Crud Removal Performance with Ion Exchange Resins in BWR Plants

Transcription

1 Journal of Nulear Siene and Tehnology SSN: (Print) (Online) Journal homepage: Crud Removal Performane with on Exhange Resins in BWR Plants Keiihi OTOHA, Takeshi ZUM, Tadamasa HAYASH, Yoshitake MORKAWA & Hideki MURABAYASH To ite this artile: Keiihi OTOHA, Takeshi ZUM, Tadamasa HAYASH, Yoshitake MORKAWA & Hideki MURABAYASH (1996) Crud Removal Performane with on Exhange Resins in BWR Plants, Journal of Nulear Siene and Tehnology, 33:1, 52-61, DO: 1.18/ To link to this artile: Published online: 15 Mar 212. Submit your artile to this journal Artile views: 279 Citing artiles: 2 View iting artiles Full Terms & Conditions of aess and use an be found at

2 Journal of NUCLEAR SCENCE and TECHNOLOGY, Vol. 33, No. 1, p (January 1996) Crud Removal Performane with on Exhange Resins in BWR Plants Keiihi OTOHA, Tokyo Eletri Power Co., n.* Takeshi ZUM, Tadamasa HAYASH, Ebara Corporation** Yoshitake MORKAWA and Hideki MURABAYASH sogo Nulear Engineering Center, Toshiba Corp.Z* (Reeived February 13, 1995) t is needless to say that one of the most important roles of the ondensate demineralizer in Japanese boiling water reators (BWR) is to eliminate suh impurities during aidental ourrene of sea water leakage from ondensate ooling system. on exhange resins paked in ondensate demineralizer have also been expeted to derease rud, or orrosion produts (CP) in ondensate water in order to finally redue ativated orrosion produts (ACP) in the reator oolant loop. t is pereived that rud removal ability of a ondensate demineralizer has been improved year by year. And we all this phenomenon as Aging Effet. Typial property hanges of aged ation exhange resin onsisted of an inrease of water retention apaity and a hange of surfae texture. Based on these findings, we formulated a new onept and developed new gel type ion exhange resins for the better rud removal. The results from olumn tests using atual ondensate water for approximately three years and full sale test at an atual ondensate polisher from Sep showed that a gel type ation exhange resin having 6% rosslinkage produed exellent rud removal performane and low leahing rate of total organi arbon. KEY WORDS: B WR tgpe reators, orrosion produts, ativated orrosion produts (ACP), ondensate demineralizer, ion exhange materials, resins, aging effets, rosslinkage, rud removal performane, water retention apaity, new gel tgpe resin. NTRODUCTON Redution of oupational radiation exposure during annual inspetion and maintenane outages of Japanese boiling water reators (BWR) is the most important subjets for their stable and reliable operations. n BWR plants, radioativities, partiularly ativated orrosion produts (ACP) produed around reator ore have to be kept as low as possible to redue radiation dose rate around primary oolant iruit. Major part of orrosion produts (CP) in reator water is iron oxides, whih is alled (rud, introdued from feedwater and it holds indued radioativities. t is known that both the deposit amount of ACP indued from rud and the radiation dose rate level at the loation where ACPs are apt to deposit derease with the redution of rud input entering with feedwater to reator. t, therefore, is easily understood that the redution of the rud introdution into reator omes to an effe- * Uhisaiwai-ho, Chiyoda-ku, Tokyo 1. ** Haneda-mahimahi, Ohta-ku, Tokyo 144. %* Shinsugita-ho, sogo-ku, Yokohama 235. tive ountermeasure for the minimization of radiation soures. n order to meet this requirement, rud generated in the ondensate water and steam systems must be redued. n reent Japanese BWR plants, one of filtering systems suh as powdered resin type filter and hollow fiber filter has been installed in addition to the ondensate demineralizer, whih enabled to eliminate the impurity of ioni speies and at the same time to redue the rud in the ondensate water effetively ). Many BWR plants whih were onstruted in the early days, however, were furnished with only deep bed type ondensate demineralizers, and so rud removal effiieny in suh BWRs was limited at unsatisfatory level, sine the rud removal effiieny of ion exhange resins was not so high. n addition, this system required frequent bakwashings with water and air and hemial regenerations to keep its rud removal effiieny as high as possible, whih aused generation of large volume of radioative waste water and heavy workload. For these plants, therefore, the improvement of rud removal effiieny of ion exhange resins has been expeted. Our efforts to keep better rud removal by deminer- 52

3 ~~ ~ Crud Ftemoval Performane with on Exhange Resins in BWR Plants 53 alizer operation at the Japanese BWRs showed that the rud removal effiieny tended to reveal better values year by year, and we have alled this phenomenon as Aging Effet of ion exhange resins( ). Our studies on this phenomenon revealed that it was mainly due to the irreversible swelling of the ation resins by oxygen dissolved in the ondensate water. The typial hanges in properties of the aged ation resins were the inrease of water retention apaity, the hange in surfae texture, et. Based on these results, we proposed a new onept on the mehanism of rud removal and developed new gel type ion exhange resins for the better rud removal. As a result of the hot olumn tests at an atual BWR plant, the new gel type ation exhange resin with 6% rosslinkage ombined with new gel type anion exhange resins developed for ombination with new ation resins indiated exellent rud removal performane ompared with the aged onventional gel The present paper desribes the results of the hot olumn tests on the new gel type ion exhange resins for more than two years and the results of their real-size, demonstration tests in an atual ondensate polisher of a BWR plant.. EXPEUMENTAL 1. Resin Samples nrease of water retention apaity was one of the typial hanges in properties whih were revealed in the aged ation resins. This finding suggested that the ontent of rosslinkage reagent, namely divinylbenzene (DVB), might play an important role of rud removal proess of ion exhange resins. Therefore, we had to try first to make sure of the relationship between rud removal effiieny and rosslinkage of fresh onventional gel type ation resins. As a parameter of ontent of DVB in ation resins, the fresh onventional ation resins tested in this experiments were three kinds of ation resins, whih ontained different three values of DVB % as rosslinkage, supplied by The Mitsubishi Kasei Corporation. The values of rosslinkage to be tested were equivalent to 4%, 6% and 8% of DVB having the ommerial names of DAON SK14, SK16 and SKlBN, respetively. And an anion resin, DAONSAlOBN, was mixed with these ation resins in order to ompensate the effet of rud removal performane played by anion resins. A mixture of onventional ation resin SKlBN and anion resin SAlOBN used for approximately 1yr in the ondensate water at an atual BWR plant was also tested as a referene to ompare to rud removal performane with the other resins mentioned above. New gel type ion exhange resins used in this study were ETR-C, CRX-2 and CRX-3 for ation resins and ETR-A for anion resins. These resins, our newly developed produts, were manufatured on trial base by the Dow Chemial Company in the United States. Table 1 shows the speifiation of the ion exhange resins tested in these experiments. The resin properties were measured about the water retention apaity, <-potential and speifi surfae area. 2. Column Tests by Condensate Water Using the test olumn unit onneted to a ondensate water line in a BWR plant, the performane test on rud removal were first studied for more than two years. Figure 1 shows the shemati diagram of the test olumn unit. This unit was installed in a deep bed type ondensate polishing bay in a turbine building of a plant. The test unit onsisted of five olumns whih were made of stainless steel pipe of 5 mm inner diameter and 1,4 mm effetive height. Cation and anion resins to be tested were mixed and settled in the olumn. Volumes of ation and anion resins Table 1 Sample resins in experiments Cation resins Brand XLt(%) Anion resins SK14 4 Conventional SK16 6 SAlOBN SKlBN 8 Aged SKlBN 7 Aged SAlOBN ETR-C 6 New gel CRX-2 8 ETR-A CRX-3 1 txl(%): Perentages of divinylbenzene (DVB) P : Pressure indiator F : Flow indiator MF: Milipore filter EP : on exhange paper TO HOT WELL) DSCHARGE) T :Thermometer FQ :Volume indiator LS :Level swith Fig. 1 Shemati diagram of test olumn unit VOL. 33, NO. 1, JANUARY 1996

4 54 K. OTOHA et al. to be mixed in eah olumn were 1,22 and 756m3 respetively, and the resulting bed depth of eah olumn was 9mm in height. This ratio of ation and anion resins is equal to that of the atual ondensate demineralizers, whih is designed based on GE speifiation for ondensate demineralizers. These five test olumns were operated in the ondensate water of 18 m/h linear veloity to simulate atual ondition of the ondensate polisher operation in Japanese BWR plants. Crud onentrations in the influent and effluent of the olumns were measured through whole test period. Samples for the measurements were olleted on Millipore membrane filters of.45pm in nominal pore size and onentrations of metal elements were determined by X-ray fluoresent spetrosopy and/or atomi absorption spetrosopy. After every test run, resins were taken out of the olumns and the amounts of rud olleted on the resins were analyzed by the proedure shown in Fig. 2. n the figure, Crud Q1 is the amount of rud deposited loosely on boundary layer between the resin surfae and water flow. We named it Boundary-Deposited Crud, whih was easily stripped off by the ombination of air srubbing and water bak washing in the separation proess of mixed resins after the period of test operation. Crud Q2 is the amount of rud absorbed tightly on the resin surfae. We named it Surfae-Absorbed Crud, whih was flaked off by a ultrasoni vibration fore of about 1 W/m2. And rud Q3 is the amount of rud diffused into resin matrix as ioni form or small partile rud. We named it Matrix-Diffused Crud, whih was extrated by hot hydrohlori aid of 2% after ultrasoni leaning. After this olumn test, the new gel resins were paked in one of ondensate polisher vessels of a BWR plant and the removal performane of rud was monitored. 3. Full Sale Test in Condensate Polisher Figure 3 shows the shemati flow diagram of an atual ondensate polisher in whih this test was introdued. The demineralizer tank is a spherial vessel with ARSCRUBBNG RESN BACKWASHED i_ri + 3 ULTRASONC Lk : : : CLEANNG RESN CLEANED Fig. 2 Chemial measurement of rud iron olleted on resins PFLTRAT~ONHF~ ANALYSS] 4 HEADER PPE (EFFLUENT4 REC~RCU~T~NG PUMPS DT: Deminaralizer tank, RS: Resin strainer (trap) The test was onduted at the No.7 demineralizer tank (#7DT). Fig. 3 Shemati flow diagram of the test at a deep bed type ondensate demineralizer in a Japanese BWR plant 2,8 mm in inner diameter. The ation and anion resins to be tested were mixed and settled in one of the demineralizer vessels, where eah volume of the ation and anion resins was 4.2 and 2.6m3, respetively, and the resulting bed depth was 9 mm in height. The ondensate water was passed through the demineralizer tanks at linear veloity of 18 m/h, the flow rate of 635 m3/h. The rud iron onentrations in the influent and effluent of the demineralizer vessel were measured in the same way as in the olumn test and the flow rate was also monitored. Whenever the rud iron onentration in the efauent showed the tendeny of apparent inrease or the flow rate dereased to a speified value, the resins were isolated from the ondensate stream and bakwashed. n addition, test resins were periodially sampled and the olleted rud were measured for their hemial forms and quantities. Based on the measurement results, the optimum frequeny of bakwashing and hemial regeneration for the new gel resins were determined from the standpoint of the redutions of workload and volume of radioative waste water. J. EXPERMENTAL RESULTS 1. Aging Effets on Crud Removal Effiieny Some properties of ion exhange resins are generally governed by the degree of the rosslinkage of DVB ombined hemially to the ation resin matrix, espeially the water retention apaity of the ation resins. Figure 4 shows the relationship between the water retention apaity and DVB ontent of the onventional ation resins. t shows the inrease of water retention apaity from the original value of 55 to 58% for 8yr usage. Moreover, sine the water retention apaity of aged ation resins used for about 8yr was equivalent to around 58%, it is thought that the aged ation resins may orrespond to approximately 7% DVB ation resins as shown in Fig. 4. t is assumed that the inrease of water retention apaity was aused from the fat that the derease of rosslinkage in the aged ation resins ourred due to JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

5 Crud Removal Performane with on Exhange Resins in BWR Plants 55 v) K m, ation resins :Convenbonal abon resins i 1, /,, DVB of ation resins 17' Fig. 4 Relationship between divinylbenzene (DVB) and water retention apaity of ation resins so-alled irreversible swelling of resin bead matrix by gradual oxidization for 8 yr with dissolved oxygen in the ondensate water('). At the same time, a series of olumn tests were performed with ombinations of onventional ation resins of different DVB ontents and onventional anion resins. Figure 5 shows the typial rud breakthrough urves obtained from the test period, while rud iron onentration in the influent stayed at approximately 2 to 25 ppb. n the ase of a ombination of fresh ation and anion resins, DAON SKlBN and SAlOBN, rud iron onentration in the effluent was kept at 7 ppb only for one day, then inreased to 9 ppb. The seond test with a ombination of the aged DAON SKlBN and SAlOBN went fairly good whih nfluent OEffluent of SKlBNEAlOBN v Effluent of AGED SK1 BN/SAlOBN A Effluent of SK16EAlOBN Effluent of SK14EAlOBN 1 n g 2. " Days of operation Fig. 5 Crud breakthrough urves from onventional ation resins ontaining different perentages of divinylbenzene (DVB) kept less than 1 ppb of rud iron onentration for the first 2 d, reahed then to 5 ppb and stayed in 5 to 6 ppb. The third ombination of fresh DAON SK16 inluding 6% DVB and fresh SAlOBN kept rud iron onentration at about lppb for the first 4d, then inreased gradually up to 4 ppb and stayed at 4 to 5 ppb. The fourth ombination of fresh DAON SK14 inluding 4% DVB and fresh SAlOBN showed almost the same trend as the third ombination test run. From the results of these blumn tests on onventional resins, the relationship between deontamination fators of rud iron by eah olumn and the ontent of DVB were evaluated. A urve in Fig. 6 learly shows that rud removal effiieny got better results by the derease from 8 to 6% of DVB. The operational experiene of the ondensate demineralizer at Japanese BWR plants has shown that the rud removal by aged resins tended to be improved in the ondensate water year by year, and we named suh a phenomenon as "Aging Effet" of ion exhange resins. Our experiene also showed that rud in the ondensate water had a slightly positive eletri harge and was easily absorbed on aged ation resins beause of negative harge of their surfae(3). t an be said that so-alled aging effet was aused mainly due to the gradual irreversible swelling of ation resin beads aused by the slight oxidation reation. The typial property hanges of the aged ation resins were identified as slight hange of the srathed surfae texture whih was observed by eletron mirosopy and an inrease of the water retention apaity indued by breakage of rosslinkage in the resin matrix as shown in Table 2. t was estimated that these hanges might inrease the surfae area of resin partiles to absorb rud on it Fig x L L - n 3-1 :Aged ation resins. Conventional ation resins Crosslinkage YO %: Deontamination fator is defined as follows: Deontamination fator (DF)=Ci,/COut (Ci,=Average rud iron onentration in the influent) (C,,t=Average rud iron onentration in the effluent) Effet of rosslinkage ontent represented by divinylbenzene (DVB) perentage in onventional resins on deontamination fator of rud iron onentrations VOL. 33, NO. 1, JANUARY 1996

6 56 K. OTOHA etal. Table 2 Properties of onventional and new gel resins WRCt XLtZ SAt3 Pot. t4 (% (% (m2g-l) (mv) Fresh Aged ETR-C t1 Water retention apaity measured by weight differene after during at 15 C for 16 h. (Refer to DAON MANUAL pubulished by Mitsubishi Chemial Company) Crosslinkage (DVB ontent) t3 Speifi surfae area measured by BET methods using Kr gas. t4 -Potential measured by eletrophoresis methods. and transform the struture of the ation bead surfae.- 8 o :nfluent :Effluent of aged SK1 BNEAlOBN Effluent of SKlOG/SAlOBN v, &Effluent Of ETR-CETR-A surfae and allowed it to diffuse into the resin matrix as ompared with onventional fresh ation resins. 2. Development of New Gel Resins for Crud Removal On the basis of above mentioned results, we have developed new gel resins, DOWEX ETR-C as ation resin and DOWEX ETR-A as anion resin, for better rud removal. Major properties of ETR-C was shown in Table 2. The main featrues are that ETR-C has about 6% rosslinkage, 2% lower than fresh onventional resins, and value has of 6 zeta times potential larger surfae as ompared area and with a larger onventional absolute. a - Q P C 2 al $ - al 3 a, a, so 2 Aged resin A : Conventional 8 1 al 5 7i 3. Crud Removal Performane by Newly Developed on Exhange Resins (1) Long Run Column Test Figure 7 shows the results of the olumn test with the atual ondensate water in order to demonstrate the advantages of the new gel resins, ETR-C and ETR-A, for rud removal performane to the onventional ones. This ombination kept rud iron onentration in the effluent less than 1 ppb though the test period, mostly far less iron onentration than by aged onventional resins whih had showed the inrease to 4ppb within 4 to 6d and saturated at 5 to 6 ppb all the time afterwards. Figure 8 shows the relationship between rud iron onentration in the effluent at eah saturated onentration level and perentage of rosslinkage in the onventional and newly developed ation resins. Those saturated rud iron onentrations were almost proportional to the perentages from 6 to 1% of rosslinkage in ation resins. Although the new gel resins and onventional resins had the same ontent of rosslinkage, the new resins revealed muh better results ompared with the Fig. 8 Effets of rosslinkage in ation resins on rud removal onventional resins. Figure 9 shows the results of the olumn test of the new gel resins for more than 65d. The rud onentration in the influent stayed at about 12 to 2ppb throughout the test period. The rud iron onentration in the effluent was 1 ppb or less through the whole test period. More preisely, it was kept at.5ppb or less during the most of the test period, while it was 2 to 4 ppb in the ase of the aged resins used as the referene. The olumn was air-srubbed and water-bakwashed every twenty days before the third bakwashing during the whole test period. t was to simulate the same intervals of air srubbing and bakwashing of the atual ondensate polisher. These first three runs showed good performane as expeted, that is,.5ppb or less in the effluent. After the fourth test run, muh longer duration tests of 4 to 8 d were made to onfirm the performane of the prolonged in-servie of the resins. t was found fairly easy to keep the rud level in the JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

7 ~ 3l Crud Removal Performane with on Exhange Resins in BWR Plants 57 7 NFLUENT. ' ' Days of operation Fig. 9 Crud removal performane of new gel resins by long run olumn test effluent at lppb or less for approximately 3d only by bakwashing the resins every 6 to 7 d and without hemial regeneration. Afterwards then the rud levels in the effluent inreased slightly. Then, in addition to the bakwashing, hemial regeneration was first made to the new gel resins and rud onentration was restored down quite easily to.5ppb or less. After then, the resins ontinued to show the same rud removal performane even after the umulative test period of some 65 d. Figure 1 shows the hanges of rud removal effiieny and differential pressure for 76 d without a bakwashing and a hemial regeneration. The effluent rud iron onentration was almost kept less than 1 ppb through the rest of the test period. Through these long test operations, the differential pressure of this olumn......" i 7- rose up from.9 kg/m2 of the initial lean ondition to 1.5 kg/m2 at the end of the test run, revealing the inrement of only.6 kg/m2. n this ase, the total amount of loaded rud irons in this olumn was about 6.8 kg as Fe. This value is 3 to 7 times higher ompared with onventional gel resins. The rud loading rate of this new resins was estimated as 47 g/m3-mixed Resin/d. (2) Results of Full Sale Tests in Condensate Demineralizer A trial run of new gel resins in ondensate demineralizer of a BWR plant was arried out to prove the rud removal performane. At the same time, hanges of the properties of the resins were also examined. Figure 11 shows the results of the rud removal performane of new gel resins. As shown in the figure, the effluent rud onentration was kept at.5 ppb or less through the entire test period and.2ppb or less during the most of that period, while that of the onventional resins used for 12 yr with suffiient "Aging Effet" inreased to 1 ppb within 2 d. At the time when the rud level in the effluent exeeded.5 ppb, the new gel resins were bakwashed using water and air. t was easy to keep the effluent rud levels of the new gel resins approximately.5 ppb or less only by bakwashing every 6 d without hemial regeneration. Another important fator to be evaluated is the amount of total organi arbon (TOC) released from resins during operation. Most of ion exhange resins 4,,,,,,,,, [Conventional resins used for 12 y].~ Q Q ' n '1 ~ 1 :Bakwashing ;.'""" 7. - T.o a "..." i..".. Bakwashing._ , 1, 1, 1, 1,,, ~, 1, 1.. L [ + 1 :Bakwashing.G W 1 - Days of operation Fig. 1 Changes of rud iron onentration and differential pressure (AP) in new gel resins olumn Days of operation % : Demineralizer tank Fig. 11 Crud removal by new gel resins in atual tests VOL. 33, NO. 1, JANUARY 1996

8 58 K. OTOHA etal. are apt to release some amount of organi ompounds most of whih were left in resin matrix during resin prodution. t is needless to say that the amount of TOC released from resins should not exeed a ertain value beause the organi ompounds introdution into the reator auses the inrease of eletri ondutivity in reator water. Before atual test, leahing harateristis of TOC from the new resins were tested on the laboratory sale. TOC leahing harateristis were evaluated from a omparison of the umulated amount of TOC leahed from the mixed bed (volume ratio between ation and anion exhange resins orresponded to 1.7/Z) during 2d in pure water. The amount of TOC is 1.5 g-toc/m3-resin from the new gel resins, 2.4g-TOC/m3-Resin from the fresh onventional resins and 6 g-toc/m3-resin from the onventional resins used for 12yr. So, the TOC leahing harateristis of the new gel resins were onfirmed to be better than the onventional resins. For all resin properties, signifiant hanges were not observed and so the results onfirmed that the new gel resins an be reliably used in BWR ondensate polishers. Trae amount of TOC leahed from the new gel resins is onfirmed to be equivalent to the onventional resins. This indiates that no leahable problems would be enountered during BWR plant operations with the new gel resins installed in the atual ondensate demineralizers. V. DSCUSSON 1. Mehanism of Crud Removal Major rystalline strutures of rud iron speies deteted in the BWR ondensate water are Fe34, a-fe23, a-feooh, y-feooh and amorphous iron speies. Among these iron oxides, Fe34, a-fe2o3 and a-feooh are rystallized well and are stable in aidi atmosphere, so that they easily deposit on the so-alled boundary layer between resin surfae and water in the demineralizer vessels(*). On the ontrary, y-feooh and amorphous iron speies are not rystallized enough and are not stable in aidi atmosphere. Therefore, when these hemial speies were immersed in more aidi surfae atmosphere of the new gel ation resins and aged ones ompared with the fresh onventional ation resins, they are easily absorbed on the resin surfae and diffused finally into the inner resin matrix. Figure 12 shows hemial omposition of iron oxides found in the influent and the effluent of the olumns. The amorphous iron speies were diffiult to be removed by the onventional fresh resins. The rud removal effiieny of the amorphous iron by fresh SKlBN and SAlOBN was up to 64% and that by the aged SKlBN and SAlOBN rose to 77% due to so-alled aging effet of ation resins. On the other hand, the rud removal effiieny of new gel resins indiated the exellent value of more than 98% for all kinds of iron speies. The amounts of rud irons aptured in various kinds of resins were separately analyzed and lassified as Boundary-Deposited Crud, Q1, Surfae-Absorbed Crud, Q2 and Matrix-Diffused Crud, Q3. The one example of the measurement results were shown in Fig. 13. The aged onventional resins indiated the higher removal effiieny for Q1, Q2 and Q3 than the fresh resins. Furthermore, the new gel resins indiated the superior rud removal effiieny to the fresh and aged onventional ones. The data obtained here suggests that the new gel resins have muh better apability to adsorb rud as Q2 and to diffuse it into the resin matrix as Q3. This interpretation meets the hypothesis fairly good that almost all rud iron oxides of FesO4, a-fe2o3, a-feooh and y-feooh are aptured as Q1 at the boundary around CR Cation resins, AR: Anion resins Fig. 13 Classifiation of rud aptured by various resins nfluent (2.4 PPb) Effluent of SK BNSAOBN (7.2 PPb) Effluent of Aged SK BN/SAlOBN (4.63 PPb) Effluent of ETR-C/ETR-A (.28 PPb) Fig. 12 Removal effiieny of 5 kinds of iron oxide ompounds by various resins JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

9 Crud Removal Performane with on Exhange Resins in BWR Plants 59 resin. On the other hand, rest of a-feooh, y-feooh and major amorphous rud iron are adsorbed as Q2 and Q3 on the surfae and diffused into matrix of ation resins. The mehanism of rud removal by the aged ation resin, we presumed, is shown in Fig. 14. While the rystalline iron oxides are aptured well as Q1 by all kinds of resins, there are muh differenes in the removal effiieny of non-rystalline rud between the different kinds of resins. The exellent rud removal effiieny of the new gel resins having with the larger surfae area and lower rosslinkage is understood well from the behavior of rud adhered on, around and inside of resin beads. Figure 15 shows the variation of the quantity of the rud aptured on the new gel resins during the ondensate demineralizer test. n this test, the olumn was washed by bakwashing treatment every 2 to 8 d and Q1 was measured eah time. The deposition rate onstant of Q1 was alulated as.4 g/l-cation Resin (CR)/d during the test. The deposition rate onstant of Q2 was.5 g/l- CR/d and it was twie to three times higher than that of the aged onventional ation resins. And the amount of Q3 tended to aumulate in ation resin during umulative operation time without hemial regeneration, beause it ould not be removed from the matrix by WATER FLOW.- WATER FLOW 4 WELL-CRYSTALLZED CRUD 477 v : NON-CRYSTALLZED CRUD SWELLNG BY-OXDATON. NCREASE OF SURFACE AREA -NCREASE OF ADSORPTON STE. LOWER CROSSLNKAGE -EASY DFFUSON NTO MATRX AGED Fig. 14 Aging mehanism of rud removal by ion exhange resins Days of operation B: Bakwashing, C/R: Chemial regeneration Fig. 15 Change of rud aptured by new gel resins during ondensate demineralizer test water bakwashing alone. During the test, the amount of Q3 in ation resin inreased at the onstant rate of.3g/l-cr/d, whih was 1 to 2% larger than that of the aged onventional ation resin. Moreover, it was onfirmed that one-half to one-third of Q3 in the ation resin was able to be removed by hemial regeneration. After the olumn was in operation for approximately 3 d without hemial regeneration, Q2 nearly reahed an equilibrium value and its inreasing rate beame fairly slow. And, just at the time, the rud onentration in the effluent began to inrease slightly. This phenomenon is thought to be aused by the following reasons. Crud irons, espeially amorphous iron speies, are first adsorbed on the resin surfae and then diffused into the resin matrix. Further looking at the adsorption and diffusion proess of this rud removal, it is onsidered that Q2 on the surfae area of the new ation resin plays an important role in retaining amorphous rud in the aidi environment adjaent to resin surfae, to dissolve them into some ioni forms and to diffuse them into inside of ation resin partiles. After the long test operation without hemial regeneration, Q2 reahed a saturated value and rud leaked through the olumn. Approximately 4% of Q2 was removed by the hemial regeneration after bakwashing treatment. For hemial regeneration of the ation resins, sulfuri aid is used in BWR plant and the ability of sulfuri aid is enough to remove the adsorping ioni speies but it is not enough to remove the small partile rud. Then, the rud removal performane was reovered as before by hemial regeneration. Anyway, they are important to deposit Surfae-Adsorbed Crud on the resin surfae and to inrease adsorption area of resin beads, in order to retain amorphous rud around the surfae of the ation resin and to dissolve them to inorporate into the inside of resin partiles. 2. Evaluation on Optimum Frequeny of Bakwashing and Chemial Regeneration Conventional resins need frequent bakwashing and hemial regeneration to maintain the rud removal effiieny by keeping the resin bed lean. This is a problem from the standpoints of worker s load and volume of proess waste water produed. Sine the new gel resins have superior rud removal effiieny to onventional resins, one would expet to dramatially prolong the time intervals for both bakwashing and hemial regeneration and to redue the workload and the volume of radioative waste water. From the results of the ondensate demineralizer tests, it was onfirmed that the new gel resins required less frequent bakwashing, that was every 6 d to maintain the exellent rud removal performane. On the other hand, the onventional resins required the bakwashing every 2 d. t was also onfirmed that the hemial regeneration of the new gel resins was not required VOL. 33, NO. 1, JANUARY 1996

10 6 K. OTOHA etal. for about 4 yr beause the loading of the ioni impurities to the resins was very small. Table 3 lists the operational performane of the new gel resins when harged in a BWR ondensate demineralizer. As shown in Table 3, both frequenies of bakwashing and hemial regeneration and the volume of waste water generated were greatly redued ompared with the onventional resins. 3. Life of Resins We have experienes to have used onventional resins for about 1Oyr as the ondensate demineralizer in Japanese BWR plants beause the rud removal effiieny of the resins was improved year by year and it was very effetive for reduing rud from the ondensate water for the purpose of dereasing radiation dose rate. Small adverse effets, however, often arose owing to suh a long term operation. Degradation in the ation resins was deteted mainly as the inrease of the water retention apaity and the release of leahables. This phenomenon was thought to be aused by oxidation with dissolved oxygen in ondensate water and oxygen in srubbing air while bakwashing. n order to keep the quality of the reator water pure, it is important to understand the leahing harateristis of the resins. Espeially, the leahables of the ation resins ontaminate the surfae of the anion resins and let the funtions of the anion resins deteriorate, whih effets beome greater year by year. So that, in order to predit the life of the new gel resins, the aelerating tests of the resins by oxidation with oxidant, H22 were arried out. Then, the operating time of the resins was simulated by the oxidation time with HzO2 based on the variation of the water retention apaity of the onventional ation resins during usage. The simulation methods of oxidation are as follows: (1) to dope ferrous ion, (2) to soak in H22 solution at 5 C for.5 h as 1 yr usage simulation, for 2 h as 3 yr usage simulation and for 3 h as 5 yr usage simulation. Figure 16 shows the relationship between the simulated operation time and the leahing rate of TOC from the resins. The leahing rate of TOC of new gel resins simulated for 5 yr usage is equal to that of aged onventional resins used for 1yr. t is shown that the new gel Table 3 Effets by appliation of new gel resins Condition of operation Conventional New gel Freauenv Everv 2 d Everv 6 d Relative Bakwash amount of waste 1.5 Every 3 Non regenera- Frequeny or Gm tion for 4yr Relative regeneration amount 1 of waste resins with a little less rosslinkage ontent are easier to deteriorate than the onventional resins. However, we estimated that it was no problem to use the new gel resins for 5 yr beause the onventional resins ould be used for 1yr. Crud removal effiieny of the new gel resins after 5 yr use was onfirmed also by a simulation test. As mentioned before, the new gel ation resin with 6% rosslinkage has muh better apability to diffuse Q3 into resin matrix than the aged onventional ones. n order to simulate the ondition of the aged ation resins saturated with rud iron, we doped 15 and 25g ferrous ions as FeZ+/Z-Resin to the fresh ation resins as preonditioning, sine the aged ation resin matrix used for about 8yr ontained 15g of Q3 rud as Fe/Z-Resin. Then we onduted the olumn test to onfirm rud removal effiieny of these iron-doped ation resins. Figure 17 shows the effet of intentional ferrous ion doping on the rud removal performane of new gel ation resins. n this figure, the vertial axis of the right side indiates the iron onentration in the effluent whih was determined by apturing rud with ion exhange filter papers after a Millipore filter, and we all this iron omponent as the filtrate rud iron. On the other hand, the vertial axis of the left side indiates the rud iron onentration in the effluent of the olumn aptured Ln. e.1 ar F. a.- D.5 Level of resins used for 1 y Simulating operation years Fig. 16 Results of aelerating tests on new gel resins - s : Crud iron A : Filtrate rud iron,:-r--_-:-.- -._ F n z a, s! 8 8 % Amount of doped Fe2+/ g-cr Fig. 17 Effet of doped Fe on rud removal by new gel resins - JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

11 Crud Removal Performane with on Exhange Resins in BWR Plants 61 on a Millipore filter. From the figure, it was onfirmed that the rud onentration in the efruent were.5 ppb regardless of the amount of the pre-doped ferrous ion, while the filtrate rud iron onentration slightly went up with the inrease of the ferrous ion. 4. Cost Benefit Evaluation For the redution of oupational radiation exposure, reduing rud in the ondensate stream is one of the most effetive measures. The appliation of the new gel resins for rud removal is a useful method solving this subjet. We estimated the ost benefits of adopting this method ompared with the onventional resins about the following items; (1) the ost of the resins inluding disposal ost after use, (2) the ost of remodeling of the present hardware, (3) the ost of the operation of ondensate demineralizer and (4) the ost of the treatment of the radioative waste water. The prime ost of the new gel resins is almost half of that of the onventional resins. As the new gel resins required the frequent replaement, the ost of the resins was the larger than that of the onventional resins. But the osts of remodeling the hardware and treatment of the waste water were smaller than those of the onventional resins. So, it is estimated that the appliation of the new gel resins is the most effetive from the viewpoint of the total ost. V. CONCLUSONS The evaluation was arried out for rud removal harateristis of several ion exhange resins. Based on the evaluation, the following onlusions ould be made. Crud removal by ion exhange resins depends on the degree of rosslinkage ontained in ation resins. t inreased with dereasing rosslinkage. Then, the new gel resins whih were newly developed based on our findings on the mehanism of rud removal showed superior rud removal performane to aged onventional resins. t was found, in addition, that the leahing rate of TOC from the new resins was very small, whih meant the use of the new resins would ause no adverse effet on reator water quality. Furthermore, it is expeted that the use of the new gel resins in plae of onventional resins will greatly redue the frequenies of bakwashing and hemial regeneration and the volume of radioative waste water. ACKNOWLEDGMENTS The authors wish to aknowledge the tremendous efforts at The Dow Chemial Company who manufatured the new gel resins. And the authors also wish to thank the tehnial staffs at the plant site for their assistane. -REFERENCES- Amano, O., et al.: Pro JAZFZnt. Conj Water Chem. Nul. PowerPlants, Apr , p.85 (1991). Hirahara, Y., et al.: Pro JAZF Znt. Conj Water Chem. Nul. Power Plants, Apr , Vol.11, p.694 (1988). nami,., et al.: Pro JAZF Znt. Conj Water Chem. Nul. Power Plants, Apr , p.462 (1991). Morikawa, Y., et al.: Pro. 5th Znt. Water Conf, Pitts., PA, ZWG89-51, (1989). zumi, T., et al.: ibid., ZWG zumi, T., et al.: Pro. 52nd nt. Water Conf, Pitts., PA, WC91-57, (1991). Morikawa, Y., et al.: ibid., ZWG Otoha, K., et al.: J. Them1 Nul. Power., 42[12], p (1991), [in Japanese]. VOL. 33, NO. 1, JANUARY 1996