit for the ice condenser flow is less than or equal to 15-percent blockage of total flow area, a change in TSs to implement a surveillance program that is more reliable utilizing a 15-percent blockage acceptance criteria will not reduce.the margin of safety. Design limits -

for the continued safe function of the containment shell and concrete containment walls and slabs are not exceeded as a result of this change.

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