ML19354D684
| ML19354D684 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/31/1975 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML19354D682 | List: |
| References | |
| NUDOCS 8912290067 | |
| Download: ML19354D684 (12) | |
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6 EFFECTS OF NON-CATEGORY A EQUIPMENT FAILURE ON SAFETY-RELATED EQUIPMENT SAN ONOFRE NUCLEAR GENERATING STATION l
UNIT 1 i
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l MAY 1975 I
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1.0 INTRODUCTION
In mid-December of 1974, Southern California Edison (SCE) received a letter from the Atomic Energy Commission (AEC) requesting a review of San Onofre Unit 1 to determine whether or not the failure of any non-Category A equipment could affect safety-related equipment required for either shutdown or in the mitigation of the consequences of an accident.
In the report
" Effects of Non-Category A Equipment Failure on Safety-Related Equipment" issued in March 1975, it was concluded that plant design and operator action provide adequate protection of safety-related equipment against postulated non-Category A equipment failure.
When the report was issued, further investigation was required to quantitatively establish the effects that certain chemicals would have upon safety-related electrical cable relative to determining what (if any) modifiqations might have to be done to assure that the cables would perform in an accident environ-ment.
Further investigation and testing has shown that the cables would not be damaged by chemical action during the period of time they would be required to perform.
It is finally con-cluded that no further action is required.
2.0 SUMHARY The safety-related electrical cables requiring inves-tigation are in Areas 5, 6 and 14.
It was identified that ammonia or dilute solutions of potassium chromate or hydra-zine could impinge upon the cables due to a postulated non-Category A equipment failure.
Additional detailed investi-gation of existing data showed that the cables could safely sustain the impingement of ammonia or dilute potassium chromate.
Tests performed by Southern California Edison showed that the cable could also safely sustain impingement of dilute hydrazine.
It is concluded that chemical release from non-Category A equipment failure will not impair the function of these safety-related electrical cables and no additional pro-tection of these cables is required.
The general conclusion that plant design and operator action provide adequate pro-tection of safety related equipment from postulated non-Category A equipment failure is confirmed.
e 3.0 CHEMICAL EFFECTS ON CABLE As identified in the report issued on March 21, 1975, it was not precisely known at that time what effects certain chemical solutions would have upon safety-related cables.
The cables requiring investigation are in areas 5, 6 and 14 and are either neoprene-jacketed, 600 volt or aluminum-armored, 4 kilovolt rated.
The chemicals that require investigation are dilute solutions of hydrazine and of potassium chromate.
In areas 5 and 6, which are under the turbine deck, the cable in question is neoprene-jacketed, butyl-insulated and rated at 600 volt capacity.
These cables are connected to some of the Safety Inj ection MOVs.
There are locations where the trays in which these cables are placed pass directly beneath the chemical feed lines.
These lines primarily contain a solution of hydrazine but may also contain ammonia.
In area 14, which is outside the turbine area and near the intake structure, the cables in consideration are l
l the neoprene-jacketed, butyl-insulated, 600 volt type and the l
l aluminum-armored, 4 kilovolt type.
These cables are used in conjunction with the Safety Injection Pumps.
The cables are in trays directly beneath the turbine plant cooling water header.
The water in the header contains a dilute solution l
(i.e., 350 ppm) of potassium chromate.
The Safety Inj ection equipment connected to the 1
cables in these areas must operate for approximately 15 minutes for a large-break loss-of-coolant accident (LOCA) and for 1
about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> during a small-break LOCA.
Therefore, a 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> minimum criterion was set for the appearance of any chemical effects that might occur to impair the operation of the electrical cables.
A more detailed discussion of the chemical effects upon the subject safety-related electrical cables appears below.
3.1 Cable in Area 14 The 600 volt cable is shown in Figure 1.
It can be seen that each conductor is covered by butyl rubber insulation.
The grouped conductors are in turn surrounded by the neoprene jacket.
If a break were to occur in the turbine plant cooling water header, 350 ppm potassium chromate solution could impinge on the neoprene jacket of this cable.
Further investigation has revealed manufacturer test data that shows for this dilute solution of potassium chromate there is no reaction on the neoprene jacket over the critical period of time considered here.
Test results indicate that some increase in volume of the jacket after long-term exposure (in the order of weeks or months) may occur.
The 4 kilovolt (kv) cable is shown in Figure 2.
In construction, the only difference between the 600 volt cable and the 4kv cable is the addition of an aluminum sheath over the neoprene jacket.
The only purpose of the aluminum armor is to provide additional mechanical protection for the cable and as such is not intended to keep liquids from contacting
4 the neoprene jacket.
If the potassium chromate solution were to impinge on this cable the liquid would pass freely to the neoprene jacket.
The ensuing chemical effects (if any) revert to those encountered when dealing with the 600 volt cable.
As has been explained above, there is no reaction on the neo-prene and hence the 4kv cable is also immune to damage from the potassium chromate solution during the time frame involved.
Therefore, it is concluded that the electrical cables in area 14 (both 600 volt and 4kv) are not subject to I
damage by the dilute potassium chromate solution over the period of time that these cables would be required to perform, and that any additional protection of the cables in area 14 is unnecessary.
3.2 Cable in Areas 5 and 6 The cable considered here is like that shown in Figure 1.
If a chemical feed line were to fail, certain lengths j
of cable could be sprayed by either ammonia or a solution of hydrazine, i
Examination of manufacturer test data shows that there is no reaction between the ammonia and the neoprene.
Other data shows significant reactions between strong hydrazine solutions and neoprene, however, no data was available that described the degree of reaction when a dilute solution of hydrazine was in contact with neoprene.
It was determined l
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that a 1.757, solution of hydrazine is present in the chemical feed lines.
Significant reaction rates with the neoprene from such a dilute solution of hydrazine over the time span con-l sidered here were not expected.
However, to assure this, an immersion test was performed to quantitatively establish the type and rate of reactions that might occur.
It was deter-i mined that the test could be performed at room temperature without having to electrify the cable samples.
The test method and rationale are described in the following paragraphs.
I The temperature of the environment in which these 0
cables are operating is around 100 F (under the turbine deck).
The test was performed at room temperature conditions, about 0
70 F, The rate of reaction approximately doubles for each 20 F increase it temperature.
Therefore, any reaction that may occur during a certain time frame at 70 F could be extrapolated to give a description of how the reaction would proceed at 0
100 F.
l In order to electrochemically speed up the reaction rate of the hydrazine on the neoprene, there must be the for-t mation of free radicals by breaking the hydrazine molecule at t
the N-N (Nitrogen-Nitrogen) bond.
To break this bond, the i
electrochemical potentiai at the hydrazine/ neoprene interface must be in the range of 1 volt for a 1 molar hydrazine solution.
(The required voltage increases with more dilute solutions.
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- A This is due to the presence of the H 0.)
The cable in question 2
has a rating of 600 volts.
The resistivity of the butyl 17 insulation is around 10 ohms /cm.
Th insulation is about 30 mm 16 in thickness and gives a resistance of about 10 ohms.
This results in a potential in the neoprene in the order of a few picovolts (10-12 volts) for an energized cable of 600 volts.
Since the few picovolts of potential that the hydrazine sees is much less than the minimum 1 volt potential required, the free g
radical formation and hence the electrochemically' accelerated l
reaction rate will not be experienced.
Therefore, energizing L
i the cable test specimens would not add useful information to the test results.
l The immersion test consisted of inserting samples of cable into several beakers containing a 1.75% hydrazine solution.
The samples were held in a "U" shape to isolate the exposed ends from the solution.
This was done to prevent 1
any possible reaction with the conductors from interfering with the desired isolated reaction on the neoprene jacket.
- The sample in each beaker was removed after a specified immer-sion time and any reaction or change in the cable or the immersion solution noted.
The actual immersion times associated with each beaker (and sample) are listed below.
Beaker No.
Specified Actual (and Sample No.1 Time (Days)
Time (Days) 1 1
1.2 2
4 4.0 3
5 5.125 4
7 7.17
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.1 For the duration of. the test, no gross deterioration (i.e., embrittlement, swelling, blistering, cracking, etc.)
of the neoprene was observed.
The only observed effect was a very slight fading of the neoprene jacket.
This effect was P
found to be slightly progressive with increased immersion time.
The solutions in beakers 2, 3 and 4 showed a slight yellowish-brown-coloration that became more pronounced with increased immersion time.
Also, no change in overall properties L-l of the neoprene jacket (such as diameter change, loss of I
ductility, etc.) were observed.
Microscopic investigation of the jacket showed no L
microscopic cracking or intrusion of hydrazine-caused effects such as local blistering, swelling, change in structure, etc.
Complete examination of cross sections of tested cable showed L
(1) no change in the neoprene jacket below the surface, (2) no l
change in the butyl insulation and (3) no change in the con-l j
ductors.
This was verified for all cable samples.
It was l
noted that all observed reactions were confined to the outer 1
surface of the neoprene jacket and did not in any way affect i
the insulation or the conductors.
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The most severe effects indicated by the observed reactions of slightly progressive fading of the neoprene and L
coloration of the immersion solutions is some possible dissocia-tion of neoprene molecules from the jacket at the neoprene /
l hydrazine interface.
Even at the 7 day mark these possible effects were very minor and did not interfere with the integ-l rity of the cable.
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l-As stated previously, the reaction rate approximately doubles for every 20 F increase in temperature.
The test was performed at 70 F and the operating environment is about 100 F.
The test was conducted for a 7 day period and at that time the cables were still found to be virtually free from damage.
At the elevated temperature the cables would be found in a comparable condition at 2 1/2 days and would still be-able to safely perform their function.
The minimum detectable reaction occurred at 4 days in the test and under the elevated temper-ature conditions this same minimum reaction would occur at 1 1/2 days.
Since the cables in question here can safely sustain possible chemical impingement (ammonia or dilute hydrazine) resulting from chemical feed line failure for a period of time considerable greater than the maximum 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> their operation is needed, it can be concluded that no additional protection of the cables in areas 5 and 6 is required.
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- 4. 0-CONCLUSIONS It has been determined that the 600 volt, neoprene-jacketed safety related cables and the 4 kilovolt, aluminum-armored safety related cables in areas 5, 6 and 14 can ade-quately sustain possible chemical impingement without impairment of operability for-the period of time their operation is 1
required.
Therefore, it is concluded that chemical release from non-Category A equipment failure will not impair the function of safety-related electrical cables and no additional protection of the cables is required, l-1 In general, it is concluded from the foregoing analysis covering chemical effects on electrical cable and from the initial' report covering other effects of non-Category A equipment failure on safety related equipment that plant design I
and operator action provide adequate protection of safety-related equipment against postulated non-Category A equipment failure.
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