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Pressure vessel surveillance at commercial light water reactors using solid state track recorder neutron dosimetry
Nucl. Tracks Radiat. Meas., Vol. 15,Nos. 1-4, pp. 491-494,1988 Int. J. Radiat. AppL Instrum., PartD
0191-278X/89$3.00+ .00
~ 1989PergamonPressplc
Printedin Great Britain
PRESSURE VESSEL S U R V E I L L A N C E A T COMMERCIAL L I G H T W A T E R R E A C T O R S U S I N G SOLID STATE T R A C K R E C O R D E R N E U T R O N DOSIMETRY F. H. RUDDYAND J. C. SEIDEL Westinghouse R~D Center 1310 Beulah Road P i t t s b u r g h , PA 15235-5098 USA
Abstract - The accumulation of n e u t r o n dose by the p r e s s u r e v e s s e l of a l i g h t water r e a c t o r r e s u l t s i n r a d i a t i o n damage i n the form of s t e e l e m b r i t t l e m e n t . I n order t o a s c e r t a i n the sa~e o p e r a t i n g l i f e t i m e of the r e a c t o r p r e s s u r e v e s s e l , the neutron dose must be monitored. S o l i d s t a t e t r a c k recorder n e u t r o n dosimeters have been developed f o r pressure v e s s e l s u r v e i l l a n c e doslmetry a t commercial power r e a c t o r s . To date a t o t a l of more than 200 n e u t r o n dosimeters from seven d i f f e r e n t power r e a c t o r dosimetry exposures have been analysed, and more than 150 a d d i t i o n a l dosimeters are c u r r e n t l y deployed. The t e c h n i q u e s f o r c a r r y i n g out t h e s e measurements and t h e i r r e s u l t s w i l l be discussed. 1. INTRODUCTION Radiation dam~e i n the form of s t e e l e m b r i t t l e m e n t r e s u l t s from the a c c u m u l ~ i o n of n e u t r o n dose by the p r e s s u r e v e s s e l of a n u c l e a r r e a c t o r . I n order t o ensure t h a t the p r e s s u r e v e s s e l behaves i n a n o n - b r l t t l e manner when s t r e s s e d under opermtlng, eu~n%enance, t e s t i n g , and p o s t u l a t e d a c c i d e n t c o n d i t i o n s the amount of p r e d i c t e d r a d i a t i o n damage t o the r e a c t o r v e s s e l must be known throughout i t s s e r v i c e l l f e . I n order t o c a l c u l a t e the amount of r a d l m t i o n damage, the cumulative n e u t r o n dose r e c e i v e d a t key l o c a t i o n s i n the p r e s s u r e v e s s e l must be known (Ruddy e t e l . , 1985). The development and deployment of S o l i d S t a t e Track Recorder (SSTR) n e u t r o n dosimeters f o r n e u t r o n doslmetry r e l a t e d t o l i g h t water r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e have been d e s c r i b e d a t p r e v i o u s meetings i n t h i s s e r i e s (Ruddy e t e l . , 1986; Ruddy e t a l . , 1984; Ruddy e t a l . , 1983). SSTR n e u t r o n dosimeters f o r r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e have been deployed i n the r e a c t o r c a v i t y r e g i o n of o p e r a t i n g commercial power r e a c t o r s (Ruddy e t a l . , 1986) and n e u t r o n doslmetry r e s u l t s ( i n the form of measured n e u t r o n - i n d u c e d f i s s i o n r a t e s ) have been o b t a i n e d from a t o t a l of e i g h t o p e r a t i n g c y c l e s a t seven d i f f e r e n t r e a c t o r s . 2. SSTR NEUTRONDOSD~ETRY Neutron doses may be monitored p a s s i v e l y by deploying SSTR n e u t r o n dosimeters a t key l o c a t i o n s a d j a c e n t to the p r e s s u r e v e s s e l . P r e s e n t p r e s s u r e v e s s e l n e u t r o n doslmetry r e l i e s on the placement of SSTR and r a d i o m e t r i c ( ~ n e u t r o n dosimeters i n the r e a c t o r c a v i t y , which i s the a n n u l a r gap immediately o u t s i d e of the r e a c t o r p r e s s u r e v e s s e l . Since the n e u t r o n f l u e n c e encountered by an SSTR n e u t r o n dosimeter d u r i n g an o p e r a t i n g cycle i s g r e a t e r than lOlSn/ca9, u l t r a low-mass f i s s i o n a b l e d e p o s i t s must be used (Ruddy e t e l . , 1986; Ruddy, 1986). T y p i c a l mass requirements are i n the nanogram to subplcogram range. These f i s s i o n a b l e d e p o s i t s are f a b r i c a t e d and c a l i b r a t e d under clean room c o n d i t i o n s , and, ~ t e r exposure a t a commerci~ power p l a n t , are r e t u r n e d t o a c l e a n room f o r disassembly and a n a l y s i s (Ruddy, 1986; Ruddy and S e i d e l , 1987). The f i s s i o n a b l e d e p o s i t i s reused i n subsequent c y c l e s , and the SSTR (mica) i s etched t o r e v e a l t h e n e u t r o n - i n d u c e d f i s s i o n t r a c k s . These t r a c k s are counted with the a i d of a c o m p u t e r - c o n t r o l l e d , automated t r a c k c o u n t e r (Ruddy e t el., 491
492
F. H, RUDDY and J. G. SEIDEL
1987). The s t e p s i n v o l v e d i n p r e s s u r e v e s s e l s u r v e i l l a n c e d o s l n e t r y are s u a a a r i s e d i n F i g . 1.
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3. ACCURACY~ ~ AND CALIBRATION Accuracy Eoals f o r l i g h t water r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e r e q u i r e t h a t SSTR f i s s i o n r a t e s be determined t o an o v e r a l l a b s o l u t e accuracy of 2-5S. This i n t u r n r e s u l t s i n comparable accuracy r e q u l r e e e n t s f o r f i s s i o n a b l e d e p o s i t mass c a l i b r a t i o n s and f o r d e t e r m l n a t i o n s o~ t h e number of t r a c k s produced. R a d l o m e t r l c mass c a l i b r a t i o n s f o r u l t r a low-mass f i s s i o n a b l e d e p o s i t s (Ruddy, 1986) have been and a r e b e i n g v e r l t i e d through i r r a d i a t i o n s i n s t a n d a r d neutron f i e l d s a t t h e U.S. N a t i o n a l Bureau of S t a n d a r d s (Ruddy and S e i d e l , 1987; Ruddy and McCarry, 1988). These i r r a d i a t i o n s have e s t a b l i s h e d t h e a b s o l u t e accuracy of t h e d e p o s i t masses t o b e t t e r than 2.5~ and have shown t h e r e l a t i v e p r e c i s i o n o~ t h e mass d e t e r a i n a t l o n s o~ i n d i v i d u a l d e p o s i t s t o be b e t t e r than 3~.
P R E S S U R E VESSEL S U R V E I L L A N C E
DEPOSIT :#:1288
237 Np
3.63 x 10-9g
CAVITY IRRADIATION
NBS B E N C H M A R K IRRADIATION
Fig. 2.
NT
XS:X/4-GG
Comparison of t r a c k d e n s i t y d i s t r i b u t i o n s o b t a i n e d i n SSTRe exposed t o the same f i s s i o n a b l e d e p o s i t d u r i n g a c a v i t y dosimetry n e u t r o n exposure and a subsequent NBS benctmark f i e l d n e u t r o n exposure
493
494
F . H . R U D D Y and J. G. SEIDEL
Manual scanning has been shown to have an absolute accuracy of 0.88% (Roberts et al., 1984). The absolute accuracy of the Westinghouse R&D Center Automated Track Counter has been shown to be 1.88% (Ruddy et al., 1987). This computer-controlled optical microscope uses stateof-the-art image enhancement and pattern recognition techniques to identify tracks. The absolute accuracy was verified by comparisons with track standards in the range from 8 x 10 s tracks/cm 2 to 8 x 10 s tracks/cm 2. The track counting efficiency was found to be independent of local track density variations and the degree of track overlap over this range. Track scanning results are stored on a local microscope field-of-view by field-of-view basis on computer disks. Typical track scanning results are shown graphically in Fig. 2. Contour and isometric plots are shown as well as selected slices through the track count distribution. The two sets of plots correspond to results o~ irradiations of the same fissionable deposit in the reactor cavity region of a power reactor and, later, in a standard neutron field at the U.S. National Bureau o~ Standards (Ruddy and Seidel, 1987; Ruddy and McGsrry, 1988). 4. RESULTS AND qUALITY ASSURANCE Computer files such as those shown in Fig. 2 will be stored on a long term basis (40 or more years) to ensure long term tracibility of the reactor dosimetry measurements. Mass calibration files (see Fig. 1) are also stored on a long term basis. As a backup to the track scanning files, the SSTR itself is stored as a long-term record of the dosimetry exposure. 5. SUMMARY To date, a total of more than 200 SSTR neutron dosimeters from r e a c t o r cavity n e u t r o n dosimetry exposures have been analysed and a d d i t i o n a l exposures axe p r e s e n t l y i n progress. SSTR n e u t r o n dosimetry has proven t o be a r e l i a b l e and a c c u r a t e method f o r o b t a i n i n g n e u t r o n exposure data f o r r e a c t o r p r e s s u r e v e s s e l surveillance. Reactor cavity neutron dosimetry results to date (Ruddy and Seidel, 1987) indicate that in all cases where proper quality control procedures are used, uncertainties in the 2-5~ range are obtained. REFERBNCES I. Roberts, J. H., F. H. Ruddy, and R. Gold (1984). Optical efficiency for fission frz~ment track counting in muscovite solid s t a t e t r a c k r e c o r d e r s , Nuclear Tracks 8, 365. 2. Ruddy, F. H., J. H. Roberts, R. Cold, and C. C. P r e s t o n (1983). Application of solid state track recorders in light water reactor pressure v e s s e l s u r v e i l l a n c e dosimetry, Nuclear Tracks 7, 62-77. 3. Ruddy, F. H., J. H. Roberts, R. Cold, and C. C. P r e s t o n - ( 1 9 8 4 ) . Light water reactor pressure vessel surveillance dosimetry using solid state track recorders, Nuclear Tracks and Radiation Measurements 8, 275-280. 4. Ruddy, F. H., W. N. McElroy, E. P. Lippincott, L. S. Kellogg, R. Gold, J. H. Roberts, C. C. Preston, J. A. Grundl, E. D. McGarry, and H. Farrar IV (1985). Standardized physics-dosimetry for U.S. pressure vessel cavity surveillance programs, Fifth International ASTM-Euratom Symposium on Reactor Dosimetry, Coestha~ht, September 1984, D. Reidel Publishing Co., Dordrecht, 473. 5. Ruddy, P. H. (1988). Neutron dosimetry in high intensity fields: a review, Nuclear Tracks 11, 197. 6. Ruddy, F. H., J. H. Roberts, R. Gold, C. C. Preston, L. S. Kellogg, E. P. Lippincott, and W. N. McElroy (1988). Light w~ter reactor pressure vessel surveillance using reactor cavity solid state track recorder neutron dosimetry, Nuclear Tracks 12, 981. 7. Ruddy, F. B., and J. G. Seidel (1988). Sol~=d state track recorder pressure vessel surveillance neutron dosimetry at commercial light water reactors, Sixth ASTM-Euratom Symposium on Reactor Dosimetry, Jackson, Wyoming, June 1987, ASTM STP 1001 (in press). 8. Ruddy, P. H., A. E. Manhardt, and J. G. Seidel (1988). Analysis of s o l i d s t a t e t r a c k r e c o r d e r s with the Westinghouse R~D Center automated t r a c k c o u n t e r , S i x t h ASTM-Euratom Symposium on Reactor Doslmetry, Jackson, Wyoming, June 1987, ASTM STP 1001 ( i n p r e s s ) . 9. Ruddy, F. B., and E. D. McGarry (1988). ~ n c ~ k irradiations of ultra low-mass fissionable deposits (to be published).
0191-278X/89$3.00+ .00
~ 1989PergamonPressplc
Printedin Great Britain
PRESSURE VESSEL S U R V E I L L A N C E A T COMMERCIAL L I G H T W A T E R R E A C T O R S U S I N G SOLID STATE T R A C K R E C O R D E R N E U T R O N DOSIMETRY F. H. RUDDYAND J. C. SEIDEL Westinghouse R~D Center 1310 Beulah Road P i t t s b u r g h , PA 15235-5098 USA
Abstract - The accumulation of n e u t r o n dose by the p r e s s u r e v e s s e l of a l i g h t water r e a c t o r r e s u l t s i n r a d i a t i o n damage i n the form of s t e e l e m b r i t t l e m e n t . I n order t o a s c e r t a i n the sa~e o p e r a t i n g l i f e t i m e of the r e a c t o r p r e s s u r e v e s s e l , the neutron dose must be monitored. S o l i d s t a t e t r a c k recorder n e u t r o n dosimeters have been developed f o r pressure v e s s e l s u r v e i l l a n c e doslmetry a t commercial power r e a c t o r s . To date a t o t a l of more than 200 n e u t r o n dosimeters from seven d i f f e r e n t power r e a c t o r dosimetry exposures have been analysed, and more than 150 a d d i t i o n a l dosimeters are c u r r e n t l y deployed. The t e c h n i q u e s f o r c a r r y i n g out t h e s e measurements and t h e i r r e s u l t s w i l l be discussed. 1. INTRODUCTION Radiation dam~e i n the form of s t e e l e m b r i t t l e m e n t r e s u l t s from the a c c u m u l ~ i o n of n e u t r o n dose by the p r e s s u r e v e s s e l of a n u c l e a r r e a c t o r . I n order t o ensure t h a t the p r e s s u r e v e s s e l behaves i n a n o n - b r l t t l e manner when s t r e s s e d under opermtlng, eu~n%enance, t e s t i n g , and p o s t u l a t e d a c c i d e n t c o n d i t i o n s the amount of p r e d i c t e d r a d i a t i o n damage t o the r e a c t o r v e s s e l must be known throughout i t s s e r v i c e l l f e . I n order t o c a l c u l a t e the amount of r a d l m t i o n damage, the cumulative n e u t r o n dose r e c e i v e d a t key l o c a t i o n s i n the p r e s s u r e v e s s e l must be known (Ruddy e t e l . , 1985). The development and deployment of S o l i d S t a t e Track Recorder (SSTR) n e u t r o n dosimeters f o r n e u t r o n doslmetry r e l a t e d t o l i g h t water r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e have been d e s c r i b e d a t p r e v i o u s meetings i n t h i s s e r i e s (Ruddy e t e l . , 1986; Ruddy e t a l . , 1984; Ruddy e t a l . , 1983). SSTR n e u t r o n dosimeters f o r r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e have been deployed i n the r e a c t o r c a v i t y r e g i o n of o p e r a t i n g commercial power r e a c t o r s (Ruddy e t a l . , 1986) and n e u t r o n doslmetry r e s u l t s ( i n the form of measured n e u t r o n - i n d u c e d f i s s i o n r a t e s ) have been o b t a i n e d from a t o t a l of e i g h t o p e r a t i n g c y c l e s a t seven d i f f e r e n t r e a c t o r s . 2. SSTR NEUTRONDOSD~ETRY Neutron doses may be monitored p a s s i v e l y by deploying SSTR n e u t r o n dosimeters a t key l o c a t i o n s a d j a c e n t to the p r e s s u r e v e s s e l . P r e s e n t p r e s s u r e v e s s e l n e u t r o n doslmetry r e l i e s on the placement of SSTR and r a d i o m e t r i c ( ~ n e u t r o n dosimeters i n the r e a c t o r c a v i t y , which i s the a n n u l a r gap immediately o u t s i d e of the r e a c t o r p r e s s u r e v e s s e l . Since the n e u t r o n f l u e n c e encountered by an SSTR n e u t r o n dosimeter d u r i n g an o p e r a t i n g cycle i s g r e a t e r than lOlSn/ca9, u l t r a low-mass f i s s i o n a b l e d e p o s i t s must be used (Ruddy e t e l . , 1986; Ruddy, 1986). T y p i c a l mass requirements are i n the nanogram to subplcogram range. These f i s s i o n a b l e d e p o s i t s are f a b r i c a t e d and c a l i b r a t e d under clean room c o n d i t i o n s , and, ~ t e r exposure a t a commerci~ power p l a n t , are r e t u r n e d t o a c l e a n room f o r disassembly and a n a l y s i s (Ruddy, 1986; Ruddy and S e i d e l , 1987). The f i s s i o n a b l e d e p o s i t i s reused i n subsequent c y c l e s , and the SSTR (mica) i s etched t o r e v e a l t h e n e u t r o n - i n d u c e d f i s s i o n t r a c k s . These t r a c k s are counted with the a i d of a c o m p u t e r - c o n t r o l l e d , automated t r a c k c o u n t e r (Ruddy e t el., 491
492
F. H, RUDDY and J. G. SEIDEL
1987). The s t e p s i n v o l v e d i n p r e s s u r e v e s s e l s u r v e i l l a n c e d o s l n e t r y are s u a a a r i s e d i n F i g . 1.
4~
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-
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3. ACCURACY~ ~ AND CALIBRATION Accuracy Eoals f o r l i g h t water r e a c t o r p r e s s u r e v e s s e l s u r v e i l l a n c e r e q u i r e t h a t SSTR f i s s i o n r a t e s be determined t o an o v e r a l l a b s o l u t e accuracy of 2-5S. This i n t u r n r e s u l t s i n comparable accuracy r e q u l r e e e n t s f o r f i s s i o n a b l e d e p o s i t mass c a l i b r a t i o n s and f o r d e t e r m l n a t i o n s o~ t h e number of t r a c k s produced. R a d l o m e t r l c mass c a l i b r a t i o n s f o r u l t r a low-mass f i s s i o n a b l e d e p o s i t s (Ruddy, 1986) have been and a r e b e i n g v e r l t i e d through i r r a d i a t i o n s i n s t a n d a r d neutron f i e l d s a t t h e U.S. N a t i o n a l Bureau of S t a n d a r d s (Ruddy and S e i d e l , 1987; Ruddy and McCarry, 1988). These i r r a d i a t i o n s have e s t a b l i s h e d t h e a b s o l u t e accuracy of t h e d e p o s i t masses t o b e t t e r than 2.5~ and have shown t h e r e l a t i v e p r e c i s i o n o~ t h e mass d e t e r a i n a t l o n s o~ i n d i v i d u a l d e p o s i t s t o be b e t t e r than 3~.
P R E S S U R E VESSEL S U R V E I L L A N C E
DEPOSIT :#:1288
237 Np
3.63 x 10-9g
CAVITY IRRADIATION
NBS B E N C H M A R K IRRADIATION
Fig. 2.
NT
XS:X/4-GG
Comparison of t r a c k d e n s i t y d i s t r i b u t i o n s o b t a i n e d i n SSTRe exposed t o the same f i s s i o n a b l e d e p o s i t d u r i n g a c a v i t y dosimetry n e u t r o n exposure and a subsequent NBS benctmark f i e l d n e u t r o n exposure
493
494
F . H . R U D D Y and J. G. SEIDEL
Manual scanning has been shown to have an absolute accuracy of 0.88% (Roberts et al., 1984). The absolute accuracy of the Westinghouse R&D Center Automated Track Counter has been shown to be 1.88% (Ruddy et al., 1987). This computer-controlled optical microscope uses stateof-the-art image enhancement and pattern recognition techniques to identify tracks. The absolute accuracy was verified by comparisons with track standards in the range from 8 x 10 s tracks/cm 2 to 8 x 10 s tracks/cm 2. The track counting efficiency was found to be independent of local track density variations and the degree of track overlap over this range. Track scanning results are stored on a local microscope field-of-view by field-of-view basis on computer disks. Typical track scanning results are shown graphically in Fig. 2. Contour and isometric plots are shown as well as selected slices through the track count distribution. The two sets of plots correspond to results o~ irradiations of the same fissionable deposit in the reactor cavity region of a power reactor and, later, in a standard neutron field at the U.S. National Bureau o~ Standards (Ruddy and Seidel, 1987; Ruddy and McGsrry, 1988). 4. RESULTS AND qUALITY ASSURANCE Computer files such as those shown in Fig. 2 will be stored on a long term basis (40 or more years) to ensure long term tracibility of the reactor dosimetry measurements. Mass calibration files (see Fig. 1) are also stored on a long term basis. As a backup to the track scanning files, the SSTR itself is stored as a long-term record of the dosimetry exposure. 5. SUMMARY To date, a total of more than 200 SSTR neutron dosimeters from r e a c t o r cavity n e u t r o n dosimetry exposures have been analysed and a d d i t i o n a l exposures axe p r e s e n t l y i n progress. SSTR n e u t r o n dosimetry has proven t o be a r e l i a b l e and a c c u r a t e method f o r o b t a i n i n g n e u t r o n exposure data f o r r e a c t o r p r e s s u r e v e s s e l surveillance. Reactor cavity neutron dosimetry results to date (Ruddy and Seidel, 1987) indicate that in all cases where proper quality control procedures are used, uncertainties in the 2-5~ range are obtained. REFERBNCES I. Roberts, J. H., F. H. Ruddy, and R. Gold (1984). Optical efficiency for fission frz~ment track counting in muscovite solid s t a t e t r a c k r e c o r d e r s , Nuclear Tracks 8, 365. 2. Ruddy, F. H., J. H. Roberts, R. Cold, and C. C. P r e s t o n (1983). Application of solid state track recorders in light water reactor pressure v e s s e l s u r v e i l l a n c e dosimetry, Nuclear Tracks 7, 62-77. 3. Ruddy, F. H., J. H. Roberts, R. Cold, and C. C. P r e s t o n - ( 1 9 8 4 ) . Light water reactor pressure vessel surveillance dosimetry using solid state track recorders, Nuclear Tracks and Radiation Measurements 8, 275-280. 4. Ruddy, F. H., W. N. McElroy, E. P. Lippincott, L. S. Kellogg, R. Gold, J. H. Roberts, C. C. Preston, J. A. Grundl, E. D. McGarry, and H. Farrar IV (1985). Standardized physics-dosimetry for U.S. pressure vessel cavity surveillance programs, Fifth International ASTM-Euratom Symposium on Reactor Dosimetry, Coestha~ht, September 1984, D. Reidel Publishing Co., Dordrecht, 473. 5. Ruddy, P. H. (1988). Neutron dosimetry in high intensity fields: a review, Nuclear Tracks 11, 197. 6. Ruddy, F. H., J. H. Roberts, R. Gold, C. C. Preston, L. S. Kellogg, E. P. Lippincott, and W. N. McElroy (1988). Light w~ter reactor pressure vessel surveillance using reactor cavity solid state track recorder neutron dosimetry, Nuclear Tracks 12, 981. 7. Ruddy, F. B., and J. G. Seidel (1988). Sol~=d state track recorder pressure vessel surveillance neutron dosimetry at commercial light water reactors, Sixth ASTM-Euratom Symposium on Reactor Dosimetry, Jackson, Wyoming, June 1987, ASTM STP 1001 (in press). 8. Ruddy, P. H., A. E. Manhardt, and J. G. Seidel (1988). Analysis of s o l i d s t a t e t r a c k r e c o r d e r s with the Westinghouse R~D Center automated t r a c k c o u n t e r , S i x t h ASTM-Euratom Symposium on Reactor Doslmetry, Jackson, Wyoming, June 1987, ASTM STP 1001 ( i n p r e s s ) . 9. Ruddy, F. B., and E. D. McGarry (1988). ~ n c ~ k irradiations of ultra low-mass fissionable deposits (to be published).