ML20052F546
| ML20052F546 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/07/1982 |
| From: | Mizuno G NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD) |
| To: | |
| Shared Package | |
| ML20052F540 | List: |
| References | |
| NUDOCS 8205130176 | |
| Download: ML20052F546 (11) | |
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05/07/82 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMf11SSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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TEXAS UTILITIES GENERATING
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Docket Nos. 50-445 COMPANY, et al.
50-446 (Comanche Peak Steam Electric
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Station, Units 1 and 2)
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NRC STAFF RESPONSE TO APPLICANTS' ANSWER TO BOARD QUESTION ONE I.
INTRODUCTION On April 19, 1982, the Applicants filed a letter and accompanying affidavit (" Applicants' Answer") with the Atomic Safety and Licensing Board (" Licensing Board") regarding Board Question 1.I/ The Applicants i
stated that they have complied with the Commission's current regulation on hydrogen control, 10 C.F.R. 5 50.44. Applicants' Answer, pp.1-2.
The Applicants briefly discussed the current Commission rulemaking on
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In its June 16, 1980 " Order Subsequent to the Prehearing Conference of April 30, 1980," the Licensing Board directed the Applicants and the NRC Staff (" Staff") to address Board Question One during the forthcoming evidentiary sessions.
Subsequently, the Licensing Board issued its April 2,1982 " Order (Following Conference Call)."
In that Order, the Licensing Board noted that while " summary disposition is not appropriate for Board questions," the Staff or Applicants may " file information with the Board which answer the questions."
Id., p. 2.
The Licensing Board stated that it would evaluate any Tnformation submitted to it, and then indicated that
".. evidence might therefore not be necessary at the June hearing."
Id. The Staff assumes that the Applicants' letter and affidavit addressing Board Question One was in response to the Licensing Board's invitation to the Applicants and Staff to submit information on Board Question One.
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hydrogen control, 46 Fed. Reg. 62281 (December 23,1981), noting that the Commission has stated that it is unlikely that additional hydrogen control systems will be required for pressurized water reactors ("PWRs")
with large dry containnents.
M.,p.2.
Finally, the Applicants referred to the decision of Atomic Safety and Licensing Appeal Board's
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decision in Sacramento Municipal Utility District (Rancho Seco Nuclear Generating Station), ALAB-655, 14 NRC 799.
In Rancho Seco, the Appeal 1
Board upheld the Licensing Board's decision not to review the issue of hydrogen control in T!!I-2 accident scenarios, because of the Commission's ongoing rulenaking on hydrogen control. M. The Applicants concluded by 1
I asserting that "... Board Question 1 has been answered fully and that the taking of additional evidence at the hearing is unnecessary. Applicants' I
Answer, p. 3.
l After reviewing the Applicants' Answer, the NRC Staff (" Staff")
j concludes that the nformation submitted to the Licensing Board by
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l Applicants is corre;t. Affidavit of Palla, Answer 13; Affidavit of David H. Shum, Answer 4.
Further, for the reasons set forth in the i
attached affidavits, the Staff does not believe that a serious safety issue is raised by Board Question 1 regarding hydrogen control I
for the Comanche Peak Steam Electric Station (CPSES). Affidavit of Palla, Answers 14 and 5; Affidavit of David H. Shum, Answer 4. Accordingly, I
the Staff supports the Applicants' view that Board Question One has been answered fully and that the taking of evidence on this issue at the forthcoming evidentiary hearing is unnecessary.
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II. DISCUSSION Combustible gases, consisting primarily of hydrogen, may accumulate inside the prinary reactor containment following a loss-of-coolant' accident ("LOCA"). These gases are generated by: (1) metal-water reaction involving the fuel element cladding; (2) radiolytic decomposition of the water for the reactor core and containment sump; (3) corrosion of certain construction materials by the spray solution; and (4) synergistic chemical, thermal, and radiolytic effects of post-accident environmental conditions on containment protective coating systems and electric cable insulation. Affidavit of Robert L. Palla, l
Answer 3.
Because of this potential for hydrogen and combustible gas I
generation, the NRC requires that systems be provided to control hydrogen concentrations in the containment atmosphere following a postulated LOCA, to ensure that containment integrity is maintained.
Id., Answer 5.
The Commission's regulations on hydrogen control are contained in 10 C.F.R. Section 50.44, and General Design Criteria 41, 10 C.F.R. Part 50, Appendix A.
With regard to hydrogen generated as a result of the fuel cladding-water reactor,10 C.F.R. Section 50.44 requires that the combustible gas control system be capable of handling either: (i) five times the hydrogen calculated to be generated as a result of degradation of the emergency core cooling system ("ECCS"), as calulated t
in demonstrating compliance with 10 C.F.R. Section 50.46; or (ii) the hydrogen calculated to be generated from reaction of all of the metal in the outside of the cladding cylinders surrounding the fuel (excluding the cladding surrounding the plenum volume) to a depth of.00023 inches;
whichever amount of hydrogen is greater.
Id.
In addition, Section 50.44 requires that nuclear plants be provided with the capability to measure the hydrogen concentration in the containment, and the capability to mix combustible gases with the containment atmosphere to prevent localized concentrations of hydrogen. Affidavit of David H.
Shum, Answers 5 and 7.
Finally, if an uncontrolled hydrogen / oxygen recombination cannot be prevented from occuring, the plant must be designed to withstand the consequences of such uncontrolled recombination without loss of safety functions.
Id., Answer 5.
The Staff's review of nuclear plants for compliance with Section 50.44 of the Commission's regulations is made in accordance with the criteria and areas of review set forth in Section 6.2.5. of the Staff's Standard Review Plan ("SRP") Pursuant to Section 6.2.5. of the SRP, the Staff must review the following areas:
1.
The production and accumulation of combustible gases within the Applicants' calculated amounts for containment following a postulated loss-of-coolant accident.
2.
The capability to mix the combustible gases with the con-taiament atmosphere and prevent high concentrations of combustible gases in local areas.
3.
The capability to monitor cumbustibel gas concentrations within containment.
4.
The capability to reduce combustible gas concentrations within containment by suitable means, such as recombination, dilution, or purging f
Affidavit of Shum, Answer 7.
1 The Staff's review of the CPSES design for hydrogen control was performed l
l in accordance with Section 6.2.5 of the SRP.
Id. The Staff concluded that the CPSES design for hydrogen control conforms to the current NRC regulation on hydrogen control, 10 C.F.R. Section 50.44.
See Section 6.2.4.,
attached to Affidavit of David H. Shum. The Staff's conclusion that the CPSES hydrogen control design was acceptable was based on the following:
(1) The Applicants' calculated value hydrogen concentration is 1.9 v/o, with operation of a single recombiner started 1 day after an accident. The value of 1.9 v/o is significantly lower than the Regulatory Guide 1.7 lower flammability limit of 4 v/o.
(2) The Staff's calculated value for hydrogen accumulation is 2.0 v/o, which is in substantial agreement with the Applicants' calculated value.
(3) Applicants comittment to use redundant Westinghouse electric thermal recombiners. The Applicants have used the assumptions of Regulatory Guide 1.7 to calculate the rate of hydrogen release, and have calculated that the 4 v/o flammability limit would not be restored until 26 days after a postulated LOCA.
(4) Design features of the recombiner System, including Seismic i
Category 1 design; protection from missile and jet imping-l ment; and redundancy to the extent that no single component l
failure disables both recombiners.
(5) An adequate nixing mechanism is provided by the containment spray system.
(6) Redundant containment hydrogen indicators will be installed at the main control board.
In addition, the parameters will be provided as input to the safety parameter display system for l
recording.
Id., Answer 8.
Thus, the CPSES hydrogen control system design of CPSES meets current NRC regulatory requirements.
Id.
The CPSES design for hydrogen control is similar to other nuclear reactor plants with large dry containments. Historically, hydrogen gene-l rated as a result of radiolytic decomposition of water, corrosion of metals l
l inside containment, and environmental effects on coating and insulation, have been controlled by conventional hydrogen control systems such as hydrogen recombiners. On the other hand, the design capability (margin) to control hydrogen generated by a metal-water reaction involving the fuel cladding has historically been provided by the net free volume of the containment.
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i Affidavit of Palla, Answer 4.
The reliance on containment net free volume is based on the inability of conventional hydrogen control systems to quickly control the hydrogen which is rapidly generated'as a result of the cladding-water reaction following a postulated accident.
Instead, reliance was placed on the containment net free volume and atmos-phere mixing mechanisms to dilute the hydrogen release to below the lower i
flammability limit.
Conventional hydrogen control systems would then be t
actuated to control hydrogen accumulation and gradually reduce the j
hydrogen concentration inside containment.
Id.
1 The accident at TMI-2 on March 28, 1979 resulted in a metal-water i
reaction involving approximately 45% of the fuel cladding. This j
resulted in hydrogen generation substantially in excess of the amounts specified by 10 C.F.R. Section 50.44, for which nuclear plants were required to control. As a result of TMI-2, the Staff undertook programmatic efforts to reduce the probability of degraded core accidents, and to require additional measures for hydrogen control and mitigation.
Affidavit of Palla, Answer 6.
In order to reduce the possibility of severe core accidents, the NRC has enhanced its requirements in the areas of operator training, technical competence of the operations staff, and the development and review of operating procedures for coping with emergencies and abnormal conditions.
Id. The Staff believes that the liklihood of events leading to severe core degradation has been substantially reduced.
Id.
Since the production of hydrogen in large quantities is dependent upon core degradation, the Staff believes that the probability of generation of I
large amounts of hydrogen has also been substantially reduced. Id.
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Upgraded hydrogen control and mitigation measures for degraded core accidents was first addressed in the Lessons Learned Report for TMI-2 (NUREG-0578). This issue was subsequently included in TMI Action Plar.
4 Item II.B.7 (NUREG-0660). Affidavit of Palla, Answer 6.
Based on these reports, the Commission determined that a rulemaking proceeding should be undertaken to define the manner and extent to which hydrogen generation must be taken into account in plant design. This "Rulemaking Proceeding on Degraded Core Accidents," Item II.B.8 in the TMI t.ction Plan, is a two step process. First, the Commission will develop, and the Staff will implement a set of interim actions and rules on hydrogen control. Second, a final rulemaking on hydrogen control would be undertaken as a long-term resolution of the issue.
Id.
The long-term final rulemaking on this issue was initiated by the Commission in an Advance Notice of Rulemaking. 45 Fed. Reg. 65474 t
(Oct. 2, 1980). Several years may elapse before the hydrogen control requirements of this final rule are developed and implements. Therefore, it is impossible to state what effect the Commissions' final rule on 1
hydrogen control may have on CPSES.
The interim rules on hydrogen control have yet to be completely promulgated and implemented. Analyses conducted by the Staff, including that reported in SECY 80-707, as well as industry-developed information, served as the bases for the development of the interim rules. These i
studies and subsequent Commission reviews indicated that containment designs for all nuclear plants can be planced into three categories on the basis of their capability for accommodating large hydrogen releases and the subsequent burning of hydrogen without loss of containment 4
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integrity. Af?idavit of Palla, Answer 7.
The three categories aresmall (Mark I/BWE and Mark II/BWR); intermediate (Ice Condensor and Mark III/BWR);
and large (large, dry containments).
The " Interim Requirements Related to Hydrogen Control," (" Interim Rules") 46 Fed. Reg. 62281 (December 23,1981) sets forth, inter alia, the proposed Staff requirements for large, dry containments.
Id. Since CPSES uses a large, dry containment, the December 23, 1981 " Interim Rules" are applicable to CPSES.
Id., Answer 8.
The Interim Rules would require owners of nuclear plants with large dry containments to perform and submit analyses showing that (i) containment structural integrity would l
be maintained during degraded ccre accidents, and (ii) equipment which will ensure cantinued containment integrity and safe shutdown capability would survive a degraded core accident. The proposed Interim Rules 1
would also require these analyses to assure reaction of up to 75% of the fuel cladding surrounding the active fuel region with water for a range of time periods.
Id.
The proposed Interim Rules were published for public comrent on l
December 23, 1981. The public comment period was extended until April 8, 1982 by a further notice in the Federal Register. 47 Fed. Reg. 8203.
15 comments were received. The proposed rule is scheduled to be published in final fonn in October or November of 1982, and is expected to be effective 60 days later.
Affidavit of Palla, Answer 9.
In addition to the Commission's interim and long-term final rulemaking proceedings on hydrogen control, there are other current efforts to address this issue. Several industry-wide research and technical programs have been initiated.
Id., Answer 11. The Office of Nuclear Reactor Regulation ("NRR") has also been conducting evaluations of
a.
hydrogen control systems.
Finally, in 1981 the Comission designated the hydrogen generation and mitigation issue as Unresolved Safety Issue
("USI")A-48. By designating hydrogen control as USI A-48, the Comission intends to assure integration of NRC efforts so that a generic resoloution of this issue will be achieved.
In addition, the Commission expects that designation of hydrogen control as USI A-48 will accelerate the resolution of the issue.
Id.
Despite the current status of the interim and final rulemaking on hydrogen control (as well as USI A-48, which merely " formalizes" the concerns on hydrogen), the Staff believes that the licensing and interim operation of nuclear plants with large dry containments-and CPSES in particular-is justified and will not jeopardize the health and safety of the public. Affidavit of Palla, Answers 12,14,15 and 16. The Staffs' conclusion is based on a number of factors. First, the Staff has analyzed the design and failure pressures for large dry containments, in order to determine the effect of hydrogen burns on large dry containments.
These containments were found to have design pressures ranging from 45 to 60 psig, and internal volumes of two to three million cubic feet. The design pressure for CPSES is " osig. Structural analyses at the Zion and Indian Point plants, which have design pressures of 47 psig, show that the failure pressure is approximately 120 psig. Thus, the failure pressure for those plants is more than twice the design pressure. Since the Zion and Indian Point containments are similar in design and construc-tion to that of CPSES, the Staff believes that the failure pressure of the CPSES containment would be considerably in excess of the design pressure. Affidavit of Palla, Answer 12.
Second, the CPSES containment has a net free volume of 3 million cubic feet. The Staff found that even if there were a 50 percent reaction of metal with water in the core, the resulting hydrogen concentration would be 8%, if it is assumed that the hydrogen is uniformly distributed throughout the containment. The 8 percent l
hydrogen concentration is well below the concentrations necessary for detonation. The 8 percent concentration is also below the limits for combustion if there is 50 percent or greater volume of steam in the containment atmosphere.
Id.
Third, calculations performed by both Applicants and the Staff show that the peak pressure in the CPSES containment resulting from the combustion of hydrogen generated from a 75 percent metal-water reaction, will be below the expected containment failure pressure for CPSES.
Id.
A fourth factor which the Staff considered was the results of industry and government-sponsored test programs on the capability of safety equipment to survive hydrogen burns. These preliminary results indicate that essential safety-related equipment will function during and after repeated (multiple) hydrogen burns.
Id.
Finally, the Staff requires applicants for operating licenses to implement the recommendations of the TMI-2 "Short Term Lessons Learned" report, prior to issuance of an operating license. Id., Answers 12 and 15.
The implementation of these recommendations will reduce the likelihood of accidents which could lead to substantial core damage. The Applicants will be required to implement these recom-mendations prior to issuance of an operating license for CPSES. Id., Answers 6,12, and 15.
l Based on these factors and considerations, the Staff concludes that the licensing and interim operation of CPSES, prior to resolution of USI A-48 and the interin and final rulemaking on hydrogen control, is i
acceptable and will not jeopardize the health and safety of the public.
Affidavit of Palla, Answer 15.
III. CONCLUSION l
The Staff concludes for the reasons previously discussed, that the licensing and interim operation of CPSES, pending final resolution of the hydrogen control issue, is acceptable and will not jeopardize the health and safety of the public. Accordingly, the Staff supports the Applicants' view that Board Question One has been answered fully and that the taking of evidence on hydrogen control at the forthcoming evidentiary hearing is unnecessary.
Respectfully submitted, J
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3 GearyS[Mizuno Counsel for NRC Staff Dated in Bethesda, Maryland this 7th day of May, 1982.
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