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AE-359 UDC 539.1.074
621.039.564.2
Vanadium Beta Emission Detectors for Reactor Sn-Core Neutron Monitoring
I. Ö. Andersson and B. Söderlund
AKTIEBOLAGET ATOMENERGI
STOCKHOLM, SWEDEN 1969
AE-359
VANADIUM BETA EMISSION DETECTORS FOR REACTOR IN-
CORE NEUTRON MONITORING
I . Ö . Andersson and B. Söderlund
ABSTRACT
In -co re flux m e a s u r e m e n t s a r e becoming increas ingly important
in both power r e a c t o r s and tes t r e a c t o r s . In pa r t i cu la r power d i s t r ibu
tion m e a s u r e m e n t s in la rge power r eac to r s have to be per formed with
a great number of neutron de tec tors capable o£ withstanding high in te
grated flux va lues .
This repor t p r e sen t s a summary of the development and appl ica
tion of a new type of nuclear radiation senso r , a beta emiss ion de tec tor ,
for m e a s u r e m e n t s at high neutron flux l eve l s .
The work has been ca r r i ed out at the Section for Instrumentat ion
(SSI) and has been the bas is for a type of neutron detector employed in
the Marviken in -core system as well as for other types .
The repor t desc r ibes the design and pr inciple of operat ion, ex
pe r imen t s and t e s t s .
Also included a r e the resu l t s and comments from a long- te rm
i r radia t ion of some de tec to rs in the Halden r e a c t o r .
Pr in ted and dis tr ibuted in June 1969
LIST OF CONTENTS
Page
1 . INTRODUCTION 3
2. DESIGN AND PRINCIPLE OF OPERATION 3
3. EXPERIMENTS 3. 1 Tes t s in the R2-0 reac to r 8
3.2 Tes t s in the Halden r eac to r 15
4. MARVIKEN IN-CORE NEUTRON MONITORING SYSTEM 15
REFERENCES 16
Appendix 1: I r rad ia t ion of vanadium beta emiss ion neutron
de tec tors in HBWR Halden, March-November
1966 17
- 3 -
1 . INTRODUCTION
The use of beta emiss ion de tec tors for neutron, moni tor ing is a
technique that has been quite recent ly adopted. The pr inc ip les were
f i rs t descr ibed in a German patent in 1938 ( l ) . Exper imenta l r e su l t s
that confirmed the feasibility of the method appeared in 1961 (Z) and
1963 (3). G. W. Hilborn, Chalk River , Canada, descr ibed in 1964(4)
a design that was fully developed for application in a r eac to r environ
ment and his r e su l t s demonst ra ted the unique and useful c h a r a c t e r i s
t i cs of these de tec tors for m e a s u r e m e n t s at high neutron flux l eve l s .
This s ta r ted a wide in te res t in beta emission neutron de t ec to r s .
We began f irst in a general way to look into the manufacturing
p rob lems and to make exper iments to find out the cha rac t e r i s t i c s of
these de t ec to r s . An important application was soon found when it was
revealed (5) that the beta emiss ion de tec to rs had favourable p roper t i e s
for use in the in terna l neutron flux moni tor ing system in the Marviken
power r eac to r . The efforts were then concentrated on the development
of de tec tors to suit this application. In Marviken the neutron flux
density should be moni tored at 48 posi t ions in the r eac to r core over
the range 10 - 10 n / c m • s at a t empe ra tu r e of 263 C. The l i fe
t ime of the s enso r s should be 2 y e a r s . The purpose of the sys tem is
to supply data for flux distr ibution optimisation and fuel burn-up
calculat ions.
This repor t desc r ibes the work on development and t e s t s of a
s e r i e s of prototype de tec tors for the Marviken sys tem.
2. DESIGN AND PRINCIPLE OF OPERATION
A beta emiss ion detector for neutrons consis ts of th ree main
pa r t s - the emi t t e r , insulator and collector - which usually a r e a r r anged
as coaxial cylinders as is shown in F ig . 1 . The emi t te r is a conduct
ing m a t e r i a l in which neutrons induce a radioisotope that d i s in tegra tes
by emiss ion of beta p a r t i c l e s . The insulator is a solid d ie lec t r ic m a
t e r i a l with a th ickness sma l l enough to pe rmi t penetrat ion of the beta
pa r t i c l e s that emerge from the emi t t e r . The collector is a conducting
m a t e r i a l that surrounds the insula tor . It should emit few beta
4^
1. Emitter, vanadium, 0 2.0 mm, length 210 mm '
2. Insulator , a luminium oxide tube, <f> 2.8x2.1 mm
3. Col lector , i ncone l , <f> 3.5 x 3.0 mm
4. Cable, 2 cores and sheath of inconel, insu la t ion A l 2 0 3 , 0D 2.0 mm ( 2 I I I20 SÖDERN)
5. Adapter, inconel , $ 3.0 x 2.0 mm
6. End plug, inconel
7. Aluminium oxide tube ( shield for insulator dur ing brazing )
Fig. 1 Vanadium beta emission detector
- 5 -
par t i c l e s in a neutron flux compared with the emi t t e r . When this
a r rangement i s i r r ad ia ted by neu t rons , a posit ive potential will be
built up on the emi t t e r re la t ive to the collector due to the beta p a r
t ic les that leave the emi t t e r . The ra te of the posi t ive charge p roduc
tion in the emi t te r could be m e a s u r e d as a cur ren t if the emi t t e r and
collector a r e connected to the input of an e l ec t rome te r . This cu r ren t
is propor t ional to the ra te of neutron absorption in the emi t t e r and
is therefore a m e a s u r e of the neutron flux densi ty.
The cur rent I that is produced at a neutron flux $ is given by
I = k • Na - $ • q o n
where
N = number of useful t a rge t nuclei
a « neutron c ross section
q = electron charge
k = efficiency factor
The efficiency factor k depends on detector geometry , decay scheme ,
neutron flux depress ion and self-shielding, and beta se l f -shie lding.
The cur rent I is the signal that is obtained in an equil ibrium s ta te ,
i. e. when the neutron flux has been constant for a long per iod, com
pared with the half-life of the emi t te r radioisotope.
The t ime dependence I(t) for a step change in neutron flux from
zero to § is
I ( t ) - I o ( l _ e - 0 . 6 9 3 - t / T ! }
and for a sudden d e c r e a s e in flux from § to zero
l ( t ) = I o e - ° - 6 9 3 - */**
where T^ is the half-life of the activated nuclei in the emi t t e r , and
t is the t ime after the change in flux level .
The nuclear p roper t i e s that a r e requi red of emi t te r m a t e r i a l s
a r e a decay by high energy beta emiss ion , a short half-l ife and a
- 6 -
react ion c ro s s section sufficient to provide a useful signal and yet small
enough to limit the burn-up of the detecting m a t e r i a l . The short half-
life is essen t ia l to give the detector a fast response to changes in
neutron flux leve ls . The energet ic beta radiation is requi red to be able
to design a detector with adequate neu t ron /gamma signal r a t io .
Table 1 summar i ze s data for isotopes with p roper t i e s of half-
life, c ro s s section and beta decay energy that make them potentially
useful in beta cur ren t neutron de tec to r s .
The choice of emi t te r m a t e r i a l has to be a compromise between
the r equ i rement s of speed of r e sponse , signal level and burn-up r a t e . 7
When fast response is needed, e . g . for reac to r control , only Li and
B can be cons idered . These isotopes have very low c ros s sec t ions ,
however , which r a i s e s problems in respec t of the s ignal- to-background
condit ions. The in -co re de tec tors in Marviken should m e a s u r e flux
distr ibution mainly for the purpose of efficient fuel uti l ization, so in
this case a response t ime of the order of minutes could be accepted. 1 4 / 2 At a t h e r m a l neutron flux density of 10 n / c m * s the burn-up of the
detecting m a t e r i a l is an important factor. Table 1 indicates the b u r n -
up ra te for different emi t t e r m a t e r i a l s . Vanadium has been chosen for
the Marviken de tec to r s , which has the advantage of essent ia l ly constant
sensit ivity for a two -year operat ion per iod.
The design that was chosen for the vanadium beta emiss ion de
tec tor is shown in F ig . 1 . The emi t t e r is a wire of d iameter 2. 0 mm
and length 210 m m . Due to the relat ively low neutron c r o s s section
it i s nece s sa ry to put a large amount of ma te r i a l in the emi t te r to be
sure of getting a signal that dominates over disturbing cu r r en t s gene r
ated, for ins tance , in the cable . The thickness of the emi t te r is l i m -52
ited by the beta absorpt ion. The V beta par t i c les have an average
range of 0.55 mm and a maximum range of 2.0 mm in vanadium. Up
to a d iameter of 2 mm the re is then a reasonable uti l ization of the
m a t e r i a l .
- 7 -
Table 1. Emi t t e r isotopes for beta emiss ion neutron de tec tors
Element
Li1
B 1 1
A l 2 7
v51
Mn 5 5
R h 1 0 3
A 1 Q 7
t . 109 Ag
Abundance %
92.48
80
100
99.76
100
100
51.35
48.65
Activation c ros s section
barns
0.033
< 0.05
0.21
4 . 5
13.2
150
45
113
Half-life
0 .85 sec
0.02 sec
2. 30 min
3. 76 min
155 min
4.4 m-» 42 s
(8%) (92%)
2. 3 min
24 sec
Maximum P energy
MeV
13.0
13.4
2.87
2 . 5
2 . 8
2 . 5
1.77
2.84
Burn-up ra te at l O ^ n / c m 2 ' s per cent /month
negligible
negligible
0.0054
0. 12
0.35
3 .9
1.2
2 . 9
- 8 -
The insula tor is a s in tered pure aluminium oxide tube of
d iameter 2 . 8 / 2 . 1 m m . The wall of the insulator has to be sufficiently-
thin to pe rmi t penetrat ion of the beta par t ic les from the emi t t e r , yet
the thickness should be great enough to secure good insulation and
sufficient mechanical p r o p e r t i e s . The gamma radiat ion will generate
energet ic e lec t rons in the emi t t e r and collector. Most of these e lec t rons
should be stopped in the insulator if low gamma sensit ivity is wanted.
We have chosen a th ickness that should give the highest possible rat io
between neutron and gamma r e s p o n s e s . The insulator ma te r i a l must
re ta in i ts p roper t i e s in an environment of high t empera tu re and intense
radiat ion exposure . Magnesium oxide and aluminium oxide appear to
be the bes t m a t e r i a l s . Magnesium oxide has not been used in this case
because of i t s intense react ion with water , which could cause damage in
case of sheath rup tu re .
The col lector i s an Inconel tube with diameter 3 . 5 / 3 . 0 m m .
The cable is a thermocoax cable type 2 III 20 made by Södern
Ltd, F r a n c e . It has an Inconel sheath and two-co re s , also of Inconel.
The insula tor is aluminium oxide. One cable core is connected to the emi t
t e r , the other is used to control the current that is induced in the cable itself.
Compensation for the cable-induced current could then be achieved by
taking the difference between the cu r ren t s flowing from ei ther cable
core to the outer sheath. The outer diameter of the cable is 2 .0 m m .
A thinner cable would give l ess cable-induced c u r r e n t s , but for
mechanical r e a s o n s , r i sk of damage e t c . , it was not a t t rac t ive to use
sma l l e r d imensions .
3 . EXPERIMENTS
3. 1 Tes t s in the R2-0 reac to r
F o r t e s t of beta cur ren t neutron detectors a rig has been instal led
in the R2-0 r e a c t o r . This r eac to r is of swimmingpool type with a core
of 600 mm high MTR fuel e l emen t s . The maximum power is 1 MW.
The cent re of the core is si tuated 7.5 m below the water sur face . A
tube of pe rspex about 9 m long is a r ranged ver t ical ly in the pool and
fixed to the r eac to r frame in a position just outside the reac to r core
- 9 -
at approximately 100 mm from the nea re s t fuel e lement . The detector
and i ts cable a r e th readed into the pe r spex tube from the top and the
detector is then guided by the tube down to a -well defined position at
the r eac to r c o r e . Here the de tec tors could be invest igated one at a
t ime under the same radiat ion condit ions. The t empera tu re of the
water is approximately 25 C.
The m e a s u r e m e n t s of c u r r e n t s were made with a Keithley
e l ec t rome te r Model 610 BR. The input r e s i s t ance of the e l ec t rome te r
has to be low compared with the in te rna l insulation r e s i s t ance in the
detector and cable . The Keithley ins t rument used with feedback -
coupled amplif ier offers favourable conditions in this r e spec t , since
the input voltage drop is < 1 mV on any range .
The insulat ion r e s i s t ances of the detector and cable a r e i m p o r
tant c h a r a c t e r i s t i c s that one wants to control during operat ion. F o r
this purpose a unit containing a switch and a 10 V bat tery is i n se r t ed
between the cable t e r m i n a l and the e l e c t r o m e t e r . F o r cu r ren t m e a s
u remen t the cable core is direct ly connected to the e l ec t rome te r and
for r e s i s t ance measu remen t the 10 V ba t te ry is connected in s e r i e s
between the cable core and the e l e c t r o m e t e r . The cable core that is
not connected for m e a s u r e m e n t s is kept at ea r th potent ial . The i n
sulation r e s i s t ance is de te rmined by observat ion of the change in
the cu r ren t level -when the 10 V source is introduced. To make it
more convenient to read this cu r ren t change, the ze ro adjust feature
on the e l ec t rome te r is used to adjust the existing signal cur ren t to
ze ro before the 10 V potential is switched on. A r e c o r d e r , Moseley
type 680, is connected to the e l ec t rome te r to pe rmi t recording of
cu r r en t va r i a t ions .
The re su l t s from the measu remen t s on vanadium detector No. 8
at varying r eac to r power a r e given in Table 2. The cu r ren t readings
were taken 20 minutes after the change of power to allow the vanadium
activity in the emi t t e r to r each sufficiently close to the equil ibrium
value . The emi t t e r cu r r en t , I , shows direct proport ional i ty to the
power level in the whole range invest igated, 0.1 - 100 kW. The
cur ren t that is induced in the cable , I , should be considerably l ess
- 10 -
than I and Table 2 shows I to be of the o rde r of 1% of the emi t t e r e c cu r r en t , which is very sa t i s fac tory . The insulation r e s i s t ances of
the detector and cable dec rease at increas ing radiat ion level . Both
radiat ion and t empe ra tu r e have an influence on the insulation r e s i s t a n c e ,
but in an approximation these two effects could be considered as inde
pendent of each o ther .
A procedure which has proved valuable for the study of detector
cha r ac t e r i s t i c s is to m e a s u r e the decay of the cur ren t after a sudden
change in neutron flux. This is done by rapid removal of the detector
out of the r eac to r core (with a r e c o r d e r on the e l ec t romete r output).
F ig . 2 shows typical r esu l t s of such m e a s u r e m e n t s . Obviously, for
c o r r e c t behaviour of the detec tor , the emi t te r cur ren t should decrease 52 with the decay t ime of V , which has a half-life of 3. 76 minu tes . In
52 F ig . 2 this V decay also appears very c lea r ly . Immediately after
the change in flux level there is a prompt dec rea se , A I , of the
emi t t e r c u r r e n t . This step has been observed in every beta emiss ion
neutron detector we have tes ted , and for a healthy detector the prompt
step is below 10% of the total cu r ren t , usually around 5%. The same
type of cur ren t decay curve is obtained for a fast shut-down of the
r eac to r power .
- 1 1 -
T a b l e 2 . D e t e c t o r c h a r a c t e r i s t i c s a t d i f f e ren t r e a c t o r p o w e r l e v e l s .
D e t e c t o r :
I r r a d i a t i o n p o s i t i o n
T h e r m a l n e u t r o n flux d e n s i t y :
No. 8
5 F in r e a c t o r R 2 - 0
0 . 8 x 1 0 1 2 n / c m 2 . s a t 100 kW.
R e a c t o r p o w e r kW
0. 1
0. 3
1
3
10
30
100
I e (Amp.)
8 . 4 • 10"12
2 . 4 • 1 0 " U
8 . 7 • 1 0 " U
2 . 5 - 10 -1°
8 . 4 - 1 0 - 1 °
2 . 5 • 1 0 " 9
8 . 3 • I Q " 9
I c (Amp)
3 . 5 •
1-2 •
8 .7 •
7-2 •
1 0 - 1 3
10-12
i o - 1 2
1 0 - u
A l e %
4 . 2
2 . 3
4 . 0
7. 1
4 . 0
7. 2
AI % c
7 4 . 3
4 9 . 2
6 6 . 0
6 3 , 0
R (Ohms) e * '
2 . 4 ' 1 0 1 1
1. 3 • 1 0 1 1
4 . 7 . 1 0 1 0
1 . 6 . 1 0 1 0
4 . 7 . 10 9
R (Ohms) cv '
3- 5
1.7
6-7
2 , 5
9-4 •
. 1 0 1 1
> 1 0 1 1
1 0 1 0
. 1 0 1 0
10 9
Detector No 8 I e : Current of
emitter conductor
I c : Current of compensator conductor
Posi t ion: R2-0, 5F
Reactor power: 100kW
_ I e , Line corresponds to T1/2"3.70min.
( V5Z , T 1/2 = 3.76 min.
I t , Line corresponds to T 1/2» 2.2 min.
i i i i_ _ 1 • • I I ' • L _1 I I l_
5 10 15
Time ( minutes ) 20 25
Fig.2. Current decay curves after rapid removal of detector from reactor core
- 13 -
The prompt step in the decay curve exists because a smal l
fraction of the emi t t e r cur ren t comes from interact ions between
gamma radiat ion and the emi t t e r and from e lec t rons ejected by the
prompt gamma rays at the neutron capture in vanadium. "Which of
these two effects is predominant s t i l l r emains to be de te rmined .
The decay curve of the cable cu r ren t , I , a lso displayed in
F ig . 2, has a relat ively high prompt negative step followed by a 2.2 ? 8
minutes half - t ime decay. It i s thought that the dis integrat ion of Al
(T-g = 2.26 minutes) in the cable insulator gives a contribution to the
cable c u r r e n t . The prompt decay par t of the cable cur ren t is most
cer ta inly due to the influence of gamma radia t ion. It is usually d e
s i rable to have the cable cur ren t as low as poss ib le , and the use of
sma l l e r d iameter cables is favourable in this r e spec t . Measurements
made under ident ical radiat ion conditions on O . D . 1 mm and O . D .
2 mm cables gave a factor-of-five lower cable cu r r en t s for the thinner
cab le s . The cable cu r ren t i s dependent both on the radiat ion conditions
and on the m a t e r i a l s that sur round the cab le . Mater ia l s that a r e highly
act ivated by neu t rons , e . g , a luminium, could give a considerable
contribution to the cable cu r ren t if placed close to the cable .
The r e su l t s from measu remen t s on 8 vanadium detec tors in the
R2-0 r eac to r a r e given in Table 3 . The emi t t e r cu r ren t values at 10
kW reac to r power agreed within +2%. The cable cu r r en t s showed some
var ia t ions but they were all below 1 . 1 per cent of the emi t t e r c u r r e n t . 1 0 The insulation r e s i s t ances at 1 0 kW were between 3 . 7 - 9 . 1 • 10
ohms for the emi t t e r conductor and between 6.7 - 14 * 10 ohms
for the compensator conductor . The t he rma l neutron flux density in
the detector position was 0 .8 • 10 nv at 1 0 kW and thus the t h e r m a l
neutron sensit ivity of the detec tors is 8.2 • 10" / 0 . 8 • 10 = 1.03 * m - 2 0 A / • 10 A/nv .
- 14 -
T a b l e 3 . D e t e c t o r c h a r a c t e r i s t i c s for a s e r i e s of 8 v a n a d i u m d e t e c t o r s .
I r r a d i a t i o n p o s i t i o n : 5 F in r e a c t o r R 2 - 0
P o w e r l e v e l : 10 kW
T h e r m a l n e u t r o n flux n % d e n s i t y : ' 0. 8 x 10 n / c m . s .
Det .
1
2
3
4
5
6
7
8
I e (Amp.)
8. 1 • H T 1 0
8 . 1 - I G " 1 0
8 . 3 • 1 0 " 1 0
8.0 • 1 0 " 1 0
8 . 2 • 1 0 " 1 0
8 . 2 • 1 0 " 1 0
8 . 1 . I Q ' 1 0
8 . 4 - H T 1 0
I c (Amp.)
- 1 2 4 . 2 - 1 0 lC
-12 5. 2 * 10
-12 9. 2 • 10 lL
-12 1. 6 • 10 lC
-12 2 . 4 • 10 lC
-12 4 . 2 « 10 ^
-12 8 .0 • 10
-12 8 .7 • 10 lC
A I e %
4 . 9
6 . 2
8 . 4
3 . 8
9 . 8
7. 3
4 . 9
7 . 8
AI % c
6 4 . 4
57. 1
72. 5
6 6 . 0
R ( e x
5 .0
3 .9
9 . 1
6 . 3
8 . 4
3 . 7
4 . 2 -
4 . 7 '
Ohms)
• 1 0 1 0
• i o 1 0
. i o 1 0
. i o 1 0
. i o 1 0
1 0 1 0
. i o 1 0
i o 1 0
R (Ohms) c v '
8 4 - 1 0 1 0
6 . 7 - 1 0 1 0
1 4 * 1 0 U
7 2 . 1 0 1 0
1 4 • 1 0 U
7 2 - 1 0 1 0
8 4 - 1 0 1 0
6 7 - 1 0 1 0
I : c u r r e n t f r o m e m i t t e r c o n d u c t o r , e
I : c u r r e n t f r o m c o m p e n s a t o r c o n d u c t o r .
Al , AI : n e g . p r o m p t change in c u r r e n t a f t e r r a p i d r e m o v a l of d e t e c t o r f r o m r e a c t o r c o r e .
R , R : i n s u l a t i o n r e s i s t a n c e s of e m i t t e r and c o m p e n s a t o r c o n d u c t o r .
- 15 -
The experience from the R2-0 t e s t s was that the detec tors and
cables functioned co r rec t ly and that the manufacturing procedure gave
reproducible r e su l t s with r e g a r d to detector c h a r a c t e r i s t i c s .
3 . 2 . Tes t s in the Halden reac to r
An important pa r t of the tes t procedure was to invest igate the
behaviour of the de tec tors under long-t ime i r rad ia t ion . This e x p e r
iment was c a r r i e d out in the Halden HBWR 20 MW reac to r in Norway.
This is an exper imenta l r eac to r with good facil i t ies for t es t of i n -co re
de t ec to r s .
A tes t assembly containing six of the vanadium detec tors that
have been descr ibed above was built for loading into a vacant fuel
element posi t ion. The de tec tors were located at t h ree different r eac to r
core elevations with two detectors at each elevation. A dry thimble to
accept an activation wire for calibration purposes was also included in the
assembly . Copper wire (diameter 0. 7 mm) activation m e a s u r e m e n t s were
made at in tervals throughout the exper iment . By comparing wire activity
with detector current at specia l low-power (30kW) sho r t - t ime (2hr) i r r a d i a
tions it was poss ible to observe whether the neutron sensit ivity was changing.
A t r a n s i s t o r i z e d electronic unit was built for the cu r ren t and
insulation r e s i s t ance m e a s u r e m e n t s . With a manual switch one
detector at a t ime could be connected to the ins t rument . Automatic
subtract ion of the cable cur ren t was a r r anged so that I - I was & e c
indicated on the m e t e r . The cable cur ren t I could be m e a s u r e d c
separa te ly . The insulation res i s t ance was determined f irst by adding
a var iable negative cur ren t for compensation of the existing signal,
then adding 1 0 V in s e r i e s and measur ing the cu r ren t .
The tes t assembly was loaded into the r eac to r in March 1 966
and the i r rad ia t ion continued to November 1966. The resu l t s and
comments a r e given in Appendix 1 . 4. MAR VIKEN IN-CORE NEUTRON MONITORING SYSTEM
Owing to the favourable resu l t s from the t e s t s in R2-0 and Halden
-we used the same design for fixed position i n - co re detectors to monitor
neutron flux distr ibution in the Marviken r e a c t o r .
- 16 -
REFERENCES
FERRAMT, W. Einrichtung zur Mes sung der Intensität von Neutronen. Deutsche Patent Nr 691575.
MITEL'MAN, M . G . , EROFEEV, R . S . and ROZENBLYUM, N . D . Transformat ion of the energy of shor t - l ived radioactive, i so topes . Soviet J . a t . energy 1 0(1 961/62) p . 70.
CASARELLI, G. A detector for high neutron flux m e a s u r e m e n t s . Energ ia Nucl . 10(1963) p . 431 .
HILBORN, J . W . Self-powered neutron detectors for r eac to r flux monitor ing. Nucleonics 22(1964) p . 69.
ANDERSSON, I . Ö. , SKAGERLUND, L - E . , SÖDERLUND, B . 1 964. AB Atomenergi , Sweden (Internal r epor t SSI-1 48, R4-351).
- 1 7 - Appendix 1
I r rad ia t ion of vanadium beta emiss ion neutron detectors in HBWR
Halden, March - N o v e m b e r 1966
Institutt for Atomenergi , Halden, and AB Atomenergi , Studsvik, made
a joint i r r ad ia t ion exper iment on vanadium detectors in HBWR during
1966o We presen t a summary of data from this exper iment in Tables
1 - 3 and F igures 1 - 4.
The detectors were manufactured by AB Atomenergi at Studsvik.
They were prototypes for the vanadium detectors used in the Marviken
in -core neutron flux monitoring sys tem.
IFA designed and built the i r rad ia t ion tes t a s sembly . It contained six
vanadium detectors with cables and a dry thimble for wire activation
m e a s u r e m e n t s . The assembly was placed in a vacant fuel element
posit ion in the r e a c t o r .
DISCUSSION OF THE RESULTS
F ig . 1. Detector cu r ren t I - I ° e c
The diagram shows the detector cur ren t at full r eac to r power (no rma l
ized to 15 MW). I is the cur ren t from the cable conductor connected
to the emi t t e r and I is the cur ren t from the free cable conductor . c
I - I is then a detector signal that is compensated for cable- induced
cu r r en t .
The cu r ren t values were r ead once a day except for detector No. 3
which was continuously followed on a separa te e l ec t rome te r and
r e c o r d e r .
The resu l t s indicate good function during the whole i r rad ia t ion per iod .
F ig . 2. Cable-induced cur rent I ° c_
I depends on the cable length that is situated in the radiat ion zone.
The de tec tors a r e grouped in th ree pa i r s which a r e placed at dif
ferent heights in the r eac to r co re . Therefore the cable cu r r en t s I
- 18 _
appear at t h ree different levels between 0 .5 - 2 . 4 per cent of the
emi t t e r c u r r e n t . The I values have been very stable during the
exper iment .
F ig . 3 . Insulation r e s i s t ances of detectors (R ) and cables (R )
The insulation r e s i s t ances were m e a s u r e d once a week. No d e
t e r io ra t ion of the r e s i s t ances due to long-t ime i r rad ia t ion could be
observed .
F ig . 4. Decay of detector cur ren t after shut-down
The displayed decay curve is typical of vanadium detec tors that a r e
operating co r rec t ly . It begins with a smal l prompt decay (5 - 7 % of 52 the to ta l signal) which is followed by a decay according to the V
half-life 3.76 min .
Table 2. Resul t s of cal ibrat ion measu remen t s
On two occasions during the i r rad ia t ion per iod the detector cu r ren t s
(I - I ) were compared with copper -wi re activation data (^ , ) .
This provided a means of investigating whether the neutron sensitivity
was changing. The re su l t s show that the ra t ios e ~ c were the same
^ r e l in the two m e a s u r e m e n t s , which indicated that the sensitivity has
been s tab le .
Table 3. Insulation r e s i s t ances of detec tors and cables at ze ro power
The re su l t s show that the long-t ime i r rad ia t ion produced no s igni
ficant effect on the insulation r e s i s t ances at the 10 -ohm level
which exis ts at ze ro reac tor power .
Fig. 1
1 - 19 + Halden exp. 1966
Detector current Ie - Ic (normalized to 15 MW)
Reactor power
Halden exp. 1966
Compensator current Tc (normalized to 15 MW)
Reactor power
Halden exp. 1966
Insulation resistances Rp and R
(normalized to 15 MW).
1. Ci. m
Halden exp. 1966
Decay of Ie after scram from 5,6 MeV,
Detector No. 3
- 23 -
Table 1. Specifications for detectors and cables used in Halden
experiment I966
Detector
Emitter
Insulator
Collector
material
diameter
length
material
OD/ID
material
OD/ID
length
Vanadium '
2.0 mm
210 mm
A1203
2.8/2.1 mm
Inconel
3.5/3.0 mm
300 mm
Cable
Sheath material
0D
Inconel
2.0 mm
Insulator material
Inner conductors (two) material
diameter
Cable length
M2°3
Inconel
O.36 mm
14 m
£harjacte£ist_ics
Thermal neutron sensitivity-
Insulation resistances
(detector + cable)
out-of-core 20
400
Maximum temperature
Response time
Burn-up rate
8.8 • 10 -21 Amp/nv
12 > 10 ohm
Q
> 10 ohm
400° T 1/2= 3.76 min.
14 0.12 #/month at 10 nv
- 24 -
Table 2. Calibration data for 6 vanadium detectors.
Halden experiment 1966
Power level:
Temperature:
Date:
c.
c.
30 kW
137°C
I. March 17, 1966
II. September 3, 1966
Det.
No.
le * Ic
(Amp.)
March iy_
1
2
3
4
5
6
s<
1
2
3
4
5
6
o 0.422 * 10
0.431 * 10 p
0.343 - 10
0.348 * 10"^
0.197 - io"3
3_p_tember ^
0.353 ' 10"^
0.354 * 10*8 0
0.281 - 10 p
0.277 * 10
0.143 * 10"^
0.143 * 10'^
E c
(Amp.)
0.77
O.76
O.36
0.42
0.44
1.0
0.9
0.6
0.6
0.5
0.5
. 10-1°
. 10-10
. 10-10
. 10-10
. lo"^
. 10-10
10-10
. 10-10
10-10
10-10
- 10-10
c
J
} ^
"rel
7.12 + 0.07
5.97 + 0.05
3.47 + 0.03
5.85 + 0.07
4.85 + 0.05
2.58 + 0.03
1 -1 e c
%rel
R e
(Ohms)
0.0600
0.0579
0.0568
O.O605
0.0575
0.0554
6.0 ' lO^
6.0 * io9
6.9 * 10^
9.6 - lo^
1.6 - loio
8.0 - io9
1.1 - 10^0
1.5 ' lo^
1.1 - 10^0
2.2 - loio
2.2 . loIO
R c
(Ohms)
1.2 *
1.2 *
1.2 *
1.6*
3.2 .
2.2 -
3-3 '
1.7 -
2.2 -
6.7 *
6.7 -
10^0
loio
loio
loio
10^0
10IO
10^0
10IO
10IO
lo o
loio
I : c
prel:
R , H : e c
current from emitter conductor
current from compensator conductor
relative thermal neutron flux density from Cu-wire activation
insulation resistances
- 25 -
Table 3» Insulation resistances Re and Re at zero reactor power
Det. March 19 March 24 Aug. 24 Nov. 16
No Temp. 210° Temp. 146° Temp. 60° Temp. 64°
R 1.1 • 1010 2.4 • 1010 1.7 • 1010 1.7 • 1010
1 e
R 1.6 • io10 7 • io10 > 7 • io10 > 7 • io10
c
R 1.2 * 1010 2.4 • 1010 1.7 • 1010 7 * 1010
e 2 RC 1.9 • lo10 7 • io10 7 • io10 > 7 • io10
Re 1.2 • 1010 1.6 • 1010 1.0 . 1010 3 • 1010
5 R 6 1.9 • io10 5 • io10 7 ' io10 1.7 • io10
c
Re 1.4 . io10 5 • io10 3 • io10 1.7 • io10
^ R 2.4 . 1010 5 • 10
10 7 • 1010 3 • 1010
c
Re 1.9 • io10 3.2 • lo10 7 . io10 7 • io10
5 R" 2.4 . 1010 > 7 • 1010 > 7 • 1010 > 7 . 1010
Re > 7 • lo10 > 7 • lo10 3 • 1010 7 • 1010
6 R 6 1.2 . lo10 5 • lo10 > 7 • io10 > 7 . io10
c
LIST OF PUBLISHED AE-REPORTS 326. An investigation of an irradiated fuel pin by measurement of the production of fast neutrons in a thermal column ana by pile oscillation technique. By Veine Gustavsson. 1968. 24 p. Sw. cr. 10:- .
327. Phytoplankton from Tvären, a bay of the Baltic, 1961-1963. By Torbjörn Willén. 1968. 76 p. Sw. 10: - .
328. Electronic contributions to the phonon damping in metals. By Rune Jonson. 1968. 38 p. Sw. cr. 10: - .
329. Calculation of resonance interaction effects using a rational approximation to the symmetric resonance line shape function. By H. Häggblom. 1968. 48 p. Sw. cr. 10:- .
330. Studies of the effect of heavy water in the fast reactor FRO. By L. I. Tirén, R. Håkansson and B. Karmhag. 1968. 26 p. Sw. cr. 10: - .
331. A comparison of theoretical and experimental values of the activation Doppler effect in some fast reactor spectra. By H. Häggblom and L. I. Tirén. 1968. 28 p. Sw. cr. 10:- .
332. Aspects of low temperature irradiation in neutron activation analysis. By D. Brune. 1968. 12 p. Sw. cr. 10:- .
333. Application of a betatron in photonuclear activation analysis. By D. Brune, S. Mattsson and K. Liden. 1968. 13 p. Sw. cr. 10:- .
334. Computation of resonance-screened cross section by the Dorix-Speng system. By H. Häggblom. 1968. 34 p. Sw. cr. 10: - .
335. Solution of large systems of linear equations in the presence of errors. A constructive criticism of the least squares method. By K. Nygaard. 1968. 28 p. Sw. cr. 10:-.
336. Calculation of void volume fraction in the subcooled and quality boiling regions. By S. Z. Rouhani and E. Axelsson. 1968. 26 p. Sw. cr. 10: - .
337. Neutron elastic scattering cross sections of iron and zinc in the energy region 2.5 to S.1 MeV. By B. Holmqvist, S. G. Johansson, A. Kiss, G. Lodin and T. Wiedling. 1968. 30 p. Sw. cr. 10:- .
338. Calibration experiments with a DISA hot-wire anemometer. By B. Kjellström and S. Hedberg. 1968. 112 p. Sw. cr. 10:- .
339. Silicon diode dosimeter for fast neutrons. By L. Svansson, P. Swedberg, C-O. Widell and M. Wik. 1968. 42 p. Sw. cr. 10:- .
340. Phase diagrams of some sodium and potassium salts in light and heavy water. By K. E. Holmberg. 1968 48 p. Sw. cr. 10:- .
341. Nonlinear dynamic model of power plants with single-phase coolant reactors. By H. Vollmer. 1968. 26 p. Sw. cr. 10:- .
342. Report on the personnel dosimetry at AB Atomenergi during 1967. By J. Carlsson and T. Wahlberg. 1968. 10 p. Sw. cr. 10:- .
343. Friction factors in rough rod bundles estimated from experiments in partially rough annuli — effects of dissimilarities in the shear stress and turbulence distributions. By B. Kjellström. 1968. 22 p. Sw. cr. 10: - .
344. A study of the resonance interaction effect between ""U and JI'Pu in the lower energy region. By H. Häggblom. 1968. 48 p. Sw. cr. 10:—.
345. Application of the microwave discharge modification of the Wilzbach technique for the tritium labelling of some organics of biological interest. By T. Gosztonyi. 1968. 12 p. Sw. cr. 10:-.
346. A comparison between effective cross section calculations using the intermediate resonance approximation and more exact methods. By H. Häggblom. 1969. 64 p. Sw. cr. 10:- .
347. A parameter study of large fast reactor nuclear explosion accidents. By J. R. Wiesel. 1969. 34 p. Sw. cr. 10:- .
348. Computer program for inelastic neutron scattering by an anharmonic crystal. By L. Bohlin, I. Ebbsjö and T. Högberg. 1969. 52 p. Sw. cr. 10:- .
349. On low energy levels in 1SSW. By S. G. Malmskog, M. Höjeberg and V. Berg. 1969. 18 p. Sw. cr. 10:- .
350. Formation of negative metal ions in a field-free plasma. By E. Larsson. 1969. 32 p. Sw. cr. 10:- .
351. A determination of the 2 200 m/s absorption cross section and resonance integral of arsenic by pile oscillator technique. By E. K. Sokolowski and R. Bladh. 1969. 14 p. Sw. cr. 10:- .
352. The decay of "<Os. By S. G. Malmskog and A. Bäcklin. 1969. 24 p. Sw. cr. 10: - .
353. Diffusion from a ground level point source experiment with thermolumine-scence dosimeters and Kr 85 as tracer substance. By Ch. Gyllander, S. Hollman and U. Widemo. 1969. 23 p. Sw. cr. 10:- .
354. Progress report, FFN, October 1, 1967 - september 30, 1968. By T. Wiedling. 1969. 35 p. Sw. cr. 10:-.
355. Thermodynamic analysis of a supercritical mercury power cycle. By A. S. Roberts, Jr., 1969. 25 p. Sw. cr. 10:- .
356. On the theory of compensation in lithium drifted semiconductor detectors. By A. Lauber. 1969. 45 p. Sw. cr. 10:- .
357. Haif-life measurements of levels in ,sAs. By M. Höjeberg and S. G. Malmskog. 1969. 14 p. Sw. cr. 10:- .
358. A non-linear digital computer model requiring short computation time for studies concerning the hydrodynamics of the BWR. By F. Reisch and G. Vayssier. 1969. 38 p. Sw. cr. 10: - .
359. Vanadium beta emission detectors for reactor in-core neutron monitoring. I. O. Andersson and B. Söderlund. 1969. 26 p. Sw. cr. 10:- .
List of published AES-reports (In Swedish)
1. Analysis be means of gamma spectrometry. By D. Brune. 1961. 10 p. Sw. cr. 6:- .
2. Irradiation changes and neutron atmosphere in reactor pressure vessels-some points of view. By M. Grounes. 1962. 33 p. Sw. cr. 6:—.
3. Study of the elongation limit in mild steel. By G. Östberg and R. Atter-mo. 1963. 17 p. Sw. cr. 6:- .
4. Technical purchasing in the reactor field. By Erik Jonson. 1963. 64 p. Sw. cr. 8 : - .
5. Agesta nuclear power station. Summary of technical data, descriptions, etc. for the reactor. By B. Lilliehöök. 1964. 336 p. Sw. cr. 15:-.
6. Atom Day 1965. Summary of lectures and discussions. By S. Sandström. 1966. 321 p. Sw. cr. 15:-.
7. Building materials containing radium considered from the radiation protection point of view. By Stig O. W. Bergström and Tor Wahlberg. 1967. 26 p. Sw. cr. 10: - .
Additional copies available from the library of AB Atomenergi, Fack, S-611 01 Nyköping, Sweden.
EOS-tryckerierna, Stockholm 1969
1—280. (See the back cover earlier reports.)
281. Collision probabilities for finite cylinders and cuboids. By I. Carlvik. 1967. 28 p. Sw. cr. 10:- .
282. Polarized elastic fast-neutron scattering of 12C in the lower MeV-range. I. Experimental part. By O. Aspelund. 1967. 50 p. Sw. cr. 10: - .
283. Progress report 1966. Nuclear chemistry. 1967. 26 p. Sw. cr. 10:- . 284. Finite-geometry and polarized multiple-scattering corrections of experi
mental fast-neutron polarization data by means of Monte Carlo methods. By O. Aspelund and B. Gustafsson. 1967. 60 p. Sw. cr. 10:- .
285. Power disturbances close to hydrodynamic instability in natural circulation two-phase flow. By R. P. Mathisen and O. Eklind. 1967. 34 p. Sw. cr. 10:- .
286. Calculation of steam volume fraction in subcooled boiling. By S. Z. Rou-hani. 1967. 26 p. Sw. cr. 10: - .
287. Absolute E1, AK = O transition rates in odd-mass Pm and Eu-isotopes. By S. G. Malmskog. 1967. 33 p. Sw. cr. 10:- .
288. Irradiation effects in Fortiweld steel containing different boron isotopes. By M. Grounes. 1967. 21 p. Sw. cr. 10:- .
289. Measurements of the reactivity properties of the Agesta nuclear power reactor at zero power. By G. Bernander. 1967. 43 p. Sw. cr. 10:- .
290. Determination of mercury in aqueous samples by means of neutron activation analysis with an account of flux disturbances. By D. Brune and K. Jir-low. 1967. 15 p. Sw. cr. 10: - .
291. Separtaion of "Cr by means of the Szilard-Chalmers effect from potassium chromate irradiated at low temperature. By D. Brune. 1967. 15 p. Sw. cr. 10:-.
292. Total and differential efficiencies for a circular detector viewing a circular radiator of finite thickness. By A. Lauber and B. Tollander. 1967. 45 p. Sw. cr. 10:- .
293. Absolute M1 and E2 transition probabilities in 1 M U. By S. G. Malmskog and M. Hojeberg. 1967. 37 p. Sw. cr. 10:-.
294. Cerenkov detectors for fission product monitoring in reactor coolant water. By O. Strindehag. 1967. 56 p. Sw. cr. 10:-.
295. RPC calculations for K-forbidden transitions in 1 "W. Evidence for large inertial parameter connected with high-lying rotational bands. By S. G. Malmskog and S. Wahlborn. 1967. 25 p. Sw. cr. 10:- .
296. An investigation of trace elements in marine and lacustrine deposits by means of a neutron activation method. By O. Landstrom, K. Samsahl and C-G. Wenner. 1967. 40 p. Sw. cr. 10:- .
297. Natural circulation with boiling. By R. P. Mathisen. 1967. 58 p. Sw. cr. 10:- . 298. Irradiation effects at 160-240°C in some Swedish pressure vessel steels.
By M. Grounes, H. P. Myers and N-E. Hannerz. 1967. 36 p. Sw. cr. 10:- . 299. The measurement of epithermal-to-thermal 0-238 neutron capture rate (P28)
in Agesta power reactor fuel. By G. Bernander. 1967. 42 p. Sw. cr. 10:- . 300. Levels and transition rates in "«Au. By S. G. Malmskog, A. Bicklin and B
Fogelberg. 1967. 48 p. Sw. cr. 10:- .
301. The present status of the half-life measuring equipment and technique at Studsvik. By S. G. Malmskog. 1967. 26 p. Sw. cr. 10:- .
302. Determination of oxygen in aluminum by means of 14 MeV neutrons with ? S « c J £ u n t ~ o f fl«x attenuation in the sample. By D. Brune and K. Jirlow. 1967. 16 p. Sw. cr. 10:—.
303. Neutron elastic scattering cross sections of the elements Ni, Co, and Cu between 1.5 and 8.0 mev. By B. Holmqvist and T. Wiedling, 1967. 17 p.
304. A study of the energy dependence of the Th232 capture cross section in the energy region O.I to 3.4 eV. By G. Lundgren. 1967. 25 p. Sw. cr. 10:-.
305. Studies of the reactivity effect of polythene in the fast reactor FRO. By L. I. Tir<5n and R. Hakansson. 1967. 25 p. Sw. er. 10:- .
306. Final report oni IFA-10, the first Swedish instrumented fuel assembly Irradiated in HBWR, Norway. By J-A. Gyllander. 1967. 35 p. Sw. cr. 10:- .
307. Solution of large systems of linear equations with quadratic or non-quadratic matrices and deconvolution of spectra. By K. Nygaard. 1967. 15 p.
308. Irradiation of superheater test fuel elements in the steam loop of the R2 reactor. By F. Ravndal. 1967. 94 p. Sw. cr. 10:- .
309. Measurement of the decay of thermal neutrons in water poisoned with the non-1/v neutron absorber cadmium. By. L. G. Larsson and E. Moller. 1967. 20 p. Sw. cr. 10:-.
310. Calculated absolute detection efficiencies of cylindrical Nal (Tl) scintillation crystals for aqueous spherical sources. By. O. Strindehag and B. Tollander. 1968. 18 p. Sw. cr. 10:-.
311. Spectroscopic study of recombination in the early afterglow of a helium plasma. By J. Stevefelt. 1968. 49 p. Sw. cr. 10: - .
312. Report on the personnel dosimetry at AB Atomenergi during 1966. By J. Carlsson and T. Wahlberg. 1968. 10 p. Sw. cr. 10:- .
313. The electron temperature of a partially ionized gas in an electric field. By F. Robben. 1968. 16 p. Sw. cr. 10:- .
314. Activation Doppler measurements on U238 and U235 In some fast reactor spectra. By L. I. Tiren and I. Gustafsson. 1968. 40 p. Sw. cr. 10:- .
315. Transient temperature distribution in a reactor core with cylindrical fuel rods and compressible coolant. By H. Vollmer. 1968. 38 p. Sw. cr. 10:- .
316. Linear dynamics model for steam cooled fast cower reactors. By H. Vollmer. 1968. 40 p. Sw. cr. 10: - .
317. A low level radioactivity monitor for aqueous waste. By E. J. M. Ouirk. 1968. 35 p. Sw. cr. 10: - .
318. A study of the temperature distribution in U O J reactor fuel elements. Bv I. Devoid. 1968. 82 p. Sw. cr. 10:-.
319. An on-line water monitor for low level ^-radioactivity measurements. Bv E. J. M. Quirk. 1968. 26 p. Sw. cr. 10:- .
320. Special cryostats for lithium compensated germanium detectors. By A. Lauber, B. Malmsten and B. Rosencrantz. 1968. 14 p. Sw. cr. 10: - .
321. Stability of a steam cooled fast power reactor, its transients due to moderate perturbations and accidents. By H. Vollmer. 1968. 36 p. Sw. cr. 10:-.
322. Progress report 1967. Nuclear chemistry. 1968. 30 p. Sw. cr. 10: - . 323. Noise in the measurement of light with photomultlpliers. By F. Robben.
1968. 74 p. Sw. cr. 10: - .
324. Theoretical investigation of an electrogasdynamic generator. By S. Palm-gren. 1968. 36 p. Sw. cr. 10:- .
325. Some comparisons of measured and predicted primary radiation levels In the Agesta power plant. By E. Aalto, R Sandlin and A. Krell. 1968. 44 p. Sw. cr. 10:- .
