A13742, Status Rept on Reserve Shutdown Sys

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Status Rept on Reserve Shutdown Sys
ML20085M591
Person / Time
Site: Fort Saint Vrain Xcel Energy icon.png
Issue date: 11/25/1975
From:
GENERAL ATOMICS (FORMERLY GA TECHNOLOGIES, INC./GENER
To:
NRC
Shared Package
ML20085M589 List:
References
GA-A13742, UC-77, NUDOCS 8311090033
Download: ML20085M591 (45)


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GA-A13742 UC-77

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4 S~~ATUS REPORT OiN RESERVE S 'UTDOWIN SYSTEiV e

by PROJECT STAFF

] Prepared under s Contract E(04-3)-633 for the San Francisco Operations Office U.S. Energy Research and Dave!opment Adrninistration DATE PUBLISHED: NOVEf.1BER 26,1975 5

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This report was prepared o an account of work spon ored by the Umted States Gnctument.

Neuber the L'nitect States nor the Umted States Enctgy Research and Development Adminnuation, nor .my of their employres, nor any of their contractors, subcontractors, or t!>cir employees, m.tke, any warr.uuy, expreu or imphed. or anumes any legal li.dnlity or re ponsibihty for the auur.ay, romp!cteness or usef ulness o! any inf ormati.m. appar.itus, proJun or I,sotess diu toscal, nr .-

represents that its use wukt not intonga penately owned rights.

Printed in the United States of Atterica Available from

!!ation :1 Tec' al. al Information Scr.' ice l U.S. Department o f Cor.:merce 5285 Port IMyal Road i Sprin;,i!cid, Virginia 22161

! Price: l'rinted Copy $4.00; Microfic' $2.25 1

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i S__A_I U S R t. _.PO R i DN I

RESERVE SHUTJOWiN SYSTEM .

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! Prepare.d under

Contract E(04-3)-633

!. fcr the San Francisco Oparations Offica I _U.S.- Energy Research and Development Administralian I

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l. GENERAL ,t 0!: llc FF,0 JECT.1900 DATE PUBLISHED: NOVEFASER 25,1975 l 4 S

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CONTENTS i INTRODUCTION . . . . . .. . . . . . . . ... ....... ... . 1

SUMMARY

AND CONCLUSIONS . . . . .. . . . . . . .. . ... ... . 2 PART I - STATUS OF RESERVE SUUTDOWN SYSTEM . . . ..... . ... . 4

1. Identification of Unusual Event . ... ... ... . 4
2. History of the Environment in the Reserve Shutdotm Hopper . . . . . . . .. .. . . .. ... . 4 -
3. Inspection of Reserve Shutdo:m System . . ...... 6
4. Characterization of Crystals . .. ... .. . ... . 8
5. Present Status of Reserve Shutdown System . ... .- . 13 PART II - PERF0PMAUCE CF RESPRVF. SHUTD0'.R1 SYSTEM . .. . . . . . . .- . 14 4-
1. Ne;;ative Reactivity Worth cf Reserve Shutdown Systea . .. . .

- . . .. . . . . . . . . . . . .. 14

, 2. Lony,-ferm fiehavior' of Kaserve Shutdotm Material .. . 15 .

3. Effcet of Cryn:al Grom:h on Recerve Shutdown SfStem Component.G . . . . . ._. . ... . .. .. . . . 16 PART III - PERFOR1!AUCE OF REACTOR FOLLOUIUG RESERVE SHUTDOWN 4

SYSTEM DUMP . . . . . . . . . . .. . ... . . .... . 18-

, 1. Behavior of Reserve Shutdotm Material in Core

... . 18

2. Reactivity Behavior of Core Following Reserve Shutdown Material Retroval . . .............22
3. :Effect on Reactor. Materials.

4 . .. . . . . . _ , . .;. . ..

23 REFEREECES . . .-. ... . . . . .. . . - . . . . _ . . . _ . . . - . . . . . - - '26

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'FICURES APPCliDICES 1

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U ()s I!'TRODUCTIO:I This report has been prepared by General Atonic Company to justify the usage of the reserve shutdown system (RSS) in its present condition. The report is divided into three parts: the status of the system, any effects on the reserve shutdeun system performance, and reactor performance following a reserve shutdown system dump.

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SLROIARY AND CONCLUSIONS During a. poison loading conversion of the reserve shutdown system, ,

crystalline deposits were found on the surfaces of several reserve chut-down balls. An extensive inspection and analysis program was performed to characterire the crystals, to determine the cource and extent of crystal-lization, and to determine the effect of the crystals on both the reserve shutdown system and the reactor itself in the event that the system is activated.

The reserve shutdown balls consist of B 4 C particles intermixed with graphite. The specification for the material allows a small amount (0.15%)

of B20) to be present in the balls. The analysis performed on balls taken from a tyylesi hoppar indicatcc that apprezimetaly 25% of the B 033 has been leached out of the balls and cryctallized into' harmless boric acid crystals.

None of the boron carbide (B4C) has been affected. The crystalline deposits are contained within the reserve shutdown hoppers either on the. hopper sur-faces or on the ball surfaces.

The performance of the' reserve shutdown system has been evaluated and found. Lo be unaffected by the presence of :the boric ~ acid crystals. There is insufficient quantity of B 023in the balls to cause.any stability pro-blems.with this material and the balls will remain intact throughcut their-30-year life. A reserve chutdcun cystem dunp test uns run which_ indicated no chanho ~ (n the release capability of' t! a ' system. .Laboratcry testa.wcre

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run to taliberately allow cryctal growth:between balls. Results showed neg1!dibin bond stranr:th and all the balla se;.4. rated fron each other:when the crperiment tray was moved. Crystals.which have been depo 01 cd on the i hoppur. .wrfaces will hnve no ef fect on its ? integrity.

/.n ovaluation han' tx.n.cado on the perforrinuce of the tr(eter fcilewias n reset- 3!t:rA.un syctym AQ. :ae crp tsla on the b:lls ulll citi.ir 2

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. .. . . > q ,1 dehydrate and convert back to 23 B 0 or they will vaporite and diffuse into the currounding graphite and then convert to B 0 Either consequence will 23 not cause any effect on the reactivity which would compromise safety of the reactor core or cause degradation of the primary coolnut spstem componenta.

It can, therefore, be concluded that the leaching out of B 0 f#

  • 3 the reserve shutdown balls and the subsequent crystal formation on the ba] ' ' and the hopper does not change in any way the capability of the sys-tem to perform its function, nor does it ec= promise the safety of the reactor in the event that the system is activated.

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PART I - STATUS OF RESERVE SHUTDOWN SYSTEM i

An unusual event has been identified in the reserve shutdown system.

Part I of this report is the investigation which has been undertaken to

, describe the event, determine the environmental history of the system, and

define the cause.

i

1. Idertific:.t. ion of Unucur.1 Etent .

On September 19, 1975, during the modification of the 37

,contr:1 red drive assemblies to minimice the bypass of primary coolc t flow from the orifice valve, CRD SN-028 was being con-i verted for use in an outer core region. This' conversion requires.

replacing the control rods and the reserve shutdoun balls con-tained in the reserve shutdoun system. hopper. In'the outer 18 core regions, reserve shutdown balls containing 40 ut % baron are used instead of those containing 20 wt % boron. While removing the boron carbide balls from the reserve shutdown hopper, it was-noted that there was a deposit of white crystals on the surface t of several of the balls. The presence of the crystals did not appear to' affect the operability of the reserve. shutdown system.

This was 'cubeequently identified as an unusual event per FSV -

Technical Specifi ation AC 7.6..

2. History of the P.nviron=ent in the Reserve She down Hopper The reserve-shutdown hopper is' vented to the FCRV. environ ment as shoun in Fig.l1.- The PCRV cnvironment from Januar_

1974 to March 1975 cas described in detall -in' Ref. ' t . Since t.he hopper is co. acted'to the FC4V.through the; vent syntem, transport 7 l

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,_ of the PCRV environment into the hopper has occurred via ordinary diffusion. -Also, this transport was greatly enhanced during periods of large pressure swings, which occurred during the time period of interest.

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-Sometime in January of this year, approximately 4230 gallons of water were inadvertently admitted into the PCRV. This was i reported in Ref. 1. Subsequent ~to the water ingress, water was removed from the PCRV through the helium purification coolers of the helium purification system from January 23 through February

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15. During that prccess, with the moisture level in excess of .;

10,000 ppm, the reactor pressure vas eyeled between 50 and-250 psig twice to create a pumping action in order to' remove the water fto'n e.he PCRV liner iuaulation. The reactor was then

, pumped do.en and evacuated' to less than 10 c:a of Hg to complete

the water removal. This was completed on 1
arch 10 and the raactor takca critical en :: arch 21 to cotablish the integrity of the fuel and core components and encure that the unter had -

been comp %taly removed.

It can, therefore,:be concluded that between mid-January and liarch 10, 1975,- the environment inside the reserve shutdown hopper was essentially the same as the PCRV. The dry helium was replaced by helium caturated with water during.th'e pressure o' scil- -

lations. This_ saturated. helium was subsequently removed ~during-the final PCRV evacuntion and replaced again with dry helium on

?! arch 10,1975.

The temperature of the hcpper, reser.a shutdown balls, and the helium within the hopper'is assumec to follc - the tempcratura of t.he heliuc. within the PCRV since considerabic bypans'of heliu-i into the pc. tsation crea was shown to occt dhrin.; startup.

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3. Inspection of Reserve Shutdown System ,

Upon discovery and identification of the crystallization,

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extensive inspection and tests were run at the reactor site. The reserve shutdown hoppers of five separate control rod drives (CRD) were inspected to determine the extent of crystal formation.

Table 1 lists these CRDs and their location in the reactor prior to removal.

TAELE 1 CONTROL ROD DRIVES SELECTED FOR RESERVE SIIUTD07:

SYSTE:1 I!OPPER INSPECTION d

Control Rod Drive Core Region

  • Serial ::o. Prior to Removal 028 13
  • (W 037 2 011 21 021 30 027 22 The fotlowing inspections ucre performed on cach of the hoppers:

Control Rod Drive Inspections and Results SN-028 Reserve shutdown balls ucre vacuuned out and a ran-doa sattple of N500 balls (650 g) was sent to San Diego for tests. Tests were ali,o conducted by PSC Chenistry which deterniced that the crystal.; were water coluble boric acid cr3stals.

S: - 17 r.oric acid crystala t.ere found ca the imiide surf. ice of the -f tiler plu;; .tn occa i.n Fig. 2. Ah. :n t 30 rcurve _hutdowa balia (40 c)' r.d :amples of the crystals f rc.a the f i! !c c p lu;. e e er.t t- nn' 6

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Contcol Rod brive __Innpections and Results independent lab for identification. They confirmed that both were boric acid crystals (Appendix 1).

These samples were later sent to CA San Diego for X-ray dif fraction analysis to determine the chemical form. The balls in the hopper were vacuumed out In layers and random samples of each layer were sent to CA San Diego for quantitative analysis. The rupture dick was removed and photographed (Fig. 3). Crystals can be seen on the balls which were left on the disk and on the disk assembly. The inside of the hopper was inspected from the top and bottom using a mirror and a borescope. The only crystals seen were near

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the top as shown in Fig. 4.

SN-011 The rilier plug and rop sur f ace of 'uallo lu huppcc indicated similar crystalline deposit as seen in~

previous hoppers.

SN-021 Filler plug and top surface of balls in hopper indi-cated the same crystalline deposit. Trace crystals were also found in hopper vent system.

SN-027 Filler plug and top surface of balls in hopper indi-cated the same crystalline deposit. Succcccfully performed test No. RT-351 to verify performance of reserve shutdown system ~ (Appendix 2) . The inside of the hopper was examined after the ducp test and it appeared similar to the CRD SN-037 hopper ubich was previously inspected and is described in Fig. 4

' Typical RSS balls photographed after RT-351 are shown in Fig. 5.

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4. -Charneterization of Crystalu Several aanples of reserve shutdown balls were sent to CA at San Diego for analysin und character!:ation and these renults are dJscissed below.

4.1. Ibserve Shutdown Balla From r 3 SN-028 The RSS for CRD SN-028 originally contained balls with >20 ut %

boron in the form of B C and 0.15 we % as B 0 . Of the sample of 4 23 balls sent to San Diego, 128 out of 497 (267.) had more than 10 crystals on their surface. Of these'128, approximately 120 were analyzed to determine their chemistry and to quantify the crystallization.

The white crystals fouc.d in the first sample of balls from CP.D SM-028 were identified to be borde acid cryctnla (Hfo,) smi anhydrous horic acid crystals (11B0 2). Further analysis of the crystals revealed only trace arounts.cf re, Si, and Mg in addition to the 11 3 03 M0 .2 The traces of Fe, Si, and Mg were present in the crystals to the same concentration as in the as-manufactured balls.

The average crystal (II M NO ) concentration was found to 3 3 2 be 0.1% of the '.all weight and the maxi. mum - any ball was 0.Y::

af the ball ueight. The average B 0 conce.ntration of thece 23 balls was 0.1% of the ball weight. - An a: . lysis of the total boron in the balls sho. d 20.9 wt %, ucl1 over the specified 20 wt T., indicating that no U,C was affected by the leachi..;

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'. in the ae-r mCactur 2d halls origin.111y conta!.ncd 0.15 ut 7, n.0, a'id slaue the !): :la hTring n re ta 10 cr".9 al, on 2 >

the i r et / f.ic a h.:d a n ' aver:ge e f 0.1 tit ' P. 0. . . E t can be n

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'. (' O s o concluded that some of the U 330 uas leached out of the balls and deposited on the surfac as H U0 r I!t0 .

2 Since the balls con-3 3 tained well over the specified quantity of boron and since there l.

was a definite decrease in the weight of the B230 in the ball, it can further be concluded that none of the B C 4 was affected.

4.2. Recerve shutdown Bn11n From CRD S:I-037 The crystals on balls taken frem the CRD SN-037 hopper were found to be a mixture of UB02 and H3 B03 crystals. We crystals taken from the face of the shield plug were H 3B03. The samples of reserve shutdown balls from the hopper were random samples taken from difforent icvels within the hopper. "his allowed a determination of the axial distribution of crystalline deposits within the hopper and aided in understanding the mechanisn uhich took placc. The distributien of crystals en the ball samples renoved from the hopper is given in Table 2.

The analysis of this hopper indicated that 6.75% of the balls exhibited more than 10 crystals on their surfaceu. The quanti-tative analysis of such balls shoucd that the boron present as un0 # tI n e sudace of those balk amages 0.C of 2 3 3 the ball weight. The analysia also indicated very clearly that crystallization was concentrated at the top and bottom areau of the hopper. Additionally, the clean balls from the mLMic of t he hopper shtaad boren renaining as B.'T 3 in d e the balin to ba 0.15" of the ball weight uhich Ls equal to the measurad au-manufactured level.

4.0. I.aboratory C:m. hwn t Seve r il laboratory c::per bwnta w.rce -underta'. a t a sluulu tt the re. car coalitlona. t -il mid.cryitac., wre r,N a on ba i '-

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TABLE 2 AXIAL LISTRIBUTIO:10F CitYSTALLIZATIO.'I ULTilIN lESERVE S!!UTD05:1 !!OPPCit OF CRD S:1-017 l

Balls Witti Balls Ulth gg >10 Crystals Any Crystals Level S le S%

% tio .  % No. No. of Ba1.ls i 23 7 43 13 30 2 6 1 11 2 18 3 0 0 0 0 21 4 0 0 4 1 24 5 0 0 0 0 25 6 0 0 4 1 27 7 0 0 0 0 30

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ti t 0 0 3 , 1 29 9 0 0 0 0 27 10 23 6 27 7 26 11 22 4 44 8 18 All 6.75 18 12.4 13 275 10 I

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G follow;.d by heating in a furnace. At %150*F H n0 crystals were 3 3 formed; at N325"F !!D02 cry tals w re formed. Subsequently, crystals of 1100 were grown betueen adjaccat balls.

3 Ilowever ,

the crystals were so weak the bond uas broken with only the slightam. movement of the specimen dish.

Another experiment was performed to simulate the hopper environment; its configuration is shown schematically in Fig. 6.

In this experiment, distilled I! 0 was vaporized at %250*F below 2

a bed of reserve shutdown balls. The water saturated vapor in the closed system condensed on the top surface (%150* to 200*F) and dripped back onto the balls. After %30 hours the balls were e::amined and found to have white crystalline deposita spattered on the surfac.3 (Fig. 7). The system was dried out by venting to the atmosphere. The white crystals on the ball surfaces remained and were identified to be !!3 " 3* .

This simulation experitent demonstrates that boran can be leached by water vapor fron the23 B 0 that is prcsont in the balls after nanufc ture.

4.4. Postuinter! !!cchan tsn--

The chemistry of the reactions of interest are defined to help understand the mechanism which tock place in the reserva shutc'oun hoppers betuaca mid-Janunry and March 10, 1975:

(1) 3H2 O + r 0 + 2H 0 3 3 3 00*F > T > 100'FA (2) II 0.+ n 0 + 21i00 3

600*F > T > 3CO*F (3) I!3 M . + E3+H0 3 MW > . T > M F

% il La teratt. ras a p p rc u te.ite .

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m G J l The qualitative identification of 11002 " " d II303 crystals on the balls and the laboratory experiments ccupletal in San Diego support the following mechanism:

(1) Unter saturated helima (%100,000 ppm !! 0) was introduced 2

into the reserve shutdown hopper through the vent to reactor coolant. As the temperature increased, the water vapor leached B 23 0 ut f th reserve shutd wn balls in the form of boric acid as shown in reaction (1).

(2) In the saturated environment some liquid H B0 settled with 3 3 liquid H O in the bottom of the hopper, while the vapor 2

permeated the entire hcpper condensing on the top and cooler sida surfaces of tha hopper and crystallicing as 11 B0 . <

3 3 (3) II B0 crystnis were formed on the up,er layers of the -

3 3 reserve shutdovn balls citner Iror H ee) 11gula con;ensation 3

drippfrg frcm the top inner surface of the hopper or from condensation of boric acid directly cnto the balls from the surrounding v.1por.

(4) As the temperature of the balls increased during the B-series startup test to 250*F to 350*F,1:S0 vas form:d on the 3

reserve chutdown balls per reactions (2) and (3).

The vapor pressure of both forms of Icric acid is very high in this t Prature range and as ter...erature incraases, equi'librita would shif t touard 11r0 f rmati n which is con-2 ni- ut with the observations of tl.ese c :p iments.

(5) As the reactor coolant was dried out, :e crystals rcmaiaed on tha re ve shutdem balls and the hop r vall.

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5. Present Status of Reserve Shutdoun System The characterization of the crystallization in laboratory tents and analyacs at San Diego, which is confirmed by the inspections performed at the reactm site, allous us to under-

. utand the present status of the 37 reserve shutdoun systems of the FSV reactor.

It has become obvious from the inspectiona and tests that sonc of the B 0 was leached out of the RSS balls by moicture 23 which was present in the hopper betucen January and March of this year. It has also been determined"that the 5 C 3 has not been affected by the moisture.

Based on the varicus analyscc perfermed, it is estimated that approximately 2 to 5 g of boron ma; ba present as crystals on balla a'nd that another 2 to 5 g may be deposited as cc,ystals in the hopper. Tha upper limit of boron precent as boric acid crystals in any one hcpper is estimatc3 to be 15 g boron. The total amount of B 0 estimated to be in a single hc;por is 60 g.

23 Therefore, it can be concluded that approximately 25% of the E0 has been leached out of the balls and crystallized into 23 boric acid crystals onto the surfaces of the hopper and tha balls.

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PART 11 - PLnFOR)!ANCE OF RESERVE S!!UTDC ! SYSTrli Part I of this report presented the results of an extensive investiga-tion to determine the preacnt statuu of the reserve si..;tdown cystem. In summary, it was concluded that because of moisture ingress into the reserve shutdoun hopper, B 03 " " E"# " 7 '"" * " * ' ""'"

graphite balls and that the resultant boric ac'd condensed onto cool surfaces of the hopper forming boric acid crystals. Part II of this report will show that thia unusual event will llave no effect on the performance of the reserve shutdown system.

o Since the reserve ch tdown system is a pass'/.'e syste:a during normal operation, it must be determined that this unusual event will have no .

effect 9n negativa reactivit,y w rth or the .nechaulcal performance of the -

cysten over its entire lifetime. The system must.be ready to perform its function at any time during its lifetime.

1. Nr"tative Reacti"ity Worth of Reser'e Shutdeun Syntom The majority of b.ron in the balls (>99%) is present as B.,.C, and the quantitativo analysis confirned that this material vas not afCected; very little of the boron has been removed from the balls. Tha reactivity vorth of the recarve eht. _down naterial wa; calculated on the basis of the B,C s present and thua the reactivity worth has not. changed. The minim = bn: en loadin:: in any happer ic 5400 g and uith this heavy boron loadin , the reserve shutdeun echt . is neutrualesily blae:<. to ~ herr.1.

neutron: It noul. reqe a p,reater th:c a 107; lcns of buren to chany,e the rca : tivity uor th ofc ti- re: ;ve uhuthm s: ; ten by I ' , t'[ 10- pr :'Se P *. U0 r tin . 91dre f4 'U, Erva thu rei..LiVIL, @n t ru i. t

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2. Long-Term Echavior of Renerve Shutdoen thterial Under normal operating conditions, the reserve shutdown material, boronated graphite bs11s, is stored in hoppers located in the control rod drive assembly. The balls remain ntored, ready for use at any time, during the reactor's 30 year lifetime.

The long-term behavior of this material, even with crystallization of B230 , vill not '.ffect the system's capability of performing its design function if and when needed.

Over the long term, while the material is in the hopper, 99.85% is in the form of graphite 'and boron carbide (11 C) and 4

0.15% is in the form of boron oxide or boric acid c.rystals. In a water Laturated environment, the B C rer.ains unaffected below 4

600*F (Ref. 1). ~ The material in the foem of 3 02 3 "ill ##*"L" I" .

its present form at the c.;pected oporating conditions. If mois-tute levelu weie to exceed 1000 ppa, cdditional B 0 m it be 23 converted to boric acid crystals. The existing boric ac'.d crye-tais will be affected by temperatures above 000*F, changing from II B0 3 3 2 as water is h en o M by the temperature ine ma s e .

Crystal formation or changes in chemical form of these crystals will not result in bonding of ballo. Crystals grown in the laboratory tcuts between balls had such negligibic band strengta that all balls brohe apart when the experiment tray was moved. Further cxe inar an at PSC indicates that no bridging van caused by any crystal formation c,n' the ballo. The quantity of IL,03& (0.15 wt % average) in insufficient to produco massive cryst al grot th between the 1 alls.

In su..rary, only the B 03 or the boric acid cryst . ? . can be affected ovcr the b or term ' r tetr;< ca ture m.d mol stare levels all a furtN' e M np*, in L .. c.e :a t s . d s . The t. a tal m .a n t i t ;. of 13'

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these materials was linited during man:Jacture through specifications to a small amount. It is therefore concluded that the behavior of the reserve shutdown material over the long term will be entirely satisfactory.

3. Effect of Crystal Grouth on Reserve Shutdown System Components The reserve shutdown systen consists of a carbon steel tank 6 in. in diameter and 8 ft long, a carbon steel plug at the top end, and a graphite rupture dish 't the botton end.

Tv0 separate 3/8-in. lines are connected to 90* elbous at the botton of the tank above the rupture disk. One line is used for pressurization of tha tank during reserve shutdown initiation.

The other is a vent to the PCF.V environment. Both lines are approxinately 15 ft long extend *ng up to the primary closure of the CEL. Cf concetu lo yi aI.hcr thc baric acid cither in th form of crystals or as a liquid kiauld have an adverse effect on the>c steel components.

Betuccn mid-January and March 10, 1975 the boric acid vapor could have been condensel on the steel to a soluble colation of boric acid and water or deposition of thenc crystals could have been by a dry transport process. Boric acid crystals in the absence of rater are :ta corrosive to steel. In the presenza of water _it is nildly cc.rrosive and could causa negligible surfaca pitting.

Tests conde.ited at GA San Diego confirmed the pittlnc node o f a t t:. k . They als- revealed that wet cryItals or a .colution of-bor

  • c acid rea::ted vJ th the steel au evidenced h-f t%2 bri'ht- ,

arance celor pi :uced in the corroda :t. At r??/ only "hi.te 8  %. k e . g s b w . D ,

depo"Itit.n Of CryGlulh 4:a 6 '

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t.iDn 0 Cit!' I!C p p 0 " d It! ". N d i :4 '; i .' ."" tl ? .wo l e ra C ! 01 o f L'.te 16 ti se aqg-

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steel; hence, corrosion of the steel apparently did n.it occur.

I t llauever, evcu if some pitting had occurred, the walls of thenc hoppers are approximately 0.200 in thick. Tha A5:!R Pressure E sc1 Code only requires a 0.090-in, wall for the pressure

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i rating of the container; therefore, it is concluded that, even j 1 .  ;

! if the surfaces were uetted with boric acid colution, the

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PART III - PERF0ldLU;CE OF REACTOR FOLLONIMG RESERVS Sill!CD0'.Gi SYSTEM DUMP )

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Part II of this report concluded that the reservu chutdown systems l I

would function as designed if and when needed. Part III assumes a dump of the reserve shutdown hoppers into the reactor core. The concequences of having boric acid crystals ac part of the reserve shutdown material have been evaluated since these crystals either as looae material or bonded to the reserve shutdown ballu will also be dumped into the cere.

The behavior of the material in the core, its removal from the core, and c the effecte of residual m.iterial on reactor components and core reacti.ity have all been evaluated. .

1. Behwlor of Renr rve Shutde in M iterint in Coro Normally, following a dump of the reserve shutdoun system, the balls are vacuumed out and returned to the hoppers. The vacuum system is designed to remove all these balls from a reserve shutdown channel. In the present situation, as described in Part I, it has been estimated that 12% of the reserve shutdoun balls have boric acid crystals on their surfaces. The behavior of these crystals chile in the reactor core is considered in this section.

1.1. Expert mutal Tests A series'af test.s have bacn performed at CA to daterr;1r.a the behavior of the RSS balls in the reactor core at different tenperatures. The experinental procedure and a detail rop.irt on the tests la procented in Ref. 2. A summary of 1.he luport: nit 18 31

1 test result is an follous:

(1) All balla ucre vicibly clean after the anneclu shoving that the surface cryntals had vaporized.

(2) The balic with crystalline deposita released tulee na cuch boron as the cican balls, indicating some degree of it crystalization within the ball.

(3) The boron released was not ec=perature dependent.

(4) Most of the boron which was relenced fron the balir van then nbuorbed by the graphite crucible used in the tcat.

The total average baron t ancporting was 5.5% of the

, Icachable boron.

(5) Ther: cre ::: ran:tiene involved when "M y 4a h m ad in a dry atac.phere: .

(a) Vaperization:  !!B02 (crystals) -* 1 :02 (6"")

(b) Dchydration: 2HB02 (crystal a or g .s) -* B 02 3 (""1 + "20 Reaction (a) accounta for the re::. oval of the crystals of f -

the curface of the balls, wherenc .caction (b) is occurrfag both vit!.'a the b 111 and withtu the surrounding grcrhtta.

1.2. Predf eted ' Jahr >10~ in Reactor -

rollowing a recerec'sht.td.nm syn te., dunp, th:: baronated graphite ball drop through a guide tute rhich in insert. ' le to the top 1.ayer of the cura. The balla t or tinue dcun a blir.

aphite clat. ml machine ' in the control ro.! fuel an 1 railcetcc h w he<
ee t h..ved f rm th.
e

! N ;u:m t i ty o f t+:u r f m.a c-  : t:= a t M G 8 '- " -0.15 n,; !:, , vhi c.h , d i. 2 ne ef ts t .n .> ch.m i ca l lin a" . -

f :.h e G. 01' ; .

19

~

elenenta eventually filling it. As F'ternJaed earlier, arproxi-raately 12% of the bc 's hava a crystal 11ue deposit of II 3 3B0 a 11B0 on their surfaces. The remaining balls have cor.c subcurface 2

11U0 or 11 m temperature in tb core C ewntually 7 3 M3 .

convert all of obe II 3M 3 to E0 2. A t c sur ace 0 2" I volatili::o and dif fuse into the graphite, while nome of the sub-surface !!B0 2 will v latilisc and the remainder will be converted bach to B,0 and re M n in th ball. De rate of this procens is 3

temperature dependent and at louer temperatures core of the !!602 will remain on the surface or in the subsurface of the ball.

Any loose boric acl- crystals in.the hopper will also be dumped into the cora and the sa.mc reactions would occur to this matcrit1. In the event that the temperature is not sufficiently (

hInh and these crystala are not completely vacuuz.cd out, then they evcntually volatilice as the reactor temperature is increased ano diffuse 1.au iue p @ ite. ,

The con:.cquencen of thic borsn transport frca the RSS b::lla to the core graphite is discussed in Sections 2 and 3, 1.3. Stm Distilj ation of Enron in the reactor, any B 0 left in the r,r ..hite ccre after 23 dropping the La]1s t:,,uld remain final ratil a stean ingre ;s event occurred (in which case the reacte wou d be shut down). At . .

tempere>nres belov about 400*C, the water vapar would ennvert the n.30 to HOO, and slouly .oiatiline the boron from tha core. T' e

.3 j r

boton t.ould terJ to conden: 2 ao l'.PO., o r II..,BO.3 on cooler ser acca in the cirecit.

The rat e of r,uch eam talat.ination .is .".a cc:surcl in anne earl-. pcri.aeats at Gli. In tha.m :: . burnt 7d pra, nit.-

. .:cinena hm:im hn.: in " 0 . coat at :re enpc ed t., f 1.n '

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l TASIA 3 STE.UI DISTILLATIO:: OF BORON (a) FROM E0 RATED GRAPillTE SPFC':lS::J(b)

Temperature "20 Presst:re Boron Dist',lled

  • C *F (atu)

(% Leachable B/br)(c) 260 500 0.03 1.5 0.30 '2.5 173 3' 0 0.03 0.4 121 250 0.03 0.1

/')

'" Volatile boroa species is either libO 2 I'3UU 3' (b)Specinens vero chunkn, 25 to 50 g cach containir.3 100 to 1000 ppa leachable boron (3 0 )*

23 (c)The rates given are initial rates. "'he boron release una found to be dependent on TE e~whi.ch sut*esta a diffusion controlled procer . Thus, at 1cnc,cr times the fractional release rates vould decrease, il L_______________________

tm *)

Q, ,

The results in Table 3 nhou that the proce.3 of utean distillation of volatile boron from graphite in relatively slow.

Dr?pending on the temperature, geometry, and steau concentration, timeu of 100 t.o 1000 he would be required for 100% removal of leachable baron fren 0 aphite materials.

These long t.imes indicate that no sudden baron loss could occur during a steam leak. In addition llE0 cannot be distilled 3

at temperatures above about 400*C.

2. Reactivity Behavior of Core Fol! owin:: Reserve Shut down " car t.11 HemovaL The experimental results reparted in Section 1 and discussed te in detail in Ref. 2 show that not more than 5.5% of the boron leached from the balls u111 be absorbed by the core graphite when the reserve shutdown cystem is activated into a hot c.o re .

If we conservatively assume the entire 60 g of presently leachable baron per hopper is available at the time the reserve shutdoun systen is activated, then the total boron' that can be distributed into the core is 122 g. This represents a r.auinum core reactivity decrease of only 0.003 Ak uhich can be cc= pen.<ited by a control red group idjustn:*et of a.. proximately 1 ft of control rod group 2B, and uhich will disappear by nentcon capture during cuhneipient reactor operation. Under scr e suis equent Siph noicture condition in the primn ; j loop, it is powi ic that tEls boren coul be 1 _ched from tbc cerc; l'owever, this would be a siou procena and-the effect on reactor operation could'again be cenipanna ed by a n=all control rod adjunt mnt.

l .

Tit.? e l a t. a ;d i - n It Taile 2 (Ce i ' n 1!). rf gef. 2 nhaU t.h f t 1. ' . (hnn 1;. o f k.i<habia tocco e trangor* -1 t hrn.h the r e.l.: t i vo l y c h i - eait t e.;t e o in '

. In the 1 1. : t . > c . be atu.e of tbe ro]at: . ly 1 tre - i. c. i

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The presence of some boric c::lde crystals remain tog in the reserve shutdown holes of the core after removal of the balls b-j vacuuming will represer* a reactivity chaar,o considerably less than the 0.003 Ak discussed above and will have a negligible effect on cure reactivity. Volatization ci these crystals and rapid burnup (by neutron capture) of this residual boron would occur upon subsequent power operation and any effect on reactor operation vill be ne:;11gible. In the FSA't, Section 3.8.3.3, it is stated that the effect on reactor operation of even a few of the balla remaining in the core would be small.

3. Effect on Reactor !',terials The e::perimental results of Section 1 (Part III) indica-ted that most of the baron volatilized fru.a the balls could be ab o rbed by the core graphite. If, hovavar, some of the nbO w uld diffuse through the gre.iphite, it could enter the 2

helium coolant flou. In tha hot coolant it would eventually dehy.: ate to B 0 an 23 depos M en other reactor component surfaces.

The ,uantity of B 0 which conid ent:.r the coolant would be 23 extremely small. Houcver, nsuunin;; tha t it wao present, the 0 could be reconverted to beric acid following a m31sture 23 ingress. incrcCore, the effect of boric acid on variouc reactor r.a.terials has been considared.

3.1. ' r f ec t m "on n ' t D ' '...n.

Thar. uti t be na detrimental c. 'fects on t'. - alumir 1/.411 Ica cont ; Laiu ; cer; nie:, (such as !!atench, Com :t ' tu:a i na , : Lite.i fiber , E: ouool f Ib ) es a rcmult of int r elon uith Lac f -

acid -t ,ae ta r

  • hu' 'ove. n . r. ec . 7.r reactor op +st!n:

21

. s s

. .- - . T y

tenperatures, boric acid crystala will lose water of hydration t :. forn boric oxide, D,,(13, which < foes not in m aet w M tlic ceranics in either the solid or n:olten state.

In regard to tha latter, it should be noted that alumina is not particularly soluble in n:olten boric oxide, and the e is no satisfactory evidence for the existence of alt.alnum borate. Therefore, there will be no problen.; in the event b

boric oxide cones in contact with alumina at the operating temperature of FSV.

An with alumina, silica vill not react with boric oxide since silica is insoluble or only slightly soluble in fuc.I ho ric' oxide (.".e f. 3) . In a short cnperim nt, moltan boric oxide was heated in a vitreous-allica vcacel uithout any visiule ofr-cre n,3 the .fi ba Ph a u. d i a gr es (n.e f . / ) +. ne t e'.uu any

, conpounda for the pre:ence of small quantities of bcrie c::Sie .

In silica at upwards of 1400*C (2550"F). Ilovaver, when silica is in the presence of large quantitics of othe oxiden such as hariun or calcium, lot;cr nelting compounda are formed. This is not a probica in PSV since the concentration of these oxides is very low compared to the amount of silica.

3.2. Effect on he. rnr "'tvla Doric acid solutions are weakly acidic with a p!! of about 6; as such it i.; only sl : -htly cerrc,>.i"e to tii- comicca .etals used for reactor components. ric ncic does not .enet wLin silver uh'ch in us:d in the.eireciator ,ealc. Porie acid c';...ald in the pr.'s w u of cate- at:1 ox;;.

  • nay proin:e n ni]d fora of pittJn: corronion 1: carbon et.91. In ti.e ahnce of c.:- . c. n ,'

e.g., h b ! l un . avi re mv.;n' , . < c reaion by e I thu . n .- liiir i c n

Y

f f ncid is negligibit: in the absence of both water and oxygen , i l (i.e., dry boric acid crystals), corrosion does not occur. It i

j may, therefore, Le concluded that the presence of borte acid i i

! in the renerve abutdown syster. and the small amount that n'r.ht i I

f enter the prinary coolant system will not cause denradation inf l l l the cysten's :..etallic component's. l 1  :

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REFERENCES I i

1. Abnermal Occurrence For Fort St. Vrain !!uclear Generatin;; Station Report io. 50-267/75/7-A Final, Appendix B-1.
2. Eurne tte, !*.. ,/J. Greemtood to R. !!crissette, "Results of Annecl Tests on FSV Reacrve Shutdcun Balls," Ccneral Atomic unpublished data, October 13, 1975.
3. I!cIlor, J. U., "A Comprahensive Treatise on Inorganic and Theoretical C:amistry," Vol. 5, p. 102, Vol. 6, pp. 447-8, Longmans, Green and Co.,

L 1 York, l ')5 2.

< l

4. Reser,II. R., ;d.,-" Phase Diagrn:c for Cerumists," The American Ceraraic Co.;1cty, Columbus, Ohio, 1904.

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, y TEST RT-351 Procedure

1. Position catch barrel assembly in llSF, west side.
2. Install CRD unit (S/11 to be established later) in the west port of the 11SF. ,
3. Connect RSD discharge pipe to barrel by positioning work stand platform in the llSF.

A rnnnner ruhing, valven. and IIe bottle to the RSD fittinn on top of*CRD unit (lle bottle pressure = 800 1 100 poig).

5. Close manual actuator valvo.
6. Open lie bottic valve.
7. Verify test setup and clear all personnel from IISF.
8. Quickly open manual actuator valve.
9. Observe / inspect results of test.
10. Replace ruptura dice and RS) balls,
11. CCT RSD unit of CRD.

TEST SETUP FOR RT-351 1/2-1l1 TUBlflG

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ACTUATOR VALVE t_ f CRD i

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l INSPECTION REPORT FRO >i RT-351 (RSD II0lTER AND BALLS FROM CRD 5/N 027 - RECION 22) R. J. NIRSCill (OCTOSER 4,1975)

Purpose:

To demonstrate that the presence of boric acid crystals (11B0 2 and ll.BO,)

3 a inside the RSD hopper did not affect its operability.

Description:

Details of the test description are given in RT-351. The CRD selected for the tcat contained boron graphite balls with 40 wt %

boron and a 9/16-in. 0.D. Three CRDs used 'in the outer core regions had been inspected visually prior to the test. All three showed r.Sout equal crystalline formation on the top and side surface of the hopper, indicating that it made no dif ference which CRD was used in the test. An. outer CRD assembly was selected beccuse of the higher weight percent boron content nna larger dirmeter bnlin The larger diareter balls would have a greater tendency to bond cad bridge.

Inspgetion Rectits:

Tha test was perforned with no unusual occurrence.

Foll ulng the test, both the hopper and balls were in.:pected visually.

The top and bottom of the hopper were inspected with a finshlight and mirror.

RSD hom2er

1. No traces of crystals were found on the bottom end. Apparently any crystals there had been bloun into the test receptacIc.
2. The only cryrtalline farcatlan preser in the hop; 2r ww on the top and sido surface near the top. The crystalline depoult on the filler plu.; and the top surface was esentially the same an it was prior to the test. ..aconable ( at: :.ite c uld be n.d.-

on Lhe aptantity of crysti. .

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3. The rupture disc assembly was as expected with no unusual marks.

RSD boron nraphite 1"ill-l

1. A significant number ef the balla still had cryntals on the t

surface. In fact, a rough estimate of the percentages showed them to be about the same as those obtained from previous hopper inspections. The crystals all adhcred to the bat.1 surface.

2. No evidence of loose crystals could be found but there was so much loose dust (black graphite) that it would have been hard to detect the crystals. .
3. A random sample was taken for later analysis and the barrel was bagged up for any future quantitative analysis, j

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