ML20011A258
| ML20011A258 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/30/1981 |
| From: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-06-01, TASK-6-1, TASK-RR 810290, NUDOCS 8110080393 | |
| Download: ML20011A258 (9) | |
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I Gs neral Offices e Selden Street, Berlin, Connecticut gggg
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September 30, 1981 Docket No. 50-245 B10290 Director of Nuclear Reactor Regulation Attn:
Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch #5 U. S. Nuclear Regulatory Commission Washington, D.C.
20555
References:
(1)
D. G. Eisenhut letter to All SEP Licensees, dated July 7, 1981.
(2)
W. G. Counsil letter to D. G. Eisenhut, dated July 29, 1981.
Gentlemen:
Millstone Nuclear Power Station, Unit No. 1 SEP Topic VI-1, Organic Materials and f
Post Accident Chemistry Reference (1) requested the SEP licensees to commit additional resources devoted to ccmpletion of the SEP.
In Reference (2), Northeast Nuclear Energy Company (NNECO) committed to develop Safety Assessment Reports (SARs) for certain SEP topics which would be submitted for Staff review.
In accordance with this commitment, NNECO hereby provides the Safety Assessment Report for SEP Topic VI-1, Organic Materials and Post Accident chemistry, which is included as Attachment 1.
We trust the Staff will appropriately use this information to develop a Safety Evaluation Report for
- his SEP topic.
Very truly ycars, NORTHEAST NUCLEAR ENERGY COMPANY e
W.'G. Counsil Senior Vice President
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8110080393 810930 ~
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I Docket !!a. 50-245 Safety Assessment Report SEP Topw VI-1, Organic Materials and Post Accident Chemistry September, 1981
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- qO SEP SAFETY ASSESSMENT REPORT Topic VI-1, Organic Materials and Post Accident Chemistry
1.0 INTRODUCTION
The purpose of this assessment is twofold:
1.
To ensure that organic coatings used inside the Millstone Unit 1 containment are suitable for use under desj7n basis accident conditions, consistent with the intent of Section 6.1.2 of the Standard Review Plan.
2.
To ensure that post-accident containment chemistry at Millstone Unit 1, does not result in unacceptable rates of steel corrosion, or increase the volatility of dissolved iodines, consistent with the intent of Sections 6.1.1, and 6.1.3 of the Standard Baview Plan.
2.0 CRITERIA 2.1 Criteria for Organic Materials Used Inside the Containment Section 6.1.2 of the Standard Review Plan requires that all significant coating systems used inside containment be suit-able for use in the environmental conditions seen after an accident.
The stability of the coatings and their decom-position products must be examined to determine the potential for interactions with engineered safety features.
Specific areas of concern are:
1.
The possibility of coa' tings peeling and clogging sump screens.
2.
The generation of volatiles from the decomposition of coatings which could interfere with the proper functioning of charcoal absorbers used to remove radio-iodine from the containment atmosphere.
3.
The generation of hydrogen and other flammable volatiles from the decomposition of coatings.
These gases could adversely impact the operation of systems used for containment hydrogen control on some plants.
According to the Standard Review Plan, a coating system is considered acceptable if:
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'It meets Regulatory Guide 1.54 or equivalant; or, the
= 'd area covered with the system is a negligible fraction of the containment interior surfaces.
2.
.No adverse interactions with engineered safety features are likely as a result'of materials released by radiation 3
decompcaition or chemical reaction of the coating system in the containment post-accident environment."
2.2 Criteria for Post-Accident Chemistry Control Standard Review. Plan Section'6.1.1, " Engineered Safety Features Metallic Materials", requires that the composition of core spray coolants be compatible with materials in the containment building, including the reactor vessel, reactor internals, primary piping, and structural and ir.sulating materials.
The intent'of this requirement is to ensure that integrity of the reactor coolant pressure boundary is main-tained, and to prevent evolution of excessive amounts of hydrogen in the containment, should an accident occur.
The acceptance criteria with regard to coolant chemistry in Section 6.1.1 of the Standard Review Plan read:
"The composition of containment spray and core cooling water should be controlled to ensure a minimum pH of 7.0, as given in tho' Branch Technical Position MTEB 6-1, Reference 11, attached.
Experience has shown that main-taining the pH of borated solutions at this level will inhibit initiation bf stress-corrosion cracking of austenitic stainless steel components for periods of more than seven months.
Hydrogen release within the containment because of corrosion of materials by the sprays in the event of a loss-of-coolant accident should be controlled as described in Regulatory Guide 1.7, " Control of Combustible Gas Concentrations in Containment following a Loss-of-Coolant Accident".
A.e the pH increases over 7.5, the rate of corrosion of aluminum increases.
The amount of aluminum within the containment should therefore be controlled, and the amount of hydrogen that could be generated within the containment should be calculated as recommended in Regulatory Guide 1.7".
Standard RevicW Plan Section 6.1.3.
" Post-Accident Chemistry",
l requires that the pH of spray and emergency coolant solutions be controlled.
The purpose of controlling the pH is to reduce the probability of chloride stress corrosion cracking leading to equipment failure or loss of containment integrity,
.and to ensure low volatility of dissolved radio-iodines.
The acceptance criteria stated in Section 6.1.3 of the Standard Review Plan are stated as follows:
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"The procedures and methods which the applicant proposes to use to raise or maintain the pH of the solutions expected
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to be recirculated.within containment after a DBA should be. straightforward and reliable.
The chemistry of the post-accident environment in the containment should not result in significant deterioration of engineered safety features".
3.0 DISCUSSION 3.1 Organic Materials Identified coatings cover approximately 93,000 ft2 of the interior of the Millstone Unit 1 containment.
Approximately 20,00C ft2 of this is in the drywell, and 73,000 ft2 is in the torus.
By comparison, the surface areas of unidentified paints are considered to be insignificant.
Both the drywell and torus were originally coated with Keeler and Long #7575 Epoxy Zinc Rich Primer.
This was top-coated with Keeler and Long #7230 Submarine White Phenolic Paint.
Table 12-2 of Reference A identifies the approximate maximum gamma-radiation resistance of phenolic coatings r.s 44x108 rads and epoxy coatings as 4 to 9x108 rads.
The total integrated dose for coctings within a typical BWR containment ranges from 5x106 to 3x109 rads, with most surfaces seeing ( 107 rads (Reference B).
There is reason-able assurance therefore, that the coating system described above will not fail due to radiation effects following an accident.
Reference C, (pp 23-61,64) states that phenolic resins have l
good chemical resistance except against strong alkalies.
Epoxy resins are ider.tified as having excellent chemical resistance to weak acids and bases.
Thus the apoxy-phenolic coating system described above is compatible with Millstone Unit 1 normal and post-accident chemistry.
(post-accident chemistry is discussed in letail in Section 3.2 of this document).
The design temperature for the Millstone Unit 1 containment is 2810F (Reference D, Section 5.2.1).
Reference C, Table 23-7a lists the maximum recommended service temperature for phenolics as 300-4250F.
The same reference lists the heat distortion temperature for general purpose epoxy as 2500F, and for heat resistant epoxy as 5000F.
Thus we would not expect the phenolic-epoxy paint system described above to fail due to temperature effects, following an accident.
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Periodic visual inspections of the paint within the contain-ment revealed that although the paint in the drywell was performing satisfactorily, paint in the torus was blistering and peeling.
In November.1980, the torus was repainted to correct this problem.
Areas containing loose paint were scraped, wet sanded, and spot primed with Keeler and Long
- 7107 Epoxy White Primer.
This primer was qualified for use in the post-accident environment according to ANSI N5.9-1967 and ANSI N101.5-1970 criteria.
The torus was then repainted with Duraflex #200 water based epoxy.
Duraflex #200 has been qualified for use under DBA conditions by.the Analytical' Chemistry Division of Oak Ridge National Laboratory.
Qualification was conducted to meet the requirements of ANSI N101.2-1972 " Protective Coatings (Paints) for Light Water Nuclear Reactor Containment Facilities", and N5.12-1974, " Protective Coatings ~ (Paints) for the Nuclear Industry".
The painting systems, both in the drywell and in the torus, will be periodically inspected.
Evaluation of coating integrity will be conducted in accordance with the require-ments of ANSI N101.2-1972, Section 4.5 According to
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Reference E, forty years exposure to the normal containment environment is considerably more severe on a coating than any postulated loss of coolitnt accident.
It is believed that the chemical, temperature, and radiation resistance of the current coating systems, together with periodic inspection and maintenar.ce, make.the possibility of torus strainer clogging due to coating failure after an accident, remote.
The generation of hydrogen from zine rich coatings under l
design basis accident conditions has been well documented (Reference F).
Millstone Unit i relies on containment inerting l
for post-accident hydrogen control.
The controlling factor I
with regard to flammability limits in a nitrogen inerted l
containment is oxygen concentration rather than hydrogen concentration.
l Thus, the generation of hydrogen or flammable organic gases from protective coatings will not adversely affect post-accident containment hydrogen control at Millstone Unit 1.
The composition of gases evolved from irradiated plastics is poorly defined, however, the total quantity of gas evolved is very low.
Table 6.3ofReference(agrads, gives the gas yield from pnenolic plastic, irradiated to 10 as 3 ml/g @
S.T.P.
Most of this gas is probably hydrogen.
Millstone Unit 1 does not rely on direct treatment of containment atmosphere via charcoal filtration for iodine removal purposes.
Neither is purging of the containment through charcoal filters required for post-accident containment hydrogen control.
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r Charcoal filters are utilized in the standby gas treatment to 13mit the release of gaseous fission products to the environment after an accident.
This system treats the air leaking from the drywell to the reactor building, before discharging to atmosphere.
At a drywell pressure of 62 psig, maximum leakage to the reactor building is 3% of the drywell free volume per day.
This quantity decreases as
,drywell pressure decays following an accident.
Thus the loading of volatiles produced by paint decomposition on the charcoal filters, is only a small proportion of the already small-quantity of volatiles present in the drywell.
On this basis, no adveroc impact upon the standby gas treatment function is expected due to gas evolution from protective coatings within the containment.
3.2 Post-Accident Chemistry The acceptance criterion in Standard Review Plan Section 6.1.1, concerned with limiting the corrosion of stainless steel after an accident, appears to be directed at pressurized water reactors which utilize boric acid solutions for reactor coolant and reactivity control.
Millstone Unit 1 is a boiling water reactor and therefore uses high purity demineralized water without additives for this purpose.
The pressure suppression pool also contains demineralized water.
All carbon steel surfaces in the torus are painted to prevent corrosion.- Even without protective coatings, the expected corrosion rate for carbon steel, used structurally in air-saturated demineralized water, is six mils per year.
Such a corrosion rate following an accident is of negligible significance.
(Reference D, Section 6.2.7.4).
In the unlikely event that the Standby Liquid Control System is actuated after a loss-of-coolant accident, sodium penta-borate solution will be introduced into the reactor vessel.
If the vessel is refilled to the elevation of the break, the sodium pentaborate solution in the vessel will spill into the torus.
When sodium pentaborate dissolves in water, it produces a mildly basic solution.
The pH of the solution varies with concentration.
For the range of concentrations we are interested in, the pH will be someplace between 7.8 and 8.6 (Reference G).
At the mav.imum expected sodium pentaborate concentration during recirculation, carbon steel will corrode at a rate of about 11 mpy, and stainless steel at a rate of less than 0.1 mpy.
Again, these rates are insignificant following an accident.
Thus, no additional provisions are required to control corrosion of steel following an accident.
As stated in Section 3.1 of this evaluation, Millstone Unit 1 relies on inerting of the containment atmosphere for post-accident hydrogen control.
Control of post-accident chemistry i
to minimize the evolution of hydrogen from aluminum corrosion is therefore not a consideration in the Millstone Unit 1 design.
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Section 3.1 ef this evaluation also discussed the fact that at Millstone Unit 1, post-accident iodine control is accocplished through containment integrity, and operation of-the standby gas treatment system.
Containment sprays are not used to remove radio-iodines from the containment atmosphere.
Therefore, post-accident chemistry control to ensure the retention of iodines in sump water is not required.
4.0 CONCLUSION
S 4.1 Organic Materials The composition of the protective coatings used inside the Millstone Unit 1 containment, is believed to be suitable for use in the worst case environment seen after an accident.
This together with regular inservice inspections and proper maintenance, ensures that clogging of containment sump screens by coating failure, will not occur.
Proper functioning of systems used to control containment hydrogen and iodine after an accident, is not compromised by the evolution of L
gases from decomposition of protective coatings.
The paint system used in the Millstone Unit 1 containment, complies with the intent of NRC Standard Review Plan, Section 6.1.2.
4.2 Post-Accident Chemistry The post-accident coolant chemistry seen in the Millstone Unit 1 containment, does not contribute to the corrosion of carbon and stainless steels.
Neither does it compromise the functioning of systems used to control containment hydrogen and iodine after an accident.
Additional provisions for the control of post-accident che,mistry are not required.
The presently expected post-accident coolant chemistry is consistent with the intent of NRC Standard Review Plan, l
Sections 6.1.1 and 6.1.3.
- 5. 0 REFERENCES A.
Bolt and Carroll, Radiation Effects on Organic Materials, Academic Press, New York 1963 i
B.
ANSI N101.2-1972, " Protective Coatings (Paints) for Light Water Nuclear Reactor Containment Facilities C.
Perry's Chemical Engineers' Handbook, Perry, Chilton, and Kirkpatrick ed.,
McGraw-Hill, New York, Fourth Edition D.
Millstone Unit 1 FSAR 4
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Carboline Nuclear Coatings Guide, Carboline Company, n.d.,
Section 3, Page 1 F.
" Post-Accident Hydrogen Generation from Protective Coatings in Power Reactors", H.E. Zittel, Nuclear Technology, Vol. 17, February 1973 G.
"U.S.
Borax Industrial Products Catalog", page 65, n.d.,
Figure titled, "pH valves in the system Na2 0-B 03-H O at 2
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