Resolution of Generic Safety Issues: Issue 136: Storage and Use of Large Quantities of Cryogenic Combustibles on Site ( NUREG-0933, Main Report with Supplements 1–35 )
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DESCRIPTION
Historical Background
This issue was identified by NRR/EIB in February 1986 when it was suggested that Issue 106, "Piping and the Use of Highly Combustible Gases in Vital Areas," be expanded to include new safety concerns associated with the siting and use of large quantities of cryogenic combustibles on site.1024 The staff decided not to expand the scope of Issue 106 and evaluated the EIB concerns separately as Issue 136.
Two new systems which require storage on site of much greater amounts of hydrogen, oxygen, and propane gases than have been previously reviewed and licensed for use are expected to be added at some operating plants. The long-term resolution of Issue 86, "Long Range Plan for Dealing with Stress Corrosion Cracking in BWR Piping," is expected to result in the installation of H2 water chemistry control systems at many of the operating BWRs. These systems will require the use of H2 and O2 in amounts far in excess of those currently consumed at operating plants. In consideration of the logistics of supply and transport, storage of H2 and O2 on site in a cryogenic liquid state and vaporization for use appears to be a practical solution. Some nuclear plants, which might require smaller quantities of H2 are planning to use a compressed H2 gas supply. Other plants may install electrolytic gas generators to generate H2 and O2 at the plants required rate. The BWR Owners Group (BWROG) for Intergranular Stress Corrosion Cracking (IGSCC) Research, in cooperation with EPRI and representatives of the industrial gases industry, has prepared a topical report1029 which provides guidance for design, operation, maintenance, surveillance, and testing of permanent hydrogen water chemistry control systems which may be located on site at operating BWRs. The staff reviewed the topical report, issued requests for additional information, and published a SER in July 1987. The SER endorses the BWROG guidelines for permanent BWR hydrogen water chemistry systems (with noted exceptions), thereby establishing acceptance criteria for staff use in plant-specific safety evaluations for individual plant licensing actions.
The second system is a portable incinerator called a Mobile Volume Reduction System (MVRS) for use as a waste volume reduction process for low level radioactive waste. Commonwealth Edison has applied to the NRC for installation and operation of an MVRS at their Dresden 2/3 site. The MVRS uses large quantities (up to 1000 gallons) of LPG (propane) for incineration of radioactive waste. The staff has completed its review of the Dresden application for modification to their operating license and has approved the siting and use of the MRVS at the Dresden 2/3 sites in a SER published on August 13, 1986.1026 It is anticipated that other licensees and/or nuclear plants may wish to utilize the MVRS (a standard design) at their facilities and will also submit license amendments to do so.
Issue 106 covers only the storage of relatively small amounts of combustible gas on site and the use and routing of those gases in safety-related areas. It does not cover the size, physical form or location of storage vessels used to provide liquid hydrogen, liquid oxygen, or (propane) on site. It does not cover the potential failure of the vessels used for these flammable/explosive materials and the effects of a resulting fire and/or explosion on reactor safety-related structures or equipment. We have, therefore, opened this new generic issue to encompass these concerns.
Safety Significance
The on-site storage and use of large quantities of liquified combustible gases pose the potential of severely damaging reactor safety-related structures and/or equipment. Failure of the liquid storage vessels could endanger safety-related structures and equipment in many ways; i.e., by explosive blast overpressure, inclusion in the combustion fireball, excessive heat flux from the fireball, a vapor cloud drifting into safety-related air intake structures, etc. If guidance for safety review of new systems is not provided, the failure of these systems could result in damage to or failure of safety-related structures and equipment, resulting in an increase in public risk.
However, the installation and operation of systems using large quantities of cryogenic combustible materials on site, such as the MVRS or BWR hydrogen water chemistry control systems, is beyond the scope of current plant licenses. Therefore, the addition of such systems at an operating plant and the use of the systems would constitute an unreviewed safety concern (i.e., potential new and different accidents from those previously considered and evaluated as a part of the facility licensing process) and would necessitate a staff review of the adequatcy of protection of public health and safety before approval to install and operate the system may be granted by the NRC. This would be accomplished through the review of a licensee request for a license modification to install and operate the system. In the resolution of this issue, it is assumed that adequate acceptance criteria for the on-site storage and use of these combustible gases can be developed which would involve very low or negligible additional public risk.
Resolution of this issue will result in a reduction in operational exposure (unquantified) because replacement of recirculation piping will not be required and the possibility that the frequency of in-service inspections may be reduced.
Possible Solution
SRP11 Sections 2.2.1-2.2.2, "Identification of Potential Hazards in Site Vicinity," and 2.2.3, "Evaluation of Potential Accidents," mention cryogenic fuels and flammable gases but offer little guidance in the evaluation of the hazards of use of these materials on site. Regulatory Guide 1.91, "Evaluation of Explosions Postulated to Occur on Transportation Routes near Nuclear Power Plants," provides a method to convert the detonation energy of a vapor cloud to an equivalent mass of TNT, but offers no further guidance other than stating that the actual gas, site topography, and meteorological conditions be considered in the hazards evaluation.
Acceptance criteria for the on-site use of large liquid propane systems have been developed and documented through the staff review of the Dresden 2/3 license amendment for the on-site use of the MVRS. Acceptance criteria for the on-site use of large liquid H2 and liquid O2 systems are currently being developed through the staff review of the BWROG topical report for the design and on-site operation of BWR hydrogen water chemistry control systems. Thus, resolution of this issue is assumed to be the modification of SRP11 Sections 2.2.1, 2.2.2, and 2.2.3, and Regulatory Guide 1.91, as appropriate, to incorporate the staff acceptance criteria developed through the Dresden 2/3 MVRS review and the BWROG guidelines topical report review.
CONCLUSION
Staff acceptance criteria for large propane systems have been developed and are stated in the Dresden 2/3 SER Supplement of August 13, 1986. Staff acceptance criteria was also developed for large LH2 and LOX systems through the staff's evaluation of the BWROG topical report for the design and operation of permanent hydrogen water chemistry control systems at BWRs.
To assure consistent evaluation and approval of future license modifications for the installation and use of MVRS and BWR hydrogen water chemistry control systems at operating reactors, this issue was classified as a Licensing Issue. It was recommended that the appropriate SRP Sections and Regulatory Guides be amended to include the acceptance criteria developed through the Dresden MVRS review and the BWROG topical report review. However, with the publication of the staff's SER in EPRI NP-5283-SR-A, "Guidelines for Permanent BWR Hydrogen Water Chemistry Installations -- 1987 Revision," in September 1987, NRR considered this issue to be resolved.1115
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