ML20235D243

Safety Evaluation Re Proposed Onsite Storage of Liquid Oxygen & Hydrogen for Implementation of Hydrogen Water Chemistry.Permanent Hydrogen Water Installation Acceptable

ML20235D243
Person / Time
Site:	Peach Bottom
Issue date:	09/22/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20235D112	List: ML20235D109 ML20235D243
References
NUDOCS 8709250167
Download: ML20235D243 (5)

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ENCLOSURE y

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO HYDROGEN WATER CHEMISTRY IMPLEMENTATION I PHILADELPHIA ELECTRIC COMPANY I DOCKET NUMBER 50-277 AND 50-278

1.0 INTRODUCTION

By letters dated May 27 and August 24, 1987, the licensee submitted the safety evaluation for the storage of liquid hydrogen and oxygen and additional information relating to the implementation of hydrogen water chemistry for review and approval.

2.0 EVALUATION The BWR Owner's Group submitted " Guidelines for Permanent BWR Hydrogen Water Chemistry Installations," 1987 Revision (hereafter referred to as the Guidelines), for staff review. By letter from James E. Richardson, NRC, dated July 13, 1987 to G. H. Neils, BWR Owners Group II for Intergranular Stress Corrosion Cracking Research, the staff accepted the Guidelines for referencing in licensee requests for approval of a permanent hydrogen water chemistry facility. The licensee states that the liquid hydrogen and oxygen storage and injection systems are sited, designed and installed in accordance with the recommendations provided in the Guidelines.

2.1 Liquid Hydrogen Storage The liquid hydrogen storage tank, with a maximum capacity of 20,000 gallons of cryogenic liquid at approximately 100 psig and -425'F, will be located 1180 feet away from the nearest safety-related structure, which is the plant stack. The next nearest safety related structure is the Unit 3 reactor building, which is 1700 feet away. The system also incorporates provisions for temporary gaseous hydrogen supply via trucks. In the unlikely event of an explosion of the tank containing 20,000 gallons of cryogenic hydrogen, the peak positive reflected overpressure at the plant stack and Unit 3 reactor building were calculated by the staff to be 1.5 psi and 2.5 psi respectively.

The fireball diameter, duration and thermal flux (Unit 3 reactor bui wascalculatedbythestafftobe20 feet,5.2secondsand1.44Kw/m} ding) respectively. The hydrogen storage area is in conformance with the Guidelines in that there is sufficient separatici distance from safety-related structures so that the thermal flux from the burring gas fire-ball or the blast overpressure from hydrogen explosion vill not ause failure of the safety-related structures. For small liquid hydrogen releases, Figure 4-7 from the Guidelines indicates that for the nearest safety-related structure air intake (1180 feet), the flannability limit would be exceeded at a leakage rate in excess of 1.1 kg/sec (liquid hydrogen piping hole size of 0.44 inches diameter). Based on the above, liquid hydrogen piping design should be either (1) totally seismically supported; (2) seismically designed and supported up to and including a structural anchor downstream of excess flow check valves; or (3) seismically supported up to and including a structural anchor downstream 8709250167 870922 PDR ADOCK 05000277 P PDR

of a flow limiting device which restricts flow to less than 1.1 kg/sec to prevent the intake of flammable concentrations of hydrogen into safety-related air intakes.

The licensee utilized option (2) above which is acceptable.

2.2 Liquid Oxygen Storage The liquid oxygen storage tank, with a maximum capacity of 11,000 approximately above grade)y 150 psig and -300 F, will be located 260 feet39away feet (gallons at from the nearest safety-related air intakes, which is the electromechanical equipment room and cooling tower air intake. The next nearest safety-related air intake is the reactor building HVAC.

also incorporates provisions for temporary oxygen supply by truck.TheFigure system 4.8 of the Guidelines indicates that the oxygen concentration at the nearest safety-related air intake will be less than 30 volume % should failure of the liquid oxyger. tank result in instantaneous vaporization of the liquid oxygen. At concentrations ignitable materials of less willthan not 30 volume % oxygen the effective combustibility of increase.

facility is acceptable. Therefore, the liquid oxygen storage 2.3 Hydrogen Injection System Hydrogen gas from the storage site is delivered at approximately 1000 psig to Units 2 and 3 where it is injected uniformly into the suction piping of the three reactor feed pumps in each Unit.

The supply line to the existing hydrogen storage tubes for generator cooling ties into the systems fill line.

The reactorhydrogen flow rate will be approximately 60 scfm into the suction of the feed pumps.

socket weld fittings. The hydrogen piping is stainless steel, schedule 160, with The distribution piping from the hydrogen storage tank to the turbine building building is 3/4 inch in size. is one inch while the injection pipe inside the turbine following. The injection of hydrogen is tripped by the SCRAM High area hydrogen concentration / area temperature Offgas oxygen concentration High hydrogen injection flowrate Less than 20% power Low hydrogen injection pressure Operator request The major safety features of the system include:

Area Hydrogen Concentration / Temperature Monitors

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Vent / Purge System with External Flame Arrestors Low Pressure Hydrogen Isolation Excess Flow Check Valves Hydrogen Isolation Spool Pieces for Maintenance Use ,

Zero-Leakage Bellows Seal Hydrogen Valves The area hydrogen monitors are located in seven hydrogen collection shrouds which contain injection system components that may leak (e.g., valves, instruments, spool pieces, etc.). When hydrogen concentrations exceed 2%

(lower flammability limit is 4%), an alarm is annunciated in the main control  :

room. The injection system is automatically shut off at 3% hydrogen. All instruments within the shrouds are of explosion proof design. Temperature monitors are also included in the shroud to isolate the system in the event nf an ignited hydrogen leak. Excess flow check valves are located outdoors in the l common supply header and indoors on each unit's distribution piping. Each excess flow check valve will isolate the hydrogen distribution system if the flowrate is 150 percent of the normal flowrate passing through it. As an added precaution no hydrogen injection piping will be routed in safety-related structures or areas containing safety-related equipment.

The hydrogen injection system meets the Guidelines by providing maximum system integrity, early detection of hydrogen leaks, excess flow protection and automatic system shutdown if a failure is detected.

2.4 0xygen Injection System Oxygen gas is delivered at approximately 100 psig to the injection point on the off-gas system preheater inlet piping to the recombiner. The oxygen flow is proportional to hydrogen flow (ratio is approximately 1:2) and a final adjustment is made based on off-gas excess oxygen. Hydrogen water chemistry suppresses oxygen in the reactor coolant and also reduces the oxygen in the condensate /feedwater. Oxygen is also' injected into the suction piping of the "B" condensate pump to maintain recommended dissolved oxygen levels of 20-60 ppb for feedwater pipe corrosion control. The oxygen flow to the condensate pump suction will be automatically isolated on low condenser vacuum.

The oxygen piping is copper with brazed fittings. The distribution piping from the oxygen storage facility to the turbine building is one and a half inch diameter (0.075 inch wa'". thickness) while the feed pump injection piping inside the turbine building is 1 inch in size (0.065 inch wall thickness). The condensate injection piping is half inch in diameter (0.065 inch wall thickness).

Following a trip of the hydrogen injection system the flow of oxygen to the recombiner will be held constant for a short time to permit hydrogen and oxygen carryover to return to a stoichiometric ratio.

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~4-Since oxygen supports combustion, an excess flow check valve is installed in the oxygen injection line to shut off oxygen flow should an oxygen line break or leak occur. This will reduce oxygen concentrations and limit the spread of potential fires. Oxygen injection lines are not run through areas housing safety related equipment. The oxygen injection system meets the Guideline recommendations.

2.5 Radiation protection The staff has reviewed the licensee's submittal regarding the radiological implications of the dose rate increases associateu with_N-16 activity increases during hydrogen injections into the reactor system. The review addresses the radiation protection /ALARA measures for hydrogen water chemistry, in accordance with 10 CFR 20.1(c) and Regulatory Guide 8.8, "Information Relevant to Ensuring the Occupational Radiation Exposures at Nuclear Power Stations Will be as Low as is Reasonably Achievable." (ALARA)

One objective of the hydrogen water chemistry program is to determine general in-plant and site boundary dose rate increases due to hydrogen addition. The licensee has stated that radiation protection /ALARA practices will be implemented. Additionally, the licensee has stated that data will be obtained for shielding design should additional shielding be necessary.

The increased dose rate due to higher N-16 activity levels will result in an increase in site dose rate during operation with hydrogen water chemistry.

The increased dose will be primarily to non-radiation workers located in the administration building and other support structures but not to workers in the plant. Hydrogen injection can be turned off for as much as eight hours, resulting in a rapid decrease in N-16 activity levels, without losing the IGSCC mitigation benefits. During the hydrogen injection shutdown time, work can be performed in areas, such as near the turbine, at reduced N-16 dose rates.

Radiation protection practices implemented for hydrogen water chemistry operation will ensure ALARA in accordance with Regulatory Guide 8.8 and are, therefore, acceptable.

2.6 Fuel Surveillance The licensee plans to implement a fuel surveillance program as suggested in Section 6.1.5 of the Guidelines. Four fuel bundles containing pre-characterized Zircaloy fuel components will be inserted at the start of the first cycle under hydrogen water chemistry. These pre-characterized fuel bundles shall be inspected following each of the first three fuel cycles under hydrogen water chemistry for unexpected corrosion of deposits which could be related to hydrogen water chemistry. Normal fuel performance has been experienced at Dresden-2 since the implementation of hydrogen water chemistry in 1983.

2.7 Water Chemistry Contro_1 Integranular stress corrosion cracking can be mitigated by suppressing the dissolved oxygen concentration by hydrogen injection and traintaining high purity in the reactor coolant. This process, referred to as hydrogen water

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l chemistry, requires the attainment of two parameters: The electrochemical corrosion potential of stainless steel must be less than -230my, Standard Hydrogen Electrode (SHE) and the water conductivity must be less than 0.3 micro Siemens per centimeter at 25 C. The licensee will have a policy statement and implementing corporate procedure for commitment to the BWROG Guidelines for Hydrogen Water Chemistry by the end of 1987.

2.8 Site Visit The staff visited the Peach Bottom Statien on August 11, 1987 to review the design and installation of the hydrogen water chemistry facility. Discussions were conducted to clarify information submitted by the licensee for incorpora-tion into this safety evaluation. System drawings and layouts were reviewed.

Finally, the tour of the hydrogen water chemistry facility was beneficial in verifying the staff's evaluation. The following areas were looked at:

liquid hydrogen storage facility liquid oxygen storage facility hydrogen injection system crack arrest verification system and electrochemical potential monitor hydrogen water chemistry control panel in main control room.

The site visit supports the staff's conclusion that the hydrogen water chemistry system is acceptable.

3.0 CONCLUSION

S On the basis of the above evaluation, the staff finds that the proposed changes and hydrogen water chemistry installation are in accordance with the BWROG (1987 Revision) " Guidelines for Permanent Hydrogen Water Chemistry Installations."

Since the staff has accepted the Guidelines for referencing in licensee requests for a permanent hydrogen water chemistry installation ( NRC letter to G. H.

Neils dated July 13,1987), the proposed changes are acceptable.

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