ML19329F917
| ML19329F917 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 07/10/1980 |
| From: | Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton, Youngblood B Office of Nuclear Reactor Regulation |
| References | |
| 606, NUDOCS 8007110361 | |
| Download: ML19329F917 (8) | |
Text
' -
VruGINIA ELECTRIC AND Powen Costnuev Rxcunoxu,Vxnora xA 20261 July 10, 1980 Mr. Harold R. Denton, Director Serial No.: 606 Office of Nuclear Reactor Regulation N0/ JOE /jmj Attention:
Mr. B. Joe Youngblood, Chief Docket No. 50-339 Licensing Branch 1 License No. NPF-7 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Denton:
ADDITIONAL INFORMATION REACTOR COOLANT SYSTEM VENTS NORTH ANNA UNIT 2 Attached you will find additional descriptive information for action iten II.B.1 requested by members of your staf f for North Anna Unit 2 full power licensing g
review. We believe this will provide sufficient detail to address your concerns for that action item and subsequent licensing approval. We also received a request from members of your staf f on July 1,1980 which requests additional information for Reacter Coolant System Vents. We are reviewing this request and will provide the additional information as soon as possible.
Please advise if you require any additional infarmation.
Very truly yours, s i
/^
di B.R.[ Sylvia Manager - Nuclear Operations and Maintenance Attachment cc:
Mr. James P. O'Reilly Officc of Inspection and Enforcement 34l
- 8 00711e
RESPONSE TO FULL POWER LICENSING REQUIREMENTS VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT NO. 2 II.B.1 REACTOR COOLANT SYSTEM VENTS 1.
DESCRIPTION OF THE DESIGN Introduction The purpose of ttti report is to present the design of modifications which allow for React ( r Conlant System Venting.
The Reactor Vessel Head and Pressurizer Ver:
-fstem is being designed to accommodate North Anna Power Station Us.
'l power licensing requirements.
The following list o; t.rerences presents the documents being used in the development of the Reactor Vessel Head and Pressurizer Venting Systems.
1.
North Anna Power Station Te.chnical Specifications 2.
North Anna Power Station Environmental Technical Specifications 3.
North Anna Power Station Final Safety Analysis Report 4.
Vepco Nuclear Power Station Quality Assurance Manual 5.
Appendix A to 10 CFR Part 50, General Design Criteria 6.
Regulatory Guide 1.7, Revision 1 7.
Standard Review Plan, Section 6.2.5 t
8.
10 CFR Part 50.46 (LOCA criteria) i 9.
10 CFR Part 50.44 (containment criteria for hydrogen generation) 10.
IEEE 279, 323, 344, and 382 11.
USAS B31.7-1969 Description The design of the Reactor Vessel Head and Pressurizer Venting Systen is being developed in such a way as to maintain similarity between North Anna Power Station Units 1 and 2.
The Reactor Vessel Head and Pressurizer Venting Systems will be capable of venting the reactor vessel head and the pressurizer through the use of remote manual operation from the control room.
This venting arrangement is designed to eliminate a condition of inadequa te emergency core cooling, inadequate natural circulation or inability to decrease RCS pressure to the Residual Heat Removal System initiation conditions.
.The Reactor Vessel Head and Pressurizer Venting Systems will discharge to the containment atmosphere in the vicinity of the refueling cavity. Pre-liminary engineering design considerations have indicated this region to have the largest area for gas dispersion and maximum cooling capability.
These considerations minimize the potential for hydrogen explosion if explosive concentrations develop.
This discharge point also allows for t
adequate drainage and handling of reactor coolant in the case of an l -
inadvertent discharge. Our Architect Engineer is performing the necessary
W S
g
. analyses to insure that the present design is compatible with the combusti-ble gas concentration limits-in containment as described in 10 CFR Part 50.44, Regulatory Guide 1.7 (Rev. 1) and the Standard Review Plan Section 6.2.5.
Preliminary engineering calculations have shown that the Reacier
- Vessel Head and Pressurizer Venting System is sized suf ficiently to vent a gas volume of one half the reactor coolant system in one (1) hour.
gactor Vessel Head Vent The reactor vessel head vent flow diagram is shown on Sketch 1.
The de-sign provides fer reactor vessel head venting through the use of safety grade equipment compa tible with the design of our nuclear steam supply system.
The reactor vessel head vest system consists of one inch vent piping with four (4) safety grade " fail closed" isolation valves.
The isolation valves are powered by vital D.C.
power supplies and are " fail closed" active valves in accordance with Regulatory Guide 1.48.
These valves will remain normally closed.
Isolation valves 1 and 2 are powered by Train A and isolation valves 3 and 4 are powered by Train B.
This design insures no single active failure which would prevent reactor vessel head venting or vent isolation.
The reactor vessel head vent with redundant paths connects to and is suo-ported by the vessel head.
Each vent path contains a restricting orifice.
This orifice res tr ic ts the flow rate from a vent pipe break such that one charging pump can provide the necessary make up to the reactor coolant system.
~
The reactor vessel head vent system is to oe supported from the seismic support plat fo rm.
Therefore, all piping aad valves remain integral with the reactor vessel head at all tmes.
The vessel head vent final design will satisfy criteria that have consitit ited an acc.eptable design for safety systems.
This design will satisfy USNRC and indus trial nuclear safety criteria including safety class, seismic design, single failure and post accident operability.
Our architect engineer has been contracted to pstform the necessary analyses to demonstrate the reactor' vessel'haad vent design will meet the intent of 10 CFR 50.44.
Fressurizer Vent The pressurizer vent system flow diagram is shown on Sketch 2.
The system provides for venting of the pressurizer by using safety grade equipment.
The system consists of one inch vent piping with four safety class " failed closed" isolation valves.
The isolation valves are powered by vital D.C..
power supplies and are " fail closed" active valves in accordance with Reg.ilatary Guide 1.48.
All of these valves are normally closed.
Isolat on valves 5 and 6 are powered by Train A and isolation valves 7 and 8 are powered. by Train B.
The system is designed such that any single active failure will 'not prevent pressurizer venting or venting isolation.
The pressurizer venting system connects to the -safety class pressurizer sample line.
The pressurizer vent lines are sized or restricted such that blev-down through the vent line will be within the capability of one charging pump.
1
= <
The pressurizer venting system is designeu to criteria that have consti-tuted an acceptable design for safety system:s.
The design will natisfy applicable USNRC and industry nuclear safety criteria, including safety
- class, se_ ismic design, single failure, and post accilent operability criteria.
The design of the pressurizer ve'n 3 systet is developed so that no modifications to the present envele je of accident analyses is required.
Operation The Reactor Vessel Head and Pressurizer Venting System design allows for the use ' of individual valve position indication that indicates in the control room each valve's true position, not just electrical supply avail-ability.
Our architect engineer has been contracted and is presently developing this design which provides indication in the control room for valve position indication for the Reactor Vessel Head and Pressur'zer Venting System.
The operation of the Reactor Vessel Head and Pressurizer Venting System allows for independent venting of the reactor vessel head and the pres-surizer.
During normal operation of the plant, all isolation valves are closed.
To operate the reactor vessel-head -vent or the pressurizer vent, the isolation valves in one train are opened.
Each isolation valve has its own set of controls including valve position.
In conjunction with opening the isolation valves, reactor coolant make up is actuated.
If one train of isolation valves is unavailable due to a single failura, the redundant train of isolation valves is opened.
The venting opatation is k
secured by closing all isolation valves.
Provisions for system testing during power operation will be provided.
Inadvertent actuation of the reactor vessel head vent or pressurizer vent is highly unlikely. The Reactor Vessel Head and Pressurizer Venting System provides series valves in parallel vent paths.
Both valves in series are normally closed, " fail closed" valves.
Each isolation valve is separately controlled.
Each isolation valve has its actual valve position indicated in the control room.
This design eliminates the possibility of inadver-tently opening and therefore does not require a separate leakage detection system.
If vent line leakage dces occur, existing leakage detection systems are capable of monitoring this leakage.
Piping Analysis The piping analysis for the Reactor Vessel Head and Pressurizer Venting System will incorporate a three-dimensional dynamic model which includes the effects of interaction with the reactor coolant system and the effect of the supports and supported equipment. The piping analysis of the static and dy.acic models will employ the displacement method, lumped parameter, stiffness matrix 'omulation and assumes that all components and, piping behave in a linear elastic manner.
For normal operating loads, the system operating parameters and ' censients are.used as the basis for the analysis of the piping.
The analysis is performed using a sta tic model to predict deformation and stress in the system during normal plant conditions and opera ting t ransients, such as
'Y 4
y heatup, ce,1down, and loss of flow.
Results of the analysis will give six generalizea - force ' components - three moments ani three forces.
These moments. and forces are. resolved into stresses in the pipe in accordance with the simplified analysis defined in subsec t ion NC-3650 of the ASME E
Code, Sec tion' III.
Forces ac t ing on the piping supports and equipment will be determined.
The analysis of the piping system consists of dynamic model analysis utilizing the response spectrum method to determine earthquake-induced.
displacements,. forces, and stresses in the piping.
The model analysis method requires that the piping systems. be represented analytically by lumped parameter mathematical models to ensure computer solution of the large number of simultaneous equations which represent the equations of motion.
The maximum displacements or forces which result from seismic disturbances will be calculated at the mass points in the system.
From these displace-ments or forces, the maxinum intra-modai stresses are calculated absolutely and combined for all the modes by the square root sum-of the squares method except for the ef fects cf closely spaced modes, to give the total seismic stresses at selected points in the piping system.
In addition, forces and displacements acting on the piping supports and cquipment will be deter-mined.
2.
REACTOR VESSEL HEAD AND PRESSURIZER VENTING SYSTEM VENT PIPE BREAK LOCA ANALYSES Westinghouse 'small break LOCA analyses are documented in UCAP 9600.
The sizes of the breaks analyzed range from less than 3/8 inch equivalent oiameter to greater than two (2) inches equivalent diame te r.
This range of break. analyses envelopes t' e full range of possible vent pipe breaks.
The nodels used in these analyses and referenced in Section 1.0 of WCAP 9600 are the Westinghouse small break models which meet the require-ments of Appendix K.
They are described in WCAP 8261, Revision 1, "WFLASH - A FORTRAN-IV Computer Program for Simulation of Transients in a Multi-Loop PWR" and WCAP 8970, '%stinghouse Emergency Core Cooling System. Small Break ' October, 1975 Model".
The current models remain appropriate for these analyses.
Analysis assumptions which were used are also in conforu:ance with Appendix K criteria as described in Section 3.1 of WCAP 9600.
Reactor Vessel Head and Pressurizer Venting System piping downstream of the isolation valves or outside of the piping class change from class 1 to' class 2. is sized or orificed to insure any break in this area is within the : capability of one high head charging pump for insuring ade-quate reactor coolant system make-up.
3.
EFFECTS OF OPERATION OF REACTOR HEAD VENT SYSTEM ON CONTAINMENT HYDROGEN CONCENTRATION The design and operation of -the reactor head vent system meets the requirements of Regulatory Guide 1.7 and Standard Review Plan 6.2.5.
The y
n e- - -
w, vm -
- .... u containment - hydrogen concentration will be li, sited to the lower flamma-bility~ limit of 4 volume percent hydrogen.
The location of the vent
~
outlet has been chosen ~ to prevent high concentrations of hydrogen in
-local areas.
"'h e vent outlet is at the operating floor level near the middle of the containment.
The region of the containment above the operating floor is a large open volume which allows rapid dispersion of the vent effluent.
There are no enclosed compartments in this region of the containment with the ~ potential to accumulate hydrogen in amounts giving high local concen- -
trations.
Operation of the vent system will be based on the current hydrogen con-centration in the containment _ as determined by the hydrogen analyzers.
It is therefore independent of the history of the event.
Procedural requirements allow opening of the vent valves with or without a hydrogen recombiner in operation and only if the hydrogen concentration in the containment has s tabilized.
The hydrogen concentration will be con,
sidered stable if the analyzers indicate no increase, or a small
-increase, over a specified time period.
The vent - time will be-determined from' a family of curves similar to -
Figure 1.
The-vent time is a function of reactor vessel pressure and the desired increase in containment hydrogen concentration.
The increase in concentration will be restricted - to result in a raaximum projected con-tainment concentration of 3 volume percent.
This allows for 0.5 volume percent error in determining the initial hydrogen concentration and 0.5 I
volume percent - allowance for hydrogen generation from other sources.
The curves in Figure 1 are based on venting 100 percent hydrogen at a temperature of 6GO*F through a thre -eighths inch orifice.
The vent rate was - based on icentropic compress 31e flow through an orifice.
The flow rate is relatively insensitive to temperature.
If the vent flow is not-100 percent hydrogen, the containment hydrogen concentration will not attain the projected level. Operat'on of the vent system can be repeated based on the new reactor vessel pressure and con-tainment. hydrogen concentration,af ter a specified period of time to allow Or attainment of a stabilized hydrogen concentration.
The venting operation would proce d as follows:
If the reactor. vessel pressure is 1000 psia, the ' containment hydrogen concentration is one volume 'pe rcent (determined from the' hydrogen analyzers), and 11 is de' sired 'to vent to the maxi-
~
mum allowable expected.concentratio-of 3 volume percent; from
)
Figure 1 with a ? 1 volume percent enange in concentration, the venting time is 5 minutes. ' Opening a single train of the vent.
valves for 5 minutes at '.1000 psia will release a volume of gas
-which had occupied roughly 10 percent of the total reactor cool-aat system volume.
O G
-R o
~;) M $ rtN2Q]e %,
3
~ '
~
_L N3 J 213d
% O 7 Q/\\
I y 3.... @
m I
_ ( _ __._- -N.O! M b_LN.3 ~%N Op 2 p j _j g F._.,c.y' y.tg-..
j-i _-},
1 f
i 9-6 4
- _,I ?, 1
- 4 a --
i
+
.u
.>f
?
i
_.1 2-PI g i -,{
W.
I l-1 s.
..-4-.4.-.
L t
i
[.{!
( j.-y TA i
. - _L -
d,-
f,.,
,. j. j ',$
~
-i I
v, i
y --*
p 1
i 4-d
}-
l-J~
~ I. _~.~3 f.
4 y.
p i
-1 f
C I I
5 y
~.
a i
pl -.__; e i.
.-3 A_.
1.
4.
)}
~I a
?
g i
,m-- t -- -
"i TT e,,,,,,.
4 e
h
$ I
~
k
""c i -
r
,i 3
l
~
f
.. ],..
. r de f
a o
j
._y,
2 w-i
. _. p
.c.
....g 2
__t (c-p
_g
<5.~
. _ _ _. _.. 7 -,__j o
. i i_. g._
}
1__
._-...J..
,&_,.(
j T
N '"
- h p_;
m_
.g-..q w
i
- .. j.,..
__4
- c. '
i
-- -f4, i.g. ( Q Q ^};
a
.j
'- t
}.
.,p l
1 :. ;.
..!.I+i-.;_L + f_' u !
. k'*
I
?
y l H._.
.._.gM f
. i_. '
[!
[
l1 1_
i
.y I
-J t
",~y 3,
.s.
f.
k p.
v-i 2-1 1
. _ j._
}
b.i
.._ M
% ~ :-
w'.
,[_.__].._ ~ b_ _.
Q
.A..
l l
.,__,.-y_-_!._
..g 2
-/
/
i I
fA l% 5 1
,i i _ s _.. f _._, _s i
\\-- -3 M
( /=__
._. :__.1H g
L.
4 j
7
~
, a q
m
,f 4
- s.._
m
_; _u m.
W1 t
V
.,_t 2
S ~'l
?
._ b A
~~ - k ~
~~~~~~~g Q
f
.q x -
w g
V, -i, _
/. _ __ M
- l h)
.%i l
I i
. _ _ n_...
- \\
r s
s 1
e 1
1
)
k<i\\
O
\\ /
t
/
. '#h
, _ ;_ }Q t/-
>f I
\\/
- -E t
i i
J
,. 9
'?
L.4 4
\\
\\
! \\
\\
_ g\\
g 1
/~1'\\g
-f '_,.
~~Y[
o 3
\\_
fi i
\\
\\
w 4.'
7;\\
i i
\\
\\ 1 i.
t m
\\
st,
i.
Tl e 1 2
G 1
?
\\
/,
\\ /
- \\ _
g P
l l
7 -/\\
-/.
N _
in
~
s 3
i____.
i
\\
i a
i
\\
l s
t i
i 8
_,,.L f
+
t o
/
g 1
U sf i-y
/
1.j
=
/
t i
- 4 l
_{__
,n n
f _,.,,..
I._,..
Q a
4
._......p _q _. _.+
. _ p _ _
-9.-
p.___. :
e
.u ;.. t_...
1
._. ;. _ _ _.__ {_
g,a
._._--.. A_y g.... g,. n MI %.. N __1.L M,3 M....
9, 3:
,. _.,, _._.,7_...
e_. r.
o
>2 o
to o
M o
in
_C, "2..
.r***
. et.
~
~ -
L._
I_
=
c.
E E5 O
ag
- e.. x.*
e-n y,a o
-s 2 s,,
- 5. 56 Q
C*
C*
a
=
s v
%v R:
g,,5 LA y b5 5hN @U 5
5 e
a p
E' El.-
a e ajo n.u
.G
.e :
S8 G5 559 Cd e
$5
?
S' ldr*a*1 55d" t
3 r
t o-o s
c o.
a m i o a:
- u. c u m
o-um c,
c, o.-
m L' !!,5 o
- T u-c:
a e
A 4
f9 Se I:
c
.f E!
y
?,
i o
il fj i
gy s
s
=.
- =
-w e
==
NM bE
?
h n
U
-g h h.
O k
/
N
,~
n 1 c
$c$ 5"; N d
e o
n
-6 !
i Fc v
.Nw
~
un
's t;
R i
Ea 49 E m=
x m3 h
E n
-e ug 5s
=
E' 5 d
m
'a d
.u
?
59 *; -o p
z.-
us 2
- a.e.E Ea >T a., n.
..sco 8, n.
s n
se
<go g
rr a
n$.o$
- E.:
A A e aV r
m E
b.
h
)
m i
t'._9 m3 3
\\
s
$1
$1 g-O ~\\
M
. a _u.
~
h h
~ ' "
LE._3 N
()
i
~
g' s-a%
S>
_J g
<=
=
72 "O
83 s..
t s '-
1 47
.'y
,. k '-'
e
-g-5 n
m Z
h31
^
d H
GV
's 01
?
a
\\
o W
()
m
.L Jf
! _o,"i
- a. r, s,c O
-