B12292, Forwards Reviews for Isap Topics 1.23, Post-Accident Hydrogen Monitors & 1.63, Hydrogen Control, Per 850517 Commitment

Forwards Reviews for Isap Topics 1.23, Post-Accident Hydrogen Monitors & 1.63, Hydrogen Control, Per 850517 Commitment

ML20214H746
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	11/17/1986
From:	Opeka J, Sears C CONNECTICUT YANKEE ATOMIC POWER CO.
To:	Charemagne Grimes Office of Nuclear Reactor Regulation
References
B12292, NUDOCS 8612010009
Download: ML20214H746 (11)

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CONNECTICUT YANKEE ATOMIC POWER COMPANY B E R L I N, CONNECTICUT P o BOX 270 HARTFORD. CONNECTICUT 06141-0270 November 17,1986 TELEPHONE m ees.sooo Docket No. 50-213 B12292 Office of Nuclear Reactor Regulation Attn: Mr. Christopher I. Grimes, Director Integrated Safety Assessment Project Directorate Division of PWR Licensing - B U.S. Nuclear Regulatory Commission Washington, D.C. 20555

References:

(1) 3. F. Opeka letter to C. I. Grimes, dated May 17,1985.

(2) H. L. Thompson letter to 3. F. Opeka, dated July 31,1985.

Gentlemen:

Haddam Neck Plant Integrated Safety Assessment Program In Reference (1), Connecticut Yankee Atomic Power Company (CYAPCO) provided a proposed scope for the Integrated Safety Assessment Program (ISAP) review of the Haddam Neck Plant. In Reference (2), the Staff formally issued the results of the ISAP screening review process, establishing the scope of ISAP for Haddam Neck and initiating issue-specific evaluations. Reference (1) also indicated that for each issue or topic included in ISAP, CYAPCO would provide a discussion of the safety objective and an evaluation of the plant design with respect to the issue being addressed to identify specific items to be considered in the integrated assessment. In accordance with this commitment, reviews for the following ISAP topics are attached:

1) ISAP Topic No.1.23 " Post-Accident Hydrogen Monitors"

2) ISAP Topic No.1.63 " Hydrogen Centrol" If you have any questions concerning the attached reviews, please contact us.

Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY b, . b 6L 2a_

3. F. Opeka i Senior Vice President MOML By: C.F. Sears Vice President 00\

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8612010009 861117 PDR ADOCK 05000213 P PDR

Docket No. 50-213 B12292 Haddam Neck ISAP Topic No.1.23 Post-Accident Hydrogen Monitors i

November 1986

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b Haddam Neck ISAP Topic No.1.23 Post-Accident Hydrogen Monitors I. Introduction During the course of an accident, monitoring of certain plant parameters is necessary for proper ' diagnosis and control. One of the significant parameters of concern is the concentration of hydrogen in the containment. Excessive levels of hydrogen can lead to a hydrogen burn and potential breach ~of containment. Therefore, installation of containment hydrogen monitors that will. fo!!ow the course of an accident is being considered.

II. Review Criteria Regulatory Guide 1.97, Rev. 2, " Instrumentation to Assess Plant and Environs Conditions During and Following an Accident" NUREG-0737, Item II.F.1.6 " Containment Hydrogen Monitors" III. Related Topics / Interfaces ISAP Topic No.1.21 " Regulatory Guide 1.97 Instrumentation" ISAP Topic No.1.63 " Hydrogen Control" IV. Evaluation The proposed project is to provide the supplemental design, procurement and installation effort necessary to install redundant containment hydrogen monitors that will demonstrate conformance to the criteria of NUREG-0737 (Reference 1) and Regulatory Guide 1.97, Rev. 2 (Reference 2).

Previously, hydrogen generation following a design basis LOCA was evaluated in the Haddam Neck combustible gas control evaluation (Reference 3). From this evaluation, it was determined that the hydrogen concentration build-up inside containment is so slow it requires approximately 13 months from the start of a design basis LOCA to reach the flammable limit. As discussed in more detail in ISAP Topic No.1.63, more conservative consideration of the corrosion of zinc and aluminium coatings inside containment could reduce this number to approximately 8.5 months. This relatively long time interval is due to the uniquely large ratio of containment volume to reactor power. Even under very pessimistic conditions, installation of containment hydrogen monitors would still produce no significant safety benefit following a design basis LOCA. At present, the Haddam Neck Plant has a post-accident samp!!ng system (PASS) .that can be used to' determine . the hydrogen concentration in containment following a postulated design basis accident. Since the hydrogen concentration inside containment would be increasing slowly over a long period of time, the periodic hydrogen analyses provided by PASS would be adequate for monitoring hydrogen levels in the containment.

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. . V. Conclusions For ' all design basis LOCAs, - continuous monitoring of hydrogen concentration inside containment using post-accident hydrogen monitors would not provide a significant safety benefit over and above that of the PASS currently in use at - Haddam Neck. Further evaluation will be undertaken in the integrated assessment.

VI. References -

1. NUREG-0737, " Clarification of TMI Action Plan Requirements,"

November 1980.

2. Regulatory Guide 1.97 (Rev. 2), " Instrumentation for ' Light Water Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During and Following an Accident," December 1980.

3. W.G. Counsil letter to D.M. Crutchfield, "Haddam Neck Combustible Gas Control Evaluation," dated March 4,1983.

4. 3. F. Opeka letter to C. I. Grimes, "Haddam Neck Plant - Probabilistic Safety Study," dated March 31,1986.

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Docket No. 50-213 B12292 1

Haddarn Neck ISAP Topic No.1.63 Hydrogen Control i

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Haddam Neck ISAP Topic No.1.63 Hydrogen Control I. Introduction -

10 CFR 50.44(c)(3)(ii) re that relies upon a purge / quires that each light-water nuclear power reactorrepres controlling combustible gases following a design basis loss of coolant accident (LOCA) shall be provided with eitner an internal recombiner or the capability to install an external recombiner following the start of the accident.

II. Review Criteria Regulatory Guide 1.97, Rev. 2 " Instrumentation to Assess Plant and Environs Conditions Durmg and Following an Accident" 10 CFR 50.44 " Standards for Combustible Gas Control Systems In Light-Water-Cooled Power Reactors" III. Related Topics / Interfaces ISAP Topic No.1.21 " Regulatory Guide 1.97 Instrumentation" ISAP Topic No.1.23 " Post-Accident Hydrogen Monitors" IV. Evaluation

, Reference (1) forwarded to the NRC Staff the Combustible Gas Control Evaluation for the Haddam Neck Plant which addressed compliance with 10 CFR 50.44(c)(3)(ii). This analysis concluded that a total of approximately 475 lbs. of hydrogen must be generated or released from the reactor coolant system following a design basis LOCA to obtain flammable gas mixtures (i.e., 4% by volume concentration of hydrogen) inside containment. Additionally, CYAPCO determined that this hydrogen concentratin.i flammability limit would not be reached until approximately thirteen (13) months from the onset of the postulated design basis LOCA.

This inherent safety margin is principally due to the large containment volume to reactor power ratio.

Under design basis LOCA conditions, an external recombiner could be installed or other remedial actions taken within the aforementioned thirteen month time-frame. Additionally, containment purging could be initiated with resultant negligible off-site dose rates well below the limits prescribed in 10 CFR 100. Another secondary method of hydrogen control would be to further pressurize the containment using the service air system. This would dilute the hydrogen concentration in containment.

Hence, with all of these options available as secondary means of combustible gas control, and by using the containment design as the primary means of combustible gas control, CYAPCO concluded that it would be unnecessary to install hydrogen recombiner capability at the Haddam Neck Plant to meet the requirements of 10 CFR 50.44(c)(3)(ii),

which is applicable only to light water reactors that rely on purge /repressurization systems as the primary means of combustible gas control.

Following subsequent Staff review of this evaluation, two concerns were identified. Each concern is addressed by CYAPCO below.

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Staff Concern: 's i The Haddam Neck 7 Plant- Combustible Gas Control Evaluation did not ~ -

provide: sufficient basis for neglecting the effects of the bxidation of ~

Aluminum (AI) and Zinc (Zn) protective coatings (primers excluded) as a source of- hydrogen 'following a desQn' basis loss of coolant accident. .

Please justify why tnis source of hydrogen was considered negilgible.-

s-CYAPCO Response: "

References (2) and (3) provided the Staff with information regardins SEP Topic VI-1, ' Organic Materials and Post-Accident - Chemistry. These submittals discussed the integrity of organicfcoatings and possible acceleration of corrosion processes immediately following design basis Ioss of coolant accident (LOCA) conditions. Also included in these discussions' ^

was the hydrogen production due ,to the: corrosion of zinc and aluminum coatings. It was determined that the production of hydrogen from Al and Zn coatings (primers excluded) was considered to be negligible due to the retention - of protective oxides in a .neutr;al (not acid or ~ alkaline) environment. CYAPCO reiterated this position in the Combustible Gas Control Evaluation. In response 'to the Staff's concern, additional information is being provided.

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Since the Haddam Neck Plant's containment spray system is not . safety grade, it would not be used for post-accident containment pressure control unless the pressure were to exceed the maximum pressure predicted by the design basis events (post-accident containment' pressure control is provided by the containment air recirculation' system)> Since the combustible gas control evaluation is a design basis evaluation, it is.not appropriate to -

assume that the coolant in the containment sump %ould be sprayed throughout the containment. Therefore, there is no mechanism which 4 ,

would cause the protective oxides on Al and Zn coatings to be removed o except in the lower regions of the containment. The analysis, below -4 .

provides a conservative evaluation of the corrosion'of Al and Zn coatings in these regions of the containment. N 3' .

The corrosion of Al is negligible in both acidic and alkaline water solutions ,

between the pH values of 3 and 9. Between these pil values, Al forms a very protective oxide in the form of hydrargillite (Al 23 O 3H O),' 2 which prevents oxidation or corrosion, with little or no' subsequent production of hydrogen gas.

Additionally, Zn is most passive in aerated alkaline water . solutions between the pH values of 7 and 11. Between these pH values, Zn forms a semi-protective mixture of hydroxides and oxides in the form of Zn(OH)2 and ZnO2 (Predominately the former). In the case of Zn, there will be a small nominal corrosion rate, and some limi;ed production of hydrogen depending on the carbonate / bicarbonate content of the water, and the total bulk of Zn available.

t The containment sump area at the Haddam Neck Plant contains baskets of trisodium phosphate (TSP) which are intended to raise the pH from the order of 5 to 7 in the event of a LOCA. The amount of TSP available is  !

}. Intended to neutralize and/or buffer the total refueling water storage tank j (RWST) and reactor cooling system (RCS) water volume, the latter being  ;

presumed to be at maximum boric acid concentration.

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- In ' order to determine the magnitude of the effects of the corrosion of Al and Zn on post-LOCA -hydrogen production, the corrosion rates were converted into metal loss per day by incorporating the total surface areas of each material. The metal loss. rates were then related to hydrogen production from the following equations:

1. Zn + 2H2O = Zn (OH)2 + H2

-2. 2Al + 3H2 O = Al23O + 3H2 Finally, as shown in Table 1, the hydrogen production from both Zn and Al were combined and added to the predicted hydrogen production curves given in Figure 5, Reference 1. Figure I shows the predicted contribution of both Zn and Al coatings to the total hydrogen generation in the Haddam Neck Plant containment following a LOCA event.

Hence, it can be concluded that the Zn and Al coatings in containment at Haddam Neck would contribute little or no hydrogen to the total combustible volume produced following . a LOCA. Presuming a very x pessimistic corrosion rate, the maximum contribution of hydrogen from these materials could reduce the time of formation of a critical hydrogen concentration in containment from approximately 13 months to about 8.5 months.

Staff Concern:

The Haddam Neck Plant Combustible Gas Control Evaluation did not include the effects of radiolysis of water in the containment sump. Justify why this source of hydrogen was not included.

CYAPCO Response: 1 The radiolytic decomposition of water under conditions of high energy radiation (gamma, beta) is a process by which water decomposes into a variety of' chemical species, the primary products being H2 , H22O , H, OH and the solvated electron. These products will further react with themselves and also with other foreign species. The analysis presented in the Combustible Gas Control Evaluation (Reference 1) assumes that the hydrogen generated from the primary interaction does not further react to '

reduce the yield of hydrogen. This assumption is conservative during the boiling phase of a LOCA and ultra-conservative in the long-term, non-boiling phase when the recombination of hydrogen would significantly reduce its yield.

The analysis further assumes that all fission products remain in the reactor core region. To assume that radiolysis also occurs in the sump (due to the presence of fission products in the coolant) would require that the radiolysis yield in the core be reduced by the amount that occurs in the sump. For this reason, radiolysis in the containment sump was not included in the evaluation.

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V. Conclusion 4 d CYAPCO has concluded that based upon varying degrees of conservatisms, a flammable concentration of hydrogen in the containment would not be reached until approximately 8.5 - 13 months subsequent to the beginning of l . a postulated design basis LOCA. Additionally, since Haddam Neck utilizes its containment design as the primary means.of combustible' gas control, I

CYAPCO reiterates its previous conclusion that the regulatory i

requirements contained in 10CFR50.44 (c)(3)([0y are not s. applicable.

Pending further Staff comment, CY,APCO co siders this issue adequately addressed.'

4 VL References

1. W.G. Counsil letter to D.M. Crutchfield, i'Haddam Neck Plant -

Combustible Gas Control Evaluation," dated March 4,'1983.

2. . W. G. Counsit letter to D. M. Crutchfield, "SEP Topic hl-fi Organic Materials and Post-Accident Chemistry," dated February 9,1982.

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3. W. G. Counsil letter to D. M.' Crutchfield, "SEP Topic VI-1, Organic Materials and Post-Accident Chemistry," dated May 3,1982.

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TABLE i BATA DSED TO CALCULATE HYDROGEN FRODUCTION Al CONFONENT/ SURFACES Za CONFOIEIrf/ SURFACES Surface Area sqpre feet 39705 27192 de 368859 252613 Mass - Ibs. 18977 1700 (1 oz/sq. ft.)

Envir M at Acid / alkaline water pH 5 to 9 Acid / alkaline water pH 5 to 9 Temperature F up to 212 F up to 212 F Reduction 2 Al + 3H O ==== "* 0 ====

1 lb A1 =20.11 lbs HA12 023+ 2 2 Zu(OH)2 1 lb Zn = 0.03 lbs H 2

2 Corrosion Eate Mdd (ag/dm / day) 0.24 120 Metal loss Este Ibs/ day 0.195 66.9 Hydrogen Production Ibs/ day 0.021 2.0 lbs/ months 0.643 50 lbs in 25 days Time to Full Usage of Metal (months) 3244 0.833 (25 days) 9

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FIGURE 1,. CALCULATED HYDROGEN GENERAT:C.1 IN CY CONTAlf# TENT FOLLOWING A 5% CORE OXIDATION LOCA

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