ML20207B613
| ML20207B613 | |
| Person / Time | |
|---|---|
| Issue date: | 12/05/1986 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Sniezek J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| Shared Package | |
| ML20204J261 | List: |
| References | |
| FOIA-87-714 NUDOCS 8612120170 | |
| Download: ML20207B613 (41) | |
Text
{{#Wiki_filter:. . b (b %'M ~ h
$86 otc H MEMORANDUM TO:
James H. Sniezek Deputy Executive Ofrector for Regional Operotions and Generic Requirements FROM: Harold R. Denton, Director Office of Nuclear Peactor Regulation PROPOSED REVISION 2 0F STANDARD RtVIEW PLAN SECTION 6.5.2, SUP1ECT:
"CONTAINMENT SPRAY AS A FI3SION PRODUCT CLEAN-UP S The enclosed generic requirement review packages are being submitted for consideration by the Comittee to Review Generic Aequirements (CRGR), as a category 2 action. This proposal seeks to revise the Standard Revier Plan section which is used by the staff to assess the degree to which ofi-site doses are mitigated by containment sprays in evaluating radiclogical consequenc assure compliance with 10 CFR Part 100. The revisions include a number of ninor changes to acknowledge the recent reorganization of the review staff, as well as changes which, by explicitly stating equations and numerical parameters previously contained in numerous references, will simplify the review procedur by anyone unfamiliar with those references.
These proposed changes constitute relaxations in current staft positions which are judged to have no significant detrimental effect on plant safetyThes while providing cost savings for the industry. current review emphasis on immediate actuation of spray additive systems and decrease the amount of additives that would be needed to achieve significant fission product clean-up. These changes affect staff positions which at present conservatively underestinate the efficacy of containment sprays as fission product clean-up systens. The major changes in this SRP relate to the need for chemical additives in the spray solution. system, and to post-accident pH control of the containme during spray injection, although licensees may retain this feature. SRP also proposes that post-accident pH control of the containment sump solution be retained (at a pH of 7 or greater) at the In contrast, the time of recirculation present SRP requires to present evolution of volatile iodine. that the sump solution pH be maintained at 8.5 or greater, it should be noted that licensees areHowever,not required to makeofany for licensees changes to their existing spray system under this SRP revision. plants to profit by this revision, it would be necessary for them to amend their FSARs and license technical specifications and, upon approval, toAs discussed perform modest changes in plant design and emergency pro be too smell to justify the expense, while other licensees may achieve signifi. ant savings.
~ -
mzew m T N (\w M-
r DEC 05 1996 James H.' Sniezek Included in the enclosed packages are a Brookhaven National Laboratory The Brookhaven technical report and a brief technical background paper. report is a technical finding document that serves to support the minimum value of a mass transfer coefficient used in the proposed review procedure. The background paper is intended as an explanation of +he most important chemical evidence dealing with the relationship of the acidity of sump solutions to the long term retention of fission product iodine. Following CRGR consideration, this package will be submitted to the ACRS. After amendment to accommodate any coments from both of these comiittees, public coments will be sought. Comittee consideration of this action prior to January,1987, would be appreciated. Original Signed By: Richard H. Vollmer Harold R. Denton, Director Office of Nuclear Reactor Regulation Attachments: As stated (*SeePreviousConcurrence) SPEB PADO PBD0 BWD0 RIB RIB RIB *RBernero
*KKniel *HThompson *FMiraglia
*JRead/rr *LSoffer *ZRoszteczy 9/ /86 9/ /86 9/ /86 9/ /86 9/ /86 9/ /86 9/ /86 Il
*DSRO BSheron
*DSRO TSpeis N
Timer l h /WS
. nthn .0G(hields 9/ /86 9/ /86 / g /86 [1/ /86 ( 11//1 /86 7
% n, p.4)._
.s LdCP s
NUREG 0800 (Form:rly NUREG 75/087) 90 nc
/, s[\ U.S. NUCLEAR REGULATORY COMMISSION STANDARD REVIEW PLAN
!R,$>f)
% OFFICE OF NUCLEAR REACTOR REGULATION
...e.
h o p: A 9-wit e t 2. % 6.5.2 CONTAINMENT SPRAY AS A FISSION PRODUCT CLEANUP SYSTEM REVIEW RESPONSIBILITIES Primary - Accident Evchatica "ranch (AES)- P\odi b dtM bCMeh Secondary . Chemical-Engineering-Branch-(CHEB) W W h I. AREAS OF REVIEW 3 a';L Yi g 974c\yL gew The-AEB reviews the containment spray and, spray additive systemgto datermine the
-{e fisfjor) product removal ef fectiveness of the system whenever the applicant claims 4
9 al ontaindnt aTrycleanup function for the system. The following areas of the y applicant's Safety Arialysis Report (SAR) relating to the fission product removal y and control functio'i of the containment spray system are reviewed,b, the ^.ES:
.z
- 1. Fission Product Removal Requirement for Containment Spray Sections of the SAR related to accident analyses, dose calculations, and fis-sion product removal and control are reviewed to establish whether fission
( product scrubbing of the containmerit atmosphere for the mitigation of offsite doses following a postulated accident is claimed by the applicant. This review usually covers Sections 6.2.3.1,,6.5.2.1, and Chapter 15 of the SAR. Design Bases M 2. The design bases of such containment spray systems are reviewed to determine whether they reflect the requirements placed upon this system by the assump-tions made in the accident evaluations of Chapter 15.
- 3. System Design The descriptive information concerning the design of the spray system, including any subsystems and supporting systems, is reviewed to familiarize the reviewer with the design and operation of the system. The review includes:
Rev. 1 - July 1981 USNRC STANDARD REVIEW PLAN star dard review plans are prepared f or the guidanceThese of the of fice ofare documents Nuclear Reactor toRegulation made aweitable staf the public as partf of responsible the for 13e appbcat.ons to construct and operate nuclear power plants Commission's policy to inf orm the nuclear indwatry and the general pubhc of regulatory pecteedures and ocScies. Standa plans are not swbstitutes for regulatory guides or the Commission's regulations and comphance with them is not requ standard review plan sektions are heted to the standard Format and Content of safety Analysis Repcerto for Nuclear Power P Not att sections of the Standard Format have a torresponding review plan. Pubbshed standard review plans Wil be revised periodiceny es appropriate. to accommodate comments and to reflect new inform tion and emperience. Comments and suggestions for improvement wist be considered and should be sent to the U s. Nuclear Regwistory Co Office of Nwcio,ar Reecto, Regulation. Washington, O C. 20555
m :,Y .;
- a. Thr. descriptive informationscontained in SAR Sections 6.2, 6.5.2.2, 6.5.2.4, 6.5.2.5, and 6.5.2.6 to establish the basic design concept, the systems, subsystems, and support systems required to carry out
. pcg*K theJe44ee scrubbing function of the system, and thn components and (
g" inst'rumentation employed in these systems.
- b. The process and instrumentation diagrams of SAR Section 6.5.2 or 6.2.2, whichever contains the relevant information.
- c. Layout drawings (plans, elevations, isometrics tion headers, from SAR Chapter 1.0 and Section/)
6.5.2 or 6.2.2.of the spray dist
- d. Plan views and elevations of the containment layout in Chapter 1.0 of the SAR.
- e. o recess-and instr = ntat4on-diagr4*s-of-any-vent 44ation-systems-oper4-
-44+aal--i n -the-po s tac c i den t-e n v &oenmee t , 3
.pj-
- 4. Testing and Inspections A 4-Section 6.5.2.4 of the SAN is reviewed to establish the details of the 5 preoperational test to be performed for system verification and the post- f operational tests and inspections to be performed for verification of the
- continued status of readiness of the spray system. U
- 5. Technical Specifications k g
At the operating license stage, the applicant's proposed technical speci- g ficat 6 s in Chapter 16 of the Final Safety Analysis Report (FSAR) are reviewed to establish permissible outage times and surveillance 4-( requirements. 40 A =andarysview.is-performed by--the-Chemice4-Eng4eecring Sr n:h (C"ES) :nd -- the--results are + sed ty-the-AEB to complete the overall review-of-thea:ontain- e mant.-spray systm CMEB-revie ~ m + -4ce' edditive :ter:;:-requir r:nts. j
.and-area s-as-.4adicated-below. The r+svit ef CMES's-analys4: :r: tr:n:-itted.
- te AEB fer use '- th: SED -4 t e up. -6 y aMvu y
In addition, 4t9-will coordinate other br:n:h:s evaluations that interface with g the review o,f the containment spray system as follows: materials compatibility and organic material decomposition including formationC"ES r:vi:= of organic iodide as part of its-pr4sary-rw4ew-re:p n ibi'ity fer SRP Sections 6.1.1 and 6.1.2... The-Containment 4ystems-Branch (CBS) revi = the heat removal and hydrogen' mixing function of the containment spra the containment sump design as part of its pr ary revice re:p:n;y ibilityJee i system and SRP Sections 6.2.2 and 6.2.5. The acceptance criteria for the revjew and the methods cf application are contained in the referenced SRP sectionh f th: eneraeneding prie:ry bran b as-stated dov . 4 II. ACCEPTANCE CRITERIA l l The AE0 acce' p tance criteria are based on meeting the relevant requirements of l the following regulations: l k 6.5.2-2 Rev. 1 - July 1981 I l .
9
.g F- ,
A. General Design Criterion 41 (Ref.1) as related to the containment atmos- g$ phere cleanup system being designed to control fission product releases - 7 to the environment following postulated accidents. - B. General Design Criterion 42 (Ref. 2) as related to the containment g '. atmosphere cleanup system being designed to permit appropriate j periodic inspections. D, C. General Design Criterion 43 (Ref. 3) as related to the containment atmos-phere cleanup system being designed for appropriate periodic functional testing, Qf gj Specific criteria necessary to meet the relevant requirements of GDC 41, 42,
'Fy M and 43 are: FT fintedfoN $g .3'.
- 1. Design Requirements for,? df e Removal 5 t!:-
The containment spray system should be designed in accordance with the ANSI requirements of Reference 4 As used da this SDD $3gtjgg, tk; t$.3 ( )' < "ccateinsent spray system"-includes-the 4 pray-sy:t:: Or.d thq aray-ede stremas ferMj TO[ 1!ve subsyster :: defined in Referene: A. cntcept MT 5f tog odd dN< of oN r PNccnh\qsb d %g yc{creetc, gece( wetyc ft,Jtwd , j f 1*
- a. System Operation 6 5h The containment spray system should be designed to be initiated auto-matically by an appropriate accident signal and to be transferred
%y g g automatically from the injection mode to the recirculation mode to r e 4 assure continuous operation until the design objectives of the system
- i i have been achieved. In all cases the operatino period should not be 4.fQ .6 less than 2 hours. V~h-+ddH4cnHhe-+5Mem sh;uld be-espeble of
_S " 'P
- operation in-the-recirculation-06 ode, Or d
- ::nd, f r : p:ried-o f-et-least 1 enth fe!!cH ng the p::t h t:d ::cid:nt, $j v
- b. Coverage of Containment Volume
< F#
ggg - In order to assure full spray coverage of the containment volume, the following should be observed: 1(R
-t t a ~
(1) The' spray nozzles should be located as high in the containment 3% as practicable to maximize the spray drop fall distance. (2) The layout of the spray nozzles and distribution headers should be such that the cross-sectional area of the containment covered by the spray is maximized and that a nearly homogeneous distribu-tion of spray in the containment volume is produced. Unsprayed regions in the upper containment and, in particular, an unsprayed annulus adjacent to the containment liner should be avoided wherever possible. (3) In designing the layout of the spray nozzle positions and orien-tations, the effect of the postaccident atmosphere should be considered, including the effects of postaccident conditions that result in the maximum possible atmosphere density. ( - Rev. 1 - July 1981 6.5.2-3
- c. Promotion of Containment Mixing Because the effectiveness of the containment spray system depends on (
a well-mixed containment atmosphere, all design features enhancing postaccident mixing should be considered. -Where-sece%% y , f orced-
-O'- t41stion -should-be-provided-to-evoid stagnant -air- cg!ow,
- d. Spray Nozzles The nozzles used in the containment spray system should be of a design that minimizes the possibility of clogging while producing drop sizes effective for iodine absorption. The nozzles should not have They internal moving parts such as swirl vanes, turbulence promoters, etc.
should not have orifices or internal restrictions which would narrow the flow passage to less than 1/4-inch diameter. h *a ' ' " ' " ' ^ " " + 4 '"' Mee--d rop a i r c d i ; t r i b u t i o n f o r t h e no z z i c , ;uch-a s--4-histogram u ,
-shemlJ Le r v,i &J. Desig,stioni su a 52 "ovciagu," "aesnr -and
"- A n" , m-X ; L .,ct prow;cc ;uf ficientij cctsiicd iMemet4on-to mit s; i tc pc tc -t cv0h ticr o f - tt pcekeence-of-t.he nozzle.
- e. ' 9 : tie- Spray Solution The partition of iodine between liquid and gas phases is enhanced by 6 the alkalinity of the solution. The spray system should be designed in such that the spray solution ralat, alas the highe<+ porribla pH, material compatibility constraints, e e 9"i rn~ e 4e ot 4 e M ad by a-spray pH -in the range of -8,5-to-10i E. -A-*iMaum-partitioning of i dke e between-44 quid-and-9as-phase; hn ake bccr demonstrated (
for beric :cid-solutions-with-teeee-%els-of impwf44es-(Refr-G). Jn. thi s -4464 r-pH -requireme nt s a re-4etermined-sole 4y. by -2 te-! al compatibility-constraints ,--which are reviewe d by C":0. Iodine scrubbing credit is given for spray solutions whose chemistry, including any additives, has been demonstrated to be effective for iodine absorption and retention under postaccident conditions. -Be%-
. theoretical-end experimental-+ee444 eat 4on-ere--requir+d.
spray solutions shown in Table 6.5.2-1 have been shown to be ef ve for removal of elemental iodine. Acceptable, values hese f the i ntaneous elemental iodine partition coefficient for 6 provides spray solu ns are also shown in Table 6.5.2-1. Refere information o ray solutions that are effective for emoval of organic iodides, s Spray Solution 4n cceptable Table 6.5. artition C ficients Spray solution ,artition coefficient see cure 6.5.2-1; ph values' sodium hydroxide in boric ' are ass ed at room temperature acid sclution hydrazine (50 ppm 2 8 5000 I ppm boron) boric acid (15J0 2500 50 t
*ater (pl in or demineralized) 100 N \
see Figure 6.5.2-1; same pH x
.,s ~ LPis ium phosphate (added to dependence as sodium hydroxideN JM'p during recirculation mode) solutions 6.5.2-4 Rev.1 - July 1981 9; ,
- f. Containment Sump Mixing The containment sump should be designed to promote mixing of emergency core cooling system (ECCS) and spray solutions. Drains to the engineered safety features (ESF) sump should be provided for all regions of the containment which would collect a significant quantity of the spray solution. Alternatively, allowance should be made for "dead" volumes in the determination of sump pH and the quantities of additives injected.
- g. Containment Sump and Recirculation Spray Solutions The pH of the aqueous solution collected in the containment sump after completion of injection of containment spray and ECCS water, and all '
additives for reactivity cor. trol, fission product removal, or other purpose, should be maintained at a level sufficiently high to provide assurance that significant long-term iodine re-evolution does not occur. Long-term iodine retention is calculated based on the expected long-term partition coefficient. Ite- imtantaneou s - iodi ne- pa rt444ea.
.coef ficients given in Table 6.5.-2-1 and figure LS,M-say-be wsed
.in the-absence of. suitable data f or equilibrium--$edine-pa4414en-cre"!cieno Long-term iodine retention with n: ;ignificent ee-eve'"tica may be assumed only when the equilibrium sump pH, after mixing and dilution with the primary coolant and ECCS injection, is Sgek 5 ,,,above 44. This pH value should be achieved at the onset of the spray
/ recir:ulation mode. The material compatibility aspect of the long-term sump and r,ecirculation spray solutions is reviewed by t'? C"E".udre e W 5 C c~em G . l. !.
- h. Storage of Additives The design should provide facilities for the long-term storage of h g' sL1. spray additives. These facilities should be designed such that the additives required to achieve the design objectives of the system are stored in a state of continual readiness whenever the reactor is critical during the design life of the plant. The storage facilities b iceJt 8 # t h i freezing, precipitation, chemical reaction,
~~~~sho0ldoedesigne%;Ddditives,4r and decomposition of prevented. For NaOH storage tanks, heat tracing of tanks and piping is required whenever exposure to temperatures below 40'F is predicted. An inert cover gas should be provideu for solutions that may deteriorate as a consequence of expo-sure to air,
- i. Sinole Failure The system should be able to function effectively and meet all the above criteria with a single failure of an active component in the spray system, in any of its subsystems, or in any of its support systems. S: ;y;ter is :=;idered f,.n ti=1 ith re; pct te ;; dine removel i f it i 5 spsble of-delivering-the-det4gn-+psy fi; rett with tM 2dditive<encentration within-the-acceptable-cange 45 deter-
' f
"-"e.
- 2. Testing Tests should be performed to demonstrate that the spray systems, a v k installed *,meetalldesignrequirementsforaneffectiveiodinegerubbing function. Such tests should include preoperational verification of:
6.5.2 5 Rev. 1 - July 1981 e
- a. .
- k c e p.v, s 1, -
4c tcw.y .f .c:. %yn
. pt3v .T ,v : rs '; L't.4
' C ('< . C .' ( t ') h $ r ,? E .N.C ,1*,' g w h , h g Sp( *#. CJskY.\ cLC Ecb ci# n : . 055tm t'id6 No up mcJc'gl
- a. freed'om of the containment spray piping and nozzles from obstructions,
- b. capability of the system to deliver the required spray flow, and
- c. of the system to deliverfddb required spray additiver,*44Me capability!:d th: :ft:i r:^g: Of c = :nte:ti = . For a system whose performance is sensitive to the as-built piping layout, such as a gravity feed system, the testing should be performed at foil flow.
- 3. Technical Spacifications A The technical specification should specify appropriate limiting conditions for operation (LCOs), tes , and inspections to provide assurance that the system is capable of ts design function whenever the reactor is criti-cal. These specifications should include:
- a. The operability requirements for the system, including all active and passive devices, as a limiting condition for operation (with acceptableoutagetimes). The following should be specifically included:
- containment spray pumps.
- additive pumps (if any),
- additive mixing devices (if any),
- valves and nozzles, oM (
- additive quantity and concentration in p additive storage tanks, and A
- nitrogen or other inert gas pressure in '64-additive storage i tanks.
Periodic inssection and sampling of the contents of additive tanks b.
'k to confirm t1at the additive quantity and concentrations are within the limits established by the system design,
- c. Periodic testing and exercising of the active components of the system and verification that essential piping and passive devices are free of obstructions.
4r III. REVIEk' PROCEDURES The reviewer selects and emphasizes aspects covered by this SRP section as appropriate for a particular plant. Thejudgmentofwhichareasneedtobegiven attention and emphasis in the review is based on a determination that the material presented is similar to that recently reviewedThe on other reviewplants of theorfission that items product of special safety significance are involved. removal function of the containment spray system follows the procedure outlined below. The reviewer determines whether the containment spray system is used for fission ( praduct removal purposes. Chapter 15 of the SAR should be reviewed to establish whether a fission product removal function for the containment spray system is If the containment spray system is not assumed in accident dose evaluations. 6.5.2-6 Rev.1 - July 1981
n.
. ( '9
- by t% AED used for dose mitigation purposes, no further review is required,the-containment The CSB reviews-the heat -removal %nd hydroger, aning-aspect 4-of-Apray-system.
Tf'the-contai,nment spray system is designed to reduce the concentrations of fission produitT1n-the ranlainment, the capability of_the system'to function ef fectively as a fission product terozal s stee-t5 reviewed. If, as a result of the review, system modifications'are requ red -the_AE8 i reviewer will advise the CSB of the . required ^ modifications f or integration with any-other requirements
,p,lar.ad-en th~e', containment spray system.
This is a coordinating revfe7hmo%
- 1. System Design Review of the system design includes an examination of the components and j
design features necessary to carry out thefed4ae scrubbing function, including: g, gg
- a. Spray Chemistry The forms of iodine for which spray removal credit is claimed in the i
accident analyses (SAR Chapter 15) are established. Containment spray systems may be designed for removal of iodine in the elemental form ndJntheparticulate i j (i.e. vapor), in the form form. 4 09 rcW Wo'. mdd 45 c of org(anic At , - compounds e (rs.thede t%-x pr.,.% t 5
< am u%'d h,. < m addt scrubbing The systems or subsystems required to carry out the, function of the containment spray, such as the spray system, recircu-l lation system, spray additive system, and water source are identified.
The design of the systems involved is reviewed in order to: effectiveness (1) -of-4be-a444Mve Determine h chemical additive and 4e ascertain for elemental and organic fodine removal, by. comparison -with-additives of proven-effec 44*:n::: (:::-4cc+ptenc+ criteri: " zuhe<tien !!) er by revica ef-thecett4 cal- Ord ::p:ri-l i montal verif.ications-supplied !er & Mdftive . (2) Ascertain that the range of additive concentrations is within the limits listed in the acceptance criteria of subsection II I above or that adequate justification is supplied for the iodine removal and retention effectiveness for the range of concentra-tions encountered. The concentrations in the storage facility, ! the chemical addition lines, the spray solution injection, the J containment sump solution, and the recirculation spray solution
! should be examined. The extremes of the additive concentrations should be determined with the most adverse combination of ECCS, spray, and additive pumps (if any) assumed to be operating, and 1
a single active failure of pumps or valves should be considered. The AEB reviewer coordinates this-review aspect with the CHEB 1 wMcA4eviews--the-storage-ef 15: :pr:y :dditiv:: rir :theea J I vedds The AEG reviewer eeexAts+4th the CNEE-4o--vudfy that the spray and ] i sump water solution stability, and the corrosion, solidification, and precipitation behavior of the chemical additives, have appropriately j besn taken into consideration for the range of concentrations encountered. 1
- 6.5.2-7 Rev. 1 - July 1981 h
c
- b. System Operation The time and method of system initiation, including additive addition, is reviewed to confirm that the acceptance criteria of sut section 11 above are met. Automatic initiation of spray and :pra, edditia flow; without mechanical delays or manual overrides, is required. Credit for immediate initiation is assumed if the system can be shown, by test, to deliver the spray solution through the nozzles within 90 seconds, post-LOCA. For those systems where the spray solution M (m is delivered after 90 seconds, post-LOCA, credit for spray removal M fl!M ine will be assumed to commence upon the time of actual flow n through the no221es. The system operation should be continuous until din removal objectives of the system are met. If a switchover b [ h M Wduring :hethis from t injection to a recirculation mode of operation is time period, the reviewer should confirm that all require-ments listed in the acceptance criteria, particularly those concerning spray coverage and solution pH, are met during the recirculation phase.
Manual switchover from the injection mode to the recirculation mode during the first 2 hours following the initiation of the spray system operation is not acceptable,
- c. Spray Distribution and Containment Mixing The number and layout of the spray headers used to distribute the spray flow in the containment are reviewed. The reviewer verifies
- that the layout of the headers assures coverage of essentially the d citedC entirecross-sectionofthecontainmentwithspray,undeninimum_f spray flow conditions. The effect of the conditions in the containment on the spray droplet {nigh tempW at'ure trajectories and pressure should ,
be taken into account in determining the area covered by the spray. 6 . The layout of the containment,: H f:r::d ;:ntil:t!:r g:t:r: (: m ey-grade) operating af ter the40 Chem reviewed to determine if any areas of the containment free volume are not sprayed. The mixing rate due to 1 natural convection between the sprayed and unsprayed regions of the
- containment, provided that adequate flow area exists between these [
regions, is assumed to be 2 turnovers of the unsprayed re ; hour,unlessotherratesarejustifiedbytheapplicant;gion(s)per .t i: : assued that f:rced air-untMati:n systs-designed to-operate--in- , t'e perten! dent cr"!rer ent r v: :f r :t 50% of their d::ign f t u
.t retee - The containment may be considered a single, well-mixed volume ,
\T -pr vided the spray covers reg, ions comprising at least 90% of the con-tainment volume and provid:d4 ventilation system is available for r adequate mixing of any unspr'ayed compartments, l l
1
- d. Spray Nozzles The design of the spray nozzles is reviewed to confirm that the spray i
nozzles are not subject to clogging from debris entering the recircu-lation system through the surp screens. l l e. Sump Mixing The mixing of the spray water containing the chemical additive and water without additive (such as spilling ECCS coolant) in the contain- ( ; i ment sump is reviewed. The areas of the containment which are exposed 6.5.2-8 Rev. 1 - July 1981
. , - - --._- --.._,_ _ _.__ _.x_
, s 4
to the spray but are without direct drains to the recirculation sump (sucF as the refueling cavity) are considered. The reviewer confirms 3 that t e required sump concentrations are achieved within the appro- < priate time intervals. The long-term suttp pH should be reviewed in regard to iodine re-evolution, using the criteria given in subsec- l tion II.1.g above. The equilibrium partitioning of iodine between the sump liquid and ( l the containment atmosphere is examined for the extremes :! the additive concentrations determined above, in combination with the range of temperatures possible in the containment atmosphere and the sump solu- : tion. The minimum iodine partition coefficient (H) determined for these conditions forms the basis of the ultimate iodine decontamination i factor in the staff's analysis described below. See Reference & & l f for a(discche: r:ti;:! : n- N t b of iodine partition coefficients, l I f. Storage of Additives < p j The design of4 4 # additive storage tanks is reviewed by C"E9 to estab- t lish whether heat tracing is required to prevent freezing or precipf- t tation in the tanks. The reviewer determines whether an inert cover gas is provided for the tanks to prevent reactions of the additive ; with air, such as the formation of sodium carbonate by the reaction of sodium hydroxide and carbon dioxide. Alternatively, the reviewer verifies by a conservative analysis that an inert cover gas is not ! required. ,
- g. Single failure l
The system schematics are reviewed by inspection, postulating single i l failures of any active component in the system, including inadvertent operation of valves that are not locked open. The review is performed l l j i with respect to the '-din: removal function, considering conditions 4 that could result in oofastaswellastooslowanadditiveinjection, i
- 2. Testing bse Fo'W I
At the construction permit stage, the containment spray concept and the ,
- preposed tests of the system are reviewed to confirm the feasibility of !
verifying the design functions by appropriate testing. At the operating ) license stage, the proposed tests of the system and its components are : - reviewed to verify that the tests will demonstrate that the system, as I i installed, is capable of performing, within the bounds established in the i description and evaluation of the system, all functions essential for effective 4d h removal following postulated accidents. f l t %w 9tsM { t 3
- 3. . Technical Soecifications !
The technical specifications are reviewed to verify that the system, as : i designed, is capable of meeting the design requirements and that it remains
}
J in a state of readiness whenever the reactor is critical.
. l
- a. Limiting Conditions for Operation (LCO) l a r The LCOs should require the operability of the containment spray pumps, ;
l 4 all' associated valves and piping, the spray additive tanks including l , Rev. 1 - July 1981 i I 6.5.2-9 f i b
. o
the appopriate quantity of additives, and any metering pumps or mixing devices.
- b. Tests Preoperational testing of the system, including the additive tanks, pumps (if any), piping, and valves is required, as discussed above.
In particular, the preoperational testing should verify that the system, as installed, is capable of delivering a well mixed solution containing , all additives with concentrations falling within the design margins ! assumed in the dose analyses of Chapter 15 of the SAR. Periodic testing and exercising of all active components should include [ the spray pumps, metering pumps (if any), and valves. Confirmation that passive components, such as all essential spray and spray addi- ' tive_ piping, and any passive mixing devices are free of obstructions ourd'be made pericciU1 1 ) The contents of the spray additive tanks , inculd be sampled and analyzed periodically to verify that the concen-trations are within the established limits, that no concentration i gradients exist. and that no precipitates have formed.
- 4. Evaluation A calcuiation of the 1__!^e Qv pd.* removal ? effectiveness of the system is performed 4
to establish the degree of 444ae dose mitigation by the containment spray I following the postulated accident. The mathematical model used for this calculation reflects the preceding steps of the review. The analysis and assumptions are as follows: gg h g.l 6 g 'r. d t 4.'s F hWO, , i.g u egregnok. . l
- a. The amountsoff ediae assumed to be Thi; released to the containment.46 l 50T Of th: :Or: i din: invent:ry. he; th: :: p::itic, ef-.WR a ;
3 i ._eleme nta l v4. 5% p a r ti c u l a t e , -a nd 2. 0% : r g a r t e . The amountsof beke 611- #Mr; [ airborne inside containment depends upon plate-out on interior contain- , ment surfaces, removal by the spray and action of other engineered j safety features present, radioactive 4 cay, and outleakage from the - containment, t i g g pr e g ; j b. The removal of,1cdina from the containment atmosphere by the spray
- 1 is considered a first-order removal process. The removal coefficients A (lambda) far.4ach.4 ara 4f f ^ dine (i.e. , el: :^te!, pwticulate, l j and e";e^ic) for each of the sprayed regions of the containment is !
computed,by the sethods such-at 'he digita! 00 puter ::6 SP!" l 1 _f Cd " Removal coefficients-representingThe time-dependent c': :-19 coefficients for spray l 4^ dine wall plate-out are also calculated. ! removal and wall plate-out are summed '^r !!:-^^te! fedf =, The removal i lambdasareusedasinputparametersIntoacomputermodelusedfor i I dose calculation. Ir :^^t-art te F-"' Mi ^-rtite , tM cM"' #0"' 4s-salculated de net hav: Or Orbitrary ::ximu 2110u:ble ::!:-a 0 uher nw < n enn<mn,,4nn m4+s+u me,-m+4-- ^ < cnv a r + u t - 4 n u a n t a c,[ 4 n bt_ [ s k , _4 c. h n_ e n _ . j A The maximum :!:::",:1 iodine decontamination factor, DF, for the i i d containment atmosphere achieved by the spray system is determined l
' from the-We equation (Ref. 4): (
l t -> l 4 6.5.2-10 Rev. 1 - July 1981 f i 1 E_. _ . . _ . _ ' _ _ __ __ _ _ __ - _ .____.~_-_,-__.-,_.._,._._.____J
i Fission Product Cleanup Models C. The reviewer estimates the area of the interior surfaces of the coi-i tainment building which could be washed by the spray system, the volume flow rate of the system (assuming single failure), the average f drop fall height and the mass-mean drop diameter of the spray from l inspection of the information submitted in the SAR. The effectiveness of a containment spray system may be estimated by [ consideration of the chemical and physical processes that could occur i during an accident in which the system operated. Models containing such considerations are reviewed on case-by-case bases. In the . absence of detailed models, the following simplifications may be ! used: r All available experiments (Refs. 6 and 7 ) and computer simulations of ( the chemical kinetics involved (Ref 8) show that the most important f
, i l
factor determining the effectiveness of sprays against elemental , ) 1 iodine vapor is the concentration of iodine in the sprayed solution. 4 For fresh sprays having no dissolved iodine. solutions have l l
! approximately equal effectiveness regardless of their pH and chemical i i
i redox potential (Ref 9). Solutions having dissolved iodine, such as recirculated sump solutions following an accident, may revolatiltre I iodine if acidic (Refs 5 and f
- 1. :
1 (
)
1 i I t
- - . - , - - _ - . . ._.,.--,m..,, _ _ _ . _ _ ... . , - _ . _ , _ , , _ _ , _ , _ _ _ _ _ _ _ _, . _ - - _ _ . - - . - - . . _ _ - - - -
10). Any chemical additive in the spray solution has no significant effect upon aerosol removal. 1.' ) Elemental iodine removal during spraying cf fresh solution, i During injection, the removal of elemental iodii;s by wall deposition I ! may be estimated by b ( f\ / V i l Here, kit the first-order spray removal coefficient to be used in the dose assessments in Chapter 15 of the SERs, A is the wetted surface j area, V is the containment volume, and K, is a mass-transfer coefficient. All available experimental data are conservatively enveloped if K,, is taken to be 4.9 meters per hour (Ref Il page 17). ) During injection, the effectiveness of the spray against elemental iodine vapor is chiefly determined by the rate at which fresh I solution surface area is introduced into the containment atmosphere. j The rate of solution surface created per unit gas volume in the ' containment nay be estinated as (6F/VD), where F is the volume flow rate of the spray pump, V is the containment volume, and D is the 4 mass-mean diameter of the spray drops. All experimental data are conservatively enveloped if h, the first-order spray removal coefficient, is taken to be (Ref 12) l j j ( ' y VB [
and if Kg, the gas-phase rass transfer coefficient, is assumed to be 3m/ min. T is the time of fall of the drops, and may be estimated by the ratio of the average fall height to the terminal velocity of the mass-mean drop.
~I to prevent extrapolation beyond
(,istobelimitedto20 hour the existing data for boric acid solutions with a pH of 5 (Ref 6).
- 2. Elemental iodine removal during recirculation of sunp solution.
The sump solution at the end of injection is assumed to contain fission products weshed from the core as well as those removed from the containment atmosphere. The radiation absorbed by the sump solution, if the solution is acidic, would generate hydrogen peroxide in sufficient amount to react with both iodide and iodate ions and raise the possibility of elemental iodine re-evolution (Ref. 5). For sump solutions having pH values less than 7, molecular iodine vapor should be conservatively assumed to evolve into the containment atrosphere. (Ref 10). The reviewer should consider all sources and sinks of acid or base that would occur naturally (e.g., alkaline earth and alkali mettl oxides) or by design (e.g., alkaline salts or lye additives) in a post-accident containment. Any active spray additive system that is not automatic should be reviewed to assure that it is capable of perforring its design function during either spray injection or recirculation or both, given a sinole failure. f [ l l
i-
, i For sequences during which the sprays would begin recirculation of the sump solution prior to releases of fission products into the containment, credit is given from the beginning of the release for any ;
spray additive either dissolved from storage baskets in the sump or added by manual or automatic initiation of an engineeered safety e feature additive system. The spray should be assumed to be free of j dissolved iodine until half of the sump solution volume has been recirculated following the beginning of fission product release, j f The first order removal coefficient for molecular iodine may be { calculated either by a staff contractor computer code such as described in reference 8 or by methods described as the "realistic model" in reference 11.
/L
- 3. Organic iodine l It is conservative to assume that organic iodidesare not !.
removed by either spray or deposition. Radiolytic destruction of iodorethane may be modelled, but such model must also consider { radiolytic production. Engineered safety features designed to remove t I organic iodides are reviewed on a case by case bases. ! l 1 I
- 4. Particulates l
I The first-order removal coefficient for particulates may be estimated i by y?
.. 3h( ~ / rc 'h !
W (tj j i t I
--_ _ l
Here, h is the fall heigFt of the spray drops, F is the spray flew and E/D is the ratio of a dimensionless collection efficiency to the average drop size. Since the removal of particulate material depends markedly upon the relative sizes of the particles and the drops, it is convenient to combine parameters that cannot be known (Ref.11). It is conservative to assume (E/0) to be 10 per meter initially (i.e., li efficiency for 1 m drops), changing abruptly to 1 per reter after the aerosol mass has been depleted by a factor of 50 (i.e., 98'. of the suspended mass is ten times more readily removed than the remaining 21).
OF=1+ H C where: H = equilibrium iodine partition coef ficient(8 te f'45N tt i ', V, = volume of liquid in containment sump and sump over flow , V, = containment net free volume less V, The maximum decontamination factor for plain water, boric acid solutions, sodium hydroxide and hydrazine additive systems is ! 0F = 200. t max p , DF is defined as the4 tai.t.ial " ^'iodine concentration in the containment atmosphere ^h nia^d ~a t'^ re e 'ed e f: 'n:t: ':- n-ty "bmd divided by the concentration of iodine in the containment atmosphere at some later time,af k.,r Stec'JMvNc58;n ' , The effectiveness of the spray in removing elemental iodine shall be
- presumed to end at that time, post-LOCA, when the maximum elemental iodine DF is reached. Because the removal mechanisms are significantly dif ferent (and slower) for organic3 and particulate iodines, there is ;
no need to limit the DF allowed in ,the analysis for these iodine forms. i IV. EVALUATION FINDINGS 9e NG . The staff's evt.luation of the iodine removal effectiveness of the containment . spray systewhould include the following parameters, which are used in the l thyroid dose calc'ulat4cas of a postulated loss-of-coolant Jecident:
- overall first-order removal constaats Jper h'our) for elemental iodine, Ag, f or organic iodine A 2, and f oy. pat'TTuT1ste iodine, A3 , .
the effective y r M me, V (ft3 ), N
- t ximum decontamination f actor for elemental iodine, DF. s l
After the AGS. reviewer determines that the containment spray :-f i r ry "iti"^ system is effective S ': din: - n M , the following can be reported in the staff's safety evaluation report (SER): ! The staff concludes that the containment spray system as a fission : product cleanup system is acceptable and meets the relevant require- i ments of General Design Criterion 41, "Containment Atmosphere Cleanup," j General Design Criterion 42, "Inspection of Containment Atmosphere r Cleanup Systems," and Gentral Design Criterion 43, "Testing of Contain- t ment Atmosphere Cleanup Systems." This conclusion is based on the IO"O*I"9 gp 9,d d d*?"A f' The concept upon which the proposed system is based has been demon-strated to be effective forg i rdi" eher T ima and retention under , postaccident conditions. The proposed system design is an acceptable
?
- 6.5.2-11 Rev. 1 - July 1981
4 application of thiJ concept. The system provides suitable redundancy 1 in Components and features such that its safety function can be accom* plished assuming a single failure. The staff concludes that the system meets the requirements of General Design Criterion 41. The proposed pre-operational tests, post-operational testing and surveillance, and proposed limiting conditions of operation for the Q n I.g. 4 3 spray system provide adequate assurance that the W 4crubbing function of the containment spray system will meet or exceed the effectiveness assumed in the accident evaluation and, therefore,
; meets the requirements of General Design Criteria 42 and 43. ,
2 l V. IMPLEMENTATION
./
a { The following provides guidance to applicants and licensees regarding the staff's ; plans for using this SRP section. ; Except in those cases in which the applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, ! i the method described herein will be used by the staff in its evaluation of i conformance with Commission regulations, i
- 1. REFERENCES
) 1. 10 CFR Part 50, Appendix A, General Design Criterion 41, "Containment '
Atmosphere Cleanup." 1 ! / 2. 10 CFR Part 50, Appendix A, General Design Criterion 42, "Inspection of Containment Atmosphere Cleanup Systems." .
- 3. 10 CFR Part 50. Appendix A, General Design Criterion 43, "Testing of Containment Atmosphere Cleanup Systems."
! 5
- 4. ANSI /ANS Standard 56.5-1979, "PWR and BWR Containment Spray System Design
] Criteria." ! 4 I ! 5. O. L, hid, C. M. Jen;;n, ;nd ^. X. N;t :, "":::rc5 :n 5:wel-+f ! -l+ din by Contatent Spreye Cont *+ning Trece i+veb-+f "ydrezinc," httelle ! he4He-htbest t:.b;retoHes, Anc- 1979, i l 4. * %. N ;t , ", ". Shu rji +*d * ! T- , "?!: M0! ;f 01 " 205 fer "0t!! i -ef-SPsy-Washout-+f-Airb0 rn: C e n t e-P "' ' i ^ ""* i --- * * "^ ' "% " - ! i WURE0/CD-O w .
' 7. L. F. Parsly, "Design Considerations of Reactor Containment Spray Systems -
, Part IV. Calculation of lodine Partition Coefficients " ORNL-TM-2412, i i Part IV, Oak Ridge National Laboratory (1970), l LpmidoNt d ht O CC t[OE N N kcNA 3
- Y Q. t \do cwd OL C'ppbN 'M'b d C#b
! tro9pi bk M YeC54% N 90 5 50 NO b [ i ! (Q G c.pbcoh wil\ 'rc quwe b mg wh % poam" c' ! i
%) rNtSt0A, Rev. 1 - July 1981 6.5.2-12
- 5. R.F. Sellers, A Review of the Radiatio _n Chenistry of lodine Compounds in Aqueous Solution, CEGB-RD/ BIN-4009 Berkeley Nuclear Laboratories.
United Kingdom (June 1977).
- 6. R.K. Hilliard A.K. Postma, J.D. McCormack, L.F. Coleman and C.E. Lunderman, Removal of lodine and Particles From Containment Atmospheres - Containment Systems Experiments, BNWL -1244, ,
Pacific Northwest Laboratories (February 1970). 4..
- 7. S. Barsali, F. Bosalini, F. Fineschi, B. Guerrini, S. Lanza, j,7
~
M. Mazzini and R. Mirandola, Removal et lodi'e by Sprays i_nn the 7 PSICO 10 Model Containmort Vessel, Nuclear Technoincy 23, pages
$ [,
'3 146-156, (August 1974). ,. y S#
=b 1 -
- 8. M.F. Albert The Absorption of Gaseous todine by Water Droplets, P~
NUREG/CR-4081 (July 1985). .4 e 5s 4.tfi 4 A.K. Postme, L.F. Coleman and R.K. Hilliard Iodine Removal from 4 Dt
- 9. *g g. 09 M .-
Containment Atmospheres by Boric Acid Spray, (July 1970).
# 6
'T YI'
- 10. A.O. Allen,TheRadiationChemistryofWat(andAcueousSolutions, [ 17l 3
Van Nostrand, New York (1961), lE . T--
..e. r
- 11. A.K. Postma, R.R. Sherry and P.S. Tam, Technological Bases for [
.g Models of Spray Washout of Airborne Containments in Containment Vessel, NUREG/CR-0009 (October 1978).
M
- 12. R.E. Davis, and M. Khatib-Rahbar, Fission Product Remval Effectiveness af Cha-ieal Additives in PWR Containment Sprays. Technical Report A3788, I ^? "T- 1986).
4 i e
\
\ /
5000 \
\ / i /
/ i / ! :
\,\ .
/ .
I i 1 i , i ; 1000 +
. g __ l /j ,/ l ,
i i \ /! / !
- i \ / !7 !
303 i \ i
/ / l
\ // .
i3 i N //i I ! E i
; I k : I a.
100
,/ f._, ---\
/ / \ l i / /
\
! / / I \
/ \
/ -
\ I 6 7 8 9 10 11 Spray pH Fig. 6.5.2 1 Partition Coefficient vs. Spray pH For Solution Containing Sodium Hycroxide (Ref. 4) 6.5.2-13 Rev. 1 - July 1981
i REGULATORY ANALYSIS OF THE AUTOMATIC 1 ACTUATION OF 3YSTEMS FOR CHEMICAL ADDITIONS TO ; CONTAINMENT SPRAY AND SUMP SOLUTIONS
- i
- 1. Statement of the problem - At most pressurized water reactors having large dry containments, the initiation of containment sprays also initiates the automatic addition of either hydrazine or sodium hydroxide into the boric acid spray solution. In those plants in which sodium hydroxide is added to the spray, three purposes are met: 1)the scrubbing of elemental iodine vapor from the containment atmosphere is enhanced 2) the evolution of dissolved iodine from containment sump is diminished, and 3) the long-term corrosive effects of hot boric acid on equipment are avoided. In those plants in which hydrazine is added L to the spra.v. only the first purpose is met, and the second and third are accomplished by storing a solid alkaline salt, trisodium phosphate, in baskets in the sump to be dissolved by the boric acid sprays. In either case, sufficient alkali or alkaline salt is supplied not only to neutralize the boric acid, but also to render the sump recirculating spray solution slightly alkaline. The resulting solution is similar in both boron concentration and basicity to that resulting from melting the borated ica in plants having ice condenser containments.
Automatic addition of hydrazine or sodium hydroxide is based upen i Regulatory Guide 1.4, "Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss-of-Coolant Accident for Pressurized Water Reactors,' Regulatory Position C.1.a. which states "Twenty-five percent of the equilibrium radioactive iodine inventory developed from maximum full power operation of the core is innediately available for leakare from the primary containment." This position flows from the TID-14844 assurptions referenced as a point of departure in 10CFR100. . As implemented by Standard Review Plan (SRP) Sections 6.5.2 and 15.6.5, ! Appendix A. radiciodine is assumed to begin to escape from the contain- L ment imediately, being diminished only as the sprays reduce the radio-iodine concentration within the containment atmosphere. In many l instances, the off-site thyroid doses calculated using SRP guidance are i due predominantly to iodine releases in the first few minutes of the ! accident. It has long been recognized that imediate release of fission products [ cannot occur, and that in any core damaging accident containment sprays ! would be initiated at least several minutes prior to the transport of I radiciodine from the reactor fuel into the containment. l t The sole reason for automatic initiation of spray additives has been to counter very rapid release of large amounts of elemental iodine vapor postulated to be instantaneously released into the containment atmosphere. ; It is now expected that much sneller cuentities of eierental iodine could j be released, and that these quantities would enter the containment atmosphere at later times during core-damaging accidents. Consequently, L [
1 ,1 the need for autoratic initiation of the edtitives no longer exists. J Furtherrore, ell existirr irforratirr indicatet that for fresh sprey solutions having no dissolvec iodire, the spray removal Hence,capability is the benefits virtually independent of the pH of the solution. The 3 of the additives thenselves are much less then previously supposed. disadvantages of spray additive systers, which include the costs of i ! naintenarce including periodic replacerent of chemicals, and the hazards to personnel and property from accidental spillage or spraying of the additives can no longer be easily justified.
! 2. Consequences The consequences of this change are judged to result in no change in Since research results safety significerce in terms of public risk. referenced in the draft revi capability is virtually independent nf the pH of the solutien, the l effectiveress of the spray in dose ritigation will not be reduced, l
j provided apprcpriate post-eccident pH control of the containmentIn additio surp solution is maintained. J i improved by elimination of hazards to personnel and property from accident 6, spillage or inadvertent spraying of additives and by reduced maintenance. I
- 3. Alterratives - Because of design differences, the preferred alternative will very widely among licensees. Three general alternatives are presented below, each with a discussier. of the dependerce of its
! costs and benefits upon variables of plant features; l No chance - This alternativt would continue the following present a) f dystenefits: The costs of raintenance, testing and purchase of replacement additive are estimated to be between !!0,000 end $100,000 per unit-year. The financial risk of plant damage caused by inadvertent actuation or the use of sprays j during non-core-damaging accidents might be large compared to
$10,000 per year for those plants having sodiun hydroxide spray additive. *:o monetary value is assigned to personnel hazards from
/ l inadvertent initiation, but licenseo concerns over such a situation j
~
are considered significant. Downtireandcleanupcoststhatcogld result from 0.01 inadvertent initiations per reactor year at 10 dollars per clean-up are $10,000/ reactor-year. For those plants at which it is possible to add chemical ! to the spray at any time or at which reutralization by trisodium phosphate stored in sump be kets will occur, i there are no identifiable advantages to this option. l Tor those few plants at which the sodium hydroxide additive l can be injected into the spray only during the early period of containrent spraying, when boric acid is being withdrawn from l the refueling water storage tank, there is en advantage to this alternative ir that the 116elihoot of failure to neutralize the boric acid solution following an accident is essentially evoided, Such 1 although there would be no recuctico in naintenance costs. plants cocid, however, profit by alternative c., below, and are / discussed further under that elternative. l I
3
, For those plant that do not have a containment spray additive ! systen, there is re cost to this alternative.
'l ] b) Delete automatic actuation of spray additive system - For those plants that are capable of adding sodium hydroxide only during 1 initial injection and not during spray solution recirculation, i this alternative would introduce the risk of failure to neutralize the boric acid due to operator error. Such plants would be unlikely to elect this option over c., below, i
; For those plants capable of sodium hydroxide addition during recirculation, there could be small reductions in the costs of
~ , maintenance and testing, and avoidance of the financial risk of
- plant damage caused by inadvertent actuation. There would also i be small licenhirg costs in documenting changes and modifying l technical specifications. No reduction in the benefits of the additives trould occur.
l c) Delete spray additive system - There would be a corplete l elimination of tne costs of maintenance and testing and of the risk of spills and inadvertent actuation. For plants which rely
- upon trisodiun phosphate to neutralize the boric acid sprays, i there would be no reduction in the benefits of acidity control, i while betwetn $10,000 and $100,000 per unit-year would be saved
) in maintenance and testing. If TSP baskets were needed as 4 replacement pil control, the savings would be recticed by abo /t i $5,000 per unit-year and by $50,000 to $100,000 initial expense, ) which are the estimated rif costs of periodic chemical renewal and sump basket installation, respectively. All plants could have small licensing cests. NRC costs for review of submittals
- supporting systen deletion are estimated at about one person-month i per plant, about $10,000.
I
- 4. Information Collection Fequirements
! Table 1 lists ell licensees and applicants having pressurized water j reactors, and identifies those plants also having automatic injection i of hydrazine or Sofium hydroxide into their contairrent sprays. Plants having automatic addition of those chemicals would be informed of the
- revised staff position, and could consider either replacing auto-
, tratic addition with an acceptable procedure to assure proper manual i actuation, or eliminating the additive syster. 4 I ho duplicatiers with other collections of information are foreseen, j and no consultations with other parties are considered necessary. l S. Impets on Other Reouirerents i j This proposal is not intended to displace any safety related backfits j or plant modifications needed to improve safety. l 6. Constraints l There are no icertifiable constraints to implementation, except those plant specific constraints discussed under each alternative. } i }
f 4
- 7. Otcision Ratienale As di)cusseo in Sectiers 1 and 2, above, thert ere bases for expecting that pressurized water reacters having automatically actuated containment spray additivt systens will demonstrate that these systems may be modified to provide either improveo safety function or equivalent safety function at less ccst. This proposal will permit affected licensees to investigate the possibility of rodifications to achieve improvements or savings and to submit proposals for irplementation where they are found to be ,
advantageous. l S. Irplementation Changes in the Standard Review Plan are presented in draft form in Attach. ; j ) ment A. This proposal is one of a series flowing from source term research ! results. This series of regulatory revisions was identified in a Commission l Infornation Paper, SECY 86-76, along with a schedule for further imple. rentations. , 1 ) i 1 J , i i 1
TABLE 1 CONTAIISOT SPRAY ADDITIVE SYSTUES A001TIVE ADOITION ! PLANT AD0!TivE PH CONTROL INITIATE SIGNAL DURINE RECIRDULATION
- Arkansas 1/2 NaOH NaOH High Pressere No i
j Seaver Valley'l Na0H h0H High Pressure No . . Seaver Valley 2 MaOH h0H High Pressure Yes Braidmood 1/2 LOH 40H High Pressure No Byron 1/2 NaOH h0H High Pressure , No Callaway I h0H MaOH High Pressure Yes 1 t . Calvert C1,1ffs 1/2 Mone TSP - Yes j Cat % 1/2 Na247 8 0 in Ice 247 N59 High Pressure - Yes f 1 Cessar NH TSP High Pressure Yes 24 ) 1 Comanche Peak 1/2 h03 h0H High P. essure Yes a D. C. Cook I h0;1 TaOH High Pressure Yes D. C. Cook 2 C' N# 82 4 7 '"
" ** ~
Na2 8M 7 1" 1 Crystal River LOH Na0W High Pressure No l 1 Nane TSP - Yes i Davis-Ber..? 1 Diablo Canyon 1/2 NaOH h0H High Pressure No P Farley 1/2 00H MaOH High Pressure No j. Ft. Calhoun Eone None -
.l R. E. Ginna N2tl NaOH High Pressure Yes None - No Haddam Neck None a s !
-_ . _ - _ _ _ _ _ _ a
. .. ' ADDITIVE ADDITION PLANT ADDITIVE PH CONTROL INITIATE SIGNAL DURING RECIRCULATIDN-Harris 1 NaOH NaOH High Pressure No Indian Point 2/3 NaOH NaOH High Pressure No Kewaunee NaOH NaOH liigh Pressure No Maine Yankee NaOH Na0ti Illgh Pressure No , ,
McGuire 1/2 Na247 B 0 in Ice Na 0 0 247 liigh Pressure Yes Millstone 2 None TSP - - 1 Hillstone 3 Na0;l Na0H liigh Pressure No North Anna 1/2 NaOH NaOH liigh Pressure ! No Oconee 1/2/3 None None - No Palisades None None - Palo Verde 1 N ii TSP High Pressure Yes 24
. air.t Cett's 1/2 Na0H NaOH High Pressure No
?n!rie Island 1/2 NaOH Na0ll High' Pressure No
. f.4ncho Seco 1 NaOH NaOH liigh Pressure Yes ,
r,ESAR SP/90 _!!one fione - - Robinson 2 - Na0li naOH liigh Pressure tio St. Lucie 1 Na0:s Na0ff High Pressure. Yes Safety Injection St. Lucie 2 N II TSP !!igh Pressure. Yes 24 Safety injection Salem 1/2 NaOH NaOH liigh Pressure No San Onofre 1/2/3 NaOH NaC:l High Pressure Yes a
ADDITIVE ADDITION '- PLANT ADDITIVE PH CONTROL; INITIATE S_IGNAL DUEING RECIRCULATION ' Seabrook 1/2 NaOH Na0h High Pressure No Sequoyah 1/2 Na 0 0 in Ice Na247 B0 247 High Pressure Yes South Text. 1/2 NaOH NaOH High Pressure No Summer NaOH NaOH High Pressure No . . Surry 1/2 NaOH NaOH High Pressure No TMI 1/2 NaOH ?"0H High Pressure No Trojan Na0ll Jeld High Pressure , Yes Turkey Point 3/4 None None - Ho
~
Vogtle 1/2 ~ NaOH HaOH High Pressure No Waterford 3 None TSP - - - Watts Bar 1/2 Na B 0 in Ice 247 Nap47 B0 liigh Pressure Yes Wolf Creek Na0H Na0li liigh Pressure Yes Yankee Rowe NO SPRAYS Zion 1/2 Na011 Na0li liigh Pressure No - h
- M _t
- 4 ' - " N
'(( i Containment Spray _s In the event of a loss of coolant accident, many PWRs are equipped with 1 pray Since the systems to condense steam from their containment atmospheres. sprayed liquid ': auld necessarily mix with any spilled reactor coolant and might be later recirculated into the reactor, the liquid used must contain a neutron absorbing solute, in all U.S. PWRs, the spray alution is the I This refueling water normally stored in tankage between refueling outages. l solution is about 0.2 M (M= molar, or moles per liter) in boric acid torthoboric acid, H 3B03 )* l Boric acid is i reak acid, meaning that it is only partially dissociated in aqueous solution. This dissociation can be written as: f M3 60 3 F W & QO 3 (1) 10 M at 20'C, such The equilibrium constant for this dissociation is 5.3 x 10 At that a 0.2 M solution has a pH of 5. The pH of pure water is 7.0 at 25'C. j higher temperatures greater fractions of both water and boric acid will dissociate. At 90'C, for example, pure water has a pH of 6.1, rather than 7. The dielectric coastant of water diminishes with increasing temperature, how-As ever, which acts to counter the tendency of increase solute dissociation. a result of these conflicting temperature variations, the pH of 0.2 M boric acid nas a minimum at 77'C of about / ,9. (see, e.g., R.W. Gurney Ionic Processes in Solutions, McGraw Hill, 1953) i
-,,-- ..,,-. ~_. _ _ - _ _ _ _ _ _ _ , . , - _ - - . , _ ,. ,. , - . - - , -
?
To prevent corrosion of retals other than stainless steel that might be exp3 sed to containment sprays, it is usual for some basic material to be stored for dissolution into the sprayed soluticr. to neutralize the boric acid. The two bases used for this purpose are trisodium phosphate TSP is a powder (TSP, Na PO 12H p 0) and sodium hydroxide (lye, NaOH). 3 4 similar to dishwater. detergent in consistency and solubility, and lye is stored as a 30% solution by weight. As purchased, TSP contains some impurities which lead to "caking" in humid atmospheres. Lye solution
'eacts with atmospheric carbon dioxide to form a sodium carbonate precipitate and must be stored in tanks with nitrogen-filled ullage. .
1 In a typical PWR containment spray system, the spray and the ECCS share the Plants refueling water, and can drain this supply in 20 to 45 minutes. using TSP keep it stored in open baskets in the containment sump where it Plants using lye are more diverse. may be dissolved by the falling spray. Some can. add the lye solution into the spray both during the initial draw-down of the refueling water storage tank and during the recirculation of the solution from the sump back into the sprey system. Other plants can only I mix lye with refueling water and cannot add it during recirculation. 4 Other processes that may be expected in a containment following an accident can also affect the pH of sump and spray solutions. Chief of these would be the dissolution of pretransition element oxides and hydroxides in these solutions. Examples would be the rubidium, cesium, strontium and borium fission products, and calciun, sodium and potassiun from concrete which
3 would be volatilized as strong or moderately strong bases. Of lesser importance would be the effects of carbon dioxide from concrete ablation and nitrogen oxides from air radiolysis. W eh would produce smaller potential A trivial effect would be the acid generated by iodine amounts of acids. hydrolysis and oxidation. For example, the acid produced by the air oxidation of iodine tc the thermodynamically preferred iodate, if all the core inventory were involved, would be less than 0.1% of the equivalence of the boric acid. 50g *1(+ %D.3 0 C 't 10 tT[ Overall, these other proechses are estimated to produce a neutralizing effect upon the boric acid, generally supplying more base than acid. In addition to preventing corrosion, the boric acid is neutralized to enhance the dissolution into the spray solution of any todine-containing vapors dispersed into the conteinment atmosphere. Although reaction (2), above, is favored in overall equilitrium, it is very slow in occurring and could taken i In addition, radiolytic processes due to many hours to approach equilibrium. tho effects of ionizing radiation on the sump and spray solution are capable of producing iodine-containing gases that might evolve into the containment atmosphere. Chief amongst these radiolytic processes it the production of hydrogen peroxide (H 22 0 ) by water irradiation in the presence of air. i .
b 4 Although it was conservatively essumed in Reg. Guides 1.3 and 1.4 that fission product iodine would be released as molecular iodine vapor (12 )' other processes that would be expected to occur within a containment after an accident would limit the occurrence of 12 . Any accident that might release iodine into the containment atmosphere would necessarily also release noble gas tission products. These Krypton and Xenon isotopes, 8 amounting to as much as 7 x 10 C1, transmute to rubidium and cesium isotopes, respectively, upon decay. For the release of the core inventory I4 such of noble gases into a large PWR containment, there would be 8 x 10 decays per cubic meter per second occurring in the early hours of the accident. Eacn alkali metal atom produced in the containment atmosphere would recoil from the decay as a highly charged cation,'and as a result of the action of its electric field upon the dipoles of water molecules present as vapor, would create a small, highly bas:0 aerosol particle. This process would neavily deplete any molecular iodine vapor also present. Any core-damaging accident would be likely to release hydrogen gas as well as iodine. The reaction between molecular iodine and hydrogen, while less ex'oergic than that between oxygen and hydrogen, proceeds rapidly without the necessity of a large activation energy (ignition). m
-t g @ 1HI
, 5 The product, hydrogen iodide (hydrofodiacid, HI) is easily oxidized by air to reforn iodine 01 + 9 HI @ Ako+1R g) The net result is the catalytic oxidation of hydrogen. Note, however, that - any molecular iodine present would spend some fraction of its time as hydrogen iodide, subject to ready solution or other depletion. Hydrogen iodide is a very strong acid, being virtually totally dissociated in aqueous solution. Molecular iodine is a comparatively unlikely substance to be made in fluids in which iodine is in low concentration. This is because the formation of I must necessarily involve the collision between two moieties each containing p a single lodine atom. If iodine atoms are very rare, then it is more likely that they will react with other components of the mixhre prior to undergoing a rare collision amongst themselves. This may be seen in the experimental results of spray t.xperiments at vai ring iodine concentrations in Y. Nishyawa, S. Oshima and T. Maekawa, "RemovM of lodine from Atmosphere by Sprays," Nuclear Technology 10_, pp 486 ?3, April 1971. These results show that as the iodine concentration 9 jecreased, both the rate of molecular iodine dissolution and the fract Nn dissolved increased markedly.
6 As an example, consider the iodine hydrolysis reaction discussed in J.T. Bell, M.H. Lietyke.and D.A. Palmer, "Predicted Rates of Formation of lodine Hydrolysis Species at pH Levels, Concentrations and Temperatures Anticipated in LWR Accidents," NUREG/CR-2900, October 1982.
~
I 3 +R gO C I + [ + HOI (5) This reaction is, in effect, first order in 1 , 2since the concentration of water in aqueous solutions is virtually unchanged by the reaction proceeding to the right. The reverse reaction is first order in hydrogen ion, but It is apparent that unless depends upon the product of two iodine species. the total of all iodine species concentrations is large compared to the nydrogen ion concentration, the net hydrolysis rate will depend core markedly upon the local iodine concentrations than upon the pH. Of much greater importance to the chemistry of iodine in a post accident The environment is the potential for reaction with radiolysis products. radiolysis of water has been described by the ecuation.
" ~
(6) 4.9 (0 -+ L3e + L3 OB + 1,9[, o.-}0H + o.95H +. . t 0.15 (0 + t 0.6 H second, i.e., the in equation 6, the coefficients are "G-values" at 10 molecules destroyed or created pte 100 electron volts of deposited ionization {- -
7 energy. The G-values decrease markedly with time after a pulse of ionizing radiation as the short-lived species on the right-hand side of equation 6 6 In a radiation field of 10 Rads / hour, reunite to form water molecules and heat. equation 6 estimates that 2 x 10~7 moles per liter per second of hydrogen peroxide are Poduced by water radiolysis. The British CEGB has produced a critical review of the literature in R.M. Sellers, "A Review of the Radiation Chemistry of Iodine Compounds in Aqueous Solution," RD/B/N4009, June,1977. The avalleble literature shows that molecular iodine production in iodide solutions under radiation is quite small unless either the pH is less than about 4 or the concentration of iodide is much larger than 10-3 M. E.C. Beahm, W.E. Shockley and 0.L. Culberson "Organic lodide Fonnation Following Nuclear Reactor Accidents," NUREG/CR-4327 show that iodomethane production in iodide solutions being sparged by argon-methane gas is similarly In both cases, there is no much greater at pH of 6 or less than at higher pH. firn evidence that more alkaline solutions would greatly 1mprove iodine retention. Iodine is also known to catalyze the decomposition of hydrogen iodide by the net effect of the two following reactions: Rot nBMfe2.H ot +.rz : (7) (o u + It= 2. I + a.H + + o L
6 l These are called the Harcourt-Essen reections. Under acid conditions the first becomes taster such that each iodine atom spends more time as 12 , on the When the hydrogen peroxide average, before reactino by the second equation. is made radiolyticly, however, the effect of pH is less clear cut, due to the likelihood of competing reactions of other species in reaction (6.) as well as trace containments. C.C. Lin, "Chemical Effects of Gama Radiation on Iodine in Aoueous Solutions," Journal of Inorganic _ano Nuclear Chemistry 42, 1101-7, 1980, reports that significant molecular iodine production occurs by radiolysis at pH value below 4, with progressively less occurring at higher pH values. Lin's experiments were performed while the sparging of the solutions with helium, which might be censidered to imitate the evolution of noble gas daughters At values of pH above 8, radio- 1 expected in a post-accident surp solution. I In general, neutral solutions (pH=7) lytic reduction of iodate was observed. l were about as effective as alkaline solutions in retaining iodine in non-volatile forms. S. Barsali et.al., "Removal of looine by Sprays in the PSICO 10 Model Containment Vessel," Nuclear lechnology 23, pp 146-56, August, 1974 reported a series of twelve spray tests using either tap water or 1% sodium thiosulphate solution (Na2235 0 ). They concluded that "the elemental iodine removal half-times obtained by spraying service water do not differ greatly from those The sprayed solution was, in some found by spraying thiosulphate solution. cases, recirculated for a period ranging from 1 to 11 hours without any l 1 i
u 9 Some runs were performed with fractions release of iodine to the etmosphere. of the model containment vessel not sprayed. The elemental iodine renoval half-times in the sprayed and unsprayed regions do not essentially differ." These University of Pisa experiments were at spray solution flow rate to sprayed volume ratios less than those in U.S. PWR containment spray designs. R.E. Davis and M. Khatib-Rahbar, "Fission Product Removal Lttectiveness of Chemical Additives in PWR Containment Sprays," BNL Technical Report A-3788, October,1986, reviewed the literature and concluded that for all cases of interest the rate of iodine removal by sprays during refueling water injection In such was limited by gas transport of iodine to the surface of the drops. cases, the composition of the spray solution itself does not have a great effect upon the rate'of removal unless the solution contains dissolved Should the solution have a significant dissolved molecular elemental iodine. iodine concentration, then its re-evolution could compete with the reverse process of iodine dissolution. Henry's Law (Joseph Henry, 1797-1878) states that the ratio of the l concentration of a substance in a gas phase to that in a liquid phase at equilibrium is a function only of temperature. Henry's Law holds only for true solutions of non-reactive gases, and does not hold for the ratio between indine vapors in the gas phase to the concentration of iodine hydrolysis i products in the liquid phase. The existing SRP 6.5.2 assumes that a "partition coefficient" exists for iodine in equilibrium between air and borate solutions which is a functier, only of the pH of the solution (Figure There is, however3 no experimental evidence that the rate of I i.5.2-1). cissnlution of iodine vapor into borate solutions is chiefly dependent upon pH, and no theoretical reason to suppose that suen might be the case.
10 r In the early years of this century, A. Einstein computed a simple relationship 2 between the mean square displacement of an atom (r ) during time interval t
~
and the diffusivity D of that atom. h # 1DI (8) the diffusivities of molecular iodine and its hydrolysis products in hot 2 Spray drops of about acueous solutions are between 2 andcm 5 x/sec. 10-5 0.1 cm diameter require several seconds to' fall through a typical PWR containment. It follows trom these comparative magnitudes that only the smallest of spray drops are capable of being diffusively mixed during their time of fall. Larger drops could be mixed by other mechanisms than diffusion, as, for example, by convective flows. In addition, due to the greatly different fall velocities of drops of different sizes, the collision and agglomeration among Nonetheless, drops will also lead to mixing, both between and within drops. it is not assured that all spray drops will be a equilibrium or steady state ' with respect to iodine during their fall, even if they do approach thennal equilibrium with steam, t Current models of core melt accidents predict that fission product iodine released into the containment in an accident will be released over a time span of at least tens of minutes, and that there will be a delay between the release In addition, that iodine of steam and that of iodine of at least ten minutes. f which is released is more likely to be in the form of an iodide in aerosol f than as molecular vapor. l
2.1 We conclude that there are no compelling reasons to adjust the pH of containment sprays prior to the recirculation of the sprayed solutions, and that there are likewise ne compelling reasons to adjust recirculated solutions to a pH of much above 7.
I : 0
- 100 6-6 - ' " "' ^ ' ' C "c " "^*
O 10 u so - a 10 " M 8 O .10-* u e , e-1 O g _ s - O' d s
~
~
__ 40 - 20 - O . 1 I O A m
~
I I o 2' 4 a to 12 s, pH Efects of pH on the 1 2yield in deserated iodide solutions irndiated at 4.5 x 10' Rlh for I hr j From C.C.Lin, J. Inorg. Nucl. Chem. 42, 1101-7, 1980 I l
.}}