ML18046B105
| ML18046B105 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/23/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| TASK-09-04, TASK-9-4, TASK-RR LSO5-81-11-054, LSO5-81-11-54, NUDOCS 8111300283 | |
| Download: ML18046B105 (17) | |
Text
.
- e.
UNITED STATES
.e NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket No. 50-255 LS05 11-054 Mr~ David. P. Hoffman Nuclear Licensing Administrator Consumers Power Company 1945 W Parnall Road*
Jack~on, Michigan 49201
Dear Mr. Hoffman:
November 23, 1 981 *
SUBJECT:
SEP TOPIC IX-4, BORON ADDITION SYSTEM (PALISADES)
- Enclosed is a copy of our draft evaluation of Topic IX-4, 11Boron Addition System 11 **for the Palisades pl ant. This assessment compares
- your facility as described in a letter from B. D. Johnson to D. M.
Crui;chfield dated October 9, 1981, Long Term Cooling EquipmentModifi-cation Design Report with the criteria currently used by the regulatory staff for licensing new facilities.
You are requested to examine the facts upon which the staff has based
- ts evaluation and respond either by confirming that the facts are correct, or by identifying*any errors. If in error, please supply corrected information for the docket.
We encourage you to supply for the docket any other material related to.this topic that might affect the staff's evaluation.
This assessment may be revised in the future if your facility design is changed or if the NRC criteria relating to this subject is modified before the integr~ted assessment is completed.
Y6ur response within 30 days of the date you receive this letter is re-quested.
If no response is received within that time, we will assume that you have no comments or c9rrections.
Enclosure:
As stated.
cc w/enclosure:
See next page c;-111 300 ~B-3 Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch No. 6.
Division of-Licensing
~
Mr. David P. Hoffman c~
M. I. Miller, Esquire Isham, Lincoln & Beale Suite 4200 One First National Plaza Chicago, Illinois 60670 Mr. Paul A. Perry, Secretary Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Judd L. Bacon, Esquire Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Myron M. Cherry, Esquire Suite 4501 One IBM Plaza Chicago, Illinois 60611 Ms. Mary P. Sinclair Great Lakes Energy Alliance 5711 Summerset Drive Midland, Michigan 48640 Kalamazoo *Public Library 315 South Rose Street Kalamazoo, Michigan 49006 Township Supervisor Covert Township Route 1, Box 10 Van Buren County, Michigan 49043 Office of the Governor (2)
Room i - Capitol Building Lansing, Michigan 48913
- William J. Scanlon, Esquire 2034 Pauline Boulevard Ann Arbor, Michigan 48103 Palisades Plant ATTN:
Mr.
~obert Montross Plant Manager Covert, Michigan 49043 PALISADES Do6ket No. 50-255 U. s.. En vi ronmenta 1 Protect ion Agency Federal Activities Branch Region V Office
- ATTN:
EIS COORDINATOR 230 South Dearborn Street Chicago, Illinois 60604 Charles Bechhoefer, Esq., Chairman
. Atomic Safety and Licensing Board Panel U. S. Nuclear Regulatory Commission Washington, D. Co 20555 Dr. George C. Anderson Department of Oceanography University of Washington
. Seattle, Washington 98195
. Dr. M. Stanley Li vi ngston
- 1005 Calle Largo Santa Fe, New Mexico 87501 Resident Inspector c/o U. S. NRC Palisades Plant Route 2, P. O. Box 155 Covert, Michigan 49043
I.
nITRODUCTION
- e.
SYSTEMATIC EVAIJJATION PROGRAM BRANCH TOPIC IX -4, DO RON ADDITION GYSTEM PALISADES PIAilT Following a I.OCA, boric acid solution is introduced into the reactor vessel by tWo modes of injection. In the initial injection mode, borated wa.ter is provicied from the refueling wa.ter storage tank. Ai'ter this initial period,- which '!r'.ay la.st
- somewhere between 20 - 6G minutes, the Emergency Core Cooling System (ECCS) is realigned for the recirculation mod~. In this mode borated water is recirculated from the containment sump to the reactor vessel a.nd back to the sump through the b.reak. A portion of the water introduced into the reactor vessel is converted into steam by the decay heat generated in the core.
Since the steam contains virtually
~o impurities, the boric acid content in the water that was vapo~ized remains in the vessel.
The concentration of boric acid in the core region will therefore continuously increase, unless a dilution flew is provided through the core. Without the dilution flow the concentration o:f' boric ac.id will eventually reach the saturation limit and a:ny further increase in boric acid inventory will ca.use its precipitation. Boric acid deposited in the core may clog flow passages and seriously compromise the performa..~ce* of the ECCS.
Topic IX-4 is intended to review the boron addition system, in particular with respect to boron precipitation during the *long term cooling mode of operation.f'.ollowing a loss of coo.lant * ~
accident, to assure that the ECCS is designed and operated in such a manner that a *su:rficient throughflow is provided before the concentration of boric acid will reach its saturation limit.
II.
Review Criteria The plant design was reviewed with regard to Append.ix A, 10CFR Part 50, General Design Criteria - 35, "Emergency Core Cooling", which requires that a system to supply abunda.i1t emergency core cooling shall b*e provided.
In addition, the plant desig:-i was reviewed with regard to 10CFR 50.46,
- 11Acceptirn.:c Criteria for Ll.<3ht Water Ifaclear. Pcrr/'er Reactors II' and Appendix K to 10CFR p~ 50 "ECCS Eval-uation 1-bdels", which set forth the requirements to maintain coolable core geometry and to provide long-term *core cooling; the bas:i,s for the* boron precipi-tation reviews.*
III. RELATED SAFETY TOPICS To~ic VI-7.A.3 reviews the ECCS actuation system with respect to the testing for operation and design performance of each component of the system.
Topic VI-7.B reviews the procedures for ESF switchover from injection to recirc~lat.i.on *mode.
IV.
REVIEW GUIDELINES Tilere are no unique SRP sections that deal with th~s issue.
The primary criterion used for r-eview of this system was discussed in a memo dated January 21, 1976*
ent.it.led, :*Concentration of Boric Acid in Reactor Vessel During Long Term Cooling-tfolhod for Reviewing Appendix K Submittals."
V-~
EVALUATION l....
Control of the r*eactor sys~em. boron' concentration, which is responsible for normal rea~tor shutdown, is provided by the Chemical and Volume Control System *.
- This is accomplished by pumping borated water from either.the Safety Injection*
and Re.fueling Water Tank (SIRW'n or either of the Concentrated Boric Acid Tanks (CBAT).
The quantity of boric acid in the SIRWT and-in each CBAT is sufficient to borate the PCS to cold shutdown conditions at any time during core life.
There are two flow paths to the PCS for each.of the three borate.cl water sources.
The water from each CBAT can be either gravity fed or pumped by boric acid pumps to the charging pumps suc*tion.
The water from the SIRWT can be either gi:-avity fed to the charging pump suction or can be pumped directly into the PCS using the HPSI pumps.
This level of redundancy provides for required PCS boration coinciden~ with any active single fail~~e.
Concern was raised by the NRC that boron precipitation could occur and impair the ability of the boron addition systems to maintain safe core*cooling following a loss-of-coolant accident.
Following a break, decay heat is removed by boilof f of water in the core.
As water is evaporated, the concentration of boron can reach the saturation point causing precipitation of boron in the core.
Without a flushing*flow through the core, the precipi"tation could result in block~ge of core channels.
The safety ob iective is to assur.e that the potential for significant boron precipitation that would restrict core flow is eiiminated by establishing such a flushing flow.
To prevent this buildup and precipitation of boron in the core dur~ng the
. long term recirculation mode, Pal*isades utilizes sim~ltan~ous hotl 11
_eghand cold leg injection following la_rge LOCA 1 $.
As descnbed in Ref 1
t e HPSI pumps inject water into the four cold *1eg ECCS nozzles as -we~l as simultaneously into loop 1 hot leg to produce the necessary flushing flow.
This method works for both large and small break LOCA's.
For s.mall LOCA's the PCS refills and decay heat is removed via the steam generators. and shutdown cooling system.
After refilling there is no steaming thus re-*_
moving the mechanism for boron precipitation. If these systems are not available, energy is removed.via the PORV's with HPSI injection providing adequate flushing flow.
Although there are se~arate procedures for large and small breaks the* applicable break sizes for each procedure s~fficiently overlap thus eliminating the possibility of the operator selecting the
,mproper procedure.
The analysis presented in reference (1) shows that there is sufficient margin between the saturation boron concentration and the maximum attain.able for both small and large break LOCA's.
The limiting break is the double-ended cold leg break.
However, even with no flushing flow boron precipi-tation does not oc.cur *for 29 hrs (long term cooling and henc*e prevention of boron precipitation procedures commence at 51/2.to 6 1/2 hrs.) With only*
a 5 gpm flushing flow the peak calculated boron concentration is about 10%
less than the s*atura ti on concentration. Actual expected fl us hi ng flows are*expected to be much greater than 5 gpm* with a resultant incre~sed margin.
VI.
CONCLUSION Based upon the above review it is concluded that th.e boron addition system at Palisades is acceptable.
Ref er enc es
- 1.
Letter from B. D. Johnson, CPCo, to D. M. Crutchfield, USNRC, dated October 9,1981, Long Term *Cooling Equipment Modification.Design Report.
- 2.
Memorandum for T. M. Novak, Chief, Reactor Systems Branch, from K. I.
Parczewski, Reactor Safety Branch, Jan. 21, 1976.
- 3.
Letter from R. A. Vincent, Consumers Power Co., to D*. M. Crutchfield, USNRC, dated October 9, 1981, SEP Topic IX-4 Boron Addition System.
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON. D. C. 20555 JM 2 l -1576..
ATTACHMENT 1 i'nomas M. Novak, Chief, Reactor Systems Branch, SS
/J_... _
THR!J:
Robert L. Baer,- Chief, Reactor Safaty Branch, OR/(/--!-'
CDNCENTAATIOt~ OF BORIC ACID IN REACTOR VESSEL DURING LONG TERM COOLING - METHOD FOR REVIEWING APPENDIX K SUBMITTALS Attached is a rremorandum entitled: "Concentration of Boric Acid in Reactor Vessal during Long Term Cooling - Method* for Reviewing Appendix K Su.bmi tta 1 s ".
Tbe memorandum is in.tended for the re vi ewers of Appendix K submittals. It describes the methods.used in reviewing the calculations of boric acid buildup during a post-LOCA long term cooling..
Attachment:
As stated
- cc:
O. Ross O. Eisenhut
~~
\\ ~. ~. \\ :.._1. .'*:*-...... :. ~..,_,*
K. I. Parczewski.'
-Reactor Sarety Sranch Division of Operating Reactors Reactor Systems Branch Members Reactor Safety Bran~1 Members
e-*.
~ *.
CONCENTAATION OF BORIC ACID IN REACTOR VESSEL CURING LONG.TERM COOLING - METHOD FOR REVIEWING APPENDIX K SUSMITTALS *.
I. Oescriotion of the Problem Following a LOCA, boric acid solution is introduced into the
- reactor vessel* by two modes of injection.
In the initial injecti9rr mode, borated water is provided from the accuwulators from the refueling water storage tank and from the boron injection tank. (Westinghouse plants only). After this initial.
per*iod, which may 1 ast somewhere between 20-60 minutes, the ECC
- system is realigned for the recirculation mode.
In this mode borated water is provided from the conta~nment sump.
It is recirculated from the sump. to the reactor vessel and back to the sump through the break. A portion of the water introduced into the reac~or vessel is converted into steam by the decay
- heat generated in the core. Since the steam contains virtually no impurities, the bor.ic acid content in the water that was
- vaporized remains in-the ves:sel.
The concentration of boric
- acid in the* core region will therefore continuously increase,
- unless* a dilution flow is provided through the core. Without the dilution flow the concentration of"bori'c acid will eventually reach the saturation limit and any further increase in bori~
acid inventory wi11 cause its prec'ipitation. Boric acid deposited in the core may clog flow passa9es and seriously compromise th~
- perfonnance of the ECC system.
- To P.revent this from happening, the ECCS shouid be designed and operated in such a manner that a sufficient. throughf1ow is provided before the concentration cf boric acid will reach its saturation limit. The general perfonnance criteria for the boron d~lution systems are given in Appendix I to this memo.
There are two situations when ECC system cannot provide sufficient diluting f1ow through the core *. It occurs *dur}ng: *
(a) cold leg injection with cold leg break (b) hot leg injection with hot leg break
.* _.. ~
In both these cases the injected fluid doe~ not have enough head to pass through the core. Since it is not possible for ~n operator to distinguish between cold and *hot leg breaks, the only way of assuring dilution flow through the core is.to provide one of
. the following modes of ope~ation for the ECC system:
(a)
(b)
(c) alternate,injectiorr to cold and.hot legs.
simultaneous injection to cold and hot legs.
simultaneous cold leg injection and hot leg suction
- II. Methods Prooosed bv the Vendors for Preventino Boric.Acid Concentration
- 1.
Babcock and Wilcox Tne B&W plants are unique in that they possess internal vent valves bet.~een the upper plenum and the downccmer.
The existence of these vent valves allows natural circulation to take place in the
~eactor vessel as long as the level of the two-phase mixture is high enough to reach the vent valves and keep them open.
B&W has performed an analysis indicating that regardless of hot or cold.
leg b*reak, the natural circulation r1ow through the core ccula be maintained for over 30 days after a LOCA and no operator action is needed during that period of time (References 1, 2 and 3). After 30 days B&W proposes three different modes of opera ti on, aiming at* ~
- establishing diluting flow through the.core. !hey are as follows:
(a)
(b}
(c) injection into the downcomer and suction or drainage from the hot leg through the decay heat line.
simultaneous injection into the dcwncomer through the injection line and into the hot leg through the.
decay heat line.
simultaneous injection into the downcomer through*the.
injection line and into the hot 1eg through the auxi*1iary pressurizer spray line.
B&W claims that any of these methods, if initiated within 30 days, will prevent boric acid concentration from reachin9 the sa~uration 1 imit.
The NRC staff has reviewed the claims made in the B&W analysis and found that, indeed, in most plants natural circulation* can provide dilution f1ow through the core well in excess of 30 days.
The
- modes of operation, proposed by B&W for-maintaining dilution flow '
beyond this time have to be reviewed individually for each plant because their performance depends on the parameters of each individual ~lant.
-- 2.
Combustion Engineering In the Combustion Engineering plants the initial injection of borated water is through the cold legs. After some specified time, cold leg injection is replaced either by simultaneous hot and cold leg injection, or by simultaneous hot leg suction and cold leg injection. rne time when the switcholler must take place is determined by_the concentration of boric acid in the reactor vessel.
In the analysis (Reference 4) Combustion Engineering makes two assumptions. It assumes ideal mixing of boric acid solution in the *reactor vessel which prQduces uniform concentration*buildup in the whole vessel and it assumes that in all cases there is a residual pressure of at least 20 psia in the reactor vessel.
This pressure causes higher boiling liquid temperatures with the resulting increase of 4 1/2 weight percent in boric acid solubility.
Both these assumptions are non-conservative and Combustion Engineering does not provide satisfactory justification for including them in the analysis.
In the *procedure provided by Combustion Engineering, hot i*eg..
suction is acc~mplished by use of the. shutdown cooling suction -
. line and the* hot 1eg injection can be made either through t_he shutdown cooling ~uction line or through the auxiliary pressurizer spray line.
In most plants these three alternatives provide a system that can withsta-nd a sipgle active failure.
The procedure proposed by Combustion Engineering has certain limitations. If the steam produced in the vessel cannot be freely vented through the hot leg, it can depress the level_
of the *liquid in the upper plenum below the bottom of hot leg nozzles and impede the suction through the shutdown cooling 1 i ne.
This case wi 11 occur when a 11 1 cop seals, formed by the U bend.in cold leas, are ~illed with water.
On the other hand,
- if the steam leaving' the vessel reaches velocities too high it may carry the injected fluid into the steam generator and prevent it from reaching the core.
Both these problems have been addressed by Combustion Engineering (References 5 and 6) and it was demonstrated that9 for the plants_
considered, these effects did not seriously affect the performance of ECC systeme
-~
- 3. * ~estinghouse After an initial period of cold leg injection, Westinghouse recorrrnends ~ot leg injection as means for providing dilution flow through the core.
The generic analysis performe.d by
.Westinghouse (References 7 and 8) assumes that the fluid injected through the hot leg to the upper plenum mixes with the fluid in the reactor vessel.
Hot leg injection, therefore, provides a continuous dilution flo\\'I through the core for both
- hot and cold leg breaks.
The Westinghouse analysis, which forms the basis for these assumptions, is not complete. Until more information is obtained, it is recornnended that the initial cold leg injection should be replaced either with simultaneous hot and cold leg injection, or alternate periods of hot and cold leg injection, so that adequate dilution flow is provided for either a hot leg or cold leg break.
III. NRC Review
- 1. General Description The NRC review of the submitted procedures includes independent evaluation of basic parameters (switchover time, minimum flow rates, etc.).
The independent evaluations have been performed- -
for the following reasons:
(a)
In some cases the information provided by the applicants were.incomplete and it was not possible to check the soundness of their initial assumptions or their methods of analysis.
(b)
Iri order to assure that under a11 operating conditions the procedures provided by the appi i cant wi 1.1 guarantee the maintenance of safe boric acid concentrations,* the NRC staff proposed a series of conservative assumptions.
It is necessary to determine hew this additional conservatism would affect. the procedures proposed by the applicants.
One *of the most important assumptions 'introduced by the* staff, was the four weigh percent margin in the saturation concentration of boric acid in the core region.
This safety margin was -
introduced to take care of inaccuracies in predicting saturation concentrations *in the core.
The NRC review consists of two parts:
(a)* analysis (calculation) of boric acid concentrations
- . {b) hardwa~ review
--s-
- 2.
Analytical Methods The fa 11 owing methods were used in ca 1cul a ting different performance paramet~rs for the systems reviewed:
(a}. Switchover time from cold leg to hot leg (or *..
simultaneous hot and cold leg) injection.
In order to determine the switchover time the following
- conservative assumptidns were made:
(1)
During the initial cold leg injection, boric acid
~
not leave the core.
- (Z)
The maximum concentration of boric acid in the core region (Cc} should not exceed 23.5 w/o (4 w/o oelow the saturation concentration at 21Z°F).
(J)~he initial injection period lasts for ZO minutes after (4) a LOCA.
At this time the concentration of bori.c acid ( C0 }
is uniform in the whale ?1ant.
The effective volume in which boric acid buildup occui-s ** -
consists of a volume of liquid in the core and in the up.per plenum up to the height of the bottom of the cold leg nozz1.e.
The rate of boric acid buildup is *expressed by the fo116wing differential equation:
'de
= A
- t-n. (C-C}
IP dt Where:
c* - boric acid concentration in core region Cci" maximum boric acid.ccncentrat~on i'f all boric acid were ccncentra ted, n core region.
t - time A - graup depending on several plant parameter'.
n - constant
-o-Solving the _equation for the following_ boundary conditions:
t=t C=C o,
0 t=t C*C s,
. c and rearranging the terms, the following expression for the switchover time (t5 ) is obtained:
s 0
t = t
~ [ 1 -
1-n A
- t 01-n Where:
A =..,..:.;K,....;.....;.P__,.. __ _,.,._
(6hf +~hfg)
- M5 1 I (1-n) for: t 5<4 x 106 sec (4'6 days}:
K = 0.156 and n = 0.283 M5 - mass of water in the ~on~inment sump, lb
.P
- reactor operating power, Btu/sec Cc - 0.3077 bori~ acid/water In the case of alternate hot a~d cold leg injections, the s~bsequent switchover times couJd be obtained by substituting tsl, ts2, ts3 etc for t 0 in the above equation.
(b}
Minimum cold leg injection The minimum cold leg injection required during recirculation (prior to switchover to dilution mode) is determined by the rate of boil-off in the core at the very beginning of the long term cooling mode.
It is detennined from the following expressi_on:
.QC :s 449 H f ;n*{~hf + ~hfg) gpm
- Where:
H0 - decay heat generated at the beginning of recirculation period, Btu/sec fin.. density of injected fluid, 1b/ft3
~f -*subcooling enthalpy, Btu/lb Ahfg - vaporization enthalpy, Btu/lb (c)
Minimum hot leg injection The minimum injection rate, after the switchover from cold ta hot leg or to simultaneous hot and cold leg injections, is.detennined by making conservative assumptions that the minimum injection
- should provide *enough flow to repl~ce the boiled-off liquid.and to maintain. sufficiently high dilution flow through the core.
The boiloff rate* is calculated using the decay heat generation rate at the switchover time from cold to hot leg injection. The dilution flow is detennined for the maximum allowable concentration of boric acid.
Expression for the minfmum injection rate is. given below:*
ah = 449 Hs fin [Ahf + (1 3.25 Co) Ahfgj Where: H - decay heat generated at switchover time, Btu/sec.
The decay heat is calculated using the methods given in Reference 9.
(d)
Steam bind*ing When the switchover from cold to hot leg injection occurs shortly after a LOCA, large volume of steam leaving the reactor vessel may induce high steam velocities in outlet nozzles. These velocities impede the injected boric acid solution from reaching the core.
In order to assure that hot leg injection is not compromised. steam velodties have to be* es.tima~ed *and *the
- rate of entrainment of. the injected liquid ca!culated..The rate of entrainment can be calculated using the methods given in Reference 10.
-e.:.
- 3.
Procedure In reviewing the boric acid submittals,.the.following procedure was used:
Step 1 Review of the subll}ittal and identi*ficttion of any special features the applicant may be taking credit for.
In most cases the applicants fo11ow the generic analyses devel_oped by the vendors.
However, occasionally the applicant may take credit for the phenomena which are not considered in the generic studies. For example, no consideration was given in the generic studies to the possible increase in the so1ubi1i(y of boric acid when sodium hydroxide is present. However, some applicant may use this phenomenon to increase the allowable solubility limits.
In such cases the reviewer should identify and individua 11y evaluate such features.
Step 2 Determination of the basis parameters identified.in
- Section III-2 of this memo.
The information needed for the determination of these parameters are.either provided in the origina1 submittal or can be found in FSAR or PSAR.
Stea 3 Hardware rev.i ~
Using the P&I diagrams or special schematic diagrams provided by the applicant, the systems are reviewed to assure that they meet the requirements identified in the analytical part of the
~eview, without violating the single failure criteria.
IV.
Conclusions The procedure for reviewing nuclear plant for boric acid precipitation is outlined in this memorandum.
It should be mentioned that although this procedure may apply to the majority of plants reviewed, there may be some cases *where the reviewer may be forced to use completely different approach.
He should be, therefore, f1exible-*in choosing his procedures, guided by the considerations described in Appendix I. Note the Appendix I is i_ntended to apply fu1 ly only to CP applications.
V.
References
- l. Babcock and Wilcox, Topical Report: BAW-10102, ECCS Evalua-tion of B&w*s. 205-FA. NS~, June 1975.
- 2.
Babcock and tUlcox, Topical Report BAW-10103, ECCS Analysis of B&W's 177-FA Lowered-Loop NSS, June 19.75.
- 3.
Babcock and Wilcox, Topical Report BAW'-10105, ECCS Evaluation of B&W's 177-FA Raised-Loop NSS,-June 1975 *.
- 4.
Sw-itzer, D. C., ('NNECO) letter to O. D. Parr (NltC), daced June 27, 1975, attachment A.
- 5.
Switzer, D. C. (NN'ECO) letter to o. D. Parr* (NRC) '* dated Septei:iber 25, 1975, attach~ent*l.
- 6.
Telecon, J *. Longo (CE,. and RS:S personnel (NRC), Octocer 30, 19.75.
- 7.
Caso, C. L.
0~estinghouse) letter CI.C~NS-309 to T. M. Novak
"(NRC), date'd. April l,.1975.
- 8.
- Cer:nak,*J. O.
0~estinghouse) letter JOC-~S-369 to T. M. Novak (NRC), dated August.15, 1975.
- 9.
ANS, Decay Energy Release Rates FolloWing Shutdown of Uranium - Fueled Ther.::al Reacto~s, (Proposed ANS Standard),
October 1971. *
- 10. Wallis, G. B., One-dimensional Two-pnase Flow, McGraw-ilill Book. Company, 1969, Section 12.10.
~.
i; J
i l
~
'J PWR BORON DILUTION SYSTEMS FOR. C? APPLICATIONS WHICH MUST MEET 10 :FR 50.46 CRITERIA FOR ACCEPTANCE
- l. The boro11 dilution function shall not be vulnerabfe to a single failure. A single active failure postulated to occur during the 1ong term cooling period can be assumed failure would then be in lieu of a single active failure during the short tenn cooling period.
- 2.
The spurious operation of any motor operated valve (open or closed) shall not compromise the boron dilution function nor shall it jeopqrdize the ability to remove decay heat from the primary system.
- 3. All components of the system which are within containment shall be* designed to seismic Category* l requirements and classified Quality Group B.
- 4.
The primary mode for maintaining acceptable levels of boron in the vessel should be established.
Should a sinQle fai1ura disable the primary mode, certain manual actions outside the control room would be allowed, depending on the nature of the action and the time available to establish back-up mode.
- 5.
The average boric*acid-concentration*in any region of the reactor vessel should not exceed the level of 4 weight percent below the solubility limits at the temperature of the solution.
- 6.
During the post-LOCA long term cooling, the ECC system *nonnaJly operates in two modes:
the initial cold leg injection mode,.
followed by the dilution mode.
rne actual operating time in the cold leg injection mode will depend. on plant design and steam binding considerations, but, in general, the switchover to the dilution mode should be made between 12 and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> ~fter LOCA.
- 7.
- 8.
The dilution mode can be atcomplishe~ by any of the following means:
(a) Simultaneous cold leg injection and hot leg suction (b).Simultaneous hot and cold 1 eg injections (c) Alternate hot and cold leg injections.
In the.alternate hot and co 1 d 1 eg i nj ecti on mode; the operating time at hot and cold leg injection should be sufficiently short.
to prevent excessive boric acid buildup.'*
- 9.
The minimum ECCS flow rate delivered to the* Vessel during the dilution mode sha11 be sufficient to accormiodate the boil-off due to fission product decay heat and possible liquid entrainment in the steam discharged to the containment and still provide sufficient 1 i aui d fl ow through the core to prevent further increases in.boric acid con~entration.
- 10.
All dilution modes shall maintain testability comparable to other. ECCS modes of operation (HPI-short tenn, LP!-short term,
.etc}.
The current criteria for levels of ECCS testability shall be used as guidelines (i.e.~ Regulatory Guides 1.. 68, 1.79, GDC 37). *
.*