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Recommendation 90-7 addresses safety issues of concern for 24 single-shell, high-level radioactive waste tanks containing ferrocyanide compounds at the Hanford Site. The waste in these tanks is a potential safety concern because, under certain conditions involving elevated temperatures and low concentrations of nonparticipating diluents, ferrocyanide compounds in the presence of oxidizing materials can undergo a runaway (propagating) chemical reaction. This document describes those activities underway by the Hanford Site contractor responsible for waste tank safety that address each of the six parts of Defense Nuclear Facilities Safety Board Recommendation 90-7. This document also identifies the progress made on these activities since the beginning of the ferrocyanide safety program in September 1990. Revised schedules for planned activities are also included.

This report compiles informationfrom a varietyof sources to provide a technicalbasis for removing tanks241-BX-102,-106,-110,-111,241-BY-101, and 241-T-101 from the FerrocyanideWatch List. Includedare detailed descriptions of waste transferoperations, and waste transferdata for the period tankswere in service. Also included is information consideredby the Departmentof Energy for authorization to stabilize tank24 IT -101. Some of the tanksreceived "sidepocketed"supematantbecause of high 6°Coor 9°Sr concentration. The soluble ferrocyanidecontent of the settled supematantwas very low, and it is importantto note that ferrocyanideion was not added in excess of nickel ion during scavenging. A thorough review of the availableferrocyanidescavenging records concluded that tank 241-T-101 (because it was refilled with metal waste and sluiced again in 1956 after receiving ferrocyanide sludge in 1953); tanks241-BX-102,-106, and 241-BY-101 (because these tanks received only ferrocyanidescavenging supematant);and tanks241-BX-110 and-111 (because these tanksdid not receive any ferrocyanidewaste, sludge or supematant)do not containthe requisite 1000 g-moles or more of ferrocyanide. Therefore, these six tanks do not belong on the FerrocyanideWatch List.

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Tank 241-C-112 is a Hanford Site FerrocyanideWatch List tank that was most recently sampled in March 1992. Analyses of materials obtained from tank 241-C-112were conducted to support the resolutionof the Ferrocyanide UnreviewedSafety Question (USQ) and to supportHanford Federal Facility i Agreement and Consent OrderI (Tri-PartyAgreement)Milestone M-IO-O0.Analysis of core samples obtained from tank 241-C-112strongly indicates that the fuel concentrationin the tank waste will not supporta propagating exothermicreaction, lt is probable that tank 241-C-112exceeds the 1,000 g-mol inventorycriteria establishedfor the FerrocyanideUSQ; however, extensive energeticanalysis of the waste has determined a maximum exothermic value of -9 cal/g dry waste. This value is substantiallybelow any levels of concern (-75 cal/g) 2. In addition,an investigationof potentialmechanisms to generate concentrationlevels of radionuclideshigh enough to be of concern was performed. No credible mechanismwas postulatedthat could initiatethe formation of such concentrationlevels ] in the tank.Tank 241-C-112waste is a complex material made up primarilyof water and inert salts. The insolublesolids are a mixture of phosphates,sulfates, and