RUBBER

SEALS

FOR

RADIOACTIVE

MEDIA

N. N. B u k a n o v a ~ I. V. Davydov, V. G . Z a v o l o k o v a , G . M. K o s t e r e v a , and N. A. Starkova

UDC 621.65-762.444 678.43+621.311.25:621.039

P u m p a s s e m b l i e s a r e v e r y i m p o r t a n t equipment in atomic e n e r g y installations; they have a c o n s i d e r able effect on the capital and o p e r a t i n g costs of a t o m i c e l e c t r i c a l stations (AES). The r e l i a b i l i t y and stability of n u c l e a r r e a c t o r o p e r a t i o n a r e d e t e r m i n e d by the w o r k - f i t n e s s of the pumping equipment, which depends on the technical c h a r a c t e r i s t i c s of the r u b b e r s e a l s which m a k e up the mobile and i m m o b i l e junctions (gaskets, r i n g s , glands, d i a p h r a g m s , oil s e a l s , and the like). Rubber s e a l s , which a r e c h a r a c t e r i z e d by such - luable p r o p e r t i e s as e l a s t i c i t y , c o r r o s i o n r e s i s t a n c e , s i m p l i c i t y in f a b r i c a t i o n , and c o m p a r a t i v e l y low cost~ ~re widely used as construction m a t e r i a l s which ens u r e r e l i a b l e h e r m e t i z a t i o n of c h a m b e r s with different m e d i a and p r e s s u r e in p n e u m a t i c , hydraulic, and v a cuum s y s t e m s [1]. In operation under the conditions of an AES, r u b b e r m a t e r i a l s , in addition to the action of such a g g r e s sive f a c t o r s as various c h e m i c a l m e d i a , high and low t e m p e r a t u r e s , p r e s s u r e of the m e d i u m , and m e c h a n i c a l loads, a r e subjected to the d e s t r u c t i v e action of ionizing radiation. On i r r a d i a t i o n of r u b b e r a r t i c l e s in the d e f o r m e d s t a t e ( c o m p r e s s i o n , s t r e t c h i n g , dynamic loads), as a r e s u l t of a loss in e l a s t i c i t y by m o s t r u b b e r s , and of a d e c r e a s e in ability to undergo elastic r e s t o r a t i o n to the original f o r m (accumulation of r e s i d u a l d e f o r m a t i o n ) , the a r t i c l e l o s e s its f o r m and a c q u i r e s s h r i n k a g e , and does not e n s u r e h e r m e t i c i t y of sealing. In this connection the p r o b l e m of choosing p r o m i s i n g r u b b e r m a t e r i a l s which a r e able to withstand radiation f o r a s s e m b l i n g pump equipment for AES has b e c o m e a p r e s s i n g one. This r e q u i r e m e n t is justified by the fact that, as c o m p a r e d with m e t a l s , c e r a m i c s , or g l a s s , p o l y m e r i c m a t e r i a l s a r e subject to the action of r a d i a tion to a c o n s i d e r a b l y g r e a t e r d e g r e e [2], and the s e r v i c e life of r u b b e r sealing units is much l e s s than the s e r v i c e life of the pump equipment. The use of r a d i a t i o n - r e s i s t a n t r u b b e r s in AES pump equipment i n c r e a s e s its operation r e l i a b i l i t y and r e d u c e s the n u m b e r of pump overhauling o p e r a t i o n s , which a r e often c a r r i e d out under the conditions of action of ionizing radiation. The a b s o r b e d d o s e of ionizing radiation at which the m a t e r i a l r e a c h e s a c r i t i c a l s t a t e s e r v e s as a quantitative m e a s u r e of the radiation r e s i s t a n c e of r u b b e r s [3]. The radiation r e s i s t a n c e of r u b b e r s depends on t h e i r c o m p o s i t i o n and the c h e m i c a l nature of the p o l y m e r b a s e (rubber). u n d e r the action of ionizing r a d i a tion, p r o c e s s e s of r a d i o c h e m i c a l c r o s s - l i n k i n g and d e g r a d a t i o n take place in p o l y m e r i c m a t e r i a l s , as a r e s u l t of which t h e i r p r o p e r t i e s change i r r e v e r s i b l y (Fig. 1). Both p r o c e s s e s take place simultaneously; the d i r e c tion of the change in p r o p e r t i e s on i r r a d i a t i o n depends on the r a t i o of t h e i r r a t e s . Rubbers based on b u t a d i e n e - nitrile p o l y m e r s (SKN), b u t a d i e n e - s t y r e n e p o l y m e r s (SKS), t e r n a r y e t h y l e n e - propylene p o l y m e r s (SKEPT), butadiene p o l y m e r s (SKD), fluorine-containing p o l y m e r s (SKF), or siloxane p o l y m e r s (SKT, SKTV, and so on) belong to the m a t e r i a l s which c r o s s - l i n k under i r r a d i a t i o n , with the following changes in p r o p e r t i e s : i n c r e a s e in s t r e n g t h in extension (in the initial s t a g e s of i r r a d i a t i o n ) , in h a r d n e s s , b r i t t l e n e s s , elastic moduli in c o m p r e s s i o n o r extension, build-up in r e s i d u a l d e f o r m a t i o n , d e c r e a s e in r e l a t i v e elongation at b r e a k , in r e l a t i v e l y r e s i d u a l elongation, and loss of e l a s t i c i t y . Rubbers based on butyl r u b b e r (BK) a r e degraded on i r radiation; in t h e i r c a s e a d e c r e a s e in s t r e n g t h , h a r d n e s s , e l a s t i c moduli in c o m p r e s s i o n o r extension, and a r i s e in r e l a t i v e and r e s i d u a l elongation at b r e a k , a p p e a r a n c e of t a c k i n e s s , flow, and s t r e s s r e l a x a t i o n a r e characteristic. Rubbers b a s e d on natural r u b b e r (NK) and synthetic r u b b e r s containing p r o t e c t i v e a r o m a t i c groups in t h e i r s t r u c t u r e (urethane r u b b e r s or b u t a d i e n e - s t y r e n e rubbers) a r e c h a r a c t e r i z e d by the g r e a t e s t r e s i s t a n c e to the action of ionizing radiation. In t h e i r c a s e s , as a r u l e , the r a t e s of the c r o s s - l i n k i n g and d e g r a d a t i o n p r o c e s s e s a r e close; in a definite r a n g e of a b s o r b e d d o s e s , a s t a b i l i t y of the moduli in c o m p r e s s i o n and e x tension, of s t r e n g t h , r e l a t i v e elongation at b r e a k , and retention of e l a s t i c i t y is noted. Values of the allowable a b s o r b e d d o s e for r u b b e r s b a s e d on v a r i o u s p o l y m e r s a r e given below: T r a n s l a t e d f r o m I
0009-2355/81/0304- 0128 $07.50

9 1982 Plenum Publishing C o r p o r a t i o n

TABLE 1 Operation conditions medium

allowable limiting absorbed re mperature dose, Gy ~

~-ffti,ze water, weak solutionso acids or alka lies Air DA.stillate

~:~s e,%;'fM-g,arbitrar units I

0,414~

/":%:v" \ 20"g

10s 35, I(~ 50q]04

104 80 9~

Y

Gradeof rubber

51-1481 5;1-1473 11]~-834

Tentative operating I lifetime, i ~ mobile / junction junction

l

45 ON) 1G 000 10 000

Fig. 1. Dependence of physicomechanical p r o p e ~ i e s of rubbers on absorbed dose of ionizing radiation: - ~ ) r u b b e r s based on SKN-26 + SKN-18 r u b b e r in air at 25~ ....... and . . . . . . . . ) r u b b e r s based on SKN-26 in a i r and in w a t e r , r e s p e c t i v e l y , at 25~ 1) radiation aging coefficient with r e s p e c t to strength, Ks = s / s 0 (here s and s o a r e the strengths a f t e r irradiation and in the original state, respectively); Z) radiation aging coefficient with r e s p e c t to relative elongation, K z = Z/Z0 (here Z and Z0 a r e the relative elongations after i r r a d i a t i o n and in the original state, respectively); 3) residual deformation.

Type of rubber

Allowable absorbed d o s e , Gy

S K U - P F , SKU-PFD S I ~ - 3 , SIx'S, NK

(500-800) • 104 (200-300) x 104

S K I P , SI
(150-200) • 104

SKN SKF SKTV

BK

1000--1200

(80-100) x 104 (20-30) • 104 (10-15) x 104

(5-10) • lo 4

In the i r r a d i a t i o n of r u b b e r s based on f l u o r o p o l y m e r s , the fprmation of significant amounts of l o w - m o l e c u l a r - w e i g h t r a d i o l y s i s p r o d u c t s is o b s e r v e d -- a g g r e s s i v e gaseous p r o d u c t s of the type of h y d r o g e n chloride (HCI), o r hydrogen fluoride (I-IF), a r e evolved, which c a u s e s c o r r o s i o n of the contacting metallic s u r f a c e s of pump p a r t s . The operation of r u b b e r - t e c h n o l o g y articles in AES, as a rule, takes place under the conditions of s i m u l taneoud action of ionizing radiation and elevated t e m p e r a t u r e s , which causes a considerable i n c r e a s e in the rate of radiative failure of the r u b b e r [4]. With i n c r e a s e in t e m p e r a t u r e f r o m 25 to 104~ the p h y s i c o m e c h a nical p r o p e r t i e s of rubbers change s h a r p l y and the rate of build-up in residual d e f o r m a t i o n r i s e s . The c h a r a c t e r of the radiative failure of r u b b e r also depends on the chemical composition of the working medium. We may differentiate physically active media, under the action of which r e v e r s i b l e changes in m a s s and volume of the r u b b e r take place (swelling of the a r t i c l e s ) , and c h e m i c a l l y active media, '~lich c a u s e i r r e v e r s i b l e failure of the rubber. Thus, for each type of medium, r u b b e r s based on the m o s t r e s i s t a n t r u b b e r y p o l y m e r should be selected. F o r work in a i r , helium, o r vacuum, r u b b e r s based on SKMS, SKI-3, BK, SKU, and SKEP r u b b e r should be used; in/ a medium of oil o r fuel, r u b b e r s based on SKN or SKU r u b b e r ; in s u p e r heated water, r u b b e r s based on SKEP o r S I ~ P T rubber; in acids, rubbers based on SKF o r SKS rubber; in a / medium of a t m o s p h e r i c oxygen, r u b b e r s based on SKTV, SKEP, or SKF rubber. The effect of the medium on the c h a r a c t e r of radiative failure of a r u b b e r based on SKN-26 r u b b e r p o l y m e r is shown in Fig. 1. Under the conditions of contact of r u b b e r s with Chemically active media in the p r o c e s s of use in AES, one should take into account the possibility of an i n c r e a s e in the activity of the medium under the action of ionizing radiation, and also the possibility of the formation of a g g r e s s i v e products d i r e c t l y in the i r r a d i a t e d m a t e r i a l o r in the s u r r o u n d i n g liquid o r gaseous media. E x p e r i e n c e in work on operating AES equipment has shown that when the m a t e r i a l is c o r r e c t l y chosen, the r e s e r v e in operation of r u b b e r seals can be c o n s i d e r a b l y i n c r e a s e d . Thus, as a r e s u l t of replacing r u b b e r of grade IRP-1225, based on SKF-32 r u b b e r p o l y m e r , by 51-1481 r u b b e r based on S I ~ P T r u b b e r b a s e , the r e s e r v e in operation of immobile junction seals of hydraulic pumps was increased f r o m 300-600 to 45,000 h. 129

In Table 1 we give g r a d e s of p r o m i s i n g m a t e r i a l s which a r e r e c o m m e n d e d for u s e in pump equipment of AES, plus the tentative r e s e r v e in o p e r a t i o n of a r t i c l e s of t h e s e m a t e r i a l s , a s c e r t a i n e d on the b a s i s of r e sults of f u l l - s c a l e t e s t s in operating AES equipment, and also f r o m stand t e s t s u n d e r conditions which a p proach o p e r a t i o n a l ones. LITERATURE 1, 2. 3. 4.

CITED

B. Kh. Avrushchenko, Rubber Seals [in Russian], Khimiya, Leningrad (1978). N. A. Sidorov and V. K. Knyazev, e d i t o r s , Radiation R e s i s t a n c e of Radiotechnical Constructions [in Russian], Sovetskoe Radio, Moscow (1976). All-Union State Standard 9,701-79. R u b b e r s . T e s t Method f o r R e s i s t a n c e to Radiative Aging. Bolt and C a r r o l l , Action of Radiation on Organic M a t e r i a l s [Russian t r a n s l a t i o n ] , A t o m i z d a t , Moscow (1965).

PULSATION T.

A.

DAMPERS

WITH

Gruzinova

and

A.

RUBBER M.

DIAPHRAGMS

Opolchentsev

UDC 621.651-278.001.5

When piston or r a m pumps a r e used in v a r i o u s s y s t e m s it is n e c e s s a r y to take into account the specifies of the pump o p e r a t i n g p r o c e s s , which c o n s i s t s of a nonuniform feed of liquid, caused by the c h a r a c t e r i s t i c s of the c r a n k d r i v e . The p e r i o d i c a l l y changing liquid velocity in conjunction with the p a r a m e t e r s of the pipeline s y s t e m and the c h a r a c t e r of the load a r e the r e a s o n s f o r the p r e s s u r e pulsations which lead, in a n u m b e r of e a s e s , to v i b r a t i o n of the pipelines, to i m p a i r m e n t of working c h a r a c t e r i s t i c s , and p r e m a t u r e failure of the pump s y s t e m , the liquid p r e s s u r e pulsations and the pipeline vibrations depending c o n s i d e r a b l y on the conditions of pump installation. The effect of local r e s i s t a n c e s on p r e s s u r e fluctuations in piston pump pipelines was shown in [1]. Pulsation d a m p e r s having a gas volume whose magnitude is d e t e r m i n e d by the p a r a m e t e r s of the pump and pipeline s y s t e m have b e e n used to reduce liquid p r e s s u r e pulsations [2]. While t h e r e is a g r e a t d i v e r s i t y of d a m p e r c o n s t r u c t i o n s at p r e s e n t , the pulsation d a m p e r s developed in the VNIIGidromash, having an elastic s e p a r a t i n g d i a p h r a g m c h a r a c t e r i z e d by c o m p a c t n e s s and the p o s s i b i l i t y of automation, c o n f o r m m o s t fully to c o n t e m p o r a r y r e q u i r e m e n t s . The pulsation d a m p e r {Fig. 1) c o n s i s t s of a housing, 1, in which is installed a r u b b e r d i a p h r a g m , 2, sealed around the u p p e r annular s h o u l d e r by cap 4. Through a s p e c i a l v a l v e , 3, the internal c h a m b e r of the d i a p h r a g m is filled with a c o m p r e s s e d g a s , whose p r e s s u r e is p e r i o d i c a l l y checked during the p r o c e s s of c h a r g i n g and o p e r a t i o n with a m a n o m e t e r or a s p e c i a l s e n s o r installed in the cap. When the pump is not o p e r a t i n g , the d i a p h r a g m is p r e s s e d against the housing wall and the bottom support, 10, by the c o m p r e s s e d gas p r e s s u r e . When the pump is switched on, the pumped liquid p a s s e s through the inlet holes in the bottom s u p p o r t into the d a m p e r housing, as a r e s u l t of which the d i a p h r a g m is c o m p r e s s e d and the initial gas volume is reduced p r o p o r t i o n a l l y to the r a t i o of the gas p r e s s u r e P6 to the m e a n liquid working p r e s s u r e , Pm" In n o n s t a t i o n a r y flow, the instantaneous liquid p r e s s u r e fluctuates r e l a t i v e to the m e a n p r e s s u r e f r o m P m a x to Pmin: Prnax =

Pm + Ap;

Pmin

Pm - - A p,

~---

where Ap is the magnitude of the fluctuations in instantaneous p r e s s u r e . Fluctuations in instantaneous p r e s s u r e c a u s e changes in the volume of gas inside the d i a p h r a g m : Vgmax-- I/. + A V;

Vgrain=l~g-AV,

w h e r e Vg is the volume of gas in the d i a p h r a g m at the p r e s s u r e Pm; and AV is the change in gas volume during fluctuations in instantaneous p r e s s u r e by the amount Ap. T r a n s l a t e d f r o m K h i m i c h e s k o e i Neftyanoe M a s h i n o s t r o e n i e , No. 3, pp. 13-14, March, 1981.

130

0009-2355/81/0304-0130507.50

9 1982 Plenum Publishing C o r p o r a t i o n