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DISTRIBIJTION: NRC PDR EE SATeets Central Files WButler RCudlin ORBt3 Rdg OParr KRGoller LShao GLear JKnight TJCcrter RMaccary R. DeYoung, Assistant Director for LWR Group 1, DRL Glainas V. Moore, Assistant Director for LWR Group 2. DRL JFSgolz KKniel RTedesco R. Purple, Chief, ORBil, DRL ASchwencer CJDeBevec D. Ziemann, Chief, ORBf2, DRL THRU: Karl R., Goller, Assistant Director for OperaEf 8f8Nfors, DRL LETTER TO LICENSEES REGARDING POOL DYNAMIC LOADS F0lt BWR'S WITH KGK I CONTAINMENT At meetings on April 10 and 16, 1975 E. Case provided guidance to representatives of DRL and DTR (R. Boyd, F. Schroeder, R. Maccary, K. R. Coller, et. al.), for the preparation of the enclosed letter to be sent to all BhR utilities having a Mark I type of containment. The letter addresses the pool dynamic loads associated with a LOCA and the question of whether the torus is capable of withstanding these loads.
, This pool dynamic load question is in addition to the vent c1 caring l and steam quenching vibration phenocena.already addressed in our
! February,1975 letter to licensees and applicants for CP's and OL's.
i I The enclosed letter has been prepared on tape. It should be sent to the i licensees with operating ('! ark I) B*..R's as soon as possible. Letters to applicants with 3'..R-!! ark I containc.cnt should be signed and sent by th'R Branch Chiefs. Note that the letter to applicants (Brown's Ferry 3 i
Brunswick-1, Hope Creek 1/2, Hatch-2, and Ferai-2) differs.from those to i licensees; instructions are provided (Enclosure 2) for typing the
- 1etter to applicants.
Following dispatch of these letters, we will provide further guidance for issuance of an Order to all licensecs with operating (Mark I) Bh"t's that I will impose temperature limits on the torus pool water. The Order will address needed actions related to the vent clearing and steam quenching vibration phenonena.
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George Lear, Chief 8604020020 860114 Operating Reactors Branch b, PDR FOIA Division of Reactor Licensing FIRESTD85-665 PDR ,
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Enclosures:
- 1. Proposed Letter to Licensees .
- 2. Instructions for Letter to Applicants nJP N l*
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ENCLOSURE 1 LAWITED STATES 4 NUCLEAR REGULATORY COMMISSION W ASHINGTON, D. C. 20555 (SAMPLE LETTER)
Docket No.
Gentlemen:
Pursuant to 550.54(f) of 10 CFR Part 50, the Nuclear Regulatory Commission (NRC) staff requires that certain information related to the design of the containment for your facility be submitted promptly to NRC for its review.
This requirement results from recent developments associated with the large-scale BWR Mark III testing being conducted by the General Electric Company. These tests indicate that suppression pool hydrodynamic loads during a loss-of-coolant accident (LOCA) should be considered in the detailed design of components and structure of the Mark III containment.
In addition, there appears to be a potential for the occurrence of similar dynamic loads on plants with a Mark I type of containment. j Therefore, we require that you provide the information specified in Enclosure 1 concerning the potential magnitude of these hydrodynamic loads, and the ef fects of these loads, in combination with other design loads, on the design of your containment structures.
Enclosure 1 specifies the information required to complete our review l of the effect of pool dynamic loads on the design of your I containment structures. Enclosure 2 contains background information on the status of ef forts directed at determining pool dynamic loads. For general informatiom, we have also provided in Enclosure 3 a description of the various phenomena during a postulated LOCA which result in possible hydrodynamic loads. Please note that certain key phrases in Enclosure 3 have been underlined. These phrases (1) identify those specific hydrodynamic loads which, as a minimum, should be considered .
in your review of containment design, and (2) establish the standard l nomenclature by which phenomena should be discussed or referenced in your documentation. l Your response to the request should be filed within sixty days of the ,
date of receipt of this letter. If you cannot meet this sch.dule ,
+ please ad. vise us within fif teen days. The scheduling of work ot this matter should parallel related efforts on other containment design /
operational control aspects, i.e., relief valve vent clearing and steam guenching vibration phenomena.
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2-Please contact us if you desire additional discussion or clarification of the information requested.
Sincerely, George Lear, Chief Operating Reactors Branch #3 Division of Reactor Licensing a
Enclosures:
- 1. Required Information
- 2. Background
- 3. Description of Potential Pool Dynamic Phenomena This request for Generic Information was approved by CAO under a blanket
- , Clearance No. B-180225 (R0072); this clearance expires July 31, 1977.
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ENCLOSURE 1
, REQUIRED INFORMATION (1) Provide large size plan and section drawings of the suppression chamber which illustrate the structures, equipment, and piping in and above the suppression pool. These drawings should be in sufficient detail to describe all equipment and structural surfaces which could be subjected to suppression pool hydrodynamic loadings.
(2) Provide a chronol'ogy of all potential pool dynamic loads during a LOCA which identifies the source of the load (see enclosure 3),
the time interval over which the load is active, and the structures which are affected. (For an example, see GESSAR, Response 3.82.)
(3) For each structure or group of structures identified in paragraph (2) above, provide the ' anticipated load as a function of time due to each of the pool dynamic loads which could be imparted to the structure.
(4) For each structure or group of structures identified in paragraph (2) above, provide the total load as a function of time due to the sun of anticipated pool dynamic loads.
(S) Describe the manner in which the pool dynamic load characteristic shown in (4) above is integrated into the structural design of each structure.
Specify the relative magnitude of the pool dynamic load compared to other design basis loads for the structure.
(6) Describe the manner by which potential asymmeric ~1oads were considered in the containment design. Charatteri:e the type and I
magnitude of possible asymmetric loads and ths capabilities of the affected structures to withstand such a imukhg profile. Include consideration of seismically induced pool senion which could lead to locally deeper submergences for certain brd: ental vent stacks.
(7) Provide justification for each of the load ks. tories given in (3) above by the use of appropriate experimenta1 data and/or analyses.
References to test data should indicate the:ppcific test runs and data points and the manner by which they wereconverted to loads.
As an interim measure, use of available expeitental data may be acceptable; however, if it appears necessary, additional tests directly applicable to the LOCA pool dynamic load phenmenon and its analyses will be required.
(8) Provide a descriptian of the structural analyis methods, and a summary of the results of your structural design evasation which either demonstrate that the containment design can withstand thepool dynamic loads imposed upon the structure within adequate margins,101the design modifiwations required to meet allowable design limits. .
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ENCLOSURE 2 BACKGROUND '
Pool Dynamics
~~" The need to consider suppression pool hydrodynamic loads in the design of certain parts of the Mark III containment developed
during the early phases of the large-scale Mark III test prcgram being conducted by the General Electric Company. A series of air tests were performed in March 1974 to scope the range and magnitude of pool dynamic loads. It was recognized that more definitive tests were required and.
therefore comprehensive tests in 1/3 scale were initiated in the summer of 1974 and are currently still in progress. Parallel efforts to develop analytical models for the various pool dynamic phenomena have-been implemented by the General Electric Company, several architect / engineers, and by Jyu: consultants. , ,
The NRC staff has maintained contact with GE regarding the planning ,
.and progress of the pool dynamics testing and associated analyses. Due to the commonality of the water pressure suppression feature in Mark I, II, and III type containments it was apparent that pool dynamic loads could also be a consideration for Mark I and II plants. GE, in fact, is in the process of planning a series of tests for ASEA / Atom of Sweden.
The purpose of these tests would be to determine pool dynamic loads for a structure lo,cated immediately above the suppression pool for a containment
'with vertical vent pipes. The basis for applying this data to specific Mark I and II designs has not yet been established. ..
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c ENCLOSURE 3 DESCRIPTION OF POTENTIAL POOL DYNAMIC PHENOMENA Following a design basis loss-of-coolant accident in the drywell, the dry-well atmosphere will be rapidly compressed due to blowdown mass and energy addition to the drywell volume. This compression would be transmitted-in the form of a compressive wave and propogate through the vent system into the suppression pool. The pool response to this effect could include a load on the suppression chamber walls.
With pressurization of the drywell, the water in the downcomers will be depressed and forced out through the vent system into the suppression pool. This movement of pool water can result in a water jet impingement load on the suppression, chamber.
Following clearing of the vents an air / steam / water mixture will flow from the drywell through the vents and be injected into the suppression pool below the surface. D'epending on the characteristics of the suppression system (i.e., the vent area compared to the drywell volume and break flow area) drywell overexpansions could occur. Overexpansion of the drywell results when the initial vent flow, following vent clearing, evacuates the drywell j more rapidly than the volume is replenished by blowdown mass and energy input. If the drywell volume is relatively small compared to the area of
- the vents, then there is insufficient capacity to absorb the transition in venting rates and loads due to drywell overerainsion oscillations can occur on the suppression chamber and vent systen. ,
During vent flow the steam component of the flow sixture will condense in the pool while the air, being noncondensible, will be released to the pool as high pressure air bubbles. Initial air bubble loads would be experienced i
by all pool retaining structures and could be of an oscillatory mode due to overexpansion and. recompression of the bubbles. 1 The continued addition and expansion of air witt2n the pool causes the pool l volume to swell and therefore an acceleration of:he surface vertically upward. This response of the pool is referred toss bulk pool swell since the air is confined beneath the pool and is driv 2gga solid ligament of water. Bulk pool swell air bubble and flow drag 3 ads are imparted to the
- suppression chamber walls and to structures, compoents, etc., which may be
' located at low elevations above the normal pool suface. Bulk pool swell impact loads will also result for low elevation stuctures and components.
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Due to the effec.t of buoyancy, air bubbles will rie fasser than the pool water mass and will eventually break through thersellen surface and relieve the driving force beneath t' ? pool. This breakupoS the water ligament leads to the upward expul- of a 2-phase mixtureof air and water and is referred to as pool swell he froth mode. Stratures which are located at higher elevations above tne initial pool surfacccould experience a pool swell froth impingement load due to impact of 2-ptse flow.
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- Froth flow will continue until the fluid kinetic energy has been expended, followed by fallback of the water to the initial suppression pool level.
. Structures located above the pool could be subject to water fallback loads.
Following the initial pool swell event the suppression system will settle
, into a generally coherent phase during which significant vent flow rates r are maintained from the drywell to the pool. A resultant effect is the occurrence of high vent flow steam condensatien loads, which can be of an oscillatory nature. on pool retaining structures. As.the reactor coolant system inventory of mass and energy is depleted, near the end of blowdown, venting rates to the suppression pool diminish allowing water to reenter the downcomers. During phases of low vent mass flux the suppression system behaves in an oscillatory manner, referred to as chugging,-khereby periodic clearing and subsequent' recovery of vents occurs since the vent flow cannot sustain bulk steam condensation at the vent exit. The resultant loca1' fluctuations ir. pressure and water levels generate chugging oscillation leada, predominantly on the vent system.
It should be further noted that the magnitude and range of any of the hydro-dynamic loads discussed above can be aggravated by an asymmetric response of the suppression system, either in the circumferential or radial direction.
One possible initiator of such response would be seismically induced pool j motion which could lead to locally deeper submergences for certain downcomers i and therfore larger pool swell loads. Full account of this potentiality '
should be made in establishing hydrodynamic load capabilities for the ,
suppression chamber structures design. --
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ENCLOSURE 2 INSTRUCTION FOR LETTERS TO APPLICANTS The utilities and plants having BWR Mark I containments that are still i
I in the CP/0L review stage are: 1 TVA - Browns Ferry-3 l CP6L - Brunswick-1 PSEG of New Jersey- Hope Creek 1/2 Georgia Power Co. - Hatch-2 j Detroit Edison Co.- Fermi-2 i For letters prepared for dispatch by LWR Branch Chiefs to these applicants, i l
you are to: i Replace the first two sentences in the third paragraph with the following: ,
Your pr'ogram and schedule for pronpt resolution of the problems i associated with LOCA-caused suppression pool hydrodynamic !
Ioads should be filed with the Commission no later than 30 days after receipt of this letter. .
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